METHOD FOR THE PRODUCTION OF Ä LINK-BELT AND A LINK-BELT PRODUCED THEREBY TECHNICAL FIELD

The invention refers to a method for the production 5. of a link-belt including synthetic materials having thermo-setting properties, and has particular, though not exclusive reference to a method for producing such a structure. BACKGROUND ART

10. It is known to produce a link-belt for use in the context of papermaking machines and the like from a multiplicity of helical coils connected together by hinge wires threaded through the interdigitated turns of adjacent coils, a typical arrangement being sho n for

15. example in German Auslegeschrift No. 24 19 751.

In this known arrangement, the coils are connected together in such a way that two successive turns of one coil receive a turn of the next adjacent coil therebetween with the said turn of the adjacent coil in contact with

20. and clamped between the flanks of the said successive turns by virtue of a spring-like tension in the indivi- dual coils. It is questionable that such a link-belt provides an adequate degree of dimensional stability. DISCLOSURE OF THE INVENTION

25. The object of the invention is to produce a link- belt of the aforesaid kind having improved dimensional

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stability and selvedge strength as compared with known structures, the belt itself being substantially flat and the hinge wires being firmly fixed in position relative to the individual coils. 5. According to one aspect of the present invention there is proposed a method for the manufacture of a link-belt. defined by a multiplicity of helical coils joined in side-by-side disposition by hinge wires of a thermoplastic monofilament material threaded through

10. the interdigitated turns of adjacent such coils, which method includes the Steps of arranging adjacent coils in interdigitated disposition, threading a respective hinge wire through the interdigitated turns of each pair of adjacent coils, subjecting the resultant link

15. structure to a suitable heat-setting temperature and longitudinal tension to cause the hinge wires to deform and assume a crimped configuration in the plane of the structure, and subsequently reducing the temperature όf the structure.

20. According to a further preferred feature, adjacent helical coils are of opposite hand.

The method of the invention makes possible the use of relatively si ply produced helical coils, the coils being wound for example, in round or oval form. The

25. heating and stretching of the link structure wherein the coils are of a thermoplastic material reshapes originally round or oval coils to a required flat form, wherein flat runs connect curved end regions. Subjecting a link structure having flat coils to tension or subjecting a

30. link structure including initially round or oval coils of a thermoplastic material to a tension beyond. that necessary to cause the cόil to assume a flat shape will deform the hinge wire and cause the same to assume a crimped form and/or will deform the coil in the region

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of the hinge wire, according to the physical charact- eristics of the material of the hinge wire and of the coils.

According to another aspect of the present invention 5. there is proposed a method for the manufacture of a link-belt from a plurality of helical coils of a synthetic thermoplastic material arranged in inter¬ digitated disposition and connected together by respect¬ ive hinge wires engaged with the interdigitated turns 10. of adjacent coils, the thickness of the monofilament defining the coil approximating to the spacing between successive turns of the said coil, which method cόm- prises the steps of arranging adjacent coils in inter¬ digitated disposition, threading a respective hinge wire 15. through the interdigitated loops of each respective pair of adjacent coils, subjecting the resultant link structure to a heat-setting temperature whilst under longitudinal tension thereby to effect a deformation of the material of the coils in those regions thereof 20. whereat the hinge wires are seated to increase the cross- sectional dimension of the said coils in such regions ' to a level in excess of the spacing between adjacent turns of the said coils as measured in the axial direction of the hinge wires. 25. BRIEF DESCRIPTION OF THE DRA INGS

The invention will now be described further, by way of example only, with reference to the accompanying drawings in which:-

Fig. 1 is a diagrammatic cross-section, drawn 30. to a much enlarged scale, through the link fabric of the invention prior to subjecting the same to heat treatment under tension; Fig. 2 is a section taken on line II-II through the structure shown in Fig. 1 after the same has

