This invention relates in general to seals and, more particularly, to a seal having a lip with two moduli of elasticity along its band of contact.
The typical antifriction bearing operates with its interior isolated from the surrounding environment by a seal fitted to the bearing itself or located immediately beyond it. The seal not only retains the bearing lubricant within the interior of the bearing, but it also excludes contaminants which might detract from the effectiveness of the lubricant or actually damage the rolling elements and raceways of the bearing.
Most seals have at least one lip which bears against a cylindrical sealing surface to establish a dynamic fluid barrier along that surface. To prevent the seal from abrading or overheating, a small amount of lubricant should lie under its lip, that is between the lip and the sealing surface. In a seal operated under moderate climatic conditions, the lubricant tends to migrate along the sealing surface and provide the lubrication for preserving the seal lip. But when a seal is operated under extremely frigid conditions, the lubricant does not flow easily, if at all, and the seal lip experiences excessive wear. Indeed, grease becomes solid at low temperatures, and when in that condition, it will not adequately lubricate a seal lip. The solid grease, however, provides adequate lubrication for the antifriction bearing itself, because the rolling elements fracture it and churn it. The churning elevates the temperature of the grease enough to render it viscous, and in that condition it provides adequate lubrication for the bearing itself.
Others have experimented with seals having two moduli of elasticity in their contact lips. The portion of the seal lip formed with the lower modulus, is usually an elastomer, and it deflects under shear forces to more effectively pump lubricants. Hence, the elastomer with the lower modulus is typically located on the lubricant side of the seal, leaving the material of higher modulus in the contaminant side. It does not pump contaminants away from the seal very well. Often the material having the high modulus is polytetrafluoroethylene (PTFE).