GB1592520A

GB1592520A - Process for the compressed air treatment of yarn on a knitting machine the yarns thus treated and a circular knitting machine

Info

Publication number: GB1592520A
Application number: GB5304377A
Authority: GB
Original assignee: Akzo NV
Current assignee: Akzo NV
Priority date: 1977-01-03
Filing date: 1977-12-20
Publication date: 1981-07-08
Also published as: FR2376237B3; AR215669A1; FR2376237A1; HK24283A; BR7708775A; ES465670A1; DE2756937A1; JPS5386862A; IT1089744B

Description

(54) A PROCESS FOR THE COMPRESSED AIR TREATMENT OF YARN ON A KNITTING MACHINE, THE YARNS THUS TREATED, AND A CIRCULAR KNITTING MACHINE (71) We, AKZO N.V., a Company organised and existing under the laws of the Kingdom of the Netherlands, of IJssellaan 82, Arnhem, the Netherlands, 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: The present invention relates to a process for the treatment on a knitting machine, more particularly a circular knitting machine, of multifilament yarns with a gaseous fluid under superatmospheric pressure, in which process loops and/or other projections are formed in the yarns in a treatment zone between the spools supplying the starting yarn and the knitting needles of the knitting machine.

Although a process of the type described above may be considered to be generally known from "Deutsche Textiltechnik" 21 (1971), Volume 7, p.440, right hand column, section 3.6, this previously described process has never been applied on a commercial scale probably because the practical difficulties met in the realization thereof were considered too great, particularly as far as the manufacture of products of acceptable quality was concerned.

We have now, surprisingly and after elaborate experiments based on many years' experience, determined process conditions by which the difficulties in the process of the type described above can be overcome.

Accordingly, the present invention provides a process for the treatment on a knitting machine of multifilament yarns with a gaseous fluid under superatmospheric pressure, in which process the yarns are provided with loops and/or other projections in a treatment zone between spools supplying the starting yarns and the knitting needles, wherein the superatmospheric pressure to which the gaseous fluid is subjected in the treatment zone is in the range of from 0.5 to 10 bar the overfeed of the yarn is 5 to 40% and the yarn tension is so chosen that the loopiness determined by the measuring method (as hereinafter described) is at least 200 at a distance of 0.6 mm from the compact yarn body and is not more than 10 at 3.5 mm therefrom, the distances being measured from the centre line of the light beam used in the measuring method to the edge of the compact yarn body nearest thereto.

Preferably, the loopiness value is not higher than 50 at a distance of 1.7 mm from the centre line of the measuring light beam to the nearest edge of the compact yarn body. In a preferred embodiment of the invention the superatmospheric pressure of the gaseous fluid under pressure, more particularly air, is 3 to 5 bar. The supply speed of the yarn to and the discharge speed of the yarn from the treatment zone are so adjusted that the speed at which the yarn is supplied to the treatment zone is 5 to 40%, and more preferably 1 5 to 30%, higher than the speed at which the yarn is discharged from said treatment zone. In other words, the overfeed of the yarn is 4 to 40%, more preferably 15 to 30%.In a practical embodiment of the process the invention is characterised in that the treatment zone is in a path between two yarn guides, which path virtually ends at the needle bed of a knitting machine. A special effect may be obtained if the process of the invention is carried out so that the ratio of the supply speed of the yarn to the treatment zone to the discharge speed of the yarn from the zone is periodically changed in accordance with a, preferably variable programme. Particularly favourable results are obtained when the yarn contains filaments having a more or less serrated, wavy, lobed, more particularly three-lobal, four-lobal, fivelobal, six-lobal or eight-lobal cross sectional shape, or some other non-circular crosssectional shape. Alternatively, the yarn may contain filaments having a hollow crosssection.A simple and inexpensive embodiment of the process of the invention is that only one multifilament yarn is treated in the treatment zone. Special effect yarns can be obtained in a simple manner if two or more multifilament yarns are simultaneously blown together in the treatment zone. According to the invention filaments having different degrees of shrinkage may advantageously be used. When two or more yarns are blown together, very attractive knitting can be obtained if at least one of the yarns has a lower tension than the other yarn(s) whereby a core-sheath yarn is obtained in which the yarn having the lower tension forms the looped sheath yarn and the other yarn(s) form(s) a core yarn. Depending on the tension used it is possible, of course, for the core yarn to contain some loops.However the loopiness or the number of loops in the core yarn will be considerably smaller than the loopiness of the sheath yarn.

