AU2017200554A1 - A Welding Carriage and Welding Apparatus - Google Patents

Abstract

Disclosed is a welding carriage for heat welding a web of material onto a substrate, the welding carriage. The welding carriage comprises a base unit supporting a pressing member for applying a pressing force onto the web during movement of the base unit. 5 The welding carriage also comprises a welding head pivotally joined to the base unit. The welding head comprises a welding nozzle arranged for welding the web to the substrate. The welding carriage further comprises an adjustment mechanism permitting adjustment of an operative aiming direction of the welding nozzle. Also disclosed is a welding apparatus, which comprises a support surface, a rail traversing 10 the support surface, and the welding carriage previously described, slidably supported on the rail. 8643782_1 (GHMatters) P101661.AU.1 27/01/17 Figure 2

Description

1 2017200554 27 Jan 2017

A Welding Carriage and Welding Apparatus HELD

The present invention relates to a welding carriage and a welding apparatus.

More particularly, the present invention relates to a welding carriage and a welding 5 apparatus for heat welding a polymer strip onto a substrate.

BACKGROUND

Manholes are often provided to permit access to underground utility pipelines. Some manholes are relatively small for accessing pipelines located close to the ground surface, e.g. some pipelines containing electricity and telecommunication cables. 10 Other manholes are much larger and are arranged to permit entry into the manhole by a person, such as by climbing down a ladder to gain access to the pipelines, e.g. sewerage pipelines. Manholes are typically constructed with a masonry lining to provide structural integrity, but the masonry lining is subject to deterioration through aging and corrosion. This is particularly the case for sewerage manholes where gases 15 produced by sewerage, most notably hydrogen sulphide, corrode concrete, brick or other masonry linings.

It is known that manholes can be refurbished, such as by attaching a polymer lining to the masonry lining within the manhole. Although the polymer lining could be bolted into place, this would be time consuming to install and thus tends to be relatively 20 expensive in terms of labour costs. Also, the bolts themselves may be subject to corrosion, which would eventually lead to the polymer lining coming loose from the masonry lining. For this reason it is preferable to fix the polymer lining in place by concrete or grout inserted between the polymer lining and the to the masonry lining.

As the concrete or grout does not always form a secure and long lasting bond with the 25 polymer lining, the polymer lining is provided with various projections that extend outwardly from the polymer lining to be anchored in the concrete to also form a mechanical attachment. 8643782J (GHMatters) P101661.AU.1 27/01/17 2 2017200554 27 Jan 2017

Such a mechanical attachment is known from AU 2014250707, wherein an anchor strip is attached to a lining. As is disclosed therein, the anchor strips can be attached by adhesive, heat welding or by mechanical stapling. When heat welding is utilised, the heat welding must result in a bond of sufficient strength and consistency to ensure 5 that the strip is and remains securely attached to the lining. As the concrete sets there may be a slight shrinkage therein and this may exert tension on the anchor strip, sometimes resulting in separation of the strip from the lining. Also, after the lining is installed in the manhole, other pipes and ladder fittings may be attached to the lining, which may further impose forces that could detach the lining from the anchor strip. 10 Such separation could eventually result in the lining from coming loose in the manhole resulting in additional danger.

It has been found that a secure bond is difficult to obtain using hand welding techniques.

It is to be understood that, if any prior art publication is referred to herein, such 15 reference does not constitute an admission that the publication forms a part of the common general knowledge in the art in any country.

SUMMARY

According to one aspect, there is provided a welding carriage for heat welding a web of material onto a substrate, the welding carriage comprising: 20 a base unit supporting a pressing member for applying a pressing force onto the web during movement of the base unit; a welding head pivotally joined to the base unit, the welding head comprising a welding nozzle arranged for welding the web to the substrate; and an adjustment mechanism permitting adjustment of an operative aiming 25 direction of the welding nozzle.

