Pump Type Follows:

Monday, September 7, 2009

Materials of Construction

All component parts of a seal are selected based on their corrosion resistance to the liquid being sealed. The National Association of Corrosion Engineers (NACE) Corrosion Handbook provides corrosion rates for many materials of construction for mechanical seal used with a variety of liquids and gases. When the corrosion rate is greater than two mils (0.05 mm) per year, double seals that keep the hardware items of the seal in a neutral liquid should be selected to reduce corrosion. In the design, only the inside diameter of the mating ring, the primary ring, and the secondary seal are exposed to the corrosive liquid and should be constructed of corrosion resistant materials, such as ceramic, carbon, and Teflon.

The operating temperature is a primary consideration in the design of the secondary and static seals in the assembly. These parts must retain their flexibility throughout the life of the seal, as flexibility is necessary to retain the liquid at the secondary seal as well a to enable a degree of freedom for the primary ring to follow the mating ring.

An additional consideration in the selection of the primary and mating ring materials in sliding contact in their PV limitation. This value is an indication of how well the material combination will resist adhesive wear, which is the dominant wear in mechanical seal. Limiting PV values for various face combinations.

Common Material of construction for mechanical seals

Components

Material of Construction

Secondary Seals: O-rings

Nitrils, Ethylene Propylene, Chloroprene, Fluoroelastomer

Bellows

Nitrile, Ethylene Propylene, Chloroprene, Pluoroelastomer

Wedge or U Cups

Fluorocarbon

Metal Bellows

Stainless steel, Nickel base Alloy

Primary Ring

Carbon, Metal-filled Carbon, Tungsten Carbide, Siliconized Carbon, Bronze

Hardware (retainer, disc, snap rings, set screws, springs)

Stainless Steel, Nickel-base Alloy

Mating Ring

Ceramic, Cast Iron, Tungsten Carbide, Silicone Carbide

No comments: