GB2078793A - Yarn False Twisting Apparatus and Method - Google Patents

Abstract

A yarn false twisting apparatus comprises a pair of friction discs with one of the discs being thin and flexible, and a pressure applying member 24, 25 for biasing the flexible disc toward the other disc locally at the twisting zone. The discs and pressure applying member are mounted to permit selective movement whereby the ratio of twist to yarn speed may be varied, and to achieve a desired twist in the advancing yarn. The biasing force of the pressure applying member is also adjustable to achieve a substantially slipless operation by ensuring that the torque exerted by the discs exceeds the natural restoring torque of the yarn. <IMAGE>

Description

SPECIFICATION Yarn False Twisting Method and Apparatus The present invention relates to a method and apparatus for yarn false twisting.

In European Patent Application No. A0022743 there is disclosed an apparatus for false twisting a yarn which comprises a thin flexible or pliable disc mounted for rotation with a cooperating disc or roller to define a twisting zone between opposing friction surfaces thereof. A pressure applying member is mounted adjacent the back face of the flexible disc for biasing the disc toward the other member locally at the twisting zone so as to firmly engage the yarn passing through the twisting zone, and while the friction surfaces remain in substantially noncontacting relationship with respect to each other. As a result, the yarn contacts the friction surfaces only in the narrowly limited and defined twisting zone.One particular advantage of this prior false twisting apparatus is the fact that the apparatus not only twists the yarn, but also effects its conveyance through the twisting zone.

According to the invention there is provided a yarn false twisting apparatus comprising a frame, a pair of twist imparting circular discs, with each disc including a yarn engaging friction surface, and with at least one of said discs being relatively thin and flexible, a pressure applying member, means mounting said discs and said pressure applying member with said discs being rotatable about parallel spaced apart axes and such that portions of the respective yarn engaging friction surfaces are disposed in opposing face to face relationship and define a twisting zone therebetween, and with said pressure applying member being positioned to locally bias said one flexible disc toward the other disc only at said twisting zone, drive means for rotating each of said discs about their respective axes, and whereby a yarn may be continuously moved through said twisting zone while having twist imparted thereto by frictional contact between the yarn and the respective opposed friction surfaces resulting from the force exerted by said pressure applying member, wherein said means mounting said discs and pressure applying member includes means permitting selective relative movement in substantially a plane parallel to said friction surfaces of said discs between said discs and said pressure applying member and such that the ratio of twist to yarn speed may be selectively varied.

The invention further provides a yarn false twisting apparatus comprising a frame, a pair of twist imparting circular discs, with each disc including a yarn engaging friction surface, and with at least one of said discs being relatively thin and flexible, at least one pressure applying member, means mounting said discs and said pressure applying member with said discs being rotatable about parallel spaced apart axes and such that portions of the respective yarn engaging friction surfaces are disposed in opposing, face to face relationship and define a twisting zone therebetween, and with said at least one pressure applying member being positioned to locally bias said at least one flexible disc toward the other disc only at said twisting zone, drive means for rotating each of said discs about their respective axes, and whereby a yarn may be continuously moved through said twisting zone while having twist imparted thereto by frictional contact between the yarn and the respective opposed friction surfaces resulting from the force exerted by said pressure applying member, wherein said means mounting said discs and pressure applying member includes means permitting selective relative movement between said discs and said pressure applying member in substantially a plane parallel to said friction surface of said discs and fixing means to adjust said means mounting said discs and pressure applying member in the form of an ososceles triangle with the discs at the base corners of the triangle and the pressure applying member at the apex thereof for selectively adjusting the ratio twist to yarn speed, the means mounting said discs and pressure applying member in the form of said isosceles triangle being adjusted in such a way that the equal angles at the base corners of said triangle are about the same as the desired angle of twist in the twisted yarn.

Thus, optimal conditions may be obtained with respect to the direction of the yarn advance, the circumferential speed of the discs, and the direction of the advancing and twisting force components imparted to the yarn. In this regard, a special advantage should be noted, in that the pressure applying member which preferably acts upon the back side of the flexible disc, preferably defines a relatively small contact pressure area, and this enables a correspondingly accurate definition of the force components of the discs in this contact pressure area or zone.

The invention also provides a method of false twisting a yarn to impart a desired twist angle to the yarn, comprising the steps of providing a pair of twist imparting circular discs, with each disc including a yarn engaging friction surface, and with at least one of said discs being relatively thin and flexible, and with said discs being rotatable about parallel spaced apart axes and such that portions of the respective yarn engaging friction surfaces are disposed in opposing, face to face relationship and define a twisting zone therebetween, providing a pressure applying member, with said pressure applying member being positioned to locally bias said one flexible disc toward the other disc locally at said twisting zone, rotating each of said discs about their respective axes, while advancing a yarn through said twisting zone so as to have twist imparted thereto by frictional contact between the yarn and the respective opposed friction surfaces resulting from the force exerted by said pressure applying member, and adjusting the relative position of said discs and said pressure applying member while maintaining the same in the form of an isosceles triangle, with the discs at the base corners of the triangle and the pressure applying member at the apex thereof, to achieve a desired twist in the advancing yarn by selecting the equal angles at the base corners of said isosceles triangle to generally correspond to the desired twist angle of the yarn in its twisted condition.

