Note: Descriptions are shown in the official language in which they were submitted.
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This is a division of application serial number 2,151,076
filed June 6, 1995, entitled Controlled Magnesium Melt Process,
System And Components Therefor
Title of Invention
5INGOT PREHEATER AND TRANSFER FOR
MAGNESIUM MELT SYSTEM
Field of Invention
Applicant's invention relates generally to improvements
in the art of magnesium die casting and more particularly to a
controlled process, system and apparatus for producing liquid
magnesium. The invention particularly concerns a process and
apparatus for a turn key, computer controlled magnesium melt cell,
with operator computer interface.
The invention is directed to a system which is controlled
beginning with transporting and preheating raw ingots of magnesium,
transferring the ingots to a furnace, melting of the ingots and
transfer of the liquid magnesium to the die cast machine shot
sleeve pour hole. The invention also particularly concerns a
controlled process and components of the system. There is complete
control of the physical movement of the raw magnesium ingot through
all of the stages necessary to introduce liquid magnesium to the
die cast machine shot sleeve pour hole. There is controlled
preheating of the ingot, control and monitoring of the level of the
liquid magnesium in the furnace melt pot. The melting process is
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controlled by maintaining suitable temperatures as well as the
quality of liquid magnesium sent to the die cast machine.
The invention also relates to interactive communication
to the die cast machine relating to the necessary signals required
for a fully automated casting operation, as well as diagnostic
messages relevant to the above.
The invention also relates to melt cell interaction with
the cell operator for introducing process set points, displaying
all cell temperatures, set points, cell cycle displays of each
facet of the cell operation, security access to limit operation of
the cell to those with the proper authorization code and diagnostic
screens to aid in problem solving, relating to the melt cell as
well as fault indications coming from the die cast machine.
The present divisional application is directed to the
ingot preheater aspect and transfer of the preheated ingots into
the melt cell.
Background of Invention
Magnesium die cast components, because of their weight
advantage and other characteristics, are used in automobiles and
other mobile equipment. Obviously there are numerous other uses
for die cast magnesium parts and pieces i.e. computer housings and
chain saw housing only to mention a few.
One of the major drawbacks with known magnesium die
casting is extensive wastage because of flaws that result when
using existing processes and equipment.
Temperatures and minimum temperature variations are
critical as well as other process variable parameters such as metal
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level in the molten bath and consistent metal pour to meet the
unique properties of a magnesium melt operation.
- Some considerations for making a quality magnesium
casting are as follows:
(1) The ingot (lS lbs. or 25 lbs.) should be suitably
conditioned (i.e. pre-heated) before being placed into the furnace
metal bath. For example should moisture be left in or on the ingot
that moisture will become super heated steam in the furnace which
can cause an explosion to occur in the metal bath.
One method of preheating used in the prior art is to lay
the ingots on top of the furnace and when the operator felt they
were ready then place them by hand in the molten bath. Another
method, when using gas fired furnace, was to use the heat radiated
from the furnace, as well as ducting arrangement of the vented heat
to be channelled into an enclosure where this heat was used to
preheat the ingots. A further method was using an electric duct
heater in a preheat chamber with little or no heat control and with
no regard to or determination or measurement of the ingot
temperature. All of the above methods are extremely dangerous as
they do not meet the various ingot supplier warning of never
introducing a magnesium ingot into the metal bath until it is above
150~C (300~F). An ingot below the noted temperature also creates
temperature gradients in the metal bath which produce dross and
sludge. There also is the risk of explosion. The end result is
scrap production parts, down time and possible injury to personnel
and equipment.
(2) Temperature variations are critical. For example
the metal bath (furnace) should stay within a selected temperature
range when an ingot has been charged. The metal bath should not
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deviate above or below a preselected temperature. If it does dross
build up can occur which filters down through the metal bath
allowing impurities to become part of the casting. Castings with
imperfections become costly scrap.
(3) The metal bath level should remain at as constant
a level as possible to ensure each metal pour is the same amount,
and to be able to realize the same amount of head pressure for each
pour. In one prior art method the machine operator would, after
making a certain number of parts, go to the furnace and add ingots
to bring the metal level to where he wanted it. In another method
after making a certain number of parts, a counter in the die cast
machine would turn on a lamp to indicate ingots needed to be added
to the metal bath. The operator would then add ingots by hand to
bring the level to the desired level. These methods rely totally
on the operator who may or may not be conscientious to the need of
a constant metal level for operating in process control. The
operator is also at risk, if the ingots being added are below a
safe temperature to do so.
(4) Transfer of the metal from the furnace through the
siphon tube should be done as quickly as possible due to the rapid
loss of heat from the magnesium when contact with the atmosphere
as well as the burning that occurs, which contaminates the metal
pour.
In the prior art melting of magnesium one method used is
gas fired furnaces, normally with two combustion blower units.
This is an effective method for melting the magnesium but by its
characteristics alone makes an extremely poor choice for magnesium
due to the following:
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(a) magnesium dust is extremely flammable and should
never be in an environment with an open flame; and
(b) due to the extremely large swing in the temperature
above and below the set point (typically +/-25~C), there is no
chance to keep the metal bath temperature within the extremely
tight metal bath requirements. The metal bath temperature
desirably should be +/-8~C, in relation to the metal bath set point.
Another method used is an electric furnace with power
contactor relays where the amount of power is selected by a
selector switch and the overall metal bath controller is used to
control the on/off operation. This furnace is in actual fact a
holding furnace used to maintain temperature. It would normally
be filled with liquid metal from a smelter. Also, since it is not
interactive to a preheater control structure, or a die cast
machine, it has no ability to anticipate the ingot being introduced
to the metal bath or to what the die cast machine mode of operation
is .
The following are a few of the prior art systems of
transferring liquid magnesium from a furnace metal bath to a die
cast machine shot sleeve:
(1) Operator uses hand held ladle to ladle magnesium to
the die cast machine pour hole. This method is time consuming and
may only be used for small parts, i.e. one to two pounds. The
operator must also ensure sulphur powder is constantly introduced
to the metal bath surface to prevent burning of the liquid
magnesium that is in contact with the atmosphere;
(2) Another method is the use of mechanical pumps which
are operated by air and function as a piston style pump device.
These units are prone to breakdown due to the high metal
2178763
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temperatures and are also prone to metal freeze up in the delivery
pipe and pump itself if not kept in constant operation. Should
there be metal freeze up the pump must be pulled out of operation
and flushed out with sulphuric acid to clear obstructions. This
method and the above other methods are very poor in relation to a
constant quality of the desired amount of liquid magnesium being
sent repeatedly time after time to the shot sleeve pour hole;
(3) Another method is the use of inert gas displacement
and pressure transfer. This method uses inert gas to pressurize
a crucible area. The inert gas tube goes into the crucible area
and the delivery tube to the shot sleeve leaves and goes to the
shot sleeve pour hole. This is a costly method as it involves
electrically heating the transfer tube as well as the cost of the
inert gas and pressurizing. This method also is inadequate in
relation to process control due to the amount of liquid magnesium
introduced to the shot sleeve. It varies greatly from one pour to
the next.
Both items (2) and (3) introduce extra ancillary
equipment that are unnecessary.
The foregoing are a few of the problems consistent with
die casting magnesium but the major problem is the fact that a
totally integrated process has never been developed before now to
include all the process requirements from raw ingot to pour of the
metal into the shot sleeve hole.
Summary of Invention
In applicant's melt system there is complete control of
the total process starting with the raw ingot of magnesium in its
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initial state through to transfer of the liquid magnesium to the
die cast machine shot sleeve.
The system may be provided as a total package turn key
operation which may communicate through dry contact closure e.g.
relays or from the melt cell processor to a compatible industrial
processor as well as remotely located processors and monitoring
systems. Individual components are also provided in accordance
with various aspects of the present invention and the present
application is directed to the ingot preheater and transfer of the
preheated ingots to the furnace.
All system process values and the entire metal process
have been engineered to meet the unique properties of the magnesium
melt operation and include:
(a) maintaining the metal bath selected temperature
preferably within a range of +/- 8 degrees C;
(b) providing consistency in the amount of metal
transferred. Each part poured in a DCM has a biscuit which is the
metal in the pour sleeve. The size of biscuit is predetermined.
The siphon tube transfer of metal accuracy provided by the present
invention permits obtaining an accuracy of about +/- .250" on a 2"
diameter biscuit. The transfer is relatively constant due to a
constant metal level head pressure;
(c) as an example the metal level is controlled
preferably to about +/- 1% where 1.6" equals 10% of the linear
measurement of the level probe which is 16" in length. This
relates to a crucible with about 4,500 lbs. of molten magnesium.
The melt rate is approximately 1800 lbs. of magnesium/hr. and the
surface variation of the molten metal is less than 1/16 inch;
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(d) the metal temperature in the tube of the siphon tube
transfer device is kept preferably within approximately 8 degrees
C. of the selected temperature by constantly monitoring and
updating the thermocouples used for the siphon inlet end and the
siphon outlet end of the tube and using this information in the
program to control the siphon-in heat contactor and the siphon-out
heat contactor.
The furnace, i.e. melt cell, has two separate zones of
heating elements. Each zone is controlled by 3 phase, zero cross
fired 4 to 20mA gated SCR's, controlled by a OFE2 module of the
PLC. The SCR's are zero cross fired to prevent RFI (Radio
Frequency Noise) and give better control and gated to allow only
the amount of power required to keep the metal bath at the desired
set point. The 4 to 20mA signal is sent to the individual firing
boards for the SCRs via an intelligent analog output module i.e.
the OFE2 module of the PLC. The control for these signals is done
in the industrial processor using a closed loop interactive P.I.D.
(Proportional Integral Derivative) function block suitably modified
to use all of the information available in the program. The
processor is programmed as desired to ensure extremely accurate
metal bath control. Factors used with P.I.D. function include.
(a) die cast machine running in semi-auto or auto;
(b) outer shell temperature of the furnace;
(c) anticipation of ingot being charged to initiate a
feed forward value to the P.I.D. block;
(d) temperature of ingot about to be charged to the
metal bath. This information comes from an infra-red ingot sensor
or direct contact thermocouple;
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(e) the amount of time between die cast machine cycles;
and
(f) the metal level.
There are also furnace routines that run automatically
when the DCM has not cycled for more than 10 minutes;
- To allow for a quick start up of the furnace;
- To allow for additional heat to offset an ingot
charge of a cooler ingot;
- Weekend routine for gradual start up of furnace to
melt bath temperature desired.
