Carbon Fiber, Graphite Fiber or Expanded Graphite?

What are the differences?

Which material is your packing, gasket and joint sealant made of?

It determines the degrees of success of sealing at your plant!

There are two processes to make Carbon fibres; either the PAN or Pitch process. The PAN process produces the highest grade of Carbon Fiber with ultra-high modulus. 90% of the carbon fibre is made from the PAN process and the balance 10% is made from the Pitch Process.

Graphite fibers produced by further treatment at a higher temperature in the PAN process.

However, expanded graphite is not man-made! It is produced from mined mineral graphite which is treated with acid and then processed in the oven to break down the bonding, thus causing it to expand or exfoliate, thus the term expanded or exfoliated graphite.

It is then formed, rolled and often marketed as Expanded Graphite Tape.

Conventional Carbon Packing

Most suppliers would use various fibres such as cotton, flax,etc., as the core carrier material

Coating of Graphite Powder and many other additives are then added to improve its performance. This is the cheapest type.

Some use Carbon fibers of varying grades; the highest grade being PAN Carbon fibre due to its high tensile strength. It is typical to find PTFE impregnation applied to provide the carbon fibre lubricating properties.

Check the MSDS sheet to be sure of what type of Carbon fibre and additives/coatings are used in your Packing to assess the risks involved.

How is the Graphite applied on to the carrier fiber?

There are 2 conventional methods:

1)Colloidal Graphite Dispersion

A liquid suspension of graphitic carbon in either water or various organic solvents

Dispersion permit application of a uniform and fine distribution of graphite on the surface of the target material (the carrier fiber)

2)Graphite Particles with Additives and Lubricants

Graphite flakes are applied on to the carrier material

Carrier fiber is then coated with added additives; like corrosion inhibitors, lubricants and blocking agents, etc.

This is where the problem lies:

1)Conventional manufacturers do not have the technology to adhere to the graphite to the carbon fibers.

2)So they have to adopt a method to achieve that adhesion visa viz the Colloidal Graphite or the Graphite Particles Dispersion methods mentioned above.

3)All added additives and suspension fluids will eventually dry up!

4)When these additives dried up, the desired properties of the additives will be lost. The packing will dry up as additives are lost.

5)Packing will experience shrinkage of volume and then fail catastrophically.

6)The packing must be replaced at this point as it is a safety risk to personnel and plant operations.