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Air-jet yarn texturing and its nozzles

1.  Introduction

Air-jet texturing is one of the most versatile methods known to convert flat syntheticfilament yarns to textured yarns. Over the years, developments in air jet texturing have been related to the developments in nozzle design. With this development yarns from finer denier to extremely coarse denier can be textured. There is no universal nozzle capable of processing any supply yarn of any linear density. The yarns produced using this method are used for applications such as car seat cover fabrics, sewing threads, sportswear, upholstery, automotive textiles, decorator fabrics etc but there is little use in apparel.

From the announcement of the first nozzle patent in 1952 to the present day, the air-jet texturing process has experienced many developments and improvements. Although texturing speeds have been increased from 10 m/min up to 600 m/min and the compressed air consumption has been reduced from about 22 m3 /h to about 6 m3 /h per nozzle, whilst the yarn properties have been considerably improved.

2. Types of air jets

Texturing nozzles are usually enclosed in a chamber not only to reduce the noise but also to collect the used water & some of the spin finish washed away from the filaments during the process.Some texturing nozzles have an impact element at the nozzle exit to be used optionally in certain cases recommended by the manufacturer. The element is believed to improve the process stability & yarn quality in texturing of certain yarns.

There are two basic types of texturing jet

  1. Axial
  2. Radial
  1. Axial jet

This was the first type of jet to be developed for air-jet texturing; initially by the DuPont Company (DuPont), using the trademark Taslan. The axial jet was developed initially to be adjusted during production, in order to obtain the optimum yarn processing tension. The radial jets have always been fixed. They require only cleaning and the replacement of seals and damaged surfaces during their lifetime.

  1. Radial jet

This jet was developed originally in Czechoslovakia using the Mirlan name but has been manufactured by Heberlein since 1977. Again, what was originally single model has developed into a wide range for different yarns and production rates. Radial jets are made from both ceramic and tungsten carbide materials.

11

Figure. 1 (a) Axial Jet   (b) Radial Jet. (Courtesy of Heberlein Fibre Technology Inc.)

Both the axial and radial jets are fitted with a form of baffle device at the point where the yarn leaves the jet. These have been given various names such as baffles or coanda bars. There are three types of jets available commercially, they are: Du Pont jet, EMAD jet & Hema jet. The air jet texturing machines are marketed by many companies namely, Barmag, Enterprise Machine Mitsubishi, Neumag, Eletx, Seam Engineering, James Makie, etc [1].

3. ConventionalTexturing Nozzles

High energy demand due to high compressed air consumption has been one of the initial reasons far the slow development of the air-jet texturing process. The lack of a thorough understanding of the basics of the process has also handicapped improvements such as improved nozzle design and systematic provision of current process parameters.

03Figure 2 : Early Texturing Nozzle

Today’s air-jet texturing technology requires no pretwisted supply yarns to produce a wide range of textured yarns ranging from very fine polyester and polyamide yarns for apparel fabrics1 to heavy carbon filaments for aerospace technologyand glass fibres [2].

Early texturing nozzle had an axial yarn feed while the compressed air was admitted to the nozzle body through a side entry. It also had an impact element of a flat plate type. Nevertheless, the lack of aerodynamic design of the inner configuration caused tremendous losses to the air flow resulting in inefficient texturing. Another early design reported by Piller [3] also suffered from similar deficiencies. The type IX jet was especially suitable for pre-twistedyams since a strong untwisting action was provided in the venturi [4].

The Taslan IX nozzle shown in Fig. 2 had an axial air flow which was accelerated by well-established converging diverging geometry, while the highly pretwisted overfed yarn was admitted to the main channel through a stepped hollow needle inclined at 45° to the nozzle axis. Type IX jet, however, had serious drawbacks. Firstly, the texturing speed was very low (10-50 m/min) and there were problems of uniformity, confining the process to the production of bulky and effect yarns. Secondly, the twisting of the yarn before or after the jet was essential for obtaining a stable yam structure; this increased the costs. Thirdly, the jet was very difficult to set and suffered from serious wear problems. Following the failure of this nozzle, the nozzle designers were forced to change the basic configuration and introduced a completely different design [5].

