US2790892A - Resistance welding machine - Google Patents

Description

April 30, 1957 A. COLON 2,790,892

' RESISTANCE WELDING MACHINE Filed June 23, 1955 3 Shets-Sheet 1 FIG. 1.

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FIG

I 59 P Z3 60 INVENTOR.

- ARTHUR COLON WM, (PM

April 30, 1957 COLON 2,790,892

RESISTANCE WELDING MACHINE Filed June 26, 1955 3 Sheets-Sheet 2 IN VEN TOR. ARTHUR C OLON BY WMIW4JJM A t t 35.

April 30, 1957 A. COLON 2,790,892

RESISTANCE WELDING MACHINE Filed June 23, 1955 3 Sheets-Sheet 3 4 INVENTOR. AR TH UR C 0L ON yfLM m M At'tuS.

United States Patent RESISTANCE WELDING MACHINE Arthur Colon, Forest, Belgium Application June 23, 1955, Serial No. 517,615

Claims priority, application Belgium July 5, 1954 6 Claims. (Cl. 219-97) The present invention relates to a resistance welding machine comprising firstly two jaws, one of which is carried by a movable table operated by a piston contained in a pneumatic cylinder and solid with another piston contained in a hydraulic cylinder, and secondly a pipe, hereinafter referred to as the braking pipe, placing the front end of said hydraulic cylinder in communication with the rear end and equipped with a brake cock, the position 'of which is controlled on the one hand by an operating member in such manner as to be maintained completely open when said member is in the position which effects the withdrawal of the mobile jaw and to be partially closed when said member is in the position which effects the advance of the mobile jaw, and on the other hand by the position of the mobile jaw during the movement of advance of the latter, in such manner as to be opened further at the end of the movement of advance of the mobile jaw.

Machines of this type enable a high upsetting speed to be obtained when the braking cock is totally opened towards the end of the stroke of the mobile j'aw towards the fixed jaw, but the maximum forging force which is obtained by the complete opening of the braking cock at the end of said stroke is relatively low unless pneumatic pistons are used which are of large dimensions or mounted in a tandem arrangement. If these machines are built to provide considerable forging forces, they are not suitable for elfecting welding which requires only a slight forging force. It is therefore necessary to have several machines having different technical characteristics if the welding work which it is proposed to do requires very different forces.

The present invention has object a machine with the aid of which, while using only compressed air as the. source of motive power for the displacement of the mobile jaw, it is possible to obtain widely different forging forces, without the pistons used having to have a larger surface, than for obtaining relatively small forging forces or having to be more numerous than in the latter case.

To this end, the welding machine of the invention is characterised in that the part of the brake pipe com-v prised between the brake cock and the rear face of the hydraulic cylinder is in communication with :a cylinder in which is engaged at plunger solid with !a piston operated pneumatically under the control of a distribution member the position of which is controlled by the position of the mobile jaw at the end of the advance of the latter in such manner that said plunger delivers liquid into the rear end of the hydnaulic cylinder during the stroke of upsetting of the metal by which the movement of advance of the mobile jaw terminates; in that the brake cock is abruptedly completely opened under the control of the mobile jaw at the moment when said plunger commences to deliver liquid; in that a liquid reservoir is connected to the part of the brake pipe comprised between the brake cock and the cylinder containing the plunger; in that an obturator is provided on the part of the brake pipe be tween said cylinder and said reservoir; and in that said "ice obturator is open in the position of rest but is abruptly closed under the control of the mobile jaw at the moment when said plunger commences to deliver liquid.

With a machine of this type, the hydraulic cylinder which acts as brake during the greater part 'of the stroke of the mobile jaw towards the fixed jaw also plays the part of a driving cylinder towards the end of said stroke. in fact, as soon as the obturator has broken communication between the front end and the rear end of said cylinder, the plunger delivers liquid behind the hydraulic piston in such manner that the latter becomes a driving piston, despite the fact that the only source of driving power available is compressed air. This hydraulic driving action is added to the pneumatic driving action. Because the piston solid with the plunger has a much larger surface than the latter, the compressed air which acts on said piston can cause the piston of the hydraulic cylinder to be acted on by a far larger hydraulic pressure than its pneumatic pressure. In addition, the pneumatic pressure acting on said piston may be greater than that acting in the pneumatic cylinder because of the use combined pressure gauges and reduction valves so regulated as to supply different pressures from a common source of compressed air.

