US3557597A

US3557597A - Riveting apparatus

Info

Publication number: US3557597A
Application number: US666876A
Authority: US
Inventors: Victor Lorraine Heslop; Leonard Saunders
Original assignee: Aerpat AG
Current assignee: Aerpat AG
Priority date: 1966-09-16
Filing date: 1967-09-11
Publication date: 1971-01-26
Anticipated expiration: 1988-01-26
Also published as: GB1183049A; SE346479B; DE1627404B2; DE1627404A1

Abstract

A REPETITION BLIND-RIVETING GUN, OF THE TYPE IN WHICH A COLUMN OF TUBULAR RIVETS IS CARRIED ON A MANDREL HAVING AN ENLARGED HEAD WHICH IS PULLED THROUGH EACH RIVET IN TURN TO EXPAND IT, HAS A PNEUMATICALLY-OPERATED DEVICE FOR FEEDING THE COLUMN OF RIVETS FORWARD AFTER EACH OPERATION. THIS DEVICE COMPRISES A PISTON, SLIDABLE ALONG THE MANDREL, TO THE REAR SIDE OF WHICH COMPRESSED AIR IS SUPPLIED ONCE IN EACH CYCLE OF OPERATION OF THE GUN. THERE MAY ALSO BE PROVIDED A RELIEF VALVE FOR AUTOMATICALLY VENTING TO ATMOSPHERE THIS COMPRESSED AIR SUPPLY IF THE MANDREL IS NOT SECURELY GRIPPED BY THE JAW-MECHANISM WHICH HOLDS IT IN THE GUN.

Description

Jan. 21s,` `1971 Filed Sept. 1l, 1967 V. L. HESLOP ET AL RIVETING APPARATUS 2 Sheets-Sheet l Jan. 26, 1971 v. L. HEsLoP ETAL RIVETING APPARATUS 2 Sheets-Sheet 2 Filed sept. 1,1, 1967 Claims priority, application Great Britain, Sept. 16, 1966 United States Patent O 3,557,597 RIVETING APPARATUS Victor Lorraine Heslop, Welwyn Garden City, and Leonard Saunders, Hatfield, England, assignors, by mesne assignments, to Aerpat A.G., Zug, Switzerland a company of Switzerland Filed Sept. 11, 1967, Ser. No. 666,876

Int. Cl. B21d 9/05 U.S. Cl. 72-391 12 Claims ABSTRACT OF THE DISCLOSURE mandrel is not securely gripped by the jaw-mechanism which holds it in the gun.

The invention relates to riveting apparatus, and more particularly to riveting apparatus of the kind which comprises: a mandrel adapted to carry a plurality of tubular rivets thereon and having an enlarged head which is pulled through each rivet in turn to set it by expanding its tail; jaws through which the mandrel extends, the jaws and the mandrel being relatively reciprocable axially of the mandrel during use of the apparatus thereby to provide a feed stroke during which the leading rivet passes through the jaws which then close to provide an abutment for the head of the rivet, and a working stroke during which the mandrel head and the jaws move relatively towards each other to expand the tail of the rivet; and rivet feeding means for automatically feeding rivets one at a time through the jaws.

Such a riveting apparatus is hereinafter referred to as riveting apparatus of the kind specified.

The invention provides, in one of its aspects, riveting apparatus of the kind specified in which the feeding means is arranged to provide a thrust on at least the leading rivet sufficient to pass it through the jaws during the feed stroke whilst exerting a compressive thrust on the mandrel which is less than the aforesaid sufficient thrust and less than the maximum compressive thrust which the mandrel can sustain without distortion.

The invention provides, in another of its aspects, riveting apparatus of the kind specified in which the rivet feeding means is arranged to provide a thrust on at least the leading rivet` sufficient to pass it through the jaws during the feed stroke without exerting any compressive thrust on the mandrel.

The invention provides, in another of its aspects, riveting apparatus of the type specified including power means for relatively reciprocating the jaws and mandrel, which power means are at least partially pneumatic, in which apparatus the rivet feeding means is pneumatically operated,

(The terms pneumatic and pneumatically are used in this specification to include the use of increased or reduced pressure of any suitable gas, unless the context demands otherwise.)

It is preferred that the riveting apparatus includes pneumatic control means for automatically operating the ice rivet feeding means in accordance with the relative axial position of the jaws and mandrel so as to pass the leading rivet through the jaws during each feed stroke.

