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Glossary P


Glossary P

Packing, Mechanical:
A deformable material used to prevent or control the passage of matter between surfaces which move in relation to each other.

Pitch, Helix Seal Rib:
The circumferential displacement between adjacent helical ribs of a lip seal.

Plasticity:
The degree or rate at which unvulcanized elastomer and elastomeric compounds will flow when subjected to forces of compression, shear or extrusion.

Plasticizer:
A material that when incorporated in elastomer or polymer, will change its hardness, flexibility, processability, and/or plasticity.

Plunge Ground:
The surface texture of shaft or wear sleeve produced by presenting the grinding wheel perpendicular to the rotating shaft without axial motion.

Polyacrylate:
A type of elastomer characterized by an unsaturated chain and being a copolymer of allkyl acrylate and some other monomer such as chloroethyl vinyl ether or vinyl chloroacetate.

Polymer:
Generic term for an organic compound of high molecular weight and consisting of recurrent structural groups.

Polymerization:
The ability of certain organic compounds to react together to form a single molecule of higher atomic weight.

Polytetrafluoroethylene (PTFE):
PTFE is a fluoropolymer with excellent thermal and chemical resistance and low coefficient of friction. PTFE is usually compounded with fillers such as molybdenum disulfide, graphite, pigments, and glass fibers to improve wear characteristics and other properties.

Porosity:
A multitude of minute cavities in the seal material.

Position, Spring:
The axial distance between the seal contact line and the centerline of the spring groove of a radial lip seal, commonly referred to as the “R” value.

Precure-Partial Cure:
The first cure of a material that is given more than one cure in its manufacture.

Pressure, Contact:
The average pressure exerted by a seal on a shaft. This pressure is computed by dividing the total lip force by the total lip contact area. Sometimes referred to as radial pressure.

Pressure, Lip Opening:
The pressure necessary for flowing air at 10.000 cm3/m between the contact surface of a radial lip seal and a shaft-size mandrel under the following conditions: the seal case outer diameter clamped to be concentric with the mandrel and the pressurized air applied to the outside lip surface.

Pressure, Seal Cavity:
The pressure of a fluid being sealed.

Pressure, Spring:
The contact pressure which results from the spring load.

PTFE Seal, Lay Down Lip:
Term used to describe a PTFE sealing element with a wide contact pattern on shaft. Often used with hydrodynamic features.

PTFE Seal, Line Contact Lip:
A seal utilizing an insert of PTFE bonded to an elastomeric back-up material. Shaft contact is over a narrow area similar to most radial lip seals.

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