Formation of felts with an isotropic structure

Claim 2

Process for continuously forming felts made of fibres of a glass material in which the felt is formed by depositing on a reception unit of fibres conveyed by a gaseous stream, the reception unit being permeable to the gases and retaining the fibres, a binder composition being applied on the fibres in their movement towards the reception unit, the felt formed in this way between its formation on the reception unit and its heat treatment and where applicable after compress- sion over its thickness being subjected to a longitudinal compression and then heat treated to interlace the composition of the binder and fix the structure of the felt, characterised in that the felt is subjected to at least two longitudinal compression operations, the ratio of which, i. e. the ratio of the mass of fibres per unit of surface area after and before the compressions is limited to a value of less than that at which folds would be formed which would affect the faces of the felt.

Claim 3

Process according to claim 1, characterised in that the longitudinal compression ratio for all the longitudinal compression operations is less than 15.

Claim 4

Process according to claim 2 in which the compression ratio for each compression operation taken in isolation is not greater than 10.

Claim 5

Process according to any one of the previous claims characterised in that the treated felt before longitudinal compression has a density of more than 10 kg/ m 3.

Claim 6

Process according to any one of the previous claims, characterised in that the treated felt before longitudinal compression has a density which is not greater than 60 kg/m 3 .

Claim 7

Process according to claim 4 or 5, characterised in that the felt before longitudinal compression has a mass per unit of surface area which is not less than 0.75 kg/m 2 .

Claim 8

Process according to one of the previous claims, characterised in that it comprises two successive longitudinal compression operations, whereby the compression ratios for these two operations are substantially identical.

Claim 9

Process according to claim 7 in which for a felt the fibres of which have a mean diameter of more than 10 micrometres the longitudinal compression ratio is held at less than 5 for each operation.

Claim 10

Process according to one of the previous claims, characterised in that after the longitudinal compression operations a compression over the thickness is carried out before heat treatment to bring the felt to a density of between 30 and 200 kg/ m3 .

Claim 11

Device for the continuous formation of felts made of fibres of a glass material according to any one of the previous claims, in which the fibres carried by a gaseous stream are arranged on a reception conveyor (4) which is permeable to the gases, whereby this device comprises two pairs of conveyors (7, 8 and 9, 10) in the extension of the conveyor (4) and these conveyors are operated at different speeds to ensure a longitudinal compression of the felt whilst the device also includes an oven (13) for the heat treatment of the compressed felt, characterised in that it includes at least three pairs of conveyors (7, 8, 9, 10, 11, 12) between the zone for the formation of the felt and that of the heat treatment located in the extension of each other, whereby the felt passes between the conveyors of each of the pairs, the distance separating the two conveyors of the same pair is adjusted so as to maintain the felt on its two faces and the speed of the pairs of successive conveyors is adjusted so that with the changeover from one pair of conveyors to the following one the speed of the felt is reduced.

Claim 12

Device according to claim 10 including three pairs of conveyors, whereby the first pair (7, 8) effects simultaneously a compression of the felt over its thickness.

Claim 13

Device according to claim 11 in which the second pair of conveyors (9, 10) also effects a compression of the felt over its thickness.

Claim 14

Device according to one of claims 10 to 12 on which slides (26, 27) are arranged in the extension of the last pair of conveyors (11, 12) to keep the felt compressed when it enters the oven (13) for heat treatment.