NO822866L - TRANSPORTBAANDDUK. - Google Patents

Description

Conveyor cloth

The invention relates to cloths for conveyor belts and methods of manufacturing them.

An overview of the older technique in this field can be found in Man Made Textile Encycloedia, pages 309-312. In general, canvases for textile-based conveyor belts can be made by the so-called "wet-woven PVC" method, where warp yarns of polyester are dipped in polyvinyl-plastisol mass and then woven together while they are still wet. Or the cloth can be made by laminating textile cloths with layers of elastomer. The resulting canvas will not be completely satisfactory for all purposes. E.g. laminated cloths could separate and fail mechanically during prolonged use.

Recently, as described in US patent specification 4 154 335 and

4,157,752 prepared a conveyor belt fabric by sewing non-woven mats of staple fibers to the woven ply/saturating the stitched fabric with liquid elastomer-forming resin and curing the resin under sufficient heat and pressure to unite the saturated mass into a uniform fabric without layer structure. The single-layer cloth produced in this way is an improvement over the older laminated multi-layer cloths, as it holds together better and has greater wear resistance.

However, the method for producing the unitary non-laminated fabric according to US 4,154,335 and 4,157,752 has not been completely satisfactory in all respects. The impregnation or saturation of porous track materials, including textile fabrics, is traditionally carried out by dipping in a wet dispersion of thermoplastic resins, crosslinking to remove excess saturant and drying and curing under heat and pressure. This requires expensive equipment and specially prepared plastisol resin compositions. Such compositions (resin dispersions)

are relatively expensive (compared to extrudable resins)

and raises a number of problems with regard to its use.

E.g. is the use of liquid plastisols risky

and associated with waste problems. The waste liquids must very often be hardened by heating in order to be disposed of on landfills.

Or the solid waste must be burned before it can be thrown away.

In addition, the curing step using saturating agents in the form of liquid plastisols is energy-intensive and slows down production. Solvents are also used which must be handled, separated and deposited and increase process costs.

one.

The method according to the invention constitutes an improvement over the prior art, as it enables one to produce a uniform unlaminated conveyor belt cloth which has all the advantages of unlaminated cloth without the disadvantages associated with the older method. The method according to the invention eliminates the need for plastisols, solvents and similar questionable materials with accompanying deposition problems. The method according to the invention requires less energy, eliminates the need for a drying step and facilitates the realization of a continuous production line with higher production speeds. It is also possible to change the product's properties to a significant extent without changing or interrupting the production line.

In addition to advantages in terms of the production process, the method according to the invention also provides a product of better quality. During drying and curing of plastisol-saturated fibre-containing masses, it often happens that the softening component evaporates. The steam is driven through the matrix of elastomer and leaves air channels as it seeps out to the surface of the cloth. The result is blisters on the product's surface and inherent weakness in the produced fabric as a result of the formation of channels and blisters.

In the method according to the invention, high concentrations of volatile substances are not used. Thus, the formation of blisters, channels and similar imperfections in cloths produced by the present method is avoided.

Other advantages of the method and the product according to the invention will appear more fully from the following description.

According to the invention (A), the present method for producing a conveyor belt fabric comprises providing a plurality of essentially parallel, wrinkle-free textile yarns which are characterized by large

tensile strength, low elongation and even shrinkage,

(B) providing a synthetic thermoplastic polymer resin

in solid form,

(C) providing a mat of separate textile staple fibers;

(D) bringing the yarns, resin and fibers together;

(E) sewing the joined material together, and

(F) uniting the stitched material under heat and pressure, whereby the resin flows around individual yarns and fibers to enclose them and bind the fibers and yarns together into a non-layered structure.

The invention also includes conveyor belts made from the cloth according to the invention, as well as the use of the cloth in belt conveyors.

The invention will be explained in more detail below with reference to the drawing. Fig. 1 is a block diagram of phases of the method according to the invention. Fig. 2 shows a longitudinal section of a piece of an embodiment of a combined system that occurs in the method according to the invention for the production of a conveyor belt cloth. Fig. 3 shows a section similar to fig. 2, but after stitching the system together. Fig. 4 shows a corresponding section after joining the sewn material. Fig. 5 shows a corresponding section of a piece of another embodiment of a conveyor belt fabric produced by the method according to the invention. Fig. 6 shows a corresponding section of yet another embodiment of a conveyor belt fabric produced by the method.

The textile yarn used for carrying out the method according to the invention can optionally be included in a cloth. E.g. these textile yarns can be made up of longitudinal yarns in a woven cloth or equivalently in a knitted cloth. However, this is not essential, and the yarn can also be provided in a mainly parallel warp pattern, where they are mutually independent. The expression "mainly parallel", as used herein, shall mean that the yarns for the most part do not cross each other randomly. The textile yarns provided must have a relatively high tensile strength, i.e. of the order of at least approx. 9 kp/thread.

