Note: Descriptions are shown in the official language in which they were submitted.
~o 93/18899i~ 3 ~ ~ Pcr/US92/02
T~E
SYSTEM FOR ~EEDING AND MIXING MULTI-COMPONENT
MOLDING COMPOSmONS
FIELDQF l~lNVENTIO~
This invention relates to a system for supplying a plurali~ of
different components in controlled amounts and component conditions to a
molding machine. More particularly, the invention relates to a system for
drying a plurali~r of different particulate molding composition ~omponents,
lO m~untaining tbe state of d~yness of the components ~roughout the system,
blending the particulate components and ~ng the components ~nth a
reinforcing component to obtain a uniform mixture of all components and
feeding the mixture to a molding machine.
; ~ BACKGROIII~QF ~E ~NTION
5Supplying a p urali~r of different components to a molding
- ~ ~ machine in precise amounts and in the desired condition has been a problem.
This problem is aggravated in molding operations involving large parts which
are being used in increasing numbers in automotive applications, and in
particular in molding such parts which are reinforced with fiberglass.
2 o The use of thermoplastic pclymers which are re~yclable is
becoming more important in large part molding applications. Many of these
polymers are subject to hydrolytic degradation at molding temperatures and
must be delivered to a mold~hg machine in a dry state.
Fiberglass which is used to reinforce the molded parts is
delivered ~om the manufactltrer in the form of chopped bundles. DuIing
handling, in particular mixing and feeding the fiberglass to a molding
machine, the bundles tend to be broken apart forming "fuzzballs" whicb
cause system pluggages and over-rich areas of fiberglass which detract from
the ntolded article properties. The fine fibers from the bundle brealc up,
blocking air filters and transport lines.
The ~ em of the present invention perm~ts combining
multiple components in precise rados while at the samc dme dlying and
maintaini~g the d~yness of the ingredients throughout the propordoDing,
~; ` transpor~ mixing and feeding operadons. Handling of the chopped fiber~pass
35 is conducted in such a way as to keep fibrillation and nPuz~ ball" formation of
the fiberglass to a minimum.
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SUMMARY OF l~E INVENTION
The system of the present invention comprises a plurality of
holding bins for the particulate moldi~g material components. Each
component requires its appropriate dr ying condition. Separate dryer hoppers
5 are provided for each component. Each hopper has its own heater control
which adjusts the temperature of the conditioned air, i.e., dehumidified air,
prior to its entry into the individual drying hopper. The transport system
from the drying hoppers to the molding machine is supplied with conditioned
air. An air transport loop is included which utilizes dehumidified air
10 provided by a dehumidif~ring dryert filter and compressor. The drying hopper
for each component is equipped with a special discharge valve to allow
pickup of the discharged contents witb dry air for transport to smaller
inventory supply bins which are a part of a compact gravimetric weigh unit.
These bins empty by gravity to vibratory pan feeders which deliver the feed
15 from the respective bins to a weigh hopper which is suspended from a
precision weighing strain cell. The weigh hoppers are filled to tbeir pre~ise
weights through automatic feedback control between weigh cells and
amplitude and timing controls to vibratory pan feeders.
A transport hopper is designed with steep sides to handle the
2 o components which have widely different physical properties and handling
characteristics. Typically, the hopper is ellipto-conical in shape and will havea ve~tical forward wall and a steep ~70) sloping rearward wall arranged in a
frustro-elliptical pattern~ -
The preweighed components are then transported vîa a
2 5 pneumatic conveying ~venturi) system using conditioned air to a holdinghopper located adjacent a molding machine.
The particulate components which have been preweighed and
held in the holding hopper are released to a mixer. It is important to release
the particulates into the mixer prior to introducing fiberglass to eliminate
3 o excess tumbling which could produce fiberglass "fuzzballs".
The fiberglass component is handled in a very special and
careful way to avoid fibrillation of the fiberglass bundles and to prevent the
formation of "fu~balls"~ The cbopped fiberglass is received from the
supplier in a bulk container, preferably in large bulk bags which typically
3 5 weigh 1000 to 2000 lbs. Fiberglass is fed to a weigh hopper until tbe correct
weight is achieved in accordance with a control set point and in accordance
,~ ~) 93/18899 PCr/US92/02141
~13~(~4~
with a set ratio and other set ratios for other ingredients. Upon command
from a central control station, the discharge gate of th_ ~Iberglass weigh
hopper is opened. Simultaneously or nearly simultaneously, a purge air
sealed gate valve is opened momentarily allowing flow of the measured
5 fiberglass charge into the mixer.
Reinforcing components în addition to or in lieu of fiberglass
may be used in the system.
The components are m~xed proximately above the molding
machine. A horizontal shaft t~pe mixer with internal lifting and directional
10 elcments causes all thc components within the mixer to be gently tumbled
together so as to create a homogenous m~xture with limited rotations and
controlled speed of the apparatus. The separate handling of the fiberglass
using only gravity (except for the vibratory feeder) to unload and direct the
fiberglass down into the mixer is important to preserve the integrity of the
- 15 fiberglass bundles thereby reducing fibrillation to a m~nimum. Once the
requi~ed number of mixer revolutions has occurred to obtain a uni~or n
~ mixture, a full bottom, close-fitting, contoured discharge slide-gate is opened
;~ on command from a central control station. This allows the charge of well
mixed` components to enter the holdup hopper and the throat of tbe molding
machine. By locating the mixer proximately above the extruder, segregation
of the components is not allowed to occur because of differences in solids
flow characteristics of ~he components. Thus the mixture's homogeneity is
preserved, via plug flow, to i`~i entry into the molding machine. Glass
breakage and nfuzzball" format~on is held to a minimum thus enhancing the
2 5 molded part pr~rties.
BRIEF I)E~CRIl~ION OF l'HE DRA~INGS
The FIGURE is a schematic diagram showing a preferred
embodiment of a component supply system according to the invention.
DETAII~ED D13SCRIPTION OF THE I~VENTION
Referring now to the drawings, a plurality of particulate
molding composition components are stored in holding bins 10, 12, 14, and
16. The components are delivered through feed lines 2Q 22, 24 and 26 to
dryer hoppcrs 30, 32, 34 and 36 which are eacll equipped with individually
controlled heatcrs. Transport air is supplied to the dryer hoppers from
- ~ 35 master dryer unit 28 through line 18. Conditioned ~dly) air is supplied to the
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2~-3;~84~ 4
dryer hoppers from dryer 110 through heaters 112, 114, 116 and 118 which
are located in conditioned air supply lines 120, 122, 124 and 126.
The particulate components may include thermoplastic
polymers among which are polyesters and polyamides, toughening agents,
s various additives such as viscosity reduction agents, colorants, mold release
agents, antioxid~nts, W light stabilizers and ~lame retardants. Recycled
thermoplastic polymer such as recycled bottle resin from postconsumer
polyethylene terephtbalate soft drink bottles may also be used. When the
components have reached the desired level of dIyness, they are transported
through feed lines 4Q 42, 44 and 46 by conditioned air to inventory supply
bins 50, 52, 54, and 56. Each bin employs one vertical wall and xteep angled
side walls to promote the evacuative flow of its particular contents. Each
feeder's receiving port is loosely connected through a coated flexible sock to
its individual feed bin and similarly at its exit to weigh hoppers 60 and 60' tolS prevent ingress of room air, excess lQSS of purge air, and the escape of any
particulate material.
0~ command from a central controller, predetermined
amounts of the components as determined by gra~nmetric weigh units 48 and
48' are fed to weigh hoppers 60 and 60'. Each hopper is suspended from a
~o weigh cell 58 and 58' controlled to yield an accurate w¢ight for tliose
components designated to pass through it. For example, a total charge could
be 50 lbs (22.7 kg) composed of components, respectively, of 35%, 35%, 25~o
and 5~o irom inventory bins~0, 52, S4 and 56. Separate wei~h hoppers 60
and 60' provide for simultaneous weigh-up and an inc~ease in ~ycle speed.
The feeders of the weighing units are preferably covered pan
high frequen~y vibrating units although auger feeders could be used. The
pan feeders have the general advantage of delivering vely uniformly under
precise control at the lip whereas auger feeders have the disadvantage of
slugg~ng slightly as material from each thread pitch is delivered.
3 o CoDsequently, the range of precision of each auger is limited more so than a
vibrating pan feeder.
Weigb hoppers 60 and 60' are filled to their precise wdghts
tbrough automatic feedback control between weigb cells and amplitude and
timing controls to vibratory pan feeders. The two or more components
3 5 designated for each weigh hopper are fed in sequence. Both weigh hoppers
can be operated in sequence or at the same time. When the designated
,vo 93/18899 21 ~ 2 ~ 9 'I PCr/US92/02141
weight charges have been reached in the weigh hoppers, the charges are
automatically dropped into a scale collection hopper 64 by the opening of
1apper valves 62 and 62' on the bottom of the respective weigh hoppers.
