US2693727A - Hydraulic vise - Google Patents

Description

E. T. OLSON HYDRAULIC VISE Nov. 9, 1954 3 Sheets-Sheet 1 Filed July 20, 1953 INVENTOR hmw 7. 0mm

BY (ML-M r S p I ATTORNEYJ Nov. 9, 1954 I Filed July 20, 1955 E. T. OLSON 2,693,727 HY'DRAULIC VISE 3 Sheeis-Sheet 2 E. T. OLSON HYDRAULIC VISE Nov. 9, 1954 3 Sheets-Sheet 5 Filed July 20, 1953 a: m T m 5 8. w d 5 1 M a I 2 mo. 0 W.

2. s a a S. /7 2. o 3 n w an l E. x a m hw a g x 3 BY Quid 44% ATTORNEY;

United States Patent HYDRAULIC VISE Elmer T. Olson, Minneapolis,.Minn., assignor of 'onehalf to William J. Rawitzer, Minneapolis, Minn.

Application July 20, 1953, Serial No. 368,928

7 Claims. (Cl. 81-17.2)

My invention relates to improvements in vises such as used by various artisans for holding their work and which tool, of'course, comprises essentially a pair of jaws which may be moved apart to receive the work and then forced together to obtain a firm, vise-like grip upon the work. i

In a large majority of cases the vise jaws are operated by means of a hand screw but for modern production work, where time is extremely important, the manual manipulation of the vise screw is slow and impractical. For such usage hydraulic or air operated vises of various types have been devised so that the operator may close the vise hydraulically. Obviously such hydraulic actuation saves time and where relatively powerful gripping forces are necessary they are available by supplying fluid under the necessary pressure. All of such hydraulic vises, however, to my knowledge have numerous disadvantages chief among which is their relatively large size by comparison with the vise which they control and the very considerable expense involved by comparison with the more ordinary types of vises. In many instances size of the operating hydraulic element is particularly important for clearance reasons and also a number of such hydraulic vises have required foot manipulation by the operator in order to develop the pressure used, so that the saving in time actually is negligible and considerable eflort is still required upon the part of the operator.

In accordance with the primary object of my invention I provide for the hydraulic actuation of the vise an extremely simple and compact fluid actuated device which may be readily associated with the vise, whether in the initial manufacture thereof or in the replacement field for conversion of present manually operated vises. As another object of my invention I provide hydraulic actuating means for a vise which interferes in no way with the normal hand screw operation of the jaws but which at the will of the operator provides for instant hydraulic actuation to close the movable jaw toward the stationary jaw through a predetermined distance suflicient to grip the work powerfully and tightly. This hydraulic adjustment of the vise jaws may be taken advantage of in any manually adjusted spacing between the jaws and it is thus necessary for the operator only to make a rough adjustment by the hand screw, following which he may handle large numbers of work pieces in an absolute minimum of time. A further object of my invention is to provide the hydraulic actuation of a vise using as the prime source of fluid pressure the ordinary shop supply of compressed air with which all shops of any size are provided. In order then to develop the relatively much greater fluid pressures necessary for proper work gripping at the vise jaws I provide an operating cylinder having a large piston moved by the air pressure and a small piston which drives fluid intothe actuating cylinder upon the vise itself, thus magnifying the. pressure effective for the movement of the vise jaw. By thus increasing the effective pressure usable at the vice I am able to use an actuating cylinder of relatively small diameter so that it becomes unnecessary to build up the vise in order to accommodate the large diameter cylinders so often necessary with present day hydraulic and air operated vises. In fact, I- find that I am able to provide a vise with more than adequate gripping power in which the operating cylinder is actually smaller than the vise "ice body itself so that there is no overhead space problem at all.

These and other more detailed and specific objects will be disclosed in the course of the following specifica tion, reference being had to the accompanying drawings, in WhlCh- Fig. 1 is a side elevation of a common type of bench vise as provided with they hydraulic actuating mechanism of my invention, the vise jaws being shown as gripping a work piece.

Fig. 2 is an enlarged vertical and longitudinal section through the vise and the associated hydraulic actuating cylinder assembly. In this case the vise jaws are shown preliminary to the operation thereof by the hydraulic assembly.

Fig. 3 is a similar sectional view through the rear portion of the vise showing the position assumed by the parts when fluid pressure is applied for closing the vise jaws on the work piece.

