US2716475A - Impact tools - Google Patents

Description

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Aug. 30, 1955 w. G. MITCHELL 2,716,475L

IMPACT TOOLS Original Filed March 17, 1949 2 Sheets-Sheet 2 United States Patent "O IMPACT TOOLS Walter G. Mitchell, Aurora, Ill., assignor to Thor Power Tool Company, Aurora, Ill., a corporation of Delaware Original application March 17, 1949, Serial No. 81,966, now Patent No. 2,585,486, -dated February 12, 1952. Divided and this application September 7, 1951, Serial No. 245,526

Claims. (Cl. 192 30.5)

This application is a division of my copending application Serial No. 81,966, tiled March 17, 1949, now Patent 2,585,486, issued February 12, 1952.

This invention relates to improvements in portable power operated impact tools for setting and removing nuts and bolts by power, and more particularly to improvements in an impact clutch mechanism employed in such impact tools for clutching and declutching the hammer and anvil members and for imparting rotational hammer blows on the anvil member to tighten or loosen anut or bolt.

In my copending parent application Serial No. 81,966, I have described and claimed various novel features of my invention and more particularly an impact clutch mechanism comprising a novel arrangement of a pair of rotatable hammer and anvil members, impact means, and

actuating means for the impact means. The present divisional application is directed more specifically to a novel arrangement of a pair of rotatable hammer and anvil members with a supporting shaft whereby to permit limited angular or cocking movement of the anvil member relative to the shaft.

Accordingly, the primary object of my invention is to provide an impact clutch mechanism having novel means for avoiding the inherent tendency of the anvil member of the device toward binding due to misalignment on the drive shaft during operation of the tool.

A further object of the invention is to provide in an impact clutch mechanism a novel combination of axially disposed rotatable anvil and hammer members and a supporting shaft with means for permitting limited angular or cocking movement of the anvil member relative to the shaft during operation of the tool.

Other and further objects and advantages of the present invention will become apparent hereinafter as the description progresses, reference being had to the accompanying drawings in which: y

Fig. l is a longitudinal sectional view with portions thereof in elevation and showing an impact tool comprising a preferred embodiment of the present invention;

Fig. 2 is a fragmentary longitudinal sectional view of the impact tool taken on the line 2-2 in Fig. 1;

Fig. 3 is a transverse sectional view taken on the line 3 3 in Fig. 1;

Fig. 4 is a transverse sectional view taken on the line 4 4 in Fig. l;

Fig. 5 is a transverse sectional view taken on the line 5 5 in Fig. 1;

Fig. 6 is a transverse sectional View taken on the line 6 6 in Fig. l; and

Fig. 7 is a perspective View of the impact unit and gear drive of the tool, showing the hammer in aligned but disassembled position with respect to the spindle and impact rods or jaws.

Referring now to the drawings, the impact tool illustrated therein comprises a four section housing including an impact unit section at the forward portion of the 2,716,475 Patented Aug" 30, 1955 tool, a gear section 20a at the intermediate portion thereof, a eld case 21 containing an electric motor, not shown, and a cap 22 at the rear end thereof. As more fully described in my earlier application Serial No. 81,966, the field case 21 is provided at its rearward end with supporting structure for a ball bearing unit having journaled therein the rear end of an armature shaft 26. A motor reversing ring 28, which may be composed of plastic or other suitable material, abuts the extreme rearward end of the housing section 21 and is held in position thereagainst for limited rotative movement by the cap y22. As explained more fully in my earlier application, relative rotative movement of the plastic ring 28 in one direction or the other serves to reverse the operational direction of the motor contained in the housing section 21. The armature shaft 26 is journaled on its forward side in a ball bearing unit 37 supported within a bushing 38 which is secured within the axial opening of an annular, cupshaped cross portion 39 extending diagonally inwardly and rearwardly from the forward end of the housing section 20a.

