GB2331484A

GB2331484A - Welding plastics profiles

Info

Publication number: GB2331484A
Application number: GB9825390A
Authority: GB
Inventors: Garry Andrew Smith
Original assignee: Rehau Ltd
Current assignee: Rehau Ltd
Priority date: 1997-11-25
Filing date: 1998-11-19
Publication date: 1999-05-26
Also published as: EP0920978A3; GB9724909D0; EP0920978A2; GB2331484A9; GB9825390D0

Abstract

A method of welding plastics profiles together to form joints, eg., corner joints of door and window frames, comprises preparing the ends of the profiles for welding by cutting back a section 5 of the profile 1 so that it lies below the remaining section 6. During heating, only section 6 is melted and the parts are brought together so that the unmelted sections 5 simply butt up to one another, or only merge to a very small extent, thus giving the appearance, when looked at towards the surface 2, of a non-welded butt joint, ie., the formation of a burr on the surface 2 is avoided. The ends of the profiles 1 may be cut with a continuous shallow slope (Figure 5) so that section (8) lies forward of the remainder of the profile. When a profile cut in this way is pushed together with another similar profile in order to make a butt joint, the two sections (8) would meet first, and thus it is these areas which are melted in order to effect the welded joint.

Description

1 "WELDING METHOW 2331484 This invention relates to a method of welding

plastics components, for example for use in the building industry and in domestic equipment. A particular application for the present invention is the joining of profiles used to manufacture plastics door and window frames.

At present various different methods are used to join profiles together. One nown method is by way of external mouldings fixed by means of adhesive or screwed fastener. This method is expensive, is of low strength and has a poor appearance; however it is relatively easy to assemble. A similar method uses internal mouldings fixed by adhesives or screwed fasteners which have similar advantages and disadvantages to the external moulding methods, except that external appearance would generally be good. The internal mouldings may be replaced by steel plates, which are screwed into position; these give similar advantages and disadvantages. A still further method involves welding, for example butt welding, of profiles. This is a relatively cheap method and produces joints of high strength; however, assembly requires a secondary operation to remove flash and the appearance is generally inferior to joints which have an internal fixing. Welding involves softening or melting the surfaces to be joined by any of the known methods, for example heating or applying solvent, and thence pushing the surfaces together to effect the joint.

The present invention seeks to provide a method of forming such joints which will provide the strength of the welded joint with the good visual appearance of the internaily-mechanically fixed joint.

According to the invention there is provided a method of joining plastics components by welding, said method comprising the steps of cutting the surfaces to be joined and thence melting at least one of the surfaces and pushing the surfaces together to form a joint between the components, said method being characterised in that at least one of the 2 1 i surfaces to be joined is cut so that a section of the surface lies forward of the remainder of the surface and in that only said section of the surface is melted.

The cutting of the surface for the purposes of the present invention can be considered in relation to a notional surface which would need to be cut in order to effect a butt joint between the components. For example, to butt join two elongate components at right angles, the ends of the components would be cut at an angle, normally 450, as a preparatory step. In the conventional welding process, the whole of the 450 surfaces thus formed would be melted, and the joint formed by pushing these two surfaces together. The present invention involves modifying such surfaces so that a section of the 450 surfaces lies forward of the remainder so that, upon pushing the two surfaces together, that section of one surface will be the first part to meet its corresponding section of the other surface. If only this section of the surface is melted, then the finished joint can appear as a butt joint because the remainder of the surface is not melted either at all, or to a lesser extent.

The modification of the surfaces for the purposes of the present invention can be realised in various different ways. For example, the surfaces, as well as being cut to effect the joint in the manner just described, can additionally be sloped in a different plane to define one section forwardly of the remainder. In this case, there is no clear distinction between the section which lies forward, and the remainder, since one gradually merges into the other and the section which lies forward, and is thus melted, can be as small or as large, in relation to the whole of said surface, as occasion demands. In an alternative embodiment, a distinct step can be formed between the section which lies forward, and the remainder. This step can be a right angle step, or can take the form of a ramp between the section which lies forward and the remainder. Preferably, in this case, the section which lies forward, and the 3 remainder lie on planes which are parallel to, but spaced from one another, as distinct from the first alternative described above, where both of the sections which lie forward, and the remainder lie on the same plane which is sloped from the plane of the notional surface which would be used to form a butt joint. If desired, a combination of the two techniques - sloped surface and step - can be used.

If a step is formed, the cut end is effectively divided into two sections: a first section at the original level of the end surface and a second section, preferably containing a selected external surface, at a lower level. The amount of the cut back will depend upon the circumstances, but will typically be in the range 1 to 5 mm, preferably 2 to 3 mm.