Fig. 4 is a somewhat enlarged diametrical vertical section taken on the irregular line 4-4 in Fig. 2.

Fig. 5 is a vertical longitudinal sectional view showing means for the hydraulic operation of machine vises such as used for holding work upon drill presses, milling machines and the like.

Fig. 6 is a similar view showing a modification of the hydraulic actuating means for the machine type of vise.

Referring now more particularly and by reference characters to the drawing, the vise as shown in Figs. 1 through 4 is of the common bench type universally used by machinists and other workers for various bench work and the same conventionally includes a vise body 10 having a base 11 by which it is firmly secured to the bench 12. Ordinarily there is a swivel connection between the base and the vise body, but the same is omitted for simplicity in the present disclosure. Formed upon the upper frontal portion of the body 10 is the stationary vise jaw 13 and therebelow the body has a forwardly and rearwardly extending bore 14 in which the correspondingly shaped and sized shank 15 of a movable vise jaw 16 is slidably mounted. As usual the jaws 1316 are provided with removable face blocks 17 and 18 respectively. The distance between the jaws 13 and 16 is ordinarily adjusted by means of a hand screw 19 having a handle 20 at its forward end for convenient manipulation. The screw 19 is journaled rearwardly through an axial bore 21 in the shank 15 and the rear portion is provided with threads 22 having engagement with corresponding internal threads 23 on the interior of an elongated tubular vise nut 24. For straight hand operation the nut 24, which is slidably mounted into the rear end of the bore 21, is secured in some fashion to the vise 10 so that the opposite rotation of the screw 19 will of necessity move the jaw 16 forwardly and rearwardly and thereby adjust the jaw with respect to the stationary jaw 13.

In order to operate the jaw 16 and its shank 15 there is a fitting 25 about the screw 19 where it emerges at the front of the vise which prevents relative axial movement of the movable jaw and the hand screw in the usual manner.

According to my invention I provide fluid actuated or hydraulic means for positioning the entire hand screw and nut assembly forwardly and rearwardly with respect to the vise body 10 so that in any adjusted position of these parts, and therefore in any adjusted spacing of the vise jaws 13-16, I am able to urge the movable jaw toward the stationary jaw by the action of fluid under pressure. When not thus in use such hydraulic actuating means serves to hold the nut 24 against forward or rearward movement so that the vise may bemanually adjusted as aforesaid. Fundamentally this hydraulic actuating assembly takes the form of a relatively movable piston and cylinder, one of which elements is attached to the vise nut 24 and the other of which is attached to cylinder, the latter being fundamentally that disclosed in my prior copending application Serial- No. 325,406, filed- December 11, 1952, and operating what is therein referred to as a fluid actuated clamp.

For the accommodation of fluid operation in the standard form of manually operated bench vise as, depicted; in the drawing, the vise nut 24' is. provided, at its rear end with a. tapped socket or opening 26 into which the diametrically reduced forward; end 27 of an anchor stud 28 is screwed. Preferably, although not necessarily, the protruding, rearward portion of the anchor stud 28 is enclosed, by a. sleeve 29; which. is, held. in place by a nut 30 screwed upon; the threaded rear end 31- of the stud. The nut 30 also holds in place upon this assembly an actuating cylinder 32 the rear. nd 33 of Which is provided with, a. central bore 34 fitting the external diameter of sleeve 29; The wall of the cylinder 32 is considerably larger in diameter, than the sleeve 29 so that space is'provided forwardly of the end 33 to slidably receive an immovably-mounted piston 35,. the external diameter of which is machined to fit, into the cylinder. The P t n 5 is a so y nd i al; as a. rear end 3.6: again provided with a bore 37; to .nic ely and slidably fit thesleeve 2 9. Thusthere are provided opposed annular end faces orsurfaces.3& upon the respective ends of the cylinder and pistonagainstwhich fluid pressure may be applied; for moving one of saidelements with respect to the other, axially along the sleeve 29. Fluid tight seals are provided by conventional inner and outer 0- rings, designated at 39. The internal diameter of the cylindrical wall or skirt of the piston is made slightly larger than the exposed rear end 40 of the vise nut 24 against which the s1eeve29-is pulled up tight by the anchor stud 28.

