US2474247A

US2474247A - Signal type torque indicating wrench

Info

Publication number: US2474247A
Application number: US544127A
Authority: US
Inventors: Hattan Mark
Original assignee: Individual
Current assignee: Individual
Priority date: 1944-07-08
Filing date: 1944-07-08
Publication date: 1949-06-28
Anticipated expiration: 1966-06-28

Description

M. HATTAN SIGNAL TYPE TORQUE INDICATING WRENCH June 28, 1949.

Filed July 8, 1944 Q 6- GE i N N\ M.\ 8A? Patented June 28, 1949 UNITED STAT PAINT SIGNAL TYPE TORQUE INDICATING WRENCH (Granted under the act ofMarch 3, 1883, as amended April 30, 1928; 370 G. 757) 8 Claims.

The invention described vher'einmay be manufactured and used byior for Govermnent for governmental purposes,"withoutthe payment to me of any royalty thereon;

This invention relates to improvements in torque indicating wrenche'sand particularly that classoi wrenches'wherein' an indicating or signal means is incorporated responsive to fiexure of an element of the wrench under torque load and eifective to indicate the applicationof a predetermined torque to awrench work head.

Torque indicating wrenches are per se old in the art and in one form'of Construction of which I am aware; the point at which the indicating mechanism becomes operative to indicate the applied torqueis adjusted by varying the effective length of a flexure or beam member which transmits the torque from a handle to a work head. This form of construction is satisfactory where the torque range is'small but requires an excessive length of wrenchwhere the torque range'is large; such as isencountered in the aircraft field. A furtherdisadvantage in prior constructions is'lack ofmean's for'altering the type of work head without requiring recalibration of.

the wrench and the in'dicationsgiven by theoptical type of indicating means of prior wrench constructions are difiicult to detect in strong lighting conditions.

In accordance with the present invention the point'of indication of the applied torque may be predetermined within a large torque range with 1itt1eOrI10 increase of wrench" length primarily by adjusting "the relative spacing of electrical contacts in the indicator-mechanism rather than bychang'ing the length of the flexure or beam member;

In accordance with the present invention various types of wrench work heads may be applied to the wrench -to adapt it to variousworking requirements and by maintaining the "axis of torque applied to the work head constant" the wrench calibration remains unchanged. Thepresent invention also provides means for shading the-signal illuminating'means fromtheeffects of strong external light -so -that the torque indications are visible even in strong daylight.

Anotherfeature of the presentinvention comprises the providing of a wrench structure having a substantially smooth cylindrical exterior free of protruding parts to facilitate handling and eliminate catching orv snagging of the wrench on surrounding parts of the mechanism being worked on.

Other structuralfea'ture's comprise providing a completely closed wrench for housing the w'ork ing parts thereof and protecting them from-me chanical injury and deterioration due to dirtand: moisture, and the provision of a compact, rugged mechanism capable of withstanding severe shock and hard usage without impairing the torque indicating accuracy of the device.

A further feature of my invention comprises" a battery holding tube wherein the dry cells" which form the energy source are inserted, where-' by the tube'is intermediate the dry cells and" the internal walls of the wrench for the purpose of protection against swelling of the batteryor corrosion caused by rupture of the casing o'f'one or more of the dry cells with use.

With the above features and objects of' the invention in mind, other features will become apparent from the detailed description taken in conjunction with the appended drawings in which:

Figure 1 is a longitudinal cross section'of 'on'e' form of my invention;

Figure 1a is a detail showing a work head place on the wrench illustrated in Figure 1;

Figure 1b is an enlarged detail of one element of the form shown in Figure 1;

Figure-2 is an exterior view of the form shown in Figure 1; and

Figure 3 is a longitudinal cross sectionof another'form of my invention.

