GB2074288A - Improved Jointing Method - Google Patents

Abstract

A method is described of joining power driven belts by cutting interlocking matching shapes in the two ends, the shapes comprising spearhead lobes alternately pointing forwards and backwards in the belt direction. The lobes have sharp points. Methods of making cutting boards suitable for cutting these shaped ends are described, together with techniques for fitting and vulcanising the joints together. <IMAGE>

Description

SPECIFICATION Improved Jointing Method My invention relates to an improved method of making joints in power-driven belts, and ways of effecting such joints. Conventionally such joints are made by stepping the cloth plies at each end in such a way that these ends can then be overlapped to form a smooth joint. The joint is actually made by vulcanising an adhesive or melting the layers together. It is also known to make joints by cutting matching zig zags in each end, fitting the ends together, and vulcanising them. With no means of preventing slip such a joint is not reliable, especially when made by relatively inexperienced personnel. An interlocking joint has also been described where each end of the belt is cut with repeated rounded spurs which interlock with each other.Such a joint is fairly easy to make, but suffers the great disadvantage that the ends of the rounded spurs approximate to straight lines running across the width of the belt. The stress on these lines is very considerable, and in use, where the belt has to flex round rollers or knife edges, these stresses cause early cracking. The thicker the belt, the greater are these stresses and in practice, therefore, such joints are limited to very thin belts.

My invention describes a way to make an interlocking joint which does not suffer this problem at early cracking because no such rounded ends are present. An interlocking shape generally illustrated by the accompanying drawing, figure 1 is cut on both ends in such a way that the two ends of the belt match perfectly together. The essential feature of the shape is that it consists of lobes, each with an end which comes to a sharp point. These points are like spearheads pointing along the travelling direction of the belt, alternately forward and backwards. In the simplest embodiment this shape can best be described by defining a line which is hypothetically drawn at right angles to the edges of the belt across the whole width of the belt. This line forms the base of each lobe, with alternate ones pointing left and right respectively. Consider one lobe.Starting on the base line travelling towards the point of this lobe the width initially becomes greater as it follows a smooth curve to a maximum, at which point it starts to becomes narrower again progressively until the final point is reached. The adjacent lobes point the opposite way but also have their base on the same hypothetical line, and follow similar changes of width as they progress to the point. It will be noted that it is not necessary for any two lobes to be identical in size or shape provided they conform to the general characteristics described.

The accompanying drawing, figure 2, illustrates the generalised shape of a single lobe, and by comparison with figure 1 the way in which the lobes of alternating direction interlock smoothly can be seen.

The angle a can vary from just less than 1800 to just over zero. However, in the former case it becomes indistinguishable from a straight line, and hence cracking is likely, and in the latter case it becomes infinitely long. The preferred range is 900 to 50 with values between 100 and 300 giving the most convenient and effective results.

Providing they conform to the description given the sides of each lobe may be convex, concave or even straight or any conforming combination of all three. For the extreme case where they are all straight sides the position of maximum width will be marked by sharp angles on each side.

In another embodiment of my invention the lobes need not be symmetrical, providing they can be drawn as a continuous line without the pen leaving the paper and that all lobes have an open base. By this is meant that a line drawn parallel to the side of the belt, and through the widest point of either side of any one lobe, does not overlap a similar line drawn through the widest point of the nearer side of the next lobe pointing in the same direction. The widest points of each side of the same lobe do not need to be on a line at right angles to the edges of the belt. The pointed ends of any two lobes pointing in the same direction do not need to be on a line at right angles to the edges of the belt.

The most convenient shape uses symmetrical lobes of uniform shape, with rounded edges except that the lines progressing to the point approximate to straight lines. Where each lobe is at a maximum width, there is also a minimum distance seperating any two lobes pointing in the same direction. Maximum strength of the joint occurs where the maximum width is close to twice this minimum separation distance, and this is therefore a preferred shape.

