To introduce our graphite based sealing materials, we must first know the Expandable Graphite and Expanded Graphite.
Natural graphite is available in several provinces in China. It is a kind of black powder with very low carbon content, about 5%. We purify them again and again in special process to get a purity of 98% to 99%. Then it can be used as a basic sealing material.
Since the graphite is in powder form, the first problem we must sole is: how to make it into a block or solid form. It is like when you want to make bread from flour, you must first put water into them to make it a whole piece that you can then handle. The powder form is never easy to handle.
Scientists have found that the interlayer combination of natural flake graphite is relatively lose. If we treat them with strong acid or electrochemically, the force between the layers can change and we get Expandable Graphite. The Expandable Graphite can expand 200 times when it is heated. That is like a very small scale explosion. It is also like that you make popcorn in your microwave oven. It is magic, isn’t it?
Look at the picture below, the left is Expandable Graphite and the right is Expanded Graphite.
before expansion after expansion
The Expanded Graphite can form into a paper or block or any shape without any binder. You only need to press it or calender it. This is a very good characteristic. You can make a sealing item of any shape from the expanded graphite and it is pure graphite that carries only the characteristics of graphite and nothing else.
The expanded graphite is heat resistant because it is expanded in a furnace of 1000 C.SL it is self lubricated. It can work under PH 0-14. It is a general service sealing material. It is much better than the harmful asbestos. That is why it is wide used for the sealing in valves, pumps, pressure vessel and pipelines.
Specifications of expandable graphite:
Specifications of sulfur-free expandable graphite:
In order to handle the Expanded Graphite easily, we make then into paper form through precise calendar . It is called Flexible Graphite. It is named Grafoil by Union Carbide (Ucar). With flexible graphite, you can process it into many sealing items. You can make die-formed graphite rings, gaskets, gasket sheeting and sealing tapes.
Type: flexible graphite rolls
Main properties for the flexible graphite: