The filament texturising machine manufacturer has as his primary target the construction of a machine which can assure a stable yarn path (without fluctuations) as well as low and controlled tensions in the zone included between the draft points situated before the first oven and those after the drawing unit, in order to attain high production speeds as well as a yarn with good characteristics in terms of elongation, tenacity, crimp and absence of broken filaments.
Owing to the considerable dimensions of the machine and to the necessity of assembling various cumbersome parts, very important are also the ergonomic characteristics of the machine in terms of compactness, accessibility, user-friendliness, and maintenance.
Moreover, it should be pointed out that, whereas guaranteed mechanical speeds reach 1500 m/min, technological speeds (processing speeds) are until now about two-thirds of that figure (higher speeds than on PES can be obtained on PA).
Best performances as to productivity and quality require solutions which optimize yarn path, oven parameters (length, temperature), cooling system (active cooling means), effectiveness in false-twist insertion (twisting force, tensions, friction heat dispersion), take-up system, process continuous monitoring.
These machines are characterized by the presence of only one oven to produce false-twist (FT) yarns mainly in PA fibre, or by the presence of 2 ovens for the production of false-twist set (FTF) yarns, mostly in PES fibre and to a lesser extent in PA fibre.
Two-oven machines are in more common use and can of course work with the FT process, excluding the setting in the second oven.
From the structural point of view, the machines can moreover differentiate on the basis of their profile which, in their usual configurations, recall the form of the letters H, M, and V.
In the H configuration, the yarn path is almost straight (in the course from feeding device through oven and cooling, till twisting unit) with consequent low tension levels and less yarn damage, whereas in the M and V configurations the yarn meets angled points which increase tensions, but on the other hand can improve path stability.
A two-oven draw-texturing machine for several users is composed of the following parts:
- Multilevel creel for bobbins (up to 20 kg each).
- Thread cutter with sensor to detect and stop possible broken threads.
- Feed shafts; in variable number (generally 3 or 4), they fix draft ratios through a yarn holding system (aprons).
- First oven: Dowtherm type (or HT type).
- Cooling zone: natural or forced systems.
- Spindle group: centralized control or control of single positions.
- Disk combination: variable (1-4-1 to 1-8-1) with polyurethane or ceramic disks (diam. 45 mm, H 6 mm).
- Second Oven.
- Contact oiling device with rotating rollers dipping in cups containing the batching oil (quantity: 1-3%).
- Take-up: placed on several levels (3 levels) with bobbin formation (4-5 kg).
- Computerized machine control system: setting and control of the various process parameters.
1. Two-Yarns Twisting Texturising Method (Duo-Twist Method)
This method falls within the systems based on thermoplastic deformation through twisting.
It is based on the principle of twisting a piece of 2 yarns coming from 2 feeding units, thermosetting the twisted yarn and then de- twisting it on a separating unit or winding them separately.
It is a process of scarce interest, suitable particularly for processing fine counts (also monofilaments) with a production speed of 600 m/min.
2. Thermo-Mechanical Processes With Deformation Obtained Without Twisting
These processes are not based on a principle of twist deformation, but on bending, curving, waving systems which produce yarns with different bulkiness/elasticity properties, but without any tendency to rotate on their own axis.
The method with mechanical compression chamber In this method the yarn is forced, by 2 feeding rollers, into a heated crimping box and is submitted to a compression which generates planar bending points (saw-teeth type) on the yarn.
The pressure inside the chamber is regulated by a device which permits the delivery of the yarn at a constant pressure.
The textured yarn which used such technology was marketed with the trademark Banlon (manufacturer: Bancroft); at present, the process is no longer in use for textile yarns and has lost ground also for carpet yarns.
This principle found on the contrary wide application in the production of crimping boxes for tow and staple fibre.
3. Air-jet Compression Chamber Method
This method can be considered a development of previously described method: yarn compression is not exerted mechanically by feeding rollers, but is generated by an aerodynamic system with jets of compressed heated air or steam.
The warm gaseous stream under pressure enters into a lateral opening of the box, flows into the yarn guiding channel, pushes the yarn into the expansion box where it is brought to a softening temperature (plasticization) and is compressed; the result on the yarn is a three-dimensionally shaped bending.
The exhausted air gets out of leaks placed at the extremity of the box and the yarn is pushed out of the box.
In order to maintain the properties gained through texturization, the yarn has to be quickly cooled on perforated drums with air suction to a temperature lower than the glass transition temperature of the fibre.
The yarn reaches the drum through rollers extracting the yarn which accumulated in the final part of the box, or which accumulates in a contact zone between box and drum.
The process is widely used for the production of carpet yarns in PA or PP according to BCF technology.
4. Knit-de-Knit Texturising Method
This is a discontinuous method which uses a knitting process on single-feed small diameter circular machine; the tubular produced is wound on support and thermo-set by steam or straight during dyeing operation.
The yarn is successively unraveled and wound on cones (speed: about 500 m/min). It shows a typical crimp, with wide planar waves of the same length as the stitch.
Owing to its elasticity, this method finds specific uses, in particular in the case of nylon; the process is less suitable to polyester, owing to its poor crimp stability
5. Blade Texturising Method
The textured yarn produced with this process bore originally the mark Agilon (producer: Milliken), but at present the process is no longer in use, owing to the poor properties (low crimp stability) of the yarn.
After being submitted to direct heating on feeding rollers, the yarn is let to glide under tension on the rounded edge of a metallic blade with a certain bending angle and successively cooled on delivery rollers.
The filaments undergo a structural change due to a compression force exerted from the blade on their contact side and to the contemporaneous drawing force exerted on the yarn side situated on the outside of the blade.
The physical strains generate structural deformations in the form of irregular three-dimensional waves.
6. Gear Texturising Method
The yarn obtained with this process was known under the trade name Pinlon; nowadays this technology has negligible importance.
The pre-heated yarn gets through two heated toothed wheels (speed up to 600 m/min), between which it is deformed and gets a flat waviness, assuming a geometry which is set by the profile of the wheel teeth.