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been subjected to heat when under tension to effect crimping of the hinge wire; Fig. 3 is a diagrammatic cross-section through a link fabric produced in accordance with 5. another aspect of the method of the invention, and shows deformation of the monofilament of the coil resulting from application of heat to the fabric when under tension; Fig. 4 is a cross-section through a link fabric 10. produced in accordance with the invention, and illustrates both deformation of the monofilament of the coil and crimping of . the hinge wire; Fig. 5 is a section on line V-V of Fig. 4; 15. Fig. 6 is a section on line VI-VI of Figs. 4 and 5; and Fig. 7 is a plan view of a part of a link fabric _. produced in accordance with the invention. BEST MODE OF CARRYING OUT THE INVENTION 20. In practising the invention, a hinge belt is first formed by the interdigitation of a multiplicity of individual coils 11 and the introduction of. a respective hinge wire 12 into the interdigitated turns of adjacent coils- to connect the same together, the 25. thickness t of the material of each of the coils 11 being substantially equal to the spacing d (Fig. 2)between successive turns of each coil. The coils 11 may initially be of the oval form shown in Fig. 1 or may be of circular or flat transverse cross-section. 30. In accordance with one procedure the hinge belt is tensioned and is then subjected to heat at such a level and for such a period as is sufficient to deform the material of the coils and/or the hinge wires, thus to introduce a degree of stability into the belt.

It is possible, by suitable selection of the physical property of the materials of the coils and of the hinge wires, to effect on thermal setting and stretching deformation of either or both of the 5. coils and the hinge wires, thereby to impart stability in different ways.

Thus, referring now to Fig. 2, by providing a hinge wire 12 of a synthetic' thermoplastic material, and subjecting the belt, when under tension, to a

10. temperature approaching the softening temperature of the material of the hinge wire 12, it being assumed that the coils 11 are either non-thermoplastic or comprise a material having a softening point at a temperature higher than that of the hinge wire 12, it

15. is possible to cause the hinge wire 12 to assume a crimped form which form will be retained when the hinge wire reverts to temperatures below its softening temperature, the deformation of the surface of the hinge wire in the plane of the structure being at

20. least 5% of the diameter of such hinge wire.

In an alternative procedure, see now Fig. 3, the hinge wire 12 is of a non-thermoplastic material or is of a synthetic thermoplastic material having a higher softening temperature than the material of the coils 11,

25. and accordingly, on subjecting a tensioned link-belt to a temperature approaching the softening temperature of the material of the .coil (but much less than the softening temperature of the hinge wire if the same is of a synthetic thermoplastic material) deformation of

30. the coils in the end regions 13 of the individual turns 14 thereof occurs in such manner as will more firmly connect the coils together and improve the stability of a link fabric.

In practice, the ost effective course is to σombine

the concept of hinge wire crimp with that of coil deformation, a structure embodying both such charact- eristics being shown diagra matically in Figs. 4 to 6. Both the helical coils 11, alternate coils being 5. of opposite hand, and the hinge wire 12 of the arrange- ment shown in Figs. 4 to 6 are' of monofilament polyester material, for example polyethylene terephthalate.

On subjecting the tensioned link belt to heat, the hinge wire 12 is caused to assume the crimped form shown, 10. whilst, subject to the tension being sufficient, the coils are themselves deformed in the end regions 13 thereof to provide alternate enlargements 15 at diamet- rically opposite sides of the hinge wire 12 in seated register with the crimp and of a dimension in the axial 15. direction of the hinge wire 12 in excess of the spacing d between successive turns 14 of the coils 111

In a typical example, as seen in Fig. 4, the hinge wire and the coils comprise monofilament yarns of approximately 0.9 and 0.7 mm diameter respectively, the 20.. deformation introduced into the hinge wire being such as to create an amplitude of deformation at the surf ce ^" of the hinge wire of approximately 5% of the yarn diameter and the deformation of the end region ^' of each turn of the individual coils incrSasing the diameter 25. thereof as measured in the axial direction of the hinge wire by approximately 10%.

In addition to the deformation of the coils readily apparent in Fig. 4, abutting flanks of adjacent coils are also complementarily deformed, as too are the abuttin 30. surfaces of the coils and the hinge wires engaged therewith.

The deformation of the hinge wire and the various deformations introduced into the coils (fitting together in intimate contact) combine to impart a high degree of

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dimensional stability to the link-belt, both in the longitudinal and in the transverse directions thereof, such as make' the same eminently suitable for use in the context of papermaking and like machines. The lateral 5. stability is believed to be due largely to the location of successive turns 14 of the coils 11 in the deformation pattern of the hinge wire 12, to the relationship between the increased thickness of the monofilament yarn of the coils and the spacing d between the successive turns

10. thereof, and to the intimate contact between opposite flanks of the end region of a given turn of one coil with the respective opposing flanks of the end regions of the successive turns of the adjacent coil between which the said turn is located, as seen at.15 in Fig. 6.