The combination of weigh hoppers, flapper valves and collection hopper is
5 referred to herein as a confluencing means. Dry air is supplied to the
confluencing means to prevent ingress of atmospheric air.
Hopper 64 is designed with steep sides to appropriately handle
the components fed thereto which have widely different physi~l properties
and handling characteristics~ Typically, this bopper is ellipto conical in sha~,0 and will have a vertical forward wall and steep (70) sloping rearward wall
~; arranged in a f~ustro-elliptical pattern.
The preweighed components are transported via a pneumatic
conveying (venturi) system 66 and feed line 68 using dry air to a dry air
purged holding hopper 70 located proximately above an injec~on molding
5 machine 96.
A iberglass source, bulk bag 80, is suspended from a holding
rack which is supported by superstructure 72 a~d travelling crane 74. Using
; long-almed glove ent~y ports 82, drawstrings on bag 80 can be untied and the
bag's downspout placed inside a funnel to discharge apparatus 84. The large
20 sacks are characterized by a bottom seal composed of an inner tubular funnel
tied together with a dra~s~ring de ~ice and with outside flaps which are also
operated with a drawstring device and tied with a knot. The ~llled sack is
lowered onto the top surface-of a discharge box 88 which contains a flexible
rubber seal which envelopes the disch rge area of the sack. Steep sides, one
2 5 vertical~ on the discharge box direct the fiberglass to a sock sealed vibrator,v
covered pan feeder 85. Through a sequence control station, the feeder
directs ~ fibergl~ss into a separate weigh hopper 86. This weigh hopper is
support~ from the superstructure with a weigh cell. Fiberglass is allowed to
enter the weigh hopper 86 until the correct weight is achieved in accordance
3 o with a control set point ar~d in accordance with set ratios with the other
ingredients.
Reinforcing components in addition to or in lieu of fiberglass,
such as mineral fibers, c~rbon fibers and aramid fibers, mica, glass or ceramic
spheres and the lL~ce may be used in the system and fed to weigh hopper 86 as
35 described above.
WO 93/18899 PCT/US92/0214.
2~3~28~
MLxer 90 is placed proximately above the feed throat of
molding machine hopper 94. Ingredients which have been fed from
inventory supply hoppers 50, 52, 54 and 56 and from the fiberglass feed
source 80 are gently tumbled together and after a homogenous mixture is
obtained are released by a contoured-discharge slide gate valve 92 on
command from a central control station to machine hopper 94. By locating
the mLxer proximately above molding machinë 96, segregation of the
components due to differences in solids flow characteristics of the
components is not al~ed to occur. Also, fu~ball formation and glass
breakage is held to a-~sinimum. - ~
It is critical that mixing of the particulate components and
fiberglass be carefully controlled. As indicated earlier herein, the
particulates should be fed into the mixer prior to feeding the fiberglass;
however, with careful control the different materials may be fed
simultaneously to the mLxer.
~- A high efficiency magnetic grate 95 is located at the bottom of
machine hopper 94 to remove any magnetic tramp materials that might have
entered the ~ystem with compvnents or from machine~y breakdown. The
- ~ ~ high effidency magnet allows for wider spacing of bars in the grating
permittingfreeflowofthecomponents~
The mixture of components is fed, via plug (gravity) flow into
the moveable portion 98 of injection moiding machine 96 where the plastic
components are melted andblended with the other components after which
the mixture is fed to tool 100 to form a molded part.
The system can be fully automated and can be programmed to
deliver the precise quantities of the various components desired for a
particular product to a molding machine. An essential requirement for the
successful operation of the system and obtaining quality molded parts is
providing dry air for the transport of components. Air is fed to the system
3 o through supply line 102 through filter 78 to heat exchanger 104. Master dryer
unit 28 includes a dew point meter 106 as well as other controls to deliver
conditioned air to tbe system. Purge air can be supplied by a separate dryer
108 througb feed line 38. The purge air dryer supplies debumidified
blanketing air to various system units thereby prcvendng ingress of nearly all
room (ambient~ air into the system.
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Modifications to the system can be made. For example, the air
supply and drying means could be combined in a single master unit, and
inventory supply bins could be eliminated with the particulate components
being fed directly to associated weighing and confluenc,ing means adjacent
5 the fiber glass supply source. Accordingly, the invention should be
understood to include embodiments which can be made without departing
from the principle of the invention set out in the appended elaims.
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