The invention additionally provides a method of false twisting a yarn to impart a desired twist angle to the yarn, and comprising the steps of providing a pair of twist imparting circular discs, with each disc including a yarn engaging friction surface, and with at least one of said discs being relatively thin and flexible, and with said discs being rotatable about parallel spaced apart axes and such that portions of the respective yarn engaging friction surfaces are disposed in opposing, face to face relationship and define a twisting zone therebetween, providing a pressure applying member, with said pressure applying member being positioned to locally bias said one flexible disc toward the other disc locally at said twisting zone, rotating each of said discs about their respective axes, while advancing a yarn through said twisting zone so as to have twist imparted thereto by frictional contact between the yarn and the respective opposed friction surfaces resulting from the force exerted by said pressure applying member, and adjustably positioning said pressure applying member relative to the position of said discs in such a way that the same maintain the form of selectable isosceles triangles with the discs at the base corners of the triangle and pressure applying member at the apex thereof to achieve a desired twist in the advancing yarn.

In one embodiment, the force components and their direction can be determined by maintaining the centre to centre distance of the discs unchanged, and by changing only the distance of the pressure applying member from the plane defined by the axes of rotation of the two discs.

By changing the position of the pressure applying member as described above it is possible to obtain the desired operating conditions in many instances. An enlarged range of operating conditions may be obtained however when the centre to centre distance of the discs is changed.

An optimal use of the entire operating range of the friction false twist apparatus is possible, when both the centre to centre distance of the discs and the distance of the pressure applying member from the plane to the axes of rotation are varied.

Preferably, the centre to centre distance and/or the pressure applying member is so changed that the pressure applying member forms the apex of an isosceles triangle, with the axes of rotation of the discs being located at the base corners of the triangle. The two discs then exert mirror symmetrical force components on the yarn. The two equal legs of the isosceles triangle preferably enclose the base to form an angle in the range between about 55 to 65 degrees.

The false twisting apparatus and method of this application are useful, inter alia, for crimping hosiery yarn having a denier ranging from 1 6 to 40 denier. Such hosiery yarns are very often so called torque yarns having the property of imparting elasticity to a fabric by their torsional forces. Such hosiery yarns are preferably false twist crimped of a twist of from 1000 to 3000 turns/m., and the angles of the base corners range from 10 to 35 degrees.

The adjustability of the centre to centre distance and/or the pressure applying member, permits the relative magnitude of the twist component and the advance component to ber determined at the twisting zone, i.e., the contact pressure area of the pressure applying member. In this condition, the circumferential speed of the disc is split at the point of twist, and the component of the circumferential speed lying in the direction of the yarn axis forms the advancing component, whereas the component of the circumferential speed which is perpendicular to the yarn axis forms the twist component.It is preferred that by correspondingly adjusting the centre to centre distance and the position of the pressure applying member, the twist zone is so selected that the base angle of the isosceles triangle defined by the axes and the pressure applying member equals the angle of twist of the yarn to be false twisted in its twisted condition.

It should be noted that the yarn undergoes a geometrical modification upon receiving a twist, which modification results in an increased diameter and a decreased length. Thus, the angle of twist in that geometrical condition differs somewhat from the angle of twist resulting from mere calculation based upon the yarn length and yarn diameters in the untwisted state.

In German Patent Publication (OS) 2,310,803 it has been proposed to select a friction false twist apparatus consisting of three shafts rotating in the same direction and carrying discs which overlap between the axes of rotation, and which permits selection of the centre to centre distance of the axes and/or the axial arrangement of the discs in such a manner that the angle between the direction of disc rotation and the thread line equal the angle of twist. This is designed to enable non-slipping operation. However, it has not heretofore been recognised that adequate normal forces should exist between the friction surfaces and the yarn to ensure that the yarn is advanced without slippage. This is an advantage which cannot be provided in the friction false twist apparatus as disclosed in the above Germ'an Publication.

Using the present invention, the texturing process of the type described in European Patent Publication No. A-0022743 can be optimized in that all decisive parameters including that of slip can be adjusted independently of each other. It should be noted that slipless operation is not alway desired, and that the occurrence of a certain amount of slip may be desirable for reducing the false twist and for regulating the yarn tension. Such operation may be especially useful for the production of speciality yarns showing particular crimp properties. In any case it is desired to control the slip to a certain amount and to keeep this slip constant in order to avoid variations in the yarn quality from position to position and over the length of the yarn.However, slipless operation is desired in many instances, and it is further proposed in accordance with one aspect of the present invention that the contact pressure of the pressure applying member may be adjusted so that the torque resulting from the product of the normal force exerted by the disc on the yarn, the friction coefficient, and the yarn radius, is greater than the untwisting moment of the yarn in its twisted state. To further explain, it should be noted that the yarn, particularly when it is under tension, may be considered a torsionally elastic structure, which posseses a certain restoring moment. Among other things, this restoring moment depends on the amount of twist, as well as the degree of heating in the false twist heating zone.