Rotary motion of the electric motor contained in the housing section 21 is transmitted to the impact unit within the forward housing section 20 by means of a planetary gear train. The forward end of the armature shaft 26 is shaped to provide a gear 46 in constant mesh with a pair of diametrically opposed, planetary gears 47 mounted for free rotative movement on short shafts 48 secured in a spider member 49. The spider member 49 isintegrally formed as the upper or rearward end portion of a drive shaft 50 and its extreme rearward end is journaled for free rotative movement in a thrust ball bearing unit 51 also received in the bushing 38. The planetary gears 47 are also in constant mesh with an internal ring gear 52 secured in and projecting somewhat beyond the extreme forward open end of the housing section 20a. The ring gear 52 is provided with an outwardly directed annular shoulder 53 which forms a seat against which the rearward end of the impact housing section 20 may be drawn up into tight engagement by means of suitable screws, as shown more fully in my copending application Serial No. 81,966. By this arrangement the assembly and disassembly of the tool is greatly facilitated. The entire front end of the tool including the impact mechanism, its housing section 20, the drive shaft 50, the spider 49, the planetary gears 47 and the ball bearing unit 51 may be withdrawn or separated as a unit from the rear portion of the tool merely by removing the screws and sliding the planetary gears 47 relative` to the pinion 46 and the ring gear 52 out of meshing engagement therewith. As will become apparent hereinafter, the impact mechanism may then be removed rearwardly out of the housing section 20. v

The forward end of the drive shaft 50, comprising the main supporting member` or stern of the impact unit, is received within an axial bore 54 of an impact spindle or anvil 56 which terminates in a square section 57 exteriorly of the housing section 20 and is adapted to mount and drive a nut or bolt engaging socket (not shown) in the f usual manner. The impact spindle 56 is adapted to rotate within a bushing 58 secured by a set screw 59 within the vaxial opening at the forward end of the housing section 20. A rotatable hammer member 60 is mounted on the drive shaft 50 above the impact spindle 56 for free and independent rotative movement relative thereto, the hammer 60 being provided with an axially extending central opening in which is secured a needle bearing 61 facilitating rotative movement between the parts. A thrust washer 62 is also mounted on the shaft 50 between the hammer and the impact spindle 56.

The hammer 60 is provided with longitudinally extending openings 63 on diametrically opposite sides of the central axial opening 55, the openings 55 and 63 thus being parallel and in alignment, and the hammer 60 thus being of solid, rugged construction and possessing great mass and inherently great strength. A pair of impacting rods or jaws 64 are slidably mounted within and extend through the hammer openings 63, the lower ends of the rods 64 being adapted to project when in impacting position, as shown in Figs. l and 3, beyond the forward end surface of the hammer 60 and into arcuate slotted openings 66 in a radially outwardly directed anged portion 67 of the anvil 56. As will be explained in detail hereinafter, 'the impact rods 64 rotate with the hammer 60 and are adapted to strike the anvil 56 at the abutments formed by thev ends of the arcuate slots 66 to cause rotation of the anvil.

The upper ends of the impact rods 64 are each provided with an annular groove 68 into which are received the edges of bifurcated portions 69 extending radially from the forward end of an arched cam lifter plate 70. The

`impact rods 64 may be readily mounted on the cam lifter plate 70 by sliding them inwardly into the slots 65 thereof from the outer edges of the bifurcated portions 69 and they are then free to rotate relative thereof. The cam lifter plate 70 is provided with a central axial opening through which the drive shaft 50 extends, the plate 70 being slidable on the shaft 50 for axial movement relative thereto. A relatively heavy compression spring 71 encireles the cam plate 70 and the forward end thereof seats against the radial edge portions of the bifurcated portions 69 outwardly of the heads of the impact rods 64. By this arrangement the carn plate 70 is constantly urged for wardly so as to project the impact rods 60 into impact* ing position. The spring 71 also serves the further purpose of retaiping the impact rods 60 in assembled position within the slots 65 of the bifurcated portions 69 during assembly of the various parts of the tool and permits the impact mechanism to be assembled and handled as an integral unit.

The upper end of the compression spring 71 bears and seats against radially directed flanges 72 of an upper spring plate 73, this plate 73 also being slidable on the drive shaft S and being separated from the forward endl surface of the spider member 49 by thrust bearings 74. The upper spring plate 73 is attened around the shaft S0 on the forward side thereof to provide -a surface 76 for engagement with a hat cooperating surface 77 on the rearward end of the cam lifter plate 70, the surface 77 being adapted to be moved upwardly into such engagement upon extreme rearward movement of the lift plate 70.

