US3008202A - Vacuum system for cold chamber die-casting machines - Google Patents

Description

Nov. 14, 1961 BAUER 3,008,202

VACUUM SYSTEM FOR COLD CHAMBER DIE-CASTING MACHINES Filed Aprll 25, 1960 3 Sheets-Sheet 1 U z k 5 $5 3.

V Q a I v In Q) ("7 n (O D o 8 o o o o o I-I I-I INVENTOR. ALFRED F. BAUER BY J @-14 Q Nov. 14, 1961 A. F. BAUER VACUUM SYSTEM FOR COLD CHAMBER DIE.- Filed April 25, 1960 CASTING MACHINES 3 Sheets-Sheet 2 30 3| /ll 48 l 40 I 29 lo 35 33 INVENTOR.

ALFRED F. BAUER Nov. 14, 1961 A. F. BAUER 3,008,202

VACUUM SYSTEM FOR COLD CHAMBER DIE-CASTING MACHINES Filed Aprll 25, 1960 5 Sheets-Sheet 3 INVENTOR. ALFRED F. BAUER BY @QQQ @w Jersey Filed Apr. 25, 1960, Ser. No. 24,398 6 Claims. (Cl. 22 73) This invention relates to an improvement in die-casting machines, and is particularly directed to an improvement in cold chamber die-casting machines in which a vacuum system is employed.

Die-castings have already found widespread acceptance in the automotive industry as well as in many other fields, but one large obstacle in the way of even greater acceptance has been the problem of controlling porosity in castings produced by pressure die-casting methods. In a pressure die-casting system, the two halves of the die forming the die cavity must be closed and sealed before the molten casting metal is injected into the cavity and the parting faces of the die block must be in contact to prevent the escape of the molten metal. The die cavity is filled with air which can escape only around the ejector pins and similar die parts. Since the clearance around these parts must be kept at a minimum to prevent the entrance of molten metal, and since the time required for filling the die cavity with metal is only a fraction of a second, most of the air cannot escape, but remains in the cavity and becomes entrapped in the solidifying metal causing porosity in the casting.

In order to produce a casting of sounder metal struc: ture, many die-casters have turned to a vacuum process or have adapted vacuum means to their present machines as a method of removing at least part of the air from the die cavity. A conventional vacuum pump of suitable size and design may be employed or a vacuum tank or accu mulator may be used in conjunction with the vacuum pump. Such evacuating means may be connected to the die cavity through special passages in the die block which may, if desired, be provided with valving means to prevent the escape of molten metal into the vacuum system. These valving means must be operated at a critical point in the cycle to remain open until the moment of molten metal into the die but to be closed at the time the molten metal reaches them so that no metal is drawn out through the valve. The vacuum producing means may also be connected to an enclosure surrounding the entire die assembly whereby the entire enclosed space is at least partially evacuated. The present invention combines these two expedients with a third which will be hereinafter described and which makes a vacuum system that is greatly superior to any previously known in the art. Regardless of the manner by which it is accomplished, obtaining and maintaining a high degree of vacuum in the die cavity is extremely diflicult because of the many parts concerned. With conventional Vacuum systems for cold chamber die-casting machines, even though the die assembly is adequately scaled against air seepage, one great source of vacuum loss is through the shot sleeve which is directly connected to the die cavity through gate runners.

A common procedure for obtaining a vacuum in the die cavity, after the die halves have been closed and the metal ladled into the shot sleeve, is to advance the shot plunger past the pour opening in the sleeve and to evacuate the air in the cavity by opening the valving means controlling the line to the evacuating system. Since the shot plunger must be capable of reciprocable movement Within the sleeve, enough clearance must be provided between these parts to prevent galling and sticking and to permit normal operation of the assembly. Regardless 3,@08,2il2 Patented Nov. 14., 196i ice of the competency of the usual'peripheral seal around the dieassembl'y, enough air will be drawn into the die cavity through theclearance between the plunger and sleeve so that a high degree of vacuum cannot be obtained and air in considerable quantities remains in the die cavity. Unequal expansion of the plunger and sleeve during operation and normal wear between plunger and shot sleeve bore tend to increase the area through which air may be drawn into the die cavity. The problem is especially aggravated if the shot sleeve is large, for example four or five inches in diameter.

It is, therefore, an object of the present invention to providemeansfor sealing the shot sleeve of a cold chamber die-casting machine so as to prevent the passage of air between shot plunger and sleeve into the die cavity and thus tofacilitate the evacuation of the die cavity.

A further object of this invention is to provide a sealing member which is deformable into an interference fit with the interior surface of the shot sleeve so as to pre-- vent the entrance of air into the die cavity from the sleeve when a vacuum is drawn on the die cavity.