Where the riveting apparatus includes a barrel or other tube-like member in fixed axial relationship to the jaws and through which the mandrel extends, the pneumatically operated feeding means preferably comprises a piston member slidable within the tube-like member and around the mandrel, and means for applying pneumatic pressure to the side of the piston member remote from the jaws.

Preferably the said means for applying pneumatic pressure includes the aforesaid pneumatic control means.

Preferably the pneumatic control means comprises a valve member reciprocable in unison with the mandrel along the tube-like member to co-operate with pneumatic port means carried by or in the tube-like member, thereby to apply pneumatic pressure as aforesaid in accordance with the relative axial position of the jaws and mandrel. Preferably the arrangement is such that pneumatic pressure is applied as aforesaid when the mandrel is positioned relatively to the jaws more than a predetermined extent in the direction opposite to that in which rivets are fed (i.e. at the beginning of the feed stroke).

Preferably the arrangement is such that after an initial application of pneumatic pressure, the pressure decays due to leakage. For example, it may be arranged that leakage occurs between the piston member and the mandrel, and/or the piston member and the tube-like member.

When the riveting apparatus includes a barrel or other tube-like member in fixed relationship to the jaws and through which the mandrel extends, and the pneumatically operated feeding means comprises a piston member slidable within the tube-like member and around the mandrel and means for applying pneumatic pressure to the side of the piston member remote from the jaws, preferably the rivetin-g apparatus also includes mandrel gripping means for receiving and gripping the tail end of the mandrel, and pressure prevention means, operated by the mandrel-gripping means, to prevent the application of pneumatic pressure to the side of the piston member remote from the jaws automatically if and whenever a mandrel is not received and gripped by the mandrelgripping means.

Preferably the pressure prevention means comprises venting means for venting or relieving any pneumatic pressure.

Where the mandrel-gripping means comprises externally-tapered jaw members urged into an internallytapered housing so that the jaw-members are urged to close together to grip a mandrel received between them, the pressure prevention means is preferably responsive to the extent to which the jaw-members enter the housing which depends upon the presence or absence of a mandrel between the jaw-members. The said responsive means may comprise valve means including a valve member which is normally biassed into one position and arranged to be moved to a second position by the jaw-members when they enter the housing to the increased extent allowed by the absence of a mandrel between them.

Where the mandrel-gripping means is pneumatically actuated to grip a mandrel, there may be provided common valve means controlling the pneumatic supply to both the aforesaid pneumatically operated rivet feeding means and to the mandrel-gripping means.

Two specific embodiments of the invention will now be described by way of example and with reference to the accompanying drawings, in which FIGS. 1 and 2` are both axial longitudinal sections through a riveting gun.

The riveting gun illustrated in FIG. l includes a mandrel 11 extending substantially throughout the length of the gun, and having an enlarged head 12. A plurality of tubular rivets 13 are threaded on the mandrel, and the head 12 is pulled through each rivet in turn to set it by expanding its tail. These rivets are of the type well known in many countries under the trademark Chobert. The gun has jaws 14 through which the mandrel etxends, the jaws 14 and mandrel 11 being relatively reciprocable axially of the mandrel during use of the gun. The jaws 14 are spring urged together to close behind a rivet which has been fed through them, so that its head end abuts against them. A tube-like member in the form of a barrel 15 extends through the gun, along most of the mandrel 11, except for a short length at each end of the mandrel. The jaws 14 form part of a jaw assembly 16 which is screw-threaded at 17 to the end of the barrel 15 nearer the head 12 of the mandrel. The rear end 18 of the mandrel 11 is securely gripped in a chuck 19 which is mounted by means of an axially adjustable device 21 and a mounting boss 56 on the rear end wall 24 of the main body casing 22 of the gun. The body casing 22 comprises a cylindrical shell 23, a rear end wall 24 and a front end wall 25. The interior of the main body 22 is divided axially into three cylinder spaces 26 by means of xed liners 27 and partitions 28. Three pistons 29 are secured to the barrel 15 to co-operate with the three cylinder spaces 26. The barrel is urged rearwardly with respect to the mandrel and main body casing of the gun by means of a strong helical compression spring 31 working between the front end of the front body member and the nearest piston 29. Thus the spring 31 urges the jaws 14 rearwardly (i.e. in the opposite direction to which rivets are fed through the jaws), with respect to the mandrel 11, into the position which is shown in the accompanying drawing.

