US2874012A - Piston ring and piston construction - Google Patents

Description

Feb. 17, 1959 M. STERN PISTON RING AND PISTON CONSTRUCTION Filed Feb. 11, 1957 This invention relates to pressure expandible piston rings for die casting machines and the likeand to an improved combination of piston rings and piston construction for die casting machine pressure chambers, and for other purposes.

In die casting machines, molten metal is forced under pressure from a molten metal pot to a nozzle, leading to the die cavity of the casting machine by means of a plunger or piston operating in a cylindrical passage or pressure chamber disposed in the molten metal pot. With the trend toward producing die castings with thinner walls and smoothersurfaces, the pressures atwhich molten die cast metal isforcedthrough the nozzle of the die casting machine into the moldlhave been increased from time to time. The piston of the die casting machine must be relatively tight fitting in respect to the cylindrical molten metal passage in which it operates. Die casting machine pistons for handling molten metal are usually equipped with split type piston rings of the type generally employed in internal combustion engines.

The life of ordinary split type piston rings for such use is not satisfactory for several reasons. In the first place, oxides and other gritty compounds work their way'between the rings and the piston ring grooves in the pistons with a result that a wedging action occurs which ofttimes prevents the normal and expected expansion and contraction of the piston rings. Secondly split type piston rings are not only subject to extremely heavy loads when metal is forced into the die, but they are also subject to abrasion and erosion during the return stroke of the piston when molten metal is sucked into the molten metal passage between the piston and the nozzle of the die casting machine from above the piston to break the vacuum in such passage. Thirdly, extreme temperature differentials cause the ends at the split of the ordinary splittype piston rings to curl or warp, and, should such curled ends work around the piston and become'in alignment with the port in the cylinder, the said ends willlsnap off and ofttimes cause irreparable damage to .either the cylinder or the piston before thedefectcan be discovered.

With the foregoing in view, the primary object of the invention is to provide an improved positive expanding and contracting continuous piston ring which will-alleviate or overcome the foregoing and other undesirable features of split type piston rings for the molten metal pressure piston of die casting machines.

; Another object of the invention is to provide an improved piston-piston ring combination wherein, pressure offluid against .the'head of the piston expands the piston ring during .the power stroke'of the piston to-eliminate to a greater degree than heretofore practicable the leakage of .fluid past. the piston.

A further-object of the invention is to provide a pressure expandible piston ring adapted to expand radially during the pressure'stroke of a piston equipped therewith and be'freetocontractradially during the return stroke of the p ston-teramit flu ;a d t Pa b w en h .p

atent 2,874,012 Patented Feb. 17, 1959 '2 and wall of the cylinder in which the said piston is mounted during the return stroke of the piston.

Other objects of the invention will becometapparent by reference to the following detailed description taken in connection with theaccompanying drawing, in which:

Fig. 1 is a more orless diagrammatic view of a die casting machine of a type in which thepiston of the cylindrical portion of the pressure chamber thereof may be equipped with a piston ring and piston embodying the invention.

Fig. 2 is a vertical sectional view through a piston ring and piston embodying the invention disposed in operating position within its cylinder.

Fig. 3 is an end elevational view of the head of the piston shown in. Fig. 2,.a portion of its cylinder being indicated in sectiontherearound.

Fig. 4 is a verticahsectionalview similar to Fig. 2 of a piston ring and. piston disclosing an alternate embodiment of the invention. 1

Fig. 5 is an end 'elevational view of the head of the piston shown in Fig.4, a portion of its cylinder being indicated in section therearound.

Fig. 6 is a vertical sectional view of a piston ring-and piston showing still another embodimentof the invention.

Fig. 7 is an end elevational view of the piston shown in Fig. 6, a portion of its cylinder being indicated in section therearound.