During the advance of the piston in the hydraulic cylinder, the inequality between the variations of volume in front of and behind this piston, is compensated by the communication of the brake pipe with the reservoir. After closure of this pipe by the obturator, the liquid escaping from the front end can also pass into said reservoir. It is to be noted furthermore that the complete abrupt opening of the brake cock, which is effected at the moment the plunger comes into action, eliminates the braking action of the hydraulic cylinder at the moment when the latter starts to drive. The opening of the obturator, after the forging is effected, has the effect of avoiding suction behind the piston in the hydraulic cylinder while the plunger is withdrawing. The result is that the mobile jaw is not urged to move away from the fixed jaw before the compressed air is admitted onto the front face of the pneumatic piston which is solid therewith.

In one advantageous embodiment, the displacement of the distribution member effecting the delivery of the liquid by the plunger, the abrupt opening of the brake cock and the abrupt closing of said obturator are effected simultaneously by the feeding of three electromagnets, the circuit of which contains a switch which is closed under the control of the position of the mobile jaw.

In order to augment the precision of the pressure of the upsetting of the metal when said pressure must be relatively low, provision is made for so constructing the machine that the hydraulic driving action can be suppressed.

To this end, the member distributing the air driving the piston of the plunger can be maintained in a position in which it leaves said piston inoperative while the circuit of the el-ectromagnets which controls said obturator contains a switch which can be opened when said distribution member is maintained in the position which has just been defined.

In this case, the pressure of the driving air necessary to obtain a relatively low forging force must not be as high as if said air were acting on the piston of the plunger, and consequently the precision of the regulation is greater.

In one particular embodiment relating to the case in which the displacement of the member distributing the air operating the piston of the plunger is controlled by an electromagnet, the circuit of this electromagnet and the circuit of the electromagnet which controls said obturator avndena 3 contain a switch enabling these circuits to be opened at will.

Further particular features and details of the invention will be clear in the course of the description of the drawings accompanying the present memorandum, which illustrates diagrammatically and solely by way of example two forms of construction of the resistance welding machine of the present invention.

Figure 1 illustrates diagrammatically, in elevation, a part of the resistance welding machine according to the present invention, the mobile table and the fixed table being shown on a smaller scale than the remainder.

Figure 2 is another diagrammatic representation of the same machine showing the relative position of certain of its elements.

Figure 3 is a representation similar to that in Figure 2 for another position of the operating member.

Figure 4 is a diagram of the electrical connections used in the construction of the part of the machine illustrated in the preceding figures.

Figure 5 shows, in a similar manner to Figure 1, another form of construction of a part of the machine according to the invention.

In these different figures, like reference numerals designate like elements.

The resistance welding machine illustrated in Figure 1. comprises, in the first place, two jaws 2 and 3intended to maintain pieces to be welded 4 and 5. The jaw 2 is carried by a fixed table 6, while the jaw is carried by a mobile table 7 adapted to move towards and away from the fixed table 6 in the direction of the double arrow X. This table is joined by a rod 8 to a piston 9 contained in a pneumatic cylinder It). The latter is connected by pipes 11 and 12 to a cylinder 13 containing a distribution slide 14. Said cylinder 14 communicates with a source of compressed air through a pipe 15 and with the atmosphere through branches 16 and 17.

The piston is solid with another piston 18 contained in a hydraulic cylinder 19. The latter contains for example oil which can pass from the front end 20 to the rear end 21 by circulating in a pipe 22 hereinafter referred to as the brake pipe. The latter is equipped with a brake cock 23, the position of which is controlled on the one hand by an operating member, and on the other hand by the position of the mobile table.

Said cock 23 is a rotary cock, the pivot of which is designated by 24 in Figure 2. Said pivot is solid with a disc 25 which carries noses 26 and 27. It is constantly urged by a spring 23 towards a position in which it partially closes the brake pipe.

The operating member to which reference has been made is constituted by a lever 29 which, in Figure 2, occupies the position in which the mobile table is at its greatest distance from the fixed table. In this position, a rod 30 articulated at 31 to said lever strikes against the nose 26 and maintains the cock 23 completely open. Said rod also carries a piece 32 connected to the distribution slide 14.

