Several different types of conveyor belts constructed of several plies and/or layers are known to the art.
A common feature of these known conveyor belts is that respective plies and/or layers are normally comprised of rubber or a like flexible/pliable material, and that the plies and layers are firmly bonded to one another, preferably integral with one another.
Thus, it can be mentioned that Patent Publication SD-A1-1 694 443 teaches a conveyor belt which comprises a central flexible ply (3) which is reinforced longitudinally with two outer rubber protectors (1) which are mutually separated with the aid of an intermediate ply provided with cord reinforcements (2).
It is proposed in this publication that the centre ply shall be thicker than the remaining plies.
The European Patent Specification 0 142 716 teaches a conveyor belt that comprises different materials in different plies. The belt is comprised of an uppermost supportive ply 12 which shall have a hardness of 85.degree.-100.degree. Shore A, a second ply 9 which shall have a hardness of 50.degree.-70.degree. Shore A, and a third ply 10 which shall have a hardness of 20.degree.-50.degree. Shore A.
The plies are thus arranged so that the ply that has the highest degree of hardness is located uppermost in the belt and the ply that has the lowest degree of hardness is located lowermost therein.
Japanese Patent Publication JP-63-47 214 teaches an elastic conveyor belt 1 which is comprised of a central rubber material 2 functioning as an elastic element, and outer layers 3 which function as reinforcing surfaces.
U.S. Pat. No. 2,875,116 also teaches a multiply conveyor belt which is adapted for use in electronic heating apparatus.
The U.S. Pat. No. 2,121,650 also teaches a multi-ply conveyor belt whose upper load-carrying surface is in the form of a rubber ply 7 and a plurality of load-absorbing plies 8.
A plurality of such plies are shown together with a ply 10 which represents the rubber ply that is intended to face towards the support rollers in an endless conveyor path.
With regard to the application to which the invention especially refers, it is known to use a conveyor system of the kind illustrated schematically in FIG. 1 that has an endless conveyor belt with a cross-section according to the embodiment illustrated in FIG. 2 or FIG. 3.
It can be mentioned here that the conveyor belt comprises an homogenous material having a hardness of about 65.degree. Shore A.
The belt has a thickness of up to 20 mm and a width of 400 to 500 mm.
The load-absorbing ply of integrated fabric structure is located slightly beneath a centre line of the belt cross-section.
Other examples of earlier known conveyor belt constructions are found in Patent Publications DE-A1-4 113 627, Derwents Abstract 92-355870/43, Derwents Abstract 87-169084/24 and Patent Abstract of Japan, Vol. 15, No. 53 (M-1079).