Jean, Normanton
Geoffrey, Houston
Alec
LIMITED ROBINSON, Jean NORMANTON, Geoffrey HOUSTON, Alec.
| 1. | A conveyor belt or belting comprising a solid woven carcass impregnated and coated with rubber, characterised in that the warp yarns comprise polyester filamentary yarns doubled with texturised polyester yarns. |
| 2. | A conveyor belt or belting according to claim 1, characterised in that the solid woven carcass is woven as a two or three ply construction in which all the warp yarns follow a similar path. |
| 3. | A conveyor belt or belting comprising a solid woven carcass impregnated and coated with rubber, characterised in that the solid woven carcass is woven as a four ply or more construction in which the inner warp yarns travel along a straighter path than the two outermost warp yarns such that the outermost warp yarns create "pockets" at the surface of the carcass. |
| 4. | A conveyor belt or belting according to claim 3, characterised in that the inner warp yarns inter¬ weave with every fourth weft yarn. |
| 5. | A conveyor belt or belting according to claim 3 or 4, characterised in that the stretch character¬ istics of the shorter inner warp yarns and the longer outer warp yarns are balanced. |
| 6. | A conveyor belt or belting according to claim 5, characterised in that inner warp yarns are comprised of polyester and the outer warp yarns are comprised of a polyamide. |
| 7. | A conveyor belt or belting according to any of claims 3 to 6, characterised in that the inner warp yarns are doubled with texturised polyester yarns. |
| 8. | A conveyor belt or belting according to claim 7, characterised in that the outer warp yarns are doubled with texturised polyester yarns. |
Hitherto, solid woven constructions have been limited to the use of PVC as the impregnant. However, for certain applications, outer covers of rubber are advantageous, for example, on steep inclines. In order to provide a rubber load bearing surface, it is known to form an outer cover of polybudadiene acrylonitrile
co-polymer (nitrile rubber) which is compatible with
PVC and can be fused to the surface of a PVC impregnated solid woven carcass in a press. This process, whilst producing a satisfactory product, is relatively costly and in some instances is not economically viable.
The object of the present invention is to provide a solid woven belting having an outer rubber cover and which avoids the costly necessity of first forming a PVC/textile substrate.
Previous attempts to produce an all rubber solid woven belting have not been successful owing to the difficulty of achieving satisfactory impregnation of a thick carcass with rubber solution. Furthermore, it has not proved technically feasible to employ chemical bonding systems as usually applied to the thin, tightly woven fabric layers used in the manufacture of ply beltings. When chemical bonding systems are used with solid woven carcasses the interstices of the woven fabric do not become filled with the impregnant polymer and this tends to impair the mechanical properties of the carcass.
The afore mentioned problems have now been overcome in a textile reinforced conveyor belting construction according to a first aspect of the present invention which provides a solid woven carcass impreg¬ nated and coated with rubber wherein the warp yarns
comprise polyester filamentary yarn doubled with poly¬ ester yarns which have been texturised by a process known as air jet texturising (controlled bulking by air) . This combination of yarns has been found to provide an optimum balance of strength, contributed by the filamentary yarns and mechanical adhesion to the rubber by the texturised yarns.
The polyester filamentary yarns are comprised of extruded continuous filaments which are assembled in parallel with or without twist. The texturised polyester yarns are comprised of polyester filamentary yarns which have been further processed to impart an appearance and character similar to spun staple fibre yarns. In this regard the polyester filamentary yarn is fed through a nozzle in which it is subjected to a jet of high pressure air. As the yarn leaves the nozzles it is incident upon an impact block. This process has the effect of causing the single filaments comprising the yarn to form loops which partially interlock with each other under the influence of the turbulant air flow through the nozzle and over the impact block. A portion of these loops remain within the yarn thereby giving rise to an increase in bulk whilst some protrude from the outer surface giving a texturised appearance to the yarn.
_ u _
When comparing a polyester filamentary yarn with a texturised polyester yarn the typical test results are as follows:-
Non-texturised Texturised
Tenacity gms/denier 8.3 4.2
Elongation at breaking point 10.94% 12.02%
Preferably the carcass is woven as a simple two or three ply construction where all the warp yarns follow a similar path. With this design, belt strengths of up to 1,250 KNs per metre of width can be achieved. To produce higher strength beltings, it is necessary to increase the number of warp yarns but the resultant more dense weave impedes the flow of impregnant into the centre of the belt.
According to a second aspect of the present invention, a solution to this problem is provided by altering the weave so as to create "pockets" at the surface of the carcass which facilitate the ingress of impregnant to the core of the belting. This has been accomplished by adopting a weave pattern in which the inner warp yarns travel along a straighter path than the yarns in the two outermost layers. Preferably, the inner warp yarns interweave with every fourth weft yarn.
Owing to the fact that the inner and outer warp yarns follow different paths it is , necessary to balance their stretch characteristics, otherwise the outer yarns which follow a shorter weave path, would carry a disproportionate share of the tensile stress and reach breaking stretch before the inner warp yarns made a full strength contribution.
In a preferred embodiment of the present invention the stretch characteristics of the inner and outer warp yarns are balanced by using polyester in the inner ply and a polyamide, such as Nylon 6 in the outer plys. The breaking elongation for polyester was 14% and that for Nylon 6 was 19.5%. This difference in breaking elongation of 5.5% compensated for the difference between the inner and outer yarn paths (typically 6%) thus ensuring full utilisation of the tensile potential of both inner and outer warps.
Preferably, the inner warp yarns and, optionally, the outer warp yarns are doubled together with texturised polyester yarns.
Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which:-
Fig. 1 shows a diagrammatic view of a solid woven carcass of simple two-ply construction having warp
yarns comprising polyester filamentary yarns and polyester texturised yarns doubled together in accordance with the first aspect of the present invention. Fig. 2 shows a schematic diagram of apparatus for texturising polyester filamentary yarns.
Fig. 3 shows a diagrammatic view of a solid woven carcass of a four ply construction in accordance with the second aspect of the present invention. Referring to Fig. 1, there is shown a solid woven carcass of two ply construction for use in the manufacture of a conveyor belt or belting. The warp yarns 10 of the carcass are comprised of polyester filamentary yarns and texturised polyester yarns doubled together.
In use, in the manufacture of a belt or belting the solid woven carcass is dipped in rubber solution before being fed into a press where preformed uncured rubber sheeting is applied to each surface of the carcass and cured under heat and pressure. The rubber sheeting may be natural or synthetic.
The texturised polyester yarns ensure mechanical adhesion of the rubber sheeting to the carcass.
Fig. 2 shows a schematic diagram of apparatus for texturising polyester filamentary yarn. The apparatus comprises a wetting device 1, a texturising nozzle 2,
and an impact block 3. As yarn to be texturised is fed through the wetting device 1 and into the nozzle 2 where it is subjected to a jet of compressed air through a port 4 in the side of the nozzle 2. As the yarn leaves the nozzle it is incident on the impact block 3. This process has the effect of causing the filaments in the yarn to separate, bunch up and form loops.
Referring now to Fig. 3 there is shown a solid woven carcass of a four ply construction. The woven carcass presents "pocketed" outer surfaces which facilitate the flow of liquid rubber into the centre of the belt. Yarns marked 12 which follow a shorter weave path are of a filamentary polyamide, and yarns marked 13 are of a filamentary polyester. The yarns 12 and 13 can optionally be doubled together with a texturised polyester yarn.