In 1960, Taslan type X jet, which is shown in Fig. 3(b), was introduced by Du Pont. In contrast to thetype IXjet, the yam in type Xjet enters axially. The airstream passes uniformly around the circumference of the yarn input channel. The needle extends into theopening of the nozzle through which the compressed air enters the so called turbulence chamber. Axialmovement of the needle alters the cross-sectionalarea of the clearance and has an influence on the airmass flow rate. An important feature of this texturing nozzle is the way in which the asymmetric flow profileis obtained. Uniform smooth flow of compressed airis disturbed by means of the eccentric setting of the jet element, thus the necessary turbulence andasymmetric swirling are achieved. With this jet the texturing speed was increased to 70-90 m/min and the expensive cost of twisting was eliminated.

A significant improvement in technological performance was achieved by the introduction of Taslan type XI jet in 1968. Although the yarn input channel and the nozzle were similar to those of type X jet, modification of the air inlet was sufficient to result in a vastly superior performance. In type XI jet, the air stream does not flow uniformly around the circumference of the needle but is fed through an inlet hole as shown in Fig. 3 (c). In other words, the flow from the air reservoirs to the needle tip is restricted to allow flow on one side of the needle only. The opening can be in the shape of a slit or any other shape.

04Taslan type XI Mark IV jet, introduced in 1973 by Du Pont, allowed processing speeds to be increased up to 500 m/min for a 167 dtex yarn. The construction of type XI Mark IV jet is very similar to that of type XI jet except for the device used at the exit point of the jet. This device is just a flap arrangement and has the function of increasing the vacuum effect and drawing extraneous loops into the body of the yarn I, thus improving the uniformity and quality.

A new jet Taslan type XIV was available by 1976. Fig. 3 (d) shows the jet with the flap arrangement. Lower air consumption was achieved through changes made in the internal design of the air flow The Taslan type XV jet, shown in Fig. 3 (e), uses a cylindrical baffle at a fixed distance from the jet exit. The air and yarn impinge onto the baffle and the yam moves around the lower surface of the baffle. Different sizes of baffle rods are provided by the manufacturer. A series of patents 2-4 from Du Pont describe the further developments related to the above jets. Fig. 3(f) shows a section of the Taslan type XXjet which has easy string-up feature with the help of cam set-up provided. Type XX jet was particularly developed for texturing fine denier yarns. However, at present, ‘Mark XX Ease-A-Matic Jet’ can handle a wide range of yarn deniers [6].

  • Shortcomings of conventional nozzles

The high level of air consumption is the major obstacle to the air jet yarn texturing process. Although air coosumptia1 levels have been reduced over the course of the years, it still constitutes more than 40% of the overall costs of the process [7]. It has been reported by some. Authors [8] and [9] mentioned that as soon as the air consumption of air-jet texturing nozzles is reduced to acceptable levels without causing any deterioration of the process itself, then air-jet texturing will make its long expected break through.

Benedict et al [10] have shown that an abrupt enlargement of any flow, both in the subsonic and supercritical ranges, causes considerable losses and hence dissipates the flow energy. By one study, all the Hema Jets suffer from these abrupt enlargement losses due to the ratio of incoming jet area to the nozzle main duct area being less than unity. A further factor is the fact that, due to the oblique opening of the inlet holes to the main duct, the incoming jets vigorously hit the opposite wall of the duct. Additionally, the backward deflection of the inlet jets increases the angle of impingement and therefore makes the losses worse. This oblique impingement therefore forms another source of loss. It is surmised that these losses are more significant in those nozzles with one incoming jet than in nozzles with two or three incoming jets. This is because the collision of the opposing air jets occurs between the jets and a1 the center line of the main duct, rather than between a single air-jet and the solid walls of the main duct. A further undesired effect of this oblique impingement of a single incoming jet is that it presses the filament yarn against the opposite wall. Since the filament yarn is in motion, this causes increased friction and hence wear of the nozzle. It has been reported by a major company of the U.K.[11] that they had to renew their nozzles every six months due to this wear problem. Nevertheless, it should be bon1e in mind that the collision of incoming jet(s) has a useful function for texturing by causing a better separation of the filaments and subsequently improving the effectiveness of the loop and entanglement formation.

Bearing in mind that the trumpet-shaped exit is not designed for the complete expansion of the flow, the flow with pressures higher than the ambient pressure expands to the atmospheric conditions creating expansion waves which dissipate a great deal of energy. Therefore it could be said that the flow energy is not fully utilized by the existing nozzles.

Furthermore, increasing input pressures increase the rate of secondary flow due to the increased backward deflection of the incoming jets, hence making the nozzles less efficient. In summary, the high level of air consumption, the sudden enlargement and oblique impingement of the incoming jet(s), the cylindrical geometry of the main duct which does not allow the flow to expandfurther, and the high level of secondary flow rate are the major shortcomings of the existing, cylindrical type nozzles.

4. Modern nozzles for air texturing

Despite the continuous development and improvement attempts, certain drawbacks such as high compressed air consumption, nozzle to nozzle inconsistency due to the need for precise adjustment of both the needle and the venturi, and the frequent contamination of the venturi with spin finish material washed away from the yarn surface, thereby requiring regular cleaning and servicing [12], still needed to be solved. Such factors have induced some other manufacturers to take an interest, particularly after the expiration of the main Du Pont patents which formed the basis of the Taslan process. They are too numerous to mention them all, but two, namely Enterprise Machine and Development Co. (EMAD) of the USA and Heberlein Maschinenfabrik A.G. of Switzerland, stand out. The latter has recently made even more contributions to the air-jet texturing process than Du Pont. Although the nozzles developed by EMAD have also followed the similar configuration to the Taslan nozzles, having converging diverging geometry, the Heberlein nozzles are of completely different geometry.

06The most significant developments in the nozzle design have thereforetaken place in the last decade. Heberlein took over the air-jettechnology developed by Berliner Maschinenbau A.G. of Switzerland in1977 and introduced its first HemaJet nozzle called the Standard-core HemaJet shown in Fig. 2.3 in 1978[13].

This nozzle is reported to be similar to an earlier design, i.e. the Mirlan nozzle fromCzechoslovakia[14]. In this design, the air is fed into the main duct ofthe nozzle through three small inlet holes, where it impinges uponthe overfed supply yarn which follows a straight axial path in the nozzle. Since the Standard-core HemaJet had no adjustable parts, the needa skilled operator for manning the Taslan nozzles has beeneliminated. Better nozzle-to-nozzle consistency is obtained bykeeping the machining tolerances very tight. The design has a self-cleaning facility, as spin finish constituents are washed away fromthe yarn surface because of the straight geometry of the main ductwhich is constantly in contact with the moving yarn[15]. Heberlein [16]later introduced six other nozzles designated as T100, T311, T341, T110, T140 and T350 with the first digit indicating the provision ofeither one or three inlet holes. Some of these nozzles for theapparel range have reduced the air consumption drastically.

05Figure 5. Technical drawing of Hema jets & Taslan nozzles

It appears that the majority of the nozzles to date have beendeveloped by the industry through practical experience. Acar[17],utilizing the resultsof his theoretical and experimentalinvestigation with the Standard-core HemaJet designed novel nozzles.The prototypes of these nozzles were manufactured by Heberlein andwere reported to yield satisfactory texturing and provided substantial saving of compressed air.

Figs. 5.la, b, and c illustrate the general features of the three Hema Jets, the Taslan XIV, these figures also 500w the technical drawings of these nozzles. Being effectively cylindrical nozzles can be included in the same category although they have two inlet roles in comparison to the one inlet hole in the T1OO and the three inlet holes in the T341 and standard-core nozzles.

The effect of the area ratio of the inlet holes to the main duct if closer the higher the velocities at the exit plane of the nozzle is attained. Although this result has been obtained from the velocity and static pressure measurements, the same result could be supported by the texturing trials of the existing nozzles. In conclusion, it could be argued that choosing an area ratio of unity eliminates the drawback of an abrupt enlargement. The consequence is that the sonic flow conditions will be introduced to the main duct of the nozzle.

The exit shapes have little effect on the air flow produced by the experimental nozzles. Therefore, from the aerodynamic point of view, exit shapes could be eliminated. This obviously will reduce the manufacturing costs of the nozzles. However, from the texturing viewpoint, a curved exit shape, i.e. trumpet-shape may facilitate a smooth right-angled turning of the textured yarn, thus contributing to the texturing process.

Conclusion

In this paper, the structures of conventional and modern jet nozzles are considered. The compressed air is admitted to the straight main channel of the HemaJet nozzle, where it is divided into primary and secondary flows, whereas in a Taslan nozzle air flows into the venturi through a circumferential gap and is then divided into primary and secondary flows. The choked flow in the throat of the Taslan nozzles is subsequently accelerated by the diverging section of the venturi, but no such controlled acceleration takes place in the Hema Jets.

References

  1. Dr V.K .Kothari IIT Delhi, Air jet texturing process, Indian Textile Journal 1989 April, Vol.No.4.
  2. EVANS M, Dunlop Aerospace, Private Communication, April 1987
  3. PILLER B, Bulked Yams, The Textile Trade Press, Manchester, 1973, 571 pages.
  4. WRAY G R, The Construction and Resultant Properties of Air textured Filament Yarns, PhD ‘lllesis, University of Manchester, 1965.
  5. P. 762 630. Du Pont de Nemours, July 19, 1954.
  6. V K Kothari & N B Timble, Air-jet texturing: Effect of jet type and some process parameters on properties of air-jet textured yarns, Indian Journal of Fibre & Textile Research, Vol. 16, March 1991, pp. 29-38
  7. WILSON D K, Apparel Fabrics-What chances Have Air-Jet Textured Yarns? Textile Institute and Industry, 1979, Vol. 17, (5), 17Q-174.
  8. WILSON D K, Breakthrough of Air Textured Yarns, Fiber Producer, August 1982, Vol. 10, (4), 86-88.
  9. ISAACS III A, Air Texturing Prepares for Lift-off Again, Textile world, 1984, (10), 48-55.
  10. BENEDICT RP, WYLER J S, DUDEK J A, and GLEED A R, Generalised Flow Across an Abrupt Enlargement, Trans. Of the ASME: Journal of Engineering for Power, July 1976, 327-334.
  11. MARKS M R, ICI Fibers Cc., Gloucestershire, UK, Private Communication, 1985.
  12. Heberlein Product Information Sheet, “Air Texturing Jets”, Heberlein Maschinenfabrik AG, watwil, Switzerland.
  13. S.P. 4 097 975. Heberlein Maschinenfabrik, Jul. 19, 1977
  14. BOCK G. and LUNENSCHLO/3 J., “Air-jet Stream and Loop Formation in Aerodynamic Texturing”, Chemiefasern/Textilindustrie, 31/83, E41, 1-8, May 1981
  15. FISCEER K and IESSLER J, Air Texturing – Spunlike Yarns Made of Filament, Melliand Textilberichte (Eng. Ed.), June 1986, Vol. 12, (6), 383-387.
  16. STEINMAN A J, Air Jet Texturing, Air Jet Texturing Conference, Clemson University, Greenville, S.C., 18-19 Sept. 1985.
  17. ACAR M, Analysis of the Air-jet Texturing Process and Development of Improved Nozzles, PhD Thesis, Loughborough University of Technology, 1984.
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