On the forward or under side of the cam lifter plate 70 are two projecting cam members 78, one on each side of the drive shaft 50, which are forced forwardly into constant bearing engagement with cam surfaces 79 on a -drive cam member or bushing 80 iixed on the drive shaft 50 for rotation therewith and restrained against axial movement relative thereto. The cam surfaces 79 slope upwardly in either direction from the low point thereof thus enabling the tool to be operated in a reversible manner in either direction of rotation. The cam bushing 80 is secured on the shaft 50iby means of balls 81 disposed within aligned and cooperating openings 82 and 83 in the bushing 80 and the drive shaft 5i), respectively. The forward end of the cam bushing 80 is received within an annular recess 84 in the rearward end of the hammer 60 and bears against a thrust washer 86 at the back of the recess.

As shown clearly in Figs. 2, 5, and 7 of the drawings, the hammer 60 is provided with two diametrically opposed and aligned ears or projections 87 which extend rearwardly in parallel relationship up within the spring 71 and on each of the opposite sides of the cam bushing 80, the cam lifter plate 70 and its cam portions 78. The outer peripheries of the hammer ears 87 are curved so as to conform to the curvature of the spring coils but they are spaced therefrom to permit free relative movement between the spring 71 and the hammer 60. The inner surfaces of the hammer ears 87 are smooth, at and parallel with each other and parallel with the drive shaft 50, and are in close, slidable engagement with the smooth, flattened surfaces 88 on the opposite sides of the cam lifter plate 70.

The hammer ears 87 thus serve to maintain the parts of the impact unit in perfect alignment and insure perfect alignment of the slots of the bifurcated portions 69 of the cam lifter plate with the axial hammer openings 63. As a consequence, the impact rods 64 are always maintained in perfect and absolute alignment within the hammer openings 63 for free relative slidable axial movement to and from impacting position. Since the parallel inner surfaces of the hammer ears are parallel with the axial openings 63 of the hammer 60 and bear against the opposite flat vparallel surfaces of the cam lifter plate 70, absolute parallelism between the parts is maintained at all. times. Any forces tending to rotate the hammer 60 in one direction relative to impact rods 64 so as to tend to effect their disalignment and to cause the rods to bear against one side of the hammer slots 63, also, through the hammer ears 87, tend to rotate the rodcarrying cam lifter plate 70 in the same direction and with equal force, thus preventing any such disalignment or binding engagement. lt is to be noted that the opposite longitudinal side edges of the cam portions 78 of the cam lifter plate extend slightly beyond the outer periphery of the driving cam bushing so that the cam bushing 80 is out of engagement with inner surfaces of the hammer ears 87. The hammer ears 87 also guide the cam lifter plate 70 in a true axial direction when it is cammed upwardly by the cam bushing 80 and serve to restrain the plate 70 against rotative movement.

On the under side of the housing section 21 is a switch grip handle 89 having a trigger block 94 slidably received within an opening in the front of the handle and adapted to cooperate with a switch device within the handle for closing and opening the electric circuit to the motor, as described in detail in my earlier application 'Serial No. 81,966. The trigger block 94 may be held in its inward position for continuous operation of the tool by a spring pressed locking plunger 112 extending through the forward portion of the handle and may be quickly unlocked by depressing and releasing the trigger block94.

When a nut or bolt is to `be tightened, the operator first places the socket (not shown), secured on the square 57, over a nut or bolt head and then presses the .trigger block 94 inwardly to complete the electric circuit and effect operation of the tool motor. As the armature shaft Z6 rotates, the pinion gear 46 on its forward end rotates theplanetary gears 47, causing them to move bodily around within the ring gear 52 in a counterclockwise directio`n as viewed in Fig. 6 and thus causing rotation oi `the spider 49 and the drive shaft 50. This driving torque is further transmitted to the impact rods 64 andthe hammer 60 through the cam bushing 80 .and the kcam .lifter plate 70.

