Abstract:
Welding apparatus utilizing a continuous belt in conjunction with a slidable guide pin and spindle disposed in a carriage that causes a welding torch to form a circumferential weld when the guide pin is in a tube and moves the torch rapidly between the tubes when the guide pin is retracted from the tubes.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     A patent application co-authored by the inventor describing similar apparatus was filed on May 9, 1981, and assigned Ser. No. 148,449. 
     BACKGROUND OF THE INVENTION 
     This invention relates to welding apparatus and more particularly to apparatus for continuously welding a portion of a row of tubes to a tubesheet. 
     When welding tubes to tubesheets initiating and extinguishing the arc as each tube is welded to the tubesheet requires a considerable portion of the total welding time. It is also during this initiation and extinguishing of the arc that the quality of the weld is likely to be lower than during other portions of the weld so that forming a continuous weld encompassing a plurality of tube junctures will reduce the welding time and improve the quality of the welds. 
     SUMMARY OF THE INVENTION 
     In general, apparatus for continuously welding at least a portion of a row of tubes to a tubesheet, when made in accordance with this invention, comprises a base, means for attaching the base to the tubesheet over at least a portion of a row of tubes, a carriage slidably disposed in the base to traverse at least a portion of the row of tubes and a spindle rotatably disposed in the carriage. The spindle has a centrally disposed guide pin, which fits inside a tube. The guide pin is slidably disposed in the spindle. The spindle has means disposed therein for sliding the guide pin in and out of the tube and a welding torch is disposed thereon adjacent the guide pin. A sheave is disposed on the spindle and additional sheaves are disposed adjacent the end of the base. Continuous belting engages the sheaves adjacent the ends of the base and loop around the spindle sheave and a motor or other means drives the belting. The apparatus also comprises means for initiating operation of the guide pin so that it moves in and out of the tubes, whereby the welding torch will move rectilinearly when the guide pin is not in the tubes and follow a circular path when the guide pin is in a tube, forming a continuous weld, to weld at least a portion of a row of tubes to the tubesheet. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The objects and advantages of this invention will become more apparent from reading the following detailed description in connection with the accompanying drawings, in which: 
     FIG. 1 is a plan view of a continuous welding apparatus made in accordance with this invention; 
     FIG. 2 is a side elevation of the apparatus; 
     FIG. 3 is a side elevation of the apparatus; and 
     FIG. 4 is a partial sectional view showing a spindle for the apparatus. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the drawings in detail, there is shown apparatus for continually welding a portion of a row of tubes to a tubesheet. The apparatus comprises a base or frame 1 and a carriage 3 slidably disposed thereon. 
     The base 1 comprises angle-shaped brackets 5 disposed on each end thereof, a mounting plate 7, a pair of stiffening bars 9 and a pair of guide bars or ways 11 connecting the end brackets 5. Each end bracket 5 has associated therewith an elastomer sleeve 13 which fits into a tube and means 15 for compressing the elastomer sleeves axially to expand them radially into holding engagement with the tubes. The axial compressing means 15 comprise pneumatic, hydraulic or some other manual or electrically operated device, a valve 17 or other actuating device is mounted on the mounting plate 7 to actuate the cylinders 15 to position the base against the tubesheet and hold it in place over a portion of a row of tubes. Each bracket 5 also has a handle 1 to facilitate moving the apparatus from one portion of a row of tubes to another portion thereof. 
     The carriage 3 is slidably disposed on the guide bars 11 so as to move rectilinearly between the end brackets 5. The carriage 3 also comprises a spindle 19 rotatably disposed within the carriage 3. 
