US2867868A

US2867868A - Die-casting machines

Info

Publication number: US2867868A
Application number: US566481A
Authority: US
Inventors: Kellett Eric; Chambers Leslie William
Original assignee: Birmingham Small Arms Co Ltd
Current assignee: Birmingham Small Arms Co Ltd
Priority date: 1955-02-25
Filing date: 1956-02-20
Publication date: 1959-01-13
Anticipated expiration: 1976-01-13

Description

Jan. 13, 1959 E. KELLETT ET AL 2,867,868

DIE-CASTING MACHINES Filed Feb. 20, 1955 4 Sheets-Sheet 1 Inventor Emc KELLETT LESLIE w. CHAMBERS y diam, M M m A Horn e y;

Jan. 13, 1959 YE. KELLETT ETA!- 2,867,868

DIE-CASTING MACHINES Filed Feb. 20. 1956 4 Sheets-Sheet 2 Inventor ERIC KELLETT} Lssus \MC HAMBERS A ttorneya Jan. 13, 1959 E. KELLETT 3 ET AL 2,867,868

DIE-CASTING MACHINES Filed Feb. 20', 1956 4 Sheets-Sheet 3 F/GS.

F/GG

' U c1055 OPEN EARTH I I I Inventor ERIC, KELLETT Lesue w. CHAMBERS A llorneys Jan; 13,1959 E.VKELLETT ETA;

DIE-CASTING MACHINES 4 Sheets-Sheet 4 Filed Feb. 20, 1956 0 U o 0 M H a W M. 0 0 m (Mum.

"mom F/G. 9

mm? Q Inventor ERR. KELl-ETT' Lssus w. Guamazns By 22070, M, 9 W Attorneys .ments of. the machine.

United States PatentO DIE-CASTING MACHINES Eric Kellett and Leslie William Chambers, Birmingham, England, assignors to The Birmingham Small :Arms Company Limited, Birmingham, England Application February 20, 1956, Serial No..566,481

Claims priority, application Great Britain Febrnary:25, 1955 11 Claims. (Cl. 22-68) This invention relates to .dieecasting machines of the oil hydraulic type, its main object'being to expedite the operational cycle of such machines.

.The basic cycle .of any such machine comprises closing of the die, injection of molten metal, opening of the'die (aftera sufiicient interval for solidification of the metal), and ejection of the. casting (sometimes aftersevering it from the runner), the necessary co-aXial movements being effected by the pressure of the oil in cylinders containing the pistons of jacks connected to the movable-ele Apart from the common source of power, such movements are independent, and are effected seriatim, so that the time for the cycle approximates to the total time taken for the individual -move- 'ments in the cycle. It is customary for the'machines to :be provided with auxiliary ja'cks'for more complicated dies-(molds) and/or for withdrawing coresfrom the completed casting, and'the necessary movements (at right-angles or oblique to the axis of the movements of the basic cycle or otherwisel'are again independentand effected seriatim, with further addition to the .timefor the cycle. Electrical control is sometimes applied to enable the movements to follow each otherprogressively, e. g., in an automatic cycle initiated by the operator;

but the seriatim order of the operations still results in a long cycle.

Thus, in a machine operatingon the cold chamber system, i. e., with the operator himself ladlingthe metal into the machine, the operator initiates eachautomatic cycle as soon as he has la'dled the-metal into anorifice in front-ofthe injection plunger; In machinesoperating on the hot chamber system, as is po-sSib-leWith low-melting metals andalloys, such as, zinc andozinc alloys, a further jack .is provided for forcinga quantity of'metal' from the melting pot into. the. path ofthe injection plunger, and the automatic cycle i s ini tiated by operation of a button by the operator .toefiect metal injection, or to effect closing of .the die, die-closing then resulting in actuation of a pressure-operated micro-switch to effect injection only when therelis. a full pressure lock on the. closed dies. j In both. .cases, the usual method begins to be injected, because of the seriatimoperation v of the subsequent individualmovements after themetal has frozen in the die.

According to the present invention, a:diecasting-.ma-

chine comprisesjacks operable by oil-under pressure ;.andin operative connection with at. least. one movable part for carrying a die part, aninjector, and an ejecton; and

control means .to elfect operating movementswofqatleast :two of the jacks that are simultaneous over atsleast ,part

of the times occupied by such of therno-vements rastake place after freezing of themetal in .the-v die. T,hus,

We ds sd ,mqve sea m be P l P F- QR W' of operation requires a long cycle fromthetim the metal throughout or may overlap in time. As a result, the time of the whole cycle is less than the total-timeof theseveral movements by the amount of complete'or partial overlap of any two or more of the movements.