Referring now to the drawing wherein like reference numerals refer to like and corresponding parts throughout the several views. Fig. v1 showsaidie casting machine 10 including a moltenmetal pot .11, a pressure chamber 12 disposed in said molten mctalpot and having anozale 13 at the discharge end thereof communicating with a die 14 mounted in the said die castingmachine 10. The said pressure chamber 12 is formed with cylinder 15 therein into which is reciprocatinglymounted a piston 16 preferably actuated by a hydraulic cylinder 17. The cylinder 15 of the pressure chamberv 12 is provided with an intake port 150 disposed slightly below the head of the piston 16 when in its retracted position as shown in Fig. l. Molten metal 18 flows into the pressure chamber-12 from the molten metal pot'll between molding shots when the piston 16 is in its retracted position. The said piston 16 is preferably formed to accommodate apiston ringQZO embodying the invention .as hereinafter described .in detail. I

The embodiment of the invention shown, in Figs. 2 and 3 consists of a continuousgenerally vU-shaped piston ring 20 disposed in a circumferential recess in the piston 16. The top and the bottom side walls of the said U-shaped piston ring 20 as viewed in Fig. 2 are preferably flanged at 21. The bottom wall 22 of thesaid U-shaped piston ring 20 is preferably formed with'a groove 220 therearound adjacent the wall of the cylinder'lS topmvide a local axially central annular area that may flex more readily than the remainder of the said piston ring The said piston 16 .has a main portion 31 which cumferential groove 34 near the bottom thereof. The said groove 34 divides the. stem. 32 into a barrel portion 320 and a head portion 321. The upper flange 21 of the U-shaped continuous piston ring 20 is telescoped neatly over the collar 33 of the stem 32 of the piston 16 to locate the piston ring 20 concentrically thereon and to provide a pressure seal between the upper flange 21 of the piston ring 20 and the main portion 3i of the said piston 16. A pair of substantially half cylindrical or arcuate pressure elements'35 are positioned around the head portion 3210f the stem 32 of the piston 16. The said arcuate pressure elements 35 each'have an inwardly disposedflange v359 extending into the circumferential groove 34 in the said stem 32. The thickness of the said flange 350 of each arcuate pressure element 35 is less than the width of the 'circumferential groove 34 in the stem 32 of the piston 16 to permit the said arcuate pressure elements 35 to move axially with respect to the piston 16. The internal radius of the flange 350 of each pressure element 35 is preferably such as will provide a slight passage 351 between the stem 32 of the piston 16 at the base of the circumferential groove 34 therein and the inner structure surface of the said flange 350 of each pressure element 35.

When the piston ring 20 and the arcuate pressure elements 35 are assembled onto the stem 32 of the piston 16 as shown in Figs. 2 and 3, the arcuate pressure elements 35 are preferably in contact with the lower flange 21 of the U-shaped continuous piston ring 20, and the saidpressure elements 35 are in an axially extended position disposed toward or against the lower end or "head portion 321 of the stem 32 of the said piston 16. The said stem 32 of the piston 16 is axially bored at 322 from its lower end or ead 321, and its barrel portion 320 is radially bored at 323' to provide communication between the cylinder below the piston 16 and the annular pressure chamber 200 inside of the said continuous generally U-shaped piston ring 20. The passage 351 between the base of the circumferential groove 34 in the piston 16 and the'inner arcuate surfaces of the flanges 350 of the pressure elements 35 communicates withthe annular space 210 betweenv the bottom flange 21 of the piston 16 and the stem 32 of the said piston 16 to permit axial movement of the arcuate pressure elements 35 with respect to the said piston 16 without entrapment of molten metal therebetween.