We shall now consider ways of cutting the ends of the belt to conform to the shapes previously described. They can, of course, be cut with a knife freehand or against a template. The most convenient way, however, is to make a cutter from sharpened strips of a suitable knife material, bent or otherwise formed into the appropriate shape to cut the belt ends. This shaped strip blade is best supported by insertion in a plate or board also cut to the same shape, with sufficient blade projecting to cut two layers of the thickest belts required. This supported cutter can then be forced through both ends of the belt at the same time, ensuring that they match exactiy. It can be forced through either by hammering or better by closing in a press which will ensure uniform and accurate cutting without accidental slippage.It is particularly convenient to use the same press as will be used to vulcanise the belt, as it can be clamped in the correct position, cut and vulcanised without moving.

Whereas simply bending the metal strip into shape can result in a cutter of the required shape, it is found that the hardened strip may crack when bent to the preferred range of accute angles. It is an important aspect of this invention that certain methods of making suitable cutters are included in the invention, and these are described.

Nevertheless cutters made by bending are the cheapest and are effective even with larger than preferred angles.

The preferred method, however, is to shape individual strips of sharpened, hardened knife steel and join them at the acute angled tips.

Because the tip is the most critical part of the pattern it is necessary to ensure that the blade edges match perfectly in a mitred joint and do not separate, thereby leaving part of the belt uncut. If the supporting back board is rigid and the shape accurately cut then the mitred joint will be forced together where the strips are held in the back board. If the strip is rigid then the blade edges will be held together, but in practice there is no guarantee of this especially if the length projecting from the back board is much greater than the thickness of the strip. Reliable cutting results have only been obtained when the strips have been fastened at the tips. The preferred ways to do this have been rivetting, spot welding and spot brazing.As welding and brazing can be subject to variation due either to excessive heat treatment softening and embrittling the edge, or to inadequate strength because the heat was too little, riveting has proved the most straightforward and reliable. Figure 3 illustrates the typical geometry of a mitred tip joint excluding the supporting back board. Both the left and right hand blade strips were pre-bent in a press jig according to the required shape. The ends were taper ground in another jig along the place ACD, and the two halves fitted together so the sharpened edges met at point B. Prior to assembly the holes were drilled and countersunk at a position G as close as practicable to B to hold the sharp edges together when cutting forces could tend to spring them apart. The holes are best drilled in a jig to ensure perfect matching.

The portion shown dotted, FCDE, was ground away as otherwise this would have cut into the belt beyond the tips, and weakened the belt. BF was chosen to be approximately the same as the strip thickness. The strips were assembled in the cutting board, the steel rivets positioned and closed by means of a pair of heavy pliers ground so the jaws matched the angle of the mitred joint.

When spot welded joints were made the weld was made in a similar position to G.

Other methods of manufacturing suitable cutting boards include taking a sharpened strip of hardenable steel in the semi-hard condition only, bending it to the required shape and then hardening it by oven or flame treatment, either fully or on the edge only. A third method involves a strip of hard but still ductile chrome carbon steel not sharpened at all, which is bent to the required shape, when fully hardened, and then sharpened by electro-chemically dissolving the edge to a sharpened form against a plate electrode parallel to the plane of the cutting edge.

When the cutting tool has been made and fixed in its board, it is used as follows in a vulcanising press.

On the bottom platen is placed a steel plate to prevent cutting into the platen. On top of this is placed a hard plastic sheet (such as polypropylene) to act as a re-usable anvil. The two ends of the belt are placed on top of each other ensuring accurately parallel edges. The cutting board is placed next, followed by another steel plate. The top platen is placed on top and the press closed. Uniform pressure enables the cut to be made uniformly.

The ends of the belt are then interlocked. If the cutter strip chosen was suitably thin there should be virtually no distortion of the cut ends, and the ends should fit tightly together.

In one embodiment of my invention the ends can be so interlocked and then the joint heated in the press to fuse the ends together using the plastic covering and/or laminate to act as its own adhesive.

In another embodiment the edges of the interlocking lobes may be painted with adhesive and fused or vulcanised together.

In another embodiment a piece of cloth which may be too thin to add directly to the strength, is placed over or behind the joint and vulcanised into the latter. The functions of this is to hold down the lobes to maintain interlock when the stresses of passing round small knife edges or rollers would otherwise tend to disengage the lobes.