If, as is frequently the case, the casting'callsfor die parts movable otherwise than co-axially ,with the movable part carrying themain die part, or-for cores to-be withdrawn at right-angles or obliquely, or for'the unscrewing of cores used in theformation of internal or external threads, this bringing into use one ormoreof they further jacks for which provision is made,-the movement of any orall of such parts may partly orw-holly overlap the movements of the basic partssor of each other, to minimise the complete cycle.

It isusual in existing machines forqthe. oil to be supplied from a hydraulic pump of a capacity suflicientfor any single jack movement, 'e. g., the die-closing jack, or from an accumulator charged by-.a hydraulic pump and of acapacity to eflect any single jackmovement, the pump continuing to charge the accumulator during inoperative periods of the. cycle,.so that in either case there to be adjusted to the casting requirements ofany individual article.

Driving the .pump -'by a variablecpeed device adjusted .to the requirements of any particular cycle enables-excessive heating of the oil in the hydrauliccircuit-to be avoided as also may be assistedby using an ;oil cooler,

.or by :diverting .excess oil by an unloading device.

The interconnecting control is preferably electrical, or mainly .so. Thus, :a-timing unit with a cam or contact arm driven throughtgearing by an electric motor and set in operation on injection of the -meta'l may be used to complete an electric circuit after a-sufiicient interval for freezing (solidification) of the metal,- to initiate the opening of the die and possibly other movements, particularly'the very early withdrawalof a core, when a separate core-is necessary, e.- g., by operating one ,or

more solenoid-controlled valves-inthe hydraulic circuit.

Anyone or more of the movements other than'for corewithdrawal or die-opening may, however, be-depen'dent on and take their timing from the core-withdrawing :and/or die-opening movements, which two moverr ients may-also-be independent. Thus one or more microswitches may be operated at any pro-determined part of that movement to initiate one or more other movements,

e. g. by operating solenoid-controlled valves. The-invention will-now be described in greater detail .with reference to the accompanying drawings,'.in which 1 Figures 1 and 2 are side and front elevations of a typical die-cast part requiring the use of a transverse core; Figure 3 is a front elevation of a die-casting machine showing the location of the main controlling mernbers and some of the associated electric switchesf Figure 4 is a hydraulic diagram, including solenoidcontrolled valves;

'Figure 5 is a section of the diagram of Eigure 4, show- ,inga modification of the hydraulicsystern;

Figurev 6 is an electric diagram, includ-ingthe solenoidcontrol for the valves that directly operate the main elementsfor the die-casting proper;

:Figure 7.. is a timing diagram, showing a comparison :with anmachine operating by seriatirn movements after ffreezingfof the metal; and

and accumulator connections, first of known machines,

next of one form of machine according to the invention, and finally of a further form of machine according to the invention. f

The article shown in Figures 1 and 2 has the portion x of? its hollow interior formed by a projectionfrom one main die part, but the transverse hollow portion y must be. formed by a core capable of being retracted transversely to the axis of the portion x. Similarly if a portion such as y is oblique to the axis of x: the core must be ret ractible obliquely. If such a portion as y is threaded (externally or internally), the part serving to form the threads must notonly be retractible, but also capable of rotation. A co-axial portion such as x may also be threaded, which again calls for a rotatable and retractible part for forming its threads. Simple retraction merely calls for simple connection of a core part to an operating jack, butas is well knownthe movement of such a jack may be transformed into a rotation of a core part by the use of a rack-and-pinion. It is also well known that, when several parts are die-cast simultaneously in one die, several core parts may be operated together from a single jack.

In Figure 3, A B C D on the control panel L at the right are associated with the respective solenoidcontrolled valves for effecting operation of the die, injection of metal, ejection of the article, and operation of the core. A firing button a is pressed when molten metal has been ladled into the machine, and constitutes a main controlling means to initiate injection, and a foot-operated button b constitutes further control means to close the die after ejection of the article. Some of a number of micro-switches operated by the die-movement are indicated at c and others operated by the core-movement at d. The movable part of the die is indicated as A and the jack for the core as D. The reference letter A is used for the die-jack in Figure 4, which also shows the core-jack D, the injection-jack B', and the ejector-jack C, these two latter not being seen in Figure 3.