The pressing member may comprise at least two discrete press wheels, wherein each pair of neighbouring press wheels are spaced apart from each other to define a slot being aligned in a direction of travel of the base unit. 8643782_1 (GHMatters) P101661.AU.1 27/01/17 3 2017200554 27 Jan 2017

The pressing member may comprise a roller having at least one slot therein, the slot extending annularly around the roller and being aligned in a direction of travel of the base unit.

The pressing member may comprise at least two slots. 5 The pressing member may comprise a circumferential tread.

The tread may be formed by parallel grooves and ridges.

The base unit may be slidably mounted on at least one rail.

The base unit may be slidably mounted between two rails extending laterally alongside the base unit. 10 The adjustment mechanism may comprise a buttress arranged to limit an extent of permitted pivoting of the welding head relative to the base unit.

The adjustment mechanism may comprise a block receiving an adjustable threaded bolt, wherein the block is fixedly mounted to the welding head and the bolt is arranged to abut against the base unit or vice versa. 15 According to another aspect, there is provided a welding carriage for heat welding a polymer strip onto a substrate, the welding carriage comprising: a base unit being slidably mounted on a rail, the base unit supporting a pressing member for applying a pressing force onto the polymer strip after a welding operation; a welding head being pivotally joined to the base unit and being pivotable 2 0 between an inoperative position and an operative position for performing the welding operation, wherein the welding head is pivotable in a plane aligned in a direction of movement of the base unit; and an adjustment mechanism permitting adjustment of the operative position of the welding head, wherein the adjustment mechanism is further configured to restrict 25 pivoting of the welding head to ensure a consistent positioning of the welding head when pivoted to the operative position. 8643782_1 (GHMatters) P101661.AU.1 27/01/17 4 2017200554 27 Jan 2017

According to another aspect, there is provided a welding carriage for heat welding a web of material onto a substrate, the welding carriage comprising: a base unit arranged to be movably mounted on a support structure, the base unit supporting a pressing member for applying a pressing force onto the web during movement of the 5 base unit; and a welding head connected to the base unit, the welding head comprising a welding nozzle arranged to facilitate heat welding of the web to the substrate.

The welding head may be movably or pivotally connected to the base unit. The welding carriage may comprise an adjustment mechanism permitting adjustment of an operative aiming direction of the welding nozzle. 10 According to another aspect, there is provided a welding apparatus comprising a support surface; a rail traversing the support surface; and a welding carriage as described herein being slidably supported on the rail.

The rail may be height adjustable above the support surface. 15 The rail may be laterally moveable to different locations across the support surface.

BRIEF DESCRIPTION OF THE FIGURES

An embodiment of the present invention will now be described, by way of example only, with reference to the accompanying schematic drawings, in which:

Figure 1 is a perspective view of a welding apparatus comprising a welding 20 carriage being movably mounted on a rail of a support table;

Figure 2 is an enlarged perspective view of the welding carriage showing its welding head pivoted into an inoperative position;

Figure 3 is a further perspective view of the welding carriage shown at a different angle; 25 Figure 4 is a front view of the welding carriage seen along arrow IV in Figure 2;

Figure 5 is a right side view of the welding carriage, in an inoperative position, seen along arrow V in Figure 4; 8643782J (GHMatters) P101661.AU.1 27/01/17 5 2017200554 27 Jan 2017

Figure 6 is a partial perspective view of the welding carriage shown with its welding head pivoted into an inoperative position with a partially welded polymer strip.

Figure 7 is a right side view of the welding carriage shown with its welding head pivoting into an operative position; 5 Figure 8 is a perspective view of the welding carriage shown with its welding head pivoted into an operative with a partially welded polymer strip.

DETAILED DESCRIPTION

Referring to Figure 1, there is shown a welding apparatus 10 for use in automated heat ίο welding of a polymer strip 12 onto a substrate 14. The substrate 14 is configured for use as a lining for refurbishing a structure. The structure may for example be a manhole to a utilities pipe, pit or well of a waste treatment or pumping station.

Flowever the lining is not limited to such application and may be used in relation to other structures. It will be appreciated that the substrate 14 may be made from any 15 suitable material resistant to the degradation and wear arising from the intended use of the substrate 14.