Applicant's system responds to a direct need of the
magnesium casting industries by providing a fully automatic
magnesium melt system that performs operations relating to the
process parameters. It meets their needs regarding the ability to
be a turn key operation which requires minimal integration to
function with any of the various manufacturers of die casting
machines while at the same time have the ability to provide process
information at the melt cell as well as being able to network with
other computers that are being used to record and log process
information for their customers, and also to have the ability to
interface the melt cell computer with the die cast machine computer
for quality and production enhancement of the casting operation.
A control scheme and the required apparatus is provided
which is user friendly and provides all aid possible for maximum
uptime. The system is able to interact to change automatically to
compensate for many variables present in an operation. There is
an ability to anticipate temperature change and react before hand
to ensure that the process control set points stay within the
process window casting using the present apparatus permits making
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parts weighing anywhere for example from approximately 3 lbs. to
59 lbs. with minimization of scrap considered essential in regards
to a profitable casting operation.
Some features provided by applicant's system include:
(1) preheated magnesium ingots. (Preferred temperature
range 150~C to 250~C);
(2) infra-red sensor or direct contact thermocouple
sensor to ensure ingot temperature suitable for transfer of ingot
to the furnace;
(3) Metal level bath kept to process desired level
within +/- 1%;
(4) Metal bath temperature kept within +/- 8~C of metal
bath set point;
(5) Metal in transfer siphon tube kept to within +/- 8~C;
(6) Metal pour time to shot sleeve equal to the time
selected by operator;
(7) Two distinct modes of furnace operation:
(a) run mode (operational);
(b) idle mode (weekend or down time cost savings);
*NOTE* in the run mode there are also features that
allow for:
(a) quick heat up (when furnace first is started
or when the die cast machine is first put into
auto);
(b) feed forward (used to off set the ingot being
introduced into the metal bath);
*NOTE* these two items are time based and must meet
program considerations.
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(8) Interactive and anticipative programming to allow
metal bath temperature kept well within the +/- 8~C process window.
There is provided in accordance with the present aspect
of applicant's invention apparatus for use in a metal melt system
comprising (a) an ingot preheater having a controllably heated
chamber for preheating metal ingots to a preselected temperature
and including temperature sensor means providing an output signal
representative of the temperature in the preheater; and (b) an
ingot transfer means for transferring a selected ingot from said
preheater into a melt furnace including actuators for effecting the
transfer and sensors providing output signals representative of the
state of operation of said actuators and functions performed.
There is also provided an ingot preheater and transfer
apparatus for a metal melt system comprising an enclosure having
an inlet end and a discharge end, means for controllably heating
a selected area in said enclosure, means for moving a plurality of
ingots in sequence into said enclosure through said inlet means and
through said enclosure to said discharge end, an ingot transfer
device at said discharge end including a drop chute, means to
transfer an ingot from said discharge end into said drop chute,
gate means in said drop chute to respectively in a gate closed and
gate open position retain and release an ingot in said drop chute
and means to move said gate from one to the other of said
positions.
In applicant's invention there is provided an
electrically heated preheater for heating metal ingots to a
preselected temperature and including a temperature sensor on the
preheater providing an output signal representative of the
temperature in the preheater; and an ingot transfer means for
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transferring a selected ingot from said preheater into a melt
furnace including actuators for effecting the transfer and sensors
providing output signals representative of the state of operation
of said actuators and functions performed said preheater and ingot
transfer being operable in a metal melt system that includes the
above-mentioned melt furnace and a programmable logic controller
(PLC) means that receives signals from sensors and in response
thereto, in comparison with preselected valves, controls power to
the preheater and furnace to maintain within selected limits pre-
selected temperatures therefor and controls feeding of ingots tosaid furnace as required to maintain the molten metal in the
furnace within a selected range of a predetermined level.
Also there is provided in accordance with the present
aspect of the invention an ingot preheater and transfer apparatus
for a metal melt system comprising an enclosure having an inlet end
and a discharge end resistance heating elements in said enclosure
arranged in a first heating zone adjacent said inlet end and a
second zone extending therefrom toward said discharge end, an
endless conveyor means for moving a plurality of ingots in sequence
into said enclosure through said inlet means and through said
enclosure to said discharge end, an ingot transfer device at said
discharge end including means to transfer an ingot from said
discharge end into a drop chute, gate means in said drop chute to
respectively in a gate closed and gate open position retain and
release an ingot in said chute and means to move said gate from one
to the other of said positions.
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List of Drawings
The invention is illustrated, by way of example, in the
accompanying drawings wherein:
Figure 1 is a diagrammatic top plan view of the overall
system;
Figure 2 is a diagrammatic side elevational view;
Figure 2A is a left hand end elevational view of the
preheater shown in Figure 2 but with thermocouple enclosure and
power distribution box differently positioned;
Figures 3 and 4 are similar to Figure 1 but containing
further details of the system and with portions omitted for
clarity;
Figure 5 is a diagrammatic elevational part sectional
view of the melt system and further illustrates, in broken line,
a die cast machine that receives molten metal from the siphon tube;
Figure 6 is a diagrammatic elevational view of the
furnace illustrating certain features thereof;
Figure 7 is a top plan view of Figure 6 and both include
an optional upper service platform;
Figure 8 is a vertical partial sectional view of a
portion of the furnace;
Figure 9 is an elevational view of the melt pot also
referred to as a crucible;
Figure 10 is a top plan view of Figure 9;
Figure 11 is an enlarged elevational view of the metal
level probe that projects into the furnace;
Figure 12 is an electric schematic for the probe;
Figure 13 is a view of the face portion of the level
probe control unit;
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Figures 14 to 16 are electrical schematics of the heating
elements of the furnace;
Figure 17 is an elevational view of the siphon tube;
Figure 18 is a sectional view essentially along line 18-
18 of Figure 17;
Figure 19 is an electrical schematic for the apparatus;
Figure 20 is a continuation of the schematic of Figure
19;
Figure 21 is a continuation of the schematic of Figure
20;
Figure 22 is a continuation of the schematic of Figure
21;
Figure 23 is an electrical schematic showing further
details;
15Figure 24 is a front view of the power supply enclosure
and operator panel view;
Figure 25 is a block schematic of the magnesium melt
system which includes the apparatus and the processor control;
Figure 26 is a detailed schematic of the furnace heat
control system;
Figure 27 is a block schematic flow diagram of the closed
loop PID and PLC programming enhancement;
Figure 28 is a block flow diagram of the melt process for
the present system;
25Figure 29 is the panel view operator processor screen for
temperature set point entry for all functions requiring a
temperature preset, and metal pour preset display of entered preset
value and the display of actual temperature and metal pour value;
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Figure 30 is the control device screen used for selection
of all control devices, i.e. conveyor off, conveyor manual and
conveyor auto;
Figure 31 is the cycle screen to display ingot charge
cycle and pour request siphon tube metal pour cycle also
description text outlining the cycles; and
Figure 32 is the fault screen used to indicate status of
all devices to address cross reference.
Description of Preferred Embodiment
System Overview:
Applicant's preferred system, described in more detail
hereinafter, includes an ingot conveyor and preheater section 100;
a crucible type, resistor heated melt furnace 200; an ingot
transfer section 300; a siphon tube, liquid magnesium discharge and
feed to die cast machine tDCM) section 400; and a control system
500. The control system via a PLC, modules associated with the
PLC, an operator's panel view, sensors and actuators inter-relates
and integrates the operation of components 100, 200, 300 and 400.
To operate the system at a specific site an electric
power supply is required as well as an air pressure system and a
gas mixture supply. In the system to be described in more detail
hereinafter the electric power supply requirement is 480 VAC, 400
A, 3 phase with ground. A 7.5 KVA transformer is required having
a 480 VAC primary and a 240 VAC/120 VAC secondary. The transformer
is preferably totally enclosed. The air pressure supply preferably
provides 90 psi and the gas mixture supply comprises CO2SF6 mixed
as protection gas for the furnace pot lid and siphon tube outlet
end.
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The components 100, 200, 300 and 500 are of applicant's
own original design and they may be selectively provided
individually or in combination or sub-combinations for integration
into existing magnesium metal melt operations or other metal melt
operations as may be obvious to those skilled in the art.
The electric power supply, air pressure supply and gas
mixture supply are normally provided on site and accordingly it is
to be understood such items, or the equivalent thereof, will be
provided for suitable operation of the complete system at a
selected site.
Referring to Figure 1 there is illustrated in block form,
(broken line) the ingot conveyor and preheater section 100, the
furnace 200, the ingot transfer section 300 and the control system
500 that inter-relates, integrates and controls operation of
components 100, 200, 300 and the siphon tube liquid magnesium
transfer section 400 shown in solid line. Figure 1 also shows
generally the gas mixture supply and distribution designated 600.
Ingots 10 are loaded from a suitable supply 11 onto the
infeed end of a conveyor 101 that passes through the preheater 100.
The ingot transfer section 300 is at the discharge end of the
conveyor.
The ingot transfer section 300 includes a pneumatic ingot
pusher 301 that moves a preheated ingot into an inclined enclosed
drop chute 302. A guillotine type gate 306 holds an ingot lOB (see
Figure 5) in the inclined chute ready for discharge into the
furnace and upon command from the control unit 500 releases the
ingot for free fall into the mass of molten metal 201 in a crucible
202 within the furnace 200.
- 17 - ~, ~ ? ~7 63
The siphon tube 400, known per se in the trade, transfers
molten magnesium from the molten metal bath 201 in the furnace to
the shot sleeve hole SH of the die cast machine (DCM).
Temperatures are critical as is also maintenance of predetermined
5 constant level of the molten metal in the furnace.
Ingot Conveyor and Preheater
Referring now to the ingot conveyor and preheater section
loo there is a metal enclosure 103 suitably supported in an
elevated position by support members generally designated 104. The
10 preheat chamber is located within the metal enclosure and is
suitably insulated with "pyro-block"* insulation. Metal ingots
within the chamber are preheated to a desired set point of for
example 150~C to a maximum of approximately 250~C. The preferred
range is 200~C to 225~C.
Heat for the chamber is provided by six banks of electric
resistance elements 105 with each element bank, by way of example,
being 10.6 KW providing total radiant heat of 63.6 KW, 460 VAC
single phase.
The six banks of resistance heating elements designated
105 A to F are divided into two zones designated in Figure 1 as
zone 1 (105Z1) and zone 2 (105Z2) with banks 105A, 105B and 105C
being in zone 1 and banks 105D, 105E and 105F in zone 2.
The preheater chamber is used to heat the ingots to the
desired set point. The preheat temperature range is 150~C to 250~C
and preferably 200~C to 225~C. The two zones of radiant heat are
independent of each other and the zones are monitored by K type
grounded thermocouples 106, 107 and 108. The values of the
*Trade-mark
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thermocouples are averaged to give zone temperature as well as the
overall ambient preheater chamber temperature.