Also forming part of the assembly is an end extension sleeve 41 which replaces the ordinary end cap and plug assembly (not shown) of the visehere chosen for illustration, and which sleeve 41 has a diametrically reduced forward end 42 to slip into the bore 14 of the vise body 19 where these parts are secured together by a tangential cross pin 43. Thesleeve 41 is bored out, as indicated at 44, to clear the vise-nut 24 but the interior of the sleeve is provided with a longitudinal keyway 45 in which there slides a key 46 on the vise nut to permit the necessary forward and=rearward movement of said nut while holding-the nut against rotation. The sleeve 41 extends rearwardly. from. the vise body 10 and has a.

rear end. face 4.7-adjacent which there normally rests the forward end face 48 of the skirt of the cylinder 32. The rear endof the sleeve is counterbored at 49 to receive the forward endjportiontof the skirt of the piston 35 which pistonis secured to the sleeve, and thereby to the vise body 10, by means of a lock screw or pin 50, as clearly seen in Figs. Z and 3. Conversion to hydraulic operation of vises presently, in.use requires replacement only of the vise nutandend plug.

Fluidunder pressure is supplied to the rear end of the cylinder 32 through a laterally opening, tapped socket 51 fromwhich thereis a forwardly opening bore 52. A conventional fitting 53 screwed in the socket is then connectedby a flexible line, 54. to the fluid pressure source. Preferably I. employ the. ordinary compressed air supply of the shop for, the development of sufficient fluid pressure in the cylinderv 32 to develop the relatively considerable thrustwh-ich is necessaryto obtain a powerful grip upon the work in the vise jaws. For this purpose, as seen in Fig. l, a line 55 from the compressed air supply is connectedthrough a manually controlled valve 56 to the end of a dual operating cylinder, designated generally at 57. Conveniently this cylinder 57 may be suspended below the bench12 and the valve 56 carried by a bracket or control panel 58a convenient to the hand of the operator, but the specific location of these parts is, of course, immaterial. In any event, the operating cylinder 57'has a large diameter cylinder section 58 communicating with a coaxial and considerably smaller cylinder section 59. A large piston 60 provided with an O-ring seal 61 is slidable in the cylinder section 58 and from its center there is extended a plunger 62 which slides in the smaller cylinder section 59 and which has O-ring seals 63. A fitting 64 conducts the compressed air from the valve 56 into the end of the large cylinder section 58 so that its pressure is brought to bear upon the large piston 60. An expansion coil spring 65 coiled around the plunger 62 acts as a return spring for the piston assembly. The extremity of-the small cylinder section 59 is closed by an end plug 66 in which there is a fitting 67' connected to the aforesaid line 54; This-line 54 and the communicating parts of the actuating cylinder 32 and of the cylinder section 59 are all filled with hydraulic fluid and thus as air pressure is brought to bear upon the piston 60 the resulting travel of the plunger 62 will move the body of fluid. through the line 54 and into the space between the end surfaces 38 of the cylinder 32 and piston 35 at the vise- Because of the difference in diameters of the piston 60 and plunger 62 the resulting fluid pressure brought to bear upon these end sur-- faces 38 is, built up to a point at which relatively tremcndous thrust may be developed even though the cylinder 32 is, as shown, actually smaller physically than is the vise body 10. Thus I am enabled to employ the relatively low pressures of the shop air supply for the eflicient operation of the vise without requiring that the vise actuating cylinder be so large in diameter as to bring on clearance problemsv as would otherwise be the case.

