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Page 2 - Seal and Screw System for the Reliable Hygienic Solution

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Seal and Screw System for the Reliable Hygienic Solution
Hygienic Usit® flat washers combined with specially made hexagon head screws and cap nuts guarantee that screw holes in the process industry are cleaned hygienically >>1. The flat washers' sealing bead is made of 70 EPDM 291. This material is FDA-compliant and likewise in conformity with the requirements of European directive EU (VO) 1935/2004. The material is also ADI-free (animal derived ingredients free) and therefore free of TSE (transmissible spongiform encephalopathy). The biocompatibility test conformable with USP Class VI (up to 121° C) rates it as appropriate for use in pharmaceutical equipment and components.
The sealing bead is scorched onto a metal disc and has a trapezoidal contour inside. With the flange seat and on tightening the screw it creates a form fit and thus presents an optimal seal. By screwing in, the sealing bead is pressed outward shy of the flange seat. In the course of this the seal adapts both to the contour of the screw flange and to the flat contact face of the machine part. This produces a screw hole and sealing point fit to clean. This combination has already been checked by the Research Center Weihenstephan for Brewing and Food Quality in conformity with the EHEDG Cleanability Method and found to be in compliance.
The dimensions of the nuts and screw heads are very similar to DIN 6921 and 6923 (DIN EN 1665), however the differences, especially with regard to the proper use of the hygienic flat washers, are significant. Contrary to the customary standard screws or cap nuts, the special screws do not have any draw marks, uneven head contact and stampings on the head. Cracks on the edges, any dents or sharp-edged flashings on the collar are precluded. The sealing bead is not damaged on tightening the screw.
The polished flange seat face ensures that the lip of the sealing bead can slide outward with ease. The lip cannot be jammed or snapped off. This guarantees that the screw hole is hygienically sealed absolutely and the formation of cavities where deposits of microorganisms build up is prevented.
In addition, the sealing washer is centred on the scew shank with a tolerance of just 0.1 mm. The assembly position of the washer for the screw and for the screw hole can be reproduced at approximately 100% as a result. Repeated tightening and loosening again does not cause any impairment of the sealing properties. This method also precludes the risk of the sealing bead being crushed. The sealing faces are not overstrained and they always readapt themselves to the screw's flange seat.
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