Referring to Figures 1 and 2, a wrench handle member is shown having a hollow cylindrical wrench body I secured to a hollow cylindrical handle! as by threading 3.' Within body I is a' generally tubular fiexure element 4 having an: end protruding therefrom adapted for attachm'ent to a work head 5 (Figure 1a). Flexureele ment 4 ispivotally secured at 6 to body I whereby relative angular movement is provided between: the free end 4a of'flexure element! and a sleeve-' like taper member 8 slidably disposed withinbody l and adapted to transmit torque stress from' handle 2 to flexure element 4. The tapered sur face 9 of ta'permember 8 is concentrically'sp'aced' from the freeend 4a offlexure' element' l; the concentric spacing being variable by reciprocating taper member 8 relative to said free endda; Reciprocal movement of taper member 8 is-ob tained by means of a sleeve In (Figure 1b) rotat ably mounted on body I and provided withan internal spiral groove ll coacting with spherical bearings l2' which are maintained in'di'ametric-" ally" opposed relationship by longitudinal slots 13': cut-through the walls of body I, the" spherical bearings l2 being retained in a peripheral-groove 54 provided externally on the taper member 8. The rotatable sleeve 50 is restrained against axial movement on body I by a shoulder l5 thereon and by a sleeve ll secured in any suitable manner on body i, such as by a shrink fit. The rotatable sleeve H) is externally knurled as indicated at l8 and is provided with a scale 19 calibrated in torque units and adapted to cooperate with a fixed index mark Isa provided on body I to indicate the torque setting of the wrench. Rotation of the sleeve I!) will, by virtue of the spiral groove ll, exert a longitudinal thrust on the spherical Hearings l2 in a direction depending upon the direction of rotation of the sleeve ill, the longitudinal thrust on spherical bearings I2 being transmitted to taper member 8 by reason of the retention of the spherical bearings l2 in the peripheral groove is on taper member 8. Accordingly, the concentric spacing between the tapered surface 9 and the free end 4a of flexure element 4 may be predetermined by the operator by rotary adjustment of the sleeve ID to effect reciprocal motion of the taper member 3 relative to said free end M. It will now be apparent that owing to the pivotal relationship provided at 6 between body I and flexure element 4, a movement of handle 2 in a torque applying direction will not transmit any torque force to the work head until taper member 8 has moved angularly with body member I relative to the free end 4a of fiexure element 4 to the point where the tapered surface 9 abuts free end to. The extent of this no-load or lost motion movement of handle 2 depends on the amount of initial concentric spacing provided between the tapered surface 9 and the free end 4a by the adjusted position of taper member 8 relative thereto, the purpose of the lost motion movement being to provide a predetermined spacing between electrical contact elements as will presently appear.

Integrally supported at 20 within flexure element 4 and concentrically spaced from the inner walls thereof is a contact rod 2| having a contact element comprising a free end 2m adapted to electrically contact either of a pair of contact screws 23, depending on the direction of torque movement of handle 2. Screws 23 are adjustably secured in a member 24 movable in a torque applying direction with the handle 2. Relative angular movement of the electrical contacts is obviously efiected during the no-load movement of handle 2 whereby an initial spacing between the contacts predetermined by the extent of said no-load movement is realized. The torque stress transmitted from handle 2 to ilexure element 4 through abutment of the free end 4a thereof with tapered surface 9 subsequent to no-load movement serves to flex the tubular portion of flexure element 4 and simultaneously decrease the initial spacing between the contact elements to the point where electrical contact is obtained, it being noted that said contact rod 2i remains substantially straight and unaffected by the fiexure of flexure element 4. The function of the contact rod 2! is to provide for coaction of the contact elements at a point substantially removed from pivot 6 whereby the arc of relative movement of the contacting elements is enlarged for structural convenience.

Member 24 is electrically insulated from ground by means of insulating washers 26 and 21 and insulating collar 28. Suitable ports are provided in insulating collar 28 in alignment with ports 29 in body member I whereby access to contact screws 23 may be had for adjustment thereof.

Member 23 abuts the center terminal of a signal lamp 3% supported within and in electrical contact peripherally with a collar 33, slidably retained and insulated from ground in a translucent, colored plastic sleeve 31% disposed within the handle 2. A spacer tube 35 is slidably disposed within the translucent sleeve 36 and abuts collar 33 whereby biasing action of a spring 36 is transmitted through a series of cells 37 to the outer end of spacer tube 35 for the purpose of maintaining electrical contact between extremity 2 2a of member 2% and the center terminal of signal lamp 3t. An end cap 39 is provided for retaining the spring 36 in compression against the negative casing electrode of the outermost cell thereby establishing a series connection of the cells 3'l to form a battery disposed Within a battery holding sleeve to which is provided for protection of the inner surface of handle 2 in the event of one or more of the cells swelling or bursting its casing and loosing a corrosive electrolyte. Although three cells are shown, it will be appreciated that the device is not limited to any specific number. The peripheral casing terminal of signal lamp 30 is electrically connected through spaced tube 35 to the positive center terminal of the battery, the negative terminal thereof being grounded through spring 36. The center terminal of signal lamp 36 in electrical contact with the extremity 24a, of member 2c is insulated from ground. Accordingly, any movement of handle 2 in a torque applying direction sufiicient to bring either of the contact screws 23 into contact with the free end Zla of contact rod 25 will complete a circuit through ground from the negative casing terminal of the battery to the center terminal of the signal lamp 38 whereby the signal lamp will be lit, the illumination thereof being visible exteriorly of handle 2 via ports M and 42 in spacer tube 35 and handle 2, respectively, the intermediate translucent, colored plastic sleeve 34 imparting its characteristic color to the light rays to enhance noticeability.