Ingots are conveyed to and in the preheater by the
endless (continuous) conveyor 101 that has a first inclined section
lOlA extending from the ground level to the elevated preheat
chamber and a horizontal section lOlB located in the preheater
chamber. The conveyor is a pair of parallel chains running on
suitable shafts and sprockets and is driven by a motor 110 through
a 50 to 1 reduction unit 111 and a conveyor chain and sprocket
drive 112 and slip clutch not shown. Pairs of paddles 113 are in
series equally spaced on the conveyor chains and they provide
support for a number of magnesium metal ingots 10.
The magnesium ingots may be 15 or 25 pounds each and the
preheater chamber has a capacity for 25 ingots. The paddles on the
conveyor are at each ingot placement and they keep the ingots
located properly for preheat operation and for positive discharge
displacement at the discharge end of the preheater.
Mounted on the preheater is an air cylinder push-rod unit
150 that carries a thermocouple 151 into and out of contact with
an ingot prior to being moved by the conveyor to the transfer push
rod cylinder unit 301 described hereinafter. The T/C is a spring
loaded probe that makes direct contact and gives a true skin
temperature reading. An infra red sensor non-contact type can be
used but it is less accurate because of background heat influences
i.e. ambient.
Mounted under the conveyor is a conveyor index limit
switch 115.
A separate free standing enclosure PS1 is provided for
the power supply or it may be mounted on the preheater (see Figure
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4). There is a thermocouple enclosure TMC1 and a motor safety
disconnect switch 116 (see Figure 4). Also as seen from Figure 2
there is mounted on the enclosure an air filter regulator and
lubricator assembly AFR1, an air valve pack (120 volt AC) AVP1.
An air pressure safety switch (not shown) connected to shut the
system down and provide an alarm if the pressure drops below a
selected amount e.g. 80 PSI.
There is a first upper observation and service platform
120 with stairs 121 leading up to the same and a second observation
and service platform 132 accessed by a ladder 123.
A limit switch LSlA is located in the pre-heater
enclosure for activation should an ingot drop from the conveyor or
become displaced. This limit switch can be connected to cause a
system shut down.
Ingot Transfer Unit
The ingot transfer unit 300 is located at the discharge
end of the preheater and includes the push rod of air cylinder 301
and the gated inclined drop chute 302. At the end of the push rod
there is a pusher plate 305 that engages an ingot lOA disposed in
position on a support plate 306 for discharge into the inclined
drop chute. The plate 305 passes over the ingot conveyor unload
plate 303. The plate 303 has a suitably located cut out 307
therein for the conveyor paddles to pass therethrough leaving the
ingot to be charged at an at rest position on the plate. The
conveyor is indexed after an ingot charge cycle has been completed.
It can readily be programmed to first index and then the charge
takes place. The ingot lOA to be charged is pushed by the pusher
plate 305 into the incline chute 302 in which there is the
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guillotine type gate 306 that is controllably moved by the push rod
of a pneumatic cylinder unit 308.
In Figure 1 the guillotine gate 306 and cylinder 308 are
shown in their home position in which the piston is fully advanced.
After the push rod cylinder 301 has discharged an ingot into the
incline chute 302 there is a timer controlled one second delay and
then the cylinder rod will retract to the rear proximity sensor 331
thereby opening the gate and allowing the ingot to fall by gravity
into the metal bath. After a 1.5 second delay in the retracted
position the guillotine will return to the home (advanced) position
activating proximity sensor 330. This helps to prevent the loss
of mixed CO2SF6 protection gas from the metal bath pot.
In Figure 5 the gate, i.e. plate 306 is shown holding an
ingot lOB (previously at the location of ingot lOA) prior to
discharge into the molten bath in the furnace. The normally closed
gate 306 prevents the gas mixture from escaping from the furnace.
The pneumatic cylinder unit 301 has a push rod advance
proximity sensor 310 and a push rod retracted proximity sensor 311
and pneumatic cylinder 308 has advance and retract respective
sensors 330 and 331.
Furnace
The furnace 200 is an insulated enclosure having a
suitable crucible 202 therein for holding a molten bath 201 of
magnesium. Normally there would be about 4,500 lbs. of the molten
metal in the crucible. The molten metal has a surface level
designated 204.
The furnace has a 6 inch thick castable floor 205 of high
temperature resistant material with a 9 inch high, 6 inch wide
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castable curb 206 extending upwardly from the perimeter of the
floor. This provides a containment area 207 for metal.
The four walls of the furnace, designated 208, 209, 210
and 211 in Figure 16, have an outer shell 212 of 3/16th inch steel
with the outside corners reinforced by 4 inch angle iron. Inside
the steel shell is a 6 inch lining 213 of insulation referred to
as "pyro-block"* walls.
Each of the four walls has resistor heating elements 215
arranged to provide an upper heating zone 1 designated 215A (see
Figures 8 and 16) and a lower heating zone 2 designated 215B. The
heating elements found suitable are overbend 70% nickel, 30%
chromium available from Thermal Ceramics of Augusta, Georgia.
There are SCRs described hereinafter with reference to the electric
schematics providing individual control for the respective zones.
The furnace has a base support and leg structure 616 to
keep the furnace off the floor to allow for easy clean up of
magnesium dust and fine chips. This also allows access below the
furnace in case of magnesium spill from the DCM.
The top of the furnace has a 5 inch thick castable
ceiling 216 on which there is a 1 1/4 inch steel top plate 217.
Depending from this into the cavity of the furnace is the pot or
crucible 202 which has an outwardly directed flange 220 spaced
downwardly a selected distance from the upper edge 221 of the
crucible. The crucible by way of example has an inside diameter
of 33 1/2 inches, an outside diameter of 36 1/2 inches and a total
depth of 43 inches with the wall thickness being 1 1/4 inches.
Three crucible lugs 222 are provided which are spaced apart 120~
from one another on the flange 220.
*Trade-mark
., ~.,
,~
- 22 - ~ 7 ~ ~
Mounted on top of the crucible or pot is a pot lid 230
in which there are a plurality of drilled and tapped holes 231 for
3/8 inch NPT pipe fittings. These drilled openings 231 provide
gas line connections for supplying CO2SF6 via piping 601 to the
5furnace from a suitable supply 600A. There is an opening 232 in
the lid for a liquid level probe 250. There is an opening 234 in
the lid for the discharge end of the inclined gated chute 302 and
a lid and opening 235 for dross removal by the operator. There is
an opening 236 for the siphon tube in an adjustment plate 237
mounted on the lid for movement back and forth in the direction of
the double headed arrow A for adjusting the location of the siphon
tube. There is an opening 240 in the lid for a metal bath
thermocouple 245.
Shown in Figure 6 is an electrical connection enclosure
15650 as being one of two connection enclosures for feeds from zone
1 and zone 2 SCR firing boards.
The furnace has the above mentioned thermocouple 245 for
monitoring the metal bath temperature and a second thermocouple 260
on the outer shell which measures the outer shell temperature.
20Mounted in the opening 240 in the lid is the thermocouple
245 which has a probe 246 that projects into the open metal bath.
A metal level probe detector 250, mounted in the lid
opening 232, has a probe 251 that projects into the molten metal
in the crucible. A state of the art proven metal level probe is
used in the present system which is available from Carli Electro
Automation GmbH. The probe measures the metal level with accuracy
of about two decimal points. The metal level value is used as part
of the closed loop PID calculation for metal bath temperature and
determining the optimum temperature for the preheater ambient
~,
~ 78763
- 23 -
temperature. The metal level is monitored by the machine program
for a process control information and for function.
The metal level measuring probe is shown in Figure 11
with the electrical connections therefor shown in Figure 12.
Referring to Figure 11 the metal level probe 250 has the
probe 251 that projects into the molten metal within the furnace,
a probe head 252 external to the furnace and a collar 253 for
mounting the probe on the pot lid 230. The probe 251 has an outer
stainless steel protective tube 251A and an inner measuring probe
251B protected by the outer tube against direct contact with the
liquid metal. The inner probe 251B has two sets of windings one
being of transmitter winding and the other a receiver winding
surrounding a ceramic tube.
The probe must be mounted so as to be completely
vertical, relative to the liquid metal free surface level. By way
of example the probe length from the terminal head to the free end
of the probe in the metal is approximately 31 inches and the lower
16 inches of this is where the actual values that are being used
come from. For operation the probe is set for 100% at the 16 inch
from the tip and 0% at the tip. The metal level 204 normally is
about 85%.
A special cable 275 (see Figure 12) is used to connect
the probe sensor terminal head to a control unit 250A in the
thermocouple enclosure. The control unit requires 110 VAC 1 phase
supply. The unit transmits a signal to the probe which is altered
by the amount of liquid magnesium it senses through heat transfer.
This signal, after being received is converted to a valve in the
4 to 20 mA range which is then taken to the analog input module 580
of the PLC 574.
217~763
~,...
- 24 -
Positioning and calibration of the probe is important and
further details of this can be obtained if need be from the
supplier of the probe. Prior to the first start up of the
apparatus the dry probe is set for 0% and the wet probe for 100%
and the adjustment for the switch point is made according to
specifications obtainable from the manufacturer. In the measuring
range, i.e. the indication of 0 to 100% provides a linear signal
output to a control box which in turn provides an output signal
current 4 to 20 milli amps to the PLC (lFE module), (output voltage
0 to 10V DC). Adjustment prior to use is by trimming
potentiometers and thereafter during operation the level is about
85.5 with 100% being about 3 inches higher.
Siphon Tube
The siphon tube, known per se, designated 400 is mounted
on the metal pot lid 230 via the mounting plate 237. The siphon
tube (see Figure 18) basically has a head portion 401 mounted on
the furnace lid, a suction tube portion 402 that projects into the
molten bath in the furnace and a delivery tube portion 403 for
delivery of molten magnesium to the shot hole SH of the die casting
machine (DCM). On the lower end of the suction tube 402 there is
a tube check valve 404 and in the head there is a siphon valve open
cylinder 405. In the head 401 there is also a siphon valve open
limit switch 406. On the siphon tube near the head 401 there is
a siphon inlet thermocouple 407 and near the outlet end is a second
or siphon outlet thermocouple 408.
The ball valve 404 includes a valve seat that is movable
away from and toward the ball 404 by the cylinder 405 respectively
to close and open the valve. The ball check valve serves two
2178763
"..
- 25 -
purposes the first being to permit magnesium liquid flow to the DCM
and the second to prevent the standing liquid magnesium in the tube
from draining back into the metal bath when the siphon tube is in
the raised or home position.