In operation, assuming that; the vise has been adjusted roughly by operation of the hand: screw 19, asit isshown: in Fig. 2, so that the spacing between the vise by the. blocks 17 and 18 is enough to permit the work to be readily placed therebetween, it is only necessary for the operator to then manipulate the valve 56 to instantly close the jaws upon the work. This valve may be of the push buttonvariety, asv here indicated for simplicitys sake, ormay otherwise becontrolled either manually, or by the foot of the-operator, itbeing evident that: littleor no effort is required merely for the operation of the valve, and. it is not necessary to laboriously pump up pressure for the operation of the vise. When thevalve 56 isopened. the air pressure thrusts the piston rod 62! toward the. left, as viewed in Fig. l, and the fluid in thesystem: is. thus forced into. the space between the end surfaces 38 of: the cylinder 32and piston 35; The piston 35 is secured by the lock pin or screw 50: to the sleeve 41 and hence, to. the vise body 10 so that the piston cann0t, of course, move forwardly or rearwardly. There fore, the cylnider 32 must: of necessity be thrust rearwardly by. the fluidand-since the cylinder is.held by the anchor stud 28'to the vise nut:24;the latter will be pulled in. a rearward direction so as. to. carry alongthe hand screw. 19. and movable vise jaw. 16, thus closing-the jaws upon the work. Actually. thepiston.35' is braced at its: end against the shoulder formed bythe counterbore-49 but; the lock screw. is providedtso that when the valve 56 is closed, andthe large cylinder section 58- vented to-atmosphere by. the valve, 21' return. spring 68' may assert itself and thrust the vise nut 24-.forwardly toreopen the jaws. This return spring=68 isan expansion coil spring: braced between'the adjacentendj40 of the vise nut and a shoulder 69'formed within the-cylindrical wall of the piston 35. The spring 68'is, of course, compressedias the vise jaws are closed'by the fluid actuating means and, as stated, the spring acts to open the jaws when the fl'uid= pressure is relieved-in-the system. The keyway 45 and key 46 provide for the necessary axial travel of the vise nut 24 while preventingthe nutfrom rotating in: the vise body-when the handscrew- 29 is used for adjusting the spacing between the vise jaws.

The stroke. and bore of'the plunger 62and'sma-ll cylinder. section 59' are both so prop'ortioned' with reference to the stroke and bore of'the piston 35 and cylinder 32 that fluid will not be supplied in such-amount'as-might otherwise force the cylinder32*entirelyoif the piston 35; should the vise behydraulically actuatedJwithout aworlc piece between the' v-ise jaws or=-the -vise be opened too far for the work. For example, the system is so .proporticmedthat the fluid displaced in.the'= small cylinder section' 59" will move the vise'ja'w'16 one-half'inchonly. and this is sufiicient since it-ispossible-for the. operator to very easily make, a rough'adjustment within this rangelby. means of the handscrew. 19. Suchproportioning-of theisystem. alsois, of course, selected so that the desired! pressure is brought to.bea-r, whiclndependsnotonlyt onthe size, of the vise andithe gripping pressures necessary, to the work but alsoupon the, available pressure; of thecompressed air in theshop.

In Fig. 5I have.f.sho wn, my. invention as adaptedtO. the operation ofJan ordinarymachine vise, ,suchasrused. upon a drill press or milling machine to hold the work and which vise differs somewhat-from the. ordinary bench; vise. As here'shown' this machine vise comprises a base" 70 at what may be referred to as the rear end of which there is a stationary jaw 71. A movable jaw 72 is supported by a suitable keyway '(not shown) upon the base 70 for reciprocating movement toward and away from the stationary jaw in the ordinary manner. The movable jaw is operated by means of a hand screw 73 extending through a heavy boss or lug 74 cast upon the base 70 at the end thereof remote from the stationary jaw. The screw 73 is, of course, threaded into the movable jaw and in its opposite end is providedrwith a crank 75 by which the screw may be rotated.

For the accommodation of my hydraulic operating means for this type of vise the lug 74 is bored out at 76 coaxially with the screw 73, with said bore opening toward the vise jaws and closed at its opposite end 77 except for an opening 78 to loosely clear the screw. This portion of the vise screw is provided with a smooth sleeve 79 which slides in the aforesaid opening 78, said sleeve being substantially longer than the lug 74 as measured axially of the screw., The recess formed by the bore 76 nicely and slidably receives the cylinder 80 of the hydraulic mechanism, which cylinder has an annular wall or skirt as clearly shown, the end 81 of which engages against the end 77 of the lug. The opposite end of the cylinder 80 is closed except for'an opening 82 through which the aforesaid sleeve 79 passes and bearing against this closed end of the cylinder is a collar 83 which is pinned to the hand screw 73, the diameter of which collar is substantially larger than that of the opening 82. Slidably arranged within the cylindrical wall of the cylinder 80 is a similarly shaped piston 84 the end 85 of which is braced against the closed end 77 of the lug 74. Sliding fluid tight seals are provided between the piston and cylinder as well as between the piston and the sleeve79 by inner and outer O-rings 86. Here again a fitting 87 is used to convey fluid under pressure to the closed end of the cylinder 80,which has a tapped socket 88 to receive said fitting and a port 89 for leading the fluid to the interior of the cylinder between the adjacent end surfaces 90 of cylinder and piston. The upper portion of the lug 74 is notched at 91 to clear the aforesaid fitting 87 and a flexible line 92 leads from the fitting to the source of operating fluid such as that disclosed in Fig. l. A second collar 93 is pinned to the screw 73 some distance forwardly of the lug 74 and an expansion coil return spring 94 is braced between the end 77 of the lug and this second collar in order to normally bias the sliding parts forwardly or toward the left, as viewed in the drawing.