The triple piston and cylinder arrangement forms part of pneumatic power means for reciprocating the barrel and jaws with respect to the mandrel.

Secured to the bottom of the main body casing 22 is a handle casting 32 which forms a pistol grip for the gun. A compressed air supply hose (not shown) is attached to the gun by means of a connector in the pistol grip. From this compressed air is supplied, under the control of valve means '33, through a main supply conduit 34 in the top of the handle casting and through three separate bores 35 in the liners 27 to the space between each partition 28 and the piston 29 adjacent to it. The valve means 33 includes a valve member 36 movable axially by pressure of the operators finger on a trigger button 37. The valve member 36 is urged by means of springs 38 and 39 into the position shown in the accompanying drawing, in which it prevents the feeding of compressed air to the three pneumatic cylinders. When the trigger button 37 is depressed, the valve member moves axially to admit compressed air to the three cylinders. The barrel 15 and jaws 14 are thereby driven, against the urging of spring 31, forwardly with respect to the mandrel 11, thus pulling the mandrel head 12 through the tail of the leading rivet 41 which is outside the jaws 14. This expands the tail of the rivet and upsets the rivet in the hole in the workpiece in which it is located. This movement of the gun constitutes the working stroke. When pressure on the trigger button 3`7 is released, the supply of compressed air to the cylinders is cut off and the barrel 15 and jaws 14 return, under the urging of the spring 31, to the position shown in the accompanying drawing. This constitutes the feed stroke, during which the next leading rivet is fed through the jaws.

The gun in this example has pneumatically operated rivet feeding means which operates by pneumatically applying a thrust to the column of rivets on the mandrel at the beginning of, and during part of, the feed stroke.

The pneumatic feeding means includes a piston member 42 which is slidable along the mandrel behind the column of rivets and inside the barrel 15. The piston 42 is a suticiently close fit inside the barrel and around the mandrel that when pneumatic pressure from the compressed air supply to the gun is applied to the rear of the piston suflicient thrust is provided to force the leading rivet through the spring-loaded jaws 14. However it is arranged that there is suicient leakage of air around the piston and between the piston and the mandrel that the compressed air applied to its rear can slowly leak away. A helical compression spring `43 is provided between the rearmost rivet and the leading side of the piston, through which the thrust is transmitted from the piston to the column of rivets. The leading side of the piston has an internal taper 44 for receiving and locating the adjacent end of the spring 43, while the rear side of the piston, to which the pneumatic pressure is applied, is counterbored at 45 so that only a small annular land 46 remains to seal (or nearly seal) around the mandrel. The periphery of the piston also has a shallow axial groove intermediate its ends thereby to leave two small annular lands 47 to seal (or nearly seal) against the barrel 15. The short axial length of the three

annular lands

46, 47 and 47 allows the above mentioned leakage of air past the piston.

In order to supply pneumatic pressure to the rear of the piston 42, a bore 48 is provided in the handle casting 32, connecting the valve means 33 with a further bore 49 running along the handle casting, parallel to but spaced apart from the passage 34, towards the rear end of the gun. The passage 49 communicates with a further radial bore 51 through the rear end wall 24 of the main body casing. A further radial passage 53 through the rear wall 24 communicates with a short axial passage 54 and thereby with the space 5S around the rear end of the barrel 15 and inside the mounting boss 56. Secured to the chuck mounting device 21 and the mounting boss 56 is a forwardly extending plug -57 in substantially sealing relationship with the rear end of the mandrel. The forward end of this plug has a circumferential groove in which is seated an O-ring seal 60 which seals with the plug and also seals slidingly with the inside of the rear end of the barrel 15. A port 58 in the rear end of the barrel communicates, by a further port 59 in a rearward extension of the rear end wall 24, with the space 55.

