GB2328452A

GB2328452A - Heating setting of belts and fabrics

Info

Publication number: GB2328452A
Application number: GB9717615A
Authority: GB
Inventors: Jan Torbjoern Stroem
Original assignee: Scapa Group Ltd
Current assignee: Scapa Group Ltd
Priority date: 1997-08-21
Filing date: 1997-08-21
Publication date: 1999-02-24
Also published as: GB9717615D0

Abstract

Heat setting apparatus, for example for belts and fabrics over 3m in width comprises a heating oven (11) through which a fabric (10) is passed, and a device for blowing cooling gas, usually air, onto the heated fabric after it has left the oven (11) comprising a conduit (14) with outlets (16) extending across the width of the fabric, one each upstream and downstream of a chamber (17) extending across the fabric. The flow of cooling gas may be variable across the width of the fabric.

Description

HEAT SETTING OF BELTS AND FABRICS This invention relates to a method and apparatus for heat setting of belts and fabrics.

The invention particularly relates to a heat setting process in the manufacture of industrial belts and fabrics notably papermaking fabrics, filter belts or conveyor belting.

Heat setting is used to lock the woven or non-woven fabric structure to eliminate any possibility of stretching or deformation of the fabric on the machine during use. It comprises essentially of applying heat to the fabric whilst it is under tension and locking the stretched structure into position as it is cooled. The temperature to which the fabric is heated will lie between the glass transition temperature and melting point of the thermoplastic yarn material used in the fabric, so that the yarns are stretched by the tension applied by the heat setting machine. The combination of heat and tension also aligns the molecular chains in the yarns, thus improving tensile properties.

A typical heat setting installation may comprise two large spaced apart heated rolls around which the fabric, e.g a press felt basecloth or a dryer fabric is driven at slow speed under tension. Typical examples of such machines are given in US 5,312,523; US 4,504,354 and US 4,495,714.

Also widely used are heat setting ovens, often 1 to 2 metres in length and heated to 100 C to 250"C, normally 150-220"C for papermachine clothing. The fabric will pass through the oven over a period of about one minute, and then leave the oven and pass through air at room temperature, optionally making a return run through a second similar oven at a slightly higher temperature.

For certain types of fabric such as carcasses for reinforcing tyres, a single oven split into different heating zones may be used. As the fabric leaves the oven it is cooled, e.g. by simply passing it through air, or over a cooled roll.

The key problem with heat setting is that it is a highly critical process, in both the heating and more particularly the cooling phases. Minute deviations from set parameters can lead to detrimental flaws in the fabric which may be severe enough to require scrapping of the fabric. The problem of control over cooling of the fabric is not significant for narrow fabrics, e.g. under 3 metres in width, but for very wide fabrics (3 - 15 metres) used for industrial belting such as papermaking fabrics, filter belts or conveyor belting, insufficient control of cooling due for example to uneven flow of air in the region where the fabric exits the oven, will lead to non-uniform locking of the fabric structure across the width of the fabric. This variation of the fabric structure makes the fabric very difficult to seam and in some cases the fabric will need to be seamed by hand rather than on an automatic or semi-automatic machine, which is a time consuming and highly complicated process. The phenomenon known as edge curl whereby the fabric edges curl up may also occur and this will require time consuming remedial action such as described in US 5,546,643. Poor heat-setting also creates the problem of slack edges with spiral link fabrics.

So critical is the cooling process that simply opening a window or door in the heat setting machine room can significantly deform the fabric structure.

An object of the invention is to provide an apparatus and method for heat setting belts and fabrics, particularly broad industrial belts and fabrics in excess of e.g.

3 metres in width which will promote a more uniform cooling of the fabric as it leaves the heating means.

In accordance with the invention, apparatus for heat setting a fabric etc, comprises heating means for heating the fabric, and disposed following the heating means, means for supplying gas into contact with the fabric over the width of the fabric.

The gas is preferably air, and is preferably supplied at a selected temperature which is controlled by temperature regulating means.

The gas may be fed to the fabric by means of a conduit extending across the entire width of the fabric.

Air may be fed to the conduit from each end to create a uniform flow along the length of the conduit.

The slots are preferably disposed as close to the exit from the heating means as possible.

Whilst preferably located immediately following the exit from the heating means, if insufficient space is available between the exit and a return roll, the conduit may be located immediately downstream of the return roll.

The heating means may be an electrical or gas-fired oven, a hot liquid bath, or hot gas (e.g. air) blower, and is preferably regulated to produce a temperature of about 100-250"C.

The invention also provides a method of heat setting a fabric, comprising heating the fabric to a selected temperature, and then after leaving the heating stage, subjecting the fabric to contact with cooling gas over the width of the fabric.

The gas is preferably air, and is preferably regulated in temperature to effect controlled cooling of the fabric.

The gas may be supplied via a conduit extending across the width of the fabric, and may be fed from each end of the conduit to create a uniform flow along the entire length of the conduit. Air may issue from two outlets to a chamber directly below the conduit and immediately above the fabric, which directs a low velocity air flow through the fabric. The length of the chamber in the machine direction is designed to cool the fabric to room temperature before it reaches the roll.

