GB2328956A

GB2328956A - Heat setting apparatus

Info

Publication number: GB2328956A
Application number: GB9718750A
Authority: GB
Inventors: Jan Torbjoern Stroem
Original assignee: Scapa Group Ltd
Current assignee: Scapa Group Ltd
Priority date: 1997-09-05
Filing date: 1997-09-05
Publication date: 1999-03-10
Also published as: GB9718750D0

Abstract

A heat setting apparatus comprises a tank or bath (11) through which a continuous belt of fabric (10) is fed. Bath (11) contains a liquid (12) in the form of a molten eutectic metal alloy and heats the fabric to a temperature in the range 150‹-220‹C. The bath also contains heating elements (17) for heating the molten alloy (12). The temperature range is suitable for softening thermoplastic yarns for stretching of the yarns under tension. Alternatively, the liquid may be water, or glycerol.

Description

Heat-Setting Apparatus This invention relates to heat-setting apparatus, for use in heat setting of woven or non-woven fabrics containing thermoplastic yarn members.

The invention is concerned mainly, but not exclusively, with heat-setting of such fabrics as used in papermachine clothing, conveyer belts or filter belts which maybe categorised as industrial belting.

A typical known heat setting machine comprises a pair of heated rolls about which the fabric, such as a press belt base cloth, or a dryer fabric is driven at slow speed under tension. Examples of such machines are described in US 5,312,532; US 4,504, 359; and US 4,495, 714.

Also widely used are ovens of say 1-2 metres in length, heated to about 100-2500C, normally 150-2200C for papermachine clothing, through which a fabric is passed to give an oven dwell time for each section of the fabric of about 1 minute. The fabric then leaves the oven and passes through air at room temperature, and optionally over a cooled roll. The fabric may make a return run, through a second oven at a slightly higher temperature than the first oven. For certain types of fabrics such as carcasses for reinforcing tyres, a single oven split into different heating zones will be used.

The key problem with heat setting is that it is a highly critical process, both with respect to heating and cooling. Minute deviations from set parameters can lead to detrimental flaws in the fabric which if serious may result in the fabric having to be scrapped.

Uneven heating of the fabric by heating in an oven filled with a gaseous medium such as air to transmit thermal radiation is hard to avoid, except by specially controlling the heating elements or burner, generally leading to a higher temperature towards the middle of the fabric, falling off towards the edges.

The target temperature of the fabric before it leaves the oven is between the glass transition temperature and the melting point of the thermoplastic material used in the yarn of the fabric, so that the yarns can be stretched on the heat setting machine, and the stretched structure is then locked into position as the fabric is cooled upon leaving the oven. If heating of the fabric is uneven, leading to over heating, typically in the centre, and / or to under heating, typically towards the edges, the fabric may be partly damaged due to full melting and fusion of the thermoplastic material, or compromised by failure of the thermoplastic yarns to soften sufficiently to be stretched under tension. This results in insufficient orientation of the polymer chains in the molecular structure of the yarns, a possible consequence of which is the belt stretching on the eg papermachine during use.

Other consequences include edge curl, which requires remedial action as described in US-5,546,643; for spiral link fabrics( see GB-A-2051154) the so-called slack edges phenomenon arises.

It is accordingly an object of the invention to provide a heat-setting apparatus which will ensure an improved, more even heating of the fabric by improving heat transfer of the fabric material.

It has been found that forming fabrics treated with a Marathon (Trade Mark) coating (see GB-A-1512558) tend to have a more uniform fabric structure than untreated fabrics heat-set in ovens. It is thought that curing of the aqueous formulation applied to the fabric is equivalent to heat-setting the fabric in water.

In accordance with this invention, heat-setting apparatus comprises means containing a heated liquid, and means for feeding a fabric through the container means to thereby heat the fabric by contact with the hot liquid.

The invention also provides a method for heat- setting a fabric comprising passing the fabric through a container which contains hot liquid.

The fabric may be passed continuously through the hot liquid, or immersed in the liquid in batches.

The liquid may be glycerol, or water.

A preferred liquid is molten metal. This may be a eutectic metal alloy.

The liquid used desirably will quickly drip from the fabric and not require heat, solvents, or washing with water to drive it off from the fabric.

The container maybe a bath or tank of the liquid, and guide rolls may be provided to guide a continuously fed fabric into, through and out of the bath or tank.

The liquid in the bath or tank may be continuously heated to be maintained at a desired temperature by electrical heating elements, gas burners or other heating means.

The fabric, on leaving the bath or tank may be subjected to cooling by a current of a gas such as air applied across its width, as disclosed in copending application No.