,Related to A, B. C, and .D are reference letters A (together with A B C D which are used in Figures 4 and 6 to indicate the corresponding solenoid-controlled valves for these four main elements of the machine, in relation to the electrical controls including the buttons a and b. These figures show that the two solenoid-controlled valves, A and A both simultaneously operated, are associated with the die-jack A, the valve A providing the direct control of pressure fluid to the jack A and the valve A effecting cushioning of the close movement of the jack.

-A typical timing diagram is shown in Figure 7, in which the various points in the total time cycle, starting from 0, a time when the die A is closed, are shown by. I, II, III, etc.

1' he operator ladles in molten metal up to point I. He then presses button -a which through an in relay e energises the in solenoid f of valve B to effect injection up to point II. Simultaneously, a process timer. g is energised. This is motor-driven, and makes a complete revolution for each complete operating cycle. The timer controls the freezing period, which ceases at point III. At this point, the timer operates a switch h to energise the out solenoid i operatingvalve D to start core withdrawal. This continues to point IV, when a micro-switch attached to the core mechanism (i. e., one of those at d in Figure 3) energises the opening solenoids k of valves A and A the latter of which starts the die opening. The function of valve A is described below with reference to Figure 4.' At point V, the normally closed micro-switch l operated by the die is opened, to cut ofi the current from the solenoids k. The valve A is a three-position valve such that when neither of its solenoidsis energised the valve returns itself to the neutral position, allowing the pressure oil to pass straight through to drain. The core D continues to withdraw to point VI, when a micro-switch m on it is closed, re-energising solenoids k, thus continuing the die opening. The core withdrawal continues to point VII and on the die at this position is a micro-switch n, energising the out solenoid 0 of the ejection valve C thus ejecting the casting. The ejection'cycle thus ends at point VIII.

The operator now presses foot-button b to energise the in solenoid p of valve D and simultaneously the close solenoid q of valve A, the current passing through normally closed micro-switch r. At point VIII when the die A is fully open, a micro-switch s energises the out solenoid t to return the injector, and cuts out solenoid f and the timer g, the button a being released. At point IX, a microswitch u on the die motion energises return solenoid v of the ejector to point X. The die closing meanwhile continues to point XI when the normally closed micro-switch r opens the circuit, allowing the valves A and A to return to neutral position. The core is still returning and a micro-switch w corresponding to position XII re-energises the close solenoid q to complete the cycle at point XIII, the solenoid p being cut out, and the button b released.

The time-scale in Figure 7 shows that the cycle take just under 6 seconds from the start of pouring the metal, the shaded rectangles showing the operations performed as described above. The white rectangles show the equivalent operations as performed in the known type of machine, the same article requiring a time cycle of 9 seconds. The saving of time begins at point III, after which, according to the invention, overlapping of the movements of'the die A, core D, and ejector C takes place, as alsofrom point IX,does overlapping of the closing movement of the die A and return movements of the core D, ejector C and injector B. The resultant saving is more than one-third of the known cycle, i. e., output is increased by more than 50%.

In Figure 4, the jacks A,.B, C, D are shown in approximately correct related position (the movable die part, the core, the injector, and the ejector plate all being omitted for the sake of clarity) together with the hydraulic connections from two supply pumps and an accumulator, and the four valves A B C D Three further solenoid-controlled valves are also shown. To avoid undue multiplicity of reference characters, like parts of the different main valves are indicated by similar references P (or P P R, S. T in each case, as appropriate.

Oil is drawn from a tank 1 (through a strainer 2) by a low-pressure, variable-speed, pump 3 and a highpressure pump 4. The pump 3 delivers through a differential unloader valve 5 and a check valve 6, and the pump 4 through a relief valve 7. A pilot line 8 from the body of valve 7 to the base of valve 5 causes the low-pressure delivery to be returned to the tank 1 if the delivery of the high-pressure pump 4 is in excess of say 1500 lbs/sq. inch (with a maximum of say 2000 lbs./sq. inch). Both pumps 3, 4 deliver to a main line 9, which is connected through a check valve 10, line 11, restrictor valve 12 and hydraulically-controlled check valve 13 with an accumulator. By a valve 15, the accumulator 14 feeds a pressure switch 16, which operates a solenoid-controlled valve 17 (electric connections not shown) that is energised when the machine supply is switched on to control the valve 13 through line 18 so as to allow free flow through the valve 13 to the line 11 so long as the switch 16 keeps the solenoid of the valve 17 energised, say at an accumulator pressure exceeding 1600 lbs/sq. inch. Below that pressure, the

valve 1 closes, to prevent flow from the accumulator.

