GB2376656A

GB2376656A - Removing notches from the weld face areas of components, to locally reduce waste sprue produced during thermal bonding, apparatus, method & preparation

Info

Publication number: GB2376656A
Application number: GB0115110A
Authority: GB
Inventors: Derek Robert Parsons
Original assignee: GTI KOMBIMATEC MACHINES Ltd
Current assignee: GTI KOMBIMATEC MACHINES Ltd
Priority date: 2001-06-21
Filing date: 2001-06-21
Publication date: 2002-12-24
Also published as: GB0204048D0; GB0115110D0; GB2376657A

Abstract

Apparatus, suitable for welding togther two extruded plastic door or window profiles, comprises a tool suitable for removing part of a surface of at least one of the profiles so that a portion is relieved at said surface. The apparatus further includes means suitable for forming a thermal weld between said surfaces whilst burning off a predetermined length of each profile to a depth exceeding the depth of the relief such that the level of waste sprue produced locally to the relieved area is reduced. The thermal bonding may take place via a heated plate (fig.4) positioned between the two profiles and may reduce waste sprue levels in shaped areas of the profiles which are hard to clean (fig.1). Also disclosed is a bonding method associated with the use of the above described apparatus. Further disclosed is a preparation apparatus which prepares profiles by cutting / notching (fig.9B) a portion of each, and removing the area of cut material to provide a relieved portion.

Description

Welding two extruded plastics door or window profiles This invention relates to a method and apparatus for welding together two extruded plastics door or window profiles, which may for example form a mitred corner joint, or a joint between an end of one profile and a right-angled notch cut into an intermediate portion of another profile.

During the process of welding frame joints in extruded PVC window and door profiles, a flash or sprue is developed and this requires cleaning off. Neither manual nor machined cleaning has been totally successful, particularly where the profiles have been produced to replicate traditional wooden window frames incorporating the so-called "ogee","ovollo", and"bevel"moulded shapes, as illustrated in figure 1 of the accompanying drawings. Profiles are generally coloured white, but some imitate wood grain with a laminated skin and these also require cleaning and have proven to be more difficult to clean than unlaminated profiles.

During the thermal welding process, a predetermined length of profile is sacrificed by "burning off" or melting. The amount of flash or sprue is generally consistent and is set by the welding machine. Often, but not exclusively, the lengths of profile required to produce a frame are sawn say 6 mm longer than the finished frame needed. A hot-plate type welding machine melts back this excess length which envelopes inside and outside the profile, and it is this sprue around the outside of the profile that actually requires cleaning.

The joints can either be mitred corners or notched transoms or mullions (intermediate frame bars).

It is possible to control the sprue with knife-type limiters manufactured from aluminium and steel and designed to surround the profile. Removal of the sprue by hand or machine is still required, although it is easier once the sprue has been limited in this way, but the tooling is expensive and cumbersome and the results remain inconsistent.

1

Accordingly, the purpose of the invention is to overcome or at least mitigate the problem of cleaning sprue in this context.

The present invention provides a method of welding together two extruded plastics door or window profiles, comprising removing part of a cut surface of at least one of the profiles so that a portion is relieved at the said cut surface to be welded, then welding the said relieved surface to a corresponding cut surface of the other profile whilst burning off a predetermined length of each profile, the predetermined length exceeding the depth of relief of the said portion, such that any sprue from the weld is substantially reduced where the said one profile had been relieved.

The invention also provides an apparatus for welding together two extruded plastics door or window profiles, comprising a tool for removing part of a surface of at least one of the profiles so that a portion is relieved at the said surface to be welded, and means for forming a thermal weld between the relieved surface and a corresponding surface of the other profile whilst burning off a predetermined length of each profile, the predetermined length exceeding the depth of relief of the said portion, such that any sprue from the weld is substantially reduced where the said one profile had been relieved.