Operating the pressure applying member in this way offers the advantage that variations in pressure have no effect on the slip. It should be noted, however, that the pressure should not reach a value at which the yarn would be damaged or where tension in the yarn would have undesirable values.

As a further aspect of the present invention, it is possible to also regulate independently of the twist, conveyance and slip conditions, the yarn tension both preceding and following the friction false twist apparatus, and in particular, the ratio of these tensions. In this regard, one must start with the fact that in order to obtain a desired crimp, the amount of twist should be first established, from which a certain optimal base angle a may be determined which is dependent on yarn denier as further describes below with reference to Figure 6. Furthermore, the yarn speed is generally preset by the machine design, as well as the processing data, such as the time the yarn stays on the yarn heater plate at given heating temperatures and heat transfer values.The circumferential speed of the discs in the pressure zone may then be adjusted to provide an optimal value for the yarn tension. It has been found and is preferred that the ratio of disc speed D in the pressure zone and yarn speed Y be adjusted as follows: D 1 - x(1t20%) Y cos a with a being the desired angle of twist in the twisted yarn. This means that the value of D/Y should be equal or approximately equal to the angle of the isosceles triangle at the corner of which the disc centres and the pressure applying member are positioned. The preferred value for this ratio D/Y is in the range between 1.5 and 2.

In the accompanying drawings: Figure 1 a is a side elevation view of a friction false twisting apparatus embodying the present invention and wherein the yarn path extends in a direction perpendicular to the plane which is common to both axes of rotation: Figure 1 b illustrates a second embodiment of a false twisting apparatus in accordance with the present invention, and wherein the yarn path extends in direction parallel to the common plane of the axes of rotation of the discs; Figure 2 is a fragmentary sectional view of the pressure applying member, with the threadadmitting guide; Figure 3 is a sectional top plan view of the apparatus shown in Figure 1 a; Figure 4 is a schematic view of the forces, moments, and speeds in the twisting zone; Figure 5 is a schematic view of a portion of a twisted yarn;; Figure 6 is a diagram revealing the empirical values for determining the base angle a as a function of the desired twist and the denier of the yarn; Figure 7 is a top plan view of a further embodiment of a false twisting apparatus according to the invention, Figure 8a and 8b are side elevation views of yet another embodiment, Figure 8a showing an orientation arranged to give S twist and Figure 8b an orientation arranged to give Z twist; and Figure 9 is a sectional top plan view of the apparatus shown in Figure 8a.

The friction false twist apparatus illustrated in Figures 1 a and 3 comprises a rigid disc 1 and a flexible disc 2. The discs are supported on the shafts 3 and 4 which in turn are rotatably mounted in the bearing housings 5 and 6. The discs are driven by drives (not shown) through pulleys 27 and 28, with the direction of rotation being indicated by the arrows 23. The rigid disc is preferably provided with a friction coating 26 which can, for example, be rubber, Vulkollan, a wear resistant metal, a plasma coating, a ceramic coating or a nickel-diamond coating.

The flexible disc 2 consists of a material or a compound material which absorbs the tensile forces caused by centrifugal forces, which at the same time, however, can easily be laterally deflected or upsey. The disc can be, for example, a rubber disc having a thickness of 0.5 to 2 mm, which has a cord thread embedded in its rubber layer to increase its tensile strength.

The pressure applying member 10 acts upon the back face of the flexible disc 2 by an oblong pressure surface 7 so that the flexible disc is upset in a direction toward the yarn 14. Thus, the yarn is clamped between the flexible disc 2 and an annular friction surface 26 of the rigid disc 1. The pressure applying member consists of a cylinder 9 and a piston 8 moving therein, which piston has a hollow cavity 13 on its pressure surface 7 facing the flexible disc 2. There is also provided a pressurized air connection 11 by means of which the piston is pressed toward the flexible disc, and in addition, pressurized air is forced into the cavity 1 3. The pressurized air connection 11 is connected to an adjustable pressure regulator 72.By this arrangement, a predetermined contact pressure force N may be exerted on the yarn 14 by the member 10 (note Figure 4) and in addition, a pneumatic lubrication is provided between the pressure surface 7 and the flexible disc. Further details concerning the pressure applying member 10 may be obtained from the above mentioned European Patent Publication.

In Figure 1 a, the yarn 14 is fed to the friction false twist apparatus via a thread-admitting guide 22 in a direction perpendicular to the plane which is common to the two axes of rotation of the discs 1 and 2. Accordingly, the oblong pressure surface 7 extends along the yarn path in a direction perpendicular to the common plane of the shafts 3, 4 and thus parallel to the yarn path. In Figure 1 b, the yarn runs through the thread-admitting guide 22 in a direction parallel to the plane which is common to the two axes of rotation.

Bearing housings 5 and 6, and the pressure applying member 10, may each be displaced. For their displacement, the housings 5 and 6 are provided with guide openings, by which they can be slidably mounted on parallel slide rods 1 5, 16.

