US3748858A

US3748858A - Apparatus for controlling the pressure at the input of casting machines

Info

Publication number: US3748858A
Application number: US00205920A
Authority: US
Inventors: W Venus
Original assignee: GUSSTAHLWERK WITTMAN AG
Current assignee: GUSSTAHLWERK WITTMAN AG
Priority date: 1970-12-10
Filing date: 1971-12-08
Publication date: 1973-07-31
Anticipated expiration: 1990-07-31
Also published as: DE2060681A1; BE774261A; NL7115241A; FR2117853A1; IT943801B; LU64158A1

Abstract

A multiplier cylinder, divided by a multiplier piston into a feed chamber and a counterpressure chamber, is associated with the input of a casting machine, particularly with a die casting machine, to control the operating pressure sequence at the input. The counterpressure chamber receives a pressure medium from a vessel, in which the medium is at a predetermined continuous pressure, through a connection having a relatively large crosssectional area for the flow of the pressure medium so as to reduce the choking effect.

Description

United States Patent 1191 Venus Jul 31 1973 [54] APPARATUS FOR CONTROLLING THE 1,970,999 8/1934 Ferris et al 60/52 HF UX PRESSURE AT THE INPUT or CASTING :31; MACHINES 2:597:050 5 1952 [75] Inventor: Willibald Venus, Munich, 2.618.822 1 /1952 Germany 3,165,979 1/1965 Clerk 60/52 R x [73] Assignee: Gusstahlwerk Wittmann AG,

HagemHaspe, Germany Primary ExammerEdgar W. Geoghegan [22] F1 d D 8 1971 Attorney-George l-l. Spencer et al.

1 e ec.

21 A l. N 205,920 1 PP 57 ABSTRACT [30] Foreign Appucafion p i it Data multiplier cylinder, divided by a multiplier piston Dec 10 1970 German P 20 60 681 9 into a feed chamber and a counterpressure chamber, is

y associated with the input of a casting machine, particu- [52] U S Cl 60 60,415 larly with a die casting machine, to control the operat- [51] Int Cl '1/02 plsb 3/00 ing pressure sequence at the input. The counterpres- [58] Fie'ld 6052 i 54 5 H sure chamber receives a pressure medium from a ves- 60/413 2 sel, in which the medium is at a predetermined continuous pressure, through a connection having a relatively [56] References Cited large cross-sectional area for the flow of the pressure medium so as to reduce the choking effect. UNITED STATES PATENTS 1,460,586 7/ i923 Howse 60/52 R 6 Claims, 1 Drawing Figure chorg/ny or dllfr'barglhgze DIM/go lll pmmw

APPARATUS FOR CONTROLLING THE PRESSURE AT THE INPUT OF CASTING MACHINES BACKGROUND OF THE INVENTION The present invention relates to an apparatus for controlling the pressure at the input of casting machines particularly for die casting machines, having a multiplier cylinder that is divided by a multiplier piston into a feed chamber and a counterpressure chamber, the counterpressure chamber being filled with a counterpressure medium.

An apparatus of the above-described type is used in casting machines, particularly die casting machines, in order to subject the casting material, e.g. an alloy, to increased pressure from the time it has been pressed into the mold cavity until it subsequently hardens. In order to produce this increase in pressure the feed chamber of the multiplier cylinder is connected, at a very precisely controlled time, with a pressure reservoir so that the multiplier piston exerts a substantial increased pressure onto the die moving the casting material.

In order to be able to set the degree of pressure increase over a wide range, the effect of the pressure multiplier must be appropriately controlled. This is generally done in the apparatus of the type described above by adjusting the counterpressure acting on the multiplier piston.

It is known in the art that one way in which the counterpressure can be set is through the use of precontrolled pressure setting valves. However, the time periods within which the full multiplier effect must occur at the die casting machine are very short. These time periods are in the order of magnitude of a few one hundredths of a second and even less. On the other hand, the counterpressure which acts on the multiplier piston and determines the effective multiplier effect, is produced in the pressure setting valve as a direct result of the passage of pressure fluid through predetermined cross sections in the valve, i.e. as a consequence of this pressure fluid being choked off. The cross-sectional areas are produced and maintained by appropriate charging of the regulating and control elements.

The counterpressure set in the pressure control valve thus is produced, at the earliest, only after a stream of pressure fluid has formed in the pressure setting valve. As a result, the counterpressure set in the pressure setting valve is influenced by the speed of the multiplier piston. Consequently the appropriately adapted and modified cross-sectional area must always be formed in the pressure setting valve to be adaptable to a changed throughput of pressure fluid per unit time.

