JPH0253529B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to an air false twisting nozzle used in a device for producing bundled spun yarn using a rotating rotor.

Prior art and its problems Conventionally, this type of air false twisting nozzle was developed by
The air false twisting nozzle proposed in Publication No. 52-37837 is known, but the air false twisting nozzle of this publication is exactly the same as the one used in a device for producing bundled spun yarn using roller draft. The injection hole is opened in a thread passage hole of the same diameter in a direction tangential to the inner surface of the thread passage hole and inclined to the axis of the yarn passage hole so as to face the yarn exit side. When compressed air is injected from the thread guide hole, this injected airflow swirls along the inner surface of the thread guide hole, imparts a false twist to the fiber bundle inside the thread guide hole, and at the same time creates suction toward the yarn inlet side end of the thread guide hole toward the yarn outlet side. An air current is generated to apply tension to the fiber bundle in the drawing direction. However, in the case of the above-mentioned air false twisting nozzle, when the twisted yarn drawn out from the rotating rotor is passed through the yarn passage hole and the twisted yarn is given false twist,
Since the yarn gripping force of the tip of the spun yarn to the rotor fiber bundle is weak, there is a risk that the twisted yarn may be pulled out from inside the rotating rotor due to the tension in the pulling direction due to the jet airflow, and the twisted yarn may be pulled out from inside the rotating rotor. There was a drawback that it could not be granted. In addition, in the conventional air false twisting nozzle described above, false twisting is created by generating a swirling air flow in the yarn passage hole with the same diameter over the entire length, so the direction of the injection hole is adjusted to the direction of the yarn passage hole. Even if the direction is perpendicular to the axis, it is difficult to impart sufficient false twist to the twisted yarn, and it is difficult to increase the spinning speed and yarn strength of the bundled spun yarn.

Purpose and Overview Therefore, the present invention eliminates the drawbacks of the conventional air false twisting nozzle described above, applies a force to the twisted yarn in the opposite direction to the yarn pulling direction, and applies false twist to the twisted yarn pulled out from the rotating rotor. An object of the present invention is to provide an air false twisting nozzle that can reliably maintain yarn grip in the rotor fiber convergence section at the tip of the twisted yarn, and can efficiently apply false twist to the twisted yarn. .