Further, the invention provides apparatus for preparing two extruded plastics door or window profiles for them to be thermally welded together, comprising a machine for cutting or notching, as appropriate, each profile to form a surface to be welded, and a tool on the same machine for removing part of the said surface to form a relieved portion.

As part of the invention, it was recognised that some particular moulding areas are difficult to clean, and are critical as far as the appearance of the finished product is concerned. Further, it was recognised that sprue could be minimised over these specific difficult areas, whilst the remainder of the joint could be left unchanged so that its strength overall need not be affected adversely. Thus the invention is to anticipate the

expansion at the joint as a result of the burning off, and compensate for this as precisely as possible by removing material locally prior to the welding process. This achieved by the relieving operation.

In order that the invention may be better understood, examples of conventional welding and of welding using the invention will now be described, with reference to the accompanying diagrammatic drawings, in which: Figure 1 shows six cross-sections through typical profile types with decorative moulding, specifically the single bevel outer frame, single bevel"T"transom, single bevel "l" transom, double bevel outer frame, ogee outer frame and ovollo outer frame; Figure 2 is a perspective view from above of the working area of a typical corner welder ; Figure 3 is a perspective view of the welder of figure 2, together with two profiles positioned for a mitre joint, and including the setting plate but omitting the clamps ; Figure 4 shows the welder of figures 2 and 3, with the heater plate in position for melting the profiles; Figure 5 corresponds to figure 4 and shows the welded profiles together with formed sprue; Figures 6A and 6B are end elevations of the heater plate of figure 4 together with the profiles, figure 6A showing the profiles in contact with the heater plate just before melt begins, and figure 6B showing them at the end of the melt, showing areas where sprue has formed; Figures 7A and 7B are views corresponding respectively to figures 6A and 6B but using the process and apparatus embodying the invention, with part of the end of each profile having been relieved ; Figures 8A, 8B, 9A and 9B are different views of one end of a profile held adjacent a saw blade for cutting the relief in accordance with the invention;

Figures 10A and 10B are views corresponding respectively to figures 8B and 8A illustrating the relieved end edges, or relieved portions, prior to welding; Figure 11 is a perspective view of a saw for cutting relief in profiles using the saw blade of figures 8A, 8B, 9A and 9B ; Figure 12 is a plan view of the saw of figure 11, showing the positions of two profiles intended for a mitred joint; Figure 13 is a view of the saw of figure 11 together with a notched profile ; Figure 14 is a plan view corresponding to figures 12 and 13, showing two profiles cut with"arrow heads" ; Figure 15 is a perspective view of a typical Z transom to reverse butt frame welded joint.

Some typical window and door profiles are illustrated in cross-section in figure 1.

These are hollow bars of extruded PVC (polyvinyl chloride) which are typically coloured white but may also be laminated with for example a wood grain effect. Typical dimensions are illustrated. The areas of the mould which are difficult to clean of sprue after thermal welding are illustrated by being encircled in figure 1, and it is these portions which are relieved in accordance with the invention, as will be described below.

The working area of a typical corner welder is shown in figure 2; this example is a single head welder, but a multi-head welder would be capable of welding more than one joint at a time. Left and right fences are mounted on left and right tables respectively, and left and right clamps are closed over the fences. Upper and lower sprue restriction knives are shown on the working edges of the clamps and tables as shown, in order to reduce the amount of sprue remaining on the joint after it has been welded.

The conventional process for forming a mitred joint comprises sawing the profiles at 45 degrees to produce mitred profiles, with an excess length of typically 6 mm to allow for burning off. These profiles are positioned against the left and right fences as

shown in figure 3, and their cut ends are made to abut against a setting plate which bisects the right-angle between the profiles. As shown in figure 4, the setting plate is removed and is replaced by a heater plate inserted between the sawn faces of the profiles. The tables close, pressing the profiles against the heater plate.

The heater plate is then withdrawn and, as shown in figure 5, the profiles are slid further and are pressed together to form the thermal joint. As shown in figure 5, external sprue is formed around the thermal joint.