The mass inertia of the moved control elements and, most of all that of the pressure fluid itself, have a very adverse effect on accurate operation and rapid actuation of the pressure setting valve. This becomes evident because, under certain circumstances, the full multiplier pressure is present only after the expiration of the above-mentioned short period of time.

If, however, the pressure setting valve is so controlled that it initially opens excessively, then the hydraulic stream pressures develop only after a certain period of time, as a consequence of which the cone of the pressure setting valve releases that cross section which corresponds to the desired pressure. As a result there is produced initially a multiplier pressure which far exceeds the set value and then slowly drops to the set pressure value. This excess pressure, however, causes the casting mold to open.

To eliminate these drawbacks it has been proposed to replace the hydraulically precontrolled pressure setting valves by those having a direct effect. These valves exhibit less over-controlling, the set pressure value however, is substantially more dependent upon the speed of the multiplier piston than it is with the precontrolled pressure setting valves.

Embodiments are also known in which the counterpressure chamber of the multiplier is connected with the liquid chamber of a pressure reservoir and with a check valve disposed in the connecting line. This arrangement, however, neither prevents the delays in starting caused by the inertial resistances of the moved masses nor the influences on the counterpressure by the variable speed of the multiplier piston, which influences are determined by the valve cross sections.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an apparatus of the type described above in which an accurately defined counterpressure, that can be set within wide limits, acts on the multiplier piston without any delay during the required period of time and this counterpressure defines the amount of pressure exerted by the multiplier on the casting material.

The above described object of the invention is accomplished in that the counterpressure chamber is in communication, via a connecting line which produces as low a choking effect as possible, with a pressure container to receive the counterpressure medium directly from the container.

Since in the apparatus, according to the present invention, the counterpressure medium, is maintained at an appropriately set permanent pressure in the counlittle choking effect as possible, it is advisable to select a connecting line between the counterpressure chamber and the pressure container which has a particularly large cross section.

In a particularly advantageous further development of the present invention a gas, e.g. nitrogen, is used in contradistinction to the known devices, as the counterpressure medium. This not only reduces the choking, which practically can never be quite eliminated, in the connection to the pressure vessel due to the considerably lesser density of the gas, but also the mass inertia of the counterpressure medium is reduced to a fraction of that which is encountered with the use of liquid counterpressure medium. As an example, when nitrogen is used as the counterpressure medium instead of oil, the ratio of the mass inertia of the mediums is about Advantageously the effective volume of the pressure container holding the counterpressure medium is made to be variable. In one embodiment the effective volume of the pressure container is varied by the addition of pressure medium from the drive system of the casting machine or by removal therefrom into the tank of the drive system.

In a further embodiment of the apparatus of the present invention the feed chamber receives pressure medium from a pressure reservoir via two parallel valves which open consecutively. The combination of two valves affords the opportunity to achieve those conditions, which best meet the requirements of the desired die casting operation by the appropriate selection of the moments when the valves open. These requirements relate, for example, to the escape of air from the mold cavity and the fill chamber and to a rapid filling of the mold cavity with a pressure increase which starts immediately thereafter before the cast material hardens.

BRIEF DESCRIPTION OF THE DRAWING The single FIGURE of the drawing is a partly schematic and partly simplified cross-sectional view of the apparatus, according to the present invention, associated with a cold chamber die casting machine having a horizontal pressure chamber.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The FIGURE shows a pressure plunger 2 displaceably disposed in a known manner in the till or pressure chamber 1, this plunger exerting a pressing force on the casting material introduced into chamber 1 at opening 1a, to press it into a mold cavity 3. The mold halves of the mold which form the mold cavity 3 are indicated at 4 and 5. Mold half 4 rests on a firm mold clamping plate 6 while the movable mold half is pressed, via a clamping box 7, against the fixed mold half 4 by a mold locking mechanism which is not shown.

The pressure force exerted on the casting material is transmitted to the pressure plunger 2 via a die rod 8 which is connected to a press piston 9. The press piston 9 is displaceable in a press cylinder 10 which is associated with a multiplier cylinder 11. A multiplier piston 14 is displaceable in multiplier cylinder 11 and can charge the interior of press cylinder 10 with pressure via a multiplier piston shaft 13. A stepped opening or bore 15 extends through multiplier piston 14 and piston shaft 13 and this opening is closed at its end facing the press cylinder 10 by a spring loaded check valve 16. This check valve 16 permits passage of pressure medium into press cylinder 10 when a certain pressure value in the feed chamber 12 of the multiplier cylinder 11 is exceeded.