Embodiments Next, embodiments of the present application will be described in detail with reference to the drawings. The drawing shows an apparatus for producing a bundled spun yarn 1 using a rotating rotor. In this device, reference numeral 2 denotes a fiber opening device which opens and drafts a continuous staple fiber bundle 1a such as a sliver to separate single fibers 1b. It comprises a main body 3 placed on a housing part. In this main body 3, a fiber supply chamber 4, a fiber supply path 5, a fiber opening chamber 6, and a fiber transfer path 7 are sequentially and continuously formed as shown in FIG. A trumpet 8 and a feed roller 9 are disposed in the fiber supply chamber 4, and a combing roller 10 having, for example, a metallic wire on its circumferential surface is rotatably disposed in the opening chamber 6. The feed roller 9 and the combing roller 10 are rotated in the direction of the arrow by a drive motor (not shown), feed the fiber bundle 1a passed through the trumpet 8 into the opening chamber 6, and convert the fiber bundle 1a into separate single fibers 1b.
The fibers are now being opened. Further, the fiber transfer path 7 is formed in a tangential direction to the circumferential surface of the combing roller 10, and one end thereof is located at the fiber outlet 7a.
The other end is opened to serve as an air intake port 7b. The fiber outlet 7a is arranged in the rotor so that the extension line of the fiber transfer path 7 faces the running surface on which the twisted yarn 1c runs between the rotor fiber convergence part and the center piece of a rotating rotor (also referred to as rotor), which will be described later. ing. The fiber outlet 7a is the single fiber 1 coming out from here.
Twisted yarn 1c with a part of b running on the running surface
It suffices if they are arranged so that they are sprayed onto the surface of the twisted yarn 1c, and are not limited to their shape or number. However, if the actual twist of the twisted yarn 1c due to rotor rotation is extremely small, the entire running surface of the twisted yarn 1c is Preferably, the structure is such that single fibers can be supplied throughout. next,
Reference numeral 11 denotes a support block which is pivotally attached to the machine base so as to be tiltable forward and is locked in the upright position and is disposed below the fiber opening device 2, which supports the rotor housing part 12, the rotor support part 13, and the nozzle support block. It consists of a section 14. A circular rotor chamber 15 is formed on the upper surface of the rotor housing portion 12, and a third exhaust passage 16 communicates the rotor chamber 15 with the outside.
It is formed as shown in the figure. Above rotor chamber 1
The upper part of the fiber opening device 5 is closed by the main body 3 of the fiber opening device 2 placed on the rotor housing portion 12 . A lower part of a support cylinder 17 is fixed to the rotor support part 13, and a rotor 19 is rotatably supported by a bearing 18 held on the inner surface of the support cylinder 17. This rotor 19 includes a container-shaped rotor part 20 that is open at the top, a warb part 22 that is integral with the rotor part 20 and has a storage chamber 21 for storing a support cylinder on the lower end surface, and a central hole in the warb part 22. A cylindrical rotor shaft 23 is fitted into the rotor shaft 23. This rotor shaft 23 is inserted into the support cylinder 17 and supported by a bearing 18, and the warp portion 22 is connected to the rotor housing portion 1.
The support cylinder 17 is stored in the storage chamber 21 through the hole 12a of the rotor chamber 1.
It is located within 5. A drive belt 24 moved by a drive motor (not shown) is brought into contact with the outer periphery of the warb portion 22, so that the rotor 19 is rotated in the direction of the arrow in FIG. Further, a base of a center piece attachment shaft 25, which is illustrated as a thread guide, is fitted into the lower part of the support cylinder 17,
This center piece mounting shaft 25 is inserted into the rotor shaft 23. This center piece mounting shaft 25 forms an exhaust chamber 100 between it and the nozzle support portion 14 . A center piece 26 is removably attached to the upper end of this center piece attachment shaft 25. This center piece 26 protrudes into the rotor section 20, and its top 26a is connected to the rotor fiber bundle section 20 of the rotor section 20, as shown in FIG.
It is located higher than a (the maximum diameter part of the inner surface of the rotor),
By separating the annular surface formed by the line connecting the top portion 26a and the rotor fiber convergence portion 20a (this surface becomes the running surface of the twisted yarn 1c) from the rotor bottom surface, a large space is created below the annular surface. It is starting to form. In addition, the center piece 26
The top 26a may be located at the bottom of the rotor fiber bundle 20a, but there is at least a space below the annular surface so that the twisted yarn 1c traveling from the rotor fiber bundle 20a to the center piece 26 runs in the air. It is important to do so. The above center piece 26 and center piece mounting shaft 25
A thread passage hole 27 is formed in. The fiber contact surface of the center piece 26, that is, the center piece 2
The upper surface of the twisting yarn 6 is formed to be a smooth surface so that the frictional resistance with the twisted yarn 1c is as small as possible, so that the false twisting of the twisted yarn 1c by the air false twisting nozzle, which will be described later, is sufficiently transmitted to the vicinity of the rotor fiber convergence section 20a. This is significantly different from the function of the centerpiece of a conventional open-end spinning frame. Next, a through hole 28 is formed in the nozzle support portion 14 on the same straight line as the thread passage hole 27. An annular spring seat 29 is formed protruding from the inner surface of the upper end of the through hole 28 . An air false twisting nozzle 30 configured as shown in FIGS. 2 and 4 is fitted into the through hole 28. In this air false twisting nozzle 30, reference numeral 31 denotes a cylindrical first body fitted into the through hole 28, whose end on the yarn inlet side projects into the exhaust chamber 100, and is spaced between the centerpiece mounting shaft 25 and the centerpiece mounting shaft 25. forming an interval.