During the welding process, it is preferred to melt only the first section so that the second section remains undistorted. After melting of the cut ends in this way, the two profiles are pushed together until the melted first section has, in effect, disappeared. At this point, and provided that both profiles to be joined are similarly treated (the preferred situation), the two unmelted second sections of the profile will be butted up to one another.

Thus the joint has the appearance, at least when viewed in the direction of the selected surface, of a mechanically joined butt joint, but is actually joined by welding. If desired the operation can be completed by removing the flash formed by excessive material from those external parts of the profiles which were not cut back. This can be done with a knife, or by machining a groove along the length of the welded seam, or by any other suitable method.

When two profiles are to be joined together, it is preferred that the extra cutting back operation is carried out on the cut end surfaces of both profiles; furthermore, that that part of each profile which is cut back corresponds as between the two profiles so that, when butted together, the w - 4 melted sections merge together and the unmelted sections come together the latter, of course, merely butting together and not merging, at least not to a significant extent. In an alternative, the two sections of the cut ends of the profiles are melted to different degrees - the first sections being melted to a greater degree than the second sections. If carefully controlled this can result in a limited melting together of the second sections not sufficient to cause noticeable distortion or flash.

The method of the invention can be used to make corner joints at any angle, or straight joints.

Generally speaking the selected external surface will be one which, in use of the profile, is the most critical from the aesthetic point of view. Ina door or window frame, for example, it might be the highly visible external surface of the 450 joint at the corner of the frame - most if not all of the remaining parts of the joint are invisible in use so the flash is not visible. However, the invention is not restricted to treating just one selected external surface of the profile in this way; if it is necessary, for aesthetic or other reasons, to make the joint between multiple external surfaces a simple butt joint, then more surfaces can be cut back. However, it is clear that the more of the cut end of the profile is cut back, the weaker the joint will be unless steps are taken to provide additional internal walls and/or ribbing within the profile to compensate.

In a preferred embodiment of the invention, the profile is such as to define an internal wall close to the selected external surface, this wall being not cut back, and thus taking part in the butt welding. This ensures that there is no loss of strength by failing to weld, or welding only weakly, particular sections of the profile.

In order that the invention may be better understood, two embodiments thereof will now be described by way of example only and with reference to the accompanying drawings in which:- Figures 1, 2 and 3 are, respectively, end, side and perspective views of a profile suitable for use in a first embodiment of the method of the invention; Figure 4 is an enlarged end view of the profile, similar to Figure 1, but showing the cut-back section of the profile; Figure 5 is a side view of a profile showing a cut end prepared in accordance with a second embodiment of the invention; and Figure 6 is a view similar to that of Figure 2, but showing the second embodiment.

The particular profile shown in Figures 1 to 4 is a door profile for domestic appliances; however, the method of the invention can be used with any joint for any purpose, particularly where an attractive finish is desired for at least some of the external surface of the joint.

It will be understood that two lengths of profile are necessary to make a joint; only one is shown, but it is preferred that the other is treated in a similar way to that about to be described.

The profile is shown generally under the reference 1 and is formed by extrusion from plastics material such as PVC or ABS. To form a corner joint, the profiles to be joined are first cut at 4511. In the known method, the thus-cut ends would then be melted by, for example, heating to melting point by contact with the hotplate of a welding machine, or by application of a suitable solvent. Finally, the two mitred ends would be pushed together to effect a strong join.

In the present method, the welding step is preceded by cutting back a selected part of the cut-end face of the profile 1. In the profile illustrated, the surface 2 is to be visible in the assembled and fitted frame and it is therefore desired to make the joints, at least as it appears between the surfaces 2, as attractive as possible.

To this end, that wail 3 of the profile which forms the surface 2 is cut back by 3 mm from the remainder of the cut end. This is illustrated clearly in Figure 4, where the hatched section 4 represents that part of the 1 1 1-1 6 profile which has not been cut back, whilst the non-hatched section 5 is cut back as described. It will be seen that the cut-back section includes the wall 3.

The cutting back operation can be achieved in any 5 convenient manner, such as by sawing or machining.

Having carried out the cutting back operation, welding proceeds as normal, except that only the section 4 of each profile is melted, while the section 5 remains unmelted. Then, the two profiles are pushed together until the two unmelted sections 5 abut.

Thus, when viewed in the direction of surface 2, the profiles appear to be joined by a mechanical butt joint whereas the joint is actually welded.

If necessary any excess material from the remaining external parts of the welded seam can be removed in the conventional manner.