The rods 1 5, 1 6 are preferably rectangular in cross section and are positioned symmetrically on opposite sides of the yarn path. Thus, the discs are movable between the inner extreme positions 29 and the outer extreme positions 30 shown in Figures 1 a and 1 b. The displacement path extends between the stops 31,32. The housings are positioned such that the two shafts or axes of rotation have the same distance from the thread line. Similarly, the pressure applying member 10 may be moved on the rectangular rod 19 and positioned at a desired location by set screw 20.

The member 10 is movable between the extreme positions 24.1 and 25.1, and positions 24.2 and 25.2.

In Figure 1 a, the positions 24.1 and 25.1 of the pressure applying member correspond to the position 29 of the discs, and the positions 24.2 and 25.2 to the position 30 of the discs. The discs 1 and 2 rotate in opposite directions 23, and the advancing yarn 14 has a Z twist imparted thereto with the pressure applying member in the positions 24, and the S twist with the pressure applying member in the positions 25. The pressure applying member is displaced between the extreme positions 24.1 and 24.2, if the ratio of the twist to yarn advance is to be changed while imparting a Z twist to the yarn. The pressure applying member is displaced between the positions 25.1 and 25.2, if the ratio of twist and yarn advance is to be changed while imparting an S twist to the yarn.

It should also be noted that between the illustrated extreme positions 29, 30 of the discs, and 24.1 to 24.2 of the pressure applying member for insertion of a Z twist, and 25.1 to 25.2 of the pressure applying member for insertion of an S twist, any intermediate operational position that is advantageous for the desired false twist process may be chosen.

It has been found that the insertion of the twist by the friction false twist apparatus is a function of the distance of the thread guides, and particularly of the thread-admitting guide, from the twisting point or zone, i.e. the point at which the yarn receives the twist. The twisting zone of the friction false twisting apparatus of the present invention is defined by the position of the pressure applying member 10. In order to ensure a constant distance, the thread-admitting guide 22 and the pressure applying member 10 are mechanically connected by a rod 21. This is illustrated in Figure 2, which shows a friction false twist apparatus with a yarn path of Figure 1 a.It should be noted that the length of the rod 21 is predetermined so that the thread-admitting guide 22 does not come into contact with the discs, even when the pressure applying member is positioned in the extreme position 25.1.

With the yarn path extending in the direction as shown in Figure 1 b, the thread-admitting guide is moved to the other side of the plane which is common to both axes of rotation of the discs, to change the apparatus from S twist to Z twist.

Also, with the yarn path as shown in Figure 1 b, a change of the rotataional direction of the discs is necessary to switch from S to Z twist. This rotational direction of the disc is shown by arrows S and Z.

Optimum operating conditions can be achieved by varying the distance between the axes of rotation of the discs and/or the distance between the pressure applying member and the common plane of the axes of rotation. In this connection, it should be noted that the axes and the pressure applying member are preferably situated at the corners of an isosceles triangle so that the components of speed of the discs are equal. In such case, a synchronization between the distance between the axes and the distance of the pressure applying member is advantageous. This is shown schematically in Figure 3 by the connecting rods or lever arms 67 and 68. In many cases, it will suffice to change only the distance between the pressure applying member and the common plane of the axes of rotation.If an optimum operating condition is not achieved by movement of the member 10, the distance between the axes may also be varied.

It should also be noted that the axes of the discs may not be exactly parallel and may be slightly inclined toward each other. When such inclination is present, the term "common plane" of the axes is not totally accurate. However, since the angle at which the axes are inclined relative to each other is very small, such term will be used in the following description.

In order to further improve the operating conditions, the contact pressure force of the pressure applying member 10 may be adjusted, as seen in Figures 2 and 3, by varying the pressure by means of the pressure regulator 72.

Further, it is to be emphasised that the speed of rotation of the discs, and the running speed of the yarn may also be adjustably set for optimum conditions.

The preferred operating condition for the geometric arrangement of the discs and pressure applying member are illustrated in Figure 1 a, with the discs and pressure applying member being disposed to define an isosceles triangle, with the discs at the base corners of the triangle and the pressure applying member at the apex thereof.

Further, the equal angles at the base corners of the isosceles triangle, which are indicated by a in Figure 1 a, preferably range from about 55 and 65 degrees. The base angle a of this isosceles triangle is preferably equal to the angle of twist of the yarn being twisted. Figure 5 illustrates the yarn while being twisted, as well as the twist angle a. It should be noted that the length of the yarn when twisted is shortened, and that its diameter is increased. Therefore, the angle a of the twisted yarn is smalier than the angle of twist of the untwisted yarn, or smaller than the angle calculated from the adjusted speed of the thread, number of twists and diameter of the yarn.In the diagram of Figure 6, there are shown empirical values for the determination of the base angle a as a function of the denier of the yarn and of the desired twist, which is referred herein as the number of twists per metre of the yarn (TPM).

By adjusting the friction false twist apparatus as described above, the yarn is conveyed and twisted with the same slip.