The feed chamber 12 of the multiplier cylinder 11 is in communication with a pressure reservoir 23 via

lines

19 and 20 containing control valves generally indicated at 21, 22. A separating piston 24 is shown disposed in pressure reservoir 23 but the reservoir 23 may, of course, also be designed without a separating piston. The reservoir is charged by the pump (not shown) of the drive system of the casting machine via

pressure lines

31, 17, 25 and 20. Line 25 has a switched-on check valve 26.

The counterpressure chamber 18 of the multiplier cylinder 11 is in communication, via line 27, with a pressure tank 28. The tank can be charged and discharged through the blocking valve 39. The pressure tank 28 itself is connected, via lines 29 with a blocking valve 30 included therein, to the pressure line 31 com ing from the pump (not shown). From that portion of the line disposed between the blocking valve 30 and the pressure tank 28 a discharge line 33, which is provided with a blocking valve 32, branches ofi.

Pressure lines 31 and 17, charged by the pump of the drive system, can be connected selectively, by means of a control slide valve 34, either with the feed chamber 12 of the multiplier cylinder 11, through

lines

19 and 19a, or with the return chamber 40 that is disposed opposite the feed chamber 41 of the press cylinder 10. Advantageously this control slide valve 34 is designed as a direct action or precontrolled magnet slide valve.

The

control valves

21 and 22 connected between

lines

19 and 20 are presettable regarding their opening widths by means of setting

spindles

21a or 22a, respectively disposed over the movable members 21' and 22' of the valves. The

pressure chambers

35 or 36, respectively, which are disposed above the movable member of the

control valves

21 and 22 are in communication either with the pressure reservoir 23 or with the discharge drain via sliding

valves

37 or 38, respectively.

The pressure tank 28 contains, as the counterpressure medium, nitrogen gas or some other inert gas at a predetermined pressure and the line 27 connecting the pressure tank with the counterpressure chamber 18 has as large a cross section as possible in order to counteract a flow of the nitrogen gas, upon displacement of the multiplier piston 14, with as low as possible a choking action.

The control device according to the present invention operates as follows. After filling the casting material into the pressure chamber 1 disposed in front of the mold cavity 3, the control slide 34 is changed in its position and pressure medium from the drive system of the casting machine flows from pressure line 31 via line 17, control valve 34 and

lines

19a and 19 into feed chamber 12 of the multiplier cylinder 11. From this feed chamber the pressure medium flows through the longitudinal bore 15, and, after lifting check valve 16, into feed chamber 41 of press cylinder 10 to the front of press piston 9. Immediately preceding this, control slide 34 had connected the return chamber 40 in the press cylinder 10 with the discharge drain.

Now press piston 9 moving at a speed corresponding to the output of the drive pump, toward the left in the drawing, closes the fill opening la of the till chamber 1 and pushes the filled-in casting material in the direction toward the fill chamber end. Upon closing of the fill opening, control valve 21 is opened by the pressure medium in line 20, at a predetermined point in time. The extent of the opening is determined by presetting of spindle 210.

Now additional pressure medium flows from pressure chamber 23 via control valve 21 and line 19 into the feed chamber 12 of the multiplier cylinder 1 1, through the longitudinal bore 15, through check valve 16 and into the feed chamber 41 of press cylinder 10. The quantity of the medium flowing in per unit of time and thus the speed of the press piston 9 is determined, with a given reservoir pressure in the reservoir 23, by the size of the opening of control valve 21. The tilled-in casting material is thus moved with increased speed to the left, toward the gate of the mold.

It is generally desired to have the speed of the press die 9 increase as soon as the casting material has reached the gate of the mold in order to fill the mold cavity 3 with casting material as quickly as possible be fore it cools. According to the present invention it is therefore provided that, at the appropriate moment, control valve 22 is additionally lifted to the extent previously set by spindle 220. This is done when the sliding valve 38 connects the pressure chamber 36 disposed above the movable member 22' with the discharge drain. The pressure of the medium in pressure reservoir 23 then raises the movable member 22 of control valve 22 quickly to the set opening height. Thus pressure medium flows into the feed chamber in front of the pressing piston 9 not only through control valve 21 but also through control valve 22 and thus further increases the speed of the piston.

