Mechanical Products

Carbon Seal

Carbon sealing rings are used as the wear face of most mechanical seals for the sealing of fluids in all industries.

APPLICATIONS ARE :

  • Process pumps
  • Rotary steam joints
  • Seals for agitators and autoclaves
  • Chemical pumps
  • Cold and warm water pumps
  • Corrosive liquid pumps.

 

Carbon is well suited to be used as a sealing ring due to having the following properties.

  • Very good chemical resistance
  • Good thermal conductivity
  • High wear resistance
  • Good corrosion resistance
  • Dry running properties
  • Good frictional properties
  • Outstanding resistance thermal shock
  • Low thermal expansion

 

Due to the need for sealing rings to be impervious the carbon material is impregnated with either resin or various metals. Assam Carbon should be contacted to ensure the correct grade is used for the application. Seal faces can be supplied unlapped or if required lapped to three helium light bands of flatness. Carbon seal faces are compatible with a wide range of metallic and ceramic counterfaces including silicon carbide and tungsten carbide.

Carbon-Graphite and Silicon Carbide Mechanical Seal Components are available in a wide variety of grades and can be Molded-to-Size or readily machined into many complex configurations.

SEAL RINGS FOR MECHANICAL SEALS

ACPL mechanical carbon-graphite materials are widely used for rotating shaft and face seals. They perform well when running against metal, ceramic, or even carbon-graphite counterfaces. Seals are manufactured in solid rings, split rings, and segmented rings for use in both liquid and dry-running applications. ACPL grades are used worldwide in aerospace, nuclear, petrochemical, and general marine industries.

Seal materials require high strength and a relatively high modulus of elasticity to withstand deformation at the interface. ACPL seal materials provide the strength and rigidity especially important in high pressure, zero leakage mechanical end-face seals. High thermal conductivity is essential when removing heat from the interface.
Carbon-graphite is inert to most chemical reagents where other engineered materials fail. Seal wear is a result of adhesive wear, chemical wear, erosive wear, and sometimes radio active wear. ACPL grades show superior adhesive wear resistance; however, chemical wear is evidenced in certain strong oxidizing environments or where the additives are attacked by specific oxidizing reagents. ACPL grades exhibit the best wear resistance to strong oxidizing fluids as shown in several field history cases and laboratory analyses.

  

Seal rings made from ACPL materials are resistant to abrasion, to high temperatures, and to attack by corrosive chemicals. Because of the inertness of the materials, these seal rings find application in chemical, pharmaceutical, and food processing industries, and in liquid, gas and vacuum environments.

ACPL offers the designer a family of customized seal ring materials developed to perform in nearly every difficult seal situation. There are two major families of materials from which these seal rings are made:



Carbon-Graphite
  

ACPL carbon-graphite seal materials are self-lubricating, chemically inert, temperature resistant, lightweight, resilient, dimensionally stable, and impermeable to gases and liquids.They can be molded-to-size or machined to close tolerances; impregnated; plated; vulcanized to rubber; and cemented or shrunk into housings or retainers.Scores of base materials are available, with hundreds of modifications that can be customized for specific designs and environments.

Design Considerations

Certain factors must be taken into consideration when deciding which combination of materials for seal ring and counterface is the most suitable for a particular application. These factors are the lubrication conditions obtainable at the interface, the pressure between seal ring and counterface.
Full fluid film or wet lubrication
This condition is that which would be found in a pump with the seal fully immersed in the liquid being sealed and arranged so that there is a constant supply of cool liquid circulating around its rubbing faces and with a seal combination designed to give full fluid film lubrication at the interface.
Boundary lubrication
This is a condition in which the only cooling of the seal is achieved by splash from the liquid being sealed or in which the seal is fully immersed but the circulation of the liquid around it is restricted or the interface film is destroyed repeatedly by evaporation
Dry
This means that the seal is out of contact with the liquid and is completely surrounded by gas. This is the most arduous operating condition and should, if possible, be avoided because in certain circumstances very high rates of wear can be experienced. If the dew point of the surrounding gas is more than 0°C there is a good chance of success. There have been applications where the dew point was down to -15°C and the resulting wear rate was acceptable. With dew points below -15°C, the wear rate becomes excessive.



Duty factors

The operating conditions defined earlier as lubricating conditions are combined in the table below to give a “Duty Factor” which is the combination of operating conditions and PV factor. This table is used to select the grades recommended subsequently for the seal and counterface rings of a particular application.


Duty Factors

In some high duty applications, special designs of seal and counterface rings including cooling of the counterface may be necessary.

Note: - Except organic solvent in all other chemical media, MY (Metal Impregnated) grades will be unsatisfactory.


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