At the outset of the tightening operation, the impact rods 64 are maintained in projected position within the slots 66 of the impact spindle 56, as shown lin Figs. l and 3, and abut against the respective ends thereof so as to rotate the impact spindle 56 and the socket and tighten the nut or bolt. As long as the nut or-bolt is Vrelatively frec running, the impact rods 64 remain vin-censtant engagement with the impact spindle 56 and -the projecting cam Vportions 78 of the cam lifter plate 70 are disposed at the low points of the cam faces 79 of the bushing 80. However, when the nut or 'bolt .approaches tightened position and resistance to rotation is. suflcient to `over- .come the driving ltorque of the tool motor and the exbushing 80 continue to rotate under the driving force of the motor '29, the'camlifterrplateif70 iwilllbefcmmc'd rearwardly in avstraig'ht-longitudinalor axial direction underthe guiding'inuenceof-the hammer ears 87. f' Since the cam lifter plate 70 carrieszand supportsI the impact rods 64, these rods l also are moved :rearwardly lrelative tothe hammer A60 andtheyare thus .withdrawnifrom the slots.66 to apoint slightly above :they rearward surface of the then stationary impact'spindle 56. Whenitheiimp'act rods 64 are fully .withdrawn the .projecting cam-members 78 .of the cam 'lifter plate .7.0 engage lthetcam-sur- .faces 79 of the bushing80 near the top of their `high points.

.In this withdrawn rearward position, the .impactrods 64 are out of driving engagement :with the impact .spindle 56 and hence are free to rotate under the drivingtorque of the drive shaft 50. .The-impact rods 64 and .the 'ha'mmer 60, consequently,v resume Erotation in a clockwise Vor tightening direction, passover. the narrow'landsbetween the impactspindleslots' 6,6.;and-.then are projected under the .urge of the spring 71 back.into theslots-66 `so that .the impact rods 6 4 will be .impactedragainstthe farA end of the slots 66 -uponcontinued rotation. From thetime that driving engagement is broken'oifjasfabove'described, until-the rods 64 impactagainstthe .ends1of `theslots V66, thedrive shaft 50 accelerates `underfthe -dr'iving force fof the motor 29 at an vever increasing rate-so `that theimpact rods 64 strike the impact ispindle 56 .with great force. Because of the solidmassive construction of..the'ham mer 60, this impacting-force `is of relatively great magnitude. Y 2 t Because of the fact that the impact :rods f64are circular and are slidably received in the. slots -:65..of `the cam lifter plate 70, theyare free torotate relativegthereto. Asa result of this-rotative connection, the frods f64.a`re rotated slightly as they are.v moving vinto impacting posi- Cil tion against the far ends of the.slots,66, thus-,presenting diierent circumferential :portions of -the lower `or blowdelivering ends of the rods tothe slotabu'tments :for each blow. The rods, therefore, present new wearingsurfaces and have a long operable life. f

.It is to be noted further that `when thedriving' `engagement is initially brokenolf between the impact -vrodsI 64 `andthe impact spindle 56, thecam portion 78fofrthecam lifter plate 70 engages Vthe cam-bushing-B-near the high point on its cam surface. Consequently, as impact rods 64 again accelerate toward impacting engagement with the impacting spindle 56, the kheavy spring 71 will 'force .the cam lifter plate 70 axially forwardly, `the cam ,portion 78 moving downwardly and forwardly over the cam surface of the cam bushing.80toward its low point. The cam lifter plate 70 is thuscaused to accelerate aheadef the drive shaft 50 and the impact rods-64 are caused-to strikethe impacting spindle-56 with-an increased impacting force and at a rate -of rotation over andv above that of the drive shaft 50. Afterimpact, which causes further mer slots 63, the sliding movement of the rods 64 is also parallel `therewith; Consequently, itis vapparent that by the arrangement of the parts they are maintained in the desired alignment so that their free operation'iis achieved at all times and no binding of the rods 64 inthe hammer slots 63 results. v 1 v When it is desired to utilize the tool for the purpose of loosening a nut or bolt, the operator need only l,rotate the plastic reversing ring 28 to its-other positionas above described, and .the electric motor will thus operate lin the reverse direction and the drive shaft 550 will also be rotated in the reverse direction. Since the work is in a tightened state, zthe impact rods 64 will immediately commence imparting blows against the spindle 56 until the resistance-to rotation offered by thework `is less than the-driving torque of the cam lifter plate `70, at which point the impacting blows cease and the impact rods l64 l remain in constant free running engagement' with the impact spindle 56. The toolmay-then'be allowed `to remain in engagement with the work until the work is entirely disengaged from a threaded opening.

Having thus described the general .mode vof operation of a rotary power tool utilizing an impact clutch mechanism-of the type illustrated,.I will now describe the specific improvement to which the present application is particularly directed. It will be understood that the specific features hereinafter described are broadly applicablev to various impact clutch arrangements other than those involving the specific impacting and actuating means described above.

