However, the new variant also comes with less good properties. Namely less flexibility and less resistance during assembly. Most damages therefore occur during the installation of PTFE oil seals.

As an example, this oil seal has a part number that corresponds to a Shaft Size of 3”, a Bore Size of 4”, a Width Size of 0.625”, a Style of TB2, and is made of Viton material. Conversely, the same size oil seal in Metric has a Shaft Size of 76.20 mm, a Bore Size of 101.60 mm, and a Width Size of 15.88 mm.

As can be seen from the seal cross-section shown in Fig. 14.2, shaft seals are complex shapes that require advanced mold design and molding techniques (see Section 7.3 for discussion of fluoroelastomer molding). For some time, most shaft seals were made in the United States by compression molding. Injection molding of shaft seals is prevalent in Europe, and is being used increasingly in the United States. An advantage of compression molding is that preforms (usually rings cut from extruded tubing) are used that closely approximate the amount of stock required for the final parts, so compound waste is minimized. For injection molding, the amount of cured stock in the central sprue and runner (actually a thin sheet leading to the seal lip) is often large compared to the stock required for the final part, so the waste of high-cost fluoroelastomer may be high. Such waste is reduced in modern injection molding designs.

Sealing process