In operation, the sleeve [0 is manually rotated to bring a desired torque indicium of scale l9 opposite the fixed index mark Hat on body memher I. The rotation of sleeve l0 serves to fix the position of taper member 8 in relation to the free end ic of flexure member 4 whereby the concentric spacing between free end 411 and the tapered surface 9 of taper member 8 is determined. Since flexure member 4 is pivotally related to handle member 2, a definite degree of lost motion is provided between free end 4a and the tapered surface 9, as heretofore described. When handle 2 is operated to apply working torque, the initial movement thereof takes up the lost motion, and one or the other of contact screws 23, depending upon the direction of torque rotation of handle member 2, is brought proportionally closer to the free end 21 a of contact rod 2|. This initial motion transmits no torque stress to flexure member 4 until the lost motion has been entirely taken up, i. e., at the end of the no-load movement when some portion of the tapered surface 9 will abut free end 4a. Continued motion of handle member 2 will cause a deflection of the tubular portion of flexure member 4, said deflection increasing proportionally with the torque stress applied to handle member 2 until a contact screw 23 approaching the free end Zia of contact rod 2! closes contact therewith. At that instant a circuit through the battery and signal lamp 3!! is comple thereby asvaeaa lighting thelamm tne light tnereof being visible to?the operator' as heretorore described.

rn tne event or an overload being applied :beyo'i'ld tlie stress for which fiexure 'ele'ment "4 is designedg tlie shoulder-44 thereon abutsth'e por tion l 'of-'*bod y l to =tal e the excess stress, thereby protecting flexure member 4 from being stress'ed beyCi-l'ld its propcrtional: limit 5 Figure-1, tne lost 'inotibn is greatest, "whereby one contact screwfls is relatively close to thefree end-'2 I a oreonta'et fod z l-"at 'th'e end of theno loa'd movement-r 'accordinglyr only a small deflction said: free-"endfltd during th subse'quent torque load movementi- Conversely, when taper mem berii isset at-tl'ie' extremeleft;'the-no-load move- I ment isleast} consequently; a greater deflection of' flexure member 4 will 'ta-ke pl'ace in the ensuing 1 motion of handle member 2. ltccordingly", the degree ot torqueexerted before the signal lamp liglits is determined by the' degre'eof lost motion"taken up'during' initial no-lo'ad movement of handle- 2, which is dependent upon the" adjusted aXial -posit-ion ot taper member Brelative to the free 'end ila of fl'e'Xuremember 4.

Adjustability pf "contact screws" 23' isprovided as a' -manufactiiringconvenience so that a zero setting be obtain'edyand also' 'from timeto' time as'usafg'e-of the wrench causeswear and tear onthdparts ancbaflectsthe elasticity of the flexure'member 4, resettingto zero'may be desirable.

Thisfeatiire' is'a refinement-andnotessential to tlie' usefulriess' ofthe wrenchfor general conditions'. In-adjustin'g' the 'ze'ro'setting,the wrench is'held'with the axis of'the screws23" vertical and the 'upp'e'r screw adjusted so-"thatthe signal "lamp I 3ll'just'lights'wlth the scale-l9 set to' zero and the wrench supported to" thehandle with no torque load other'than the weight of theother end. Each "screw"23 is' 'ad-jlisted in 'theupper position, since 'th'atis-the positionwhrein contact is made with'the free 'end 2 [it of contact 'rod 2 i when the weight 'of' one end Of the wrench'is used to produce 'a torque stress.

