US1999961A - Method and apparatus for die casting - Google Patents

Description

April 30, 1935. J. R. DAESEN ET AL METHOD AND APPARATUS FOR DIE CASTING Filed Aug. s, 1952 JOHN R.-DAESEN LELAND E. WEMDLE @5v @mm 1W/WM;

Patented Apr. 30, 1935 PATENT OFFICE METHOD AND APPARATUS FOR DIE CASTING John R. Daesen, Oak Park, and Leland E. Wemple, Chicago, Ill.

Application August 3, 1932, Serial No. 627,376

7 Claims.

Our invention relates to a method and apparatus for die casting metals and more particularly to a method and apparatus for die casting zinc base and aluminum base alloys.

Heretcfore die castings of substantially pure zinc and aluminum have been defective to a considerable extent due to the contamination of the molten metal by the metallic parts of the die casting machine. In the case of zinc base die castings generally, aluminum has been and is used as a component part of the alloy to reduce the alloying action between the metallic parts of the machine and the molten metal, in spite of the fact that it has been proven that this addition of aluminum to retort smelted zinc or electrolitically rened zinc which contains small amounts of lead, cadmium, iron and other impurities, is the cause of serious intergranular corrosion of the a1- loy. Because of the lack of a suitably designed die casting machine which would prevent such contamination, users o'f zinc base die castings have generally been forced to use alloys which are inherently unstable and subject to disintegration in the presence of moisture, while zinc alloys of improved physical and chemical properties have not been available for die casting due to the absence of the alloying inhibiting aluminum.

This contamination of the molten metal results from continued contact of the molten metal with some metallic part of the machine which becomes or remains heated to a degree approaching the heat of the molten metal. On the other hand, it has been proven that parts of the machine which are but momentarily in contact with the molten mass and are maintained at temperatures substantially lower than the molten metal, are very slowly attacked. Therefore, the present invention provides for the shortest period possible for contact between metal parts and the molten mass, and the cooling of the metal parts that must necessarily contact.

The invention has as one of its objects the re'- duction of contamination of the molten metal by contact with the die casting' apparatus, thereby -making available for die casting, alloys of superior physical and chemical properties which cannot be advantageously usedu in the usual type of die casting machine.

Another object is the simplification oi' the apparatus with consequent reduction, of maintenance costs.

Still another object is the simplification of the steps of the process of die casting.

A further object is to increase the safety in de casting metals under great pressure.

(o1. ca -69) Other objects and advantages will be apparent from the followingA specication, when read in connection with the accompanying drawing which discloses diagrammatically one form of apparatus used in carrying out our invention.

In the drawing Fig. 1 is an elevation, partly in cross section, of one type of apparatus which may be used in "carrying out my invention.

Fig. 2 is a cross section showing a water-cooled duct and die.

A retort 2 of graphitic or ceramic material holds the molten metal 4. The retort is heated by any suitable means such as the electrical resistance plates 6 or the burner 8. Surrounding and enclosing the retort is a casing I0. The casing is 15 made air-tight with the exception of a tapered port I2 for receiving the die (hereafter described) and a proper opening for the pipe I4. A valve I5 is used for regulating the gas pressure fed through the pipe I4 to the chamber. A split die 20 with halves I6 and I8 is removably seated within theport I2. The joint between the die and the port, when the parts are in casting position, is as nearly air-tight as possible in view of their operation. A relatively massive duct 20, prefer- 25 ably made integral with the halves of the die, extends through the port I2 and a short way below the surface of the molten nmetal in the retort.

The outer diameter of this duct very closely 30 approaches the smallest inside diameter of the port, so that any metal freezing on the outside of the duct is dislodgedA as the die is withdrawn. The die and ducty may be water-cooled in any conventional manner if desired.

The top 22 of the air-tight chamber supports a mechanism for raising and opening the die. The raising mechanism includes vertical guides 24 and 26 secured to the top 22 of the chamber. A

die holder plate 28 is slidably mounted on the 40 I guide rods and has a dove-tail groove in its lower face in which the die halves I6 and I8 are held by means of corresponding dove-tail tongues. Thehalf I8 is capable of sliding in the groove, while the half I6 is fixed. A platform 30 is sup- 45 ported by the guide rods and carries an air cylinder 32. A piston 34, within the cylinder, is actuated by pressure from conduits 36 and 38 to lower or raise the die holder plate 28 through the mediumrof the plunger 40.