     The spindle 19 has a centrally disposed guide pin 21, which fits inside a tube. The guide pin 21 is slidably disposed in the spindle 19 and has a piston 23, which slides in a centrally disposed bore 25 in the spindle 19 to provide means for moving the guide pin 21 in and out of a tube. The guide pin 21 has a bullet-shaped end or nose 27 to assist it to enter tubes, which are irregularly located. The spindle 19 also has a welding torch 29 with a non-consumable electrode 31 disposed adjacent the guide pin 21 to form a weld at the juncture of the end of a tube and the tubesheet. The spindle 19 also has disposed thereon a sheave 33 and a plurality of circumferential grooves 35 with sealing means including an O-ring 36 cooperatively associated with each circumferential groove 35. 
     The carriage 3 has a bore 37 adapted to receive the spindle 19. Individual ports 39 are disposed in fluid communication with the individual circumferential grooves 35, which have individual ducts 41 in communication therewith to supply operating fluid to the guide pin 21 and piston 23, cooling fluid to the spindle 19 and torch 29 and inert gas for blanketing the weld to the torch 29. An electrical lead 43 is also connected to the spindle to provide power for the welding torch 29. The sealing means provide a dual function of separating the fluid streams and providing frictional resistance between the spindle 19 and carriage 3 so that an appreciable amount of torque is required to rotate the spindle 19 and the carriage 3. 
     The base 1 has sheaves 45 rotatably mounted on the ends thereof, one adjacent each corner. A drive motor 47 with a sheave 49 is affixed to the mounting plate 7. A multiple groove sheave 51 is rotatably attached to the carriage 3 so that it is tilted with respect to the other sheaves. A continuous rope, wire, chain or belt 53 loops around the sheaves 45 adjacent the corners of the base 1, the sheave 51 attached to the carriage 3, the sheave 33 on the spindle 19 and around the sheave 49 on the drive motor. It is understood that one of the corner sheaves could be motor driven or some other device could be utilized to continuously drive the belt 53 to form a continuous weld at the juncture of the end of the tubes and tubesheet at least over a portion of a row of tubes. 
     A microswitch 55 is disposed to contact a dog or cam 57 on the spindle to initiate extraction of the guide pin from the tube and actuate a timer 58 which after a predetermined time interval extends the guide pin 21 into a tube. 
     The sheave 33 on the spindle 19 is larger in diameter than a circle scribed by the electrode 31 so that the linear speed of the electrode 31 is slower forming a weld at the juncture of the end of a tube and the tubesheet than when traveling rectilinearly between the tubes. 
     The operation of the apparatus is as follows. 
     The elastomer sleeves 13 at the ends of the base 1 are placed in tubes and actuated to hold the apparatus against the tubesheet. The welding torch 29 is disposed adjacent one of the side margins of the base and is energized along with the motor drive 47. The blanketing gas and cooling water are also being supplied to the spindle 19 and torch 29. The guide pin 21 is in a tube causing the torch 29 to circumscribe a weld at the juncture of one end of a tube and the tubesheet. As the torch 29 completes 360° a dog 57 on the spindle 19 actuates the timer 58 and also extracts the guide pin 21 from the tube. Once the guide pin 21 is extracted from the tube friction from the O-rings 36 on the spindle 19 stop its rotational motion and the carriage 3 and spindle 19 move rectilinearly a predetermined time interval after which the guide pin is extended into the next tube. The bullet-shaped nose 27 compensates for pitch tolerances and assists the guide pin 21 in entering a tube. Once the guide pin is in the next tube, the spindle 21 begins to rotate forming a weld subscribing the juncture of the end of the tube and the tubesheet. Since the sheave 33 disposed on the spindle 21 is larger in diameter than the circle scribed by the torch tip 31, the linear traveling speed is reduced and allows a puddle to form providing a good weld between the end of the tube and the tubesheet. However, once the pin 19 is extracted from the tube, the carriage 3 moves rectilinearly at an increased speed either reducing the size of the puddle or eliminating a puddle until the speed is again reduced to weld the next tube to the tubesheet. 
     The apparatus described hereinbefore advantageously produces continuous welds over a portion of tubes disposed in a row in a tubesheet, is relatively simple, light in weight, and is easy to maintain and operate as it has a minimal number of parts.