US2825387A - Machine for successively convoluting tubing - Google Patents

Description

March 4, 1958 c. H. ALLTOP ET AL MACHINE FOR SUCCESSIVELY CONVOLUTING TUBING 3 Sheets-Sheet 1 Filed Jan. 19, 1954 INVENTORS:

55 7/m/M ATTORNEYS.

March 4, 1958 c. H. ALLTOP ET AL 2,825,387

MACHINE FOR SUCCESSIVELY CONVOLUTING TUBING Filed Jan. 19, 1954 5 Sheets-Sheet 2 23% MM wa wm w ATTORNEYS.

United States Patent MACHINE FOR SUCCESSHVELY CONVOLUTIN G TUBING Ceril H. Alltop and Garold K. Logsdon, Elgin, 11]., as-

signors, by mesne assignments, to Dunbar Kappie, Inc Geneva, 11]., a corporation of Illinois Application January 19, 2.954, Serial No. 405,il61

Claims. (Cl. 153-73) This invention relates to a new and improved machine for forming annular convolutions in metal tubing. Tubing thus convoluted is useful in making up flexible metal conduit or hoses, for example.

One object of the present invention is to provide a machine adapted to form an annular convolution in a length of tubing and then to advance the tubing in an improved manner so that succeeding adjacent convolutions may be formed.

Another object of the invention is to provide a machine of the foregoing character having improved means for positively and accurately advancing the tubing so that the successively formed convolutions will be regularly spaced along the tubing.

It is a further object to provide a convoluting machine having improved means for engaging each newly formed convolution and advancing the tubing into position for the formation of an adjacent convolution.

Another object is to provide a convoluting machine in which the advancing of the tubing is accomplished in a minimum of time.

A further object of the invention is to provide a convoluting machine having an improved control system for coordinating the operations of the machine.

It is another object to provide an improved convoluting machine achieving a high rate of production while obviating any possibility of damage to the machine due to improper adjustment or operation.

Further objects and advantages of the invention will appear from the following description of an illustrative embodiment of the invention, as shown in the accompanying drawings, in which:

Figure 1 is a general side elevational view of a convoluting machine constructed in accordance with the invention, certain parts being shown in section and others being removed for clarity of illustration.

Fig. 2 is a fragmentary enlarged transverse elevational sectional view taken generally along a line 22 in Fig. 1.

Fig. 3 is a view similar to Fig. 2 but with certain parts of the machine in changed positions.

Fig. 4 is a fragmentary horizontal sectional view taken generally along a line 44 in Fig. 2.

Fig. 5 is a view similar to Fig. 4 but with certain parts of the machine in changed positions.

Figs. 6-10 are sectional views illustrating successive stages in the convoluting of tubing. Fig. 6 shows the tubing before being convoluted. Fig. 7 illustrates the tubing in place on the machine. Fig. 8 shows an initial step in the formation of a convolution by means of certain die parts on the machine. Fig. 9 illustrates the final stage in the formation of a convolution. Fig. 10 showsthe tubing formed into a flexible metal hose having several convolutions.

Fig. ll is a wiring diagram illustrating the electrical control arrangement for the machine.

Considered in greater detail, the drawings illustrate a convoluting machine 10 capable of forming narrow "ice annular convolutions or loops 12 in ordinary cylindrical sheet metal tubing 14 so as to convert the tubing into flexible metal conduit or hose 16 of the type shown by way of example in Figure 10. In the present case, the machine 10 is constructed with a supporting frame 18 comprising a pair of adjacent horizontal beams or main members 20.

To receive and support the cylindrical tubing 14 while it is being convoluted, the machine is provided with an elongated, tubular, horizontal arbor 22 supported solely at its rear end in a heavy block 24 mounted on the rear ends of the main beams 20. In this way, the front end of the arbor 22 is left free so that the tubing 14 may be slipped over the arbor.