The die-splitting mechanism includes a vertical support 4I xed to the top 22 and the platform 30. Pivotally mounted on the vertical support, as at Y42, are curved guides 44. These l curved guides have grooves 46 in which slide lugs 55 48, formed on the outside of the die-half I8. Compression springs mounted between the vertical support and the lowerv ends of the guides 44 urge the die halves together when in their lowered position. It should be noted that the lower portions of the grooves 45 are straight, so that proper engagement of the two die halves is made before they enter the port I2.

The proper manipulation of the above described apparatus is extremely important in order to obtain the desired results. Metal is introduced into the retort through the port until the surface level is sufficiently high. The heating element melts the metal or maintains it in a molten condition. Compressed air is introduced into the cylinder 32 through the upper conduit, thereby moving the piston and plunger downwardly and pushing the plate with the die-halves toward the retort. The die-halves are pressed together as they .are lowered, and the air compression in the cylinder aids in a tight t between die and port when they register. Immediately after the die is seated, the valve I 6 is opened, admitting air or any suitable gas under pressure to the chamber. It is important that this pressure be introduced immediately upon the seating of the die, in order to lessen the time of contact between die and molten metal.

` As soon as the pressure in the chamber acting on the surface of the molten metal has forced sufficient metal into the die and the casting has become set, compressed air is introduced through the conduit 38 to raise and open the die.

The timing of the above steps is important in reducing the period of contact of metal parts. with the molten bath. Since the retort is of graphitic or ceramic material, 'it will be seen that the duct from the die is the'only metal part to contact with the molten mass. The steps of immersion, compression, and withdrawal follow in as rapid succession as possible in the proper operation of the device. In other words, the steps are timed as follows: l

1. 'I'he die is lowered.

2. Immediately after the die is seated, pressure is introduced to force the metal into the die.

3. Immediately after the metal is set in the die, the die is withdrawn and opened.

Our apparatus permits continuous rapid repetition of these steps, interrupted only by occasional stops to replenish the metal in thel retort and maintain it at the proper level, and so yields a high output of castings per unit time.

The greatly increased safety of our method of die casting as compared with the submerged gooseneck type yof machine, is shown by the fact that no chamber or machine part, directly in contact with molten metal (and thereby subject to weakening corrosive attack) is subjected to any pressure beyond that of the weight of the molten metal itself, with the exception of the die and duct which are very massive, and are in contact with molten metal for only very brief intervals.

Furthermore, in the gooseneck type of machine, imperfect seating of the die on the outlet Iresults in the spraying of molten metal, to the possible injury of attendants, while with our type of machine, imperfect seating of the die on the port of the pressure chamber could only cause leakage of air without any expulsion of metal.

In order to lessen the overheating of the duct,

in addition to the common water-cooling of the die. the duct itself may be water-cooled. One

simple method of water-cooling is shown in Fig. 2. In this figure the numerals I6 and I8 again indicate the two halves of thedie and the numeral 20 indicates the duct. The water-cooling jacket is indicated by the numerals I'I and I9, these jackets being fed through water conduits 2| in the usual fashion. 'I'he die cavity is indicated at 23. As mentioned above, the duct is made relatively short and massive. The short length of the duct permits a minimum part of its surface to contact with the molten bath. The massive structure of the duct promotes the sudden chilling of the surrounding metal before there is time for alloying between it and the duct, and also prevents a susbtantial increase of temperature of the duct, since the total heat absorbed from the molten metal is distributed through a relatively large mass. With proper timing of the operation of the machine, it will be seen that the duct can therefore be kept very cool indeed.

Of course, the cool duct in contact with the molten metal will freeze a skin or film on the outer surface of the duct, but the sudden chilling of the metal forming the film prevents any appreciable corrosive action of the molten metal of the port as the die is withdrawn.