In a further embodiment this back cloth may be cut on the bias to give the joint more flexibility than if it is cut straight.

In a further embodiment the adhesive may be one or more sheets of a hot melt adhesive, placed above or below the belt or both sides at once.

Suitable belting constructions for use with this technique include those with cloth made from glass, polyester, nylon, cotton and rayon, or any mixture of these fibres, suitable laminations and coatings include poly vinyl chloride (PVC), polyurethane, various rubbers both synthetic and natural, polyethylene, polypropylene, silicone and polytetrafluorethylene.

A conveyor belt 3 mm thick made from two plies of polyester coated and laminated with PVC was threaded round a conveyor, the ends overlapped over an anvil inside a press, the cutting board with rivetted ends described above was placed over the belts and the top of the press carefully positioned on top of the board. Closing the press forced the board uniformly through both belts leaving two matching ends. The blades in the cutting board were 0.9 mm thick which led to virtually no permanent distortion in the belting material. The edges of both ends were coated with a PVC adhesive, the ends fitted together in the same press, excluding the anvil and cutting board, and the joint vulcanised at 1 500C. The belt, which also included a conventionally made overlapped joint for comparison purposes, was run under arduous flex test conditions. The interlocked joint was still satisfactory when the conventional joint failed.

Another example used a single ply polyester conveyor belt coated with thermoplastic polyurethane, overlapped and cut in the same way. Two such joints were made in a single belt, one without a reinforcing cloth and the other was pressed with a piece of polyester scrim (cut on the bias and treated with primer for adhesion to polyurethane) laid on top of the belt.

No discernible flexibility difference between them was apparent after these joints had been separately vulcanised. However, on testing for durability in a long term test the reinforced joint took nearly twice as long before failure occurred.

Claims (17)

Claims

1. A method for joining belts which comprises cutting at each end matching, interlocking shapes consisting of a series of spearhead shaped lobes with sharp points pointing alternately in the forwards and backwards direction of the belt, interlocking these shaped ends and vulcanising or glueing them together.

2. A method according to Claim 1 wherein the lobes are of uniform shape and size forming a pattern across the belt such that the maximum width of each lobe equals twice the minimum separation distance between two adjacent lobes pointing in the same direction, or is close to this ratio.

3. A method according to Claim 1 wherein the points of the lobes may have an included angle of between 5 and 900.

4. A method according to Claim 1 whereby the cutting is effected by a cutting board comprising strips of sharpened knife steel bent or assembled together into the correct shape, and forced through a base board cut to the same shape as a support.

5. A method according to Claim 4 whereby the cutting board and the belt ends are placed in a press and the board cuts the ends to the correct matching shapes when the press is operated.

6. Cutting boards according to the construction given in Claim 4.

7. Cutting boards according to Claim 6 wherein the sharp ends of the lobes are formed by mitring two separate pieces of steel strip together so the sharp edges of the strips meet at a point.

8. Cutting boards according to Claim 7 wherein the separate pieces of steel strips are fastened together in addition to being held together by the supporting back board.

9. Cutting boards according to Claim 8 wherein the fastening is effected by countersunk rivets near to the blade edge.

1 0. Belt joints made according to any one of more of Claims 1 to 5.

11. Belt joints made according to Claim 10 using a cutting board conforming to any one or more of Claims 6-9.

12. Belt joints made according to Claims 1011 wherein the joint is reinforced with a thin fabric on either side to prevent the interlocking lobes disengaging.

13. Belt joints made according to Claim 12 wherein the cloth used is cut on the bias.

14. Belt joints according to Claims 10-11 wherein the belt is coated and/or laminated with a thermoplastic material which on heating in a press fuses the joint together.

1 5. Belt joints according to Claims 10-11 wherein a separate adhesive, thermoplastic or thermosetting, is used in a hot press to vulcanise the joint.

16. Belt joints according to Claims 10-11 wherein a cold setting adhesive is used to vulcanise the joint.

17. Belt joints according to Claims 10-11 wherein the belt may comprise one, two or more plies of fabric.

1 8. Belt joints according to any one or more of Claims 10-16 wherein the belt is used as a conveyor belt.