WELDING APPARATUS

Abstract: Welding device for use in the welding of grooves between plate-like, substantially non-magnetic materials using a welding burner, said welding device comprising a supporting frame (1) mounted in conjunction with the welding burner and movable along the surface of the material to be welded; a counter frame (2) on the opposite side of the supporting frame, said counter frame being placed against the material to be welded and having a boss (3) covering the groove area being welded; and at least one magnet (4, 5, 6, 7) in the supporting frame and the counter frame to keep the supporting frame and counter frame aligned with each other on opposite sides of the material to be welded when the supporting frame is being moved on as the welding work progresses.

Description: WELDING APPARATUS The present invention relates to a welding device as defined in the preamble of claim 1. In particular, the invention relates to the welding of metal sheets of mainly non-magnetic material, but it can also be used for other types of joining of different materials. It is only essential to the material to be welded that it is mainly non-magnetic. In other words, the material to be welded must not significantly disturb the magnetic field acting through it. This means that the proportion of magnetic material may be at most a few tens percent . The invention has been developed especially for the welding of products, such as containers, manu- factured from austenitic stainless steel, aluminium or titan. Longitudinal and circumferential welds on the products must almost always be shielded from the root side by a separate shielding gas flow when the plasma arc or TIG welding method is used. The shielding pre- vents oxidation of the root in the molten state and deterioration of its corrosion resistance. In the case of circumferential welds, shielding the root is difficult because the root gas shoe must be supported inside the container and the rotary motion of the contai- ner must be taken into account in the shielding arrangements . In practice, root shielding is nowadays implemented by having an assistant welder support the gas shoe manually inside the container during the wel- ding operation. Corresponding problems and a need for an assistant are also experienced in many other corresponding cases when large plate-like objects are being welded. One of the applications of the invention is backing of the weld root. Single-side welding is a significant method that can be used to improve produc- tivity. Generally, this requires root backing to ensure a sufficient weld quality. Moreover, the use of backings reduces the precision requirements regarding groove preparation and allows welding with a larger current. The tasks of mounting and dismounting the backings currently used, such as copper rings or ceramic bars, increase the manufacturing costs of the product . With current methods, the use of bosses is difficult. Especially in small containers, the conditions are disagreeable due to the smoke and heat produced during welding, and ventilation cannot be easily arranged. Nevertheless, the boss should be supported and moved accurately along the groove. In addition, a welding assistant is generally always needed, which significantly increases the costs. The use of magnets to keep the bosses in place has also been proposed, but no practicable solutions based on this technique have yet been created. The object of the present invention is to eliminate the drawbacks described above. A specific object of the invention is to present a new type of welding device by means of which a welding boss can be held as accurately as possible in the right position on the opposite side of the weld during the progress of the welding in a simple and easy manner without an assistant, and which obviates the time-consuming mounting and dismounting operations. As for the features characteristic of the in- vention, reference is made to the claims. The welding device of the invention comprises a supporting frame mounted in conjunction with the welding burner and movable along the surface of the material to be welded. The supporting frame may be at- tached directly to the welding burner or suitably connected to it or mounted on it in a suitable position so that the supporting frame will move along the sur- face of the material being welded as the welding burner is being moved along the groove. Moreover, the welding device comprises a counter frame which is placed on the opposite side of the supporting frame against the material to be welded and which is provided with a welding boss covering the groove area being welded. In addition, the supporting frame and the counter frame are provided with at least one pair of magnets, preferably permanent magnets, which keeps the supporting frame and counter frame aligned with each other when the supporting frame is being moved on as the welding work progresses. The supporting frame and the counter frame are also provided with bearings that support the supporting frame and counter frame on the material to be welded. According to the invention, at least in the counter frame, the perpendicular distance of the bearings from the weld/groove is larger than the perpendicular distance of the magnets from the weld/groove, so that the magnets will press the wel- ding boss towards the material to be welded. If the supporting frame and counter frame are light enough, even one pair of magnets of sufficient strength will suffice to keep them aligned with each other, but a better and more reliable grip is achieved if both the supporting frame and the counter frame are provided with at least two pairs of permanent magnets placed on opposite sides relative to each other and at a suitable distance from each other. The boss used in the welding