GB2324543A - Belt with edge reinforcements. - Google Patents

Abstract

Belt edge reinforcement to increase wear resistance is provided on a fabric belt by partially fused particles within the fabric. Belts suitable for such reinforcement include those used in paper machine clothing, filters and conveyor belts. Due to the flexibility offered by sintered polymer structures, the reinforcing particles are preferably polymeric, although other materials such as metals or ceramics may be used. Preferred polymers include polyalkenes, e.g. polyethylene, polypropylene, polyurethane, EVA thermoplastic polyurethane or EPDM (ethylene propylene diene monomer). The strengthened region may be prepared by spreading polymer powder over the edge region, and then heating it to 230-240 degrees C. This heating may be in an oven via infrared heaters, and the belt may be treated mechanically after heating.

Description

SINTERED BELT EDGES The present invention relates to fabrics with significantly improved edge regions and more particularly to fabrics comprising partially fused particles with improved edge regions.

Fabrics such as papermachine clothing, filters, conveyors or other belts all frequently share the problem of abrasion and wear at their edges.

For instance papermaking fabrics are constantly contacted by guide spades which are used to guide the fabric around the machine. The abrasion of the guide spades against the fabric causes short and long term wear that leads to marking of the fabric and often forces early replacement of the fabric.

At present, so-called edge seals are commonly applied to the edges of papermaking fabrics for reinforcement. These edge seals comprise a continuous strip of up to 3 inches wide of extruded polymer material, for example, polyolefin or hot-melt polyesters or polyamides which fills the fabrics interstices at the edge regions.

This process is time consuming and usually takes place after the fabric is manufactured, requiring an additional stage in the overall process.

This creates the problems of the necessity to transfer the fabric from one piece of equipment to another, to set up additional equipment etc., all leading to increased costs.

A further instance of the problem of wear at or near the edges of a fabric is in connection with known drum filter belts comprising a rubber edge track with run-in guides to keep the filter cloth running perfectly straight. The rubber edge track is attached to a fabric reinforcement by means of several rows of stitching, the conventional edge track may also be bonded by hot-air or ultrasonic welding. The fabric reinforcement is also secured to the filter cloth.

The stitching connecting the rubber edge track to the fabric reinforcement tends to wear in the regions where it is prominent and the perforations made by the sewing needle are a frequent cause of failure to the rubber component. Overall, much time is taken in producing these filter belts.

The present invention is made from a consideration of the above mentioned and related problems.

According to the present invention there is provided a fabric comprising partially fused particles at the edge regions of the fabric.

The fabric of the present invention results in a substantially solid mass at the edge regions which is consequently more resistant to abrasion.

Clearly, any fabric made from partially fused particles or based on standard woven or nonwoven (e.g. needle felt) textile structures and which suffers from the problem of abrasion and wear at its edges may be used in the present invention.

Preferred fabrics for edge reinforcement are those used for papermachine clothing, filters, conveyor belts or other belts.

The particles are preferably polymeric, although other materials such as metals or ceramics may be used. Polymeric particles are preferred due to the flexibility of sintered polymer structures.

Preferred polymers for partial particle fusion to create the sintered fabric edge regions include polyalkenes such as polyethylene and polypropylene, polyurethane, EVA thermoplastic polyurethane or EPDM (ethylene propylene diene monomer). One example polymer is the Hostalon GUR (trade mark of Hoechst AG) range of UHMW polyethylene having a molecular weight of 3.2 to 8 x 106 g/mol. Another example is the Goodrich TPU product 58810 (trade mark) which has Shore A hardness of 90.

In a preferred embodiment of the invention for a fabric comprising partially fused particles, the particles used to form the edge regions and the particles forming the main body of the papermachine clothing are not the same. The particles may differ in one or more of the following characteristics:- size, melting point, density, molecular weight of chemical composition, or a combination thereof.

Preferably, the polymer composition at the edge regions comprises the introduction of polymers from the same homologous series, e.g. adding polypropylene to polyethylene, resulting in a tougher fabric at the edge regions, making the edges more abrasion resistant.

A fabric edge region of partially fused polymer may be prepared by evenly spreading the polymer powder into a layer of uniform thickness of between 1 to 20 mm and then heating the polymer. Preferably, the thickness of the edge region is between 1 and 10 and further preferably between 3 to 4 mm. The uniform polymer layer may be obtained by using a metering roller or blade. Continuous or discontinuous edge strips of sintered material may be formed on pre-formed fabrics which are optionally internally reinforced woven, non-woven or needle felt structures, by spreading the polymer particles onto the edges of the fabric.