When using the above-described method, attention needs to be paid to the finished joint, particularly in the area of section 5 where there is only an abutting of surfaces, and not an attachment. If this is a problem, one solution would be to just lightly heat bond the sections 5 or even use an alternative method of fixing altogether, for example adhesive. This has the advantage of sealing the abutting surfaces against ingress of moisture. An alternative solution, and the one illustrated in the attached drawings, is to provide the profile with a wall, probably an internal wall, which forms part of section 4 (and is therefore welded) and which is reasonably physically close to the non-welded section so as to compensate for a possible lack of strength in this area. Such a wall might, for example, extend along the intersection between sections 4 and 5 (but in section 4). Such a wall is illustrated in the drawings under reference 6.

The angle of cut does not need to be 450. A 450 angle will be used to join like profiles at an angle of 900. Other angles can be used to form different types of corner joints - for example at different angles, or 7 between different (but compatibly shaped) profiles. Straight joints can also be made by this method, using angled or 901 transverse cuts. Furthermore, the welded and non-welded sections do not necessarily have to be cut at the same angle: there may be circumstances, with certain shapes of profile, where a slightly different angle would be used, but still with the ultimate aim of bringing together the unmelted sections to a neat butt join.

Figures 5 and 6 illustrate a profile 1 cut for use with a second embodiment of the method of the present invention. The cut end surface 7 of the profile 1 is cut at a compound angle which is at 450 to the elongate axis of the profile (for the purpose of forming a right angle joint), and at 130 to the normal cut end which would, of course have been made at 901 to the plane of Figure 6. If a profile cut in this way is pushed together with another similar profile in order to make a butt joint, then the two sections 8 of the surface of each of the profiles would meet first. It is thus these areas of the profiles which are melted in order to effect the welded joint. The extent to which the surface 7 is melted will depend upon the circumstances, an example being given in Figure 5 where the hatched section 8 is intended to represent that part which is melted, whilst the nonhatched section 9 represents the part which is not melted. Thus, in this case, at the top surface 2 the profiles are subjected only to a butt joint.

The angle of 131 can be adjusted to suit the circumstances and will be such as to give a total "height" h between the ends of the sloping surface in a similar range to the height of the step described in relation to the first embodiment - i.e., in the range 1 to 5 mm, with a typical value of between 2 and 3 mm.

8

Claims

1. A method of joining plastics components by welding, said method comprising the steps of cutting the surfaces to be joined and thence melting at least one of the surfaces and pushing the surfaces together to form a joint between the components, said method being characterised in that at least one of the surfaces to be joined is cut so that a section of the surface lies forward of the remainder of the surface and in that only said section of the surface is melted.

2. A method as claimed in claim 1 wherein, after melting, the surfaces are pushed together to the extent that said remainder of the surface becomes butted up to a corresponding part of the other surface.

3. A method as claimed in either one of claims 1 or 2 wherein said section of the surface is melted to the extent that, upon pushing the surfaces together, the joint is formed wholly or primarily by said section of the surface, whilst the remainder of the surface is substantially undistorted.

4. A method as claimed in claim 3 wherein only said section of the surface is melted so that, upon pushing the surfaces together, said remainder of the surface forms a butt joint with a corresponding section of the other surface.

5. A method as claimed in claim 3 wherein both the section of the surface which lies forward, and the remainder, are melted, but to different degrees, so that said section of the surface becomes more melted than the remainder.

6. A method as claimed in any one of the preceding claims wherein both of the surfaces to be joined are cut in the aforesaid manner, the section which lies forward in each case being in a corresponding position with respect to the corresponding section of the other surface.

7. A method as claimed in any one of the preceding claims wherein both said sections of the surface and the remainder of the surface 9 lie in substantially parallel planes, and are separated by a step.

8. A method as claimed in claim 7 wherein the step is in a plane substantially at right angles to said parallel planes of said section.

9. - A method as claimed in claim 7 wherein the step forms a sloping ramp between said section of the surface and the remainder.

10. A method as claimed in either one of claims 7 to 9 wherein the height of the step is in the range 1 to 5 mm.

11. A method as claimed in claim 7 wherein the height of the step is in the range 2 to 3 mm.

12. A method as claimed in any one of claims 1 to 6 wherein the surface is cut with a continuous shallow slope so that said section of the surface comprises a part of the sloped surface which lies forward of the remainder.

13. A method as claimed in claim 12 wherein the surface is sloped at an angle in the range 101-151.

14. A method as claimed in any one of the preceding claims wherein the components to be joined take the form of hollow profiles.

15. A method as claimed in claim 14 wherein additional internal wall means are provided in the area of the remainder of the surface in 20 order to compensate for lack of strength in that area of the joint.

16. A method as claimed in any one of the preceding claims wherein the remainder of the surface extends to an edge of the surface to be joined, said edge being one which is required, in the finished joint, to have the appearance of a butt joint, with little or no melting between the components in the area of the edge.