To effect closing of the jack A, when the valve A is energised, a further solenoid-controlled valve A is simultaneously energised. Oil flows from the main line 9 through a restrictor valve 19 and a check valve 20 to the valve A' jt'rom which it"pass'es b'oth' t'o IIi'e' vaIve 'A (through a check valve 21) and to an inner cylinder 22 of the 'die jack A (through'aline 23). From the valve A oil flows by a line24 to'a valve 25 to open a pre-fill'er tank 26 to the rear cylinder 27 of the jack A,"so that oil is sucked into 27 as the jack closesthe die. By a trip (one of'the switches c"irr'Figure 3), the'"valve 'A is reversedtoclose the valve "25 (byline 28), and to over- I come a check valve'29' connecting the 'line 28 'to"a"pressure switch '30, which 'keeps the solenoid of the valve A energised to hold' the 'valve in reversed'position. At this time, a port'27a'is uncoveredto'put the cylinder '22'into communication with the: cylinder 27, so thatoil 'is'now directed tojthe cylinder '27 and thejack'A movesat'a slower speed. This cushions 'the closing of the jack A.

To open the die,"the valve 'A is reversed by solenoidactuation, and oil flows through a checkva'lvel30 to the valve A which is simultaneously operated to re-open'the valve 25 of the pre-fillertankflfi. Oil also flows by line 31 to the forward 'cy1inder32 of the jack A. Oilis pushed from the rear cylinder 27 to the tank 26,-an'd from the inner cylinder 22 through'the valve A to the tank I. To efiect injection, o'il' from'the' main line 9-passesby a line 33 toport' P of valveE and by the check valve and a line 34'to port P of the valve- E. In the'valve-E, either P or P is blocked, so that either P communicates with a line 35 or P with a line 36. The valve B isen'ergised by one of its solenoids and pilot oil from the main line 9 passes to the right-hand control end of 'the 'valve' E, so that main pressure passes 'by'the line 36 and a restrictor valve 37 to the end 38 of the injector jack B. Pilot oil also passes to the base of a valve 39 at a rate to operate valve 39 slightly in advance'of valve E, and

oil can pass freely thnough the valve 39, in either direction. This permits oil displaced from the other end-"40 of the jack-Bto the end 38 througha check valve 41, and avery fast injection speed is obtained from the 'oil supply in the accumulator 1 4, through the lines 11 and34. When the pressure in the end 38 of the jack B exceeds say 1350 lbs/sq. inch, the end 40 is unloaded through the valve E and an adjustable difierential unloading" valve 42, to Which pilot oil is fed from the line 36.

To return the injector, the solenoid of valve B is deenergised, and pilot oil passes from the line 9 through the valve to the left-hand controlling sideof the valve E;

'a restrictor valve 43 to one side of the jack C (the'other side of which exhausts through the valve C ),'and to a pressure switch 44, which keeps the valve C energised 'to hold the jack C out after ejection has ended. Reversal of the valveC effects return of the ejector.

To effect retraction of the core, oil from the main line 9 passes to the valve D ,whi ch is energised for' the oil to pass to the underside of the jack D, oil'exhaustin'g from the upper side through a restrictor valve 45. Reversal of the valve D passes oil to the upper side of the jack D through the valve45. I

The groups of switches c and d (Figure 3) may be adjusted for precise operation at any desired times in the cycle, as'dictated by the size'and shape of the-article to be die-cast, and (in conjunction with the solenoids they control) they provide for any desired movement to be interrupted or changed in course. Thus, any desired interlocking ofthe interdependent controls of the system may be effected. Thus, in the'case-of a component with a screwed-core, the following sequence may take place after the solidification period; the screwed core begins to withdraw continuously, 'after a'brief interval (say /2- 6 second) 'die opening' commences, arida-fter completewithdrawal of thescrewe'd' core, the ejector ram operates,

"Although reference above has been largely to the injection of molten metal, similarprovision'm'ay be made in machines for die-casting-plastic materials.

