GB2106810A

GB2106810A - Compensating for longitudinal creep of rotating cylindrical workpieces

Info

Publication number: GB2106810A
Application number: GB08128062A
Authority: GB
Inventors: Eric Bode
Original assignee: BODE AND SONS Ltd F
Current assignee: BODE AND SONS Ltd F
Priority date: 1981-09-16
Filing date: 1981-09-16
Publication date: 1983-04-20
Also published as: GB2106810B

Abstract

A rotator for holding a cylindrical work-piece 12 for welding, includes sets of wheels 14, 16, 18, 20 for supporting the work-piece for rotation about its axis, one of said sets 20 being mounted on a support 30 which is pivotable about an axis transverse to the said axis of the work-piece to cause longitudinal movement of the work-piece. A stylus 22 is biassed against a datum line provided on the workpiece and longitudinal creep of the work-piece sensed by the stylus is transmitted to electronic control means which operate motor 44 and gearing 42, 40, 38 to pivot support 30 about shaft 32 so that the creep is compensated for. <IMAGE>

Description

SPECIFICATION Improvements in or relating to work-piece rotators The present invention concerns an improved workpiece rotator, especially but not exclusively a rotator for supporting circular-section work-pieces which have to be welded together end-to-end, for example sections of cylindrical pressure vessels.

Rotators for supporting work-pieces of this type are well known and comprise pairs of support wheels arranged, equispaced on either side of the vertical longitudinal mid-plane of the rotator, in sets of two there being several sets longitudinally spaced along the rotator. One or more of the wheels of at least one of the sets may be driven such that the work-piece can be rotated.

Normally the work-piece comprises two cylindrical sections arranged co-axially in end-to-end relationship such that the sections may be welded together.

In such an arrangement, each section to be welded rests on two sets of rollers and when the said driven set is actuated the entire work-piece may be rotated past a welding station arranged at the periphery of the work-piece.

One disadvantage of an arrangement of this type is that the work-piece is restrained from longitudinal movement relative to the wheels only by the frictional engagement between the wheels and the workpiece, this engagement being enhanced by providing solid rubber tyres on the wheels. This has limited the relative linear displacement or "creep" and, in the past, creep has been maintained at tolerable levels. Welding techniques have changed, however, and whereas, in the past, the weld preparation provided a V-shaped gap, welding techniques now employed utilise a relatively narrow parallel-sided gap and it will be immediately realised that if there is any appreciable creep of the work-piece, the welding element will contact the side of the gap and be burned out.

It is therefore desirable to control the creep of the workpiece on the rotator and it is an object of the present invention to provide this control.

According to the present invention, there is provided a rotator having a plurality of sets of wheels adapted to rotatably support a cylindrical workpiece, in which at least one wheel is mounted in a support which is pivotable about an axis lying in a plane transverse to the longitudinal axis of the work-piece whereby pivotal movement of the or each of the said wheels results in longitudinal movement of the work-piece on rotation thereof, drive means for pivotting said support, a biased stylus arrangement, means for detecting deflections of the stylus arrangement from a central position and control means for said drive means, the control means actuating said drive means in accordance with deflections experienced by said stylus arrange ment.

Preferably the pivotal axis of the said support is arranged at an angle to the horizontal.

Preferably each set of wheels comprises four wheels arranged in two pairs, one pair on each side of a vertical plane through the longitudinal centre line of the rotator.

Preferably the stylus arrangement comprises a plunger adapted to abut an end face of the workpiece but any suitable arrangement capable of tracing a predetermined line may be employed. The movement of the plunger is preferably sensed by a linear transducer.

Preferably the drive means for causing pivotal movement of the support comprises an electric motor connected by way of a gear-box to a threaded rod and boss assembly connected with said pivotally mounted support so that rotation of the rod causes pivotal movement of the support.

Preferably the said control means incorporates a thyristor connected to said linear transducer and which actuates the motor. The support is preferably connected to a further linear transducer which is electrically connected to said thyristor to provide a feed-back signal to de-actuate the motor when the desired amount of pivoting of the support has been achieved.

An embodiment of the present invention will now be described by way of example only with reference to the accompanying drawings in which: Figure 1 shows diagrammatically an end elevation of a rotator, Figure 2 shows a side elevation of the rotator, and Figure 3 shows, in detail, a cross sectional elevation through the pivotal support for a pair of wheels of the rotator.

It is desired to weld together in end-to-end relationship two sections 10, 12 of a cylindrical pressure vessel. The sections are supported on four sets of wheels 14, 16, 18, 20 of a rotator, the wheels being so arranged that the axis of one drum section is co-axial with that of the other. The sections are so arranged on the positioner that the gap therebetween is appropriate to the welding technique to be employed in joining the sections. A preliminary weld is carried out manually to tack the sections sections together and it will be realised that when at least one of the wheels of the set 14 is driven by any suitable means the sections will rotate, the wheels of the sets 16, 18 and 20 being idler wheels.

