The yarn produced by twisting at the delivery of the drafting arrangements is guided with the aid of a thread guide to a position directly over the spindle. Before passing to winding up on the spindle, the yarn turns through a second guide position, the balloon control ring. Winding on the spindle itself arises from interplay between the speed of the traveller rotating on the ring and the rotational speed of the spindle.
The later is therefore the third most important machine element, following the drafting arrangement and the ring/traveller combination. Mechanically, the spindle is capable of speeds up to 28,000 rpm, but this maximum speed cannot be exploited commercially because the traveller speed is limited.
Influence of the spindle on spinning
Spindles, and their drive, have a great influence on power consumption and noise level in the machine.
The running characteristics of a spindle, especially imbalance and eccentricity relative to the ring, also affect yarn quality and of course the number of end breakages. Almost all yarn parameters are disadvantageously affected by poorly running spindles. Hence, the mill must ensure at all times that centering of the spindles relative to the rings is as accurate as possible.
Since the ring and spindle form independent units and are able to shift relative to each other in the operation, these two parts must be re-centered from time to time. Previously, this was done by shifting the spindle relative to the ring, but it is now usually carried out by adjusting the ring. Mechanical or electronic devices are used for centering.
Figure 1. Components of the Spindle
Figure 2. Spindle Supports and bearings
A ring frame spindle consists of two separate parts, spindle center shaft and enclosed bearing housing as shown in Figures 1 and 2 . Usually, the center shaft is made of an aluminum alloy and has slight taper, say 1:64. To ensure that the tube is firmly seated on the shaft, it has a tube coupling at the top. For large spindles there is one more at the bottom.
The bottom end of the shaft is in the form of a cap wharve. It is hollow and can therefore be fitted over the spindle collar accommodated in the bearing housing. The tensile forces generated by the drive belt therefore act directly on the bearing, which favorably influences the smooth running of the spindle. However, the size of the wharve is important as well as its shape. If its diameter can be kept small, equally high spindle speeds can be achieved at lower drive speeds (cylinder/belts). This results in lower energy consumption. However, in order to ensure that the drive belt rotates the spindle slip-free, the diameter of the wharve must also not be too small. Wharve diameters of 19 to 22 mm are common at present. Bearing section is bolted firmly to ring rail by nut.
The spindle bearing consists of 2 parts, a spindle collar bearing and a spindle step bearing. Both parts are connected via housing. The spindle collar comprises a precision roller bearing. The spindle step, designed as a friction bearing (conical bearing), is responsible for the elastic centering and cushioning of the spindle center shaft. Two centering and cushioning elements control the bearing shaft. An oil-filled spiral mounted symmetrically with the spindle step ensures optimum cushioning. Spindle step also absorbs all vertical forces acting on the spindle.
The spindle collar can be a friction bearing or a roller bearing. The noise level can be reduced considerably by using friction bearings, but energy consumption is somewhat higher. Most spindles are therefore equipped with roller bearings. The spindle collar is rigidly friction-set in the bearing housing in standard spindles. Bearing vibration is therefore transmitted to the spindle frame without damping. This results in high noise levels at higher speeds. For speeds over 18 000 rpm, spindles are therefore mostly used in which not only the spindle step, but also the spindle collar is attached flexibly to the bearing housing. These spindles are more expensive, but permit higher speeds and reduce noise levels in ring spinning machines by some 10 dB compared with standard spindles.
Spindle step is always a friction bearing and flexible, i.e. it can tilt sideways to a small extent. The spindle is therefore able to center itself, which enables it to operate in hypercritical ranges. This results in a significant reduction in bearing forces. High-performance spindles are inconceivable without damping devices. Various systems are used, such as damping spirals, damping tubes or damping oil around a steel tube.
If damping spirals are used, spiral spring (a) is compressed at one side when the spindle is deflected to side (b) (Fig. 20). The oil therefore flows from this side to the other side, where the gaps become wider (c). The resistance the oil has to overcome in the process damps the vibration in the spindle step and ultimately in the shaft.
The cavity between the spindle blade and the bearing housing is largely filled with lubricating oil. Since the oil is used up, it has to be replenished from time to time. This is necessary after about 10 000 - 25 000 operating hours.