US3891126A

US3891126A - Injection cylinders of die cast machines

Info

Publication number: US3891126A
Application number: US412548A
Authority: US
Inventors: Kazuyoshi Segawa
Original assignee: Toshiba Machine Co Ltd
Current assignee: Shibaura Machine Co Ltd
Priority date: 1972-11-14
Filing date: 1973-11-05
Publication date: 1975-06-24
Anticipated expiration: 1992-06-24
Also published as: DE2356711A1; IT996420B; CH569575A5; JPS4971369A; JPS5312033B2

Abstract

In an injection cylinder of a die cast machine of the class wherein the piston of the cylinder is operated by pressurized fluid, the piston is moved in the forward direction for performing injection moulding by the expansion of gas contained in a gas accumulator and the piston is moved in the rearward direction by pressurized liquid. When the piston is moved in the forward direction the flow rate of the pressurized liquid discharged from the cylinder is controlled by means of a flow control valve.

Description

United States Patent Segawa June 24, 1975 [5 INJECTION CYLINDERS 0F DIE CAST 2.224.956 12 1930 Ernst et a1 1 92 134 x 1632.246 HI) 2 lchikawa et al 1 1 1 1 425/135 MACHINES T J 3,638.423 2/l972 Heijst .l 92/134 X {75] Inventor. Kazuyoshl Segawa, okyo, apan FOREIGN PATENTS OR APPLICATIONS AssigmcI Shim Kikai Kabushiki Kaisha- 1.1101783 2/1971 Germany .4 92 134 Tokyo. Japan [22] Filed; N 5 [973 Primary Examiner-Robert B. Reeves Assistant E,ruminer-David Scherbel [2| I Appl' 412548 Attorney. Agent, or Firmwenderoth. Lind & Ponack [30] Foreign Application Priority Data ABSTRACT Nov, 14 1972 Ja n ,4 47414 32 in an injection cylinder of a die cast machine of the class wherein the piston of the cylinder is operated by [52] [1.5. CI. H 222/334; 94/l34; 222/372 pressurized fluid. the piston is moved in the forward [5| Int. Cl 822d 17/04 direction for performing injection moulding by the ex- [58] Field of Search 92/l34; 222/334. 372; pansion of gas contained in a gas accumulator and the 425/135; 94/134 piston is moved in the rearward direction by pressurized liquid. When the piston is moved in the forward (56] References Cit d direction the flow rate of the pressurized liquid dis- UNn-ED STATES PATENTS charged from the cylinder is controlled by means of a 2 11x1 ,134 7/1937 Hacssler .1 92 134 x flow comm Valve 1163.982 6/1939 Mercier o. 92/134 X 6 Claims, 3 Drawing Figures C I I7 70 1 B 1% I\ l C 2 PATENTEDJUN24 ms 3.891.126

SHEET 1 F I G.l PRIOR ART SHEET PATENTEDJUN 24 1975 FIG.3

INJECTION CYLINDERS OF DIE ('AST MACHI BACKGROUND OF THE INVE 'IION This invention relates to a die cast machine. more particularly to a fluid pressure operated injection cylinder of a die cast machine capable of operating at a high speed and under a high pressure.

In a conventional liquid pressure circuit for operating the high pressure. high speed liquid pressure cylinder therein-after. merely termed high speed cylinder) of a die cast machine. high pressure liquid is admitted into a vessel (hereinafter, merely termed a pressure accumulator) sealed with compressed gas. the gas is com pressed to store energy in the pressure accumulator. and the high pressure liquid is admitted into the high speed cylinder at a high speed through a direction change over valve. a speed regulator. etc. by the ex pansion of the gas in the pressure accumulator, thus moving at a high speed the piston of the high speed cylinder. In such a conventional liquid pressure circuit. since the liquid flows at an extremely high speed through the conduit extending between the pressure accumulator and the high speed cylinder. an extremely severe \vater hammering phenomenon occurs at the time when the moving piston comes to stop at which the kinetic energy of the piston is converted into pressure. Although this water hammering phenomenon continues only for an extremely short interval. the force of water hammering created in the injection cylinder of a die cast machine is transmitted to the molten metal introduced into a metal mould. thus forming fins about cast products. In addition. such water hammer ing phenomena imparts an excessively large percussive load or surge pressure upon the liquid conduit. high pressure cylinder, component parts of the machine and the metal mould. For this reason. it has been common to design the high speed cylinder to well resist against such large surge pressure. Moreover. when the machine is operated at its rated pressure. as there is a tendency of forming fins it has been the practice to operate the machine under a pressure lower than the rated pressure. To obviate these difficulties it has been proposed to use a cylinder provided with an accelerator which transfers the liquid on the back pressure side of the piston to the high pressure side or a booster. However. these proposals are not satisfactory because the output thereof decreases during operation.