Prior to the welding operation commencing, the end faces of the drum section 12 have been machined, the machining at one end providing the weld preparation and at the other providing an edge parallel to the weld preparation edge and transverse to the central axis of the section. A welding arrangement (not shown) is set up to weld the gap between the sections as they are rotated past it and it will be realised that it is required that the sections are controlled to obviate longitudinal creep during their rotation. To this end a stylus 22 having a rotatable ball 24 is positioned against the outer end face of the section 12. The stylus is springed biased against the end of the drum and is connected with a linear transducer which signals any movement of the stylus to either side of a datum point, the signal being passed to an electronic control apparatus (not shown) including a thyristor.The stylus 22 is mounted on a portable stand 26.

When the linear transducer detects any movement to either side of the datum point, that is it detects creep of the sections the object is to cause the rotator to return the sections to their original position. To this end one pair of wheels of the set 20 is mounted on a support 30 which is pivotally mounted on a rotatable shaft 32, the axis of which lies in a plane which is transverse to the central longitudinal axis of the sections. It will be realised that when the support 30 is orientated such that its wheels are in line, that is they lie on the plane transverse to the central longitudinal axis of the drum, they will cause no longitudinal movement of the sections.If, however, the support 30 is pivoted about the axis of its support shaft 32 the wheels will no longer be in line and will impart a movement to the sections in the longitudinal direction thereof, the direction of this movement being dependent upon the direction of pivotal rotation of the support 30. Thus this pivotal movement can be used to counter-act any creep.

To cause this pivotal rotation the support 30 is provided with a control arm 34 (see Figure 3) pivotally connected by a rod 36 to a threaded bush 38 which receives a threaded shaft 40, the shaft 40 being the output shaft from the gearbox 42. It will be realised therefore that the rotation of the shaft 40 by the gearbox 42 causes pivotal movement of the support 30. A further linear transducer (not shown) is connected to the bush 38 and provides a feed-back signal to the electronic control arrangement described above, the thyristor of which controls the supply of power to an electronic motor 44 which drives the gearbox 42.

In operation, therefore, when creep occurs it is detected by the stylus 22 and the linear transducer associated with it signals the direction and extent of creep to the electronic control means which, by means of the thyristor causes power to be supplied to the motor 44 which in turn drives the gearbox 42 to cause rotation of the threaded output shaft 40 and thus pivotal movement of the arm 34 of the support 30 about its shaft 32. The linear transducer in association with the bush 38 feeds back a signal to the electronic control means dependent upon the direction and amount of displacement of the bush 38 when this signal indicates that the required pivotal movement of the support has been attained the thyristor cuts off the power supply to the motor which remains inactive until the stylus 22 signals that a further movement of the support is required.

As a safety precaution, limit switches (not shown) are provided on each side of the arm 34 to provide for electrical cut-out of the motor if the pivotal movement exceeds a predetermined value.

Various modifications can be made without departing from the scope of the invention, for example, if it is not possible to track on the end face of the section 12, a line parallel to the face to be welded may be drawn on the periphery of the section, this line being scanned by a photo-electric cell which tracks on the line, the support on which the cell is mounted being associated with the lineartransducer such that signals corresponding to the direction and amount of creep can again be supplied to the electronic control means. In another modification a bead can be formed on the outer circumference of the drum parallel to the face to be welded and the stylus can be provided with a roller at its end, the roller having a peripheral groove in which the bead is accommodated.

Claims

1. A rotator having a plurality of sets of wheels adapted to rotatably support a cylindrical workpiece, in which at least one wheel is mounted in support which is pivotable about an axis lying in a plane transverse to the longitudinal axis of the work-piece whereby pivotal movement of the or each of the said wheels results in longitudinal movement of the work-piece on rotation thereof, drive means for pivotting said support, a biased stylus arrangement, means for detecting deflections of the stylus arrangement from a central position and control means for said drive means, the control means actuating said drive means in accordance with deflections experienced by said stylus arrangement.

2. A rotator as claimed in claim 1, in which the pivotal axis of the said support is arranged at an angle to the horizontal.

3. A rotator as claimed in claim 1 or claim 2, in which each set of wheels comprises four wheels arranged in two pairs, one pair on each side of a vertical plane through the longitudinal centre line of the rotator.

4. A rotator as claimed in any of claims 1,2 or 3 in which the stylus arrangement comprises a plunger adapted to abut an end face of the work-piece.

5 A rotator as claimed in claim 4, in which the movement of the plunger is preferably sensed by a linear transducer.

6. A rotator as claimed in any one of the preceding claims, in which the drive means for causing pivotal movement of the support comprises an electric motor connected by way of a gear-box to a threaded rod and boss assembly connected with said pivotally mounted support so that rotation of the rod causes pivotal movement of the support.

7. A rotator as claimed in any one of the preceding claims, in which the said control means incorporates a thyristor connected to said linear transducer and which actuates the motor.

8. A rotator as claimed in claim 7, in which the support is connected to a further linear transducer which is electrically connected to said thyristor to provide a feed-back signal to de-actuate the motor when the desired amount of pivoting of the support has been achieved.

9. A rotator substantially as hereinbefore described with reference to the accompanying drawings.