A groove 32 is formed around the entire circumference of the intermediate portion of the first body 31, and an annular space 33 is formed between the first body 31 and the inner surface of the through hole 28. This annular space 33 is connected by a supply line 101 via a valve to a source of compressed air. The upper and lower sides of this annular space 33 are O-rings 3 fitted on the outer periphery of the first main body 31.
4,34. In addition, a fitting hole 3 is provided at the end of the first body 31 on the yarn exit side (lower end side).
5 is formed, and a second body 36 is inserted into this fitting hole 35.
is fitted and is replaceably fixed by a retaining nut 37 screwed onto the outer periphery of the end of the first body 31 on the yarn exit side. The first main body 31, the second main body 31,
The main body 36 and the retaining nut 37 are the nozzle main body 38.
A thread passage hole 39 is formed in the center of the nozzle body 38 in a penetrating shape. The thread passing hole 39 has a large diameter hole 40 on the thread inlet side and a small diameter hole 41 on the thread exit side, and a stepped portion 42 is formed in the middle of the thread passing hole 39 of the second body 36. The upper end portion of the large diameter hole 40 is formed as a tapered hole 40a that expands upward, and the lower end portion of the small diameter hole 41 is formed as a tapered hole 41a that expands downward. A plurality of injection holes 43 are opened in the large diameter hole 40 and are provided in the first main body 31 from the annular space 33 to the large diameter hole 40 . These injection holes 43 are tangential to the inner surface of the large diameter hole 40, as shown in FIG. It is formed in an inclined direction. The opening direction of the injection hole 43 to the yarn passage hole 39 is the same direction as the direction in which the compressed air jetted from the injection hole 43 is applied to the twisted yarn 1c passing through the yarn passage hole 39, and the direction in which the twisted yarn 1c is twisted by the rotation of the rotor. Direction to provide temporary combustion (direction to generate vortex airflow in the opposite direction to rotor rotation)
is set to . The distance between the outlet of the injection hole 43 and the stepped portion 42 is such that the swirling airflow caused by the jetted air flow can reach the stepped portion 42.
As long as the range can be rotated by contacting 2, it is not limited to what is shown in the figure. The hole diameter d of the small diameter hole 41 is such that when the twisted yarn 1c is passed through the small diameter hole 41, the air injected from the injection hole 43 is
The hole diameter D of the large diameter hole 40 is set to a size that hardly flows out from the large diameter hole 40 to the yarn exit side.
The jet airflow is set to a size that can efficiently rotate the twisted yarn 1c to cause ballooning. According to experiments by the applicant, the diameter d of the small diameter hole 41 is 0.5 mm<d<2.0 mm considering the count of the spun yarn.
It is preferable that the formula is satisfied, and the large diameter hole 40
It is preferable that the pore diameter D satisfies the formula D≧2.0d, but when spinning a special yarn, conditions other than the above conditions may be used. The first main body 31 and the second main body 36
The first body 31 and the second body 36 are made of a wear-resistant material because the yarn passage hole 39 is worn out due to friction with the twisted yarn 1c.
The material of the second main body 36 is made of neuceramic because the parts are easily worn out, and by preparing a spare one, the second main body 36 can be easily replaced with another one when it wears out. It's becoming like that. In this case, since the material cost of neuceramic is high, it is preferable to divide the second main body 36 into two parts, the step part 42 and the other parts, and make only the step part 42 a material of neuceramic in order to reduce the cost. It goes without saying that the nozzle main body 38 may be constructed of one member. Next, on the outer periphery of the end of the first body 31 on the yarn entrance side, there are two small diameter portions 31a, 31.
b is formed and a stepped portion 31c is formed as a stopper in the middle.
A closed cylinder 44 is fitted into this small diameter portion 31a so as to be slidable in the axial direction of the first main body 31. A flange-shaped piston portion 44a is formed at the downstream end of the closed cylinder 44 and is slidably fitted into the inner surface of the through hole 28. The closing cylinder body 44 is urged toward the yarn exit direction by a spring 45 compressed and sealed between the piston part 44a and the spring seat 29 of the nozzle support part 14, and normally the stepped part 31c
The position is fixed by being in contact with the In addition, the closing cylinder 44 forms an annular piston chamber 46 between the piston portion 44a, the outer periphery of the small diameter portion 31b, and the inner surface of the through hole 28 when it is in contact with the stepped portion 31c, and the end portion on the yarn entrance side is It extends to the same position as the end of the first body 31 on the yarn entrance side. When the closing cylinder 44 is slid toward the yarn entrance, the end of the closing cylinder 44 on the thread entrance side is connected to the center piece mounting shaft 25.
The closing part 4 is in close contact with the lower surface of the thread passage hole 27 and the thread passage hole 39 so as to connect it in a straight line.
4b. The annular piston chamber 46
is connected via a valve to a source of compressed air by a supply line 102. The annular piston chamber 46 and the yarn passage hole 39 are inclined with respect to the axis of the yarn passage hole 39 so that compressed air can be injected toward the yarn entrance side, and a plurality of jets of air are directed toward the axis of the yarn passage hole 39. The holes 47 communicate with each other. Further, the exhaust chamber 100 is connected to the newer by an exhaust path 103. Next, 48 is a pair of delivery rollers, which are rotated in the direction of the arrow by a drive mechanism (not shown). Further, 49 is a wine day roller, which winds the spun bundled spun yarn 1 around the cheese 50.