When the lever 25* is brought into a position such as that illustrated in Fi ure 3, giving rise to the advance of the mobile jaw towards the fixed jaw, the rod 30 is moved away from the nose 26 and the disc 25 occupies the position in which the cock 23 is only partly closed. This position is brought about by the encounter of the nose 27 with a piece 33. In Figure 3, the nose 27 is nevertheless illustrated at a distance from the piece 33, but this position will be explained hereinbelow.

The piece 33 is mounted on a rod 34 of regulable length which carries, at its opposite end, a roller 35. The latter strikes against a cam 36 which is movable with the jaw 3 in the direction of the double arrow X. When the mobile jaw moves towards the fixed jaw, the cam. 36 pushes back the nose .27 in such manner as. to open to an increasing extent the brake cock 23. Everything which has just been described is well known in the welding machines to which the invention is an improvement.

According to the invention, the part of the brake pipe 22 comprised between the brake'cock 23 and the rear face 21 of the hydraulic cylinder 19 is in communication with a cylinder 75 in which is engaged a plunger 37 (Figure 1). The latter is solid with a piston 38 contained in a pneumatic cylinder 39. The pneumatic cylinder 39 illustrated has a double action and is connected by two pipes 40 and 41 to a distributor 42 in communication with a source of compressed air (not shown) through a pipe 43.

The distribution member 44 contained in said distributor 42 is constantly urged by a spring 45 to occupy a position such as that illustrated in Figure 1. In this position, the compressed air is admitted onto the upper face of the piston 38 through the medium of the pipe 40, while the bottom face of said piston is in communication with the atmosphere through the medium of the pipe 41.

The distribution member 44 can be displaced against the action of the spring 45 when a current passes in an electromagnet 47. During the passage of this current, the distribution member 44 occupies a position in which the pipe 41 is no longer in communication with the atmosphere but is in communication with the pipe 43 supplying the compressed air, while the pipe 40 is in communication with the atmosphere.

The brake cock 23 is likewise solid with a lever 48 connected to the armature 49 of an electromagnet 50. When a current passes in the latter, under the conditions which will be explained hereinbelow, the brake cock 23 is abruptly completely opened.

A liquid reservoir 51 is connected to the part of the pipe 22 comprised between the brake cock 23 and the point where the cylinder 75 is connected to the pipe 22. The latter is equipped between the reservoir 21 and the point where the cylinder 75 is connected to said pipe with an obturator 53 which is closed while the plunger 37 is delivering liquid towards the hydraulic cylinder 19. To this end, the obturator 53 is solid with a lever 54 articulated to the armature 55 of an electromagnet S6. The closing of said obturator is elfected by the passage of a current in the electromagnet 56, under the conditions which will be described hereinbelow. This obturator is opened during the stroke of the plunger 37 in the opposite direction.

The electromagnets 47, and 56 form part of an electric circuit such as that illustrated in Figure 4. The latter shows nothing regarding the feeding of the welding electrodes, in order not to be needlessly overburdened with detail. The source of current available is applied for example between terminals 57 and 58. The terminal 57 is connected by a conductor 59 to a switch 60, the closure of which is effected at the moment when the lever 29 is moved from the position in Figure 2 to the. position shown in Figure 3. By this operation, a cam 61 displaces a roller 62 and closes the switch 60. If it is assumed that a switch 63 has previously been closed, the electromagnets 47, S0 and 56 are nevertheless not yet excited because a switch 64, connected in series with the switch 64), is still open. Said switch 64 is closed towards the end of the stroke of the mobile jaw towards the fixed jaw. A cam (Figures 2 and 3) driven by the mobile table 7 at that moment pushes back a roller 66 carried by the mobile part of the switch 64. The position of said cam is such that said switchis closed at the moment when the stroke of the upsetting of the metal, by which the movement of: advance of the mobile jaw is terminated, is to commence.