Advantageously, the textile yarn provided should be without curling and have little stretch, e.g. of the order of magnitude at least approx. 4-5% (k nominal breaking load) to approx. 15-20%.

It is important that the yarns are uniform in terms of shrinkage properties, i.e. that yarns with high shrinkage should not be mixed with yarns with low shrinkage, as far as possible to avoid bulges and wrinkles in the produced fabric.

The provided yarns can be selected from a variety of different synthetic yarns, e.g. polyester-polyamide yarn and the like. Preferably, it should be spun yarns or the like, with tendencies to anchor in and hold softened thermoplastic resins.

In one embodiment of the invention, the textile yarns are provided in the form of longitudinal yarns in an open-woven strip. Any form of binding can be used, however a canvas binding is stable and beneficial. In such an embodiment, the nature of the transverse yarns is not decisive, and any conventional artificial or natural fiber yarn can be used. Advantageously, the denier of the yarn and the density of the weave are chosen to give a canvas weight of approx. 1.4 - approx. 14 kg/m 2 for optimal strength.

The thermoplastic polymeric synthetic resins are supplied

in solid form, e.g. such as films, granules, single particles, powders and the like. One prefers thin films and single particles that can quickly be softened to a flowable state by heating under pressure. Representative of such forms are webs or films with a thickness of approx. 0.38 to 2.3 mm, and particles with an average diameter from approx. 20 - to approx. 200 microns.

In the method according to the invention, a variety of thermoplastic polymeric synthetic resins can be used. Representative of such resins are polyethylene, polypropylene, poly-butadiene, polyvinyl chloride, polyurethane, neoprene, polyamides, styrene-butadiene copolymers and the like. The elastomeric resins are preferred, although this is not necessary as long as the resins are sufficiently flexible to be used in conveyor belts.

As part of the method, a non-woven mat of separate textile staple fibers is provided. The mats can have randomly oriented staple fibers such as fibers of polyamide, polyester, polyolefin, acrylic and the like and mixtures thereof as well as natural fibers such as jute and mixtures thereof. If desired, one can also choose fibers that are directionally oriented in the mats using well-known methods.

The mats of staple fibers that are selected to be sewn into textile

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the yarns, preferably have a weight of approx. 0.07-0.68 g/m . The denier of Stabel fibers can lie within a wide range. The mats may be pre-stitched using conventional techniques to

give a certain firmness to the fibers before the mat is sewn to the yarn.

The provided yarns act as a core in the fabric produced by the method according to the invention. As indicated in the flowchart in fig. 1, the core of yarn is brought together with the mats of staple fibers and the resin material in the initial phase of the method according to the invention. Fig. 2 shows a longitudinal section of a piece of the joined material 10. This material 10 comprises a core of warp and weft yarns, respectively 12 and 14, woven together to form a strip 16. The yarns 12 and 14 can e.g. consist of spun polyester. On the upper side and the lower side of the strip 15, the joined structure has films 18,20 of solid thermoplastic synthetic resin. The outer sides of the films 18,20 are covered by mats, respectively 24 and 28, of staple fibers 22 and 26. These are the preferred positions of the constituent parts of the structure, although the resin films will be able to exchange positions with the respective adjacent mats of staple fibers, if desired.

In one embodiment of the invention, separate particles of the thermoplastic resin are combined with the yarn core. and the staple fibers. This can be done by spreading the separate resin particles in an even distribution in the staple fiber mat.

The proportion of resin material combined with the mats of staple fibers and yarns/reckoned by weight is at least sufficient to contain all fibers and yarns. In general, the proportion will be such that the fabric produced will have a resin matrix that makes up 50-500%, preferably 100-300%, of the textile fabric component's weight.

In the next phase of the method according to the invention,

the separate staple fibers as they exist in a non-woven fiber mat, sewn to the mentioned textile yarns and the accompanying solid resin. As can be seen from fig. 3, which corresponds to fig. 2, but shows the state after the stitching of the system, a layer of interconnected staple fibers 22, 26 is formed which, by entanglement with the yarns 12, 14, are connected to them. If fiber mats are only sewn to one side of the yarns, fibers are carried to the opposite side to give a weak "fluff" on this side containing the yarns 12 and 14. The latter embodiment is likewise within the scope of the invention. Furthermore, it will be seen from fig. 3 that the resin film 18,20 is attached by sewing.

When single particles of resin are used instead of films, the sewing usually helps to distribute the particles in the joined structure 10.

The techniques for sewing fiber mats to yarn and tablecloths woven or knitted from textile yarn are well known and do not need to be referred to here. The coarseness of the needles used, barb shapes, number, size and

other variables depend somewhat on the size of the openings between the textile yarns/due to the desire to avoid breakage in these. In general, it has been found that needle gauge 48 with the barbs oriented so that they do not wear the longitudinal yarns, is suitable for sewing. The needle frame can be equipped with needle boards with high or low needle density, e.g. a board with needle density 34. The sewing is preferably carried out to give a stitched structure with a weight in the range of approx. 0.2. to.approx.. 3 kg/m 2.....

