GB1584446A

GB1584446A - Treatment of yarn

Info

Publication number: GB1584446A
Application number: GB21517/76A
Authority: GB
Original assignee: BOC Ltd
Current assignee: BOC Ltd
Priority date: 1976-05-25
Filing date: 1976-05-25
Publication date: 1981-02-11
Also published as: ZA773143B

Description

(54) TREATMENT OF YARN (71) We, Boc LIMITED, of Hammersmith House, London W6 9DX, England, an English company, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to the treatment of yarn and, more particularly, to heat setting of yarn. The term 'yarn' is used herein to include a single length (or filiment) of fibrous material (natural or synthetic) or a multiplicity of such filaments.

Yarn is usually set by stretching it and then applying heat to the stretched yarn. In this way the inherent elasticity of the yarn is set. Further operations may also be performed on the yarn at the same time to give a required finish to the threads thereby enhancing their appearance, for example the stretched yarn may be crimped, twisted, or drawn over a sharp edge, to produce a regular pattern such crimping being set by the application of heat to stretched yarn.

However, after such heating a sufficient path for the set yarn must be provided to allow cooling thereof before the yarn is wound onto a storage bobbin. Hitherto, such cooling has been effected by heat exchange with the surrounding atmosphere. More recently, the speeds of the processing apparatus for setting the yarn have increased to such an extent that the time allowed for natural cooling is insufficient. Attempts have been made to solve this problem at least to some extent by increasing the path between the heat applying device and the final storage bobbin, but this has led to apparatus which is much greater in height and which therefore takes up much more space in the factory.

This disadvantage can be quite severe: often sixty or more of such machines are provided and space is usually fairly restricted in a factory.

Another alternative is to traverse the yarn over many vertical passes. This affects the yarn tension considerably.

The invention provides a method for setting yarn comprising heating and stretching the yarn, and then cooling the yarn by heat exchange with a cooling medium which is at a temperature of minus 20"C or below.

It is preferred that the cooling medium is a liquefied gas, usually liquid nitrogen. It is further preferred that, when a liquefied gas is used as the cooling medium, a heat exchange device is used which has means for bringing back into heat exchange relationship with the yarn that vapour which is formed during heat exchange by evaporation of the liquefied gas.

In some embodiments of the invention, said heat exchange device may comprise a hollow member, which may be in the form of a plate, into which member the liquefied gas can be fed, the yarn, in use, being fed across a surface of the member, means being provided to feed gas vaporised during heat exchange with the hot yarn, to an enclosed space through which such yarn passes. One wall of such enclosed space may be provided by said hollow member such that the hot yarn fibres are simultaneously in heat exchange relation with the liquified gas within the hollow member and gas enclosed in said space.

One embodiment of the invention will now be described by way of example and with reference to the accompanying drawings of which: Figure 1 is a diagrammatic representation of an apparatus for setting yarn embodying the invention, and Figures 2 to 5, illustrate diagrammatically respect examples of heat exchange devices for use in the apparatus shown in Figure 1.

Figure 1 of the drawing, there is shown a yarn setting apparatus comprising a bobbin 10 of unset yarn. The yarn is drawn from the bobbin 10 by a pair of driven rolls 11 and 12, the yarn passing around a stationary spindle 13. The roll 12 is driven at a high speed than roll 11 so that the yarn is stretched in the region between the rolls. In this region the yarn passes across the surface of an electric hot plate 14 so that the stretched yarn is heated in order to reduce the inherent elasticity of the yarn and thereby to set the yarn. The temperature of the hot plate is usually of the order of 270"C.

The hot yarn is passed through a heat exchange device 15 in which it is cooled to about ambient temperature before it passes to a storage bobbin 16. The device 15 compirses a hollow plate 17 into which liquid nitrogen is fed through vacuum insulated supply conduits 18 and 19. The path followed by the yarn passes across a curved heat exchange surface 23 of the plate 17.

A housing 20 defines with the surface 23 of the plate 17 an enclosed space 21 through which the yarn passes. Nitrogen gas vaporised from the bath of liquid nitrogen in the plate 17 passes through conduit 22 into the space 21 to provide further cooling for the hot yarn. Such gas then passes to atmosphere, for example, through an air conditioning system which utilizes any residual cold in the nitrogen gas.