A knitting having a particularly attractive appearance may be obtained in the process of the invention when a filament yarn crimped by falsetwisting, stufferbox crimping, gear crimping or some other direct crimping method is fed to the treatment zone. Advantageously, a multifilament yarn having a substantially latent crimp may be fed to the treatment zone. The latent crimp in the yarn may have been formed by the knifeedge crimping method or by temporarily creating a temperature gradient across the cross-section of the filaments, for example by asymmetrical heating and cooling of the yarn. Alternatively, a latent crimp yarn may be used in which the filaments of the yarn in side-by-side or asymmetrical sheathcore arrangement are each formed by at least two different polymer components.In the manufacture of a sheath-core yarn by the process of the invention it is preferred that the sheath yarn is a latent crimp yarn, whose filaments have a non-circular cross-sectional shape.

In carrying out the process of the invention several different synthetic multifilament yarns, such as yarns from polyester or polyamide or combinations thereof, may be used. The invention also comprises knitted fabrics produced by the process of the invention. After it has left the knitting machine, the knitted fabric may be subjected to a few known aftertreatments, such as washing, dyeing and stabilizing at elevated temperature. It is preferred that the latent crimp present in the sheath of a core-sheath yarn is converted into a visible crimp. The shrinkage taking place in the sheath yarn provides a knitted material having surprisingly favourable properties, such as very good handling. The most favourable results are obtained with knitted fabrics of the weave knit and the interlock type.

The invention is particularly suited for obtaining a good quality endproduct in the fonn of circular knitting. To achieve this desired result the supply of the gaseous fluid under pressure is continued for the duration of a delay time after the drive of the needle cylinder of the knitting machine has been switched off. Consequently, the knitted fabric obtained does not show any deviations formed as a result of interruptions in the knitting process. A simple method of achieving this result is that after the drive, more particularly the drive motor, of the needle cylinder has been switched off, the supply of the gaseous fluid is not stopped until a delay time has passed. Advantageously, the delay time corresponds approximately to the time that the needle cylinder takes to come to rest after the drive of the needle cylinder has been switched off.This delay time may be from 1 to 10 seconds, and preferably from 2 to 5 seconds. Preferably, after the drive motor for the needle cylinder has been switched off, the supply of the gaseous medium is reduced in accordance with a, preferably variable, programme. This reduction may optionally be carried out gradually. After the drive motor for the needle cylinder has been switched off, the reduction of the supply of the gaseous medium under pressure may be controlled, optionally via a transmission device, by the decreasing speed of the needle cylinder as it runs down.

The present invention also includes within its scope a circular knitting machine for carrying out the above described process, which machine comprises a frame provided with take-up and guiding members for the yarn to be processed and blowing members connected to a supply of a gaseous fluid under pressure, a needle cylinder equipped with a plurality of feeders, which cylinder can be rotated by means of a switch on/off drive, means for stopping, via a time delay, the supply of the gaseous fluid under pressure, after the drive for the needle cylinder has been switched off and means for winding the knitted tube.

The needle cylinder may be fitted with a plurality of, say, 24 or 48 feeders.

The means for stopping the fluid supply advantageously comprise a time relay. In a preferred embodiment of the circular knitting machine of the invention the members for operating the drive of the needle cylinder are coupled by means of a transmission device to control members for the supply of the gaseous fluid under pressure. These control members advantageously operate in accordance with a variable programme. An important advantage of the process of the invention is that use can be made of supply spools of flat yarns or other smoothly unwinding yarns, so that the entire treatment process on the knitting machine can be carried out without any interruptions and at high speed.

The present invention will be further described with reference to the schematic accompanying drawings, in which a circular knitting machine is represented in Figure 1. A rotating cylinder I carrying needles has 24 feeders disposed about the periphery of the cylinder. The direction of rotation of the cylinder is indicated by the arrow 2. In the embodiment shown in the drawing, two yarns 3 and 4 are supplied to each of the feeders.