A case will be described in which the bundled spun yarn 1 is manufactured using the apparatus having the above configuration.

First, the annular space 3 in the air false twisting nozzle 30
When compressed air is supplied to the annular piston chamber 46 while the supply of compressed air to the cylinder 3 is stopped, the pressure inside the annular piston chamber 46 increases and pushes the piston part 44a of the closed cylinder 44, causing the closed cylinder 44 to is slid toward the yarn entrance side against the spring 45 to close the closing part 44b.
is brought into contact with the lower surface of the center piece support shaft 25. Therefore, the yarn passage hole 27 of the centerpiece support shaft 25 and the yarn passage hole 39 of the nozzle body 38 are isolated from the inside of the exhaust chamber 100, and are no longer affected by the suction airflow caused by the newer. Furthermore, by supplying compressed air to the annular piston chamber 46, the compressed air is injected upward from the blowhole 47 into the yarn passage hole 39, and this jetted airflow passes through the yarn passage hole 27 and enters the rotor chamber 15. At the same time, suction force acts in the yarn inlet direction in the yarn passage hole 39 of the nozzle body 38 due to the ejector effect caused by the jet of the compressed air. In this state, when the tip of the seed yarn is brought close to the tapered hole 41a of the yarn passage hole 39, the seed yarn is sucked into the yarn passage hole 39 by the suction force, and is transferred to the rotor 1 by the air jet from the injection hole 47.
9 into the rotor section 20, and this rotor section 2
The tip of the seed yarn placed in the seed yarn is gripped by the rotor fiber bundle section 20a by the centrifugal force caused by the rotation of the rotor 19. Thereafter, the supply of compressed air to the annular piston chamber 46 is stopped. As a result, the closed cylinder 44
is slid downstream by the force of the spring 45 and returns to its original position, and the injection of compressed air from the blowhole 47 into the thread passage hole 39 is also stopped. In this state,
When the feed roller 9 is rotated, the fiber bundle 1a is supplied to the surface of the combing roller 10, and as the combing roller 10 rotates in the direction of the arrow, it is opened and drafted into separate single fibers 1b by the teeth on the peripheral surface. The single fibers 1b are carried by the airflow supplied to the fiber transfer path 7 and are supplied into the rotor section 20 of the rotor 19. The single fibers 1b supplied into the rotor section 20 come into contact with the inner surface of the rotor section 20, which is being driven to rotate, and are rotated together with the rotor section 20, and the centrifugal force caused by this rotation causes the inner surface of the rotor section 20 to The rotor fibers are transferred toward the rotor fiber collection section 20a and deposited in layers on the rotor fiber collection section 20a, and the rotor fiber collection section 2
Join to the seed thread held by 0a. When the seed yarn is guided between the delivery rollers 48 in this state, a detector (not shown) detects this and compressed air is supplied to the annular space 33 in the air false twist nozzle 30. Note that compressed air may be supplied to the annular space 33 by operating a manual switch. Further, the supply of compressed air for inserting the seed yarn may be stopped in response to a detection signal when the seed yarn is guided between the delivery rollers 48. By supplying compressed air to the annular space 33, the compressed air is injected from the injection hole 43 into the large diameter hole 40 of the yarn passage hole 39 in the tangential direction toward the yarn exit side, and this jet air flow It rotates along the inner surface in the opposite direction to the rotation of the rotor and comes into contact with a step 42 , and after turning at this step 42 , it flows through the large diameter hole 40 in the direction of the yarn entrance, and then passes above the air false twist nozzle 30 . Exhaust chamber 1
It is exhausted into 00 and sucked into the newer. As described above, since a swirling airflow is generated within the large-diameter hole 40, the seed yarn is swirled by the swirling airflow at the same time as it is pulled out, and a false twist is imparted to the seed yarn, and its tip imparts a twist to the joined fiber bundle. The twisted yarn 1c is then pulled out. Therefore, when the drawn-out twisted yarn 1c is guided between the winding roller 49 and the cheese wood pipe 50a, the twisted yarn 1c is wound around the cheese 50. In this case, the jetted airflow injected into the yarn passage hole 39 by the air false twisting nozzle 30 becomes a swirling airflow as shown in FIG. 5 and comes into contact with the stepped portion 42.
Since the airflow swirls around this stepped portion 42, the swirling airflow inside the large diameter hole 40 flows through the yarn passage hole 3.
It is expected that a phenomenon will occur in which the twisted yarn 1c is pressed against the stepped portion 42 in the large diameter hole 40 and actively rotated in the inside of the twisted yarn 1c.
A strong false twist can be applied extremely efficiently in the same direction as the twist direction of c. According to experiments conducted by the applicant, it has been confirmed that the strength of the bundled spun yarn 1 using the air false twisting nozzle 30 of this embodiment is significantly greater than that using the conventional false twisting nozzle. I was able to do that. Further, the compressed air injected into the large diameter hole 40 as described above flows in the direction of the yarn entrance after contacting the stepped portion 42 as described above, and flows into the twisted yarn 1c in the yarn passage hole 39 and the yarn passage hole 27. Since no tension is applied in the yarn exit direction (thread pull-out direction),