With the construction disclosed in Figs. 2 and 3, when the piston '16 is on its power stroke, pressure of molten metal on the head thereof (against 35 and 321) moves the pressure elements 35 axially upwardly in the circumferential groove 34 in the axially depending stem 32 of the said piston 16 as viewed in Fig. 2, whereupon the end flanges 21 of the piston ring are forced toward each other to bow the wall 22 of the said piston ring 20 outwardly into firm contact with the inner wall of the cylinder 15. At the same time, molten metal under pressure flows through the bores 322 and 323 of the piston 16 and enters the annular pressure chamber 200 between the inner face of the U-shaped piston ring 20 and the stem 32 of the said piston 16 further urging the said wall 22 of the piston ring 20 radially outwardly into a pressure contact with the said inner wall of the cylinder 15. During the return stroke of the piston 16, the pressure within the said annular pressure chamber 200 and the pressure on the pressure elements 35 is relieved, whereupon the wall 22 'of the piston ring 20 may flex radially inwardly and permit molten metal to be sucked past the piston 16 and the piston ring 20 thereof without undue abrasion and erosion of the said piston ring 20 and the cylinder 15.

The embodiment of the invention shown in Figs. 4 and 5 consists of a continuous generally U-shapcd piston ring 20 disposed in a circumferential recess 40 in the piston 160. The top and the bottom of the piston ring 20 as-viewed in Fig. 4 is preferably flanged at 21. The outer wall 22 of the said piston ring 20 is preferably formed with a groove 220 therearound adjacent the wall of the cylinder 15 to provide a local axially central annular area that may flex more readily than the remainder of the said piston ring wall. The said piston 160 has a main portion 41 which is suitably machined to provide an axially depending stem 42 having a collar 43 at the top thereof and a threaded shank 44 of reduced diameter at the bottom thereof forming an axially facing annular seat 420 at the lower end of the said stem 42 adjacent its threaded shank 44. A bored and counterbored piston head 45 is telescoped-onto the said threaded shank 44 and is secured centrally onto the stem 42 by a nut 46 with a lock washer 47 thcrebetween. The said piston h 45 and the stem 42 of the piston 'are'so mated'at the seat 420 that the said'piston head 45 is held concentrically with respect to the main portion 41 thereof when the nut 46 is tightened.

When the piston ring 20 and the piston head 45 are assembled onto the stem 42 of the piston 16 as shown in Figs. 4 and 5, the upper portion of the said piston head 42 as viewed in Fig. 4 firmly contacts the lower flange 21 of the U-shaped continuous piston ring 20. The said stem 42 of the piston 160 and the threaded shank 44 thereof are axially bored at 422 and the said stem 42 is radially bored at 423 to provide communication from the cylinder 15 below the piston 160 and the annular pressure chamber 200 inside the continuous generally U- shaped piston ring 20.

With the construction shown in Figs. 4 and 5, when the piston 160 is on its power stroke, pressure from molten metal at the head 45 thereof enters and flows through the bores 422 and 423 into the annular pressure chamber 200 between the inner face of the U-shaped piston ring 20 and the stem 42 of the said piston 16 urging thewall 22 of the piston ring 20 radially outwardly into a pressure contact with the inner wall of the cylinder 15. During the return stroke of the piston 16, the pressure within the said annular pressure chamber 200 is relieved, whereupon the wall 22 of the piston ring 20 may flex radially inwardly and permit molten metal to be sucked past the piston 16 and the piston ring 20 without undue abrasion and erosion of the said piston ring 20 and the cylinder 15.

The embodiment of the invention shown in Figs. 6 and 7 consists of a continuous generally S-shaped piston ring 50 disposed in a circumferential recess 60 in the piston 1600. The said continuous S-shaped piston ring has an inner annular free wall 51 flanged at its upper edge at 52, an outer annular free wall 53 having a depending edge at 54, and a central annular Wall 55 con nected to the said free walls 51 and 53 by curved portions forming contact annuli 56 and 57 respectively. The said piston 1600 has a main portion 61 which is suitably machined to provide an axially depending stem 62 having a collar 63 at the top thereof and a plain shank 64 of reduced diameter at the bottom thereof forming an axially facing annular seat 620 at the lower end of the said stem 62 adjacent its plain shank 64. 'A' centrally bored and counterbored piston head 65 is telescoped in axially slidable relationship onto the said plain shank 64 and is held thereon by means of a transverse pin 66 pressed into a round hole 650 in the piston head and extending through a vertically elongated hole 621 in the stem 62. The piston head 65 is thus slidably secured on the stem 62' of the piston 1600 to permit the piston head 65 to move axially upwardly with respect to the stem 62 on its shank 64 from the downwardly extended position of the said piston head 65 shown in Fig. 6. a