The operation of the pneumatic rivet feeding means and the pneumatic control means therefor is as follows. The arrangement of the bore 48 with the valve means 33 is such that, when the trigger button 37 is not depressed (i.e. when it is in the position shown in the accompanying drawing) the bore 48 communicates with the compressed air supply from connector 30, so that compressed air is fed into the space and through the barrel port 58. However, the positioning of the barrel port 58 with respect to the O-ring seal 60 is such that when the gun is at the beginning of a working stroke (which is the normal condition of the gun when it is not actuated and is the condition shown in the accompanying drawing), the seal 60 lies between the port 58 and the piston 42, thereby preventing the application of pneumatic pressure to the piston. The arrangement of the bore 48 with respect to the valve means 33 is also such that, when the trigger button is depressed to produce a working stroke of the gun, the valve member 36 cuts off the supply of compressed air to the bore 48. Consequently, when, during the working stroke of the gun, the barrel 15 moves forwardly with respect to the mandrel so that the barrel port 58 moves to a position between the O-ring seal 60 and the piston 42, there is no supply of compressed air behind the barrel port 58 so that pneumatic pressure is not applied to the piston 42 during the working stroke of the gun. (Any residual air pressure in the space 55 and its associated conduits is insucient to have any substantial effect on the piston 42.) When the working stroke has been completed and the rivet is set, the release by the operator of the trigger button 37 not only allows the barrel to return under the urging of spring 31 to its original position as previously described, but also reconnects the bore 48 to the gun compressed air supply and consequently reconnects the compressed air to the space 55 and to barrel port 58. When this reconnection of compressed air occurs, at the beginning of the feed stroke, the barrel port 58 is, as previously explained, between the O-ring seal 60 and the piston 42. Consequently the compressed air applies pneumatic pressure to the rear of the piston 42, thus transmitting suflicient thrust through the spring 43 to the column of rivets on the mandrel to pass the next leading rivet through the spring-loaded jaws 14 as the jaws move rearwardly with respect to the mandrel under the urging of spring 31. As the feed stroke progresses the O-ring seal 60 again passes the barrel port 58 and seals off the supply of compressed air to the rear of piston 42. Any residual air pressure in the space between the piston 42 and the O-ring seal 60 leaks away around the'piston 42, as previously explained, so that by the time the barrel and mandrel have returned to the relative positions illustrated in the accompanying drawing, there is substantially no pneumatic thrust on the piston 42.

The rivet feeding means previously provided on' such guns have relied upon the axial thrust imparted to the mandrel, in the direction towards the mandrel head, by the chuck 18, to force the rivets towards the jaws and pass the leading rivet through the spring-loaded jaws. When using a riveting gun for small diameter rivets, which is itted with a correspondingly small diameter mandrel, such a rivet feeding means can cause the rear part of the mandrel to distort or even collapse under the thrust required to force the leading rivet through the jaws. The gun described in the foregoing example, incorporating the pneumatic feeding means as described, is advantageous in that no compressive thrust is applied to the mandrel during the feed stroke, the thrust required to force the leading rivet through the jaws being applied to the rivet quite independently of the mandrel.

The cutaway portions of the piston 42 reduce the mass and inertia of the piston. This low inertia is advantageous. When a rivet is set and the mandrel head pulled through the rivet, the mandrel head is suddenly released and iiies back through the jaws and strikes the tail end of the next rivet inside the jaws. If the piston and column of rivets have a high inertia, they will resist movement and the rivet struck by the mandrel head may be prematurely expanded. The low inertia of the piston helps to reduce this possibility.

The riveting gun illustrated in FIG. 2 is a modification of that illustrated in FIG. 1. It is essentially the same in construction and illustration as that illustrated in FIG. 1, and only the differences between the two guns will be described.

