Expandable Graphite Mould
expandable graphite mould are mainly used for sealing purposes in the petrochemical, machinery, metallurgy and atomic industries. Compared to traditional sealing materials, expandable graphite is more resistant to extreme conditions such as high temperature, low pressure and corrosive media. However, the expansion ratio of expandable graphite is not constant. It varies according to the treatment type, particle size and various other factors.
The expansion of expandable graphite is accompanied by exfoliation which leads to an increase in the surface area of each flake. The increase in surface area is proportional to the expansion ratio. Consequently, large flakes exhibit greater expansion ratios than smaller ones.
To achieve a more constant expansion of the graphite, it is possible to mix the material before its pre-expansion with additives and/or acid phosphates, in order to achieve a desired expansion level. The expanded mixture is then inserted into the mould, which is closed but permeable to the gases, air and steam that are released during expansion.
The mould is preferably made from ceramics or metals, and can be protected, to prevent caking, with customary release agent formulations, for example those based on graphite, talc and carbohydrates. The walls of the mould can be lined, to limit contamination by volatiles, with paper, woven fabrics, varnish coatings or metallic foils. The lining can also be coated with an oxide layer to prevent corrosion of the expandable graphite mould. In addition, the mould may be filled with additional binders to improve its performance in certain applications.