The upper annular portion 651 of the piston head 65 seats against the curved contact annulus 56 of the S-shaped piston ring 50, and an axially disposed beveled seat 610 formed at the lower end of the main portion61 of the piston 1600 is normally in contact with the curved contact annulus 57 of the piston ring 50. With such an arrangement of elements, movement of the piston head 65 axially upwardly from its position shown in Fig. 6 expands the said S-shaped piston ring 50 radially. The head 65 of the piston 1600 is provided with longitudinal bores 652 therethrough to provide communication between the cylinder 15 below the piston 1600 and an-annular pressure chamber '500 within the piston ring 50 between the outer annular free wall 53 and the central annular wall 55 thereof. The upper end of the piston head 65 is provided with an upwardly disposed annular lip 653 spaced radially from the outer periphery of the said piston head 65. The said annular lip 653 is formed to cam or urge the depending edge 54 ofthe outer annular free wall 53 of the piston ring 50 radially outwardly against'theinner periphery'of the cylinder when the said piston head 65 moves upwardly as viewed'in Fig. 6.

With the construction shown inFigs. 6 and 7,' when the piston 1600 is on its power stroke, pressure from molten metal at the. head 65 thereof enters andflows through the. bores 6 52 therein into the annular pressure'chaniber 500 between the outer annular free wall 53 and'the central annular wall 55 of the piston ring 50 urgingithefree wall 53 of the said piston ring 50 outwardlyin firmsurface contact with the wall of the cylinder .15. Simultaneously, pressure from molten metal on the head 65 of the piston 1600 urges the said. piston head upwardly as viewed in Fig. 6 whereupon the annular portion 651 .of the piston head-65 contacts the-contact annulus 56 .of the piston ring 50 forcing the contact annulus 57 .of .the said piston ring 50 against the-axially disposed beveled.-s'eat.610 of the mainportion 61 of the piston 1600. This localized axial Squeezing force on the piston ring 50 tends to mechanically expand it radially to further tighten the sliding .seal' between the outer free wall 53 of the piston ring 50-andthe inner .wall of the cylinder 15.. During the return stroke of the piston 16, the pressurewithin the; said annular pressure chamber 500 is relieved and the pressure tending to mechanically expand the piston ring 50 radially is also relieved whereupon the outer free wall- 53 of the piston ring 50 may flex .radially inwardly and permit molten metal to be sucked past the piston 1600 and the piston ring 50 without-undue abrasion and erosion of the saidpiston ring and the cylinder 15.

Obviously more thanone piston ring may be employed on a single piston whenever the requirement for a plurality of piston rings on a single piston is indicated, In such event, the piston will be altered. in detail to accommodate more than one piston ring, ,Howevenbecause of theefliciencyof piston rings embodying the invention,

the use of more than one piston ring ona single piston would be unnecessary in most installations.

Although several embodiments of the invention have been disclosed and describedherein, it is obvious that many changes may be made in the size, shape, arrangement and detail of the various elements of the invention, all without departing from the spirit and scope thereof as defined by the appended claims.

I claim: 4

I 1. In a piston reciprocable in a'cylinder and having a circumferential recess therein, a continuous piston ring of a laterally flanged'U-sha'ped cross section disposed in said recess forming an annular pressurechamber between said piston ring and said piston at said recess there'irnthe said piston'having a communicating passage therein between the head of said piston and said pressure chamber, a portion of said piston head being axially movable responsive to fluid pressure thereon to apply mechanical pressure to the flanges of said U-shaped piston ring and bulge the bottom wall thereof against the wall of said cylinder.