The two major differences of the gun illustrated in FIG. 2 from that illustrated in FIG. l are firstly that it has a pneumatically operated mandrel-gripping means in the form of a chuck mechanism 61, and secondly that the arrangement for the supply and control of the compressed air to the gun are rather different. As in the previously described example gun, the chuck comprises a pair of externally tapered jaw members 62 urged into an internally tapered housing 63 to close together to grip the end part 18 of the mandrel between them. However, in the gun illustrated in FIG. 2 the jaw members 62 are urged into the tapered housing 63 by pneumatic pres` sure against the urging of a hedlical compression spring 64 which surrounds the jaw members. The rear end of the jaw members are held in a plunger 65 with an O- ring seal 66 around its periphery which seals against the walls of a bore 67 in the rearward extension 68 of the boss 56a at the rear of the gun which contains the chuck mechanism. The jaw housing 63 has an externally extending annular ange 69, the forward side of Iwhich abuts against an annular .shoulder 71 in the bore 67 and against the other side of which acts one end of the spring 64. The other end of the spring 64 acts against the plunger 65 which carries the rear of the jaw members. The space in the bore 67 behind the plunger 65 is sealed by an end plug 71 through which compressed air can be supplied by a pipe connection 72. When compressed air at a suitable pressure is thus applied to the rear of the plunger 65, the urging of the spring 64 is overcome and the jaw members 62 are urged into the tapered housing (Le. from right to left as viewed in FIG. 2) and forced together to grip the tail end 18 of the mandrel received between them. Each jaw member is provided 'with a hardened steel pad 73 having a serrated face to firmly grip the mandrel. When a mandrel is thus gripped between the jaw members, the extent to which the jaw members can enter the tapered housing is restricted by the fact that the mandrel between them does not allow them to close beyond a certain extent (Le. the position illustrated in FIG. 2). If there is no mandrel between the ja=w members when compressed air is applied through the pipe 72 to actuate the jaw members, the jaw members will move further into the tapered housing (i.e. further to the left as viewed in FIG. 2). In this example of the invention, this further movement of the jaw members when there is no mandrel between them, is utilized to vent to atmosphere the compressed air which is applied to the rivet feeding mechanism, thereby preventing operation of the rivet feeding mechanism if the mandrel is not received and gripped between the jaw members. In this example, this is achieved by modifying the plug 57 of the gun illustrated in FIG. 1 so that it acts as a venting valve which is opened if the jaw members move too far into their housing as previously mentioned. It will be seen from FIG. 2 that this valve member 57a comprises a cylindrical body portion 70 with a central bore which is a sutiiciently close fit upon the mandrel to prevent the escape of compressed air between them to any appreciable extent. The rear end of the valve member has a radially extending flange 74 the rear face of which is provided Iwith a sealing ring 75 which seats against an annular shoulder face 76 inside the housing 68. The valve member 57a is urged against this seat by means of a saucer spring 77 acting against a circlip 78. The space on the radially inner side of the port 58 and behind the O-ring seal on the member 57a is in communication with one side of the valve thus provided. The other side of the valve is vented to atmosphere between the jaw members and through a passage 79 in the wall of the housing 68.

If compressed air is applied to the rear of the plunger in order to urge the jaw members 62 into their tapered housing, and there is no mandrel between the jaw members, then the jaw members move so far into their housing (to the left beyond the position illustrated in FIG. 2) that they abut a small extension 81 on the rear of the valve member 57a and drive the member forwards (Le. towards the left as viewed in FIG. 2) against the urging of the saucer spring 77. This movement unseats the valve seal from the face 76 and so vents to atmosphere the compressed air in the space 55, thereby preventing the mandrel feed piston 42 from urging the column of rivets forwards.

The other major difference of the gun illustrated in FIG. 2 is the arrangement for supplying compressed air to the various parts of the gun for the various functions. Instead of being provided with a main trigger-controlled valve in gun handle 32, supply of compressed air for operation of the gun to set a rivet is controlled by a separate valve 82 with a control pedal 83 for foot operation. This valve is connected to the gun by means of a iexible hose 84. The valve 82 and pedal 83 are mounted in a valve block 85 arranged for connection to a main compressed air feed hose 86. The valve block 85 is also provided with a permanent connection from the main compressed air inlet 86 via a connector 87 and a further flexible hose 88 to a secondaryt control valve 89 provided with an operating handle 91. The output from this control valve 89 is fed through a T-junction 92, firstly via a flexible hose 93 to a connector 94 supplying compressed air to the space 55 for operation of the rivet feeding mechanism, and secondly through a flexible hose 98 and connector 72 for operation of the mandrel-gripping jaw mechanism previously described.

The common valve 89 controlling the supply of compressed air both to the rivet feeding mechanism and to the mandrel-gripping mechanism ensures that the rivet feeding mechanism will be actuated only if and when the mandrel-gripping mechanism is also actuated. However, it may be that an operator does not insert the mandrel far enough into the gun for it to be properly gripped by the jaws. The valve mechanism incorporating the release valve 57a described above ensures that, should this happen, then the rivet feeding mechanism is not actuated. lf the supply of compressed air to the rivet feeding mechanism were not vented to atmosphere in these circumstances, the application of compressed air to the rear side of the piston 42 would violently eject the complete column of rivets and the mandrel from the gun, which would be exceedingly dangerous.

The invention is not restricted to the details of the foregoing examples.