The individual convolutions are formed in the tubing 14 by means including a hollow female die 26 of annular configuration disposed around one end of the arbor 22. An annular inwardly opening die cavity 28, formed in the interior of the die 26, determines the shape of the convolutions. To provide for radial and axial opening of the die 26, it is formed with four parts 30, 31, 32 and 33. In order that the die 26 may be opened radially, the left hand parts 363 and 32 are mounted on a slide 36 while the right hand parts 31 and 33 are mounted on a slide 37. Both slides are movable laterally relative to the arbor 22 along stationary undercut ways 38 formed on a supporting bed 40. It will be seen that the bed is mounted on the front ends of the beams 20. To provide for axial opening of the die 26, the front parts 30 and 31 are mounted on longitudinally movable slides 42 and 43, while the rear die parts 32 and 33 are mounted directly on the laterally movable slides 36 and 37. In this case, the slides 42 and 43 are movable along undercut ways 44 and 45 formed on the slides 36 and 37. Upright die holders 46, 47, 48 and 49 are mounted on the slides 42, 43, 36 and 37 to support the die parts 3ti33.

For the purpose of effecting radial opening and closing of the die 26, the convoluting machine 10 is equipped with suitablepower actuating means, such as the illustrated double-acting fluid cylinders 52 and 53, connected to the die holders 46 and 47 on the laterally movable slides 36 and 37, the cylinder being operated by air in this instance, although hydraulic actuation would also be suitable for these cylinders and the others to be described shortly. Axial opening and closing of the die 26 is effected by means of a similar double-acting air cylinder 54 mounted underneath the beams 20. To connect the air cylinder 54 to the axially movable slides 42 and 43, a generally vertical lever 55 is pivotally mounted on the beams 20 and is pivotally connected at its lower end to the air cylinder. A link 56 is connected between the upper end of the lever 55 and the slides 42 and 43, the connection being such as to permit the lateral movement of the slides. In this case, the rear end of the link 56 may be connected to a cross bar 57 slidably received in a pair of slots 58 formed in the front ends of the slides 42 and 43.

To expand the cylindrical wall of the tubing 14 into the cavity 28 in the annular die 26, the outer end of the arbor 22 is fitted with an expansible die 60, in the form of a compressible rubber disk disposed between a pair of collars 61 and 62. The rear collar 61 may have a reduced portion 63 fitted within the outer end of the hollow arbor 22. In order that the tubing 14 may he slipped easily over the arbor 22, the front collar 62 may be tapered forwardly.

To compress the rubber die and thereby expand it outwardly into the die cavity 28, a rod 66 is arranged to extend through the arbor 22, the die 63 and the collars 61 and 62. The outer endof the rod 66 is fitted with a Patented Mar. 4, 1958 V pair of nhts 67 to provide the outer collar 62.

an abutment engageable with The rod 66" is actuated'in this instance by means of a double; acting aircylinder17 flmountedunder: the beams 205mg the re a-r end rot-ttheearbor -22 A lever 71; pivotally;

' mounted ong the block- 24, ;is; piyotallyconnected Qadjav cent its; oppositegends to thei'rod --6f and the air: cylinder e 170;, theear rangement-of the-lever, arms being such :as :to

providea considerablemechanicalcadvantage tor: compressing the rubber die 60.

s Afterr'the 1( 11 68 '26'3Ild ;60 --have formed an annular: cot

volution -tlieitubing 14;-is:indeXed along :thearbori22 by? V an 'indexing meehanisnrz 74 comprising a sleeve-'75: disposed around i-the arbor j;22-, immediately; to; the; rear; of

that it willgreceive. the tu'hingzletwith asliding; fit. tRe-V- ciprocation of the sleeve 75 may begefiectediby means-oft adouble acting jaincylinder 76iconnect-ed to -the lowerend of ta lever'77ibyimeans 'ofI-ailink 78;, Two links 79; are

employedftojconneetthe bifurcated'npperiend of th'e lever 77; to the sleeve-75: After'the, dies: 261311611 601have formed -a-. convolution,- the sleeve 75 is; advanced so as to engage the;convolution and move :the. tubingtld into positron for the, formationof another. adjacent convolution.

.Compressed:air 'to-operate' the:machine 10 is obtained: 2

from;an:air-line181.: The operationlof the machine is controlled by; meansxof electrically'operable solenoid reversingvalves B2; 83, 84,185 and 186*connected; between the: air line 81*and the. respective airticylinders 52 53, 54,-.70;a'nd 76. The valves,, 82+86, which may. be'of'well knownconstruction; are adapted to supply? compressed air-to;the oppositezendsof the air cylinders. Each of the valves 82 86 may beyprovidediwith. a; pair .1 of solenoids- Slam c1 88.: Momentary-energization of the solenoid 87' will shift the valve into oneposition and thus supply air" toone end of; the particular cylinder; Likewise, momentar! energization' ofiithe othert'solenoidt88 will reverse the ,setting;,of; the: valve so as toksupplytair to the opposite.;.end V ofithe cylinder. In eachcase, theendof-the cylinder not supplied with air is vented through the valve to the-at mosphere.; One :end ofjthe solenoid 87-is-connected toa terminal 89. fwhile tlie -,other end is connected to a groundedterminal 901;" The: solenoid 88 :is connected 1 between the. 'groundedterminalflll andja-termina1.91. I