The tip of the twisted yarn 1c pulled out from inside the rotor 19 can be reliably held by the rotor fiber convergence section 20a, and an accident such as the twisted yarn 1c falling out from inside the rotor 19 due to false twisting can be prevented. be able to. Next, as described above, the twisted yarn 1c spun from within the rotor 19 is strongly false-twisted by the air false-twisting nozzle 30 at a position just below the rotor 19, so that this strong false-twisting is applied to the twisted yarn 1c spun from within the rotor 19. Fiber convergence part 2
It is propagated to near the fiber layer of 0a. At this time, since the upper surface of the center piece 26 is smoothly finished as described above, the air false twisting nozzle 30 is able to falsely twist the twisted yarn 1c in the rotor fiber convergence section 20a.
It can be twisted well up to the position of . Therefore, the center piece 26 and the rotor fiber bundle 20
It is possible to propagate false twist, which has a significantly higher number of twists than the actual twist due to the rotation of the rotor 19, to the twisted yarn 1c between the spaces a, thereby preventing yarn breakage even when the number of rotations of the rotor 19 is reduced. Further, as described above, when the fiber layer of the rotor fiber bundle 20a is drawn out of the rotor 19 as the twisted yarn 1c, the twisted yarn 1c is given an actual twist by the rotation of the rotor 19, but this actual twist is It is attached incidentally as a result of rotating the rotor 19 in order to collect and grip the single fibers in the fiber bundle part 20a, and in reality, it is almost untwisted, and this actual twist is applied to the bundled spun yarn 1. It's not that important. For example, English cotton count is 30's,
The rotation speed of rotor 19 is 13000 rpm, and the spinning speed is
If the speed is 150m/min, the actual twist will be 2.2 twists/inch.
This actual twist alone does not make it a yarn.
Further, as described above, when the fiber layer of the rotor fiber bundle 20a is drawn out of the rotor 19 as the twisted yarn 1c, the twisted yarn 1c heading from the rotor fiber bundle 20a toward the center of the center piece 26 centers around the center piece 26. The twisted yarn 1c is rotated in the air in the rotor section 20, and the separated single fibers 1b are supplied from the fiber transfer path 7 of the fiber opening device 2 toward a part A of the running surface of the twisted yarn 1c. Therefore, some of the single fibers fed toward this transfer surface are blown onto the outer periphery of the twisted yarn 1c which has been strongly false twisted as described above, become entangled and rolled up around this twisted yarn 1c, and the remaining The single fibers 1b are bundled in the rotor fiber bundler 20a as described above. In this case, the twisted yarn 1 in the part where the single fiber 1b is supplied
Since a strong false twist is applied to c by the air false twisting nozzle 30 as described above, the number of twists of the twisted yarn 1c in this false twisted state and the number of twists attached to the outer periphery of this twisted yarn 1c is The difference in numbers becomes extremely large as shown in FIG. Further, the twisted yarn 1c between the rotor fiber bundle part 20a and the center piece 26 is rotated in the air around the center piece 26 as described above, and this twisted yarn 1c comes to cross the supply portion of the single fibers 1b. Therefore, a large number of single fibers 1b can be entwined around the outer periphery of the twisted yarn 1c.
Furthermore, by appropriately selecting the number of revolutions of the rotor 19 and the spinning speed, the single fibers 1b can be entangled uniformly around the outer periphery of the twisted yarn 1c in the longitudinal direction.
Next, the twisted yarn 1c with the single fibers 1b entwined around its outer periphery as described above is then pulled out by the delivery roller 48 through the yarn passage hole 39 of the air false twisting nozzle 30, but the twisted yarn in the false twisted state is When 1c passes through the air false twisting nozzle 38 position and receives an untwisting action,
The twisted yarn 1c becomes a real twisted state with a small number of twists as the number of false twists becomes zero, and at the same time, the twisted yarn 1c
As the twisted yarn 1c is untwisted, the entangled fibers 1d on the outer periphery are given a binding twist in the direction opposite to the twisting direction of the actual twist, and these entangled fibers 1d cover the outer periphery of the twisted yarn 1c in a slightly actually twisted state. The yarn is spirally wound and bound, and when it passes the delivery roller 48, it becomes a bundled spun yarn 1 as shown in FIG. 7, and this bundled spun yarn 1 is wound around the cheese 35. When producing the bundled spun yarn 1 as described above, most of the compressed air injected from the injection hole 43 of the air false twisting nozzle 30 is discharged into the exhaust chamber 100 and sucked into the newer, and at this time, false twisting is imparted. At the same time, dust such as fiber waste generated by the process is removed. In addition, air false twisting nozzle 30
If the stepped portion 42 of the second main body 36 is worn out, the second main body 36 can be
The main body 36 can be easily replaced with another new one.