SUMMARY OF THE INVENTION It is an object of this invention to provide an improved fluid operated injection cylinder for a die cast machine which can obviate difficulties mentioned above.

According to this invention. there is provided an injection cylinder of a die cast machine of the class wherein the piston of the cylinder is moved in the forward and rearward directions by admitting and discharging pressuri/ed fluid into and out of the cylinder. characteri/ed in that there are provided a gas accumulator containing pressurized gas and connected to the cylinder on one side ofthe piston for tnoving the piston in the forward direction by the evpansion of said pressuri/ed gas for performing injection moulding. a source of pressurized liquid. means for admitting the pressuri/cd liquid into the cylinder on the opposite side of the piston to mine the same in the rearward direction thereby compressing the gas in the gas accumulator.

l l l and means for controlling the flow rate of the pressurized liquid when it is discharged from the cylinder when the piston is moved in the forward direction.

BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings:

FIG. I is a diagrammatic representation of a typical prior art high pressure. large output liquid pressure cylinder;

FIG. 2 is a diagrammatic representation of the basic form of this invention; and

FIG. 3 is a diagram showing a modified embodiment of this invention applied to an injection cylinder of a cold chamber type die cast machine.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring first to FIG. I which shows a typical construction of a prior art liquid pressure circuit for the injection cylinder of a die cast machine. the liquid pressure circuit shown therein comprises a cylinder 1 containing a piston 2 whose piston rod 24: acts as a piston of an injection cylinder 20 for injecting molten metal into a metal mould of a die cast machine. not shown. and an accumulator 3 containing pressurized liquid 21 and compressed gas 22 thereabove. The pressurized liquid 2I is forced into accumulator 3 from a pump 23 via a conduit L and a check valve 6 to compress gas 22. thus storing energy therein. When a change over valve 4 is operated toward the left. the pressurized liquid 2I in accumulator 3 flows into cylinder 2 via a flow control valve 5 and a conduit 7 to move piston 2 toward the left. this flow of the liquid being assisted by the expansion of the compressed gas 22, whereby the piston 2 is moved at an extremely high speed to inject the molten metal in the injection cylinder 20 into the metal mould. Under these circumstances. the liquid in the cylinder 1 to the left of piston 2 is returned to a reservoir. not shown. via change over valve 4, and a stop valve 9 is held closed. After the metal mould has been filled v ith molten metal the piston 2 acts to apply pressure to the cast metal. With this conventional liquid pressure circuit as the liquid flows through conduit 7 at an ex tremely high speed during the forward or injection stroke of piston 2. when piston 2 is stopped after completely filling the metal mould to begin to apply pressure to the cast metal an extremely severe water hammering phenomenon occurs.

FIG. 2 shows a diagram of the liquid circuit embodying the invention in which elements corresponding to those shown in FIG. I are designated by the same reference characters. According to this invention. chamber B ofcylindcr I to the right ofpiston 2 is communicated with a sealed gas accumulator 3 through a relatively thick conduit 71! and liquid under pressure is admitted into chamber C of cylinder 1 to the left of piston 2 from pump 23 via a check valve 64:. change over valve 4 and a flow control valve 50 which are connected in conduit 8. A check valve 10 is connected in parallel with flow control valve Su and a pressure meter I I is provided for accumulator ll. According to this invention. the liquid circuit is designed such that the force applied to the left-hand side of piston 2 by the pressurized liquid is larger than that applied to the righthand side of piston 2 by the compressed gas in accumulator 3.

Under normal condition. stop valve 9 is held closed. I'nder these conditions. upon operation of pump 23.

3 pressuri/ed liquid is admitted into chamber of piston 1 via the circuit described abov e. Since L'hLL'l'v valve ll) is opened at this time. piston I is moved quiclsly toward the right to compress the gas in accumulator 3 and store energy therein until the forces acting upon both sides of piston 2 become equal.