Figure 8'shows,fin-very simplified form, the known'u'se of a single pump with'anaccumulator, with no attempt to show control valves, or indeed reversal of operation of the four jacks A, B, C, D. 'Figure 9 shows "in comparative manner one use of two pumps according to the *inven tion, with the accumn'lator 14' available to supply oilto the-die jack 'A and the injectionjack 'B; and-Figure 10 another use of two pumps, with the accumulator supplied by'one-pu'inp only to operate tne injection jack B, leaving the other pump to operate the jacks A, C,'and'D.

Figure 5 shows, in a hydraulic s'ystem generally similar to that of Figure 4, a' separate pump directly operating the eore-jack -D and the ejection jack C, as well as contributing (through a check valve) to the operation of the injector jack B, a relief valve 52 being provided in advance of the valve 51.

A'restrictorvalve 53=acts-as a variable by-pass for a pressureswitch 54, which keeps the 'valve D energised to hold the cores out after withdrawal. A restrictor valve 55 conne'cts the line9 to a pressuregauge-56 for checking line pressure.

What weclaim'is:

1. .A die-cas'ting mach'inecomprising two'movable parts for-carrying die -members, withone of those movable parts capable oi a-movement other than coaxially with the-movement'of the other,-jacks operable by oil under pressure and in respective operative connection with said parts, electrically operated valves'to control 'the'supply 'ofoil to-the jacks, anelectric s'witchadjustably disposed for-operation by jack-effected movement of one of said parts tooperate'thevalve"supplying oil to the 'jack for the: other of said parts, 'whereby -'both of the said parts may partake of their respectivesa'id movements-simultaneously, control means to initiate-the movement ofthe first mentionedof said parts by electric operation of the valve supplying oil'toits jack, and -an electric control system connected to said electrically operated valves-and to said electric switch.

2. A die-casting machine comprising movable parts for carrying die-members, with one of thosemovable parts capable of a movement other than co-axially withthe movement of the other, and also an injector, jacks operable by oil underpres'sure and in respective operative connection with said movable'parts and the injecto'r, electrically operated valves to control the supply of oil to the jacks, an electric switch adjustabl'y disposed for operation by' jack efiectedmovement of one of said movable parts to operate the valve supplying oil' to the jack for the other-of 'said"par ts, -control means to effect operationof the injector, and a timing device'also "op- 'erated"by the control means, the timing tdevice initurn initiating an opening. jack-effected movement of the-first of said movable parts by'electric operation of thenvalve supplying oil to its jack, and the jack-effected'm'ovement of 'thatfirsti'part in turnetfecting a simultaneous opening movementof the other of said parts. 7

3; A die-casting machine 'as' in claim 2, comprising *also anejector, an oil-operated jack for theiejector: and

an associated electrically operated valve, and a further electric switch adjustably disposed for operation by =jackefiected movement of one of the saidmovable parts to sure arid in respective operative connection with said parts, electrically-operated valves to control'thesupply'ofi oil to the jacks, control means to initiate a jack-effected movement of the first of those movable parts, an electric switch adjustably disposed for operation by movement of that part to operate the valve supplying oil to the jack for the other of said parts, and thus to effect a simultaneous jack-effected movement of the other of said parts, further control means to initiate a jack-effected return movement of one of said parts, and a further electric switch adjustably disposed for operation by such movement of that part to reverse the valve supplying oil to the jack for the other of said parts, and thus to effect a simultaneous return jack-effected movement of that other part.

5. A die-casting machine comprising movable parts for carrying die members, together with an injector and an ejector, jacks operable by oil under pressure and in respective operative connection with said parts, the inje ctor, and the ejector, electrically operated valves to control the supply of oil to the jacks, control means to effect an injection operation of the injector, a timing device also operated by the control means, the timing device in turn initiating a jack-effected opening movement of one of said movable parts by electric operation of the valve supplying oil to its jack, electric switches adjustably disposed for operation by and during the said opening movement of that part to operate the valve supplying oil to the jacks for the other said movable part and for the ejector, thus effecting a simultaneous jack-effected opening movement of the other of said parts and a jackeflfected ejection movement of the ejector, further control means to initiate a jack-effected return movement of one of said movable parts, and further electric switches adjustably disposed for operation by and during the return movement of that part to reverse the valves supplying oil to the jacks for the other of said parts and the injector and the ejector, thus effecting simultaneous jack-effected return movements of both movable parts and of the injector and the ejector.