Still another object of the invention is to provide a method of evacuating a die cavity in which the major portion of the air therein is withdrawn through a valvecontrolled line, and inwhich evacuation is continued by subjecting. the die cavity to evacuation through a clearance space around ejector pins or the like during entrance of the casting metal.

A still further object of this. invention is to provide a vacuum system for a, cold chamber die-casting machine by means of which the die cavity may be readily and quickly evacuated after the pour opening is closed through" a valve the timing of which is. not critical. The valve may be opened during an initial forward movement of the plunger in the shot sleeve and closed at any time after the pour opening is closed and prior to the entrance of metal into the die cavity, evacuation being continued during the entrance of the metal through minor passages remote from said valve.

These and other objects of this invention will become apparent from the following description and the drawings, in which:

FIG. 1 is a side elevational view, of a die-casting machine embodying FIG. 2 is an isometric view of a cold chamber shot sleeve provided with means for trimming the sealing member at the time of its introduction into the shot sleeve;

FIGS. 3, 4 and 5 are diagrammatic sectional views, of a shot sleeve and a portion of the plunger with a sealing member located; first in position in the shot sleeve; secondly advanced beyond the pour opening thereof; and finally adhered to the casting while the plunger is on its return stroke; and FIG. 6 is a somewhat enlarged but fragmentary view of the die and ejector mechanism of a die-casting machine constructed in accordance with the present invention;

The invention comprises briefly the method and means for evacuating the die of a die-casting machine which comprises, sealing the shot sleeve of themachine against all leakage by a soft metal, disposable seal, withdrawing the majorportionof the air-from the die through a large, valve-controlled passage, injecting molten metal into the evacuated die and continuing the withdrawl of air nom the die cavity around the ejector pins and similar small openings during injection of the molten metal. The method difiersfrom the prior art largely because of the "fact that the entire machine can for the first time be sealed forevacuation since the shot sleeve is completely sealed oii due to the use of a disposable close-fitting soft sea-ling'member, whereas in prior machines of this nature there has alwaysexisted a clearance space between the with parts in section, the present invention;

shot plunger and the shot sleeve; and further, by the continued evacuation of the die cavity through minor evacuation passages during injection of the metal and after closure of the valve controlled passage. By this method, a vacuum in excess of 29 inches of mercury may be drawn on the die so that the injected metal forms a casting which is much more dense and has greatly reduced air inclusion than castings made on known machines.

- This invention contemplates the evacuation of the die both before and after injection pressure is put on the shot sleeve so-that the air is withdrawn from the shot sleeve through the die, provision being made for the formation of a complete, air-tight seal ahead of the plunger of the machine. This latter provision contemplates the use of a separate disposable soft sealing member which engages the interior surface of the shot sleeve with an interference fit and thereby provides a seal, the seal adhering to the slug of metal remaining in the shot sleeve at the end of the casting operation. This invention also contemplates the use of a shot sleeve having an internal configuration which assure an intimate gas-tight, sealing fit the peripheral surface of the separate, soft sealing memher as the sealing member is advanced into the sleeve by the plunger. The internal configuration of the shot sleeve and the exact form of the sealing member used to accomplish the object of this invention are subject to considerable modification;

FIGURESB, 4 and 5 show the preferred form of sealing member used in conjunction with the shot sleeve hav- 'ing the preferred circular internal configuration.

' In the following description, the terms inner end and inner portion". refer to that end of the shot sleeve closer to the gate runner, while the terms outer end and outer portion refer to that end of the shot sleeve near the pour opening. H

' In the drawings, the shot sleeve, of generally cylindrical shape is indicated by reference numeral and its inner end passes through the front machine platen 14 and cover die 16 communicating with gate runner 18 which leads to the die cavity 19. The interior surface of the shot sleeve, as indicated'in general by reference numeral 20, is, in its preferred form as shown in FIGS.

V the runner 18 by a horizontal and not l-.-5, a cylindrical element of substantially constant diameter although some taper may be used at the outer end if desired.

Theshot plunger 30 is reciprocably movable within the sleeve 10 and is affixed to one end of a plunger rod ill the other end ,of which is affixed to a hydraulic cylinder or some other source of movement, as indicated diagrammatically in FIG. 1. The'plunger may be provided with a tapered portion 32 to centrally locate and guide a sealing member 40. The outward movement imparted to the plunger-30 withdraws the plunger beyond a seal receiving seat 33, and of course, beyond a pour opening 34 in one side of the shot sleeve.