For the sake of clarity, the supply of yarn to only one of the feeders is shown. A flat starting yarn 3 is drawn from a spool 5 and passes over a thread guide 6 and feed member 7 formed by a forwarding roll with separator roll. The yarn 3 then passes over a thread guide 8 on its way to the feeder, an air texturing device 9 which exerts a pulling-force and a thread guide 10.

These devices are not shown in detail. For each feeder, a special thread guide 8 is mounted on the frame of the knitting machine, and for each feeder an air texturing device 9 is provided.

The device 9 may be of the type described in British Patent Specification No 825,327. In similar fashion, the yarn 4 is supplied to the air texturing device 9 via a thread guide 11, feed member 12 and a second guide 13. In the air texturing device 9 the yarns 3 and 4 are blown together to form a core-sheath yarn, as a result of the tension and the degree of overfeed of the yarns fed to the device 9 being suitably controlled by setting the feed members 7 and 12 to particular speeds. These speeds must be such that the tension in device 9 of the sheath yarn 4 is lower than that of the core yarn 3, whereas the overfeed of the sheath yarn is higher than that of the core yarn. Using a filament yarn, such as a polyester, having latent crimp which is preferably obtained by asymmetrical heating and/or cooling of the yarn, loops are formed in the core sheath yarn in the air texturing device 9.The two spools 5 and 14 are formed from flat starting yarns, so that no unwinding difficulties are encountered. Tubular knitting 15 produced on the circular knitting machine is discharged from the cylinder in known manner, wound and aftertreated in the usual manner at a later stage. During knitting a number of the loops in the yarn may be severed.

Figure 2 shows a somewhat different embodiment of a schematically represented circular knitting machine of the present invention. A rotating cylinder 200 carrying needles and driven by a motor 100 has 24 feeders disposed about the periphery thereof.

The direction of rotation of the cylinder is indicated by the arrow 300. In the embodiment shown in the drawing, two yarns 400 and 500 are supplied to each of the feeders.

For the sake of clarity, the supply of yarn to only one of the feeders is shown. A flat starting yarn 400 is drawn from a spool 600 and passes over a thread guide 700 and feed member 800 formed by a forwarding roll with separator roll. The yarn 400 than passes over a thread guide 900 on its way to the feeder, an air texturing device 100 which exerts a pulling force and a thread guide 110. These devices are not shown in detail. For each feeder, a special thread guide 900 is mounted on the frame of the knitting machine, and for each feeder an air texturing device 100 is provided.

The device 100 may be of the type described in British Patent Specification No 825,327. In similar fashion, the yarn 500 is supplied to the air texturing device 100 via a thread guide 120, feed member 130 and a second guide 140. In the air texturing device 100 the yarns 400 and 500 are blown together to form a core-sheath yarn as a result of the tension and the degree of overfeed of the yarns fed to the device 100 being suitably controlled by setting the feed members 800 and 130 to particular speeds.

These speeds must be such that the tension in the device 100 of the sheath yarn 500 is lower than that of the core yarn 400, whereas the overfeed of the sheath yarn is higher than that of the core yarn. Using a filament yarn 500, such as a polyester, having latent crimp which is preferably obtained by asymmentrical heating and/or cooling of the yarn, loops are formed in the core-sheath yarn in the air texturing device 100. The two spools 600 and 150 are formed from flat starting yarns, so that no unwinding difficulties are encountered.

Tubular knitting 160 produced on the circular knitting machine is discharged from the cylinder in known manner, wound and aftertreated in the usual manner at a later stage.

During knitting a number of the loops in the yarn may be severed.

A coupling device is provided between the drive or the drive motor 100 for the cylinder 200 and the air texturing device, schematically indicated with a dashed line 170. The coupling device is used, after the drive motor 100 has been switched off, to stop the air supply to the blower 100 after a suitable and adjustable delay. The schematic illustration shows the yarn supply to one of the 24 feeders provided in the cylinder 200. When the cylinder contains 24 feeders, an air texturizer 100 mounted on the machine frame is provided for each feeder.