As shownrmore particularly in Figs. `l yand 2 of the drawing, the lower or forward end portion of the drive shaft is constructed so as 'to permit limited tilting or cocking movement of the impacting spindle or anvilv56 relative to the drive shaft 50. When the tool is in .opera- `tive engagementwith the work and is in the hands of an fop'era'tor, the impacting forces and the handling of y the Etool bythe operator tend to force the impacting spindle -56 .out vof alignment with the drive shaft 5 0. --Because fof this' inherent tendency toward misalignment which ;wou`ld cause binding'of the impact spindle56 if 4there, was

a1tightfit lbetween the parts and hence would `reduce the effective output of the -driven shaft `50 `and the spindle -56 .the extreme forward end of the -driven shaft V50'=is rounded ortaperedas'at 13'4 leaving avreduced lilat end face ',136 for abutting engagement with :a thrust washer annular-.bearing surface 139 which is adapted to engage limited rotative and tightening movement ofithe impact spindle 56, the impact rods 64-are againwithdrawn .as above described and are again rotated relativeato the-irnpact spindle 56 and thrown again intofimpactingrengagement with the spindle 56 at the far ends of the next succeeding slots 66. The :impactfrods 641thus'strike the impact spindle 56 two impactingblowsfor every revolution of the hammer 60 and these blows maybe repeateduntil the work has been. tightened toi-the desired degree. A'

'During the operation-of lthe tool when the impacting blows are .being .delivered to thewoi'ln the impact vrods v64 are freely slidable within-'the hammer slots `6'3't`o and from spindle engaging position since they are maintained in perfect alignment therewith by the hammer ears 87 which engage the ilat sides 88 of the cam lifter plate 70. The hammer ears 87 also by their slidable engagement with the flat sides of the cam lifter plate 70 cause that plate to move in a truly longitudinal direction and parallel to the inner sides of the hammer ears. Since the inner sides of the hammer ears 87 are also parallel with the ham- ;the walls of-the yspindle bore 54overa limited area. This limited .bearing surface 139 serves to .prevent too .loose J,a mounting between. the spindle 56 and theshaft 50 but .at the same time permits limited tilting movement therebetween. The forward and inward edges of the bearing surface 139 wear away or round off after a relatively short :period oftooloperation so thatthis bearing surface, as the .tool wears in and the parts adjust themselves vto eachother, also becomes slightly rounded tothe desired .degree n i' v,'lheportionof the drive shaft 50 next aboveor rearwardlyv'ofithe bearing surface 139.is of reduced diameter, as indicated at 140, and is slightly spaced from the sides ofthe spindle .bore 54 and the thrust washer 62 to provide aclearance `141 for the limited tilting movement. The "diameteriof the drive-shaft portion indicated at 142 within the central bore 5S of the hammer 60 is also of lesser extent than the diameter of that bore so as to provide clearance therebetween, and the needle bearing 61 serves to maintain the proper bearing relationship between the hammer 60 and the drive shaft 50. Also for the purpose of permitting the relative tiltingmovement, the marginal or radially outer portion of the annular flanges 67 of the v impact spindle 56 are cut away so as not to extend rearmaeva wardly as far as the central portion thereof, thus providing a slight clearance`143 between the opposed end faces of the hammer 60 and the spindle 56 at their outer portions and for engagement therebetween and with the thrust washer 62 only at their central portions around the drive shaft 50.

Thus, by reason of the special construction of the shaft and the pair of anvil and hammer members thereon, the clearances indicated at 141 and 143 are provided so that the anvil or spindle 56 can undergo limited cooking movement or axial misalignment without binding and thereby facilitating easy operation of the tool. v

It is to be further understood that while the preferred embodiment of the present invention has been described above as an impact wrench, the very same tool by means of special attachments secured on the square 57 may be adapted for other uses such as a screw driver, tapper, reamer, drill, sander, polisher or wire brush driver. When utilized for these latter purposes, the tool will be primarily free running without operation as an impacting wrench. However, such impacting features are permitted to become elective when used as a screw driver or when used as a drill and the drills or bits become Jfrictionally held against rotation before the drill hole has been completed. The impacting blows of the hammer rods 64 then are applied to the drills and bits to overcome such frictional resistance and any overload on the motor is eliminated. Although there has been described above and illustrated in the drawings a preferred embodiment of an impact tool comprising the present invention, it is apparent that modifications and changes may be made in the details of structure .and mode of operation withontdeparting from the spirit and scope of the appended claims.