Typically the polymer strip 12 will be a strip of plastics material, for example, polyvinyl chloride (PVC).

Typically the substrate 14 will be a sheet of plastics material, for example, polyvinyl 2 0 chloride (PVC) or high-density polyethylene (FIDPE). Flowever, the substrate 14 could also be made of a suitable metal or metal alloy.

The substrate 14 may come in various shapes, forms, configurations and sizes suitable for a particular purpose. For example, the substrate 14 may be in the form of a planar or curved square or rectangular sheet, or other shapes such as a triangular, circular or 25 irregularly shaped sheet of material. After one or more polymer strips 12 have been welded to the substrate 14, the substrate can be curved, bent or cut to a desired shape for use as a lining.

The welding apparatus 10 comprises a table 16 with a support structure, in this embodiment, in the form of rails 18 for movably supporting a welding carriage 20. In 8643782_1 (GHMatters) P101661.AU.1 27/01/17 6 2017200554 27 Jan 2017 use, the substrate 14 is initially configured as a flat sheet that is placed on the table 16 while the polymer strip 12 is fed through the welding carriage 20 for attachment to the substrate 14 as the welding carriage 20 traverses the substrate 14 at a substantially uniform speed. The rails 18 guide the movement of the welding carriage 20. 5 The welding carriage 20, as shown in greater detail in Figures 2 to 8, comprises a base unit 22 with a welding head 24 pivotally attached thereto at pivots 26. Thus the welding head 24 is able to pivot around a pivot axis 28a in the directions indicated by arrow 28b from an inoperative position, shown in Figures 2 and 6, and an operative position, shown in Figures 7 and 8. The pivot axis 28a is normal to the direction of 10 travel of the base unit 22 and thus the welding head 24 pivots through a plane that is aligned with the direction of travel of the base unit 22.

The base unit 22 comprises opposed side plates 30a, 30b (generally referred to herein as side plates 30) that are arranged substantially parallel to each other and held in a spaced apart manner from each other by intermediate spacer arms 32 so as to define 15 a gap 34 between the side plates 30. Each of the side plates 30 are attached to the rails 18 by guide brackets 36 projecting laterally outwardly from the base unit 22. The rails 18 have protruding male prong members that are slidably received in recesses 38 formed in the guide brackets 36 so that the base unit 22 can move along the rails 18 in a constrained to-and-fro manner. In another embodiment, the guide brackets 36 could 2 0 comprise the protruding male prong members to be received in slots formed in the rails 18.

The base unit 22 further comprises a drive motor 40 and two sets of press wheels 42, 44 that are mounted in the gap 34. The press wheels 42, 44 are each respectively rotatably mounted on axles 46a, 46b (generally referred to herein as axles 46). 25 The first set of press wheels 42 is configured as font press wheels, whereas the second set of press wheels 44 is configured as back press wheels. In this regard, the directions front and back are relative to the direction of movement of the welding carriage 20 during operative use while welding the polymer strip 12 to the substrate 14. Both sets of press wheels 42, 44 have a tread 48 on their outer circumference, which 30 tread 48 can be constituted by integrally formed knurling, grousers or cleats. Clearly, 8643782_1 (GHMatters) P101661.AU.1 27/01/17 7 2017200554 27 Jan 2017 other forms of treads can also be provided. In the exemplary embodiment the tread 48 is in the form of a gear wheel comprising parallel ridges and grooves that are arranged axially with the press wheels 42, 44 and extend fully across the width of the press wheels 42, 44. 5 As is more clearly visible in Figure 6, the press wheels 42, 44 define two upright slots 50 that are provided annularly in their outer annular face. In the exemplary embodiment the slots 50 do not extend fully through the press wheels 42, 44 but only extend to a depth of about half the radius of the press wheels 42, 44. Thus the press wheel 42 is in the form of a single unitary roller defining three press faces; a similar 10 configuration applies for the press wheel 44. However, it will be appreciated that in other embodiments the slots 50 can be extended fully through the press wheels 42, 44 so that the press wheels 42, 44 each comprise three separate wheels. Having such separate wheels will permit adjustment of the spacing between neighbouring wheels, i.e. the axial width of the slots 50 can be altered. 15 The slots 50 are arranged to accommodate ribs 52 projecting from the polymer strip 12 as is shown in Figure 6. In this manner the press wheels 42, 44 do not press on or flatten the ribs 52 during use while pressing the polymer strip 12 against the substrate 14. The skilled addressee will appreciate that if the polymer strip 12 is only provided with a single rib 52, then the press wheels 42, 44 will each merely need to define a 2 0 single complementary slot 50. Similarly, in polymer strips 12 having more than two ribs 52, the press wheels 42, 44 will each need to define at least an equal number of complementary slots 50.