The siphon tube is moved from a raised position 400A to
a lower or pour position 400B by a pneumatic cylinder 411 connected
at one end thereof to the siphon tube by a swivel joint 412 and at
the other end by a swivel joint to a slide adjustment plate 413.
The slide adjustment plate 413 is mounted on the outer face of one
of the furnace walls. There is, operational with respect to the
air cylinder position, a tube raised proximity sensor 420 and a
tube lowered proximity sensor 425.
The siphon tube 400 is shown in greater detail in Figures
18 and 19 and in Figure 5 there is diagrammatically illustrated the
siphon tube on the furnace in each of two different positions one
being a raised at rest home position and the other a lower charge
position for charging the shot sleeve of the die cast machine.
The siphon tube has an outer (discharge) end heating
element 415 and an inlet end heating element 416. Each of these
heating elements are 220 VAC, 3,840 watts and are connected by way
of heater element high temperature pyratamic cable set in a
connection box 417.
The thermocouples 407 (inlet end) and 408 (outlet end)
are K-type thermocouples. Thermocouples 407 and 408 monitor the
temperature of the magnesium by conduction through the siphon inner
tube. Temperature value from 408 and 407 are used in the PLC
program to control power to the siphon inlet and outlet elements.
The temperatures are also monitored in relation to the process as
well as being monitored for fault condition. The respective
217876~
- 26 -
temperatures are displayed on the operator computer interface
(Panelview) to be described hereinafter. The siphon inlet and
outlet temperature preset is entered via the operator interface.
For handling the unit there is provided a lifting lug 420.
A section through the siphon tube is illustrated in
Figure 19 and consists of an outer tube 430 with a 1/8 inch thick
paper insulation layer 431 on the inside, a glass or ceramic
insulation 432, a paper layer insulation 433, a heating element 415
and an inner tube 435.
The siphon valve open limit switch 406 is used to give
two individual signals to the PLC program:
(a) the siphon valve is closed;
(b) the siphon valve is open.
This limit switch is monitored for fault and cycle conditions.
Relevant safeties involving safety timers in the PLC program
monitor this limit switch at all times.
Gas Distribution and Supply
The gas distribution and supply 600 includes a C02SF6
mixed gas balancing unit. There are two separate control
assemblies and distribution designated respectively 600A and 600B
(Figure 1) one being used to control the mixed gas to the metal
bath via conduit distribution means 601 to ensure that atmosphere
in the melt bath pot is free of oxygen and the other unit is used
to supply and control the mixed gas to the outlet end of tube via
distribution conduit 604 to prevent the magnesium at the outlet end
from starting to burn.
~1787b~3
.. ..
- 27 -
System Operation
Preheater (100) and Ingot Charge (300)
In the auto mode the following is a brief description of
the system ingot charge:
(1) Metal level in pot is low enough to require an ingot
charge which is requested by the metal level probe 250 and the PLC
logic controller of the control system 500;
(2) Loaded ingot conveyor indexes one position through the
preheat chamber 102 and the ingot conveyor control resets to home
position;
(3) Ingot 10A that is in the charge position (and has been
heated to temperature preset by the preheater - max. 250~C) is
advanced by push rod cylinder 301 with there being verification of
ingot temperature by an infra-red sensor or contact thermocouple
151 and the ingot drops into chute 302. The ingot (then designated
10B in Figure 5) is held by the gate 306. Push rod cylinder 301
as it advances it activates proximity sensor 310;
(4) After a delay (about 1.5 secs. after push rod cylinder
301 makes proximity sensor 310), the gate 306 will open allowing
the preheated ingot to drop into the molten metal in the pot. The
gate is opened by retracting cylinder 308 which activates sensor
311. There is a dwell period controlled by a dwell timer (PLC
Programmer) of about 1 second in the gate open position;
(5) The gate will close by advance of cylinder 308 which
activates sensor 310;
(6) After the gate has closed, the pusher 301 will retract
(proximity sensors 310 and 311 activated by push rod cylinder 301
and proximity sensors 330 and 331 by pneumatic cylinder 308);
2:178763
- 28 -
(7) Preheat conveyor sees that it is clear to advance ingots
one position, will then advance the one position;
(8) If the Die Cast Machine is requesting a metal pour, the
above sequence is kept in a hold mode to allow the siphon tube to
cycle and complete the metal pour. An ingot cannot be charged
while the siphon tube is in cycle with DCM. Upon siphon cycle
complete the ingot charge will continue if called for.
In the event of furnace temperature overshoot there is
an auto ingot charge routine the conditions being as follows:
(1) Preheater and furnace control power both on (respective
switches 555 - Figure 20 and 561 Figure 21);
(2) Ingot charge enable selected on (operator panel view 511)
(F13 Figure 30);
(3) Metal level in metal bath pot must be below 90% max;
(4) The preheater control must have been on for at least 5
minutes (initial start up safety);
(5) The preheater, preheat chamber must be over a preselected
temperature for minimum of two minutes e.g. 150~C;
(6) No faults or invalid data conditions relating to the cell
may be active. If active they must be rectified and then the fault
reset function key on the panel view must be operated to clear the
fault or invalid program latches before the program will recognize
a clear condition;
(7) Metal bath temperature must be greater than a preselected
desired temperature for example 630~C;
(8) Air pressure safety switch must be reading over 80PSI
(nominal reading should be approximately 90PSI);
(9) Motor safety disconnect llOA (and the auxiliary contacts
used for the PLC program) must be on.
~178763
- 29 -
Manual ingot charge can occur as follows:
(1) Ingot conveyor manual mode;
(2) Ingot conveyor loaded;
(3) Charge enable selected on;
(4) Press manual ingot charge function key;
(5) Ingot conveyor will index one paddle position;
(6) Ingots index one position through preheat chamber;
(7) Ingot conveyor back to reset position;
(8) 1.5 second dwell, then push rod cylinder 301 advances to
proximity sensor 310 with preheated ingot;
(9) Preheated ingot drops into ingot chute, stopped by
guillotine gate 306;
(10) 1.5 seconds after push rod cylinder 301 made forward
proximity 310, a 1 second dwell takes place, when timer is done,
the guillotine gate cylinder 308 retracts and activates proximity
331;
(11) When the guillotine cylinder 308 is fully retracted to
activate proximity sensor 331, a 1.5 second dwell timer begins to
time;
(12) Preheated ingot enters metal bath;
(13) When the guillotine dwell timer is done, the guillotine
gate advances fully forward to proximity sensor 330, at the same
time the push rod cylinder 301 retracts fully to the rear to make
proximity sensor 311;
(14) Manual cycle complete/to cycle over, press manual ingot
charge function key (F6 Figure 30).
The same safety considerations as those that apply for an auto
ingot charge apply to the manual ingot charge, with one major
exception, that being the preheat chamber being over a preselected
2178763
- 30 -
desired temperature (e.g. 200~C) for at least 2 minutes. The
machine operator is made aware of this and is cautioned only to use
this function in an extreme case.
There is a manual ingot load function to facilitate
loading the conveyor. Paddle positions can be located for
convenience of loading. The steps for this are:
(1) Ingot conveyor selected manual mode (panel view F14
Figure 30);
(2) Charge enable selected off (F13 panel view);
(3) Press manual load conveyor function button (F14 panel
view);
(4) Conveyor will index one paddle position;
(5) Conveyor stops at index reset position;
(6) Load ingots as required;
(7) Repeat step 4 to continue.
(In this mode no charge sequence takes place).
If for some reason the conveyor does not make it to the
index reset position, fault indication is given and the following
sequence may be used:
(1) The conveyor may be homed with the conveyor mode auto
selected, or the conveyor mode manual selected;
(2) Select charge enable off (F13 Panel View);
(3) Press the conveyor home function key (F10 Panel View),
conveyor will move to the index reset position;
(4) Press the fault function reset key (F7 Panel View) to
clear the latched fault in the PLC program.
l~ 2178'763
- 31 -
PREHEATER OPERATION
To monitor preheater temperatures zone 1, zone 2, and
ambient the operator enters a valid temperature preset using the
panel view 511 operator terminal. Available presets are 0~C to
260~C. If all safety conditions are met in the program, zone 1
contactor comes on, 1 second delay then zone 2 contactor comes on.
There are three thermocouples used to monitor and control the
preheater temperature. The three thermocouples (T/C) are load zone
108, MI preheater 107 and charge zone 106.
lo T/C 108 temperature plus T/C 107 temperature divided by
2 equals zone 1 ambient temperature, this value controls the on/off
status of the zone 1 electrical contactor.
T/C 107 temperature plus T/C 106 temperature divided by
2 equals zone 2 ambient temperature, this value controls the on/off
status of the zone 2 electrical contactor.
T/C 108, 107, 106 temperatures divided by 3 equals the
preheater ambient. This value is used to ensure the preheater has
reached equilibrium in relation to the ambient temperature,
required for ingot heat up to set point, also used to drop out both
zone 1 and zone 2 contactors if the upper ambient temperature
deadband is exceeded.
An ingot in the precharge position (Plate 306) or the
ingot next to be moved to the load plate 306 is monitored by an
infra-red sensor, (emulates a K type thermocouple) to ensure ingot
is equal to or above the ingot preset temperature for charging to
the metal bath. A suitable infra-red thermocouple is available
from Exergen Corporation of Newton MA under the Trade-Mark IR t/c.
Instead of an infra-red sensor applicant prefers a direct contact
T/C as there is more accuracy in the measured temperature. This
~ ~17876~
- 32 -
is previously described as T/C 151 movable into and out of contact
with the ingot by air cylinder 150. T/C 151 may be a spring loaded
T/C N sensor type available from Ogden Manufacturing Company,
Arlington Heights, Illinois.
A known format is used to calculate the Kw'S required for
the ingot preheater.
To monitor preheater temperature zones and ambient
108 107 106 checked for open T/C
108 107 106 checked for invalid data
108 107 106 checked for hi-limit
Zone 1 checked for hi-limit
Zone 2 checked for hi-limit
Ambient checked for hi-limit
Zone 1, Zone 2
Upper Deadband 7~C above set point
Zone 1, Zone 2
Lower Deadband 7~C below set point
Ambient Temperature maximum heat preset 260~C.