device of the invention may be a plate-like backing. The backing material may be e.g. copper and the backing may have a channel that runs parallel to the groove to be welded and determines the size of the weld root. In another embodiment, the boss is a shiel- ding gas shoe consisting of a suitable space filled with shielding gas and open on one side, being held against the welding spot and moved along the groove. It is also possible to use a backing inside the shielding gas shoe. To enable the welding device to move as smoothly as possible along the groove, the supporting frame and the counter frame are provided with suitable bearings that support them on the surface of the material to be welded and allow them to move along the surface. The bearings may consist of various rollers, balls, wheels or equivalent elements, but also of a relatively lubricous solid surface in certain applications. The best bearing system consists of relatively large, individual balls that have no directional effect restricting the motion of the welding device. They also form good knuckle points about which the counter frame can be turned against the weld/groove by the magnets. The bearings are preferably so disposed that they maintain a clearance between the material to be welded and the magnets attached to the supporting fra- me and counter frame while still keeping the magnets as close as possible to the material surfaces, e.g. at a distance of about 1 mm. In this way, the attractive force of the permanent magnets can be maximised without subjecting them to mechanical strain or wear. The welding device of the invention has significant advantages as compared with prior art. The welding device allows shielding or other treatment of the weld from the opposite side without assistants, without difficult and unpleasant working conditions and without time-consuming mounting work. By just connecting the supporting frame to the welding burner and placing the counter frame on the opposite side, the entire groove can be welded without having to perform any actions on the opposite side while the counter frame, magnetically adhering to the supporting frame, is accurately following the groove and the progress of the welding operation. As the supporting frame is car- ried by the welding burner and the counter frame accurately follows the supporting frame, the weld root can be effectively shielded and supported. By virtue of the accuracy and precision of the welding device, a shielding gas shoe of a very small structure can be used, thus significantly reducing the amount of shielding gas needed. Moreover, the welding device can be easily moved from one groove to another within the object under construction by simply moving the suppor- ting frame along the surface of the object while the counter frame is following on the opposite side. This brings a significant additional saving in time in the case of large objects comprising several different grooves to be welded. In the following, the invention will be described in detail by referring to the attached drawings, wherein Fig. 1 presents a side view of a supporting frame according to the invention, Fig. 2 presents the supporting frame of Fig. 1 as seen from below, Fig. 3 presents a counter frame according to the invention in side view, Fig. 4 presents the counter frame of Fig. 3 as seen from above, Fig. 5 presents an additional application for the counter frame in Fig. 4, and Fig. 6 presents an alternative structure for the counter frame in Fig. 4. Figures 1 and 2 illustrate a supporting frame 1 comprised in the welding device of the invention. The supporting frame consists of a rigid central frame 15 and end frames 17 connected to it by parallel joints 16. The end frames can be turned in relation to the central frame so as to give the supporting frame as a whole a desired curvature, i.e. a curvature substantially corresponding to the surface to be welded. Each one of the end frames comprises a bearing element 13, i.e. a ball, which is free to rotate in any direction. In addition, each end frame 17 is provided with a permanent magnet 4, 5, which protrudes from the end frame 17 by a distance smaller than the distance of protrusion of the bearing element 13, so that when the bearing elements 13 rest on a straight or curved surface, depending on the shape of the supporting frame as a whole, a small air gap is left bet- ween the surface and the magnets 4 and 5. Via a swaged link structure 18 known in itself, the central frame 15 is connected to a supporting arm 19, via which the supporting frame is attached to the welding burner or to a suitable element moving in conjunction with the welding burner, so that the supporting frame and the welding burner always move and advance simultaneously in the direction of the groove . Figures 3 and 4 illustrate a counterpart of the supporting frame of the welding device, i.e. a counter frame 2. In a manner corresponding to the supporting frame, the counter frame consists of a rigid central frame 20 and end frames 22 connected to it via parallel joints 21. Each end frame 22 is provided with a ball acting as a bearing element 14 as well as a permanent magnet 6, 7. The dimensions of the counter frame correspond to the supporting frame so that, when placed opposite to each other on opposite sides of the material to be treated, permanent magnets 4 and 7 form a pair of magnets precisely aligned with each other while permanent magnets 5 and 6 form another pair of magnets precisely aligned with each other. Rotatably attached to the central frame 20 via a joint with a shaft 23 is a shielding gas shoe 12 acting as a boss 3. The joint used is preferably a universal joint, which keeps the shielding gas shoe correctly oriented while allowing it to turn both in the longitudinal and in the transverse