Figure 6A is a side elevation showing the end edge of the heater plate and the ends of the profiles, immediately prior to welding. Figure 6B shows how the sprue 61 is formed as the profiles are pushed against the heater plate and part of the length of each profile is sacrificed by burning off. An embodiment of the invention is illustrated in figures 7A and 7B, which show that a portion of the end of each profile, after it has been cut to shape, is further cut (or otherwise formed), to produce a relieved section as shown. The relief is formed normal to the plane of the pre-cut surface to be welded, although it is not essential for the portion removed to be exactly rectangular-so long as the same end result is achieved, namely minimising the material at that region. By reducing the amount of plastics material at this section, less sprue is generated as the profile is sacrificed during welding. As illustrated in figure 7B, the major part of the end section generates the full amount of sprue, whereas the relieved section generates a minimum amount of sprue. The area of relief is predetermined to give the minimum amount of sprue, for a given predetermined length of sacrificial burning.

This relieving operation is achieved by sawing just the predetermined portion of the previously-cut end of the profile, as shown from different views in figures 8A, 8B, 9A and 9B. An alternative tool would be a milling or grinding tool. In this example, the relieving is carried out on a bar cut at 45 degrees, but corresponding relieving is intended to be carried out on selective portions of, for example, a right-angle notch cut

into an intermediate portion of a bar, or over one angled surface of an arrowhead shaped end.

The resulting relieved surface is shown in figure 10A, which corresponds to figure 8B. and in figure 10B which corresponds to figure 8A. The relief is cut normally into the cut end surface of the profile, so that it extends in the direction in which the profile is to be melted and sacrificed. Thus the relief may typically be at 45 degrees to the length of the profile. The depth of relief is adjustable to suit various different welder burn off settings, and one example would be a depth of 1.6 mm for a 6 mm burn off. The depth of relief may typically vary between 0.5 mm and 3 mm, and typically it is about one quarter of the length of intended burn off. A preferred range would be from 0.1 to 0.4 of the length of burn off. The burn off length is easiest to measure linearly along the profile's length, so for example a measurement of 6 mm for a 450 end would instead be 4.2 mm for a 900 end.

A machine for cutting the relief in profiles is shown in figure 11 in perspective view, and comprises fixed locating fences at right-angles to each other, adjacent a saw blade. Adjustable guides are affixed on either side, to support the profiles. A plate is inserted and clamped adjacent the saw blade and parallel to it, to act as a relief depth stop, to control the amount of relief cut into the exposed end surfaces of the pre-cut profiles.

This machine of figure 11 is shown in use, in plan view, in figure 12, with left and right hand profiles abutting against the relief depth stop, and the saw blade cutting a relief into just a portion of the end surfaces of the profiles, simultaneously. An alternative use is shown in figure 13, in which a previously-notched profile is given a relief cut over a portion of one side of the notch. The other side of the notch would be similarly treated by turning the profile through a right-angle and using the other side of the machine.

A further example is shown in figure 14, in which two profiles, pre-cut with arrowheads, are simultaneously given relief cuts over a portion of one side or both sides of the arrowhead. It is also possible to work a notched profile and an arrow-headed profile at the same time.

A joint comprising of an arrowhead and a notched cut is made to create a dividing bar in a window or door and is generally known as a transom or mullion or midrail.

A typical Z transom, welded to a reverse butt frame, is shown in figure 15. In this example, the Z transom was given an arrowhead cut, both surfaces of which were given relief cuts over the portions illustrated by circles in figure 1. The abutting portions of the other frame member were also given relief cuts, prior to welding.

In the process illustrated with reference to figure 11, the profiles need to be precut using a different saw (not shown). They are then given the relief cuts, and then moved to a welding machine such as that shown in figure 2. Alternative processes which are intended to be more efficient are also envisaged.

