See Figure 148. Rubber recipe ingredients are carefully selected and precisely weighed (1). Thanks to sophisticated computer controls, the process cannot move forward unless the right amounts of the correct ingredients are chosen. Once assembled, the ingredients are fed into an internal mixer that uses rotors to heat and mix the compound (2). The rubber then goes onto a mill that further kneads it to ensure uniform dispersion of the ingredients (3).

The resulting rubber sheets are dipped in stearate to reduce stickiness (4), then air cooled to prevent premature curing, or scorch (5). Samples are taken for batch testing (6). If approved for production, the rubber is fed through an extruder to produce pre-forms (small pieces of rubber compound) for use in compression molding (7). If rubber is used in a transfer molding process, strips or pads are prepared for insertion into the transfer pot. Long strips of rubber are extruded for insertion into an injection press screw feeder.

Most shaft seals have metallic cases that have been press-stamped from strip steel (8). After stamping, the mild steel cases are placed in a rotating basket and submersed in a series of tanks designed to both clean the cases and apply a coat of zinc phosphate (9). This coat helps prevent rust, and it roughens the case’s surface, making the metal more amenable to being bonded to rubber during molding. Adhesive is generally sprayed on the case and then oven- or air-dried as a last step before molding (10).

Mold making begins with a design generated by an engineer based on the desired final dimensions of the seal (11). Typically made of hardened tool steel, the mold is produced using computer numerical control (CNC) equipment (12). Once cut, the mold is hand-polished to a blemish-free finish, then cleaned prior to use or storage (13).

HOW A SHAFT SEAL IS MADE MAIN PAGE