The-work'- head '5 is afiuiedto an adapter" head 41 by: means" or stud "48 and reciprocating spring biased= ba1rdetent '49; heads may be"'utilized'since adaptenheadel is detachable from flexure elementfl by"reason"of thespr-ing bia'sed ball de'tent 50$" Keying pin 5| extends through fixure Various types of work" 'eler'n'ent 4 and engages the sidesi-of openended slots 52"cu't'int'o the rim" ofadapten ll for the purpose'of preventing rela-' tive rotary "motion" therebet'ween;

The calibration of torque scale I9" is calculated for atorq'ue' axis extending axially through the Work head carrying stud 483 215 illustrated on Fig ure"2." The =torque 'aX-is lies outside the physical pectfsincesuc-h a construction permits the design and attachment 'ofz varioustyp'es of work headsf e. g1, a tubing nut type'; as ill'ustrated in Figure 3,"

directly to flex'ure member '4, fpr'ovided that such" other type' is designed tohaveits torque axis identical' with thatshown' ior the adapter '41. Ac cordi-ngly,"- a, isingle ca'librated scale is operable-in conjunction with a variety bf work"heads.-= Work heads of varioustypes may -be attached to flex'ure element 4 in tnemanner' sh'own for the adapter 41 by being eonstructed #:to -:coact' 'witnr-b'au de tent 5c and keying piri I a Likewise} special-' adapters to held various typesoi worlrheaus maw wit'h frosted sl-id'ab'ly disposed: within:

be constru'cte'tig e. g.'; :theispecificadapter l'lrshown' isiintended for socket type 'of work' heads;

A.i'furztner'=f ature-cr me invention resides in tne use otiithei -translueent; colored plastic sleeve tSMbothas aninsulating means and as a means for?enhancing visibility ofthe light rays. It has been foun'd in practice-that a red colored sleeve produbes a quality of light which is very distinguishablei The sleeve 34 is used in conjunction plasticinserts fi' in ports 42. The purpose offi'inserts 55 'is to weaken the incident and refl'ecte'd rays ef outside lightwhereby con trasflw'ith' thedirect rays from the signal lamp ez 'is' 'increase'd promoting visibility to the operator when working inf-strong light dept-ii of thevports dfinrelation to their diameter has .a::shading' eflfeet"against outside light, the

frosted plastic inserts Shareventing ports 42from" filling upiwith oilvan'd grease.

Iri'themodifieationshown in Figure 3, is a handl'e threadedly secured to a body BI and "axi-' al-lYadjfistaible relativethereto; A look nut is provided to 'secure handle'member 60' in adjusted osition. Pivotaillysuppiorted at 62 within body 6| is a work1head holding m'ember 63 adapted for attachment to'a work head 64. Axially supported biasing 'ac'tibn ofi spring "1! transmitted through button '-'l2;'dry"c'ell 73, signal lamp 16' andclip TI;

The positive center electrode of dry cell 'lfiabuts the:centen 'terminal orsignal-lamp 75. Consideration of the structure will make it apparent that thenegative'side'orthe dry 'cell 13 is'electrically connected to 'fleisuremember 61' through button fiflpspringfil andbutt'cn 12; all aforementioned elements being"electricallyinsulated from ground bysleeve-lfl andplastio eup GS'. The peripheral casing terminal of:signal lamp 16 is grounded.

In view of the pivotal relationship provided at 62 between the sleeve Ill and the tapered end 58 of flexuremember 'fi 1-" when handle 60 is adjusted relative axially torthe bod y the sleeve "Ill and the tap'ered end 68' by virtue'of the'taper provided thereon. As the handle member is adjusted axially outwardly, the lost angular niotionwbetwe'en sleeve 70 andthe tapered end 68 of flexure member 61' may 'be' seen to increase,

whereby'initial-motionof the'handl'e member fill in a torque'applying direction will have a correspondi-ng='-no-lo'ad= movement. Conversely, as the handle member is ad-justed axially inwardly, the lost-angular'motion-between sleeve l0 and tapered end 68 of. flexure memberfi'! is decreased, whereby the-corresponding no-load movement of han-' die member is lessened: Subsequent to a 'no- 1oadmove'mentOfeither'high or low degree, an

abutting: action between-the inner peripheral edge ofi-thei sleeve flfl' and some adjacent portion of=' th'e =taperedend "68'bf fiexure member til will resul t an'd'the 'ensui-ngbowing effect on fiexur-e' membe'z fi-T wili -cause the center portion thereof to contact the surface of the surrounding-bore Also, the