After sewing, it may be beneficial to calender the sewn pieces. webs when further consolidation is desirable, particularly in such embodiments where a mat is sewn to only one side of the yarn. The calendering densifies and unites the staple fibers to reduce fluid permeability of the sewn web. This improves the hold of the resin, which will be softened by heat to flow in a subsequent phase. In general, it is desirable to have a cloth capable of holding the softened resin until resolidification occurs. If the sewn fabric lacks this property, calendering can be beneficial. Calendering is not generally necessary if fiber mats are sewn to both sides of the textile yarns 12,14.

In an optional phase of the method according to the invention, the sewn and optionally calendered cloth can be heat-cured in an oven to shrink the cloth. During heat curing, the textile fabric can be stretched lengthwise (along the axis of the textile yarns) with a force of 0.09-3.4 kp/cm fabric width or more. This prevents a large degree of stretch in the final product, and wrinkles are avoided across and lengthwise of the produced cloth. Heat curing is carried out under temperatures which depend on the nature of the fibers and yarns used in the sewn fabric. Professionals will know which temperatures to choose. Used e.g. components that only consist of polyester, heat curing can be carried out at temperatures within the range of approx. 145-220°C.

In the final phase of the method according to the invention, the stitched cloth is united under sufficient heat and pressure to soften the thermoplastic resin and cause it to flow through the entire textile mass while enclosing the fibers 22,26 and the associated yarns 12,14 as illustrated in fig. . 4, which shows the structure 10 of fig. 3 in longitudinal section, but after the unification operation. The joining is advantageously carried out by passing the system 10 (in Fig. 3) through a heated flat press at a sufficiently high temperature to soften (but not melt) the resin. Advantageously, the system 10 is simultaneously pressed to give a cloth 10 as shown in fig. 4. Press approx. 3.5 to approx. 14 kp/cm 2 is suitable and is illustrative of the pressures that can be used. Preferably, the system 10 is pressed and cured under pressure of approx. 60-90 kp/cm 2. The resulting conveyor cloth is, after cooling for renewed hardening of the resin matrix, free of voids, blisters, etc. and generally exhibits very good bonding between the fibers 22,26, the yarns 12,14 and the resin matrix 18,20.

At the same time as the said union or consolidation of

the joined and sewn resin and textile material can be embossed on the surface of the cloth to give a relief or a discontinuity in it. Cloths with embossed surfaces are useful on conveyor belts when it comes to sorting and separating goods, especially sheet-like materials such as tobacco leaves etc.

In addition to passing the cloth through a flat press as mentioned above, consolidation can be carried out by passing the stitched, joined material through the gap between heated calender rolls, especially if a continuous process is desired.

In the case of continuous operation, the resinous cloth can be passed through a so-called Roto-Cure unit and hot-pressed between a heated embossing roller and a running steel belt. Under heat and pressure in the Roto-Cure unit, an embossed surface can be formed, and a continuous web of the resinous web continuously travels through the apparatus to provide a continuous web of manufactured web.

Regardless of whether the composite cloth by the method according to the invention is produced in batches or in a continuous process, an advantage lies in the possibility of producing an extensive diversity of different cloth structures without interrupting the flow in a process line. E.g. reference can be made here to fig. 5, which shows a longitudinal section of an alternative embodiment for a transport cloth produced by the method according to the invention. The cloth 10' in fig. 5 is produced in the same way as described above with regard to the cloth 10 in fig. 4, except that the press plates or the calender roll on the upper side are kept at a temperature significantly below the temperature of the press plate or roll which is pressed against the lower side. As a result, a proportion of the ends of the fibers 22 remain clear. of the resin 20. A "textile structured" canvas is obtained; which is distinctive and is useful in certain applications when a textile surface is desired, e.g. with a view to a low coefficient of friction.

In a series of experiments, the applicants have observed that when the consolidation by the method according to the invention is carried out between two surfaces with different temperatures, one heated and the other cold, there is a difference in flow from side to side, as more flows towards the heat than against the cold roller. This suggests that it is possible to achieve a regulated flow of the thermoplastic material by suitably choosing the temperature of the calender rolls. E.g. two heated rollers can achieve movement to the outer rafts. When desired, movement to one side and partial movement to the other side is obtained with the resulting low coefficient of friction.

Other deviations are possible within the scope of the invention itself

in continuous production lines. Thus, fig. 6 longitudinal section of a piece of a conveyor cloth in another embodiment, also produced by the method according to the invention. In the cloth 10" in Fig. 6, a surface layer 30 of polymer synthetic resin, e.g. a polyethylene or polyvinyl chloride film, is attached to a substrate which may have a structure similar to the cloth 10 in Fig. 4. This layer 30 can be laminated to the base fabric 10

at the same time as the consolidation operation described above, which saves energy.