The sealing member or plunger seal 40, in its preferred form as shown in FIGS. 3 and 4, includes a main body or hub 41 forming the center of the seal and an outer cylindrical rim or lip 42 having its thinnest section at the leading edge 44. The inner surface 46 of'the rim or lip is tapered and it together with the'flared web 48 forms a V-shaped annular groove '52. Flared web 48 joins the main body or hub 41 to present a continuous surface between the molten casting metal, indicated by reference numeral 29, and the face of the plunger 30. In the preferred form of the invention, the seal 40 is initially cast somewhat larger than the diameter of the shot sleeve and is sheared oif as indicated in FIG. 2 by forcing it into theentrance end of the shot sleeve by the force of the plunger 30. This shearing action assures that the external diameter of the rim or lip of. the soft seal will be exactly the diameter of the entrance end or outer end of the shot sleeve.

A further function of the separate sealing member 40 is to prevent metal fiom by-passingtbe plunger 30 during the injection cycle of the casting operation. As the plunger and soft seal are advanced toward the inner end of the shot sleeve and the level of the molten metal rises, filling the space within the sleeve between the plunger seal so ,and gate runner 18, pressure exerted by the plunger on the molten metal 29 is transmitted in all directions and against all surfaces in contact with the casting metal. One of the surfaces subjected to this pressure is the tapered inner surface 46 of the seal which is pressed into even tighter contact with the interior surface of the shot sleeve preventing any possibility of the molten metal by-passing the plunger.

It is contemplated that each sealing member 40 will be used only one time; the sealing member remaining with the solidified slug of metal in the sleeve and being removed therewith when the die is opened. A new seal is then inserted in the shot sleeve before the casting metal for the next shot is ladled in. The sealing member is preferably made from the same or a closely similar metal to that being cast, and since the cold chamber process is commonly used for aluminum, the seal is desirably made of aluminum or an aluminum alloy.

It is, however, possible to use the technique herein described when pressure die-casting other metals such as magnesium, zinc, alloys thereof, and the like.

The sealing member is of such shape that it readily lends itself to being produced by the die-casting process. While the seal may be produced on a separate machine, the most economical method, if the seal is of the same material as is being cast, is to provide the die assembly with a subsidiary die cavity or impression .53 for the seal which is connected to the gate runner 18 of the main die cavity 19 such that a sealing member is cast each time a production casting is made. (In the drawing the impression 53 is shown in the same vertical plane as the main die cavity 19. In practice, however, this cavity is displaced horizontally so that its runner connects to a vertical passage.) If the sequential method is used, the sealing member produced with one casting maybe used as the seal in pro ducing the next casting, thus eliminating the storage and handling of separately cast seals. It is anticipated that some metal or other material entirely dissimilar to that being cast may be used to form the seal, but it is preferred that the material of construction should be much softer than the material of which the shot sleeve is made so that any wear which may occur will be in the peripheral surface of the disposable seal rather than in the interior surface of the shot sleeve.

By. making the seal somewhat larger initially than the internal diameter of the shot sleeve and by shearing off the outer portion thereof during the initial inward movement of the plunger, a tight fit is assured. The seal is placed manually in seat 33 and the plunger 30 advanced. The outermost end of the shot sleeve is formed with a sharp shearing edge which acts to remove anyexcess metal from the periphery of the seal as it is forced into the shot sleeve by the initial inward move ment of the plunger.

One formbf the machine embodying the present invention and which may be used to carry out the present method is provided with a movable die portion 54 which is advanced and retracted from the cover die 16 by any suitablemechanism such as appropriate toggle links 56. When the die halves 54 and 16 are in the closed position, a conventional peripheral seal 57 (see FIG. 6) prevents the entry of air into the die cavity. The movable die portion comprises, as is common in the art, a plurality of ejector pins 58 which extend, with minor clearance in the passages therefor, through the movable half of the die and which are operated by a separate hydraulic cylinder 60 and a separate platen 62. In many machines that are presently used, this mechanism is simply exposed to the atmosphere. In the present instance, however, the ejector pin operating mechanism is housed in a closed chamber 63 and provision is made for evacuating this chamber through an evacuating line 64. The evacuating line 64- may run to any suitable source of vacuum such as chambers 65. It will thus be seen that air is withdrawn from the die through the clearance space around the ejector pins 58 even though this space is made quite small since the chamber or cavity 63 is at subatmospheric pressure. Provision is made for rapid evacuation of the air from the die cavity into the chamber 63 by a separately controllable major evacuation passage 66 having a valve 67 disposed therein, the valve being operated in timed relation to the movement of the plunger 30 or with any other part of the machine cycle. Inasmuch as it is useless to open valve 67' before the shot plunger seal 40 advances beyond the pour opening 34, the simplest actuator for valve 67 will comprise a cam 69 on the plunger rod which will close an electrical circuit when the plunger 30 advances to the point where the pour opening 34 is closed. A solenoid can be utilized to operate the main evacuation valve 67 or the valve may be operated pneumatically through an electrically actuated air valve, of a type that is entirely conventional. Thus, for purposes of illustrating the present method, the cam 69 is shown in association with a legend denoting its function. Because the valve controlled passage 66 can be made very large, it need be opened only briefly to take all of the air out of the die and shot sleeve. Thus the plunger cam 69 can be limited in its longitudinal extent so that the valve is opened and closed in sequence as the plunger moves up to the position at which high pressure is applied for injection of metal into the die.