In the case where the body of the fabric is a sintered polymer, the reinforced edge regions may be prepared by spreading a thicker layer of polymeric particles thereon resulting in a higher bulk density of partially fusible polymer particles at these regions compared with the main body of the optionally sintered fabric body. GB 9414981.2 and GB 9420963.2 disclose details of manufacture of a fabric where the main body of the fabric is sintered. A vibration moulding technique such as described in connection with Fig. 6 of EP-A-0,010,914 may be used for moulding the particulate material.

In a preferred embodiment of the invention, a surface profile or void region may be formed into these edges. These may comprise a track, groove or tunnel. This is particularly useful in applications such as drum filter belts, where a rubber edge track with run-in guides to keep the filter cloth running perfectly straight is attached via means which are easily worn.

The present invention allows the rubber edge track to be replaced by an integral track, groove or tunnel to aid guiding of the belt, without the necessity for additional steps to secure the track to the filter belt.

The layer for the edge region of polymer is heated to say 230"C to 240"C for a time period in the order of 1.9 mins per mm of sheet thickness, allowing for shrinkage due to partial fusion forces. Continuous sheet production may involve distributing the powdered polymer onto a tensioned metal belt which passes through an oven where the belt is heated from above and underneath by IR heaters to facilitate partial fusion. The finished sintered fabric edge regions may be mechanically treated, e.g. by grinding to give a smooth finish.

Some materials such as thermoplastic polyurethanes on being subjected to a high energy input partially fluidise and partially adopt a viscoelastic form as previously described so as to provide a partially fused product having superior toughness.

Such edge regions comprising partially fused polymeric particles and possibly the edge region of the fabric may contain an additional reinforcing structure to improve strength, flexibility, and abrasion resistance. This structure may be partially or preferably wholly embedded in the sintered edge region structure. This may comprise a random dispersion or oriented array of standard staple or bicomponent fibres extending through the partially fused product. Alternatively the reinforcement may comprise a fabric such as a nonwoven fabric, a mesh fabric, a plain weave fabric or a felt or membrane Melt-bondable or bicomponent fibres are preferred as the reinforcement structure, the melting or softening point of which is greater than that of the polymeric particles. On a macro scale the fibres may be formed into yarns. The yarns may form a woven or nonwoven matrix.

An example bicomponent fibre is Danaklon ES-C (trade mark) which comprises a polyethylene core and a polypropylene sheath. The fibre has a high adhesion strength and a low bonding temperature of 135 to 1 450C.

An example bonding fibre is Dacron 134 (trade mark of DuPont) which is a polyethylene terephthalate fibre with a melting/softening point of 205"C.

One particularly suitable fibre is polyamide 6, having a melting point of 235"C. A sheath core bicomponent fibre with a polyamide 6 sheath and polyamide 6:6 core may also be appropriate.

The permeability of the partially fused product may be improved by incorporating a blowing agent into the edge region during partial particle fusion or using a porous support medium (e.g. partially fused metal) to enable the partially fusible powder to be fluidised immediately prior to melt bonding.

The particles may be layered in different size fractions to produce a pyramidal porosity profile and, therefore, a permeability gradient.

A further advantage of this method is the ease of addition of pigments, for example, a logo can easily be incorporated.

The above embodiments have been described by way of example only. Many modifications and variations are possible.

Claims (10)

ClAIMS

1. A belt having edge reinforcements provided by a fabric comprising partially fused particles.

2. A belt according to claim 1 wherein the particles are polymeric and comprise any one or more of polyalkenes, polyurethane, EVA thermoplastic polyurethane or EPDM.

3. A belt according to claim 1 or 2 comprising a fabric comprising partially fused particles wherein the particles used to form the edge reinforcement are different from the particles forming the main body of the belt, by reason of size, melting point, density, molecular weight and/or chemical composition.

4. A belt according to claim 3 wherein the polymer composition at the edge region comprises polymers introduced from the same homologous series as the main body of the belt uses.

5. A belt according to any preceding claim wherein a fabric edge region of partially fused polymer has been prepared by evenly spreading the polymer powder into a layer of uniform thickness of 1 to 20 mm and then heating the polymer.

6. A belt according to any preceding claim wherein the polymer layer is supported by a preformed textile woven or nonwoven fabric.

7. A belt according to any preceding claim wherein the edge region is formed to be thicker than the body of the belt, by spreading a thicker layer of polymeric particles at these regions.

8. A belt according to claim 7 wherein a surface profile or void region is formed into said edges in the form of a track, groove or tunnel.

9. A belt according to claim 6 wherein the fabric includes melt bondable or bicomponent fibres, having a melting or softening point greater than that of the polymeric particles.

10. A belt according to any preceding claim wherein the edge region is rendered porous by an incorporation of a blowing agent into the polymer.