The axles 46 also carry pulley wheels 54, while the drive motor 40 has a drive wheel 56. Although not shown in the drawings, a drive belt is arranged to pass around the 25 drive wheel 56 and the pulley wheels 54 to impart driving motion to the press wheels 42, 44. In use, such driving motion causes the welding carriage 20 to traverse the substrate 14 by moving along rail 18. Preferably, the drive motor 40 comprises or is part of a drive control system capable of allowing precise speed control of the welding carriage 20 along the rail 18. The drive motor 40 may for example be a servomotor. 8643782_1 (GHMatters) P101661.AU.1 27/01/17 8 2017200554 27 Jan 2017

In the exemplary embodiment the axles 46 project through holes in the side plate 30a so that the pulley wheels 54 and the drive wheel 56 are located on an outside of the base unit 22 and not within in the gap 34. Although the skilled addressee will appreciate that the pulley wheels 54 and drive wheel 56 could easily be located within 5 the gap 34, the location on the outside is considered preferable so as to avoid the drive belt from interfering with the movement of the polymer strip 12 through the gap 34.

The welding head 24 comprises a mounting plate 58 that is supported between two pivot arms 60a, 60b (collectively referred to as pivot arms 60) that are pivotally joined to the pivots 26. The mounting plate 58 is located remote from the pivots 26 and 10 carries an air heater 62. A spout 64 of the air heater 62 is directed to extend towards the pivots 26. A nozzle 66 is provided on the spout 64.

When the welding head 24 is pivoted into its operative position the nozzle 66 is located near to the front press wheels 42. The nozzle 66 is flattened in a plane so that, in use, a flattened jet of air is blown out from the nozzle 66. The nozzle 66 is adjustable on 15 the spout 64 so that the orientation of the air jet can be altered as needed. However, in most cases the nozzle 66 will be orientated parallel to the axles 46 so that the air jet can be evenly directed towards a contact region between the polymer strip 12 and the substrate 14.

As can be more clearly seen in Figures 3 and 4, a trim block 68 is mounted to each of 20 the pivot arms 60. The trim blocks 68 each have a threaded bolt hole for receiving a threaded adjustment bolt 70. The adjustment bolts 70 for buttresses that are arranged to limit the degree of forward pivoting of the welding head 24 and thus the angle and/or direction at which the nozzle 66 directs the air jet in use. Screwing the adjustment bolts 70 deeper into the trim blocks 68 results in the welding head 24 being able to 2 5 pivot farther forwards and directs the nozzle 66 to blow the air jet closer towards the front press wheels 42, i.e. having a shallower acute angle with respect to the substrate 14. Screwing the adjustment bolts 70 out from the trim blocks 68 results in reducing the extent of forward pivoting of the welding head 24 and directs the nozzle 66 to blow the air jet farther forward of the front press wheels 42, i.e. having a steeper acute angle 30 with respect to the substrate 14. 8643782_1 (GHMatters) P101661.AU.1 27/01/17 9 2017200554 27 Jan 2017

The skilled addressee will appreciate that in other embodiments the trim blocks 68 could be mounted on the side plates 30 with the adjustment bolts 70 being arranged to abut against the pivot arms 60.

