Note: Descriptions are shown in the official language in which they were submitted.
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Back~round of the Invention -
It has been common knowledge for many years that
the microstructure of a cast iron casting can be controlled
by adding inoculants, nodulizing agents, alloys or other
additives to the molten metal immediately before the pouring
of the casting. By controlling the microstructure of the
casting, the mechanical properties thereof are controlled t-o
meet specific criteria such as increasing the strength and
toughness, improved machinability, and so forth. Heretofore,
the common practice of the foundry industry has been to add
the additive material to the entire casting providing uniform
mechanical properties throughout the entire casting. Thus,
the lmmediate disadvantage of such practice is that it adds
~ to the cost of the casting in that a greater amount of the
additive is used than is really necessary to obtain the
desired mechanical properties of only a small section. The
long range disadvantage of such practice is that the additive
materials are normally metals which are becoming scarce such
as copper, molybdenum, magnesium, etc., and such practice
further depletes the reserves thereof. It would be advanta-
geous to control the microstructure of only a selected
section of the casting instead of the entire casting.
Summary of the Invention
This invention provides an improved method of
introducing additive mater~als into a molten metal for
controlling the microstructure of selected sections of a
castlng formed by the molten metal. The additive material
is added only to preselected portions of the molten metal
being poured into a castIng mold.
3o According to the present invention9 there is
provided a method of controlling the microstructure o~
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selected sections of a casting, comprising the steps of
providing a casting mold having a casting cavity therein and
a flow path in communic~tion with the casting cavity, pouring
a molten metal into the ~low ~ath from a pouring device
separate from the casting mold, beginning the feeding o~ a
wire of additive material from a ~ire feeder remote from the
casting mold into the molten metal flowing through the flow
path when a preselected volume of molten metal has been
reached in the casting cavity, continuing the feeding of the
wire and the pouring of the molten metal into the flow path
simultaneousl~ so that the wire meltably intermixes only
with the molten metal which flows through the flow path
after the preselected volume is reached, stopping the feeding
of the wire when the volume of molten metal in the casting
cavity reaches a second preselected volume, and stopping the
pouring of the molten metal into the flow path when the
casting cavity is filled.
Brief Description of the Drawing
The sole figure is a schematic representation of
one form of apparatus for controlling the microstructure of
selected sections of a casting.
Description
One apparatus for accomplishing the method is
schematically illustrated in the drawing and includes a
; 25 timlng device operatively connected between a sensor and a
wire feed apparatus for starting and stopping the feeding of
a ~ire of additive material into the molten metal in the
casting mold at preselected times after pouring of the
molten metal has commenced.
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Referring now to the drawing, the apparatus includes
a casting mold generally indicated by the reference numeral
10 having a pouring basin 11 formed in its upper surface and
connected to a casting cavity 12 though a vertically extending
downsprue 13 and a horizontal runner 14. The casting mold
typically may have several casting cavities formed therein
connected to a pair of downsprues by a gating system, but
only one casting cavity and a single downsprue has been
shown for illustrative convenience. A ladle 16 is positioned
; 10 separate from and positioned for pouring a liquid molten ~ -
metal 17, such as molten iron, into the pouring basin
where it flows through the downsprue and runner and into the
casting cavity.
A wire feeder 18 is dlsposed above the casting
mold 10 for ~eeding an additive materlal in the form of a
wire 19 into the molten metal flo~ing through the do~nsprue
13. A supply of the wire of additive material is carried on
a spool 20 rotatably supported by a b:racket 21. The wire
~eeder includes a pa~r of rollers 22, at least one of which ~;
20 is driven by a variable speed drive motor 23. A photoelectric
sensor 24 i5 positioned above the pouring ~asin 11 of the
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casting mold and is actuated by re~lected light ~rom the --
molten metal in the pouring basin ln the usual manner.~ ~he
sensor is connected to an electronic timer 26 through a
signal line 27 with the timer in turn connected by a signal
; line 28 to a drive motor activating switch 2~ operatively
~ connec~ed to the drive motor. It is to be understood that
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`` the drive motor, electronlc timer and photoelectric senaor
are suitably connected to a source of electrical energy, not
3o shoun, in the usual manner.