.6. A die-casting machine comprising a movable part for carrying a die member, and a core member movable at an angle to the direction of the movement of the said movable part, jacks operable by oil under pressure and in respective operative connection with the movable part and the core member, electrically operated valves to control the supply of oil to the jacks, an electric switch adjustably disposed for operation by jack-effected movement .of one of said parts to operate the valve supplying oil to the jack for the other of said parts, whereby both parts may partake simultaneously of their respective jack-efiected movements at an angle to one another, and control means to initiate the movement of the first of said parts by electric operation of the valve supplying oil to its jack.

7. A die-casting machine comprising a movable part for carrying a die member, and a core member movable at an angle to the direction of movement of the said movable part, jacks operable by oil under pressure and in respective operative connection with the movable part and the core member, electrically operated valves to control the supply of oil to the jacks, control means to initiate a jack-effected movement of one of the two parts, electric switches adjustably disposed for operation by and during jack-effected movements of the two parts to operate the valves supplying oil to the jacks, so that either one of the two parts may control the movement of the other part, further control means to initiate a jack-effected return movement of one of said parts, a further'electric switch adjustably disposed for operation by such movement of that part to reverse the valve supplying oil to the jack for the other of said parts, and thus to effect a simultaneous jack-effected return movement of that other part, and further electric switches adjustably. disposed for operation by and during such return movements to operate the valves supplying oil to the jacks,.so as to control the return movement of the parts. 1

8. A die-casting machine comprising movable parts for carrying die members, including a core member, together with an injector and an ejector, jacks operable by oil under pressure and inrespective operative connection with said parts and with the injector and the ejector, electrically operated valves to control the supply of oil to the jacks, control means to effect an injection operation of the injector by its jack, a timing device also operated by the control means, the timing device in turn initiating an opening jack-effected movement of the core member by electric operation of the valve supplying oil to its jack, electric switches adjustably disposed for operation by and during the opening jack-effected movement of that part to operate the valves supplying oil to the jacks for another of the movable parts and for the ejector, thus effecting a simultaneous opening movement of that other part and an ejection movement of the ejector, both by their jacks, further control means to initiate a jackeffected return movement of one of the movable parts and the core member, and further electric switches adjustably disposed for operation by and during the return movements of those parts to reverse the valves supplying oil to the jacks to control simultaneous jackefiected movements of the parts and of the injector and the ejector.

9. A die-casting machine comprising movable parts for carrying die members, together with an injector and an ejector, jacks operable by oil under pressure and in respective operative connection with said parts and with the injector and the ejector, electrically operated valves to control the supply of oil to the jacks, at least one pump to supply pressure-oil and an accumulator connected to such supply, the accumulator serving to supply oil for an injection movement of the injector jack, control means to operate one of the valves to effect such injection movement, a timing device also operated by the control means, the timing device in turn operating another of the valves to initiate a jack-effected opening movement of one of the movable parts,'electric switches adjustably disposed for operation by and during movements of the movable parts to operate the valves so as to effect and control jack-effected opening movements of the parts and of the ejector, and in turn their jack-effected return movements and that of the injector, and further control means to initiate the return movements, the switch operation providing for overlap of the opening movements and in turn of the return movements by control of valves supplying oil to the jacks direct from the pumped supply.

10. A die-casting machine as in claim 9, wherein two pumps are provided, conduits and valving connecting one of said pumps with certain of said jacks for effecting opening and return movements thereof, conduits and valving connecting the other of said pumps with the accumulator, means connecting said other pump with certain of said jacks for effecting the opening and return movements not accomplished by said first named pump, with the exception of the injection movement of the said injector, and means connecting said accumulator with the injector jack to accomplish the last named injection movement.

11. A die-casting machine as in claim 9, wherein two pumps are provided and means connecting one of said pumps with the injector jack and with a jack for a movable part adapted to carry a core for effecting opening and return movements of said jacks, and means connecting the other pump to a jack for moving a main die part to effect opening and return movements thereof.

(Other references on following page) 9 UNITED STATES PATENTS Pack June 5, 1934 Haessler Nov. 13, 1934 Lester Feb. 5, 1935 Stern Feb. 7, 1939 Lester et a1. Dec. 19, 1944 10 Veale Jan. 10, 1950 Butner Aug. 22, 1950 Kohl Jan. 8, 1952 Beuscher Feb. 12, 1952 Broden July 29, 1952