direction of the groove. The shielding gas shoe consists of a chamber that is open on the side facing the groove to be welded and is provided with a sealing 24 covering its entire underedge . Connected from outside to the chamber is a pipe 25 used to supply shielding gas into a shielding gas distribution pipe 26 circling inside the chamber and provided with holes allowing the shielding gas to be uniformly discharged into the shielding gas chamber. The reference numbers used in the second embodiment presented in Fig. 5 correspond to the embodiment in Fig. 4, but in the embodiment in Fig. 5 the shielding gas shoe 12 is additionally provided with a backing 8 placed inside the chamber. The backing consists of a plate-like body with a channel 10 in its surface facing the weld, said channel being of a curved shape in cross-section and running in the direction of the weld. The underside of the weld is shaped and moulded against the channel as the backing is sliding along the weld. Fig. 6 shows a third embodiment of the counter frame, which only has a backing 9 attached to the central frame 20 via a shaft 23 and provided with a channel 11 running in the direction of the weld and supporting and shaping the root of the weld. In the embodiment in Fig. 6, as in the other figures, the bearing elements 14 and permanent magnets 6 and 7 are so disposed that the line 27 passing via the centres of the bearing elements 14 is farther removed from the boss 3 than the line 28 passing via the centres of the permanent magnets 6 and 7. Thus, as the permanent magnets are located closer to the weld or groove than the bearing elements, the attractive force of the permanent magnets will press the boss 3 against the weld. In this way, the shielding gas shoe is held with a sufficient tightness around the weld by the force of attraction of the permanent magnets alone and the backing is pressed against the weld with a pressure required for sufficient shaping of the weld. The supporting frame and the counter frame are preferably made of light non-magnetic material, such as aluminium. In this case, the frames are provided with oppositely disposed pairs of permanent magnets, which position the frames very accurately relative to each other. In the foregoing, the invention has been described by way of example by the aid of the attached drawings, but different embodiments of the invention are possible within the framework of the inventive idea defined by the claims.

Claims: CLAIMS Welding device for use in the welding of grooves between plate-like, substantially non-magnetic materials using a welding burner, said welding device comprising a supporting frame (1) mounted in conjunction with the welding burner and movable along the surface of the material to be welded; a counter frame (2) on the opposite side of the supporting frame against the material to be welded, said counter frame being provided with a boss (3) covering the groove area being welded; at least one pair of magnets (4, 5, 6, 7) in the supporting frame and the counter frame to keep the supporting frame and counter frame aligned with each other on opposite sides of the material to be welded when the supporting frame is being moved on as the welding work progresses; and bearings (13, 14) in the supporting frame (1) and in the counter frame (2) to support the supporting frame and counter frame on the material to be welded, charact eri s ed in that, in the counter frame (2) , the perpendicular distance of the bearings from the weld/groove is larger than the perpendicular distance of the magnets from the weld/groove, so that the magnets will press the boss towards the material to be welded. 2. Welding device as defined in claim 1, charac te ri sed in that both the supporting frame (1) and the counter frame (2) are provided with magnets (4, 5, 6, 7), which are placed on opposite side of the material, forming two magnet pairs that keep the supporting frame and the counter frame aligned with each other. 3. Welding device as defined in claim 1, charac t eri sed in that the boss is a platelike backing (8, 9) . 4. Welding device as defined in claim 3, character i sed in that the backing comprises a channel (10, 11) for shaping the weld, running in the direction of the groove. 5. Welding device as defined in claim 1, ch a r a c t e r i s e d in that the boss is a shielding gas shoe ( 12 ) . 6. Welding device as defined in claim 5, ch a r a c t e r i s e d in that the shielding gas shoe (12) comprises a backing (8) placed inside it. 7. Welding device as defined in claim 1, ch a r a c t e r i s e d in that both the supporting frame (1) and the counter frame comprise two bearings (13, 14) serving to support the supporting frame and counter frame on the material to be welded. 8. Welding device as defined in claim 7, ch a r a c t e r i s e d in that the bearings (13, 14) consist of balls, rollers, wheels or equivalent elements . 9. Welding device as defined in claim 1, cha r a c t e r i s e d in that the counter frame (2) comprises two bearings and two magnets so that the line (27) passing through the bearings (14) is farther removed from the boss than the line (28) passing through the magnets . 10. Welding device as defined in claim 1, cha r a c te r i s e d in that the supporting frame and the counter frame consist of at least two, preferably three sections to permit the sections to be turned in the longitudinal direction of the groove into a position corresponding to the curvature of the materials to be treated.

Inventors: HEIKKINEN ANTTI, JERNSTROEM PETTERI, KORHONEN AARNE, HEIKKINEN, ANTTI, JERNSTROEM, PETTERI, KORHONEN, AARNE
Applicants: HEIKKINEN ANTTI, JERNSTROEM PETTERI, KORHONEN AARNE, HEIKKINEN, ANTTI, JERNSTROEM, PETTERI, KORHONEN, AARNE
Application year: 1998
Main classification: B23K37
IPC codes: B23K37