The above described apparatus usually comprises one element of a machine having 64 similar elements. The conduit 19 with several similar conduits 18 constitutes a manifold for- the supply of liquid nitrogen which is contained in a header 23 tank located to provide a gravity feed of the liquid nitrogen. The header 23 receives liquid nitrogen from a main storage vessel 24 which is periodically replenished with liquid nitrogen.

Figure 2 illustrates a heat exchange device 15 having a hollow cooling plate 211 providing a cooled curved heat exchange surface 212 over which the heated yarn 213 is passed. Liquid nitrogen is supplied to the interior of the plate 211 through insulated supply conduits 214. A level control device 215 extends into the interior of the plate 211 and is connected to control the supply of liquid nitrogen so as to maintain a required level thereof in the plate. The device 215 may for example include electrical winding, the resistance of which alters when contacted with liquid nitrogen. The device controls a relay which regulates the flow of liquid nitrogen into the plate 211. Another example of control device is a float controlled regulator.In some applications, it may be desirable to provide a hinged housing 216 through which nitrogen gas evaporoted from the liquid nitrogen within plate 211 is channelled by means of a conduit (not shown). This arrangement makes it possible to shield the yarn as it passes through the heat exchange device.

The plate 211 may, if desired, have its walls insulated, apart that is from the yarn contacting surface 212.

The heat exchange device 15 shown in Figure 3 comprises a pair of coaxial tubular elements 321 and 322 connected to provide an annular chamber 323 for containing liquid nitrogen, which surrounds a contral passage 324 for heated yarn. The diameter of the passage 324 is about 1 to 1.5 times the diameter of the yarn. A level control device 325 is provided in the chamber 323.

Alternatively the supply of liquid nitrogen to chamber 323 may be controlled by signal generated by temperature sensitive device 326, shown in dotted lines, located in passage 324.

The heat exchange device shown in Figure 4 comprises a cylindrical member 430 through which the yarn 431 is passed. The internal diameter of the member 430 is about 1 to 1.5 times the total yarn diameter.

Nozzles 432 for providing sprays of liquid nitrogen. The supply line 433 may be restricted to provide high pressure liquid nitrogen spray or, for other installations, a low pressure liquid nitrogen supply may be adequate. A temperature measuring device 434, e.g. a thermocouple, is located within the cylindrical member 430 and is connected to control the supply of liquid nitrogen to the nozzles 432 so as to maintain a required temperature in the heat exchange device.

Figure 5 illustrates a heat exchange device similar to that shown in Figure 4 with the exception that the cylindrical member 540 is hollow to provide a chamber for receiving liquid nitrogen. The liquid nitrogen nozzles 541 comprise apertures in the internal wall of the member 540 at a high pres- sure supply of liquid nitrogen is fed to the member 540 through a restricted conduit 541 and an annular manifold 542 encircling the lower end of the member 540. In an alternative use of a heat exchanger as shown in Figure 5 an unrestricted low pressure flow of liquid nitrogen to which compressed air is introduced in order to provide the required sprays of liquid nitrogen through nozzles 541.

WHAT WE CLAIM IS:- 1. A method for setting yarn comprising heating and stretching the yarn, and then cooling the yarn by heat exchange with a cooling medium which is at a temperature of minus 20"C or below.

2. A method as claimed in Claim 1, in which the cooling medium is a liquefied gas.

3. A method as claimed in claim 2, in which the liquefied gas is liquid nitrogen.

4. A method as claimed in claim 2 or claim 3, in which the yarn is passed along a heat exchange surface cooled by liquefied gas.

5. A method as claimed in claim 4, in which the heat exchange surface is an external surface of a hollow plate containing a liquefied gas.