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Utilizing the above-described apparatus ~or carrying
out the method of controlling the microstructure of selected
sections of a casting initially includes the step of providing
the casting mold 10 with the casting cavity 12 and the flow
path in communication with the casting cavity formed therein
wherein the flow path in the illustration includes the
- pouring basin 11, downsprue 13 and runner 14. The ladle 16
is then tipped for pouring the molten metal 17 therefrom
into the pouring basin of the casting mold initially at a
pouring rate to quickly fill the downsprue and pouring basin
and thereafter at a ra~e to maintain the molten metal at a
substantially constant predetermined level in the pouring
basin. The photoelectric sensor 24 senses the presence of
the molten metal in the pouling basin by light reflection
therefrom and sends a signal through the signal line 27 to
start the timer which has been preset to delay actuation of
the drlve motor 23 until a preselected time lapse after the
pouring of the molten metal has started. ~he flow rate of
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molten metal through identically shaped downsprues Is rela-
tIvely constant and predictable so that the time lapse
between the starting of the pour and when a preselected
volume o~ molten metal is reached-in the casting cavity is
readily determined and the time preset into the timer accord- ~ -
ingly. Thus~ after a predetermined time lapse comensurate
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with the volume of molten metal reaching a predetermined
volume, the timer sends a-sIgnal to ~the switch 29 ~hich
activates the drive motor 23 for beginning the feeding o~
the wire 19 of additive material Into the molten metal
flowing through the flow path. For-a predetermined time
3o after the activating o~ the drive motor, the ~eeding of the
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wire and the pouring of the molten metal into the flow path
continues simultaneously so that the wire meltably intermixes
only with the molten metal which is poured into the flow
path after the preselected volume is reached. The predeter-
mined time is comensurate with the volume of molten metal inthe casting cavity reaching a second predetermined volume.-
After such predetermined time, the rate of feed is changed,
such as by reducing the rate or stopping the feeding of
wire. In the illustrated apparatus, the timer deactivates
the drive motor stopping the feeding of the wire. Another
possible means of controlling the beginning and stopping of
feeding the wire into the molten metal when preselected
volumes of molten metal have been poured into the flow path
is through the use of a weighing device. ~uch means would
include weighing the casting mold prior to pouring the
molten metal thereinto and thereafter continuously throughout -
the pour. Starting and stopping of the drive motor of the
wire feeder would be controlled by the weighing dèvice so
that as the weight of the casting mold increases due to the
addition of molten metal thereinto, the drive motor ~ould be
started and stopped Nhen preselected volumes of molten metal
are reached in the casting cavity as determlned by when the
casting mold and molten metal therein reaches predetermined
~eights. When the casting cavity is filled to capacity, the
-ladle is tilted to stop the pouring of the molten metal into
the flo~ path.
It is no~ deemed apparent that a wire of additive
materlal is selectively ~ed into only a portion of the total
~olume of molten metal being poured into a casting cavity
~or controlling the microstructure of one or more selected
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sections of the casting. The feeding of the wire of additive
materlal from the wire feeder remote-from the casting mold
into the molten metal flowing through the flow path is begun
after a preselected volume of molten metal has been reached
in the casting cavi~y. The feeding of the wire and the
pouring of the molten metal into the flow path is continued
simultaneously so that the wire meltably intermixes only
~ith the molten metal which ia poured into the flow path
after the preselected volume is reached. The feeding of the
wire is stopped when the volume of molten metal in the
casting cavity reaches a second preselected volume, and the
pouring of the molten metal into the flow path is stopped
when the casting cavity is filled.
The above method is particularly suited for castings
in which the molten metal entering the downsprue at a given
time in the pouring sequence will flo~ to a specific section
~lthin the casting cavity. Thus, if the wire is fed into
the molten metal flowing through the cLownsprue during that
particular time, the additive material will intermix with
only that molten metal flowing through the downsprue at that
given time thereby controlling the microstructure of that
particular section of the casting. One possible example of
thls type of casting is a c~linder liner formed by the
casting caYity æhown in the drawing. The casting cavity is
bottom gated so that if mixing within the casting cavity is
minimized, then the first metal into the casting cavity
rises to the top while the last metal entering the casting
cavit~ remains at the bottom. In a cylinder liner, the
~lange is subjected to high thermal stress during engine
operation and requires alloylng additions of molybdenum and
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lOqZZ95
copper to attain the strength levels sufficient to resist
cracking. Using the method of the present invention, the
molybdenum and copper are added toward the end of each pQU~
so that the treated molten metal ends up in the casting
cavity in the area of the flange which~ as shown in the
drawing, is disposed at the lower end of the casting cavity.
- The above described method of controlling the
microstructure of selected sections of a casting may be
utilized for achieving totally different microstructures in
different areas of the casting. This could involve the use
of two wire feeders and two wires, each of which is formed
with a dlfferent additive material. Again using the cylinder
liner as an example, one type of additive material may be
added to the molten metal immediately at the start of the
pour and until the volume of molten metal in the casting
cavity reaches a preselected volume at which time the first
wire ~eeder is stopped and the second wire feeder ls started
to ~eed the second wire into the molten metal until the end
o~ the pour.
The invention in its broader aspects is not limited
to the specific steps and embodiments herein shown and
described, but departures may be made therefrom without
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; departing from the principles of the invention and without
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sacrificing its chief advantages.
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