Shaft seal molding process

During the shaft seal molding process, the elastomeric compound has relatively large distances to travel/ flow in the mold, particularly when using shelf loaded compression molding (Fig. 17a) and injection molding (Fig. 17b). History has shown that without the use of a vacuum, either applied directly through the mold or... 

In the two typical shaft seal manufacturing processes shown in Fig. 2, the extrusion process is only required if the compression molding process is being used. There are basically two types of extruders in general use, the cold feed and the hot feed. In both cases their role is to produce the preforms for use with compression molding. The critical issues with the preform are the shape, the dimensions, and the weight. 

In the manufacture of shaft seals, the molding is the process where the compound and treated metal stamping (phosphated and adhesive applied) are brought together to form the conventional lip type shaft seal. Therefore, it is critical that the compounds used are formulated to suit the molding process. There are three fundamental molding processes in use today compression, injection, and injection/transfer. 

An alternative approach for injection molding is the use of a rotary table injection machine. This type of machine uses the multistation concept, each station having a single cavity mold generally using a point gating/ injection point as previously mentioned. Consider a rotary table machine with eight stations, station one would be the injection station and station seven would be the unload and load metal insert station. This type of process has been successfully used for different types of lip type rotary shaft seals where more expensive elastomers are used and waste needs to be kept to a minimum. 

R. Bond, Shaft Seal Manufacture—Alternate Molding Techniques. Polymer Processing Society European Regional Meeting, Prague, Czechoslovakia, September 21-24 (1992). 

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