To operate the die cast machine. the change over valve 4 i switched to the left to communicate chamber C with a drain. Then. the compressed gas in accumulator 3 expands to move. at a high speed. piston 2 toward the left. ln the prior art liquid pressure circuit. as pressurized liquid in accumulator 3 is used to operate piston 2. and hence the injection cylinder of a die cast machine. an intense water hammeringphenomena was inevitable when the movement of piston 2 is stopped as described hcrcinabove. whereas according to this invention. since compressed gas having a much smaller specific gravity than liquid has been stored in the accumulator and is used to operate piston 2. the water hammering phenomena would not occur because the gas is compressed when the piston is stopped. When compared with liquid. the resistance of a conduit of a given diameter to the flow of gas is evtremely small so that it is possible to greatly increase the operating speed ofthe piston relative to the prior art liquid circuit. The speed of the piston 2 during the forward stroke (to the left as viewed in FIG. 2 can be controlled by the flow control valve 5. The check valve 10 connected in parallel with flow control valve 5 functions to eliminate the resis tance to the How of liquid afforded by check valve 5 when the piston 2 is returned.

After advancing the piston 2. operation of the changeover valve 4 introduces the pressurized liquid supplied by pump 23 into chamber C of the cylinder 1. the piston 2 to retract to the position shown in FIG. 2. During this retracting stroke. the gas in chamber B is pushed back into accumulator 3 to store energy. The purpose of check valve 6a is to prevent piston 2 from moving forwardly when pump 23 is stopped. Valve 9 is opened for draining the accumulator 3.

FIG. 3 diagrammatically shows a modification of this invention applied to the injection cylinder of a cold chamber type die cast machine. in which elements corresponding to those shown in FIG. 2 are designated by the same reference characters. In this modification. a second llow control valve Sb is added to operate the piston 2 at any one oftvvo speeds. There are also added electrically operated change over valves [2 and I}. a second accumulator [4 connected to the output of the pump through a stop valve 15. and a stop valve 16 for connecting the accumulator 3 to the output of pump 23. In this embodiment. a predetermined quantity of liquid 2] is charged in accumulator 3 for the purpose of adjusting the pressure of the gas contained therein.

When pump 23 is operated. the pressurized liquid is admitted into the chamber C of cylinder I via check valve 61! and change-ov er valve 4 to retract piston 2. The pressure of the gas contained in accumulator 3 and the opening olllovv control valve l7 are predetermined such that the pressure applied to the molten metal in the mould increases gradually at the cvtremc forward stroke of the piston 2. that is after the molten metal has been filed. (ias is filled in accumulator l4 under a predetermined pressure and valve 15 is normally held open. \'alvc I6 is closed normally. In order to prevent piston 2 from moving in the forward direction vv hen pump 23 is stopped. as by interruption of electric supply. a pilot chcclv valve It) is inserted between piston l and change over valve 4. 'l he pilot check valve ltl is normally held open by the electrically operated change over valve l2 so that upon interruption of electric supply. valve 10 is closed to prevent accidental forward movement of piston 2.

Then the change over valve 4 is switched to discharge the pressuri/ed liquid in chamber through conduit 8.

valves

10 and 4 and the low speed llovv control valve 5h. Accordingly. piston 2 is advanced at a low speed by the pressure of the gas in accumulator 3. Then changeover valve 13 is energized to switch the How control valve to high speed side in. thus increasing the speed of piston 2. Upon completion of the moulding operation. valve 4 is svvitched to the original state to again supply the pressurized liquid from pump 23 to chamber (1 thus retracting piston 2. Accordingly. the gas is again compressed in accumulator 3. To accelerate the returning motion of piston 2. valve 15 is opened normally to cause the pressuri/ed liquid in accumulator H to assist pump 23. valve 16 is opened when it it desired to increase the gas pressure in the accumulator.

This invention has the following advantages.