lclaim:

T? An impact clutch comprising relatively rotatable axially aligned hammer and anvil members having aligned axial bores therein and an aligning shaft in said hammer bore supporting said hammer for rotatable movement thereon and extending into the bore of said anvil for rotative movement relative thereto, the portion of the shaft within said anvil bore being of lesser diameter and spaced from the walls of said bore along a major portion of vits extent and having a generally cylindrical enlargement of relatively short axial extent in bearing engagement with the walls-of said bore whereby said anvil and hammer members may moveangularly out lot axial alignment to a limited extent without interference lwith free relative rotation.

2. An `impact clutch comprising relatively rotatable axially aligned hammer and anvil members having aligned axial bores therein and an aligning shaft in said hammer bore supporting said hammer for rotatable movement thereon and having a free end extending into the bore of said anvil for rotative movement relative thereto, the portion of the shaft within said anvilbore being of lesser diameter and spaced from the walls of vsaid bore along a major portion of its extent and having adjacent the free end thereof a generally cylindrical enlargement of relatively short axial extent in bearing engagementjwith the walls of said bore whereby said anvil and hammer members may move angularly out of axial alignment to a limited extent without interference with free relative rotation. j

3. An impact clutch comprising relatively rotatable axially aligned hammer and anvil members` having aligned axial` bores thereingand an aligning shaft in said hammer bore supporting said .hammer for rotatable movement thereon and havingI a free end extending into the bore of said anvil for; rotative movement relative thereto, the portion of the`- shaft .within said anvil bore being of lesser diameter and spaced from the walls of said bore along a major portion of iitsextent and having its freeend rounded' and having a generally cylindrical enlargement of relatively short axial extent adjacent said rounded end in bearing engagement with the Walls of said bore whereby said anvil. and hammer members may move angularly. out-of axial alignment .to a limited extent withoutinterferencewith free relative'rotation. 4.- Aniv impactlclutch. comprisingV relatively rotatable axially aligned hammerf andi anvilmembers having aligned .axial bores ltherein and: having' axially opposed wall portionswith abutments on' the axially opposed wall portion of the anvil member,k impact means rotatably movablewith said hammer and axially movable independently of saidihammerinto-an'd out of the path of the abutments for. clutching-,and declutchingsaid members and for imparting rotational hammer blows on the anvil member at said abutments, anda driving shaft-in ysaidhammer bore supporting said hammer for-rotatable movement therein and having a lfree Vend extending into the bore of said anvil forrotative movement relative-thereto, the portionof-,the shaft-within,` said anvil'bore being of lesser diameterand spaced from the walls of said bore along a major portion of its extent and having a generally cylindrical enlargement vof relatively' short 'axial' extent in bearingengagement withthe Walls of said bore,-and said hammer vand anvil members being-n bearing engagement with each .other atftheir central axial portions and being axiallyk spaced from each other at'their outer portions whereby said Vanvil and hammer members may move angularly out of axial alignment to a limited extent durlng operation thereof-'without interferencewith free re1- ativeirotation.

5. In. an impact clutchj'a' rotatable hammer member havingA anpaxial -bore therethrough, a rotatable anvil memberhaving van laxial recess in alignmentl with said bore, and av'shaft extending through said bore'and having an `end-.portionextending into said'recess, said end portron being provided adjacent its kvouter extremity with/a generally'cylindrical enlarged bearing portion of relatively short axiallext'ent substantiallyless than the axial depth of said recess and disposed in bearing engagement with the wall of said recess for normally retaining the hammer and anvilv members in axial ialignment, the remainder of said-end portion inwardly of saidfbearing portion being of reduced diameter relative to said recess whereby to provide -an annular' clearance therebetween, and said hammer and anvil members havingtheir opposed endsaxially spaced from each other adjacent the outer peripheries thereof, whereby to permit limited angular displacement of said anvil member relative'to said shaft and said hammer member' without interference with .relative rotary movement of theparts. i

References Cited in the file of this patent STATES PATENTS 1,871,227. smith etal. An 9 1932 75,004V Behr 1 Ma 3I 1942 ,j 33,703 .,wilh'de et a1. D l 2,564,224 ec. 12, 1950 Mitchell et al. Aug..14, 1951

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