GB2053059A - An improvement in or relating to the welding of tubes to tube plates - Google Patents

Abstract

A method of bringing a welding head (10) into exact alignment with the bore of a tube when welding tubes to tube plates. In order that the welding head (10) can be positioned independently of the work, the method includes the step of bringing a datum or probe member (22), offset by a fixed distance from the axis of the welding head (10) into alignment with the axis of the tube and the further step of moving the datum or probe member (22) and said welding head (10) through said fixed distance to bring the welding head (10) into the position previously occupied by the datum or probe member (22) and into alignment with the axis of said tube. <IMAGE>

Description

SPECIFICATION An improvement in or relating to the welding of tubes to tube plates.

The invention relates to the welding of tubes to tube plates such as are used in the manufacture of high pressure heat exchangers.

When welding tubes to tube plates it is necessary to align the rotatable welding head of the welding apparatus with the ends of the tubes which are to be welded before each welding operation is carried out by circumferential welding or by back face welding. If the welding head has not been accurately centred relative to the tube to be welded, the out of centre rotation of the electrode will result in a poor quality weld and in fact may burn through the tube wall. Heretofore, it has been usual to bring the welding head into register with the bore of the tube which is to be welded in position, but it is thought that, for various reasons, it will be advantageous to control the positioning of the welding head independently of the work, that is to say so that the welding equipment is no longer carried by the work.One advantage of this will be that heat build-up in the welding equipment will be avoided, especially when the work is to be pre-heated. Another advantage will be that the welding equipment will then be capable of being positioned, for the welding of a series of tubes in turn, by numerically controlled adjustment means. However, a particular problem in this connection is that since the spacing of the tubes in a tube plate can vary very much more than the allowable out of centre tolerance when circumferential welding or when back face welding, it is necessary to centre the welding head prior to each welding operation, to within a pre-determined maximum tolerance, relative to the axis of the tube concerned.

The invention has for its object to at least alleviate the problem referred to above.

According to one aspect of the invention, there is provided a method of accurately centring a welding head of a welding apparatus relative to a particular tube in a tube plate, the method including the step of bringing a datum or probe member, offset by a fixed distance from the axis of the welding head, into alignment with the axis of the tube and the further step of moving the datum or probe member and said welding head through said fixed distance to bring the welding head into the position previously occupied by the datum or probe member and into alignment with the axis of said tube.

According to another aspect of the invention, there is provided apparatus for use in welding tubes to tube plates such as are used in the manufacture of high pressure heat exchangers, the apparatus including a rotatable welding head forming part of a welding gun; a welding head carriage on which the welding gun is mounted; a datum or probe member also mounted on said welding head carriage and located thereon a fixed distance from the axis of said welding head; a main carriage on which said welding head carriage is mounted in guides for adjustments in the horizontal plane, that is to say for adjustments towards and away from a tube plate adjacent to which it is to be mounted and adjustments at right angles thereto, parallel to the face of the tube plate; and a main carriage beam on which said main carriage is mounted in guides for adjustments in a vertical plane spaced from the face of said tube plate, that is to say for lateral adjustments relative to said tube plate and for vertical adjustments relative to said main carriage beam, the latter also being vertically adjustable, the arrangement being such that when a tube is to be welded in position in the tube plate, the datum or probe member can be brought into alignment with the axis of said tube by the appropriate adjustment of the main carriage on the main carriage beam, and the welding head and datum or probe member can then be displaced together, by the appropriate adjustment of the welding head carriage on the main carriage, through the fixed distance by which said welding head and said datum or probe member are spaced apart, to bring the welding head into the position previously occupied by the datum or probe member and into alignment with the axis of the tube. The datum or probe member may be constituted by a mounting member and a conical head element mounted on said mounting member for limited pivotal movement in a universal manner but spring loaded towards a position in which its axis is aligned with that of said mounting member, the apparatus also including four electric switches so located in relation to the conical head element that respective switches are closed as said conical head element is caused to tilt either in the vertical plane or in the horizontal plane, a first two of said swtiches being adapted to control, respectively, the forward and reverse rotation of an electric motor operable to effect vertical adjustments of the main carriage on the main carriage beam, and a second two of said switches being adapted to control, respectively, the forward and reverse rotation of an electric motor operable to effect horizontal adjustments of the main carriage on the main carriage beam, the arrangement being such that when the datum or probe member is advanced into engagement with the bore of a tube with which it is approximately aligned the conical head element can tilt either upwards or downwards relative to the mounting member as a result of any deviation in the vertical plane of the axis of said mounting member from the axis of the tube and can also tilt to either side relative to said mounting member as a result of any deviation in the horizontal plane of the axis of the mounting member from the axis of said tube, whereby, as the conical head element of the datum or probe member is brought into engagement with the bore of the tube it brings about selfcentring adjustments until all four of the electric switches are in the open condition.