In order to achieve slipless yarn advance and twisting, it is generally necessary that the contact pressure of the pressure applying member be set to a value which ensures that the torsional moment or torque (MS) exerted by the friction discs on the thread exceeds the untwisting moment or torque (MF) of the yarn. The torsional moment (MS) may be determined by the formula DF MS=Nxux 2 where N stands for the normal force, u for the coefficient of friction, and DF represents the diameter of the yarn.

To this point, the description has dealt with achieving the optimum twisting conditions for the texturizing process. Another aspect of the present invention relates to the adjustment of the ratio of yarn tension in an optimum manner. In this aspect the present invention proceeds from the fact that hitherto all known false twisting apparatus, of both the spindle false twist type and the well known friction false twist type, have not offered the possibility of freely choosing the ratio of yarn tension. On the contrary, the ratio of yarn tension has been dependent on the twisting conditions. With the present invention, the yarn tension can be adjusted upstream and downstream of the friction false twisting apparatus by setting the ratio of speed of the discs to the speed of the yarn.The reason for this is the fact that the velocity vector of the friction discs has a component in the direction of yarn advance and a component in the direction of twist. Since the angles formed by the force components are not changed, it is possible to adjust the yarn tension freely before and after the friction false twisting apparatus by setting the velocity of the yarn or the circumferential speed of the discs. For the ratio of the speed of the discs D to the speed of the yarn Y, the following formula is preferred D 1 = x(1+20%), Y cos a with a again being the desired angle of twist of the yarn when twisted, or the base angle of the isosceles triangle which is defined by the axes of the discs and the pressure applying member.

It should further be mentioned that the friction false twist apparatus can operate with the yarn path as shown in Figure 1 b. The operation may be geometrically set in such a way that the angle a is about half the apex angle of the isosceles triangle formed by the axes of rotation and the pressure applying member, and is about equal to the angle of twist of the twisted yarn.

The embodiment shown in Figure 7 is similar in many respects to that shown in Figure 1 a, and components in Figure 7 corresponding to those of Figure 1 a are denoted by the same numerals increased by 100. However, in Figure 7 the pressure applying member having the pressure applying surface 107 is kept fixed. Furthermore, the slide rod 1 5 extends in a direction generally perpendicular to the axis of rotation of the shaft 103 and parallel to a line which is a tangent to the disc at a point immediately adjacent the twisting zone when the disc is disposed at a midpoint along its path of travel, i.e., at position 134. Thus as seen in Figure 1, the rod 11 5 is parallel to the line 136, which line in turn is parallel to the defined tangent. Similarly, the rod 11 6 extends in a direction parallel to the line 137.This arrangement makes it possible to displace the housings 105 and 106 with a technically sufficient accuracy between the extreme operational positions 129 and 130, without the circumferential speeds of the discs in the thread clamping zone changing significantly. As will be apparent, displacement of the discs between the positions 129 and 130, results in the ratio of twist to yarn conveyance speed being changed, with insertion of an S twist. It should also be noted that any intermediate operational position that is advantageous for the desired false twist method can be chosen between the extreme positions 129 and 130 of the discs.

Figures 8a, 8b and 9 illustrate yet another embodiment of the present false twisting apparatus. An S twist is imparted to the yarn with the friction discs 101 and 102 positioned as shown in Figures 8a and 9, and a Z twist is imparted with the friction discs 101 and 102 positioned as shown in Figure 8b. The friction false twisting apparatus shown in Figures 8a, 8b and 9 includes a bracket 138, which is U-shaped in its transverse section to define two parallel upper and lower arms as seen in Figure 9. The arms define a central axis 139 extending transversely therebetween, and the lower arm of the bracket mounts the pressure applying member 110 which consists of cylinder 109 and piston 1 08. The member 110 is aligned with the central axis 139.

Rocking arms 140 and 141 are pivotally supported between the arms of the brackets 138 in the coaxial relationship on the axis 1 39. The arms 140, 141 are secured in a selected rotational position by nuts 142 and 143. The housings 105 and 106 for the discs 101 and 102 are positioned in the ends of the rocking arms.

The friction false twisting apparatus is driven by a tangential belt 145, which extends in a longitudinal direction along the apparatus and runs at a constant speed and in one direction, the tangential belt 145 is in contact with a main whorl 144 of the friction false twist apparatus, which is rotatably mounter in a whorl support member 146, and carries on its shaft a drive pulley 147. The pulley 147 is looped about 180 degrees by the endless belt 148, of which a segment 149 winds around belt pulley 150 of the friction discs 102, and a segment 1 51 winds around belt pulley 152 of the friction disc 101.

The belt 148 also loops about a freely rotatable idler or reversing pulley 1 53. The mounting 154 of the pulley 1 53 is movable in the belt tensioning direction 1 56 and is pressed in the tensioning direction by a pressure spring 1 55. The pr r sure spring is mounted to a frame by a bolt 1 57.