Previous attempts to evacuate the air from the die cavities of cold chamber die-casting machines have centered largely around attempts to evacuate the air from the die cavity alone, and to rely upon the advancing metal to close ofi the opening between the shot sleeve and the gate runner. Other attempts have been made to evacuate the die through the shot sleeve, but it is apparent that evacuation will fail unless all leakage around the plunger is completely prevented, and that such evacuation can continue only until injection of the metal begins. The shot plunger in cold chamber die-casting machines must have a clearance of five to ten thousandths of an inch on the diameter to prevent the plunger from sticking in the shot sleeve and galling the latter during reciprocation. In a four inch plunger machine this clearance represents an open space of .06 to .13 square inch through which air can flow into the shot sleeve and die cavity, and is restricted only to the extent that a portion of the opening is closed by metal in the partially filled shot sleeve.

In those instances in which evacuation of the die cavity is attempted through a valve such as Valve 67, and the advancing metal relied upon to close off the gate opening against the entrance of air from the shot sleeve, the timing of the operation of the valve becomes critical since the metal is injected into the die with great rapidity, and the valve must be closed before the metal reaches it, otherwise the metal will be drawn out into the evacuation line. By utilizing the present method which seals the shot sleeve as soon as the soft plunger seal has passed the pour opening, the timing of the valve 67 becomes much less critical. The machine can be arranged so that a pause in the advancing motion of the plunger 30 takes place as soon as the pour opening 34 is passed as shown in FIG. 4, and the valve 67 can remain open during this pause. Before the dwell or pause time has elapsed, and injection of the metal is commenced, the valve 67 can be closed at any time. Thereafter, evacuation of the die will continue through the clearance around the ejector pins 58 during the time the metal is entering and filling the die. The die is thus under the influence of the evacuating system constantly from the time the pour opening 34 is passed until the metal has completely entered and filled the die. Sound castings even of devices having very thin fins and similar protuberances and sections are thus assured. In practice the thin flash that occurs around the ejector pins by entrance of the metal into the minor evacuation passages has been found to be easily displaced and to create no practical problems.

Regardless of whether the two-step operation in which there is a dwell in the actuation of the plunger is used, or whether the plunger motion is made initially slow and finally rapid, the effective function of the sealing member 40 is the same. The seal remains in intimate contact with the walls of the shot sleeve and prevents air from being drawn into the die cavity through the shot sleeve thus eliminating one of the greatest sources of vacuum leakage.

When the metal has been injected into the die, it will have filled the main die cavity and will also have filled the subsidiary cavity 53 in which a new plunger seal is formed. This plunger seal can be broken away from the main casting after ejection and used on the subsequent stroke of the plunger, having been placed into position as shown in FIG. 2, sheared to fit the interior of the shot plunger and advanced into position to seal the shot sleeve for the reception of metal as indicated in FIG. 3.

In operation, sealing member 40 is inserted in shot sleeve 10 ahead of plunger 30 before the molten metal is ladled into the sleeve through the pour opening 34. This may be accomplished by inserting the seal aheadof the plunger, after the plunger is completely Withdrawn from the outer end of the sleeve permitting the seal to be seated on seat 33, as shown in FIG. 2. By having the shot sleeve arranged with a seal-receiving'seat at its end, the necessity of a separate trimming operation for removing the flash from the seal in its as cast condition is obviated. Plunger 30 is completely withdrawn from the end of the shot sleeve before the seal is placed on its seat. The seal, with its flash attached, is inserted or placed on the seat. The flash which extends radially around the periphery of the seal is trimmed off by the vertical end face of the shot sleeve and the trimmed flash falls through a clearance space 35 into a suitable receptacle. With the seal completely trimmed, it is ready to be advanced into the sleeve where it will perform its sealing function. The trimming operation may be accomplished by a continuous movement of the plunger whereby the seal is moved into position adjacent the outer end of the pour opening 34. At this point the motion of the plunger is halted and the casting metal is ladled into the sleeve through the pour opening 34.

