A textile spindle is a device with oscillatory properties which, depending on the speed of rotation due to its unbalanced state, is vibrationally excited.

The spindle can be described as a spring-mass system with a damping device proportional to rotation speed. The running performance of a spindle is directly influenced by the individual bending stiffness and the damping characteristics of the system.

For spin-technological reasons a quiet run of the spindle, concentric to the spinning ring and with minimum amplitudes at the top of the spindle, is required.

All spinning spindles are operated in the hypercritical speed range. The first critical speed is, according to spindle design, between 2,000 and 4,000 rpm. This speed is only relevant during the start of the machine. The occurrence of a second critical speed within the working speed range of the spindle must be avoided at all cost. Apart from other factors, this is achieved by making the spindle upper part sufficiently resistant to bending deflections.

HP-S 68 Spindle Design

Modern spindles must be designed for spindle speeds above 20,000 rpm. The special aim is to ensure that belt or tape speeds do not increase in the same ratio as the spindle speed. The objective is therefore to reduce the wharve diameter still further. This can only be achieved by reducing the dimensions of the neck bearing and, consequently, the shaft diameter of the spindle upper part. Smaller spindle shaft diameters with otherwise the same bearing dimensions are however less rigid.

As mentioned above, a reduced stiffness of the spindle upper part would have a negative influence on the running performance of the spindle. Consequently, when reducing the diameter of the spindle shaft of HP-S 68 spindle to 6.8 mm, the distance between the neck bearing and the footstep bearing was reduced at the same time. As a result the HP-S 68 spindle shaft is in fact more rigid than the shaft of conventional spindles with a diameter of 7.8 mm.

In addition, the design ensures a high stiffness over the complete length of the spindle upper part. The steel spindle wharve embraces the aluminum bush and, therefore, strengthens the press-fit connection between the spindle shaft and the aluminum bush.

The shorter distance between the neck bearing and the footstep bearing places higher demands on the latter. The flexibly supported footstep bearing guides the spindle upper part continuously back to its given axis of rotation. The footstep bearing will deal with this task all the better, if the dynamic forces can be transmitted from the footstep bearing to the spindle shaft without any radial clearance.

For this reason, the HP-S 68 spindle bearing incorporates a footstep bearing design, which has been used with excellent results in millions of spindle bearings for more than a quarter of a century.