In one example, the relief cuts are made immediately following the sawing of the profiles to length, or the V-notching of the profiles. Using an independently driven milling, sawing or grinding unit, corresponding to the saw blade of figure 11, and fitted to the main sawing machine which is used for shaping the profiles, the relief cuts can be given whilst the profile or profiles remain clamped in position, immediately following their sawing to length or V-notching. Thus one milling, sawing or grinding unit is fitted for each main sawing machine saw blade.

In an alternative arrangement, the relief cuts are made immediately before the profiles are welded together. Using an independently-driven milling, sawing or grinding unit, similar to the saw blade of figure 11, and fitted to a welding head corresponding to that of figure 2, the relief cutting operates immediately after the profiles have been inserted into the welding machine and clamped, but immediately before the welding

process begins. It is envisaged that one such relief-cutting unit would be provided per corner joint, and two such units per transom joint. A vacuum extraction unit would be fitted to the same machine, for removal of the swarf after the relief cutting and prior to the welding.

Claims

CLAIMS 1. A method of welding together two extruded plastics door or window profiles, comprising removing part of a cut surface of at least one of the profiles so that a portion is relieved at the said cut surface to be welded, then welding the said relieved surface to a corresponding cut surface of the other profile whilst burning off a predetermined length of each profile, the predetermined length exceeding the depth of relief of the said portion, such that any sprue from the weld is substantially reduced where the said one profile had been relieved.
2. A method according to Claim 1, comprising cutting or notching the profiles to mitre them prior to the relieving.
3. A method according to Claim 2, comprising clamping the profiles and cutting or notching them to mitre them, and then using an independently-driven milling or sawing or grinding tool to perform the relieving operation whilst the profiles are still clamped.
4. A method according to Claim 2, comprising clamping the profiles after they have been cut or notched to mitre them, using an independently-driven milling or sawing or grinding tool to perform the relieving operation whilst the mitred profiles are clamped, extracting the swarf, and welding them together whilst they are still clamped.
5. A method according to any preceding claim, in which the relieving is performed by milling, sawing or grinding the said portion to a predetermined depth normal to the plane of the surface of the profile to be welded, over a predetermined portion or over two or more predetermined portions of the surface of the profile to be welded.
6. A method according to Claim 5, in which two profiles are welded end to end to form a mitred corner joint, and both ends are relieved over corresponding portions which abut during welding.
7. A method according to any preceding claim, in which the profiles are of PVC.

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8. A method according to any preceding claim, comprising forming a thermal weld using a hot plate welding process to melt back the or each profile surface to cause the said burning off, immediately prior to the abutment of the profiles.
9. Apparatus for welding together two extruded plastics door or window profiles, comprising a tool for removing part of a surface of at least one of the profiles so that a portion is relieved at the said surface to be welded, and means for forming a thermal weld between the relieved surface and a corresponding surface of the other profile whilst burning off a predetermined length of each profile, the predetermined length exceeding the depth of relief of the said portion, such that any sprue from the weld is substantially reduced where the said one profile had been relieved.
10. Apparatus for preparing two extruded plastics door or window profiles for them to be thermally welded together, comprising a machine for cutting or notching, as appropriate, each profile to form a surface to be welded, and a tool on the same machine for removing part of the said surface to form a relieved portion.
11. Apparatus according to Claim 9 or 10, comprising means for guiding the profiles during the relieving process to control precisely the depth and extent of relief over the or each portion.
12. Apparatus according to Claim 9,10 or 11, in which the guiding means is also for clamping the profiles whilst cutting or notching them to mitre them prior to the relieving process.
13. Apparatus according to Claim 12, comprising a saw for cutting or notching the profiles, and an independently driven milling or sawing or grinding tool for performing the relieving operation.
14. Apparatus according to any of Claims 9 to 13, comprising means for extracting swarf produced during the relieving operation.
15. A method of welding together two extruded plastics door or window profiles, substantially as described herein with reference to figures 7 to 14.

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16. Apparatus for welding together two extruded plastics door or window profiles, substantially as described herein with reference to figures 7 to 14.