member 6!; a specific degreeof lo'st-angular'motion is provided between 8| in handle 59. Accordingly, the negative casing electrode of the dry cell 13 will be grounded whereby a circuit will be completed through the signal lamp 15, the illumination thereof being visible to the operator through the colored, translucent plastic cap i9 and the ports til. In the specific illustration of Figure 3, the handle member 69 is shown as screwed to the inward limit of its motion relative to the body member 6|, the tapered end 68 of the flexure member 61 then protruding as far into sleeve iii as it is possible for it to go whereby a small degree of lost motion is provided in relative angular movement therebetween. The lock nut 55 is shown tightened against the outer end of the body member 1 6| to secure the handle member 60 in position. In this specific illustration, the wrench is set for the uppermost limit of the torque range inasmuch as movement of the handle Ell in torque applying direction will involve the least possible no-load movement prior to transmission of torque stress to the fiexure member 6?, whereby the spacing between the central portion thereof and the internal surface of the bore 3! within the body member iii will be relatively large at the end of the no-load movement, thus necessitating a relatively large fiexure of the ilexure member 67 to produce a contact, corresponding to a large torque stress.

Calibration in torque units of a wrench of the type shown in Figure 3 has been provided in practice by means or" a simple longitudinal scale on the exterior of handle 68 whereby distances relative to the edge 82 of locknut 55 are readable in torque units for convenience in setting the wrench to operate the signal lamp when a desired degree of torque reached. Inasmuch as the change in bending resistance of the flexure member 6'! at various settings along the tapered end 68 introduces factors which complicate calibrating this type of wrench by a purely mathematical process, it has been found feasible to provide a scale calibrated empirically rather than by calculation.

It will be understood that my invention is not L limited to the specific structure herein disclosed, but is capable of modification without departing from the spirit thereof and I seek protection of United States Letters Patent for the novel features and structure set forth in the appended claims.

I claim:

1. A signal type torque indicating wrench in cluding a tubular handle member, a beam member pivot-ally supported by said handle member and having a projecting portion adapted to be connected to a work head, said beam member serving to transmit torque from the handle to the work head, said beam member extending into said handle member and having a tapered end portion, a sleeve concentrically mounted within said handle member and surrounding the tapered portion of the beam with a spacing therefrom dependent upon the axial position of said sleeve with respect to the tapered portion of the beam, means for axially adjusting said sleeve with respect to said beam to adjustably vary an initial no-load movement of the handle with respect to the beam member, a signal circuit electrical contact positioned within the handle, said beam member forming a second electrical contact, axial adjustment of said sleeve member varying the point of contact to thereby vary the amount of torque load applied to said beam member to cause engagement of said contacts.

2. In a signal type torque indicating wrench mechanism, a handle member having a relatively movable work head mounted thereon, a beam-like flexure member secured at one end to said work head, said handle member being operative to transmit torque stress to said flexure member, a hollow tapered member carried by said handle member and adjustable longitudinally relative to said flexure member, said tapered member having spaced internal taper surfaces with the free end portion of said flexure member being adjacent to and between said taper surfaces, transmission of torque stress from said handle member to said flexure member being through said tapered member whereby adjustment of said tapered member is operative to determine the point of torque transmission therethrough and the extent of noload movement of said work head relative to said handle member, and indicating means operative to give a signal upon a predetermined amount of bending of said fiexure member after completion of said no-load movement.

3. In a signal type torque indicating wrench, a handle, a work head pivotally connected to said handle for relative angular movement with respect thereto, a yielding beam member secured to the work head for yieldingly transmitting torque from the handle to the work head, an abutment member associated with the handle and having a portion adapted to engage a portion of the beam member to transmit torque load to the beam member, one of said portions being inclined so that adjustment thereof relative to the other portion in a direction longitudinally of the beam member varies the point of engagement between said portions and the extent of no-load movement of said handle relative to said work head, and said portions being adapted to engage after a predetermined initial no-load movement of the handle to transmit torque load to the beam member, means for adjusting said inclined portion in a direction longitudinally of the beam member, signal means adapted to indicate the application of a selected torque to said work head, means for actuating said torque indicating signal. means upon completion of a definite and predetermined movement of said work head relative to said handle, and said latter movement consisting of said no-load movement as determined by the adjustment of said inclined portion plus a torque applying movement sufficient to complete said latter movement.