6. A method as claimed in claim 5, in which vapour evolved by the liquefied gas

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. the inherent elasticity of the yarn and thereby to set the yarn. The temperature of the hot plate is usually of the order of 270"C. The hot yarn is passed through a heat exchange device 15 in which it is cooled to about ambient temperature before it passes to a storage bobbin 16. The device 15 compirses a hollow plate 17 into which liquid nitrogen is fed through vacuum insulated supply conduits 18 and 19. The path followed by the yarn passes across a curved heat exchange surface 23 of the plate 17. A housing 20 defines with the surface 23 of the plate 17 an enclosed space 21 through which the yarn passes. Nitrogen gas vaporised from the bath of liquid nitrogen in the plate 17 passes through conduit 22 into the space 21 to provide further cooling for the hot yarn. Such gas then passes to atmosphere, for example, through an air conditioning system which utilizes any residual cold in the nitrogen gas. The above described apparatus usually comprises one element of a machine having 64 similar elements. The conduit 19 with several similar conduits 18 constitutes a manifold for- the supply of liquid nitrogen which is contained in a header 23 tank located to provide a gravity feed of the liquid nitrogen. The header 23 receives liquid nitrogen from a main storage vessel 24 which is periodically replenished with liquid nitrogen. Figure 2 illustrates a heat exchange device 15 having a hollow cooling plate 211 providing a cooled curved heat exchange surface 212 over which the heated yarn 213 is passed. Liquid nitrogen is supplied to the interior of the plate 211 through insulated supply conduits 214. A level control device 215 extends into the interior of the plate 211 and is connected to control the supply of liquid nitrogen so as to maintain a required level thereof in the plate. The device 215 may for example include electrical winding, the resistance of which alters when contacted with liquid nitrogen. The device controls a relay which regulates the flow of liquid nitrogen into the plate 211. Another example of control device is a float controlled regulator.In some applications, it may be desirable to provide a hinged housing 216 through which nitrogen gas evaporoted from the liquid nitrogen within plate 211 is channelled by means of a conduit (not shown). This arrangement makes it possible to shield the yarn as it passes through the heat exchange device. The plate 211 may, if desired, have its walls insulated, apart that is from the yarn contacting surface 212. The heat exchange device 15 shown in Figure 3 comprises a pair of coaxial tubular elements 321 and 322 connected to provide an annular chamber 323 for containing liquid nitrogen, which surrounds a contral passage 324 for heated yarn. The diameter of the passage 324 is about 1 to 1.5 times the diameter of the yarn. A level control device 325 is provided in the chamber 323. Alternatively the supply of liquid nitrogen to chamber 323 may be controlled by signal generated by temperature sensitive device 326, shown in dotted lines, located in passage 324. The heat exchange device shown in Figure 4 comprises a cylindrical member 430 through which the yarn 431 is passed. The internal diameter of the member 430 is about 1 to 1.5 times the total yarn diameter. Nozzles 432 for providing sprays of liquid nitrogen. The supply line 433 may be restricted to provide high pressure liquid nitrogen spray or, for other installations, a low pressure liquid nitrogen supply may be adequate. A temperature measuring device 434, e.g. a thermocouple, is located within the cylindrical member 430 and is connected to control the supply of liquid nitrogen to the nozzles 432 so as to maintain a required temperature in the heat exchange device. Figure 5 illustrates a heat exchange device similar to that shown in Figure 4 with the exception that the cylindrical member 540 is hollow to provide a chamber for receiving liquid nitrogen. The liquid nitrogen nozzles 541 comprise apertures in the internal wall of the member 540 at a high pres- sure supply of liquid nitrogen is fed to the member 540 through a restricted conduit 541 and an annular manifold 542 encircling the lower end of the member 540. In an alternative use of a heat exchanger as shown in Figure 5 an unrestricted low pressure flow of liquid nitrogen to which compressed air is introduced in order to provide the required sprays of liquid nitrogen through nozzles 541. WHAT WE CLAIM IS:-

1. A method for setting yarn comprising heating and stretching the yarn, and then cooling the yarn by heat exchange with a cooling medium which is at a temperature of minus 20"C or below.

6. A method as claimed in claim 5, in which vapour evolved by the liquefied gas

is conducted out of the hollow plate and over the heat exchange surface.

7. A method as claimed in claim 2 or claim 3, in which the yarn is passed through a passage defined by the inner wall of an annular chamber containing liquefied gas.

8. A method as claimed in claim 2 or claim 3, in which liquefied gas is sprayed onto the yarn.

9. A method for setting yarn substantially as described herein with reference to Figure 1 of the accompanying drawings.

10. A method for setting yarn as claimed in claim 1, in which a cooling device substantially as described with reference to any one of Figures 2 to 5 of the accompanying drawings.