The drive motor 100 must be connected to all 24 blowers by means of identical coupling devices 170. The delay between switching off the drive motor 100 and stopping the air supply to the air texturizing device 100 by means of the coupling 170 is of considerable importance when large amounts of blowing air per unit time are used at relatively high yarn speeds of, say, 100 to 600 m/min., or when the air texturizing treatment is applied to a single filament yarn. After the drive motor has been switched off, the running down time of the cylinder is fairly long as a result of its great mass and relatively high speed. If the air supply is continued at high air speeds when the needle cylinder is stationary, then not only might streakiness in the knitted fabric result but also thread breakage.The air treatment of single filament yarns at high knitting speeds would then not be feasible because after each standstill the yarns would have to be re-threaded into the machine. Various modifications may be made within the scope of the present invention.

For example, a special buffer vessel may be provided with air under pressure, from which air is fed to the air texturizing devices upon the drive or the driving motor of the cylinder 200 being switched off. Simultaneously a valve upstream of the buffer vessel can be closed, as a result of which the air supply to the air texturizing devices is similarly retarded.

In a somewhat modified embodiment the valve before the buffer vessel is closed with some delay via the time relay, and some time later a valve after the buffer vessel is closed, so that a simple form of programmed stoppage of the air texturing devices is obtained. Finally, in a different embodiment a valve controlled by the cylinder speed may be placed in the air line, the control being effected in accordance with a particular programme.

Figure 3 is a schematic representation of an apparatus for measuring the loopiness of the yarn. The light of a lamp 16 is transformed into a narrow beam of parallel rays by means of an axicon lens 17. The diameter of the light beam is about 0.5 mm. The light beam 18 strikes a photo-transistor 19. This phototransistor emits an electric signal which is dependent on the intensity of light collected by it. Between the lens 17 and the phototransistor 19 the yarn 20 whose loopiness is to be determined is placed. The axes of the yarn and the light beam across each other at right angles and the distance between the yarn surface and the light beam can be adjusted.

The yarn 20 is moved at a speed of 30 m/min.

by means of a guiding system. When a yarn filament intersects the light beam, a change in the electric signal is caused and this pulse is amplified by the amplifier 21 and counted by the electronic adder 22. The loopiness meter is of a type known per se and is provided in the usual way with a knob 23 for adjusting the light intensity, a pilot lamp 24, a calibration switch 25, a feed amplifier 27 and a meter 28 for the light intensity. The distance between the yarn surface and the light beam can be set (in a way not shown) by a micrometer screw, which forms part of the yarn guiding system. To set the distance between the yarn surface, i.e. the edge of the compact yarn body, and the beam of light one starts from the point where the centre line of the yarn core or the yarn body passes through the centre line of the light beam.This point can be established on the apparatus for each yarn, because the intensity of the transmitted light is at its minimum value there. With the aid of the micrometer screw the yarn is raised from the point until the desired distance between the centre line of the light beam and the edge of the yarn core has been reached.

To set the distance between the centre line of the yarn core and the edge of the yarn the diameter of the yarn core is measured with a projection microscope (magnification 125x).

25 measurements are carried out and the average result is calculated. The yarn core diameter of a loop yarn which must be known for positioning the edge of the yarn core on the loopiness meter is measured with a projection microscope. The loop yarn which is to be examined is longitudinally placed on a slide (2.5 x 7.5 cm) while at a tension of 3 cN, i.e. a tension equal to that used in the loopiness meter, and so taped at the ends that a free piece of at least 5 cm is left. In all, 5 of these preparations are made. Subsequently, each preparation is placed on the stage of the projection microscope and projected with transmitted light onto a frosted graduated glass plate and the core diameter of the thread is measured at 5 different points thereof. By turning various knobs, the preparation is so shifted that the diameter is measured at 1 cm intervals.The yarn core is the compact yarn body 29 shown in Figure 7. To determine the actual yarn core diameter the mean value of the 25 yarn core diameters measured must still be divided by the magnification of 125 x.