It goes without saying that the air false twisting nozzle of the present application can be used for producing various types of spun yarn using a rotating rotor.

Effects As described above, in the present invention, the yarn entrance side of the yarn passage hole is formed as a large diameter hole, and the yarn exit side is formed as a small diameter hole, and a stepped portion is formed in the middle of the yarn passage hole, so that the large diameter Since the injection hole is opened in the direction tangential to the inner surface of the large diameter hole and inclined toward the stepped part with respect to the axis of the large diameter hole, the twisted yarn can be passed through the thread passage hole and exit from the injection hole. When compressed air is injected, the compressed air swirls along the inner surface of the large diameter hole and can impart false twist to the twisted yarn, which can be used to produce bound spun yarn. It is possible to press the twisted yarn against the step part and actively rotate it, significantly increasing the false twisting efficiency of the twisted yarn, thereby reducing the consumption of compressed air and improving high-speed spinning. This has the effect of increasing the strength of the yarn when used. In addition, since it is configured as described above, the air injected into the large diameter hole toward the yarn exit side can be reflected at the stepped portion and flowed out in the opposite direction to the spinning direction of the twisted yarn. When used in a device for producing bundled spun yarn that imparts false twist to the twisted yarn pulled out from the rotating rotor, no undue force is applied to the twisted yarn between the rotating rotor and the air false twisting nozzle in the drawing direction, and the rotor fibers Yarn gripping of the yarn end on the converging surface can be reliably maintained, and bound spun yarn can be favorably produced using a rotating rotor.

[Brief explanation of drawings]

The drawings show an embodiment of the present application, and FIG. 1 is a cross-sectional view showing an apparatus for producing bundled spun yarn using a rotating rotor, FIG. 2 is an enlarged cross-sectional view of an air false twisting nozzle portion,
Figure 3 is an enlarged sectional view taken along the - line, Figure 4 is a sectional view taken along the - line, and Figure 5 is an explanatory diagram of the action of the air false twist nozzle.
FIG. 6 is an explanatory diagram showing the yarn structure of the center piece portion, and FIG. 7 is an explanatory diagram showing the yarn structure of the bound spun yarn. 30... Air false twist nozzle, 39... Yarn conduction hole,
40... Large diameter hole, 41... Small diameter hole, 42... Step portion, 43... Injection hole.

Claims (1)

[Scope of Claims] 1. In an air false-twisting nozzle that has a yarn passage hole and uses compressed fluid to impart a false twist to the twisted yarn passing through the yarn passage hole, the yarn entrance of the yarn passage hole A large diameter hole is formed on the side with an outer diameter large enough to cause ballooning in the twisted yarn, and a small diameter hole is formed on the yarn exit side with an outer diameter large enough to be almost blocked by the twisted yarn. A stepped portion is formed in the middle of the conducting hole in a direction substantially perpendicular to the axis of the thread conducting hole, and the jet air flow is tangential to the inner surface of the large diameter hole and directed toward the stepped portion. An air false twisting nozzle with an injection hole opening in a direction inclined to the axis of a large diameter hole. 2. The air false twisting nozzle according to claim 1, wherein the diameter d of the small diameter hole satisfies the formula 0.5 mm<d<2.0 mm. 3. The air false twisting nozzle according to claim 1 or 2, characterized in that the step portion is made of neuceramic.