1 There is no water hannncring phenomena because the gas in the accumulator provides cushioning ac tion.

I. The maximum speed of the piston is much higher than prior art devices:

3. The device can produce a large output and can operate stably during the forward stroke;

4. The construction is simple and less susceptible to failure;

5. Consumption of the gas in the accumulator is minimal because there is no liquid in the accumulator. or even when liquid is filled therein. liquid is not moved. If the liquid is discharged and refilled into the accumulator as in the prior art. gas will dissolv e in the liquid and be carried away therewith; and

6. Vibration ofthe piping and hence the noise caused thereby is small.

A die cast machine utili/ing the novel pressurized liquid circuit has the following advantages:

7. It is possible to east larger products with a machine of the same rating:

ts. It is possible to alleviate the casting condition and to improve the quality of the product and to decrease the number of rejects because the die cast machine operates stably and because the pressure rises very quickly at the final stage of the injection moulding:

9. The manutacturing cost of the castings is greatly reduced.

lt). It is highly safe and less noisy. and

l l The life ofthe machine and moulds can be greatly prolonged.

I claim:

I. la an injection cylinder of a die cast machine ofthc class wherein the piston ofthe cylinder is moved in forward and rearward directions by admitting and discharging pressuri/ed tluid into and out of said cylinder. the improvement which comprises a gas accumulator containing pressuri/cd gas and a predetermined quantity of liquid. said predetermined quantity of liquid being used for adjusting the pressure of the gas contained in said accumulator. said gas accumulator having substantially larger volume than said cylinder. at llow control valve connected between said cylinder and said gas accumulator l'or admitting said gas into said cylinder thereby moving said piston in the forward di rection by the expansion olsaid pressuri/ed gas for per forming die casting. a source of pressuri/ed liquid. means operatively coupled l'or admitting said pressurized liquid into said cylinder on the opposite side of said piston to move the same in the rearward direction therehy compressing the gas in said gas accumulator. and means opcratnely coupled for controlling the llovv rate of said pressurized liquid while the liquid is discharged from said cylinder when said piston is moved in the forward direction 2. The injection cylinder according to claim 1 wherein said tlovv controlling means is comprised of a valve and further comprising a check valve connected in parallel with said valve. said check valve opening when the pressurized liquid is admitted into said cylinder from said source.

3. The injection cylinder according to claim l which further comprises an accumulator for said pressurized liquid and a normal open valve connecting said liquid accumulator to said source of pressurized liquid.

4. The injection cylinder according to claim 1 wherein said flow rate controlling means comprises a plurality ol flow control valves for providing different flow rates 5. The injection cylinder according to claim I which further comprises a pilot check valve connected in the conduit of said pressurized liquid and an electrically operated valve means for normally holding said pilot valve in an opened state so that said pilot check valve is closed when supply of electricity is interrupted.

6. The injection cylinder according to claim I wherein the quantity of said liquid contained in said gas accumulator is variable.

Claims

1. In an injection cylinder of a die cast machine of the class wherein the piston of the cylinder is moved in forward and rearward directions by admitting and discharging pressurized fluid into and out of said cylinder, the improvement which comprises a gas accumulator containing pressurized gas and a predetermined quantity of liquid, said predetermined quantity of liquid being used for adjusting the pressure of the gas contained in said accumulator, said gas accumulator having substantially larger volume than said cylinder, a flow control valve connected between said cylinder and said gas accumulator for admitting said gas into said cylinder thereby moving said piston in the forward direction by the expansion of said pressurized gas for performing die casting, a source of pressurized liquid, means operatively coupled for admitting said pressurized liquid into said cylinder on the opposite side of said piston to move the same in the rearward direction thereby compressing the gas in said gas accumulator, and means operatively coupled for controlling the flow rate of said pressurized liquid while the liquid is discharged from said cylinder when said piston is moved in the forward direction.

2. The injection cylinder according to claim 1 wherein said flow controlling means is comprised of a valve and further comprising a check valve connected in parallel with said valve, said check valve opening when the pressurized liquid is admitted into said cylinder from said source.

3. The injection cylinder according to claim 1 which further comprises an accumulator for said pressurized liquid and a normal open valve connecting said liquid accumulator to said source of pressurized liquid.

4. The injection cylinder according to claim 1 wherein said flow rate controlling means comprises a plurality of flow control valves for providing different flow rates.

5. The injection cylinder according to claim 1 which further comprises a pilot check valve connected in the conduit of said pressurized liquid and an electrically operated valve means for normally holding said pilot valve in an opened state so that said pilot check valve is closed when supply of electricity is interrupted.

6. The injection cylinder according to claim 1 wherein the quantity of said liquid contained in said gas accumulator is variable.