T :operate the air-cylinders,';52, 53, .54; 170 and 76in- V the ngroundedr transfoi'mers secondary terminal ll'l and;

' will be closed at the same time.

one ungronnded terminaltof each of the valves 82 and 83 mounted on the'air cylinders 52 and 53. Closure of the switch 121 at the beginning of the cycle of'operations will. operate the valves 82 and 83' in such a direction that the 1 cylinders 52 and 53 will move-ith'e slides 36 and 37 Ward each other and' thus will close thedie 26 i radia1ly In orderto expand the; rubber die -60 simulta-neously with the closure of the annular'diej26, the first and second cams 101' and 102*:are-arranged with their projectinglobes' 128 substantially alignediso that'the switches :121 and 12-2 The switch 122' is con- 'nected inrserieswithga lead 132 extending between'the ungrofinded transformer terminal 118'and the nngrounded terminal 91 of the solenoid valve 85. When the cam 102 closes the ,switch 122, the valve 85 will supply air to the 7 rear end of the air cylinder 70 and the cylinder will thus cause. the lever 70 tolcxerta pull on the; rod 66, soas'to compress :the rubber-die". 60.; -Asjafresultg the die; -will.. expand thetcylindrical ;wall of "the tubing-14. into theidie= 7 cavity 28. t h t Forjthe purpose of: contracting-the rublber die,60,sthe

switch 123 associated-with the third :cam 103 'is-conne'c'ted in series with a lead 133 extending between the ungrounded.

transformer terminal :118-;=and;the ungrounded terminal ,89:

of the'solenoid valves 85. The camli103 is oriented so' that itsprotruding. lobe 128 will close the switch -123after the'switches 121 and-122;have been opened. As, 8.;16Sl1lfi1; the setting of thesolenoidjvalve SS will be reversed and t 7 airv willbe 'suppliedto. the'rfront endeorf v the cylinder. r so as to push the rod 66 back into 'its initiaLposit'ion and! permit contraction of the die:60;,

in order to compress. thenewly-formed convolution V a aroially, so that it willassume itsrfinal form, the-fourth cam 1.04 is arrangedto-close the die 2 6;axially; To this end, the switch'124'is connected'in series with'lead V 134 extending between the transformer; secondary the proper sequence,. tlie:machine;10jis.provided with-a p timing device which; in" thisjnstance, comprises sev en cams,-; 101 102',.-103, 10.4; 105,106, .and: 107, driven by antelectrical motor 108r 1 As;indicated"diagrammatically in Figure 11, all-,of the cams maybe -mO11Ilt6d' On--a Sli1gl8- shaft 109. During;the:greater.part of. the cycle Of OPCIZJ" tions, the motor 108 is energized from alternating currentpower line wires-109.,and 110;. Atmaster. switch 111 may he connectedainseries :with, the line. 110 I to l control t-heenergization ofthe; motor 108 theacontrol' system i V V V 7 To supply powerfor; operating the electrieal valv'es '82- and the: other elements 0f 86,, the: illustrated: control: system ism equipped with three step, down transformers .114; 1151an l 116-having the endsof.their primary-windingsconnected to the line' wires 109 V and 110.. Each of the transformers 114116-has-its sec-- ondarywinding arrangediwith one end grounded; The

' other: ends of thetwindihgs arejbrought outto ungrounded terminals 117, 118tand 119.2 V