If it is supposed that a switch 67 (Figure 4), which will be discussed later on, is closed, the closing of the switch 64 has the eflect of simultaneously feeding the group of the three electromagnets 47, 50 and 56 com nected to one another in a shunt arr-angement,-said group being in turn connected in series with the switch 64. The feeding of the electromagnet 56 effects the closing of the obturator 53, while the feeding of the electromagnet 47 effects the displacement of the plunger 37. I

The movement of the plunger 37 has the effect of cansing the hydraulic cylinder 19 to act as a driving cylinder. The delivery of the oil through the front end 20 into the tank 51 can be effected easily, because the brake cock 23 is at that moment completely open because the electromagnet 50 is being fed. This explains why the nose 27 is not in contact with the piece 33 in Figure 3.

If it is not desired to operate the cylinder 19 as a driving cylinder, the switch 67 is opened, the consequence of which is that the plunger 37 is not displaced and the obturator 53 is left constantly open. In these circumstances, therefore, the mobile table can be moved solely under the driving action of compressed air acting on the piston 9, while the pressure of said compressed air can be regulated by a combined pressure gauge and reduction valve, which pressure is higher than if the table were simultaneously displaced by the driving action of the pneumatic cylinder 10 and hydraulic cylinder 19.

It is to be noted that the pressure of air acting on the piston 38 in the pneumatic cylinder 39 can likewise be regulated if desired with the aid of a combined pressure gauge and reduction valve interposed between said cylinder and a source of compressed air, which may be the same as that feeding the pneumatic driving cylinder 10 through another combined pressure gauge and reduction valve.

When a weld has been effected, the forging force is eliminated before opening the jaws, and to this end the lever 29 is brought into a position intermediate between those illustrated in Figures 2 and 3. In said intermediate position, known as relaxation position, the cam 61 ceases to act on the switch 60 and the latter opens, so that the armatures of the three electromagnets 47, 50 and 56 return to their initial position. After the suppression of the forging force and the opening of the jaws, the lever 29 is brought into the withdrawal position illustrated in Figure 2.

Figure 4 also shows a switch 68 mounted in a shunt connection on a branch containing the switches 60 and 63 in series. Said switch 68 has the purpose of permitting a manual control of the machine instead of automatic control by means of the switch 60. In the case of manual control, the switch 63 is first opened.

In the embodiment described above, the displacement of the distribution member 44 is controlled by the position of the mobile jaw during the advance of the latter, through the medium of the electromagnet 47. It will be understood that the control of the distribution member 44 by the position of the mobile jaw can also be effected otherwise than through the medium of an electromagnet.

Figure shows a form of construction of the machine according to the invention in which use is made of a cam 69 fixed on the rod 30 in order to control the displacement of the distribution means 44. The latter is solid with a rod 70 carrying a roller 71 in contact with the cam 69.

The position of the distribution member 44 is also controlled by another cam 72 on which a roller 73 carried by the rod 70 can bear. It prevents the distribution member 44 from being displaced under the action of the spring 45 from the position in which it is shown at the moment when the lever 29 is passing into a position such as that illustrated in Figure 3 in order to bring the mobile jaw near the fixed jaw.

The cam 72-is regulable in position on the rod 8, parallel to the axis of the latter, so that it can always be brought into the suitable position for initiating the start of the upsetting operation.

At the moment when delivery commences through the displacement of the distribution member into a position in which the pipes 41 and 43 are in communication while the pipe 40 is connected to the atmosphere, the rod 70 drives the pusher 74 of the switch 64, which elfects the closing of the latter and consequently the feeding of the 6 l electromagnets 50 and 56 at the moment when the plunger 37 commences to deliver liquid. The cam 72 therefore also plays the part of the cam 65 in Figures 2 and 3, which was driven with the mobile jaw. I

When the operating lever 29 is returned into the relaxa tion position, the distribution member 44 is returned into the position in which it is shown in Figure 5 by the cam 69, and as result the plunger also resumes the position shown, while the switch 64 opens again and the brake cock 23 and the obturator 53 return into their illustrated position.

It is obvious that the invention is not exclusively limited to the embodiments illustrated and that many modifications can be made to the form, arrangement, and constitution of certain of the elements used for its performance, provided that these modifications are not in contradiction with the object of each of the following claims.