2. In a piston having a circumferential recess therein, a continuous piston ring of S-shaped cross section disposed in said recess forming an annular pressure chamber between said piston ring and said piston, the said piston having a communicating passage therein between the head of said piston and said pressure chamber.

3. In a piston reciprocable in a cylinder, said piston including a main portion and an axially movable head, the said piston having a circumferential recess therein with the said axial movable head forming one wall of said recess, a piston ring disposed in said recess formed to provide an annular pressure chamber between said piston ring and said piston, the said piston having a communicating passage therein between the head of said piston and said pressure chamber, said axially movable piston head being arranged to grip said piston ring responsive to axial fluid pressure applied on said piston head and bulge an annular wall of said piston ring into contact with the wall of said cylinder.

6 .:4..In-alpistoii-reciprocable in a. cylinder, said piston including .a. main. portion and an axially movable head, the. said piston .having a. circumferential recess therein with the. said axialmovablehead forming one wall .of said recess, a 'U-shaped piston ring having outwardly flanged side wallsand a bottom cylinder contacting wall disposed in said recess to provide an annular'pressure chamber between. said piston. ring and said piston, the said pistonhavinga communicating passage therein between the head of said piston. and said pressure chamber, saidaxially movable piston head. being arranged to grip the flanges said -U-shap.ed pistonring between the main portionihereof .and said .head and bulge said bottom 9Y1. inder contacting wall thereof into contact with the wall of saidcylinder, the said bottom cylinder. contacting wall of said u-shaped piston ring having a groovetherearound whereby to provide an annular area of greater flexibilitythan the remainder of said pistonring', fluid under pressure insaid. annular pressure chamber acting to urge said bottom cylinder contacting wall of said U-. shaped. piston. ring into firm contact with said cylinder when. said piston is on its .compression stroke. 5. In a piston reciprocable in a cylinder, said piston including. a main portion and an, axially movable head and having. a circumferential recess therein with the said axialmovable head forming one wall of said recess, a continuous piston ring disposed in said recess formed to provideaan annular pressure chamber between said piston .ring and said piston, the said piston having a communicatingv passage therein between its head and said pressure chamber through which fluid under pressure against said piston head during the pressurestroke of said piston-enters said pressure chamber and forces an annular. Wall of saidpiston ring against the wallof said cylinder whereby to establish firm contact between. said pistonringand the wall of said cylinder during the said pressure stroke vof .said piston, said piston ring being formed for engagement by said axial movable head to bulge \mechanically. responsive to fluid pressure in said cylinder thereby increasing the said firmness of contact of the piston ring against said cylinder wall.

6'..-In a pistonreciprocable in a cylinder, said piston including a main portion and an axially movable head and having a circumferential recesstherein with the said axiallmovablehead forming one wall of said recess, a continuous resilient metallic U-shaped piston. ring disposed in said. recessformed to provide an annular pressure. chamber between said piston ring and said piston, the, .said piston having a communicating passage therein between its head and said pressure chamber through which fiuid under pressure against said piston head during the pressure stroke of said piston enters said pressure chamber whereby to urge said piston ring wall into firm contact with the wall of said cylinder during the said pressure stroke of said piston, said U-shaped piston ring including flanges axially disposed between and contacted by said main portion and said movable head of said piston whereby said piston ring is axially squeezed mechanically responsive to fluid pressure on said movable head to further urge said piston ring wall into firm contact with the wall of said cylinder during the power stroke of said piston.

7. The construction claimed in claim 6 wherein the outer peripheral wall of said continuous piston ring is grooved to assure radially outward flexing of said piston ring against said piston ring during the power stroke of said piston.