In order that the invention may be fully understood and readily carried into effect, the same will now be described, by way of example only, with reference to the accompanying drawings, of which: Figure 1 is a diagrammatic view of apparatus embodying the invention for use in welding tubes to tube plates such as are used in the manufacture of high pressure heat exchangers, Figure 2 is a diagrammatic plan view of a part of the apparatus, and Figure 3 is a sectional view on the line 3-3 in Fig. 2, of a so-called datum or probe member forming part of the apparatus.

Referring now to Fig. 1 of the drawings, the apparatus there illustrated includes a rotatable welding head 10 forming part of a so-called welding gun generally indicated 12.

In the example illustrated, the welding gun is of the kind for carrying out so-called "Tungsten Inert Gas" welding and consequently also includes a non-consumable electrode 14, a welding power source (not shown), a filler wire 16, and means (not shown) for feeding the filler wire from a spool 18 to the weld "pool" at the work surface by arcing between the work and the electrode.

The welding gun is mounted on a welding head carriage 20. Also mounted on the welding head carriage is a datum or probe member generally indicated 22 and this is located a fixed distance from the axis of the welding head.

The welding head carriage 20 is itself mounted in guides on a main carriage 24 for adjustments in the horizontal plane, that is to say for adjustments towards and away from a tube adjacent to which the apparatus is to be mounted (as indicated by the double ended arrow 26) and adjustments at right angles thereto, parallel to the face of the tube plate (as indicated by the double ended arrow 28).

The main carriage 24 is mounted in guides on a main carriage beam 30 for adjustments in a vertical plane spaced from the face of said tube plate, that is to say for lateral adjustments relative to said tube plate (as indicated by the double ended arrow 32) and for vertical adjustments relative to said main carriage beam (as indicated by the double ended arrow 34). The main carriage beam is mounted at its opposite ends on frame structure (not shown) and is vertically adjustable.

Referring now in particular to Figs. 2 and 3, the datum or probe member 22 is constituted by a shaft 36 carrying at a forward end a conical head element 38. The conical head element is mounted on the shaft for limited pivotal movement in a universal manner but is spring loaded towards a position in which its axis is aligned with that of the shaft. The arrangement is such that when the datum or probe member is advanced into engagement with the bore of a tube with which it is approximately aligned the conical head element can tilt either upwards or downwards relative to the shaft as a result of any deviation in the vertical plane of the axis of the shaft from the axis of the tube and can also tilt to either side relative to the shaft as a result of any deviation in the horizontal plane of the axis of the shaft from the axis of the tube.Immediately behind the conical head element there are located four equally spaced electric switches, a first two of which, indicated 40 and 42 in Fig. 3, are located in a vertical plane containing the axis of the shaft 36 and a second two of which (not shown) are located in a horizontal plane containing the axis of said shaft. The first two of said switches are adapted to control, respectively, the forward and reverse rotation of an electric motor (not shown) which is operable to effect the vertical adjustment of the main carriage 24 on the beam 30. The second two of said switches are adapted to control, respectively, the forward and reverse rotation of an electric motor (not shown) which is operable to effect the horizontal adjustment of the main carriage 24 on the beam 30.Thus it will be seen that as the conical head element of the datum or probe member is brought into engagement with the bore of a tube which is to be welded in position in a tube plate, the datum or probe member brings about self-centering adjustments until all four of the electric switches referred to are in the open condition. The conical head element can then be retracted from engagement with the bore of said tube and the welding head carriage 20 can be traversed parallel to the face of the tube plate, through the fixed distance which separates the axis of the datum or probe member from the axis of the welding head, so that the latter is located in alignment with the axis of the tube within very close limits of accuracy.

