Sealing washers, F design
The shaft washer of a set of F-design sealing washers (fig 1) has an additional thin flocked plastic washer. The velvet-like flock consists of short, wear-resistant polyamide fibres.
As the fibres of the flock only exert a slight pressure on the counterface of the housing washer, there is no marked increase in friction compared with the standard washers. The only difference is noticed when operation is started. The friction is initially relatively high but sinks rapidly after a few revolutions. The friction torque is dependent on many factors including mounting accuracy, degree of contamination etc. and is therefore difficult to predict.
The flocked sealing washers are superior to the standard washers as regards efficiency in the following cases:
- In surroundings which are unfavourable for rolling bearings, particularly where material containing abrasive particles such as sand, soil, cement etc. is handled.
- Where, because of wet and dirty surroundings, grease-filled bearings fitted with rubbing seals are used, the rubber lips of which require protection against abrasive particles (fig 2).
- Where limited space prohibits the use of a number of standard sets.
- Where operating conditions, e.g. speed or temperature, are such that grease cannot be retained between the standard sealing washers.
The advantages of using flocked sealing washers are that relubrication intervals can be extended and that the service life of the bearings is lengthened. It has been found that bearings in agricultural equipment, for instance, which have to operate in close proximity to soil, water and vegetation, require much less maintenance when they are protected by flocked sealing washers.