Referring now again to Figure 1, it can be seen that table 16 has opposed ends 72, 74 5 and opposed sides 76, 78 defining a table top 80. The rails 18 are spaced above the table top 80 and joined to opposed end frames 82 that are mounted in runners 84 extending along the opposed ends 72, 74. The welding carriage 20 is mounted on the rails 18 so that the press wheels 42, 44 are spaced apart from the table top 80 but arranged to be in close proximity to an upper surface of the substrate 14 lying on the ίο table top 80.

The welding carriage 20 is height adjustable above the table top 80 to cater for different thicknesses of substrates 14 and/or polymer strips 12. Such height adjustment can be achieved by either enabling the table top 80 to be adjusted closer to or farther away from the rails 18, i.e. relative to the welding carriage 20 supported on 15 the rails 18. Alternatively, the height adjustment can be achieved by enabling the end frames 82 to be adjusted to lower the rails 18 and the welding carriage 20 to be closer to the table top 80. The height adjustment is suitable not only to facilitate the use of different sized substrates but also to increase or decrease pressure between the substrate and the polymer strip being welded. 2 0 During operation, the welding carriage 20 is configured to start at a location closest to the end 72 and then to traverse the length of the table top 80 towards the end 74 while welding a single polymer strip 12 onto the substrate 14. Thereafter the welding carriage is manually returned to the end 72 for the start of a subsequent run to weld a second polymer strip to the substrate 14. Although it would be possible to simply slide 25 the substrate 14 over the table top 80, this could be cumbersome with larger heavier sheets. Thus the welding carriage 20 is moved laterally across the table top 80 by moving the end frames 82 along the runners 84 to locate the welding carriage 20 at a desired position for welding the second polymer strip 12 to the substrate 14 at a spaced apart position. 8643782_1 (GHMatters) P101661.AU.1 27/01/17 10 2017200554 27 Jan 2017

Clearly the welding apparatus 10 can be further automated so that the return of the welding carriage 20 from the end 74 to its start position near the end 72 can proceed automatically without requiring manual intervention. Similarly, the progressive lateral movement of the end frames 82 across the table can also be automated. Yet further, 5 the welding apparatus 10 can include multiple welding carriages 20 supported by their own rails 18 at discrete positions so that more than one polymer strip 12 can be welded to the substrate 14 at the same time.

With reference to Figures 7 and 8, in use, with the welding carriage 20 located at or near to the end 72, the welding head 24 is pivoted into its operative position. Figure 7 ίο shows the welding head 24 en route to the operative position when pivoted about the pivots 26 in the direction of the arrows 73a and 73b. Figure 8 shows the welding carriage 20 in use in the operative position, wherein the nozzle 66 is positioned adjacent a forward lower edge 75 of the side plates 30 between the strip 12 and the substrate 14. 15 The precise desired angle of the air jet to be blown from the nozzle 66 is set by selective adjusting the adjustment bolts 70. Such adjustment will normally only be required once at the start of the welding run as it is largely dependent on the thickness of the polymer strip 12 that is used.

In the exemplary embodiment, the adjustment of the bolts 70 is done by the steps of 2 0 raising the welding head 24, adjusting the adjustment bolts 70 and reseating the welding head 24 to determine if the desired angle is obtained. This can be repeated as necessary. However, it is also envisioned that the adjustment bolts can have suitable geometric heads, e.g. hexagonal heads, enabling the adjustment bolts 70 to be screwed in or out with a tool such as a spanner while the welding head 24 is in situ in 25 the operative position. Thus, once properly adjusted, the welding carriage 20 can be repeatedly utilised to weld a number of similar polymer strips 12 without requiring any readjustment of the adjustment bolts 70 as they will not be altered by the simple pivoting of the welding head 24 between its operative and inoperative positions.

