Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to die casting molds made of
mold halves each oi which has a high pressure heat exchange
cavity. The die casting half molds of this invention have a
thin wall between the die casting area of the half mold and
the high pressure heat exchange cavity. The thin wall between
the die casting area and the high pressure heat exchange cavity
covers substantially the whole surface area between the die
casting area and the high pressure heat exchange cavity.
A high pressure heat exchange cavity enables the heat
exchange medium in the high pressure heat exchange cavity to
be maintained as a liquid at a high temperature relative to
the temperature at which the metal being cast in the mold is
introduced in the mold. A die casting half mold having a thin
wall of large surface area between the die castiny area of
1~ khe half mold and the high pressure heat exchange cavity was
created to take advantage of the relativelv lower temperature
differential between the metal being cast and the heat exchange
medium for removing the heat obtained by utilizing a relatively
high temperature heat exchange medium.
Die casting molds currently in use utilize water at
atmospheric pressure as the heat exchange medium to remove
heat from the die cavity. Heat exchange is achieved by
drilling a series of conduits through the die block which
enables water to be circulated through the die block and thus
cool the die cavity. As the systems in use to exchange heat
from the die cavity are not pressurized, sufficient cool
water must be circulated through the die block to sufficiently
cool the die cavity so that the cast metal may be shot into
the die cavity, cooled, solidified and removed. The
temperature of the hot metal introduced into the die cavity
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varies from metal to metal. zinc is usually introduced into
molds at about 800 Farenheit while aluminium is introduced
into molds at about 1200 Farenheit, while the temperature
of the circulating water is normally between 70 and 200
Farenheit. The resultant temperature differential between the
hottest and coldest parts of a conventional mold when casting
zinc and aluminium respectively is about 600 and 1000
Farenheit.
The heat exchange conduits of conventional molds are
normally spaced at least several inches away from the die
casting cavity and several inches away from each other so
that the steel between the heat exchange conduits and the die
cavity will disseminate the cooling effect of the cold water
~lowinc3 throuyh the heat exchange conduits before the cooling
.15 efeect reaches the die cavity. The greater the thickness of
steel between the die casting cavity and the heat exchange
conduits in conventional molds, the more even will be the
temperature profile across the die casting cavity. On the
other hand, the greater the thickness of steel between the
heat exchange conduits and the die cavity the slower will heat
exchange take place.
If the heat transfer conduits of conventional molds
are placed close to the die cavity there is an increased
possibility of thermal fatigue occurring ln the mold because
of the substantlal temperature differentlal occurring over
a narrow thickness. A further disadvantage of placing
conventional heat transfer conduits in close proximity to the
die cavity is the creation of temperature distortions caused
by wide temperature differentials between those areas of the
die cavity most proximate to the heat transfer conduits and
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those areas of the die cavity furthermost from the die castingO
With a die casting mold having a pressurized heat
exchange cavity, it is possible to raise the temperature of
the heat exchange medium to any desired temperature up to 450
Farenheit. The temperature differential between the die cavity
and the high pressure heat exchange cavity across the die
casting area of the front wall is substantially less than that
found with molds cooled by water running through conduits in
the mold. The lower temperature differential has resulted in
the manufacture of a mold having a die cast wall with a
thickness as thin as three-tenths of an inch depending on the
dimension of the casting and the heat to be removed therefrom.
The die casting area generally includes all that part of the
front wall which receives the hot casting material.
The lower heat differential between the die cavity and
the high pressure heat exchange cavity has also made it
possible to increase the surface area of the high pressure
heat exchange cavity in contact with the die cast area of the
front wall. The surface area of the thin wall is the die
casting area of the front wall receiving hot liauid.
I~ith the increased surface area of the high pressure
heat exchange cavity in contact with the die casting area of
the mold, it is possible to obtain both a larger heat exchange
surface and an improved temperature profile on the die casting
area of the mold.
Pieces which are to be cast in die casting molds have
an endless variety of shapes and thickness. The amount of
hot metal to be cooled increases with the thickness of piece
to be cast, decreases with the thinness of the piece to be
cast and is directl~ related to the surface area of the piece
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to be cast. By utilizing a high pressure heat exchange cavity
and high temperature heat exchange medium, it is possible to
conform the configuration of the main heat exchange wall in
the high pressure heat exchange cavity to create a temperature
profile on the die casting part of the mold substantially
conf.orming to the heat to be removed from various parts of
the piece being cast.
The thicker parts of the piece being cast must have
more heat transferred therefrom while the thinner parts of
the heat being cast require less heat to be removed therefrom.
By substantially inversely profiling the thickness of the
inside of the main heat exchange of the wall of the high
pressure heat exchange cavity to conform to the heat to be
removed from various parts of the die casting area, a cooling
~5 profile may be obtained which will remove more heat from
those parts of the casting requiring more heat loss in
solidifying and less heat will be removed from those parts of
the casting requiring less heat loss to solidify.
Another difficulty with elongated tubular heat
transfer conduits of conventional molds is that the continual
passage of water through these conduits leads to the build up
of slime or scaling on the sides of the walls of the conduit.