7 To control; the, energization of; the -eleotrical valves- 82-86, ;thercams 101 101 are arranged to' operaterespectiveanormallyopen switches 121=, 122, 123; 124;;125; 126

and 127; Each of the cams l0'l -lj07 is provided with 1 a projecting cam 1obe1 28 'adapted-to-effect momentary closure of the corresponding switchr g In this instance, the 'firs'tcamf 101is employedto iiiitiate the: cycle of operationseby closing-*the die' lfiFradl' Y" V To this end, the switch 121 associated with-tliis= 10 is connected in series with a lead -1311 extendingbetweem terminal 119'and one ungrounded terminal of;the sole-j neid valve 84.. The cam-10.4 is arranged to close the switchv 124- afiter' the die} 60 has beencontracted by the" operatiomof thcswitch 123,; Theclosureofthe'switch '12;4will result in shifting ofthevalve Sd-to such a P051- 1 tion-:that-the cylinder s -a-Wlll movethe front die-parts 30and31toward the rear die parts 32 and 33,; iihedie parts preferably are brought into closely COHtlgllQllSlP: lation butnot into actual engagement in order to avo d an'impactbetween the die parts. a

The axialclosing of 7 7 tion of the convolution '12and thus the next stepis to openttheadielfi so thatthe tubiri'gldmay be advanced into position fbrjthe'formation, of anothervconvolution. For this: purpose; g hierfi fih andsixthi cams 1057' and ,106

terminal 117" andtofie nsroundd; terminal of; ca

32"from' theparts. 31"and133: The switch 126 iseon-f nected inserieswith a: lead 'ext'endingbetween the ungrounde'd transformer. terminal 119' and; one-un grouncled terminal oi'the' reversing valve 84;: Whenathe switch 126 isclosed; the valve-'84- is-shifted to1a pos'ition h that air .will beasupplied to'the'front'endof-thfe' r cylinder 54;". This; will resu1t1'in movement oftheffont;1

die parts 30 and; 31 'away'fromqh rears di Parts: 372 and33." H r t 'In orderto;advancethetubing- .14 I V the formation of 'anotlicrconvolution the switch 127, as-L sociated with the earn 107; is connected in series with-a lead, 137 extending between the ungroun'ded transformer;

v terminal=- 118} and "oneungrounded terminalj on; the

solenoid reversing valve 86"mounted on theindexingi;

cylinder-16., The seventhfcam-107,is 'oriented'soasf to close". the "switch 12.7 aftenqthei-diehas heen openedzthe diefZQcdmpletes the forma into 7 position for radially and axially by the operationof the cams 105 and 105. When the switch 127 is closed, the cylinder 76 will advance the indexing sleeve 75 into engagement with the newly formed convolution 12. The stroke of the indexing cylinder 75 is such as to advance the tubing 14 into position for the formation of another convolution.

When the sleeve 75 is thus advanced it moves into the annular die 25 and thus is vulnerable to damage in the event that the die should close prematurely. However, in accordance with aspect of the present invention, the machine is arranged so that closure of the die 26 will be prevented until the indexing sleeve 75 has been fully withdrawn. This is true even though the movement of the sleeve '75 may be retarded due to friction, low air pressure or any other cause. To prevent closure of the die 26, a rear limit switch 146 is arranged to be held closed when the sleeve 75 is in its normal retracted position. As shown, the switch 14%; may be operated by the upper end of the lever 77. in this instance, the switch 14 is connected in a series circuit 141 which includes the timing motor 168 and is con nected between the power lines 16? and 115). When the cylinder 76 advances the sleeve 75, the switch 149 will open and thus will stop the motor 198. The operation of the motor 168 will not be resumed until the sleeve 75 again returns to its fully retracted position. Only then will the cam'lill be advanced to a position such as to close the switch 121 controlling the closure of the die 26.

It will be understood that the closure of the sleeve advancing switch 127 by the cam it?! is only momentary, such momentary closure being sufiicient to shift the valve 86. Even before the motor 198 is stopped by the opening of the rear limit switch 146, the cam M7 is advanced to a point such as to open the switch 127 and thus condition the valve 36 for a subsequent reversal.

In order to provide for retraction of the sleeve '75 even though the timing device 1% has been disabled, a front limit switch 143 is arranged to be closed when the sleeve 75 has been fully advanced. In the illustrated construction, the switch 143 is operated by the upper end of the lever 77. In this instance, the switch 143 is in series with a lead 144 connecting the ungrounded transformer terminal 113 to one ungrounded terminal on the solenoid reversing valve :35. Thus, the closure of the front limit switch 143 will be effective to reverse the valve 85 and thus initiate retraction of the sleeve 75.