The polymer strip 12 is cut to the requisite length and then inserted into the gap 34 with 30 an end of the polymer strip 12 being positioned to be fed underneath the front press 8643782J (GHMatters) P101661.AU.1 27/01/17 11 2017200554 27 Jan 2017 wheels 42. The remaining length of the polymer strip 12 extends forwardly over and rests on the welding head 24, as shown by the dotted line 12s in Figure 7, illustrating where the strip 12 would be positioned. As also evident in Figures 7 and 8, a portion of the polymer strip 12 may rest on a resting bar 77 (see also Figures 2 and 6) extending 5 between the side plates 30 in the vicinity of the forward lower edge 75 of the side plates.

In one embodiment the gap 34 has a width being similar to a width of the polymer strip 12 so that once the polymer strip 12 is positioned in place, the side plates 30 assist in correctly aligning the polymer strip 12 within the gap 34. In an alternative embodiment, l o and particularly when the polymer strip 12 has a width substantially narrower than the width of the gap 34, additional guides (not shown) can be joined to the base unit 22 to correctly align the polymer strip 12.

Thereafter both the drive motor 40 and the air heater 62 are activated so that a hot air jet is blown onto an underside of the polymer strip 12 causing it to partially melt so that 15 it can fuse with the substrate 14. During use, the resting bar 77 may assist in ensuring adequate clearance between the strip 12 and the substrate 14, for the nozzle 66 to access a portion of the underside of the strip 12 about to be welded. The air jet delivered by the nozzle 66 may also partially melt an adjacent region of the substrate 14. Activation of the drive motor 40 causes the welding carriage 20 to roll forward on 20 the press wheels 42, 44 and slide along the rails 18. The partially melted polymer strip 12 is then fed under the front press wheels 42, which presses it firmly against the substrate 14 so that the polymer strip 12 fuses or otherwise adheres to the substrate 14. The adhesion between the polymer strip 12 and the substrate 14 is further enhanced by force applied by the rear press wheels 44 whereafter the melted 25 polymer strip 12 is allowed to cool to ambient temperature so that it resolidifies.

As the air jet is blown on an underside of the polymer strip 12, the heat is not sufficient to cause substantial melting of the ribs 52. Also, as the ribs 52 are received in the slots 50 the ribs 52 are not deformed or damaged during the heat welding process. 8643782J (GHMatters) P101661.AU.1 27/01/17 12 2017200554 27 Jan 2017

Once the entire polymer strip 12 has been attached to the substrate 14, the drive motor 40 and the air heater 62 are deactivated and the welding head 24 pivoted back to its inoperative position so that the welding carriage can be returned to the end 72.

By supporting the welding carriage 20 on the rails 18 along both its sides, no torque is 5 applied to the welding carriage 20 so that an even distribution of pressure is applied by the press wheels 42, 44 onto the polymer strip 12. The regulated constant movement imparted by the drive motor 40 to the welding carriage 20, together with the correctly directed air jet ensures that the polymer strip 12 is evenly partially melted across its width as it is brought into contact with the substrate 14 and prevents certain areas of 10 the polymer strip 12 being over melted or under melted. It will be appreciated that over melting a part of the polymer strip 12 can cause weaknesses therein that may lead to rupturing of the polymer strip 12 and which may further lead to the ribs 52 being inadequately joined to the polymer strip 12; this could result in the ribs 52 pulling loose from the polymer strip 12 during use. It will be further appreciated that under melting a 15 part of the polymer strip 12 can result in a weak attachment of the polymer strip 12 to the substrate 1, which could result in the polymer strip 12 pulling loose from the substrate 14 during use.

In one embodiment a lining was manufactured with both the polymer strip 12 and the substrate 14 being made of PVC. The lining was subsequently tested at ambient 20 temperature to determine a tensile load that the ribs 52 could withstand without either the ribs 52 or the polymer strip 12 separating from the substrate 14. The testing indicated that a tensile load of about 2kN could be applied to a single rib 52 without any separation being detected and that a tensile load of about 4kN could be applied to a double rib 52 without any separation being detected. 25 It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. For example, the welding head 24 may be movable relative to the base unit 22 in a nonpivoting manner. In one example, the welding head 24 may be linearly extendible and 30 retractable with respect to a front portion of the base unit 22. Alternatively, in another example, the welding head 24 may be fixed to the base unit 22 provided that a polymer 8643782_1 (GHMatters) P101661.AU.1 27/01/17 13 2017200554 27 Jan 2017 strip 12 can still be positioned for welding. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.