Siphon Tube (400) Operation
The siphon tube moves the liquid magnesium from the
furnace metal bath pot to the die cast machine shot sleeve pour
hole. The cycle of the siphon tube is as follows:
(a) The die cast machine sends a signal to the melt cell
(furnace) processor requesting a metal pour. As long as all safety
~ 7~763
- 33 -
considerations and temperature limits are met in the melt cell
processor, the siphon tube is given the signal to cycle;
(b) Upon receiving the signal the siphon tube lower valve is
energized and the siphon tube cylinder retracts lowering the tube
to the pour position;
(c) When the tube is lowered proximity sensor 425 is
activated causing the siphon valve cylinder to be energized and
thus advancing the valve seat allowing the magnesium to flow
through the siphon tube for the amount of time selected (F4) by the
operator, via the operator computer interface (Panview 511). Pour
times are preselected dependent upon need and normally not less
than 1 second for safety and maximum dependent on part size;
(d) Upon time out of the metal pour timer, the valve seat
retracts to the check valve ball. At this point the siphon valve
closed limit switch 406 is made, the siphon tube will begin to
raise, the siphon tube drip timer times out at this point, the
signal is sent to the die cast machine that the siphon pour is
complete, the siphon tube will continue to raise to the home
(upright) position;
(e) This completes one full cycle for the siphon tube pour
function. To begin another cycle the die cast machine must open
and proceed with the recycle of the die cast machine. This is done
as a safety to ensure the siphon tube may pour only once during the
die cast machine cycle. A pour is aborted at any time should there
be a fail safe condition from the DCM.
Melt Furnace (200) Heating Operation
SCR's and their Firing Boards controlled by a OFE
intelligent module 581 of the processor 574 are used to control
~78763
- 34 -
power to the furnace elements 215. Some features of this control
are:
(i) 3 phase zero cross fired;
(ii) 4 to 20 mA input signal to the SCR firing control
boards;
(iii) gated SCR's used for proportional control;
(iv) closed loop control;
(v) no mechanical moving parts.
This type of system allows for:
(i) much longer element life;
(ii) less power consumption; and
(iii) interactive to the machine control program,
providing much better control over metal bath temperature than can
be achieved using contactors or selector type selection of power.
The metal bath temperature is kept extremely close to
preset by using closed loop PID formula acting with anticipative
program development which checks many variables relative to the
metal bath temperature. A preset temperature may for example be
680~C (1260~F). As previously discussed a system can be designed
to operate with a variation of +/- 8~C.
With respect to the metal bath level it is measured
accurately by the level probe previously described and that level
is measured to two decimal points. A level can be maintained
accurately and for best process results the metal temperature
measurement and draw of metal are taken at the same level. The
level is used as part of a closed loop PID calculation for metal
bath temperature and determining the optimal temperature for the
preheater ambient temperature. Metal level is monitored by the
~17876~
.
- 35 -
machine program for processed control information and pour
function.
Referring to Figures 19, 25 and 26 the furnace heating
elements 215 of the upper zone 215A and lower zone 215B are
controlled by signals from an OFE2 module 581 of the PLC 574. The
signals 4 to 20 mA from the module are sent to firing boards FBl
and FB2 of the respective mother boards Cl and C2. As seen from
Figure 26 firing board FB1 controls power to zone 1 (elements 215A)
via SCR1 and SCR2. Similarly power for zone 2 heating is
controlled by firing board FB2 via SCR3 and SCR4.
The SCR's are type 319 (SDA-035) connected by way of a
power distribution block to a 480 VAC 3 phase power supply through
a 400 amp main switch PSlA. Cooling fans F1 and ~2 are shown
schematically in Figure 26. The SCR's, type 319 (SDA 035) are
available from Elkon Inc. of Dorval P.Q.
Referring to Figures 19 and 24, the latter being the
power supply enclosure there is shown the main disconnect switch
PSlA for the 480 VAC 400 amp 3 phase power supply to the furnace
heater respective upper and lower zones 215A and 215B. Zones 1 and
2 are controlled by the SCR mother boards C1 and C2.
Figure 20, a continuation of the schematic of Figure 19
shows an emergency stop switch 550, a hi-limit controller 552 with
contacts 552A and 552B and a furnace off or stop switch 554. The
hi-limit controller 552 receives signals from the furnace outer
shell T/C 260. There are light indicators 556 for main power on,
furnace hi-limit fault 558 and furnace enable 560. Mounted in the
cabinet are the mother boards C1 and C2.
Figure 21, a continuation of the furnace electrical
schematic Figure 20, shows the preheater start switch 561 and
- 2~787~
- 36 -
preheater stop switch 562 and preheater indicator enable light 562
located on-power supply cabinet PS1 (Figure 24). There is a keyed
selector switch 566 and the electrical schematic for the same as
shown in Figure 23.
The operator processor designated panel view 511 is shown
located on the power supply enclosure in Figure 24 and Figure 22
is a partial schematic for the same.
A known format is used for determining Kw rating of the
furnace. The molten bath of magnesium in the crucible acts as both
a heat sink and heat source. Enough thermal energy must be stored
in the melt to liquify an ingot to the bath temperature in a given
period of time without dropping the bath temperature a specified
amount. Acting as a heat sink, the bath can be used to control
climbing temperature by injecting ingots.
Consideration when sizing a furnace must be given to:
(1) heat loss to atmosphere, when drossing (cleaning);
(2) conduction of heat out of the melt;
(3) effects of dross acting as an insulator on the
crucible bottom;
(4) decrease in die cast machine cycle time;
(5) the use of the next larger size ingot (25 lbs.);
(6) changing to a magnesium ingot with different melt
characteristics: some of the various ingots
available are AZ9lD, AM60B, or AS41XB.
For the furnace heat control reference may be had to
Figure 27 which is a flow chart illustrating a closed loop PID
with program PLC enhancement. Interactive programming controls the
metal bath melt process by sending output signals to the two zone
firing boards FB1 and FB2. The greater the error between the set
21~876~
. .".
- 37 -
point and the process variable input, the greater the output
signals and vice versa. Additional values (feed forward or bias)
can be added to the control output as an offset (interactive PLC
programming is also used with this value and others in the PID
equation). The goal of the PID and the interactive factors
introduced by the PLC programming is to maintain the metal bath
temperature as close as possible to the desired set point.
Referring to Figure 27, 512 designates the metal bath set
point entered by an operator via panel view 511 to PLC program.
513 designates metal bath set point and metal bath temperature
descaled in PLC program for move to PID instruction. 514
designates move the above with accompanying errors determined by
PLC programming logic. Diagrammatically illustrated is the furnace
200 with the metal bath temperature thermocouple 245 and the
furnace outer shell temperature thermocouple 260. The furnace
outer shell 212 has a known area. The metal bath in the furnace
is designated 204. Reference 518 designates the PID equation.
Reference 520 designates introduce PLC programming, with reference
to furnace mode selected as well as other items to be described in
the explanation of how the closed loop PID function is used in the
program. Reference 521 refers to the biasing value controlled by
the PLC program (reference explanation).
581 is an OFE/2 module of the PLC used to output the four
to twenty milli amp control signals to the SCR firing boards FB1
and FB2. References 524 and 525 are respectively channels 1 and
2 from OFE/2 module 581 to respective zones 1 and 2 SCR firing
boards FB1 and FB2. Reference 526 designates a 4 to 20 mA signal
to zone 1 SCR firing board (gating signal) and reference 527
'~ 2178763
- 38 -
designates a 4 to 20 mA signal to zone 2 SCR firing board (gating
signal).
References 530 and 532 designate respectively firing
board power to respective zones 1 and 2 of the furnace. Reference
535 designates the metal bath temperature to IXE/B thermocouple
module 579 and includes the outer shell furnace temperature as
measured by thermocouple 260.
A programmable logic controller is designated 574 and the
operator console panel view is designated 511.
Furnace operation modes
1. Furnace Run Mode
This mode is selected by the operator via the panel view
511 (F3):
metal bath selected set point (F1) is entered by the
operator using the panel view function keys. The PLC program is
designed to accept only a valid preset, the maximum value for
example 1292~F (700~C).
the PLC program uses the metal bath set point, the metal
bath temperature from the metal bath T/C 245 and the functions
related to, and including the PID instruction to deliver a 4 to
20mA output from the OFEt2 module 522 to control the power level
sent from each zone firing board to its heat zone (215A, 215B) in
the furnace.
There are two heat subroutines also used with the furnace
run mode that are automatically controlled by the PLC and are put
into effect when proper conditioning is found in the PLC program.
Subroutine 1 - Ouick Heat - This routine becomes active for a set
time period and moves a specified feed forward value into the PID
2~7~763
- 39 -
calculation when the furnace mode is first selected and also when
the die cast machine is first placed in the auto mode.
Subroutine 2 - Feed forward Dwell
This routine becomes active for a set time period and
moves a specified feed forward value into the PID calculation only
when an auto ingot charge to the metal bath is going to take place.
This routine is used to introduce additional heat into the furnace
to offset the metal bath temperature drop before the ingot is
actually charged, this additional heat is absorbed by the ingot
through the metal bath with the heat actually coming from the
furnace outer shell.
2. Furnace Idle Routine
This mode is selected by the operator using the panel view
511:
- metal bath set point is entered and has the same conditioning
as the furnace routine. The idle routine differs in that the outer
shell thermocouple 260 is monitored for the active temperature.
By doing this the metal bath temperature and the furnace outer
shell temperature reach equilibrium, and only enough power is used
to keep the metal bath at or slightly below the lower deadband, the
program automatically switches to using the metal bath temperature
reading to move temperature back up to set point. This procedure
is a cost savings as the need for precise temperature is not
necessary for weekend or down time periods.
Furnace Safeties Include
(1) hardwire hi-limit safety controller;
21 78763
~" ,,."~
- 40 -
(2) two safety control relays, one for each zone
control safety back up contactor;
(3) Two, 100 AMP 3 phase safety contactors, one for
each SCR firing board;
(4) PLC program monitors both the metal bath
thermocouple and the furnace out shell thermocouple
for the following:
(a) hi-limit conditions;
(b) broken or shorted thermocouple;
lo (c) valid data;
(d) temperatures within safety ranges.
The above items drop out PLC logic to the main back up contactors
and void logic for firing signals to the SCR firing boards.
