IES990437A2 - A method and apparatus for making welded frames - Google Patents

Abstract

An apparatus (1) for making welded frames is provided, the apparatus (1) includes a pair of support beds (2) having a support fence (3), the beds (2) are provided with actuating means for moving towards and away from each other. Above the beds (2) is mounted a pair of flat plates (5) which are movable towards each other in one horizontal plane to form together a horizontal welding plate, which then has means for lowering and raising it. A vertical welding plate (7) is mounted above the plates and is movable up and down. <Figure 1>

Description

“A method and apparatus for making welded frames* Introduction The present invention relates to a method and apparatus for making welded frames formed from substantially hollow extruded plastics material sections.

Essentially, the method generally comprises clamping the sections, heating their end faces until they melt and then pushing them together so as to form a but weld. Unfortunately, there is a weld bead or burr which is formed in the joining line between the sections which has to be removed. Such moulded frames are usually for the making of door frames, window frames and the like and the welded joints are usually mitre joints cut at an angle of 45°. Typically the surfaces are heated by pressing against a welding plate. A further problem is that deformation of the plastics section can also occur during the welding operation itself. The removal of the welding bead is required, not just simply for aesthetic reasons but also often to ensure that, for example, the sections forming a window frame fit snugly within the frame of the ope.

Ideally, what is required is to ensure that a flush surface is provided on all faces of the frame. At the same time, the more the plastics material is melted and the more liquid it is, the greater the difficulties that arise. Obviously, the plastics material needs to be heated so as to be sufficiently molten to form a strong joint; a problem arises particularly with thin walled hollow frame sections in that at the top of the joint, that is to say, the uppermost part of the two sections when joined together in the welding machine, the material tends to flow at the top, not outwards to form a bead, but down inwards through the section so that there is a hollow groove formed between the two mating sections, which hollow groove is also undesirable and indeed when the section is a relatively light section, it can lead to a serious loss in structural rigidity.

Heretofore, considerable attention has been placed on the avoidance of the welding bead or its removal and relatively little attention has been paid to the fact that when the plastics material is melted sufficiently to allow it to form a good weld, very often it causes the plastics material to flow away from the joint, leaving the aforesaid groove in one of the faces of the formed frame. a „ „,. . z ...

INT IE 990437 -2For example, in US Patent Specification No. 4,752,350, there is provided a method for making welded corner joints between hollow plastics sections where the sections are cut to a mitre and all heated on a heated welding plate and then, after removal of the welding plate, are pressed against one another. In this US patent specification during the heating operation and during the actual welding process itself when the sections are pushed together, there are provided parts which are adapted to the cover the outer contour of the plastic section and which prevent the softened plastics from seeping outwards. The problem is that it does not prevent plastic material from seeping inwards and leaving not just an unsightly but possibly a structurally unsound joint.

British Patent Specification No. 1,459,004 discloses the manufacture of a mitre joint, again between two members of thermoplastic material and the burr is removed by a knife arrangement. However, the problem has been that heretofore the emphasis has been on the removal of the burr or weld bead, rather than on producing a joint of sufficient strength particularly in thin walled sections.

Unfortunately, as mentioned above, once the end sections are melted sufficiently to ensure that there is an adequate joint, almost certainly the resulting joint, if the section is relatively thin, will not be adequate.

The present invention is directed towards overcoming these problems and providing a method and apparatus for making welded frames formed from substantially hollow extruded plastic material sections that will be structurally strong and aesthetically pleasing.

* Statements of Invention According to the invention, there is provided a method of making welded frames 30 formed from substantially hollow extruded plastics material sections comprising the steps of:cutting mitre joints in the sections; IE 990437 -3holding two sections with their mitre joints spaced-apart and aligned for subsequent joining; lowering a vertical welding plate between the exposed mitre joints; pushing the mitre joints against the welding plate; heating the welding plate; raising the welding plate; pushing the heated mitre joints into contact, to form a butt joint; placing a filler strip of plastics material across the exposed upper part of the contacting mitre joints; lowering a horizontal welding plate onto the strip of material; and heating the welding plate and fusing the strip into the joint The advantage of putting the strip across the exposed surface is that there will now be no hollow or recess in the face of the frame and this will be aesthetically pleasing. Further, the frame will be structurally strong in that there will be sufficient material in the weld so that the but joint will have adequate strength.

