Thermal insulation structures comprising layers of expanded graphite particles compressed to different densities and thermal insulation elements made from these structures

Method for manufacturing a thermal insulation structure, characterised in that it comprises the following steps:

• a) making at least one “thick” sub-dense strip with a thickness of less than 40 mm, typically between 5 and 20 mm, by limiting the density obtained by compression of graphite particles to small values within the range of 0.05 g/cm3 (50 kg/m3) to 0.30 g/cm3 (300 kg/m3));
• b) making a “thin” dense strip with a thickness of less than 2 mm, typically between 0.15 and 1.5 mm, with a density within the range of 0.5 to 1.6 g/cm3 (500 to 1600 kg/m3);
• c) joining said two strips, typically by co-lamination, so as to form multilayer structures that comprise an alternation of adjacent thick sub-dense/thin dense layers, with at least two elements, said assembling being made as follows:
• c1) the said sub-dense thick strip is coated with a liquid solution rich in carbon, typically a phenolic resin, a furfuryl resin or pitch;
• c2) almost all solvents in the solution, if any, are then eliminated by slow drying;
• c3) the said dense thin strip is then added to the coated surface;
• c4) heat treatment of thus joined strips under a non-oxidising atmosphere at a temperature of not less than 800° C.

Method for manufacturing a thermal insulation element designed to be fitted on furnaces operating in a non-oxidising atmosphere and at temperatures of more than 800° C., characterised in that it comprises the following steps:

• a) a sub-dense compressed expanded graphite layer is made with a density between 0.05 and 0.3 g/cm3 (50 and 300 kg/m3) and with a thickness of less than 25 mm,
• b) the said strip is curved so that it is in the form of a portion of a cylinder,
• c) after bending, the strip is glued,
• d) a reinforcing layer made of a dense compressed expanded graphite, with a density between 0.5 an 1.6 g/cm3 (500 and 1600 kg/m3), is applied directly on one or two of the faces of the curved strip,
• e) the assembly is then heat treated while being held in shape by a graphite conforming jig surrounding the product.