We claim:

1. Riveting apparatus, comprising:

a mandrel adapted to carry a plurality of tubular rivets thereon, said mandrel having an enlarged head which is pulled through each rivet in turn to set it by expanding it;

jaws through which said mandrel extends, said jaws and said mandrel being reciprocable relative to one another in a direction axially of the mandrel to provide a feed stroke during which said mandrel head and said jaws move relatively away from each other and the leading rivet nearest the mandrel head passes through the jaws which then close to provide an abutment for said rivet, and a working stroke during which said mandrel head and said jaws move relatively towards each other to pull said mandrel head through said rivet to expand said rivet;

a tube-like member connected to said jaws in concentric relation with said mandrel;

and pneumatically operated rivet feeding means including a piston member slidable on said mandrel within said tube-like member to feed rivets along said mandrel towards and through said jaws upon the application of pneumatic pressure to the side of said piston member remote from said jaws.

2. Riveting apparatus as claimed in claim 1, said apparatus further including means for controlling the application of pneumatic pressure to said piston member in accordance with the relative axial positions of said jaws and said mandrel.

3. Riveting apparatus as claimed in claim 2, in which said control means comprises port means carried by or in said tube-like member, and a valve member reciprocable in unison with said mandrel along said tube-like member to cooperate with said port means, thereby to apply pneumatic pressure to said piston member as aforesaid in accordance with said relative axial positions of said jaws and said mandrel.

4. Riveting apparatus as claimed in claim 3, in which the relative axial positions of said mandrel, said port means and said valve member are such that pneumatic pressure is applied as aforesaid when said mandrel is positioned relatively to said jaws more than a predetermined extentin the direction opposite to that in which rivets are fed.

S. Riveting apparatus as claimed in claim 1, which apparatus includes a pneumatic motor operatively connected to said jaws and'said mandrel for moving them relatively to each other to provide said working stroke Cil upon the application of pneumatic pressure to said pneumatic motor; rst pneumatic valve means for controlling the application of pneumatic pressure to said pneumatic motor; and second pneumatic valve means for controlling the application of pneumatic pressure to said piston member of said rivet feeding means; said first pneumatic valve means and said second pneumatic valve means being operatively interconnected so that said second pneumatic valve means allows application of pneumatic pressure to said piston member only when said rst pneumatic valve member interrupts application of pneumatic pressure to said pneumatic motor.

6. Riveting apparatus as claimed in claim 1, including pressure leakage means, such that after termination of application of pneumatic pressure to said side of said piston member, said pressure drops due to leakage through said leakage means.

7. Riveting apparatus as claimed in claim 6, in which said pneumatic leakage means is provided by a gap between said piston member and at least one other member, either said mandrel or said tube-like member.

8. Riveting apparatus as claimed in claim 1, which apparatus further includes mandrel-gripping means for receiving and gripping said mandrel at a tail-end portion thereof remote from the head thereof, and pressure prevention means, operable by said mandrel-gripping means, effective'to prevent the application of pneumatic pressure to said side of said piston member remote from said jaws automatically if and whenever said mandrel is not received and gripped by said mandrel-gripping means.

9. Riveting apparatus as claimed in claim 8, in which said pressure prevention means comprises means for venting or relieving said pneumatic pressure.

10. Riveting apparatus as claimed in claim 8 in which said mandrel-gripping means comprises an internally tapered housing, externally tapered jaw members and means for urging said externally tapered jaws members into said internally tapered housing for gripping said mandrel, and in which said pressure prevention means is repsonsive to the extent to which said jaw members enter the housing in dependence upon the presence or absence of a mandrel between said jaw members.

11. Riveting apparatus as claimed in claim 10, in which said responsive pressure prevention means comprises valve means including a valve member which is normally biased into a rst position and which is moved to a second position by said jaw members when they enter said housing to the increased extent allowed by the absence of a mandrel between them.

12. Riveting apparatus as claimed in claim 8, in which said gripping means is pneumatically actuated, and in which there is provided common valve means controlling the pneumatic supply to both the aforesaid pneumatically operated rivet feeding means and to said gripping means.

References Cited UNITED STATES PATENTS 2,340,066 1/1944 Lee 72-391 2,401,724 6/1946 Dowdle 72-391 2,408,431 10/1946 Lutes 72-391 2,570,801 10/1951 Hamlin 72-391 FOREIGN PATENTS 578,107 6/1946 Great Britain 72-391 CHARLES W. LANHAM, Primary Examiner G. P. CROSBY, Assistant Examiner U.S. Cl. X.R. 72-453