Furnace Logic and Control Programminq
(1) Enter valid metal bath preset;
(2) Ensure valid preset in program;
(3) Move bath preset value to panel view 511 display;
(4) Move metal bath temperature T/C 245 to panel view;
(5) Move furnace outer shell temperature T/C 260 to
panel view;
(6) Data valid check metal bath PLC prQgram;
(7) Data valid check outer shell PLC program;
(8) Metal bath hi-limit check PLC program;
(9) Outer shell hi-limit check PLC program;
(10) Metal bath temperature to decimal format PLC
program;
(11) Outer shell temperature T/C 260 to decimal format
PLC program;
~1787~3
- 41 -
(12) Metal bath preset to decimal format PLC program;
(13) Metal bath temperature checked for hi/low
temperature PLC program;
(14) Metal bath deadband upper limit PLC program;
(15) Metal bath deadband lower limit PLC program;
(16) Metal bath high temperature warning PLC program;
(17) Metal bath low temperature warning PLC program;
(18) Furnace metal data valid check PLC program;
(19) PID base timer (continual recycle) 10mS time base;
(20) Metal bath T/C 245 move for PID;
(21) Outer shell T/C 260 move for PID;
(22) Furnace run selected on store;
(23) Furnace idle selected on store;
(24) Metal bath temperature is over 1200~F;
(25) Furnace run selected on store (Variable file for
PID);
(26) Furnace idle selected on store (Variable file for
PID);
(27) Descale metal bath T/C 245 value, outer shell T/C
260 value;
(28) Descale value multiplied by constant;
(29) Move set point to PID function;
(30) Feed forward dwell timer (auto ingot charge);
(31) Feed forward biasing program block;
(32) Quick start up timer (initial furnace start/DCM in
auto one shot);
(33) Acceptable temperature range difference (set up for
quick start dwell timer);
~17~7~3
,. .~.
- 42 -
(34) FAL (File Arithmetic Logical) used to move 0-4095
value for each SCR channel to the module which will
send the 4 to 20mA signal to each board;
(35) Safety and conditioning logic for safety main back
up contactors for SCR firing boards;
(36) PID analog output block transfer read (OFE/581)
sends the 4 to 20mA signals to boards;
(37) PID analog output block transfer write (OFE/581).
The control system 500, for the melt cell, preheater,
ingot transfer and siphon tube is schematically illustrated in
Figure 26. The system includes a PLC 5/20 or PLC 5/30 processor
574 in an 8 slot rack with an integral PS4 power supply designated
582. Also resident in the rack are:
(1) 2 - 1771/IAD 120 VAC 16 point Input Modules
designated respectively 575 and 577;
(2) 2 - 1771/OAD 120 VAC 16 point Output Modules
designated respectively 576 and 578;
(3) 1 - 1771/IXE-B Thermocouple Module designated 579;
(4) 1 - 1771/IFE Analog Input Module designated 580
and;
(5) 1 - 1771/OFE-2 Analog Output Module designated 581.
The control system includes the panel view operator
terminal 511 which is connected via an I/O link to the PLC 574 and
interactive therewith, allowing operator control by assigned
function keys, access to display menus that monitor temperature
conditions, set point displays, fault conditions and allowing the
operator to monitor cycles in progress for both the ingot request
cycle and the ladle pour request cycle.
2:L78763
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Level control of the molten magnesium is done by use of
the level probe 250 which sends two separate signals to the level
control unit 250A which are then converted to a 4-20 mA output
signal which is taken to the 1771-IFE Module 580 for use in the PLC
574.
Preheating of the magnesium ingots is done using two
zones 105Zl, 105Z2 of radiant heat. Each bank of heat is made up
of three 480V 1 phase 10.2 kw radiant heating panels. A total of
six, 480V 1 phase 10.2 kw radiant heating panels provides an
intermittent load of 61.2 kw of preheater heat. Thermocouples 106,
107, 108 monitor temperatures in the preheater and output signals
to the thermocouple module 579 which interacts with the PLC 574 to
control the temperature to a preselected value.
Magnesium melt is accomplished by using two 3 phase 100
Amp 480VAC SCR Firing Boards FB1 and FB2 which are zero cross fired
and controlled by logic in the PLC 574 program. There are two
zones 251A, 251B of elements in the furnace which are 480VAC, 3
phase, 62.5 kw, 75.2 Amps. The PLC program design is set up so
that only the amount of power required to achieve and maintain the
metal bath set point is used to allow for major energy savings
compared to other furnaces on the market. Zero cross firing of the
3 phase SCR's provides for the most efficient and maximum control
while eliminating RFI as well. The three phase is Wye configured
as seen from Figure 19 for each of zones 1 and 2. Each zone is
controlled by 2 SCR's i.e. two of the three legs of the Wye
connection. Further details are shown in the schematic designated
Figure 26.
Devices associated with the furnace include:
~178763
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(a) hardwire hi-limit safety control unit 552 for
furnace with a push to test red lense pilot lamp
labelled Hi-Limit Fault 558. Back up safety hi-
limit relays CR2 and CR2A used to ensure the 100
Amp SCR contactors drop out if there ever was a PLC
failure;
(b) 240VAC white lense pilot lamp 556 to indicate
240VAC power is on/no control fuses blown;
(c) furnace start push button 555 (green);
(d) furnace stop push button 554 (red);
(e) furnace enabled pilot lamp 560/green lense push to
test;
(f) system emergency stop push button 550, red mushroom
head. Pressing this button will drop out the melt
cell as well as the die cast machine. It should
only be used in an emergency.
Other Devices Include
(a) a fault alarm buzzer which gives a signal for major
faults and an alternate signal for system warnings;
(b) a fault light beacon mounted on the control panel
preheater platform;
(c) a 3 phase 480VAC motor safety disconnect is located
above the drive motor to allow for lock out
procedure. The motor safety also has safety
interlock contacts used in the PLC program and as
a hardwire safety.
A fault light beacon mounted on the control panel
preheater platform becomes active on a fault condition. The
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audible alarm signals are delayed for two minutes after the fault
beacon becomes active to allow operator time to clear a fault
before activation of audible alarm.
Associated with the preheater are:
(a) preheater hi-limit fault, push to test pilot lamp
with red lense;
(b) preheater enabled pilot lamp, push to test with
green lense;
(c) preheater start push button (green);
(d) preheater stop push button (red);
(e) three position keyed selector switch for the siphon
tube control, auto-off-manual. The key may only be
removed in auto position.
Some considerations with respect to the control system:
(a) all contactors and relays are surge governed by
MOV's to protect sensitive electronic components;
(b) to protect these electronic components, installed
is an Islatrol Mod. IC+115, 120VAC, 15 Amp, 60 Hz
unit. This unit protects against line surges,
transient voltages and as a filter for RFI noise
that exists where welding units are used;
(c) both the furnace and the preheater are safety
interlocked with the DCM. If the emergency stop is
pressed at the DCM, both the furnace and the
preheater will drop out.
(d) all thermocouples, metal level probe and
temperature presets are monitored by the PLC to be
within specified high and low limits whether the
data is valid and for High/low limit fault
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conditions. Set point values are also clamped not
to exceed a certain value;
(e) interface between the magnesium melt cell and the
die cast machine is accomplished through hardwire
dry contact closure. Loss of a signal during a
ladle pour operation voids the metal pour and will
necessitate reset of the pour logic at the melt
cell after fault has been cleared. At no time
should the hardwire closure be bypassed as this may
lead to possible hazardous conditions, either with
the die cast machine or the melt cell.
The PLC processor 574 is linked with the DCM processor
500A and if desired as shown in Figure 26 an optional remote
computer 500B. The remote computer 500B provides process
information as well as programming and trouble shooting from a
remote location.
The panel view operator console 511 is an interactive
unit linked to the PLC 574 via a remote I/O link. This allows for
information concerning temperature displays, metal level, operator
set points and presets relating to temperature and time which is
used for the amount of pour time requested by the operator.
Excluding the hardwire safety devices previously
mentioned, all control of the melt cell unit is done through the
panel view operator terminal 511. There are four different screens
available to the operator, each screen having a different function
and accessible by the menu function key designated on the display
for the desired menu. The screens 1, 2, 3 and 4 are as follows:
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Screen 1 - Main Screen - Fiqure 29
Temperatures, metal level, pour time displays (actual),
displays of the set point or preset, selected for each function.
Set point function keys used to access the numeric key pad to enter
a new value. There are also three indicators which indicate system
conditions, which are: (a) system data (valid/invalid); (b) set
point (valid/invalid); (c) system (faults/no faults). There is
also a fault reset function key designated as well as the function
keys to access the other menus.
Screen 2 - Control Screen - Fiqure 30
The control screen is made up of all the devices and
indicators necessary to run the melt cell in an auto mode or to
perform certain functions in a manual mode. The control screen
also has indicators for system faults and system alarm condition.
There are function keys assigned to this screen to both reset a
cleared fault condition as well as a 5 minute silence alarm
function key which will also reset the alarm if it has been
cleared. If not cleared, after 5 minutes, the alarm will sound
again. If the alarm has been silenced, the indicator will flash
and show this message "ALARM SILENCED". This screen also has three
function keys assigned to menu selection to allow the operator to
go to any desired menu.
Screen 3 - Cycle Screen Menu - Figure 31
The cycle screen menu is made up of three state
indicators which react to the state of the device being monitored.
There are two independent logic cycles and both are shown with a
brief description of each adjacent to the indicator stack. Also
~78763
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on the cycle screen there is a system fault indicator and three
function keys assigned to screen menus to allow the operator to
move to any other menu.
*NOTE* Fault reset cannot be achieved from this menu.
Screen 4 - Fault Screen Menu- Figure 32
This menu is intended to give specific recognition of
individual fault conditions and as an excellent diagnostic trouble
shooting tool to decrease any down time due to a fault condition.
Also on this screen are a system fault indicator, system alarm
indicator and reset function keys for both. There are also three
function keys assigned to allow the operator access to the other
menus.
A further screen not shown is a Power Up menu. This
screen is the first screen that will come up on power up of the
magnesium melt cell. To move from the power up screen, it is
necessary to input a security code (5 digit) which will allow one
to use the menu bar to move to the menu for view.
By way of example application settings (running system)
may be as follows:
R Type Set Low High Preset
Thermocouples Used Point LimitLimit Clamped
For Temperature
Measurement
Furnace Outershell 1590~F -- 1590~F Yes
T/C 260 Part Low Safety Do
Hi Limit Not
adjust
Furnace Outershell 1540~F -- 1540~F 1540~F
PLC 5/20 In PLC-
Metal Bath T/C 245 1292~F 1202~F 1382~F 1280~F
-In PLC-
Preheater T/C 106, 425~F 200~F 600~F 500~F
107, 108 -In PLC-
2:17~763
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R Type Set Low High Preset
Thermocouples Used Point Limit Limit Clamped
For Temperature
Measurement
Siphon Inlet T/C 1256~F 1150~F 1380~F 1330~F
408 -In PLC-
Siphon Outlet T/C 1256~F 1150~F 1380~F 1330~F
407 -In PLC-
Metal Pour Time Part 1.0 3.5 Less than
Depen- seconds seconds 3.5
dant seconds -
In PLC-
Metal Level 250 84% 72% 92% Varies
slightly
on an
ingot
charge-In
PLC-
Normal metal level range between 81% to 86%
NOTE:
(1) Low and high limit values are fault conditions for the
temperature devices when the set point in the column is being
used.