In the claims which follow and in the preceding description of the invention, except where the context requires otherwise due to express language or necessary 5 implication, the word “comprise” or variations such as “comprises” or “comprising” is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention. 8643782J (GHMatters) P101661.AU.1 27/01/17

Claims (18)

1. A welding carriage for heat welding a web of material onto a substrate, the welding carriage comprising: a base unit supporting a pressing member for applying a pressing force onto the web during movement of the base unit; a welding head pivotally joined to the base unit, the welding head comprising a welding nozzle arranged for welding the web to the substrate; and an adjustment mechanism permitting adjustment of an operative aiming direction of the welding nozzle.

2. A welding carriage as claimed in claim 1, wherein the pressing member comprises at least two discrete press wheels, and wherein each pair of neighbouring press wheels are spaced apart from each other to define a slot being aligned in a direction of travel of the base unit.

3. A welding carriage as claimed in claim 1, wherein the pressing member comprises a roller having at least one slot therein, the slot extending annularly around the roller and being aligned in a direction of travel of the base unit.

4. A welding carriage as claimed in claim 2 or 3, wherein the pressing member comprises at least two slots.

5. A welding carriage as claimed in any one of the preceding claims, wherein the pressing member comprises a circumferential tread.

6. A welding carriage as claimed in claim 5, wherein the tread is formed by parallel grooves and ridges.

7. A welding carriage as claimed in any one of the preceding claims, wherein the base unit is slidably mounted on at least one rail.

8. A welding carriage as claimed in claim 7, wherein the base unit is slidably mounted between two rails extending laterally alongside the base unit.

9. A welding carriage as claimed in any one of the preceding claims, wherein the adjustment mechanism comprises a buttress arranged to limit an extent of permitted pivoting of the welding head relative to the base unit.

10. A welding carriage as claimed in any one of the preceding claims, wherein the adjustment mechanism comprises a block receiving an adjustable threaded bolt, wherein the block is fixedly mounted to the welding head and the bolt is arranged to abut against the base unit or vice versa.

11. A welding carriage for heat welding a polymer strip onto a substrate, the welding carriage comprising: a base unit being slidably mounted on a rail, the base unit supporting a pressing member for applying a pressing force onto the polymer strip after a welding operation; a welding head being pivotally joined to the base unit and being pivotable between an inoperative position and an operative position for performing the welding operation, wherein the welding head is pivotable in a plane aligned in a direction of movement of the base unit; and an adjustment mechanism permitting adjustment of the operative position of the welding head, wherein the adjustment mechanism is further configured to ensure consistent positioning of the welding head when pivoted into the operative position.

12. A welding carriage for heat welding a web of material onto a substrate, the welding carriage comprising: a base unit arranged to be movably mounted on a support structure, the base unit supporting a pressing member for applying a pressing force onto the web during movement of the base unit; and a welding head connected to the base unit, the welding head comprising a welding nozzle arranged to facilitate heat welding of the web to the substrate.

13. The welding carriage of claim 12, wherein the welding head is movably connected to the base unit.

14. The welding carriage of claim 12 or 13, wherein the welding head is pivotally connected to the base unit.

15. The welding carriage of any one of claims 12 to 14, comprising an adjustment mechanism permitting adjustment of an operative aiming direction of the welding nozzle.

16. A welding apparatus comprising a support surface; a rail traversing the support surface; and a welding carriage as claimed in any one of claims 1 to 15 being slidably supported on the rail.

17. A welding apparatus as claimed in claim 16, wherein the rail is height adjustable above the support surface.

18. A welding apparatus as claimed in claim 16 or 17, wherein the rail is laterally moveable to different locations across the support surface.