In operation the movable jaw 72 is roughly adjusted to accommodate the work and upon the admission of fluid to the interior of the cylinder 80 the cylinder will be thrust rearwardly or toward the right, as viewed in the drawing, and by the engagement of the end of the cylinder with the collar 83 will move the entire assembly of the movable jaw and screw 73 in the direction of the stationary jaw in order to close the vise upon the work. The action is thus essentially identical to that previously described and, of course, when the work is to be released and the fluid pressure holding the work is relieved the return spring 94 will act to return the jaw 72 to its starting or roughly adjusted position.

While the foregoing structure is arranged in and about the lug 74 of the vise I may also locate the operating mechanism within the body of the movable jaw itself as shown in Fig. 6. Here the base of the vise is designated at 70', the stationary jaw at 71, the movable jaw at 72', hand screw at 73 and the lug at 74. In this case, however, the screw 73 is not threaded into the body of the movable jaw but the same is provided with an elongated cylinder or bore 95 in which there is slidably mounted an operating piston, designated generally at 96. This piston is generally tubular in form having an annular wall 97 which is internally formed to threadedly engage the screw 73. A portion 97a of the wall of the piston is enlarged to closely fit the bore 95 and this part of the piston has a longitudinal keyway 98 in which there slidably fits a key 99 secured within the bore 95 so that the piston may slide within the bore but cannot turn therein. At the end of the jaw nearest the lug 74' there is an annular collar 100 which is screwed into the tapped end of the bore 95 to guide the piston and at the opposite end the piston is closed, as indicated at 101, so that adjacent end surfaces 102 are provided between the closed end of the piston and the closed extremity of the bore 95. A fluid tight sliding seal is provided between the bore and the piston by means of an O-ring 103 and fluid may be ad-'a mitted to the interiorof the bore for'coaction .with the surfaces 102 through a port 104.communicating with-a laterally extending channel. .105 which leads to afitti'ng and flexible line, such as that shown at 87, 88 and 92in; Fig. 5. The structure is completed by theprovision of an expansion coil return spring 106 which-is bracedbetween the aforesaid collar and the enlarged part 97a of the piston wall.

The rotation of the hand screw 73 will, of-co'urse, here also roughly position the movable jaw 72' and the vise may then be hydraulically operated and closed upon the work by the admission of the fluid tothe closed end of the bore 95. As the fluid enters through the port 104 the movable jaw is of necessity urged toward the stationary.

made in the structure as disclosed, provided such modifications come within the spirit'and scope of the appended claims. Having now therefore fully illustrated and described my invention, what I claim to be. new and desire to protect by Letters Patent is: H

l. A combination manually and hydraulically actuated work holding vise, comprising a body having astatlonary aw, a movable jaw having apart slidable in said body for moving that jaw toward and away from the stationary aw, a hand screw and a nut threaded thereon in said body for manually positioning the movable jaw toa ward and away from the stationary jaw, a cylinder anchored to said nut, meansfor supplying fluid under pressure to one end of the cylinder,'and a piston inside the cylinder and over which piston the cylinder is slidable, the cylinder being operative upon admission of said fluid thereinto and the thrust of said fluid against the piston to thereby draw the screw and nut lengthwise and force the movable jaw toward the stationary jaw.

2. A combination manually and hydraulically actuated work holding vise, comprising a body having a stationary aw, a movable jaw having a part slidable in said body for moving that jaw toward and away from the stationary aw, a hand screw and a nut threaded thereon in said body for manually positioning the movable jaw toward and away from the stationary jaw, a cylinder anchored to said nut, means for supplying fluid under pressure to one end of the cylinder, a piston secured to the vise body, said cylinder being slidable over the piston, and the cylinder being operative upon admission of fluid thereinto to draw the movable jaw toward the stationary jaw, and a spring operative to normally urge the jaws apart.

