About Seals- Chapter one About Oil Seals and Grease Seals

Mackintosh

About Oil Seals and Grease Seals
6 _, b* a$ {8 u: t$ J! qOil seals and grease seals have a flexible lip that rubs against a shaft or housing to prevent the leakage or ingress of fluids and dirt. For proper installation, the seal lip should point towards the medium being contained. Some oil seals and grease seals have a spring to help keep the lip in contact with the shaft.  The sealing orientation and direction is important to consider for oil seals and grease seals.  The orientation and direction can be internal or rod seal, external or piston seal, symmetric seal, or axial seal.  Rod seals are radial seals.  The seal is press-fit into a housing bore with the sealing lip contacting the shaft. Also referred to as a shaft seal.  Piston seals are radial seals.  The seal is fit onto a shaft with the sealing lip contacting the housing bore. V-rings are considered external lip seals.  A symmetric seal is symmetrical and works equally well as a rod or a piston seal.  An axial seal seals axially against a housing or machine component.
The seal type for oil seals and grease seals can be oil seals or other types.  An oil seal can also called flexible lip, radial lip, or rotary shaft seal. Oil & grease seals are used to retain or separate lubricants or fluids.  These seals are primarily used for rotary applications only.  Common configurations include single lip, double lip, triple lip, and four or more lips.  Other seal type choices include U-ring or block vee ring, V-ring, clearance or labyrinth seals, and bearing isolators.  U-ring or block vee ring seals are also called U-packings or Block Vee packings.  Depending on their construction, U-rings and block vee rings can be used as a rod seal, a piston seal or a symmetric seal. U-rings and block vee rings are single acting, or unidirectional seals, and must be mounted back-to-back in double-acting cylinder applications.  A Block Vee seal is more compact and has better performance characteristics under high pressure than a U-ring.  V-ring seals are all rubber seals used primarily to exclude dirt and other contaminants. V-rings stretch over a shaft and seal against the side of a housing or other machine component.  There are many different styles of clearance, or labyrinth seals.  The one thing they all have in common is that they all operate on a principle of positive clearance (i.e., no rubbing against the shaft or housing).  Many labyrinth seals are comprised of a rotor (rotating) and stator (stationary) member with a radial gap between the two members.  The gap must be larger than the radial clearance of the bearing being sealed. In addition, the operating speed and temperature must be considered when using a labyrinth seal.  These seals generally do not perform well at low operating speeds.  Another form of labyrinth seal is a laminar-sealing ring, which uses a series of flat metal washer-like rings of varying diameters to create a labyrinth seal.  Bearing isolators are dynamic seals designed to protect bearings from outside contaminants.  They are comprised of a rotor (rotating) and stator (stationary) member.  Some bearing isolators are of labyrinth construction while others use O-rings or other positive seals.
Important seal construction parameters to consider include metal casings, and dual lip elements.  Important dimensions to consider when specifying oil seals and grease seals include shaft outer diameter or seal inner diameter, housing bore diameter or seal outer diameter, axial cross section or thickness, and radial cross section.  Important service limits parameters to consider include maximum operating speed, maximum operating pressure, vacuum rating, and operating temperature.  Rubber sealing element or lip material choices for oil seals and grease seals include ethylene acrylic, EDPM, fluoroelastomer, fluorosilicone, nitrile, nylon or polyamide, polychloroprene, polyetheretherkeytone, polyoxymethylene, polytetrafluoroethylene, polyurethane or urethane, and natural rubber.  Metallic choices include sintered bronze, cast iron, and stainless steel.  Other materials include felt and leather.  Many seal manufacturers use their own proprietary material.  Consult with manufacturer for proprietary material specifications.  Common features for oil seals and grease seals include spring loaded, integral wiper, and split seal.