The evacuation of the die cavity takes place through a major evacuation passage controlled by valve 67 into the chamber 63 and thence, through evacuating lines 64 to the vacuum source 65, during the initial stage of the evacuation which occurs with the plunger advanced past the pour opening as shown in FIG. 4 Thereafter, the plunger continues to advance at a rapid rate and fills the die cavity which has been under continuous evacuation through the main valve 67 and through the minor evacuation passages comprising the clearance space around the ejector pins 58, the valve 67 being closed while the plunger is making this final advancing movement. It will thus be seen that the die has been much more effectively evacuated than has heretofore been the practice, and that the soundness of the castings produced therein is considerably increased.

This application is a continuationin-part of my application Serial No. 808,273, filed April 22, 1959, now abandoned, which was, in turn, a continuation-in-part of my earlier application Serial No. 701,209, filed December 6, 1957, now abandoned.

It should be understood that the method of this invention is subject to further modification and that the apparatus shown in the drawings is for purposes of illustration only and is not intended to limit the scope of the appended claims.

What I claim is:

l. The method of making a casting in a cold chamber pressure die-casting machine which comprises closing the two halves of a die assembly, inserting a separate plunger seal in a shot sleeve ahead of the plunger, introducing a charge of molten metal into said sleevetthrough the pour opening therein, exerting pressure on the plunger toadvance said plunger and plunger seal past said pour opening and deforming said plunger seal to establish a gastight relationship between the separate plunger seal and shot sleeve prior to building up pressure on said motlen metal, evacuating the air from the die cavity and communicating parts including the space in the shot sleeve above the molten metal through a major evacnationrpassage, advancing the plunger and plunger seal toward the gate runner by means of pressure exerted on the plunger to force the molten metal into the die cavity, closing said major evacuation passage, continuing the evacuation of the die cavity through minor evacuation passages during entrance of the metal into the-die cavity, allowing .the molten metal to solidify to form a casting, the plunger seal adhering to the slug of metal remaining in the shot sleeve as it solidifies, separating the die halves, and removing the casting and gate with the seal adhered thereto. 7 f2, The method of making a casting in a cold chamber pressure die-casting machine which comprises closing the two halves of a die assembly, inserting a separate plunger seal in a. shot sleeve ahead of the plunger, introducing a charge of molten metal into said sleeve through the pour opening'therein, exerting pressure on the plunger to advance said plunger and plunger seal past said pour opening and deforming said plunger seal to establish a gas-tight relationship between the separate plunger seal andshot sleeve prior to building up pressure on said molten metal, evacuating the air from the die cavity and communicating parts including the space in the shot sleeve above the molten metal, advancing the plunger and-plunger seal toward the gate runner by meansof pressure exerted on the plunger to force the molten rnetal into the die cavity, continuing the evacuation of the die cavity through clearance spaces around ejector pins entering therein during entrance of the metal into the die cavity, allowing the molten metal to solidify to form a casting, the plunger seal adhering to the slug of metal remaim'ng in the shot sleeve as it solidifies, separating the die halves, and removing the casting and gate withth e seal adhered thereto.

3. In a cold chamber die casting machine having a frame, a .die mounting portion comprising a stationary platen and a movable platen carried by said frame, cooperating die halves carried by said platens and forming a die cavity, a shot sleeve extending through said stationary platen and terminating at a gate into the die cavity, and a metal injecting plunger reciprocable in said shot sleeve, the improvement comprising an evacuated chamber carried by said die monntingpor-tion, means forming a major evacuation passage between said die cavity and said evacuated chamber, a valve in said major evacuation passage, at least one constantly open minor evacuation passage between said die cavity and said evacuated chamber, a peripheral seal around said die cavity effective to prevent the'entrance of air when said die halves are closed against each other, and a non-reusable seal in said shot sleeve ahead of said plunger effective to prevent the entrance of air into said die cavity through said shotsleeve. 4; The improvement defined in claim 3 in which said non-reusable seal comprises a deformable sealing member of the same material as the metal being injected into said die cavity.

5. The improvement defined in claim 3 in which said minor evacuation passage comprises a clearance space around an ejector pin extending into the die cavity.

6. The improvement defined in claim 3 and means to open and close said valve in timed relation to the movement of said metal injecting plunger.

References Cited in the file of this patent UNITED STATES PATENTS 2,774,122 Holder Dec. 18, 1956 2,904,861 Morgenstern Sept. 22, 1959 2,932,865 Bauer Apr. 19, 1960

Images