What I claim is:

1. In a resistance butt welding machine in combination a jaw for maintaining one of the pieces to be welded, a movable jaw for maintaining a piece to be welded to the first one, a movable table on which this second jaw is mounted and which is capable of being moved towards and away from the first jaw, a pneumatic cylinder, a piston in this cylinder connected to said movable table, a distributor for controlling the admission of compressed air into said pneumatic cylinder, a hydraulic cylinder, a piston in the latter connected to the first piston, a brake pipe between the front end and the rear end of the hydraulic cylinder, a brake cock on this brake pipe capable of being partly closed during the first part of the stroke of the movable jaw towards the fixed jaw and of being completely open when the movable jaw moves away from the fixed jaw, an operating member for controlling the position of said distributor and the position of the brake cock, a third cylinder communicating with the part of the brake pipe between the brake cock and the rear end of the hydraulic cylinder, a plunger in said third cylinder, a piston fixed to said plunger, a second pneumatic cylinder in which said last named piston is movable, a distribution member for controlling the admission of compressed air into said second pneumatic cylinder, means for controlling the position of this distribution member by the position of the movable jaw in such manner that liquid is delivered by said plunger into the rear end of said hydraulic cylinder during the stroke of upsetting of the metal to be welded which occurs at the end of the stroke of the movable jaw towards the fixed jaw, means for abruptly completely opening the brake cock under the control of the movable jaw from the moment when said plunger begins to deliver liquid, at liquid reservoir communicating with the part of the brake pipe comprised between the brake cock and said third cylinder, an obturator on the part of the brake pipe between said third cylinder and said reservoir, said obturator being normally open, and means for abruptly closing this obturator under the control of the movable jaw at the moment when said plunger begins to deliver liquid.

2. In a resistance butt welding machine in combination a fixed jaw for maintaining one of the pieces to be welded, a movable jaw for maintaining a piece to be welded to the first one, a movable table on which this second jaw is mounted and which is capable of being moved towards and away from the first jaw, a pneumatic cylinder, a piston in this cylinder connected to said movable table, a distributor for controlling the admission of compressed air into said pneumatic cylinder, a hydraulic cylinder, a piston in the latter connected to the first piston, a brake pipe between the front end and the rear end of the hydraulic cylinder, a brake cock on this brake pipe capable of being partly closed during the first part of the stroke of the movable jaw towards the fixed jaw and of being completely open when the movable jaw moves away from the fixed jaw, an operating member for controlling the position of said distributor and the position of the brake cock, a third cylinder communicating with the part of the brake pipe between the brake cock and the rear end of the hydraulic cylinder, a plunger in this third cylinder, a piston fixed to said plunger, a second pneumatic cylinder in which this last piston is movable, a distribution member for controlling the admission of compressed air into this second pneumatic cylinder, means for permanently urging said distribution member towards a position for which said plunger is at the end of said third cylinder opposite to the part of the latter communicating with the brake pipe, at first electromagnet for moving said distribution member into a position for which said plunger delivers liquid into the rear end of said hydraulic cylinder when the circuit of said first electromagnet is fed with current, a switch in said circuit, means movable with said movable jaw for closing said switch during the stroke of the upsetting of the metal to be welded which occurs at the end of the stroke of the movable jaw towards the fixed jaw, a second electromagnet for abruptly completely opening the brake cock when the circuit of said second electromagnet is fed with current, a switch in this last circuit, means movable with said movable jaw for closing this last switch from the moment when said plunger begins to deliver liquid, a liquid reservoir communicating with the part of the brake pipe comprised between the brake cock and said third cylinder, an obturator on the part of the brake pipe between said third cylinder and said reservoir, said obturator being normally open, a third electromagnet for abruptly closing said obturator when the circuit of said third electromagnet is fed with current, a switch in this last circuit, and means movable with said movable jaw for closing this last switch from the moment when said plunger begins to deliver liquid.