It will be understood that the method of accurately centering a welding head relative to a tube by the method described above, that is to say by the step of bringing a datum or probe member into alignment with the axis of the tube and the further step of moving the datum or probe member and said welding head through a fixed distance by which these are spaced apart to bring the welding head into the position previously occupied by the datum or probe member, is advantageous in a number of respects. Firstly, since the welding head is spaced apart from the datum or probe member the latter can be brought into alignment with the axis of a tube in a region of the tube plate which has already become heated during previous welding operations, and during this first step in the method referred to the welding head does not become unduly affected by conduction of heat from the tube plate.Secondly, the method lends itself ideally to the welding in sequence of a plurality of tubes in a tube plate by the appropriate programmed control of the adjustments referred to for the welding head carriage, the main carriage and the main carriage beam, all the tubes being welded within the allowable out of centre tolerance regardless of the fact that the spacing of the tubes may vary considerably from the nominal spacing.

Various modifications may be made without departing from the scope of the invention. For example, it will be understood that the datum or probe member may be very differently constructed; it could be adapted to engage with the external diameter of a tube to sense an initial out of alignment location. It will also be understood that the welding gun may be different from that illustrated by way of example, indeed the tubes could be welded to the tube plate by a back face welding technique instead of by the circumferential welding technique illustrated (see for example our prior Patent No. 1372057).

The programmed control of the adjustment means referred to, that is to say for the welding head carriage, the main carriage and the main carriage beam, will present no problem to a designer of numerically controlled machine tool equipment.

Claims (5)

1. A method of accurately centring a welding head of a welding apparatus relative to a particular tube in a tube plate, the method including the step of bringing a datum or probe member, offset by a fixed distance from the axis of the welding head, into alignment with the axis of the tube and the further step of moving the datum or probe member and said welding head through said fixed distance to bring the welding head into the position previously occupied by the datum or probe member and into alignment with the axis of said tube.

2. Apparatus for use in welding tubes of said plates such as are used in the manufacture of high pressure heat exchangers, the apparatus including a rotatable welding head forming part of a welding gun; a welding head carriage on which the welding gun is mounted; a datum or probe member also mounted on said welding head carriage and located thereon a fixed distance from the axis of said welding head; a main carriage on which said welding head carriage is mounted in guides for adjustments in the horizontal plane, that is to say for adjustments towards and away from a tube plate adjacent to which it is to be mounted and adjustments at right angles thereto, parallel to the face of the tube plate; and a main carriage beam on which said main carriage is mounted in guides for adjustments in a vertical plane spaced from the face of said tube plate, that is to say for lateral adjustments relative to said tube plate and for vertical adjustments relative to said main carriage beam, the latter also being vertically adjustable, the arrangement being such that when a tube is to be welded in position in the tube plate, the datum or probe member can be brought into alignment with the axis of said tube by the appropriate adjustment of the main carriage on the main carriage beam, and the welding head and datum or probe member can then be displaced together, by the appropriate adjustment of the welding head carriage on the main carriage, through the fixed distance by which said welding head and said datum or probe member are spaced apart, to bring the welding head into the position previously occupied by the datum or probe member and into alignment with the axis of the tube.

3. Apparatus according to claim 2, in which the datum or probe member is constituted by a mounting member and a conical head element mounted on said mounting member for limited pivotal movement in a universal manner but spring loaded towards a position in which its axis is aligned with that of said mounting member, the apparatus also including four electric switches so located in relation to the conical head element that respective switches are closed as said conical head element is caused to tilt either in the vertical plane or in the horizontal plane, a first two of said switches being adapted to control, respectively, the forward and reverse rotation of an electric motor operable to effect vertical adjustments of the main carriage on the main carriage beam, and a second two of said switches being adapted to control, respectively, the forward and reverse rotation of an electric motor operable to effect horizontal adjustments of the main carriage on the main carriage beam, the arrangement being such that when the datum or probe member is advanced into engagement with the bore of a tube with which it is approximately aligned the conical head element can tilt either upwards or downwards relative to the mounting member as a result of any deviation in the vertical plane of the axis of said mounting member from the axis of the tube and can also tilt to either side relative to said mounting member as a result of any deviation in the horizontal plane of the axis of the mounting member from the axis of said tube, whereby, as the conical head element of the datum or probe member is brought into engagement with the bore of the tube it brings about selfcentring adjustments until all four of the electric switches are in the open condition.

4. A method of accurately centring a welding head of a welding apparatus relative to a particular tube in a tube plate, the method being substantially as hereinbefore described with reference to the accompanying drawings.

5. Apparatus for use in welding tubes to tube plates, the apparatus being constructed, arranged and adapted to operate substantially as hereinbefore described with reference to and as illustrated by the accompanying drawings.