(2) Pour time range is valid from zero to five seconds but no
longer.
(3) Metal level values shown are valid.
(4) Set point values for process temperatures are shown as a guide
or point to establish your own process temperatures required,
which will vary from part to part and die to die.
The main screen (Figure 29) displays are as follows:
Metal bath temperature display - Degree F (4 digit);
Metal Level Display - % (3 digit);
Siphon Inlet temperature Display Degree F (4 digit);
Furnace Outershell Temperature Display - Degree F (4
digit);
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Preheater Ambient Temperature Display - Degree F (3
digit);
Pour Time Display - Seconds (3 digit);
Siphon Outlet Temperature Display - Degree F (4 digit);
Metal Bath Operator Preset Display F (4 digit);
Preheater Operator Preset Display (3 digit);
Siphon Inlet Operator Preset Display (3 digit);
Siphon Outlet Operator Preset Display (4 digit).
Set Point:
Function Keys
Metal Bath Set Point F1 Function Key
Siphon Inlet Set Point F2 Function Key
Preheater Set Point F3 Function Key
Pour Time Set Point F4 Function Key
Siphon Outlet Set Point F5 Function Key
To enter a new set point or preset:
(1) Choose the function set point key for the desired
process set point or preset value that requires
updating.
(2) Press the function set point key and two things
will happen: (a) the representation of the function
key on the screen will change from black lettering
on a white background to gold lettering on a blue
background, and (b) an area at the top of the
screen will appear in yellow, this area is called
the scratch pad.
~ 2~7~76~
- 51 -
(3) Use the numeric key pad to enter a new value into
the scratch pad. When this is done, press enter.
This allows logic in the PLC program to determine
whether the value entered is valid or not.
(4) A valid preset or set point entered is acknowledged
by the PLC and will result in this new value being
displayed in the appropriate preset window. The
function key representation on the screen will
revert to black lettering on a white background and
the value that was entered is now the PLC working
value. At this point, press cancel to remove the
scratch pad from the screen.
(5) An invalid value entered will result in a message
across the bottom of the screen in red and flashing
which says "N0 HANDSHAKE". Also all zeros will
appear in that process preset display and the
function key representation will stay gold
lettering on a blue background. To clear the
fault, press F8 function key and then re-enter a
valid value for that particular process.
The cycle screen (Figure 31) monitors both the request
and the pour request cycles by using multi-state indicators with
tent messages to allow the operator to be able to monitor these
cycles and also as a trouble shooting aid to pin point quickly a
fault source in either cycle. This screen monitors the appropriate
devices in both auto mode cell operation as well as in an operator
driven manual mode select.
Sequence of events on pour requests are:
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(1) Die cast machine requests a ladle pour (amount of
metal determined by pour timer preset selected on man screen).
(Minimum pour 1 second/3.5 seconds maximum pour value).
(2) All logic safety conditions for the die cast machine
and the melt cell are valid.
(3) Metal bath level is in the 72% to 92% range
(desired level is between 81% to 86%);
Metal bath temperature is in the 1292~F to 1382~F
range;
Siphon tube temperature is in the 1256~F to 1380~F
range;
Pour time preset is valid, between 1 second to 3.5
seconds;
Preheater ambient temperature has been above 200~F
(minimum value) for 2 minutes at least.
(4) All above conditions met, pour request will then
initiate siphon cycle on.
t5) Siphon tube lowers to die cast machine shot sleeve
pour hole.
(6) Siphon tube lowered LS425 becomes true when tube is
in the pour position at DCM pour hole.
(7) Siphon valve opens making siphon valve LS406 true.
(8) Siphon valve will close after pour preset timer
times out.
(9) Siphon valve closes LS406 no longer true.
(10) Siphon tube drip timer times out/shot release/ to
DCM.
(11) Siphon tube begins to leave DCM pour hole, LS425
siphon tube lowered no longer true.
~178763
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(12) Shot release 2 is now sent to the DCM, this signal
initiates die cast machine cycle shot.
(13) Siphon tube has risen to home position LS420 is made
indicating tube home.
(14) Pour request is a latched condition in the PLC 574
program, it unlatches after a successful pour or when there is no
longer a ladle request and the die cast machine toggles locked
signal is no longer true;
Siphon cycle latched condition is monitored in many
different ways in the PLC program to cancel the cycle if a fault
occurs. Some of these are as follows:
(a) siphon tube cycle timer
(b) siphon watch dog timer
(c) valve fault timer
(d) metal level under range
(e) pour request from DCM no longer present
(f) emergency stop condition
Ingot Charge Routine
Auto Ingot Charge:
When all safety logic conditions are met, the melt cell
will maintain a metal level of 85% plus or minus 2%. The minimum
and maximum values for metal level are valid from 72% to 92%. An
ingot charge may only take place when the preheater ambient
temperature has been over 200~F for at least five minutes. This is
done to ensure that the ingot have had a minimum amount of time to
heat up to help avoid shocking the metal in the pot and causing
high outer shell temperature build up.
~178763
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The preheater will also charge ingots at a times interval
if the metal bath temperature is over the set point range by 10%
but will only charge to a metal level of 92%.
With reference to the cycle screen - Figure 31
Sequence of events (auto):
(1) Ingot request enabled.
(2) Ingot conveyor is checked for home position LS115.
(3) Push rod advances to LS310, charges ingot to chute.
(4) Time delay, then guillotine retracts to LS331, ingot
slides into metal bath.
(5) Time delay, guillotine advances to home position
LS330.
(6) PLC 574 logic checks the cycle okay.
(7) Ingot conveyor indexes one position to present next
ingot to the charge ingot position.
Referring to the control screen - Figure 30, all of the
control devices needed to operate the magnesium melt cell are
contained on this screen.
The exceptions to this are:
(1) Associated with the furnace hardwired start and stop
for the furnace control and a system emergency stop mushroom head
push button (the emergency stop will drop out power to the melt
cell and the die cast machine); and
(2) associated with the panel view hardwired start and
stop push buttons for the preheater control. Also, a keyed
selector switch for selecting the siphon tube control
Auto/Off/Manual.
217~76~
.
- 55 -
A remote pendant on a twenty foot cable may be used for
manual control of the siphon tube, a selector switch for raising
or lowering the tube, and a push button for opening and closing the
siphon tube valve. There is also an emergency stop push button
that will if used, drop out the control circuit for the preheater
only, which will in turn close the siphon valve and raise the
siphon tube to the home position. Manual siphon control is only
used for set up purposes and must meet safety precautions
established in the PLC program before the siphon tube control
manual selected indicator hi-lites indicating manual tube control
enabled.
Control devices peripheral to the panel view control
screen include:
(1) The manual siphon tube control pendant which has
already been discussed earlier in this section.
(2) A motor safety disconnect mounted on the top
platform of the preheater melt cell to be used when working on the
conveyor unit. This device also incorporates an auxiliary contact
unit that monitors as well as mechanically opens the control
circuit to the motor conveyor contactor. Disconnect switch open
is indicated on screen four (fault screen - Figure 32).
(3) Air supply shut off which is part of the air filter,
regulator, lubricator unit.
(4) An alarm annunciator mounted on the main control
cabinet (left hand side when facing the electrical control main
cabinet). The annunciator used for system fault and system invalid
data. There are two different audio signals.
(a) Priority System Faults (i.e. metal level high,
preheater hi-limit, metal bath hi-limit, outershell
~ ~ 78763
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furnace temp hi-limit, etc.). The alarm is
continuous and annunciator will sound without stop.
(b) Priority System Cycle Faults (i.e. conveyor
faulted, guillotine cycle fault, siphon tube cycle
fault, etc.). The alarm will sound for 45 seconds
on, 30 seconds off.
(c) Alarm annunciator may be silenced by pressing
Push/Alarm Silence Function Key P.B. F8 on the
control screen. This will silence the alarm for
five minutes. If fault cleared before time out,
the alarm will not sound again. If fault not
cleared, the alarm will sound again, etc.
(d) Remote fault beacon signal mounted on top of
preheater control cabinet on platform to signal
selected fault conditions.
It is the operator's responsibility to ensure all safety
procedures are followed before, during, and while the magnesium
melt cell is in operation in either a manual cycle routine or in
the auto run mode. The following is a list of checks that should
be made before operation:
(1) Ensure the main supply switch is turned on.
(2) White power ON pilot lamp must be lighted to ensure
control voltages are present.
(3) Ensure both the furnace Hi-Limit Fault and the
preheater Fault Pilot Lamps are OFF (these pilot lamps are push to
test type and should be checked by operation at the beginning of
every shift or as set out by the purchaser).
(4) Ensure that the CO2SF6 protection gas mixture is
active and acceptable (set out by the purchaser).
~17~763
,
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(5) Ensure the air is turned ON to the magnesium meIt
cell (minimum 90 PSI required).
(6) Ensure the motor safety disconnect is in the upright
position (ON).
(7) Ensure thermocouple wiring to the metal bath, siphon
tube inlet, siphon tube outlet and the level probe are in good
repair. Ensure all thermocouple jacks are firmly seated in their
appropriate receptacles.
(8) Visually inspect the 240VAC 1 phase cables going to
the siphon tube connection box mounted on the tube. At this time,
check the valve open/closed limit switch (LS3) for mounting
tightness and that the activator arm is also tight.
(9) With appropriate safety apparel check both metal
bath thermocouple and the level probe for dross build up on them.
Both must be dross free as possible for accuracy. Caution must be
taken with both devices as they are easily broken if not treated
with care. Also, after these units are set up, if moved it is
imperative they be replaced to the height they were set up for.
(10) Start the furnace and then start the preheater. It
is a good practice to operate the emergency stop on the cabinet to
ensure that the E-Stop string is intact. When operated, the
furnace, preheater and die cast machine will stop. Restart the
devices and continue with the start up routine.
(11) On the panel view operator terminal, using the
screen select buttons, do a visual check to ensure all menus are
accessible.
(12) At this point, the power on pilot lamp (white),
furnace enabled lamp, and preheater enabled lamp should all be on.
On the panel view operator terminal, go to the main screen and
~l ~8763
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select the presets desired for the application temperatures and
pour preset.
Temperature and pour preset are retentive and when set
will not need to be re-entered when the cell or preheater is turned
off.
On the control screen, certain devices are also retentive
and care must be taken to de-select or push off when no longer
required or desired. These items on the control screen are
labelled as PUSH ON/OFF.
Manual Ingot Conveyor Load
(1) Ensure all normal start up conditions are met.
(2) Use conveyor cycle selector to select manual
conveyor.