This problem may be alienated somewhat by conditioning or
treating the cooling water prior to use. Scaling or slime
reduces normal heat transfer between the water and the mold
and causes uneven distribution of heat in the mold. The
mold must be continually treated to remove slime or scale to
maintain satisfactory heat transfer. With a pressurized heat
exchange medium such as for instance, water, only sufficient
water needs to be added to the heat exchange cavity to repLace
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the steam driven off by the heat exchange occurring as a
result of each shot of metal into the die cavity. As a
result, sliming or scaling does not occur and the above
problem does not exist within the pressurized heat exchange
cavity.
The above and other features will be understood from
the following disclosure and accompanying drawings wherein:
Figure 1 is a cross-sectional view through half of the
permanent mold.
Figure 2 is a crcss-sectional view through the
permanent mold including means for retaining the mold halves
in line.
Referring to Flgure 1, there is shown a mold halE 1
compris~d of a front wall 2, side walls 3 and a backing member
4. The backing member 4 is fastened to the bottom of the
side walls 3 by bolts 5. A thin high pressure gasket 6
capable of withstanding high temperatures and high pressures
is placed between the bottom of side walls 3 and backing
member 4 before the bolts 5 are securely fastened. A high
pressure heat exchange cavity 7 is formed between the front
wall 2, side walls 3 and the backing member 4. An inlet valve
8 is provided in the side wall 3 to add fluid to the
high pressure heat exchange cavity 7 when required. An outlet
valve 9 is provided in side wall 3 to remove gas from the
high pressure heat exchange cavity 7 after each casting
sequence. The front wall 2 includes a die casting area 10
which receives the hot casting liquid. The central part of
die casting area 10 forms part of the die cavity in which the
cast article is formed. The shape of front wall 2 and die
casting area 10 will vary from mold to mold reflecting the
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shape of the article being cast. The thin wall 11 between
the die casting area 10 and the high pressure heat exchange
cavity 7 may be as thin as 0.3 inches in thickness depending
upon the size and configuration of the part being cast and
correspondingly the heat to be removed from any part of the
die casting area 10. In the mold half 1, shown in Figure 1, a
column 12 is formed through the high pressure heat exchange
cavity 7 to provide additional support to the front wall 2.
An ejector pin 13 runs through the column 12.
Referring to Figure 2, there are shown two mold halves
14 and 15 in closed position forming die cavity 16. Mold
half 14 is fastened to a block 17 which is fastened to one of
the platens 18 of the die casting machine which will move
mold half 14 towards, closed on or away from mold half 15.
.IS ~imilarly mold half 15 is fastened to block 19 which is
fastened to the other platen 20 of the die casting machine
which will move mold half 15 towards, closed on or away from
mold half 14. Mold half 14 is comprised of front wall 21,
side walls 22 and backing member 23. High pressure heat
exchange cavity 24 is formed between front wall 21, side
walls 22 and backing member 23. Mold half 15 includes two
or more guidepins 25 and 26 which are retained within bushings
27 and 28 respectively to maintain mold halves 14 and 15
aligned. When mold halves 14 and 15 are closed as shown in
Figure 2, the die cavity 16 is formed between die cavity
areas 29 and 30 of mold halves 14 and 15 respectively.
With the mold halves 14 and 15 in closed position,
hot casting metal is introduced at gate 31 and air is vented
at vent 32 until die cavity 16 and overflow 33 are filled with
hot casting fluid. The hot casting metal is introduced at
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pressure of up to 2000 p.s.i. and 800 Farenheit for zinc and
up to 5000 p.s.i. and 1200 Farenheit for aluminium. When
casting wlth zinc the high pressure heat exchange cavity 24
contains heat exchange fluid 34 under pressure having a
temperature up -to 450 Farenheit. The same is true of mold
half 14.
With a temperature differen-tial of about 400 Farenheit
when zinc is being cast in die cavity 16 and the heat exchange
fluid 34 in high pressure heat exchange cavity 24, heat will
flow through die cavity area 29 to the heat exchange fluid
34 causing a small portion of the heat exchange fluid to
vaporize. The vapor will be bled to the atmosphere through a
pressure control valve as indicated in Figure 1.
When the casting is solidified the mold halves 14 and
15 are moved apart by the platens 18 and 20, the casting is
ejected from the die casting cavity by ejecting rods such as
13, 36 and similar rods not indicated in the drawing.
An additional advantage of high pressure heat exchange
cavity 24, is that prior to start up of the casting operation,
the heat exchange fluid 34 can be heated under pressure and
the temperature of each of the half molds can be raised to
450 Farenheit or any other desired temperature before the
casting is started. The temperature of the mold can be
controlled by a combination of a pressure controls on inlet
valve 8 and outlet valve 9 of high pressure heat exchange
cavity 7 in combination with an immersion heater in high
pressure heat exchange cavity 7.
While the invention has been shown and descrlbed in
one embodiment, it will be clear to those skilled in the art
that the precise details of construction will vary from
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article to article which is to be cast. The invention is not
confined to the precise details of construction which are
shown in the drawings but includes those changes and variations
which must necessarily be made by those skilled in the art in
preparing permanent metal molds incorporating the teachings
of this invention, without departing from the spirit of the
invention, or exceeding the scope of claims.
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