The whorl support member 146 is mounted on a guide plate 159 of the bracket 138 in two positions 160 and 161, by means of a connection piece 158. The whorl support member 146 is connected to the connection piece 158 by a parallelogram leaf spring 162. This spring consists of two parallel spring plates 163, whose ends are firmly fixed to each other so that the spring plates 1 63 can carry out only a parallel movement, upon leaving their rest position. A lever 1 64 is pivotally mounted at a pivot pin 1 65 to the bracket 138. Upon pivotal movement of the lever 1 64, a bolt 1 66 at the end thereof slides on a slide piece 167 to a notch 168.In the position shown in Figure 8a, the whorl 144 is pressed against the tangential belt 145 by the force of the parallelogram spring 162. When bolt 166 moves into the notch 1 68 by a pivotal movement of the lever 164, the whorl 144 is separated from the tangential belt 145.

When the whorl support member 146 is moved to the mounting position 161 as illustrated in Figure 8b, another slide piece 1 69 having a notch 170 is brought into operative position. For separating the whorl 144 from the tangential belt, i.e., for interrupting operation of the friction false twisting apparatus, bolt 1 66 is inserted into the eye on lever 164, which eye is adjacent the slide piece 169. Thus when the lever 164 is depressed, the bolt 166 is moved into the notch 170, to disengage the whorl 144 from the belt 145. In order to maintain the tension of belt 148 constant, the fastening point for the pressure spring 1 55 can be varied.Thus upon switching the whorl support member from position 160 to position 161, the bolt 157 is moved from the eye 1 71 in the bracket 138 and inserted into the eye 172.

It is preferable that the pressure spring 1 55 have a very level characteristic, so that the force exerted by the spring is independent of the spring travel within the limits given by the operationaL positions.

The operation of the friction false twist apparatus illustrated in Figures 8a, 8b and 9 will now be described. With the friction discs positioned as shown in Figure 8a, the yarn receives an S twist. Thus, the twisting zone, i.e., the zone determined by the pressure applying member, and at which the thread is in frictional contact with the friction discs, can be kept stationary. However, the twisting zone can also be displaced relative to the discs by changing the angular position of the rocking arms 140 and 141 with respect to each other. In order to switch the twist formation from S twist to Z twist, the position of the discs is changed such that disc 102 lies to the right and disc 101 to the left of the yarn path as shown in Figure 8b.Simultaneously, the whorl 144 is moved from its position on the left side of the tangential belt 145 as shown in Figure 8a to the position on the right side of the tangential belt as illustrated in Figure 8b, without the direction of run of the belt being changed.

For the displacement of the whorl 144, the connection piece 1 58 is moved from position 160 into position 1 61. To further interrupt operation of the false twist apparatus by separating the whorl from the tangential belt, bolt 1 66 in lever 1 64 is shifted from that eye which is in work engagement with slide piece 167 and notch 168, to the eye in engagement with slide piece 1 69 and notch 170.

Due to the displacement of the whorl, the direction of run of the endless belt 148 is changed from the direction 1 73 to direction 174 shown in Figure 8h so that the rotary direction of the discs 101 and 102 also changes. To maintain the belt tension, the bolt 157 of the pressure spring 1 55 is concurrently removed from the eye 1 71 and inserted into eye 172. The yarn then receives a Z twist. To return to an S twist, the above procedure is reversed.

Claims 1. A yarn false twisting apparatus comprising a frame, a pair of twist imparting circular discs, with each disc including a yarn engaging friction surface, and with at least one of said discs being relative thin and flexible, a pressure applying member, means mounting said discs and said pressure applying member, with said discs being rotatable about parallel spaced apart axes and such that portions of the respective yarn engaging friction surfaces are disposed in opposing, face to face relationship and define a twisting zone therebetween, and with said pressure applying member being positioned to locally bias said one flexible disc toward the other disc only at said twisting zone, drive means for rotating each of said discs about their respective axes, and whereby a yarn may be continuously moved through said twisting zone while having twist imparted thereto by frictional contact between the yarn and the respective opposed friction surfaces resulting from the force exerted by said pressure applying member, wherein said means mounting said discs and pressure applying member includes means permitting selective relative movement in substantially a plane parallel to said friction surface of said discs between said discs and said pressure applying member and such that the ratio of twist to yarn speed may be selectively varied.

2. An apparatus as claimed in claim 1, wherein said means mounting said discs and pressure applying member permit such relative movement while maintaining said disc and pressure applying member in the form of an isosceles triangle, with the discs at the base corners of the triangle and the pressure applying member at the apex thereof.

3. A yarn false twisting apparatus comprising a frame, a pair of twist imparting circular discs, with each disc including a yarn engaging friction surface, and with at least one of said discs being relatively thin and flexible, at least one pressure applying member, means mounting said discs and said pressure applying member, with said discs being rotatable about parallel spaced apart axes and such that portions of the respective yarn engaging friction surfaces are disposed in opposing, face to face relationship and define a twisting zone therebetween, and with said at least one pressure applying member being positioned to locally bias said at least one flexible disc toward the other disc only at said twisting zone, drive means for rotating each of said discs about their respective axes, and whereby a yarn may be continuously moved through said twisting zone while having twist imparted thereto by frictional contact between the yarn and the respective opposed friction surfaces resulting from the force exerted by said pressure applying member, wherein said means mounting said discs and pressure applying member includes means permitting selective relative movement between said discs and said pressure applying member in substantially a plane parallel to said friction surface of said discs and fixing means to adjust said means mounting said discs and pressure applying member in the form of an isosceles triangle with the discs at the base corners of the triangle and the pressure applying member at the apex thereof for selectively adjusting the ratio twist to yarn speed, the means mounting said discs and pressure applying member in the form of said isosceles triangle being adjusted in such a way that the equal angles at the base corners of said triangle are about the same as the desired angle of twist in the twisted yarn.