Once the mold cavity 3 is completely or almost completely filled so that the pressure plunger 2 can no longer move due to the resistance of the casting material, the further influx of pressure medium ceases when the check valve 16 closes under the influence of its spring.

The continuous pressure of the nitrogen which has been maintained in pressure tank 28 acts on the annular surface of the multiplier piston 14 facing the coun terpressure chamber 18. The term continuous pressure here indicates that this pressure, contrary to the known control devices, is not produced only at a movement of the multiplier piston but rather is present continuously, i.e. also when the multiplier piston 14 is in its rest state. This continuous pressure is selected to be at least high enough that the pressure force exerted by it on the annular surface of the multiplier piston 14 is greater than the pressure force acting on the multiplier piston 14 during passage of the pressure medium of the driving system through check valve 16. The pressure force produced by the pressure medium of the drive system tends to push the multiplier piston 14 to the left as seen in the drawings. If the check valve 16 is now closed, the full reservoir pressure of pressure reservoir 23 is built up in the feed chamber 12 of the multiplier cylinder 11. Thus a force acts on the multiplier piston 14 toward the left as seen in the drawing and force is computed from the cross-sectional area of the feed chamber 12 and the reservoir pressure. Acting against this force is the counterpressure force which is computed from the pressure of the precompressed nitrogen and the annular surface of the multiplier piston 14 associated with the counterpressure chamber 18. The resulting force acting on the multiplier piston 14 is thus the difference between the two forces. Due to this force, differential piston shaft 13 of multiplier piston 14 is pressed into the feed chamber 41 in front of press piston 9, whereby the multiplied pressure in the feed chamber 41 is the quotient of this resulting force dividend by the area of piston shaft 13.

The more the pressure of the nitrogen in tank 28 and in counterpressure chamber 18 approaches the pressure in the pressure reservoir 23, and thus in feed chamber 12, the smaller becomes the multiplied pressure. As soon as there is a pressure equilibrium, the multiplier effect ceases.

Due to the large cross section of connection line 27, the speed of flow of the nitrogen during displacement of the multiplier piston 14 and, thus the flow resistance, remain very low. Moreover, with the selection of nitrogen as the counterpressure medium, only slight delays, caused by the very low mass inertia of the gas, need be anticipated. Thus the counterpressure is almost completely constant in the counterpressure chamber corresponding to the pressure in tank 28 and there is an extraordinary acceleration in the response of the multiplier effect. Therefore it is possible in the very short time interval immediately before or at the point of complete fill of the mold cavity 3, which time interval is so very important, to set a precisely defined multiplier pressure.

To vary and set the multiplier pressure, the pressure in the counterpressure chamber 18 and in the connected pressure tank 28 is changed by charging from a nitrogen supply tank, not shown, via the blocking valve 39 or by release of nitrogen into the atmosphere via this valve.

In order to be independent of the availability of nitrogen supply tanks when varying the multiplier effect, the effective volume of tank 28 can be varied by the addition or removal of pressure medium from the drive system of the casting machine. In this case the pressure medium enters into tank 28 through line 29 and blocking valve 30 and can flow off, if required, through blocking valve 32 and line 33 into the tank of the drive system. The pressure medium in tank 28 has no hydraulic function in the drive system of the machine but rather serves only to vary the effective volume of tank 28, which contains nitrogen, and thus vary the pressure of the nitrogen. The operating range of the press cylinder 10 of the casting machine is set according to the selected size of tank 28. This range is one in which it is possible to set at will any desired final multiplier pressure from a maximum to a minimum merely by the addition or removal of pressure medium.

In some cases the casting conditions require that the movement of press piston 9 which has been produced only by opening of control valve 21 be continued be yond the point where the casting material reaches the mold gate. The casting material then fills the mold cavity 3 relatively slowly in accordance with the speed of press piston 9. This is of advantage, for example, when, for east objects having a larger wall thickness, the air contained in the mold cavity 3 must be permitted to escape. Only when mold cavity 3 has been filled to a substantial extent or even entirely with casting material, will control valve 22 be opened, which now increases the speed of press piston 9 until mold cavity 3 is completely filled and then moves the multiplier piston 14 correspondingly rapidly in order to effect a rapid pressure increase in the casting material before it hardens.

The points in time at which

valves

21 and 22 are opened are advisably determined by limit switches, timers or pressure switches. In the extreme case, it is thus possible, without difficulties, to initially displace the casting material in the fill chamber at the speed set in the control valve 21 and then press it into the mold cavity 3 until it completely fills the latter, whereupon it is suddenly charged with the multiplied pressure of the multiplier piston 14 when control valve 22 has fully opened. instead of the pressure-dependent switching of control valve 22 it is also possible to use, for example, a time-dependent circuit so that the control valve 22 opens a predetermined time before mold cavity 3 is filled completely.