3. In a resistance butt welding machine in combination a fixed jaw for maintaining one of the pieces to be welded, a movable jaw for maintaining a piece to be welded to the first one, a movable table on which this second jaw is mounted and which is capable of being moved towards and away from the first jaw, a pneumatic cylinder, a piston in this cylinder connected to said movable table, a distributor for controlling the admission of compressed air into said pneumatic cylinder, a hydraulic cylinder, a piston in the latter connected to the first piston, a brake pipe between the front end and the rear end of the hydraulic cylinder, a brake cock on this brake pipe capable of being partly closed during the first part of the stroke of the movable jaw towards the fixed jaw and of being completely open when the movable jaw moves away from the fixed jaw, an operating member for controlling the position of said distributor and the position of the brake cock, at third cylinder communicating with the part of the brake pipe between the brake cock and the rear end of the hydraulic cylinder, a plunger in this third cylinder, a piston fixed to said plunger, a second pneumatic cylinder in which this last piston is movable, a distribution member for controlling the admission of compressed air into this second pneumatic cylinder, means for permanently urging said distribution member towards a position for which said plunger is at the end of said third cylinder opposite to the part of the latter communicating with the brake pipe, first electromagnet for moving said distribution member into a position for which said plunger delivers liquid into the rear end of said hydraulic cylinder when the circuit of said first electromagnet is fed with current, a switch in said circuit, means movable with said movable jaw l or closin said switch during the stroke of the upsetting of the metal to be welded which occurs at the end of the stroke of the movable jaw towards the fixed jaw, a second electromagnet for abruptly completely opening the brake cock when the circuit of said second electromagnet is fed with current, a switch in this last circuit, means movable with said movable jaw for closing this last switch from the moment when said plunger begins to deliver liquid, a liquid reservoir communicating with the part of the brake pipe comprised between the brake cock and said third cylinder, an obturator on the part of the brake pipe between said third cylinder and said reservoir, said obturator being normally open, a third electromagnet for abruptly closing said obturator when the circuit of said third electromagnet is fed with current, a switch in this last circuit, means movable with said movable jaw for closing this last switch from the moment when said plunger begins to deliver liquid and a fourthswitch which can be opened at will, situated between the electromagnet for controlling the obturator and the said switches in the circuits of the three electromagnets,

4. In a resistance butt welding machine in combination a fixed jaw for maintaining one of the pieces to be welded, a movable jaw for maintaining a piece to be welded to the first one, a movable table on which this second jaw is mounted and which is capable of being moved towards and away from the first jaw, a pneumatic cylinder, :1 piston in this cylinder connected to said movable table, a distributor for controlling the admission of compressed air into said pneumatic cylinder, a hydraulic cylinder, a piston in the latter connected to the first piston, a brake pipe between the front end and the rear end of the hydraulic cylinder, a brake cock on this brake pipe capable of being partly closed during the first part of the stroke of the movable jaw towards the fixed jaw and of being completely open when the movable jaw moves away from the fixed jaw, an operating member for controlling the position of said distributor and the position of the brake cock, a third cylinder communicating with the part of the brake pipe between the brake cock and the rear endof the hydraulic cylinder, 21 plunger in this third cylinder, a piston fixed to said plunger, a second pneumatic cylinder in which this last piston is movable, a distribution member for controlling the admission of compressed air into this second pneumatic cylinder, means for permanently urging said distribution mem er towards a position for which said plunger is at the end of said third cylinder opposite to the part of the latter communicating with the brake pipe, a first electromagnet for moving said distribution member into a position for which said plunger delivers liquid into the rear end of saidhydraulic cylinder when the circuit of said first electromagnet is fed with current, a switch in said circuit, means movable with said movable jaw for closing said switch during the stroke of the upsetting of the metal to be welded which occurs at the end of the stroke of the movable jaw towards the fixed jaw, a second electromagnet for abruptly completely opening the brake cock whenthe circuit of said second electromagnet is fed with current, a switch in this last circuit, means movable with said movable jaw for closing this last switch from the moment when said plunger begins to deliver liquid, a liquid reservoir communicating with the part of the brake pipe comprised between the brake cock and said third cylinder, an obturator on the part of the brake pipe between saidithird cylinder and said reservoir, said obturator being normally open, a third eledtromagnct for abruptly closing said obturator when the circuit of said third electromagnet is fed with current, this third electromagnet being electrically connected in shunt with the electromagnet for operating said distribution member, a manually operable switch in series with the group of these two electromagnets in shunt, a further switch in series with this last switch, and means movable with said movable jaw for closing this further switch from the moment when said plunger begins to deliver liquid.