3. A vise comprising a hollow elongated body and a stationary aw at one end thereof, a cooperative movable aw having a slide reciprocably mounted in the body, an elongated tubular vise nut slidably and non-rotatably located in said slide and a hand screw threaded therein for rough positioning of the movable jaw with reference to the stationary aw, an anchor member secured to the nut and extending from the end of the vise body opposite the aws, a hollow vise actuating cylinder secured by one end to the anchor member, a hollow piston inside the cylinder and over which piston the cylinder is slidable, the anchor member extending slidably through the piston, means securing the piston to the vice body, and means for supplying fluid under pressure to the cylinder to move the cylinder and plston relative to each other and thereby urge the movable jaw toward the stationary jaw in any position of the latter as adjusted by the hand screw.

4 A v1s e comprising a hollow elongated body and a stationary aw at one end thereof, a cooperating movable aw having a slide reciprocably mounted in the body, an elongated tubular vise nut slidably and non-rotatably located in sa1 l slic ie and a hand screw threaded therein for rough posltloning of the movable jaw with reference to the stationary jaw, an anchor member secured to the nut and extendlng from the end of the vise body opposite the aws, a hollow vise actuating cylinder secured by one end to the anchor member, a hollow piston inside the 5. A vise comprising ahollow elongated bodyand astationary jaw at one endlthereof, a cooperating movable jaw having at slidereciprocabl y' mounted in the. body, an. elongated tubular vise nut slidably and nonrotatabiy. located in said slide and a hand screw threaded therein for rough: positioning of the: movable jaw withreference to: the. stationary jaw, an anchor stud screwed into the vise nut1andprojecting axially therefrom, an end extension sleeve secured tothe rear end" of the vise body, a hollow piston slidably receiving said anchor stud and braced against said end sleeve, a cylinder surrounding the piston and: secured rearwardl'ythereof to said: anchor stud; both the pistonand" cylinder having end' faces, andmeansfor supplying fluid to thecylinder between said end faces totthrust the'cylinder'rearwardly and thereby drawthe visenut rearwardly and close the movable jaw toward: the. stationary jaw.

6. A- vise comprising a hollow elongated body and astationary jaw atone end thereof, a cooperating-mow" able jaw having a. slide reciprocably'mounted-in the body, an elongated tubular vise nut slidably and non-rotatably located in; said slide and: a hand screw'threaded therein for rough" positioning of the movable jaw with reference to the stationary jaw, an: anchor stud screwed into the vise. nut and projecting axially therefrom, an end extension sleeve. secured to the rear end of the vise body, ahollow piston slidably receiving'saidl anchor stud and braced against said: end sleeve, a cylinder surrounding the piston and seoured rearwardly thereof to said anchor: stud, both the: piston and-cylinder having end faces, meansfor supplying" fluid to the cylinder between said'end faces to-thrusb the cylinder rearwardl'y and there-- by draw the vise nut rearwardly and close the movable jaw toward the stationary jaw, meanssecuring the pis-' ton: to the end plug, and a spring braced between the piston and the vise nut to normally urge the movable jaw forwardly.

7. A vise comprising a hollow elongated body and a stationary jaw at one end thereof, a cooperating movable jaw having a slidereciprocably mounted in the body, an elongated tubular vise nut slidably and non-rotatablylocated in said slide and ahand screw threaded therein for rough positioning of-the movable jaw with reference to the stationary jaw, an anchor stud screwed into the vise nut and projecting: axially therefrom, an end extensionsleeve secured to the-rear end of the vise body, a

hollow piston slidably: receiving said anchor stud and braced against saidend sl'eeve, a cylindersurroundi'ng the piston and secured rearwardly. thereof 'to'said anchor stud, both the piston and. cylinder. having end faces, meansfor supplying fluid to the cylinder between: said end faces to' thrust the cylinder rearwardly and thereby draw the vise nut rearwardly andclose the movable jaw toward the stationary jaw, and said vise nut and-end sleeve having a cooperating key and keyway to lock the nut against rotation but permit forwardand rearward movement thereof:

Refere'nces-Gited in the file of this patent UNITED STATES PATENTS Number Name Date 2,222,941; Freeman Nov. 26, 1940 2,258,466 'Naylor Oct. 7, 1941 2,402,411 Kent June 18, 1946 2,444,304 Miller- June 29, 1948 FOREIGN PATENTS Number Country Date 332,372 Germany Jan. 31, 1921

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