With the sleeve 75 retracted, the rear limit switch 149 will again be closed to start the motor 193 and initiate another cycle of operations. repeated indefinitely until the desired number of convolutions 12 has been formed in the tubing.

Although the operation of the machine has already been described and will be clear from the foregoing description, a brief resume may be of some assistance. Initially, a length of the tubing 14 is slipped over the outer end of the arbor 2-2. Closure of the main switch 111 will then initiate a cycle of operations. The first step in the cycle is to close the die 25 radially and simultaneously expand the rubber die 69. The cams 101 and 102 initiate these operations by closing the switches 121 and 122 to shift the valves 32, S3 and 35 so that the cylinders 52 and 53 will close the die 26 and the cylinder 7% will expand the rubber die 6%.

Radial closing of the die 26 and expansion of the rubber die 66 results in the formation of a convolution which is wider and smaller in diameter than the desired final form. in order .to compress the convolution axially so that it will become narrower and larger in diameter, the rubber die 66 is first ccntratced by operation of the cam 103. Then the annular die 26 is closed axially by the action of the cam 104, which closes the switch 124 and thus initiates operation of the air cylinder 54 so as to move the front die parts 3% and 31 into contiguous relation with the rear die parts 32 and 33.

The cycle may be Next in the cycle, the cams and 107 act simultaneously to open the die 26 radially and axially through the medium of the air cylinders 52, 53 and 54. After the die 26 has been opened, the cam 107 closes the switch 127 and thus causes the air cylinder 76 .to advance the indexing sleeve 75 so that it will engage the newly formed convolution move the tubing forwardly on the arbor 22 into position for the formation of another convolution.

initial forward movement of the indexing sleeve 75 opens the rear limit switch 14% and thereby stops the timing motor 1% so that the advancing movement of the cams 161ltl'l will be suspended. In this way, premature closing of the die 26 is prevented. However, there is sufficient delay in the operation of the valve 86 and the air cylinder 76 to permit the cam switch 127 to open before the motor 1% stops. Thus when the indexing lever 27 closes the front limit switch 143 at the completion of the indexing movement, the valve 86 will be reversed and the sleeve 75 will be retracted. This will again close the rear limit switch 149 to initiate another cycle of operations.

it will be evident that the arrangement of the limit switches and 143 positively obviates any possibility of damage to the indexing sleeve 75 due to premature closing of the annular die 26. Moreover, the use of the front limit switch 143 to initiate retraction of the sleeve 75 results in the tubing being indexed in the minimum possible time. Because of the safety feature provided by the rear limit switch 149, the cams may be set so that the first switch 121 will be closed immediately after the motor 108 is started. in this way, there will be a minimum of delay in the initiation of each cycle of operations.

While details of the exemplary machine have been described and illustrated it will be understood that there is no intention to limit the invention to such details. Rather the invention is to cover all modified constructions, alternatives and equivalents falling within the spirit and scope of the invention as defined in the following claims:

We claim as our invention:

1. A machine for convoluting tubing comprising an arbor for receiving the tubing, a hollow annular die around one end of said arbor, said annular die having a plurality of parts arranged for radial and axial opening of said die, a plurality of reciprocable fluid motors for opening said die axially and radially, an expansible die at said one end of said arbor in the form of an axially compressible and radially expansible rubber disk for expanding the tubing partway into said annular die and thereby partially forming a convolution, means including a draw rod extending through said disk and said arbor for compressing said disk, a reciprocable fluid motor connected to said draw rod for expanding and contracting said disk, a sleeve disposed around said arbor for receiving the tubing, means including a reciprocable fluid motor for reciprocating said sleeve along the tubing to enter said annular die, engage the newly formed convolution and advance the tubing into position for the formation of an adjacent convolution, control means for controlling said fluid motors and including a plurality of electrically operable control valves therefor, a plurality of timing cams, an electrical motor for driving said earns, a plurality of switches operable by said cams and connected to said valves for sequentially closing said annular die radially, expanding and then contracting said expansible die, closing said annular die axially to complete the convolution, opening said annular die radially and axially and advancing said sleeve, a rear limit switch operable by initial advancing movement of said sleeve for disabling said electrical motor and thereby preventing premature closure of said annular die and a front limit switch operable by complete advancement of said sleeve for retracting said sleeve.