15. The longitudinal stability of the fabric, and also its rigidity, is believed to arise from an effective overlap of the enlarged end regions of respective adjacent coils when considered in a direction at right angles to the axis of the hinge wire, from the increased

20. dimension of the end regions in relation to the spacing of successive turns of the individual coils and from the bedding of the hinge wires into the end regions of the coils as seen at 16 in Fig. 5.

According to the degree of stability and/or rigidity

25. required of a link-belt, so reliance can be placed on either or both of the hinge wire deformation and coil deformation.

The heating will ordinarily take place at a temperature of between 120 to 250 C, and preferably

30. at a temperature of between 180 C to 200 C, although this will be determined with particular reference to the characteristics of the thermoplastic material involved.

Typically in producing a spiral fabric in accord¬ ance with the invention a polyester monofilament of

hydrolysis resistant quality, and of diameter of 0.7mm is converted to spiral form by winding the monofilament onto a forming mandrel with the application of heat. The size and cross-sectiori of the mandrel correspond 5. to the internal size of the spiral and produces an oval spiral of major and minor internal dimensions of 5.3mm and 2.4mm. Spirals are produced with left and right hand configurations.. A plurality of spirals is combined together and a hinge wire of hydrolysis

10. resistant polyester monofilament of 0.90mm diameter is inserted down the centre of adjacent intermeshed spirals. The process is repeated until sufficient length of fabric has been produced.

A finishing process is carried out in which the

15. fabric is subjected to tension and heat when mounted on the parallel revolving cylinders of a stretching and heat-setting machine. A tension of not less than 5kg/cm is applied under a temperature not less than 170 C. This causes the spiral to deform into a flat elongated

20. section of major and minor internal dimensions of 5.8mm X 1.2mm. Deformation .of the hinge wire also occurs which prevents movement of the finished spirals and greatly increases the stability of the fabric. This deformation . gives the impression of a crimping of the hinge wire,

25. although it cannot be a true crimp in that its initial length is maintained, and is not less than 8% of its diameter.

The fabric produced as described is finally cut to the required width and the edges are filled with adhesive

30. to prevent da age and unwinding of the spirals during use.

A plan view of a typical link fabric produced in accordance with the present invention is shown in Fig. 7, such fabric comprising a multiplicity of individual coils

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of a monofilament polyester material arranged in inter¬ digitated side-by-side disposition and adjacent coils being connected together by respective hinge wires threaded through the tunnel formed by such interdigi- 5. tated coils. Adjacent coils are of opposite hand. The hinge wires are deformed into crimped appearance and the end regions of the individual turns are deformed, the deformation being of the kind shown in Figs. 4 to 6, and being produced by subjecting the fabric, when under

10. tension, to a suitable heat-setting temperature for the polyester material, thus to impart dimensional stability to the fabric.

The dimensional stability which results from a practising of the invention is contrary to all expect-

15. ations, in that ;conventional textile technology would suggest that a structure assembled from helical coils and hinge wires would inevitably possess a degree of dimensional stability quite inadequate for such structure to have application in contexts, particularly the con-

20. texts of papermachine or like clothing, where dimensional stability is important.

Whilst the stability necessary for use of the fabric in the context of papermachine and like. clothing may well require that the thickness of' the monofilament

25. forming the coils approximate to the spacing between successive turns of the coils, ^' it is not thought that such requirements exist for conveyor belts which are intended to operate under less stringent conditions, and the invention is accordingly not limited to structures

30. wherein this particular requirement is satisfied.

Furthermore, the invention is not limited to the intro- duction of deformation of the hinge wire and deformation of the end regions of the successive turns of the coils,

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since advantageous characteristics of the end product as regards its dimensional stability are thought to arise from the introduction of. one only of these features. Although the invention has been disclosed in the 5. context of monofilaments of circular cross-section, it may be preferred in some instances to use monofila¬ ments of differen form, for example, of flat cross- section.