A preferred embodiment of the invention will now be described by way of example, with reference to the accompanying drawing, which is a diagrammatic view of a heat setting machine according to the invention.

In a heat setting machine according to the invention, a wide belt of fabric, such as a papermachine dryer fabric or press felt basecloth 10, is fed through a heating oven 11. This is an electric oven and the temperature of heating elements in the oven, selected in relation to the dwell time of the fabric 10 within the oven (determined in turn by the speed of the fabric and the length of the oven) to effect heating of the fabric 10 to a temperature in the range of eg 100"-2500C. The exact temperature is determined by the composition of thermoplastic fibres or yarns present in the fabric, and falling in the range between the glass transition temperature and the melting point of the compound or blend used in the fabric.

The fabric leaves the oven 11 and proceeds via a free reach to a cooled return roller 12, and then returns via a return reach 13 of the fabric.

A conduit 14 is in accordance with the invention mounted above the fabric immediately following its exit 15 from the oven 11. The conduit 14 has outlets 16 extending across the width of the fabric 10, to discharge temperature regulated cooling gas (usually air) onto the heated fabric 10 at it leaves the oven to either side (upstream and down stream) of a chamber 17 extending across the fabric, and open downwardly to the fabric 10. The air is introduced to the conduit from each end, e.g. using fans or blowers.

The flow of cooling air from each outlet 16 may be adjusted to be variable in width across the fabric 10 in response to a controller. The controller may access information provided for example by thermal imaging equipment, which maps the temperature distribution of the fabric as it cools, interpret the data thus provided, and determine how the flow of cooling air needs to be controlled to correct any faults found in the temperature distribution, by varying the widths of the outlets 16, and adjusting the delivery rate of fans introducing air at each end ofthe conduit 14.

The above embodiment is described by way of example only, and modifications and improvements may be made.

The cooling gas may be other than air, in which case elaborate arrangements would be needed to enable recycling with minimum waste.

The control of the outlets may be effected by any known means, and be manually or partially or fully automatic.

The conduit may be in the form of a manifold with an array of discharge nozzles, which may be formed with fishtail orifices to provide elongated slot outlets.

Claims

1. Apparatus for heat setting of belts and fabrics comprising heating means for heating the fabric, and disposed following the heating means, means for supplying gas into contact with the fabric over the width of the fabric.

2. Apparatus for heat setting of belts and fabrics as claimed in claim 1 wherein the gas brought into contact with the fabric over the width of the fabric is air.

3. Apparatus for heat setting of belts and fabrics as claimed in claim 1 or claim 2 wherein the gas brought into contact with the fabric over the width of the fabric is supplied at a selected temperature.

4. Apparatus for heat setting of belts and fabrics as claimed in any preceding claim wherein the temperature is controlled by regulating means.

5. Apparatus for heat setting of belts and fabrics as claimed in any preceding claim wherein the gas is brought into contact with the fabric over the width of the fabric by means of a conduit extending across the entire width of the fabric and having one or more outlet slots for the gas.

6. Apparatus for heat setting of belts and fabrics as claimed in any preceding claim wherein the gas brought into contact with the fabric is fed into the conduit from each end of the conduit.

7. Apparatus for heat setting of belts and fabrics as claimed in any preceding claim wherein the slots are disposed as close to the exit from the heating means as possible.

8. Apparatus for heat setting of belts and fabrics as claimed in any preceding claim wherein the conduit is located downstream of the return roll.

9. Apparatus for heat setting of belts and fabrics as claimed in any preceding claim wherein the heating means is electrical.

10. Apparatus for heat setting of belts and fabrics as claimed in any preceding claim wherein the heating means is a gas fired oven.

11. Apparatus for heat setting of belts and fabrics as claimed in any preceding claim wherein the heating means is a hot liquid bath.

12. Apparatus for heat setting of belts and fabrics as claimed in any preceding claim wherein the heating means is a hot gas blower.

13. Apparatus for heat setting of belts and fabrics as claimed in any preceding claim wherein the heating means is regulated to produce a temperature of 100-2500C.

14. A method of heat setting a fabric comprising heating the fabric to a selected temperature, then, after leaving the heating stage, subjecting the fabric to contact with cooling gas over the width of the fabric.

15. A method of heat setting a fabric as claimed in claim 14 wherein the cooling gas is air.

16. A method of heat setting a fabric as claimed in claim 14 or claim 15 wherein the temperature is regulated.

17. A method of heat setting a fabric as claimed in claims 14 to 16 wherein the cooling gas is supplied via a conduit extending across the width of the fabric.

18. A method of heat setting a fabric as claimed in claims 14 to 17 wherein the cooling gas is fed into each end of the conduit.

19. A method of heat setting a fabric as claimed in claims 14 to 18 wherein the cooling gas can vent from a number of outlets to a chamber below the conduit and above the fabric.

20. A method of heat setting a fabric as claimed in claims 14 to 19 wherein the length of the chamber in the machine direction is designed to cool the fabric to room temperature before it reaches the roll.