A preferred embodiment of method and apparatus according to the invention for heat-setting of fabrics such as papermachine clothing, will now be described by way of example, with reference to the accompanying drawing, which is a diagram of the apparatus.

A continuous belt of fabric 10, which may for example be a dryer fabric or a press felt base cloth, is fed through a tank or bath 11 which comprises heating apparatus for heating the fabric 10 to a temperature eg in the range 150-220 C where thermoplastic yarn will soften sufficiently to be stretched under tension.

The bath 11 contains a liquid 12, in which are immersed guide rolls 13, 14, 15, 16 for guiding several passes of the fabric 10 through the liquid, and a plurality of electrical resistance heating elements 17.

The liquid 12 is a molten eutectic metal alloy, a class of substance which is suitable for the purpose as such alloys have relatively low melting points. The bath 11, is enclosed with a cover 18 provided with inlet and outlet slots 19, 20 for the fabric, in order to prevent or minimise escape of metal vapour, which in the case of many metals are toxic.

A conduit 21 extends across the width of the fabric 10 immediately following the outlet slot 20, to blow a controlled flow of cooling air for controlled cooling of the fabric in accordance with our copending application for patent, mentioned above.

In place of a molten eutectic alloy, a range of other liquids may be used, notably water or glycerol.

Examples of eutectic alloys are given in the following table:allov proportions (%) melting point (OC) In / Sn 52 / 48 1180 Bi / Pb 55 / 45 1240 Sn / Pb 63 / 37 1830 Bi / Sn 58 / 42 1380 Sn / Zn 92 / 8 1990 Sn / Cu 99 / 1 2270 Generally the lower melting point alloys, such as Indium - Tin, or Bismuth - lead are favoured as providing the appropriate temperatures for the softening and stretching of thermoplastic yarns in the heat-setting process.

The apparatus particularly and generally described above may also be used as a bath for use in drawing thermoplastic yarns- ie extruding softened yarns under tension during heating in the bath, followed by setting of the drawn yarns by air cooling for forced cooling after leaving the bath.

Claims

1. Heat-setting apparatus comprising container means for containing a heated liquid, and feeding means for feeding a fabric through said container means to thereby heat the fabric by contact with the heated liquid.

2. Heat-setting apparatus according to claim 1, wherein said feeding means is adapted to pass the fabric continuously through the liquid.

3. Heat-setting apparatus according to claim 1, wherein said feeding means is adapted to immerse the fabric in the liquid in batches.

4. Heat-setting apparatus according to claim 1, 2 or 3, wherein the container means comprises a bath or tank containing the liquid.

5. Heat-setting apparatus according to claim 4, having guide rolls to guide a continuously fed fabric into, through and out of the bath or tank.

6. Heat-setting apparatus according to any preceding claim, wherein heating means are provided for continuously heating the liquid to maintain the liquid at a desired temperature.

7. Heat-setting apparatus according to claim 6, wherein said heating means comprise electrical heating elements, or gas burners.

8. Heat-setting apparatus according to any preceding claim, wherein cooling means are provided to cool the fabric on leaving the container means by means of a current of a gas across the width of the fabric.

9. Heat-setting apparatus substantially as hereinbefore described with reference to and as illustrated in the accompanying drawing.

10. A method for heat-setting a fabric, comprising passing the fabric through a container which contains hot liquid.

11. A method according to claim 10, wherein the fabric is passed continuously through, or immersed in the liquid in batches.

12. A method according to claim 10 or 11, wherein the liquid is water.

13. A method according to claim 10 or 11, wherein the liquid is glycerol.

14. A method according to claim 10 or 11, wherein the liquid comprises molten metal.

15. A method according to claim 14, wherein said metal is a eutectic metal alloy.

16. A method according to any one of claims 10 to 15, wherein the liquid in the bath or tank is continuously heated to be maintained at a desired temperature.

17. A method according to claim 16, wherein the fabric, on leaving the bath or tank, is subjected to cooling by a current of a gas such as air applied across the width of the fabric.

18. A method according to claim 16, wherein said eutectic alloy comprises any one or more of: Indium/Tin; Bismuth/Lead; Tin/Lead; Bismuth/Tin; Tin/Zinc or Tin/Copper.

19. A method for heat-setting a fabric substantially as hereinbefore described with reference to the accompanying drawing.

20. A yarn quenching bath for treating a molten or semimolten monofilament or multi filament synthetic polymer yarn, forming part of heat treating apparatus according to any of claims 1 to 9.

21. A yarn quenching bath for treating a molten or semimolten monofilament or multifilament synthetic polymer yarn, when used in a method according to any of claims 10 to 19.