The following examples give an account of the manufacture and use of the invention and in the best way contemplated by the inventors in terms of carrying out the invention,

but is not to be perceived as limiting.

Example 1

A fabric is plain woven from Multiplex Dacron polyester 5000 denier (DuPont type 97; average elongation (nominal breaking load) 8.4%; breaking strength 20.4 kp; heat-dry shrinkage at 160°C 9.0%) in the longitudinal direction and spun polyester yarn 1150 denier in the transverse direction. The yarn density is 4.3 per cm in the warp

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and 3.9 per cm in weave, and the cloth weighs 0.3 kg/m. The cloth is combined with a non-woven sewn mat of 100% polyester fiber with fiber denier 6 and pile length 7.6 cm and with a surface weight of 0.14 kg/m 2 t with a 0.38 mm thick web of polyvinyl chloride on each side in a single pass through a needle chair. The sewn web is calendered at a speed of 5.5 m per min. to an average thickness of 1.8 mm and then heat hardened under moderate longitudinal tension by running at a speed of 2.75 m per my. through a 27.5 m long oven with a temperature of 160°C in the entrance zone, 180°C in a middle zone and 200°C in the end zone. The heat-cured cloth is then pressed at 150°C for 3 min. under 8.5 kp/cm<2> in a smooth hydraulic flat press to form a flexible-el manufactured web with thickness 1.9 mm, basis weight 1.93 kg/m 2 , breaking strength 215 kpm per cm width and 2% elongation at 14 kp per cm width.

Example 2

A textile cloth is plain woven using Multiplex Dacron polyester 5000 denier in the longitudinal direction and spun polyester 1150 denier in the transverse direction. The cloth includes 7 yarns per cm. in warp and 4 yarns per cm in weft and weighs 0.43 kp/cm 2.

The particles of polyvinyl chloride (PVC) are distributed evenly over the surface of the tarpaulin, which may have retained its condition after weaving or been treated by combining with a light web (0.035-0.1 kg/cm 2 ) of polyester fibers in a layer which helps to retain the PVC particles. The treated strip consists of 100% polyester fibers (non-woven) with fiber denier 6 and stack length 7.6 cm, weight 0.24 kg/cm 2. The sewn strip with distributed PVC particles is then turned over, and another layer of PVC -particles are applied evenly, after which another mat is applied

0.24 kg/cm<2> of polyester is sewn on.

Calculated by weight, the PVC particles are added in a range between 0.6-1.0 kg/cm 2 . A weight of 0.85 kg/cm gave the best results in terms of flow and cohesion in the fabric in this design.

After sewing, the resin-treated cloth was passed through an oven with air circulation and with time and temperatures. adapted to heat the mass to 190 C. Immediately after the pre-heating, the cloth is densified and calendered to the desired thickness, in this example approximately 3.2 mm. This means a reduction in thickness of 1 mm from the thickness of the sewn blank of 4.2 mm. Different process conditions were used with regard to calendering, however treatment with a transport speed of 0.9 m/s and a temperature of both rollers of 190-205°C gave satisfactory results.

Those skilled in the art will realize that it is possible to make many deviations from the preferred embodiments described above, without deviating from the main idea and scope of the invention. For example: will it be possible to make tablecloths from the combined resin and textile material where the resin is in the form of thermoplastic fibres, or where the staple fiber component is coated with thermoplastic resin before sewing.

Claims (7)

1. Method of manufacturing a conveyor belt fabric/ comprising (A) providing a plurality of substantially parallel non-crimped textile yarns characterized by high tensile strength, low elongation and uniform shrinkage, (B) providing a thermoplastic polymeric synthetic resin in solid form; (C) providing a mat of individual textile staple fibers; (D) joining yarns, resins and fibres; (E) stitching together the merged system, and (F) densifying the stitched system by heat and pressure, whereby the resin flows around the individual yarns and fibers to enclose them and bind the fibers and yarns together in a non-layered structure. 2. Procedure as stated in claim 1, character-. serted by sewing a mat of fibers to each side of the yarns. 3. Method as stated in claim 2, characterized in that the yarns are included in a woven cloth. 4. Method as stated in claim 1, characterized in that the sewing is done on one side of the yarns and the sewn fabric is then calendered for further densification of the sewn fabric. 5\ Procedure as stated in crawl, characterized by the yarns being held under tension while the sewn item is heat cured. 6. Method as stated in claim 1, characterized in that the saturation is carried out by dipping the heat-hardened object in the liquid. 7. Method as stated in claim 1, characterized in that the densification is carried out by passing the joined blank through a heated flat press.