In one embodiment of the invention, the vertical welding plate is lowered to extend both above and below the two sections. This means that a full and adequate heating of the plastics materials takes place, not as in some of the methods heretofore proposed.

Ideally, there is a time lag between the moving of the heated mitre joints into contact to form the mitre joint and the lowering of the horizontal welding onto the strip of material to allow the heated plastics material form a recess for the strip. If there is not a time lag, then it is possible that the strip of material will itself progress down into IE 990437 -4the joint and ideally the time lag allows a certain amount of welding to have taken place. Ideally, the time lag is between 2 and 5 seconds.

In one embodiment of the invention, the welding plates are heated for between 5 to 20 seconds. One of the advantages of the present invention is that longer lengths of heating time may be achieved.

In a still further method of carrying out the invention, the vertical welding plate is heated for between 7 and 14 seconds and the horizontal welding plate is heated for between 6 and 8 seconds. Once it is desired to ensure that the top surface of the frame will have a smooth outer surface, it is often necessary to reduce the heating time of the welding of the strip to prevent undue flow of material into the joint Ideally, the joint is held with the sections in contact as the joints cool for a period of between 25 and 40 seconds and this may in certain circumstances be 30 to 35 seconds.

Ideally, for each mitre joint the section is cut oversize relative to the desired final size by between 1 and 5 mm. It will be seen that if such a substantially amount of material is used, the joint must be adequately melted and fused in manufacture. Generally speaking, the cut-over size should be of the order of 2 to 3.5 mm.

Further, the invention provides an apparatus for carrying out the method comprising a pair of support beds each for secure retention of a section therein, the beds being movable apart and into contact with each other; a vertical welding plate which can be lowered between and raised free of the beds; a pair of flat plates movable towards and away from each other in the one horizontal plane, each having a mitred exposed end contact edge movable into contact to form a composite horizontal welding plate and apart to allow the passage of the vertical welding plate therebetween. This is a particularly satisfactory way of making the apparatus because it allows the horizontally arranged welding plates may also act as a support for the sections during the previous welding operation.

In one embodiment of the invention, each support bed includes a planar section IE 990437 -5supporting base having an exposed mitred end edge for mutual contact on raising the vertical welding plate to provide a contact surface against the bottom of the butt joint formed to force molten material up into the joint. The advantage of this is that there is now support beneath the frame as the joint is being formed which will further reduce the amount of weld bead build-up.

Detailed Description of the Invention The invention will be more clearly understood from the following description of an embodiment thereof, given by way of example only, with reference to the accompanying diagrammatic drawings, in which:Fig. 1 is a perspective view of the apparatus prior to use; Fig. 2 is a view of the apparatus during a welding operation; Fig. 3 is a typical sectional view of the apparatus in the position of Fig. 2; Fig. 4 is a view of the apparatus with one of the welding operations completed and the other about to start; and Fig. 5 is a view showing the final welding operation.

Fig. 6 is a cross-sectional view of a typical section used in forming a frame; and Fig. 7 is a perspective view of a machine incorporating the apparatus.

Referring to the drawings and initially to Fig. 1, there is illustrated an apparatus identified generally by the reference numeral 1. The apparatus includes a pair of support beds 2 having a support fence 3 for mounted of a section identified by the reference numeral 4 and illustrated in Fig. 6. The beds 2 are provided with actuating means (not shown) for moving them towards and away from each other in the direction of the arrows A. Above the beds 2 is mounted a pair of flat plates 5 which IE 990437 -6are movable towards each other in the one horizontal plane to form together a horizontal welding plate which then has means (not shown) for lowering and raising it in the direction of the arrows B. A vertical welding plate 7 is mounted above the plates 5 and is movable up and down in the direction of the arrows B. All the control mechanisms and the heating mechanism 5 and 7 are not illustrated but they are of conventional construction.