4. An apparatus as claimed in claim 3, wherein the equal angles at the base corners of said isosceles triangle range from about 55 to 65 degrees.

5. An apparatus as claimed in claim 3 or 4 wherein said drive means includes means for adjusting the rotational speed of said discs, and such that ratio of disc speed (D) to yarn speed (Y) in the pressure zone of the pressure applying member may be adjusted to be equal to 1 x(1 +20%) cos a with Q being the equal angles set at the base corners of said isosceles triangle.

6. An apparatus as claimed in claim 5, wherein the ratio of disc speed (D) to yarn speed (Y) may be adjusted to range between 1.5 and 2.

7. An apparatus as claimed in any preceding claim, wherein said pressure applying member includes means for adjusting the biasing pressure and such that the torque exerted by the discs of the yarn is equal to the untwisting moment of the yarn in the desired condition of twist with said desired twist angle.

8. An apparatus as claimed in any one of claims 1 to 6, wherein said pressure applying member includes means for adjusting the biasing pressure and such that the torque exerted by the discs on the yarn is adapted to exceed the untwisting moment of the yarn in the desired condition of twist.

9. An apparatus according to claim 1, wherein thetistance between the axes of the discs remains constant, while the distance from the pressure applying member to said axes is varied.

1 0. An apparatus according to claim 1, wherein the distance between the axes of the discs is varied, while the distance from the pressure applying member to said axes remains constant.

11. An apparatus according to claim 1, wherein the distance between the axes of the discs and the distance from the pressure applying member to said axes are both varied.

12. A method of false twisting a yarn to impart a desired twist angle to the yarn, comprising the steps of providing a pair of twist imparting circular discs, with each disc including a yarn engaging friction surface, and with at least one of said discs being relatively thin and flexible, and with said discs being rotatable about parallel spaced apart axes and such that portions of the respective yarn engaging friction surfaces are disposed in opposing, face to face relationship and define a twisting zone therebetween, providing a pressure applying member, with said pressure applying member being positioned to locally bias said one flexible disc toward the other disc locally at said twisting zone, rotating each of said discs about their respective axes, while advancing a yarn through said twisting zone so as to have twist imparted thereto by frictional contact between

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

Claims (21)

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

   member being positioned to locally bias said one flexible disc toward the other disc only at said twisting zone, drive means for rotating each of said discs about their respective axes, and whereby a yarn may be continuously moved through said twisting zone while having twist imparted thereto by frictional contact between the yarn and the respective opposed friction surfaces resulting from the force exerted by said pressure applying member, wherein said means mounting said discs and pressure applying member includes means permitting selective relative movement in substantially a plane parallel to said friction surface of said discs between said discs and said pressure applying member and such that the ratio of twist to yarn speed may be selectively varied.
2. 2. An apparatus as claimed in claim 1, wherein said means mounting said discs and pressure applying member permit such relative movement while maintaining said disc and pressure applying member in the form of an isosceles triangle, with the discs at the base corners of the triangle and the pressure applying member at the apex thereof.
3. 3. A yarn false twisting apparatus comprising a frame, a pair of twist imparting circular discs, with each disc including a yarn engaging friction surface, and with at least one of said discs being relatively thin and flexible, at least one pressure applying member, means mounting said discs and said pressure applying member, with said discs being rotatable about parallel spaced apart axes and such that portions of the respective yarn engaging friction surfaces are disposed in opposing, face to face relationship and define a twisting zone therebetween, and with said at least one pressure applying member being positioned to locally bias said at least one flexible disc toward the other disc only at said twisting zone, drive means for rotating each of said discs about their respective axes, and whereby a yarn may be continuously moved through said twisting zone while having twist imparted thereto by frictional contact between the yarn and the respective opposed friction surfaces resulting from the force exerted by said pressure applying member, wherein said means mounting said discs and pressure applying member includes means permitting selective relative movement between said discs and said pressure applying member in substantially a plane parallel to said friction surface of said discs and fixing means to adjust said means mounting said discs and pressure applying member in the form of an isosceles triangle with the discs at the base corners of the triangle and the pressure applying member at the apex thereof for selectively adjusting the ratio twist to yarn speed, the means mounting said discs and pressure applying member in the form of said isosceles triangle being adjusted in such a way that the equal angles at the base corners of said triangle are about the same as the desired angle of twist in the twisted yarn.
4. 4. An apparatus as claimed in claim 3, wherein the equal angles at the base corners of said isosceles triangle range from about 55 to 65 degrees.
5. 5. An apparatus as claimed in claim 3 or 4 wherein said drive means includes means for adjusting the rotational speed of said discs, and such that ratio of disc speed (D) to yarn speed (Y) in the pressure zone of the pressure applying member may be adjusted to be equal to 1 x(1 +20%) cos a with Q being the equal angles set at the base corners of said isosceles triangle.
6. 6. An apparatus as claimed in claim 5, wherein the ratio of disc speed (D) to yarn speed (Y) may be adjusted to range between 1.5 and 2.
7. 7. An apparatus as claimed in any preceding claim, wherein said pressure applying member includes means for adjusting the biasing pressure and such that the torque exerted by the discs of the yarn is equal to the untwisting moment of the yarn in the desired condition of twist with said desired twist angle.
8. 8. An apparatus as claimed in any one of claims 1 to 6, wherein said pressure applying member includes means for adjusting the biasing pressure and such that the torque exerted by the discs on the yarn is adapted to exceed the untwisting moment of the yarn in the desired condition of twist.
9. 9. An apparatus according to claim 1, wherein thetistance between the axes of the discs remains constant, while the distance from the pressure applying member to said axes is varied.
10. 1 0. An apparatus according to claim 1, wherein the distance between the axes of the discs is varied, while the distance from the pressure applying member to said axes remains constant.
11. 11. An apparatus according to claim 1, wherein the distance between the axes of the discs and the distance from the pressure applying member to said axes are both varied.
12. 12. A method of false twisting a yarn to impart a desired twist angle to the yarn, comprising the steps of providing a pair of twist imparting circular discs, with each disc including a yarn engaging friction surface, and with at least one of said discs being relatively thin and flexible, and with said discs being rotatable about parallel spaced apart axes and such that portions of the respective yarn engaging friction surfaces are disposed in opposing, face to face relationship and define a twisting zone therebetween, providing a pressure applying member, with said pressure applying member being positioned to locally bias said one flexible disc toward the other disc locally at said twisting zone, rotating each of said discs about their respective axes, while advancing a yarn through said twisting zone so as to have twist imparted thereto by frictional contact between

