The opening point at the spinning box is comparable with the infeed at the licker-in of the card. The rotating teeth of opening roller (Fig. 10, a) pass at high speed through the fiber beard and remove individual fibers from the sliver clamped between feed table (b) and feed roller (c). The sliver beard in this case is being moved slowly forward by the feed roller. By means of this continuous operation, the opening roller carries along by friction all fibers emerging from the clamping point between the feed roller and feed table. A fixed fiber beard support (d) provides uniform combing even in the event of mass deviations in the sliver. After leaving the rotating opening roller, the fibers are transported to the fiber channel. It is important to ensure that the speed of the air and fiber flow at the opening roller is greater than the peripheral velocity of the roller itself. If the roller velocity is equal to or higher than the air-flow speed, which can occur with very high roller speeds, this leads to fiber buckling at the lift-off point; this in turn causes deterioration in yarn quality and running performance. When the fibers are detached from the opening roller clothing, the trash included in the fiber material is removed via an opening under openin reg roller (e). The degree of trash removal can be adjusted via a bypass system (f) (refer also to section Trash removal).
The surface of the combing roll can consist either of a solid steel ring in which the appropriate tooth design has been machined by grinding or of a toothed wire which has been spirally wound on a ring or a body. Form, geometry and coating of the clothing and the opening roller itself are, alongside the rotor, of particular importance for the function and quality of yarn formation.
Opening rollers are available for every application to match both the thermal and physical properties of the raw materials being processed and the yarn properties required. Their clothing differs mainly in the following respects:
- in the shape of the teeth and their angle of inclination, tooth height and width of the tooth point;
- the density of tooth points;
- the geometric layout of the teeth; and
- different coatings.
Refer to section Range of application of the opening roller. for the correct choice of opening rollers with reference to their range of application.
The opening roller is a part subject to wear and must be periodically replaced, depending upon the rate of wear. If this is delayed too long, yarn quality and spinning conditions deteriorate.
In addition to the correct choice of opening roller clothing, special attention must also be paid to the setting of the opening roller speed. The opening roller speed range is between 6 000 and 10 000 rpm; speeds between 6 500 and 8 000 rpm are usually used. Opening roller speeds that are either too high or too low, always relative to the specific application, can have a negative impact on yarn formation and yarn quality. Opening roller speeds that are too low can result in:
- inadequate separation of the sliver into individual fibers;
- inadequate opening of fiber neps and fiber clumps;
- inadequate trash removal;
- tendency toward lap formation on the opening roller.
Inadequate removal of trash particles because opening roller speeds are too low not only affects spinning stability through an increase in ends down, the yarn itself also contains more trash particles. Yarn irregularity also deteriorates and the frequency of thick places, thin places, neps and Classimat defects (rarely disturbing yarn defects) increases.
However, opening roller speeds that are too high can also have a negative impact; an improvement in opening performance is by no means achieved. Excessively high opening roller speeds result in:
- more or less severe damage to – i.e. shortening of – fibers, and thus
- losses in yarn tenacity and the strength of the fabrics produced from them,
- an increase in fiber fly on the spinning machine and in downstream processing,
- smelting points when processing man-made fibers.
The manufacturer‘s recommendations regarding type and speed of opening roller should therefore be disregarded only in exceptional cases (for processing especially critical materials) and only after conducting thorough spinning trials.
Opening roller housings exist in both open and closed designs. Uncovered housings are an advantage to the extent that disturbing accumulations of fibers on the front of the opening rollers are avoided. The opening rollers themselves are protected against secondary air and ambient influences by means of effective multi-stage sealing. The opening rollers can be checked and replaced much more easily than with enclosed systems