(3) Ensure (a) ladle select is off; (b) auto charge is
off.
(4) Conveyor mode indicator should show - MANUAL -
selected.
(5) Press load ingot conveyor, one shot on PB (F14).
(6) This will cause the ingot conveyor to index one
position (with no ingot charge sequence taking place).
(7) To repeat process, repeat step 5.
This routine allows the set up operator to load the ingot conveyor
to a comfortable height and then advance the conveyor to a position
where loading ingots can be continued. The operator is not
overloaded, surplus ingots will be dropped onto the upper platform
if this happens.
~ 217~76'3
- 59 -
Auto Cycle Mode Set Up
(1) Ensure all normal start conditions are met.
(2) Furnace enabled on indicator is on.
(3) Preheater enabled on indicator is on.
(4) Siphon tube control, auto selected indicator is on
(Key S/S 1 must be turned to auto).
(5) Furnace run mode select (F3) must be on.
(6) Ladle select on mode (F5) must be on.
(7) Auto charge selected on mode (F13) must be on.
(8) Conveyor cycle selector must have auto cycle
conveyor on SELECTED (it will be in reverse video). Conveyor mode
indicator will show AUTO SELECTED.
In auto running mode, all cycles are controlled by the
magnesium melt cell PLC 574 and in conjunction with the die cast
machine. Siphon tube cycles, ingot charges and conveyor movement
take place when required. Personnel working in close proximity to
the cell need to be aware of the fact that they must be extremely
careful when the cell is running in auto mode with the die cast
machine.
Manual Inqot Charqe
(1) Ensure all normal start up conditions are met.
(2) Use conveyor selector to select manual conveyor.
(3) Ensure (a) ladle select is off; (b) auto charge is
off.
(4) Conveyor mode indicator should show - MANUAL -
selected.
(5) Press manual ingot charge, one shot on, PB. F6.
(6) Push rod will charge ingot into chute.
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(7) Guillotine will open after time delay.
(8) Ingot charges to pot, guillotine closes after delay.
(9) Push rod retracts to home position.
(10) Conveyor will index one position to place an ingot
in the charge position for next cycle.
(11) To repeat process, repeat step 5.
This routine is useful to recharge the pot after changing
from one ingot alloy to another when the metal level was lowered
considerably. Monitor the metal level bath display when using this
routine to ensure against overfill condition.
Manual Conveyor Home
(1) Ensure all normal start up conditions are met.
(2) Use conveyor selector to select manual conveyor.
(3) Ensure (a) ladle select is off; (b) auto charge is
off.
(4) Conveyor mode indicator should show - MANUAL -
selected.
(5) Press conveyor home, one shot on, PB. F10.
(6) Conveyor will advance until the conveyor home LS115
is made, then the conveyor stops.
This routine is only available when, if for some reason,
the conveyor when indexing never made it to the home position or
if LSllS has gone out of adjustment. Indicator message blocks on
the control screen show the conveyor mode, cycle and status of the
conveyor at all times. Fault screen would also show a fault
condition if the conveyor was not in the position when program
logic says it should be.
~ '3~ 7~7~
- 61 -
Manual Siphon Control Mode
(1) Ensure all normal start up conditions are met.
(2) Preheater control ON (preheater enabled).
(3) Siphon Tube manual enable S/S2 ON.
(4) Die closed signal from DCM true.
(5) Die open signal from LOCKRMAT (trade-mark)
protection is false.
(6) Die open signal from DCM is false.
(7) DCM in auto/or semi auto signal is false.
(8) Shot rod fully returned at DCM is true.
(9) When these conditions are met, the function siphon
tube manual enable will be true.
This mode is used for checking:
(1) Operation of the siphon tube raise/lower.
(2) Valve open/close to check for proper seating of the
valve.
(3) To ensure guide bars allow for smooth raising and
lowering of the siphon tube.
(4) To check proper indications from the siphon devices,
LS425 siphon tube down; LS420 siphon tube raised; and the siphon
valve open/closed LS406.
(5) Used also for lining the siphon tube to the DCM pour
hole and checking appropriate clearances.
This mode is not intended, nor programmed for manual shot
capacity. It is intended to be used only as an aid for setting up
a tube for operation and as an aid for trouble shooting problems
with the siphon tube and its peripheral devices.
~1 78763
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A manually controlled shot is controlled by the DCM logic
and is treated by the appropriate logic in the melt cell processor
as such.
A program can be readily varied, provided and/or
redesigned by those skilled in the art to provide the previously
described sequences or the other process sequences as may be
desired dependent upon the metal and/or employment of the molten
form thereof.
In the foregoing melt system the computer control system
is provided with signals from the various sections as follows:
Preheater and conveyor
Temperature sensors 106, 107, 108 conveyor index
limit switch 115 and 151 motor safety switch 116;
Ingot transfer
Push rod cylinder unit 301 advance proximity sensor
310;
Push rod cylinder unit 301 retract proximity sensor
311;
Gate cylinder 308 advance proximity sensor 330
(gate closed);
Gate cylinder 308 retract proximity sensor 331
(gate closed).
Furnace
Metal bath temperature sensor 245;
Furnace casing temperature sensor 260;
Metal level sensor 250.
Siphon Tube
Temperature sensor inlet 408;
Temperature sensor outlet 407;
2~78763
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Tube lower (pour) proximity sensor 425;
Tube raised proximity sensor 420;
Pour valve limit switch 406.
This provides a system operable with small variations
from preset values, i.e. metal bath +/- 8~C as one example and with
approximately 1/16 inch variation in metal level.
A fewer number of sensors can provide an operable system
where wider variations from set values could be tolerated.
For example a single temperature sensor could be used in
lo the preheater to control the temperature therein and permit ingot
charging when the ingot is deemed to have reached a suitable
temperature. The furnace perhaps could have signals only from
sensors responsive to metal bath temperature and molten metal
level. The siphon tube for example could perhaps have only one
temperature sensor and the position proximity sensors.
In both the sophisticated system and sample system all
signals from the sensors are processed and utilized by the
processor to control the system at all times.
Trouble Shootinq Tips
(1) The panel view has been set up to make locating a
fault as easy and as quick as possible by using the control, cycle
and fault screen. In most cases, the fault itself will be
indicated and the associated text tells what the condition is.
(2) An intermittent fault might best be found using the
cycle screen and watching the cycle develop. In more than 90% of
all indicated fault conditions, the fault will latch an associated
latched store in the program to latch the fault indicator so even
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if the condition clears itself, you will still know what took
place.
(3) For improper or faulted temperature devices, the
thermocouple wiring is always a good place to start as it is very
susceptible to magnesium being splashed on it or resting against
hot surfaces.
(4) In case of level control faults; check cable, dross
build up on the level probe or damage to the probe itself.
(5) In auto mode, no siphon cycle yet no faults showing;
ensure all safety conditions that come from the die cast machine
are true. If not, the siphon tube will not cycle. Does screen 2
(control screen) show a ladle pour request?
(6) Furnace temperature is too low; check that the metal
bath preset is set so that the furnace should be on. Look at the
SCR firing boards and see if they are firing. If they are, the
leds on the control boards should be coming on and then going off.
If need be, check the 100 amp line fuses to the board and the SCR
fuses on the board itself. Other things to check - conductor
connections to the elements, resistance leg to leg of the elements
themselves.
(7) Furnace comes on but the preheater won't; ensure the
remote siphon control pendant emergency stop button hasn't been
pressed.
A thorough start up routine is not only good for a safe,
smooth production run but it is also when a number of potential
problems can be spotted before they become a down time factor, i.e.
melted insulation on thermocouple wiring, loose proximity sensors,
air leaks or motor/conveyor fittings requiring lubrication.
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The overall life of a furnace is dependent on several
factors. It would be impossible to list all areas of concern.
However, there are a few procedures that can improve the overall
life. For greater heating element life and module longevity, the
following is recommended.
Initial Heat-Up - Ceramic Fiber
Pyro-Bloc ceramic fiber modules contain a small amount
of lubricant, tless than 1/2% by weight). This is added during
production and enhances the handleability of the fiber. In most
applications this does not present any concerns.
For the initial heat-up open the furnace to the ambient
air and slowly elevate to the maximum heating element use limit.
This will eliminate a majority of the lubricant from the ceramic
fiber. The organic material will start to carburize at 250~F and
will be totally burned out at 600~F. This is especially wise in
cases where the furnace is tightly enclosed, an atmosphere is
introduced, or in a slight vacuum. This process can be
accomplished in approximately seven to ten hours, (steady state or
equilibrium may vary depending on the material thickness and the
operating conditions). Outside venting is advisable in a small
building.
Initial Heat-Up - Heating Elements
The life of a resistance heating element depends on a
continuous presence of a dense oxide layer completely coating the
element surface. Corrosion results from the interference with this
formation and replenishment of the oxide layer by the presence of
specific compounds in the atmosphere. The greater the
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interference, the shorter the element life. The effect of the
corrosive compounds is often temperature dependent.
Pre-oxidized elements provide a protective oxide coating,
ensuring a longer life. It is recommended that the element be re-
oxidized after 250 service hours (held at service temperature for
5-10 hours in an oxygen-containing atmosphere).
Heat-up rates for refractories (castables, IFB, etc.)
require additional time.
The use of circulating fans should be discontinued until
after the heat-up procedure is completed.
Special precautions are required for electrically heated
ceramic fiber lined furnaces operating with an endothermic
atmosphere. Periodic carbon burn out procedures are required to
eliminate carbon build up. Carbon precipitates from the atmosphere
at temperatures below 1400~F and may build up with the lining where
the thermal gradient drops below this temperature. Carbon build
up may not be apparent on the fiber surface; therefore, it is
critical that the burn out procedure be followed. Carbon within
the lining may cause premature failure of the elements and element
supports through electrical shorting and arcing. To remove the
carbon from the furnace lining, the furnace should be heated to
1800~F or above. An air atmosphere should be in the furnace
chamber. Once at temperature, the furnace should be opened
slightly, allowing air to infiltrate. The carbon will burn as long
as the temperature is above its ignition point and there is
adequate oxygen.
A surface coating of Unikote M (trade-mark) is
recommended to improve the lining integrity during burn out. The
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coating should be applied after the element supports are installed.
For ease of application, spraying of the coating is recommended.
Rod type heating elements are preferred as they are
superior to ribbon elements in an endothermic atmosphere. The
carburization of the thin cross section of a ribbon element occurs
much more quickly than through the thicker rod type elements.
Proximity sensors 310, 311, 420, 425, 330 and 331 are
activated by a magnetized selected area on the push rod and
activation is thus dependent upon the extended or retracted
lo position of the push rod.