8. In a piston reciprocable in a cylinder, said piston including a main portion and an axially movable head and having a circumferential recess therein with the said axial movable head forming one wall of said recess, a continuous S-shaped piston ring disposed in said recess formed to provide an annular pressure chamber between said piston ring and said piston, the said piston having a communicating passage therein between its 7 head and said pressure chamber through which fluid under pressure against said piston head during the pressure stroke of said piston enters said. pressure chamber and forces the outer annular wall'of said S-shaped piston ring against the wall of said cylinder whereby to urge said piston ring wall into firm contact with the wall of said cylinder during the said pressure stroke of said piston, the said outer annular wall of said S-shaped piston ring having a free annular edge disposed toward said axially movable head of said piston, the said movable head of said piston including an annular lip formed to engage said free annular edge of said S-shaped-piston ring and earn the same against the cylinder wall during the pressure stroke of said piston.

9. The construction claimed in claim 9 wherein the outer periphery of the main portion of said piston is axially beveled at said recess in said piston whereby to engage the axially disposed annular portion of said S-shaped piston ring axially spaced'from the said free anular edge thereof and additionally urge the outer annular wall of said S-shaped piston ring radially outwardly into firm contact with said cylinder wall during the pressure stroke of said piston.

10. In a piston reciprocable in a cylinder, said piston including a main portion and an axially movable head, the said piston having a circumferential recess therein with the said axial movable head forming one wall of said recess, a continuous resilient metallic generally U- shaped piston ring disposed in said recess formed to provide an'annular pressure chamber between said piston 9 ring and said piston, the said piston having a communicating passage therein between the head of said piston and said pressure chamber, flanges outwardly extending from said U-shaped piston ring grippable between said main portion and the axially movable portion of said piston head responsive to axial pressure applied on said piston head during the compression stroke thereof where by to bulge the annular wall of said U-shaped piston ring adjacent said cylinder into contact with the wall of said cylinder.

11. In a piston reciprocable in a cylinder, said piston including a main head portion and an axially movable head portion with a circumferential recess formed between the said head portions, a continuous resilient metallie generally U-shaped piston ring disposed in said recess formed to provide an annular pressure chamber between said piston ring and said piston, the said piston having a communicating passage therein between its head and said pressure chamber through which fluid under pressure against said piston head during the compression stroke of said piston enters said pressure chamber and forces the annular wall of said U-shaped piston ring against the wallof said cylinder whereby to establish firm contact between said piston ring and the wall of said cylinder during the said compression stroke of said piston, said axially movable head portion of said piston being movable against a portion of said piston ring responsive to fluid pressure on said movable head to flex said piston ring wall mechanically and increase its firmness ofvcontact with said cylinder wall.

12. In a piston ring and piston construction for use in die casting machine pressure chambers, a cylinder in which said piston reciprocates to move molten metal under high pressures, the said piston having a circumferential piston ring recess therein bounded by oppositely disposed axial facing walls, one of said walls being fixed and the other axially movable, the piston body forming the said fixed wall of said recess, an axially movable head on said piston forming the axially movable wall of said recess, an annular cup shaped continuous piston ring positioned in said piston recesshavingaxially extending flanges at the inner periphery thereof and a flexible wall disposed between said flanges and adjacent the wall of the cylinder in which said piston reciprocates, the said fixed and movable axially facing walls defining said piston ring recess normally contacting the axially extending flanges of said piston ring, the said piston having a molten metal passage therein through said piston head and communicating with said piston ring recess and within said annular cup shaped piston ring, said flexible wall of said piston ring being expandible radially outwardly into positive sealed relationship with the wall of said cylinder responsive simultaneously to hydraulic pressure of molten metal from within said piston ring and mechanical pressure against the axially extending flanges of said piston ring, said mechanical pressure being created by hydraulic pressure of molten metal against said axially movable piston head.

References Cited in the file of this patent UNITED STATES PATENTS

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