Aprons in the drafting system are, with the top roller cots and the ring travelers, those components having a strong influence on the quality of the yarn and the efficiency of the ring spinning machines.

Increases in output of the ring spinning machines, updated design of components of top weighting arms and nose bars have increased the demands put on aprons considerably. If one considers that over the last 15years the speeds of spindles have increased by about 40%, yet the lifespan of aprons whose working life is defined by the frequency of flexing, has remained practically the same, the improvements in polymer materials are obvious.

Construction of aprons

Synthetic rubber, mainly NBR based, is the most widely used material for the manufacture of top and bottom aprons. There are also leather, synthetic leather, PU and PU-coated materials. Synthetic rubber has become a leading material for this purpose because of its long life, a wide range of uses and because of its resistance to fibre finishing additives and abrasion.

A typical rubber compound for the outer or inner layer of an apron contains the base polymer as well as between 10 and 15 different additives, which also affect the various physical and mechanical properties of the various aprons.

Basically, aprons made of synthetic rubber are made in endless tubular form whereas leather or synthetic leather aprons are made open in strips and subsequently glued together to form an apron. The advantage of the tubular construction is the lack of a seam. The apron is uniform along its entire circumference.

Aprons for use on ring spinning machines and roving frames are made of three layers; in some special applications used in the long staple spinning they only have two layers.

  • Outer layer
  • Reinforcement layer
  • Inner layer

The outer layer is finish ground to give it a defined roughness for optimum fibre guidance, but also must not be so rough as to prevent the release of the fibres at the turning point. The heaviest load is placed on this layer in the traverse zone. Here abrasion and the pressure from the bundle of fibres lead to smoothing and the formation of grooves.

This effect is especially noticeable in machines, which work with a very narrow traverse zone, such as for compact yarn or core yarn. The length of time for which an apron can create optimum yarn quality therefore depends on performance of the rubber compound. Resistance to abrasion and elasticity determine how long the initial structure of an apron outer layer lasts. (Fig. 2)