2. A machine for convoluting tubing comprising an arbor for receiving a length of the tubing, a hollow radially and axially openable annular die around one end of said arbor, an expansible die within said annular die and on sai ene efid ofi said anb'o'r for-fexpanding 'the-tubingpartfor fon'nation'tof' an' adjacen't convolution, control means forsuccessively; closing said annular die radially, expand-. ingandfthen contracting saidexpansible die, closing said aimul'a'r'die axially,' sai'd" convolution thereby being corn- 7 pleted opening said annular die radially and advancing 7 said isleeve, means operable by initial advancing movement ofisai'dsleevefor disabling said controlnieans and thereby preventing closu're of said annular die, and means for retrach'ng said sle'eveand 'reinitiating operation of said" control means;

3. A" machineifor 'convolutin'g tubing comprising anf arborfor receiving thei'tubing, a hollow annular radially and'airially openablejdie around one endof saidarbor, arr eXpansi-b leydi'e withi sai'd annular die and on said one end of"s'aid'a'rb'or for'expanding the'tubing partway into saidjannular' diejand thereby partially forming a convolutionin the;t ubing,a sleeve reciprocable on said arbor; and receivable over thetubing forengagin'g the newly formed convolution and advancing the tubing into position for formation of a succeeding convolution, control'means forsuccessivelyclosing-said annular die radially, expanding;- said expansible die, contracting said. expansible' die closingsaid annular dieaxially, said con 'v'olutiion therebybeingcompleted, opening said annular 7 die radially and advancing said sleeve, meansv operable f V by initial advancing-movementof said sleeve to suspend operation of saidcontro'l means to' prevent closure of said annulardie; and-meanso'perable at the completion of the-advaneing' movement of said sleeve for retracting said sleeve and'thereby reinitiating operation of said controlmeans. 1 a g 4. A machine for' convoluting tubing comprising an arbor for receiving the tubing-,a'hollow' annular die around one'end of saidarbor, said annular vdie having a plurality-of parts arranged for-radial and axial" opening of-"saijd f'die power means for opening saiddie radially, an expansible die at said one end-of said arbor for expanding the tubing partway into said' annular die and thereby partially forming a convolution, power meansfor expanding andi contractingsaid expansible die, a sleeve- 7 V disposedaround said-arbor for receiving the tubing, power 1 means for' reeiprocating said sleeve along the tubing to enterflsaid annular die, engage' the 'newly formed con-- volution and advance the tubing into position for the clos'in'gl said annular die radially, expanding iandithfefi 8 formatiofi of an adjaeent convolutidn, I control 'r'necontrolling re'lation to said powerineans foresequen a y contracting 'said er'rpansible die, closing said j'annular axially, said convolution thereby being completed; open; 7

ing said annular'die radially and advancingsaid isleevega rear; limit control device operable by initial advancing movement of said sleeve for disabling said control means? and thereby preventing premature closure of said annu lar die and a front ,limit control device operable b complete advancementof said sleeve for etfectin'g reg tractionof said sleeve and; thereby reinitiating operation of'saidcontroltmeansp i r V '5'. A machine for convoluting tubing comprising an arbor for receiving the tubing, a hollow annula'r die around one, end of said arbor, said annular die having'alf V plurality of parts arranged for radial and axial openi of said die, power means" for opening said dieaxi rand radially, an expansible die atrsaid one end offsa" j arbor in the form ofan axially compressible and radia expansible'rubber disk' for expanding the, tubing'fkp way into said annular die and thereby partially form ng. a convolution, means including a draw'rod extending; through said disk and said arbor for compressing, said disk, power means connected to said draw rod'for ex: panding and contracting said disk, a sleeve disposed: around said arbor for receiving the tubing,'power n1eans. for reciprocating said sleeve along the tubing to enter; said annular die, engage the newly formed convolution and advance the tubing into position fortthe, formationo fan adjacent convolution, timing means in controlling relation to said-power means for sequentially closing}, said annular dieradially, expanding and then contrac ta ing said eX-pansible die, closing said'annular die axially a to complete the convolution, opening said annular die radially and. axially and advancing said sleeve, a rean thereby preventing premature closure of saidannular;die V and a front lmiit control device operable byrcompleten advancement of said sleeve. for retracting saidsleeve;

7 References Cited in the file of this' patent o 7 'UNTTED STATES PATENTS Fentress Dec, 22; V I 2,581,787 Dreyel l 'Jan. 8, 191521 De Mers Dec. 11,1956

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