    the yarn and the respective opposed friction surfaces resulting from the force exerted by said pressure applying member, and adjusting the relative position of said discs and said pressure applying member while maintaining the same in the form of an isosceles triangle, with the discs at the base corners of the triangle and the pressure applying member at the apex thereof, to achieve a desired twist in the advancing yarn by selecting the equal angles at the base corners of said isosceles triangle to generally correspond to the desired twist angle of the yarn in its twisted condition.
13. 13. A method of false twisting a yarn to impart a desired twist angle to the yarn, and comprising the steps of providing a pair of twist imparting circular discs, with each disc including a yarn engaging friction surface, and with at least one of said discs being relatively thin and flexible, and with said discs being rotatable about parallel spaced apart axes and such that portions of the respective yarn engaging friction surfaces are disposed in opposing, face to face relationship and define a twisting zone therebetween, providing a pressure applying member, with said pressure applying member being positioned to locally bias said one flexible disc toward the other disc locally at said twisting zone, rotating each of said discs about their respective axes, while advancing a yarn through said twisting zone so as to have twist imparted thereto by frictional contact between the yarn and the respective opposed friction surfaces resulting from the force exerted by said pressure applying member, and adjustably positioning said pressure applying member relative to the position of said discs in such a way that the same maintain the form of selectable isosceles triangles with the discs at the base corners of the triangle and pressure applying member at the apex thereof to achieve a desired twist in the advancing yarn.
14. 14. A method as claimed in claim 13, wherein the step of adjustably positioning said pressure applying member includes selecting the equal angles at the base corners of said isosceles triangle to generally correspond to the desired twist angle of the yarn in its twisted condition.
15. 15. A method as claimed in claim 12 or 13, including the further step of adjusting the biasing force of the pressure applying member such that the torque exerted by the discs on tye yarn is at least equal to the untwisting moment of the yarn in the desired condition of twist.
16. 1 6. A method as claimed in any one of claims 12 to 15, including the further step of adjusting' the yarn tension upstream and downstream of the discs by adjusting the disc rotational speed with respect to the yarn speed.
17. 17. A method as claimed in any one of claims 12 to 1 5, including the further step of adjusting the disc speed (D) in the area of the pressure applying member, with respect to the yarn speed (Y), according to the formula Y D= x (1 ~20%) cos Q with a being the angle at the base corners of said isosceles triangle.
18. 1 8. A method as claimed in claim 17, wherein said ratio of the disc speed (D) to yarn speed (Y) is adjusted to range between 1.5 and 2.
19. 19. A method as claimed in claim 12 wherein a hosiery yarn of 1 5 to 40 denier is false twist crimped by applying a twist to said yarn of 1,000 to 3,000 turns per metre, said equal angles at the base corners of the triangle being selected to range between 10 and 35 degrees.
20. 20. An apparatus for false twisting a yarn substantially as herein described with reference to any one of the embodiments shown in the accompanying drawings.
21. 21. A method of false twisting a yarn substantially as herein described with reference to any one of the embodiments shown in the accompanying drawings.