The extent to which the molten metal in the retort is heated above its melting point will affect the operation of the machine in that an excessively high temperature will prevent the rapid freezing of thelayer of metal surrounding the duct, and by allowing action between the molten metal and the duct, partly defeat the purposes of the invention. If the molten metal be maintained at a temperature too close to its freezing point, the immersion of the duct will chill and solidify too massive a layer of molten metal which, if it does not interfere with withdrawal of the duct will nally cause the whole contents of the retort to solidify. In addition, the molten metal must be kept hot enough to readily melt the additions of solid ingot which replace the metal cast.

Since the degree of superheating of molten metals usually affects the amount of gasl they will absorb from the atmosphere, we prefer to cast in our machine at as low a temperature as possible, and therefore recommend adjustment of.

duct size and duct cooling to the point which allows steady operation at the lowest possible temperature of the molten metal in the retort, without substantial alloying attack of the duct by the molten metal. 1

While we have indicated one example of our new method of die casting with specific illustrations, it should be understood that the new principle disclosed may be used to advantage in a. number of combinations. For example, the means of raising and lowering the die may be changed to work by toggle arangements and the springs shown closing the die halves may be replaced by clamps. Again, some advantages of the invention may be gained by using a metallic retort in place of a graphic or ceramic yretort in cases where the metal to be cast does not seriously attack the metal of the retort. In such a case the retort itself may possibly be dispensed with and the metal held in the air tight chamber itself. In this case the air port I 4 would have to be at the top of the chamber, and the heaters would be immersed in the molten metal, or heat would be supplied to the outside of the chamber.

Furthermore, the use of heat insulating linings to conserve heat, and pyrometers to indicate or control the temperature of the molten metal or Adie, are customary additions which may well be used in our invention and need not be described or specied.

Having described our invention, what we claim as new and desire to secure by Letters Patent of `tion at a temperature enough lower than the melting point of the molten metal, to freeze rapidly the contacting l'ayer of molten metal before corrosive action takes place between 'it and the duct.

2. In a process of die casting metals, immersing the duct of a die in the molten metal and maintaining the duct during its period of contact with the molten metal at a temperature enough lower than the melting point of the molten metal, to freeze rapidly the contacting layer of molten metal before corrosive action takes place between it and the duct.

3. In a process of die casting metals, immersing the duct of a die below the surface of a molten mass of metal a distance just sufficient to form a seal therewith, compressing the metal into the die, and withdrawing and opening the die while maintaining the duct at a temperature enough lower than the freezing point of the molten metal, to freeze rapidly the contacting layer of molten metal before corrosive action takes place between it land the duct.

4. In av die casting apparatus, an air-tight heating chamber for the molten metal, a split die above said chamber, a duct made integral with said die, means for raising and lowering said die, said duct when said chamber has molten metal therein being adaptedto extend into said molten metal and to close a port on the top of the air-1 tight heating chamber when the die is in the lowered position. l

5. In a die casting apparatus, an air-tight heating chamber, a nonmetallic retort within said chamber for holding molten metal, means for heating said molten metal, asplit die above said retort, a duct made integral with said die, means for raising and lowering said die, said duct closing an opening at the top of said air-tight chamber, Y,

and extending into the molten metal when the die is in its lowered position.

6. In a die casting apparatus, an open, non metallic retort for holding molten metal; a combined heating chamber and pressure chamber' 'enclosing said retort, the side walls and the top of said chamber being spaced from the side walls and open top of said retort and the top of said chamber having a discharge port therein above the open top of the retort, a die supported above said chamber, a duct integral with said die, said duct being relatively massive with respect to said die, means for raising and lowering said die and duct, said duct being adapted to close the dis-K charge port and to extend into the molten metal when in its lowered position, and means for creating pressure within said chamber when said port is closed and said duct issubmerged, whereby metal is forced through said duct into said die.

'7. In a die casting apparatus, a heating chamber, a non-metallic retort within said chamber for holding lmolten metal, a die above said retort, a duct made integral with said die and having sumcient mass relative to the surface area which contacts with the molten metal to absorb heat from the metal rapidly enough to prevent the temperature of the duct from rising as high as the melting point of the metal during the period of contact therewith, and means for creating pressure on the molten metal.

JOHN R. DAESEN.

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