4. A signal type torque indicating wrench mechanism comprising, a hollow handle member having a work head mounted thereon for limited rotary movement relative to the handle member, a flexure member secured at one end to said work head and eXtending axially through a portion of said hollow handle member, torque transmitting means carried within said handle member for engagement with means on the other end of said fiexure member, one of said means being of tapered form so that adjustment thereof relative to the other means in a direction longitudinally of said fiexure member varies the point of engagement between said means and the extent of no-load movement of said handle member relative to said work head, signal means adapted to indicate the application of a selected torque to said Work head, means for actuating said torque indicating signal means upon completion of a definite and predetermined movement of said work head relative to said handle member, and said latter movement consisting of said no-load movement as determined by the adjustment of said means of tapered form plus a torque applying movement sufiicient to complete said latter movement.

5. In a signal type torque indicating wrench, a handle member having a, work head mounted thereon for limited rotary movement relative to the handle member, a beam-like fiexure member secured to said work head, torque transmitting means carried by said handle member and adapted for engagement with a portion of said flexure member spaced from said work head, said means being of tapered form and being adjustable with respect to said portion of the flexure member in a direction longitudinally of the latter member to vary the point of engagement between said means and said portion of the flexure member and to vary the extent of no-load movement of said handle member relative to said work head, signal means adapted to indicate the application of a selected torque to said work head, means for actuating said torque indicating signal means upon completion of a definite and predetermined movement of said work head relative to said handle member, and said latter movement consisting of said no-load movement as determined by the adjustment of said means of tapered form plus a torque applying movement sufiicient to complete said latter movement.

6. In a signal type torque indicating wrench, a handle, a work head pivotally connected to said handle for relative angular movement with respect thereto, a yielding beam member secured to the work head for yieldingly transmitting torque from the handle to the work head, abutment means associated with the handle and having a portion inclined with respect to the length of the beam member, said inclined portion being adapted to engage the beam member after a predetermined initial no-load movement of the handle relative to said work head to transmit torque load to the beam member, means for adjusting the abutment means in a direction parallel with the beam member to vary the extent of no-load movement of the handle, and torque indicating signal means responsive to a definite and predetermined extent of relative movement between said work head and said handle for indicating the application of any selected torque to the wrench handle.

7. In a signal type torque indicating wrench, a handle member for applying a torque load, a work head pivotally connected to said handle member for relative angular movement with respect thereto, a flexure means through which said torque load is applied to said work head, an adjusting means associated with said handle member and said flexure means including a tapered member selectively positionable relative to said flexure means and adapted to transmit the torque load from said handle member to said flexure means at a selected position on the tapered member whereby a no-load condition is provided for the initial movement of said handle member in a torque applying direction, the extent of said noload movement being determined by the selected position of said tapered member relative to said fiexure means, and torque indicating signal means responsive to a definite and predetermined extent of relative movement between said work head and said handle member for indicating the application of anyselected torque to the handle member.

8. A signal type torque indicating wrench comprising, a hollow handle member having a relatively movable work head rotatably mounted thereon and having a yielding means within the handle member for transmission of torque (from said handle member to said work head, means to provide a lost motion movement of said handle member relative to said yielding means in applying torque to said work head, means for adjusting the extent of said lost motion movement, signal means adapted to indicate the application of a predetermined torque to said work head, means for actuating said torque indicating signal means upon completion of a definite and predetermined movement of said work head relative to said handle member, and said latter movement consisting of said lost motion movement as determined by the adjustment of the second named means plus a torque applying movement sufficient to complete said latter movement.

MARK HA'ITAN.

REFERENCES CITED The following referenlces are or record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,122,100 Gilsey Dec. 22, 1914 1,304,423 Walker May 20, 1919 1,519,800 Riiflard Dec. 16, 1924 1,662,424 Judge Mar. 13, 1928 2,190,862 Condon Feb. 20, 1940 2,250,941 Zimmerman July 29, 1941 2,303,411 Van Horn Dec. 1, 1942 2,371,901 Livermont Mar. 20, 1945 FOREIGN PATENTS Number Country Date 636,170 France Jan. 7, 1928 675,755 Germany May 16, 19-39 679,042 Germany July 27, 1939