As appears from the above description of the loopiness meter, only those loops or filament portions are counted that intersect a flat plane, which is positioned at a distance A from the yarn surface, i.e. the edge of the compact yarn body. The procedure is further described with reference to the schematic drawings in Figures 4 and 5. In Figures 4 and 5 the yarn 20 is shown in cross-section and the light beam 18 in longitudinal section. The core of the compact yarn body is referred to by the numeral 29 and a few loops projecting from the compact yarn body are referred to by the numeral 30. The above-mentioned edge of the compact yarn body is indicated by the tangent line 31, and the centre line of the light beam 18 is indicated by numeral 32. Figures 4 and 5 are not drawn to scale and only differ in that the distances A are not equal.Figure 4 schematically represents the situation in which the distance A = 0.6 mm, whereas in Figure 5 the distance A = 1.7 mm. As also appears from the Figures 4 and 5, the distances A are measured between the centre line 32 of the measuring light beam and the nearest edge 31 of the compact yarn body 29. In some cases a loop will just end in the light beam and will just be counted or not, depending on the magnitude of the electric pulse produced. The number of loops N counted per 5 metres of yarn length are referred to herein as the loopiness of the treated yarn, N being the average value of 5 measurements. It will be clear that this loopiness N is dependent on: a. the distance which the loops project from the core and the distance A between the centre line 32 of the light beam 18 and the edge 31 of the compact yarn body; b. the number of loops per unit length of the yarn; and c. the shape of the loops.

The loopiness can be measured on the yarn both before and after knitting. Figure 6 shows the relationship between the distance A and the number of loops measured for two polyester filament yarns that were unravelled from finished cloths and had been air textured on the knitting machine of the invention. From Figure 6 it follows that for the two yarns I and II, the loopiness strongly increases with decreasing distance from the yarn surface.

The yarn of the curve I is formed by a blown core-sheath yarn having a flat polyester multifilament yarn as the core and a flat multifilament yarn having latent crimp obtained by asymmetrical heating as the sheath. When the distance A = 0.6 mm, the loopiness N = 360; when A = 1.7 mm, the loopiness N is very low and in any case below 50, whereas when A = 3.5 mm the loopiness is even lower and in any case below 10.

The yarn of the curve II is formed by a blown core-sheath yarn having flat noncrimped polyester multifilament yarns as the core and as the sheath. When the distance A = 0.6 mm, the loopiness N = 950; when A = 1.7 mm, the loopiness N = 30, whereas with a distance A = 3.5 mm, the loopiness is very low, and in any case below 10.

By way of example an attractive knitted piece was made from a large number of the core-sheath yarns. The sheath consisted of a 50 decitex, 24 filament semi-dull polyester yarn having latent crimp obtained by asymmetrical heating, whose filaments had a square hollow cross-section. This sheath yarn was fed to the air texturizing devices at a steed of 250 m/min. The core consisted of a flat 76 decitex, 24 filament polyester yarn of round cross-section. This core yarn was fed to the air texturizing devices at a speed of 200 m/min. The composite coresheath yarn was fed to the cylinder 1 of the knitting machine at a speed of 200 m/minute.

In a second example another attractive knitted piece was made from a large number of the sheath-core yarns. These yarns differed from the ones just described in that the sheath yarn consisted of filaments having a four-lobal hollow cross-section.

WHAT WE CLAIM IS:- 1. A process for the treatment on a knitting machine of multifilament yarns with a gaseous fluid under superatmospheric pressure, in which process the yarns are provided with loops and/or other projections in a treatment zone between spools supplying the starting yarns and the knitting needles, wherein the superatmosphereic pressure to which the gaseous fluid is subjected in the treatment zone is in the range of from 0.5 to 10 bar, the overfeed of the yarn is 5 to 40% and the yarn tension is so chosen that the loopiness determined by the measuring method (as hereinbefore described) is at least 200 at a distance of 0.6 mm from the compact yarn body and is not more than 10 at 3.5 mm therefrom the distances being measured from the centre line of the light beam used in the measuring method to the edge of the compact yarn body nearest thereto.

2. A process as claimed in Claim 1 wherein the loopiness is not higher than 50 at a distance of 1.7 mm.

3. A process as claimed in Claim 1 or Claim 2 wherein the super-atmospheric pressure of the gaseous fluid under pressure is in the range of from 3 to 5 bar.