5. In a resistance butt welding machine in combination a fixed jaw for maintaining one of the pieces to be welded, a movable jaw for maintaining a piece to be welded to the first one, a movable table on which this second jaw is mounted and which is capable of being moved towards and away from the first jaw, a pneumatic cylinder, a piston in this cylinder connected to said movable table, a distributor for controlling the admission of compressed air into said pneumatic cylinder, a hydraulic cylinder, a piston in the latter connected to the first piston, a brake pipe between the front end and the rear end of the hydraulic cylinder, a brake cock on this brake pipe capable of being partly closed during the first part of the stroke of the movable jaw towards the fixed jaw and of being completely open when the movable jaw moves away from the fixed jaw, an operating member for controlling the position of said distributor and the position of the brake cock, a third cylinder communicating with the part of the brake pipe between the brake cock and the rear end of the hydraulic cylinder, :1 plunger in this third cylinder, a piston fixed to said plunger, 21 second pneumatic cylinder in which this last piston is movable, a distribution member for controlling the admission of compressed air into this second pneumatic cylinder, means for permanently urging said distribution member towards a position for which said plunger is at the end of said third cylinder opposite to the part of the latter communicating with the brake pipe, a first electromagnet for moving said distribution member into a position for which said plunger delivers liquid into the rear end of said hydraulic cylinder when the circuit of said first electromagnet is fed with current, a second electromagnet t or abruptly completely opening the brake cock when the circuit of said second electrornagnet is fed with current, a liquid reservoir communicating with the part of the brake pipe comprised between the brake cock and said third cylinder, an obturator on the part of the brake pipe between said third cylinder and said reservoir, said obturator being normally open, a third electromagnet for abruptly closing said obturator when the circuit of said third electromagnet is fed with current, a common switch in the circuits of the three electromagnets, means movable with said movable jaw for closing said common switch during the stroke of the upsetting of the metal to be welded which occurs at the end of the stroke of the movable jaw towards the fixed jaw.

6. In a resistance butt welding machine in combination a fixed jaw for maintaining one of the pieces to be welded, a movable jaw for maintaining a piece to be welded to the first one, a movable table on which this second jaw is mounted and which is capable of being moved towards and away from the first jaw, a pneumatic cylinder, a piston in this cylinder connected to said movable table, a distributor for controlling the admission of compressed air into said pneumatic cylinder, a hy- (lraulic cylinder, a piston in the latter connected to the first piston, a brake pipe between the front end and the rear end of the hydraulic cylinder, a brake cock on this brake pipe capable of being partly closed during the first part of the stroke of the movable jaw towards the fixed jaw and of being completely open when the movable jaw moves away from the fixed jaw, an operating member for controlling the position of said distributor and the position of the brake cock, at third cylinder communicating with the part of the brake pipe between the brake cock and the rear end of the hydraulic cylinder, a plunger in this third cylinder, a piston fixed to said plunger, a second pneumatic cylinder in which this last piston is movable, a distribution member for controlling the admission of compressed air into this second pneumatic cylinder, a combined pressure gauge and reduction valve for controlling the pressure of the compressed air admitted into said second pneumatic cylinder, another combined pressure gauge and reduction valve for controlling the pressure of the compressed air admitted into said first pneumatic cylinder, a common source of compressed air for feeding these two pneumatic cylinders through these two combined pressure gauge and reduction valves, means for controlling the position of said distribution member by the position of the movable jaw in such manner that liquid is delivered by said plunger into the rear end of said hydraulic cylinder during the stroke of upsetting of the metal to be welded which occurs at the end of the stroke of the movable jaw towards the fixed jaw, means for abruptly completely opening the brake cock under the control of the movable jaw from the moment when said plunger begins to deliver liquid, at liquid reservoir communicating with the part of the brake pipe comprised between the brake cock and said third cylinder, an obturator on the part of the brake pipe between said third cylinder and said reservoir, said obturator being open, and means for abruptly closing this obturator under the control of the movable jaw at the moment when said plunger begins to deliver liquid.

References Cited in the tile of this patent UNITED STATES PATENTS 1,892,208 Ferris ct a1. Dec. 27, 1932 2,298,051 Gordon et a1. Oct. 6, 1942 2,455,526 Sciaky Dec. 7, 1948 2,640,134 Doutt May 26, 1953

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