In operation, a method of making welded frames will now be described with reference to Figs. 1 to 5. Various sections such as the section 4 as are appropriate for making the frame are cut to length. The sections 4 have to be cut oversize to accommodate the reduction in size that will occur when the sections 4 are melted and butt welded together. Obviously, the melting and fusion of two sections together will lead to a reduction in length. It is important that the section be cut in such a way as to ensure that sufficient material is melted to provide an adequate butt joint but at the same time that there is not an over abundance of material melted which would lead to excess material as beads or buns when the joint cooled generally a maximum 5.0 mm oversize is sufficient for each joint namely 2.5 mm additional length for each section. This can be between 1 and 5 mm or preferably between 2 and 3.5 mm. Thus with a flour sided frame with an oversize of 3.0 mm per joint each section would be cut 6.0 mm oversize.

Then with the beds 2 apart, the sections 4 are placed on them. At this stage, as well as the beds 2 being apart, the vertical welding plate is in the raised position (Fig. 1). When the vertical welding plate 7 is lowered to lie between the beds 2 and the plates 5, the sections 4 are pushed against the vertical welding plate 7 which is heated (Figs. 2 and 3). Usually it is heated for between 5 and 20 seconds and ideally between 7 and 14 seconds.

Then the vertical welding plate 7 is raised to the position illustrated in Fig. 4, the two sections 4 are pushed together as the beds 2 are also forced together causing melted ends of the sections 4 to contact each other and start to form the mitre joint. As the plastics material melts, a recess will be formed where the two sections meet at the top. Into this recess is placed a strip of plastics material identified by the IE 990437 -7reference 10. The plates 5 are moved together and lowered to the position illustrated in Fig. 5 where they are heated to weld the strip 10 into the mitre joint. This produces a clean face and strong joint.

Because the beds 2 are tightly joined, there is little or no protrusion of material to form a burr or bead on the underside of the frame.

Fig. 7 shows a typical machine incorporating the apparatus illustrated in Figs. 1 to 6 for the manufacture of a window frame having a horizontal mullion.

Using PVC which is the preferable material or the material most commonly used for the manufacture of such sections and frame members, it has been found that the ideal welding temperature is of the order of from 235 to 255°C.

The invention is not limited to the embodiments hereinbefore described but may be varied in both construction and detail.

Claims (5)

1. A method of making welded frames formed from plastics material sections comprising the steps oftcutting mitre joints in the sections; holding two sections with their mitre joints spaced-apart and aligned for subsequent joining; lowering a vertical welding plate between the exposed mitre joints; pushing the mitre joints against the welding plate; heating the welding plate; raising the welding plate; and pushing the heated mitre joints into contact, to form a butt joint.

2. A method as claimed in claim 1 in which the additional steps are performed of: placing a filler strip of plastics material across the exposed upper part of the contacting mitre joints; lowering a horizontal welding plate onto the strip of material; and heating the welding plate and fusing the strip into the joint.

3. A method as claimed in claim 1 in which the vertical welding plate is lowered to extend both above and below the two sections and in which there is a time lag of between 2 and 5 seconds between the moving of the heated mitre joints into contact to form the mitre joint and the lowering of the horizontal IE 990437 -9welding onto the strip of material to allow the heated plastics material form a recess for the strip and in which the welding plates are heated for between 5 to 20 seconds, and preferably the vertical welding plate is heated for between 7 and 14 seconds and the horizontal welding plate is heated for between 5 and 8 seconds and in which the joint is held with the sections in contact as the joints cool for a period of between 25 and 40 seconds, preferably between 30 and 35 seconds and in which for each mitre joint, the section is cut oversize relative to the desired final size by between 1 and 5 mm and preferably between 2 and 3.5 mm.

4. Apparatus for carrying out the method as claimed in any preceding claim, comprising:a pair of support beds each for secure retention of a section therein, the beds being movable apart and into contact with each other; a vertical welding plate which can be lowered between and raised free of the beds; a pair of flat plates movable towards and away from each other in the one horizontal plane, each having a mitred exposed end contact edge movable into contact to form a composite horizontal welding plate and apart to allow the passage of the vertical welding plate therebetween and in which each support bed includes a planar section supporting base having an exposed mitred end edge for mutual contact on raising the vertical welding plate to provide a contact surface against the bottom of the butt joint formed to force molten material up into the joint.

5. A method as claimed in claims 1 to 2, substantially as described herein with reference to and as illustrated in the accompanying drawings.