4. A process as claimed in any one of the preceding claims wherein the gaseous fluid is air.

5. A process as claimed in any one of the preceding claims wherein the speed at which the yarn is supplied to the treatment zone the overfeed is 15 to 30% higher than the speed at which the yarn is discharged from the treatment zone.

6. A process as claimed in Claim 5 wherein the ratio of the supply speed of the yarn to the treatment zone to the discharge speed of the yarn from the zone is periodically changed in accordance with a programme.

7. A process as claimed in Claim 6 wherein the programme is a variable programme.

8. A process as claimed in any one of the preceding claims wherein the treatment zone is positioned in a path between two yarn guides, which path ends at the needle bed of the knitting machine.

9. A process as claimed in any one of the preceding claims wherein the yarn contains filaments having a serrated wavy or lobed noncircular cross-sectional shape.

10. A process as claimed in Claim 9 wherein the filaments have a three-lobal, four-lobal, six-lobal or eight-lobal cross-sectional shape.

11. A process as claimed in any one of the preceding claims wherein the yarn contains filaments having a hollow cross-section.

12. A process as claimed in any one of the preceding claims wherein only one multifilament yarn is treated in the treatment zone.

13. A process as claimed in any one of Claims 1 to 11 wherein two or more multifilament yarns are simultaneously blown together in the greatment zone.

14. A process as claimed in Claim 13 wherein the yarns used comprise filaments having different degrees of shrinkage.

15. A process as claimed in Claim 13 wherein at least one of the yarns has a lower tension than the other yarn(s) whereby a core-sheath yarn is obtained in which the yarn having the lower tension forms the looped sheath yarn and the other yarn(s) form(s) a core yarn.

16. A process as claimed in any one of the preceding claims wherein a filament yarn crimped by falsetwisting, stufferbox crimping, gear crimping or some other direct crimping method is fed to the treatment zone.

17. A process as claimed in any one of the preceding claims wherein the yarn fed to the treatment zone has a substantially latent crimp.

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. the number of loops measured for two polyester filament yarns that were unravelled from finished cloths and had been air textured on the knitting machine of the invention. From Figure 6 it follows that for the two yarns I and II, the loopiness strongly increases with decreasing distance from the yarn surface. The yarn of the curve I is formed by a blown core-sheath yarn having a flat polyester multifilament yarn as the core and a flat multifilament yarn having latent crimp obtained by asymmetrical heating as the sheath. When the distance A = 0.6 mm, the loopiness N = 360; when A = 1.7 mm, the loopiness N is very low and in any case below 50, whereas when A = 3.5 mm the loopiness is even lower and in any case below 10. The yarn of the curve II is formed by a blown core-sheath yarn having flat noncrimped polyester multifilament yarns as the core and as the sheath. When the distance A = 0.6 mm, the loopiness N = 950; when A = 1.7 mm, the loopiness N = 30, whereas with a distance A = 3.5 mm, the loopiness is very low, and in any case below 10. By way of example an attractive knitted piece was made from a large number of the core-sheath yarns. The sheath consisted of a 50 decitex, 24 filament semi-dull polyester yarn having latent crimp obtained by asymmetrical heating, whose filaments had a square hollow cross-section. This sheath yarn was fed to the air texturizing devices at a steed of 250 m/min. The core consisted of a flat 76 decitex, 24 filament polyester yarn of round cross-section. This core yarn was fed to the air texturizing devices at a speed of 200 m/min. The composite coresheath yarn was fed to the cylinder 1 of the knitting machine at a speed of 200 m/minute. In a second example another attractive knitted piece was made from a large number of the sheath-core yarns. These yarns differed from the ones just described in that the sheath yarn consisted of filaments having a four-lobal hollow cross-section. WHAT WE CLAIM IS:-

1. A process for the treatment on a knitting machine of multifilament yarns with a gaseous fluid under superatmospheric pressure, in which process the yarns are provided with loops and/or other projections in a treatment zone between spools supplying the starting yarns and the knitting needles, wherein the superatmosphereic pressure to which the gaseous fluid is subjected in the treatment zone is in the range of from 0.5 to 10 bar, the overfeed of the yarn is 5 to 40% and the yarn tension is so chosen that the loopiness determined by the measuring method (as hereinbefore described) is at least 200 at a distance of 0.6 mm from the compact yarn body and is not more than 10 at 3.5 mm therefrom the distances being measured from the centre line of the light beam used in the measuring method to the edge of the compact yarn body nearest thereto.

