Note: Descriptions are shown in the official language in which they were submitted.
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Background of the Invention
The wire feed process of adding treating agents
to molten metal being poured into a casting mold cavity
for controlling the microstructure of the solidified
casting heretofore included determining the average
pouring rate of the molten metal and then feeding the
treating agent in wire form at a preselected constant
feed rate into the molten metal flowing through the down-
sprue. The average pouring rate was calculated by timing
the length of time it took to pour the molten metal into a
particular casting and then weighing the finished casting.
It has been found in practice that the rate of
liquid molten metal flowing into some casting mold cavities
may change as the cavities are filling due to changes in
pressure head, mold atmosphere pressure, fluid flow be- -
havior and the temperature of the molten metal. With the
wire feed process of adding treating agents to mol~en metal
being poured into such cavities, the treating agent may not
be added uniformly throughout the pour since the wire feed
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rate is constant and the molten metal pouring ~ag~ varies
throughout the pour.
Summary of the Invention
The invention provides an improved method and
apparatus for introducing an additive material into a
molten metal at a variable rate in which the additive
material in wire form is fed into the molten metal at a
variable rate which is determined by the instantaneous
pouring rate of the molten metal throughout the pour.
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According to the present i.nvention, th,ere. is pro-
vided a method of ïntroducing an additive material i.nto a
molten metal at a variable rate., ,comprising the s,teps of:
pouring a molten metal i.nto a downsprue of a casting mold;
feeding the additive material în the form of a wire, into the
molten metal in the downsprue initially at a preselected
feed rate; weighing the casting mold prior to pouring
the molten metal thereinto and thereafter continuously through-
out the pour; comparî.ng incremental weight changes throughout
the pour; converting th.e incremental Neight changes into an
instantaneous pouring rate of the molten metal; providing
an output signal commensurate with the pour;ng rate of the
molten metal; transmitting the output signal to a varia~le
speed drive motor of a wire feeder; and automatically de-
creasing the speed of the variable speed drive motor and hence
- the feed rate of the wire in direct response to a decrease in
the pouring rate. ~:
According to the presen~ invention there is also
provided an apparatus for introducing an additive material
into a molten metal of the type having a wire feeder to feed
an additive material in wire form into a stream of molten
metal flowing through a downsprue of a casting mold and into
a casting cavity, a varia~le speed drive motor for
varyi.ng the rate at which the wire i.s fed into the molten
metal and a speed control device associated with the variable
speed control motor for controlling the speed thereof, the im-
provement comprising: means for electronically weighing the .
casting mold initially prior to pouring molten metal there- ,
into and thereafter continuously throughout the pour .
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so that a signal is generated commensurate to the increase
in weight caused by the addition of the molten metal to the
casting mold; and a computer operatively connected to the
weighing means to receive the output signal and being connec-
ted to the speed control device associated with the vari-
able speed drive motor of the wire feeder, said computer
being of a construction sufficient for determining the
instantaneous pouring rate of the molten metal by com-
paring incremental weight changes and for directing an
output signal to the speed control device to decrease the
feed rate of the wire in direct response to a decrease in
the pouring rate of the molten metal.
Brief Description of the Drawing_
The sole figure is a schematic representation of
one apparatus for practicing a method of introducing an
additive material into a molten metal at a variable rate
embodying the principles of the present invention.
Description of the Preferred Embodiment
The method of the present invention relates to
varying the rate of feed at which a wire of additive
material is introduced into the molten metal in response to
changes in the instantaneous pouring rate of the molten
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metal. The term "pouring rate" as used herein refers to the
rate at which the molten metal flows through the downsprue
of the casting mold. The method includes the steps of
feeding the additive material in wire form-into the molten
metal in the downsprue initially at a preselected feed rate,
determining the instantaneous pouring rate of the molten
metal continuously throughout the pour, and automatically
varying the feed rate of the wire in direct relation to
changes in the pouring rate of the molten metal.
One apparatus for accomplishing the aforesaid
method is schematically illustrated in the drawing with the
apparatus including a casting mold generally indicated by
the reference numeral 11 and which has a pouring basin 12
formed in its upper surface. The casting mold is positioned
to receive a stream of molten metal 13 in the pouring basin
from a ladle 14. The moIten metal flows from the pouring
basin through a downsprue 16, a runner 17, and into a casting
cavity 18 which, in this case, is for a cylinder liner of a
- diesel engine. Typically, several individual casting cavities
are provlded in the casting mold ~ith the casting cavities
alI connected to a runner. However, for illustrative conveni-
ence, only a single cavity is shown.
A wire feeder is schematically illustrated at 19
and is operative to feed the additive material in the form
of a wire 21 from a spool 22 downwardly into the downsprue
16 ahd the molten metal flowing therethrough. The wire
feeder includes a pair of rollers 23 at least one of which
is driven by a variable speed drive motor 2ll. A feed rate
control 26 is operatively mounted on the drive motor for
controlling the speed of the drive motor and thus the rate
at which the wire is fed into the molten metal.
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The casting mold 11 is supported by an electronic
weighing platform 27 whieh includes upper and lower plates
28 and 29, respectively, the plates being separated by a
plurality Or load cells, two of which are shown at 31. Each
load cell typically includes sensitive electrical strain
gauges, not shown, in which the electrical resistant changes
with strain. The strain in this case is created by the
weight of the casting mold and molten metal poured thereinto.
A pair of signal lines 32 and 33 connect each of the load
cells to a summing amplifier 34 which in turn transmits an
amplified output signal through a connecting signal line 36
to a computer 37. An output line 38 connects the computer
to the feed rate control 26 of the wire feeder 19. The
computer may be of any suitable type capable of receiving an
electronic input signal and converting the input signal into
an output signal in accordance with a code or program prefed
into the computer. Although not essential to the present
invention, such a computer typically may have other input
- leads, two of which are shown at 39 and 41, for receiving
signals from other sensors, not shown, for ~eeding into the
eomputer other variables, sueh as temperature and chemistry
of the molten metal in the ladle.
Operation
While the operation of the present invention is
believed clearly apparent from the foregoing description,
further amp~ification will subsequently be made in the
following brief summary of such operation. The pouring
sequence is commenced by tipping the ladle 14 to pour liquid
molten metal therefrom into the pouring basin 12 initially
at a rate to quickly fill the downsprue 16 and pouring basin
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and thereafter at a rate sufficient to maintain the molten
metal at a predetermined level in the pouring basin. The
method of introducing an additive material into a molten
metal at a variable rate includes the step of feeding the
additive material in ~ire form into the molten metal in the
downsprue initially at a preselected feed rate. Thls step
is initiated by a photoelectric eye or other sensing device,
pr~s~nce
not shown, which senses the ~rcsch~ of molten metal in the
pouring basin and actuates the variable speed drive motor 24
of the wire feeder 19 to feed the wire 21 into the molten
metal flowing through the downsprue. The initial feed rate
may be preset manually or by the computer 37 based on what
the initial pouring rate is calculated to be.
The next step of the method is determining the
instantaneous pouring rate of the molten metal continuously
throughout the pour. To determine the pouring rate, the
casting mold is placed on the weighing platform 27 so that
an output signal is~transmitted from the load cells 31 of
-- - the weighing platform to the summing amplifier 34 which in
turn transmits an amplified signal to the computer 37 which
is programmed to provide an automatic tare at this point.
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As the weight of the casting mold increases due to the
- molten metal poured thereinto, the increase in weight is
monitored continuously by the computer. The computer takes
discrete measurements of the weight at Predetermined timed
intervals and calculates the instantaneous pouring rate from
the difference in weight between each consecutive interval.
Thus, the step of determining the instantaneous pourlng rate
includes the steps of weighing the casting mold prior to
pouring the molten metal thereinto and thereafter continuously
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throughout the pour and comparing incremental weight changes
throughout the pour with the computer and converting the
incremental weight changes into an instantaneous pouring
rate. The weighing step includes placing the casting mold
on the weighing platform, amplifying the output signal from
the weighing platform with the summing amplifier and transmit-
ting the amplified output signal to the computer.
The method also includes the step of automatically
varying the feed rate of the wire in direct relation to
changes in the pouring rate of the molten metal. ~his is
accomplished by programming the computer to provide an
output signal co~mensurate with the pouring rate calculated
thereby, transmitting the output signal to the feed rate
control 26 operatively attached to the variable speed drive
motor 24 of the wire feeder l9 to vary the feed of the
variable speed drive motor in direct relation to variations
in the pouring rate.
As an example, it has been found in practice that
with the casting mold shown in the drawings, the pouring
rate decreases as the casting cavity fills with molten
metal. Thus, with the method of the present invention, as
the pouring rate decreases the computer directs a signal to
the feed rate control to reduce the feed of the variable
speed drive motor and thus the feed rate of the wire. In so
doing, the additive material is uniformaly added to the
molten metal regardless of variations in the pouring rate of
the molten metal.
In view of the foregoing, it is readily apparent
that the method of the present invention provides an improved
method of introducing an additive material into a molten
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metal at a variable rate dependent upon the pouring rate so
that the additive material is added uniformly throughout the
pour regardless of variations in the pouring rate of the
. molten metal. This is accomplished by continuously weighing
the casting mold with an electronic weighing device, feeding
the output signal into a computer which calculates the
instantaneous pouring rate from inc:remental weight changes,
and féeding an appropriate signal to the wire feeder to
adjust the feed rate o~ the wire accordingly.
While the invention has been described and shown
with particular reference to the preferred embodiment, it
will be apparent that variations might be possible that
would fall within scope of the present invention, which is
not intended to be limited except as defined in the following
claims.
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