It is also possible to open control valve 22 before the casting material reaches the mold gate so that the time between filling of the chamber 1 and complete fill of the mold cavity 3 becomes as short as possible. The

correct moment of opening of control valve 22 can in this case most advisably be determined by a pathdependently actuated limit switch. Other suitable types of actuation for opening of

control valves

21 and 22 at a defined point in time are of course also possible. Although the control device according to the present invention has been described only in connection with a cold chamber die casting machine, it is of course understood that the principle of the present invention can be used for any similarly operating casting machine where it is of importance to subject the casting material at a defined moment in time to an increased pressure with the least possible delay and a precisely defined effect. The apparatus according to the present invention can therefore also be used, without restriction, for example, in hot chamber die casting machines or injection molding machines for thermoplastic masses.

Control valves

21 and 22 can moreover be so selected that they either have the same dimensions and opening cross sections for flow of the pressure medium or are opened to different extents or have different dimensions and perform the same valve stroke.

It will be understood that the above description of the present invention is susceptible to various modifications, changes and adaptations, and the same are intended to be comprehended within the meaning and range of equivalents of the appended claims.

I claim:

1. ln apparatus for controlling the sequence of application of a pressure medium at the input of a casting machine having a drive system which provides the pressure medium, the apparatus including a multiplier cylinder that is divided by a multiplier piston into a feed chamber which receives the pressure medium, and a counterpressure chamber filled with a counterpressure medium, the improvement which comprises in combination:

a. a pressure vessel containing gas constituting said counterpressure medium;

b. means for maintaining said gas at a predetermined continuous pressure; and

a connecting line between said pressure vessel and the counterpressure chamber, said line having a relatively large cross-sectional area, whereby said gas, upon motion of said multiplier piston can flow substantially unthrottled through said large crosssection area for maintaining a continuous determined pressure of said gas in said counterpressure chamber irrespective of the motion and the position of said multiplier piston.

2. An arrangement as defined in claim 1, wherein the effective volume of said pressure vessel for containing the counterpressure medium is selectively variable.

3. An arrangement as defined in claim 2, wherein the effective volume of said pressure vessel is varied by the addition of pressure medium from the drive system of the casting machine into said pressure vessel and by the removal of pressure medium from said pressure vessel and the return of this pressure medium to the drive systern.

4. An arrangement as defined in claim 1, further comprising:

c. a reservoir for the pressure medium;

d. a pair of control valves connected in parallel between said reservoir and the feed chamber; and

e. means for consecutively opening said control valves to admit the pressure medium to the feed chamber.

5. An arrangement as defined in claim 4, wherein one of said control valves is actuated by said means within a time interval of no more than one hundredth of a sec- 0nd.

6. An arrangement as defined in claim 1, wherein the casting machine is a die casting machine.

a: a: a:

Claims

1. In apparatus for controlling the sequence of application of a pressure medium at the input of a casting machine having a drive system which provides the pressure medium, the apparatus including a multiplier cylinder that is divided by a multiplier piston into a feed chamber which receives the pressure medium, and a counterpressure chamber filled with a counterpressure medium, the improvement which comprises in combination: a. a pressure vessel containing gas constituting said counterpressure medium; b. means for maintaining said gas at a predetermined continuous pressure; and c. a connecting line between said pressure vessel and the counterpressure chamber, said line having a relatively large cross-sectional area, whereby said gas, upon motion of said multiplier piston can flow substantially unthrottled through said large cross-section area for maintaining a continuous determined pressure of said gas in said counterpressure chamber irrespective of the motion and the position of said multiplier piston.

3. An arrangement as defined in claim 2, wherein the effective volume of said pressure vessel is varied by the addition of pressure medium from the drive system of the casting machine into said pressure vessel and by the removal of pressure medium from said pressure vessel and the return of this pressure medium to the drive system.

4. An arrangement as defined in claim 1, further comprising: c. a reservoir for the pressure medium; d. a pair of control valves connected in parallel between said reservoir and the feed chamber; and e. means for consecutively opening said control valves to admit the pressure medium to the feed chamber.

5. An arrangement as defined in claim 4, wherein one of said control valves is actuated by said means within a time interval of no more than one hundredth of a second.