A well-designed shaft seal is valuable only if manufactured well. What follows is an overview of the most common imperfections arising from manufacturing or handling variables. They do not reflect changes in a seal as a result of use.

These defects will typically be visible without magnification. Most may be seen in more than one part of a seal, so the importance of a defect depends on location and on the seal’s purpose (e.g. oil or grease retention, or contaminant exclusion). A blister at the lip contact point of a seal used to retain oil is critical and can easily cause leakage; a blister on the seal’s interior surface should not hurt sealability. These descriptions are general and may not be equally true for all applications. For a summary of these defects, see Table 49.

BLISTERS
CUTS
DAMAGED MOLD
DEFORMATION
DIRTY MOLD
FLASH
IMPROPER TRIM
KNIT LINE
MATERIAL CONTAMINATION
NICKS
NON-FILLS
POOR BOND
POROSITY
ROUGH TRIM
SCOOP TRIM
SCRATCHES
SPIRAL TRIM
SURFACE CONTAMINATION
TEARS
UNBONDED FLASH