18. A process as claimed in Claim 17 where

in the latent crimp in the yarn is formed temporarily creating a temperature gradient across the cross-section of the filaments.

19. A process as claimed in Claim 17 wherein the filaments of the yarn in side-by-side or asymmetrical sheath-core arrangement are each formed by two or more different polymer compoents.

20. A process as claimed in Claim 15 wherein a yarn whose filaments have a noncircular cross-section form the sheath yarn into which open and/or closed loops are blown.

21. A process as claimed in Claim 15 wherein a latent crimp yarn forms the sheath yarn into which closed and/or open loops are blown.

22. A process as claimed in any one of the preceding claims which is effected on a circular knitting machine.

23. A process as claimed in Claim 22 for the treatment on a circular knitting machine of multifilament yarns with a stream of gaseous fluid under superatmospheric pressure wherein the supply of the gaseous fluid under pressure is continued for the duration of a delay time after the drive of the needle cylinder of the knitting machine has been switched off.

24. A process as claimed in Claim 23 wherein after the drive of the needle cylinder has been switched off, the supply of the gaseous fluid is stopped after a delay time.

25. A process as claimed in Claim 24 wherein the delay time corresponds approximately to the time that the needle cylinder takes to come to rest after the drive of the needle cylinder has been switched off.

26. A process as claimed in any one of Claims 23 to 25 wherein the delay time is from 1 to 10 seconds.

27. A process as claimed in Claim 26 wherein the delay time is from 2 to 5 seconds.

28. A process as claimed in any one of Claims 23 to 27 wherein after the drive for the needle cylinder has been switched out, the supply of the gaseous medium is reduced in accordance with a programme.

29. A process as claimed in Claim 28 wherein the programme is a variable programme.

30. A process as claimed in Claim 28 or Claim 29 wherein after the drive has been switched off the supply of the medium under pressure is gradually reduced.

31. A process as claimed in any one of Claims 23 to 30 wherein after the drive for the needle cylinder has been switched off, the reduction of the supply of the gaseous medium under pressure is controlled by the decreasing speed of the needle cylinder.

32. A process as claimed in Claim 1 and substantially as hereinbefore described with reference to the accompanying drawings.

33. A knitted fabric when produced by a process as claimed in any one of the preceding claims.

34. A knitted fabric as claimed in Claim 33 which is of the weave knit type.

35. A knitted fabric as claimed in Claim 33 which is of the interlock type.

36. A circular knitting machine for carrying out the process claimed in any one of Claims 23 to 31 which machine comprises a frame provided with take-up and guiding members for the yarn to be processed and blowing members connected to a supply of a gaseous fluid under pressure, a needle cylinder equipped with a plurality of feeders, which cylinder can be rotated by means of a switch on/off drive, means for stopping, via a time delay, the supply of the gaseous fluid under pressure, after the drive for the needle cylinder has been switched off and means for winding the knitted tube.

37. A circular knitting machine as claimed in Claim 36 wherein the means for stopping the supply of fluid comprises a time relay.

38. A circular knitting machine as claimed in Claim 36 or Claim 37 wherein the members for operating the drive of the needle cylinder are coupled by means of a transmission device to control members for the supply of the gaseous fluid under pressure.

39. A circular knitting machine as claimed in Claim 38 wherein the control members operate in accordance with a variable programme whereby the air supply to the blowers can be stopped as a function of time.

40. A circular knitting machine as claimed in any one of Claims 36 to 39 wherein a buffer vessel is provided in the supply line to the blowers.

41. A circular knitting machine as claimed in Claim 36 and substantially as hereinbefore described with reference to Figure 1 or Figure 2 of the accompanying drawings.