Toothed belt comprising a resistant layer and resistant layer thereof
There is described a toothed belt comprising an elastomeric material body, in which a plurality of longitudinal filiform resistant inserts is embedded, and a toothing coated by a coating fabric. A resistant layer that increases the resistance to abrasion and thus the resistance to wear of the toothed belt is adhered over the coating fabric. The resistant layer comprises a vulcanization agent and more than 75% of an elastomer formed by at least one copolymer modified with an unsaturated carboxylic acid salt and obtained from a dien monomer and a nitrile group-containing monomer. The resistant layer is advantageously separated from the fabric and is calendered on the fabric itself.
1. A toothed belt comprising:
physical properties for maintaining the belt in an oil wet condition in a timing system, including a body made of a first elastomeric material formed by a mixture of one or more copolymers, obtained from a dien monomer and a nitrile group-containing monomer, and a plurality of teeth; said teeth being coated by a fabric; said fabric being covered by a resistant layer, said resistant layer totally adhering to the fabric and forming in use the working surface of the toothed belt and wherein said resistant layer comprises a vulcanisation agent and more than 85% of a second elastomeric material formed by at least one copolymer modified with an unsaturated carboxylic acid salt and obtained from a dien monomer and a nitrile group-containing monomer,
wherein said first elastomeric material has an unsaturation level lower than 1%,
wherein said second elastomeric material is formed by a mixture of one or more copolymers, obtained from a dien monomer and a nitrile-group containing monomer in which the nitrile group-containing monomers are in a percentage in the range between 33% and 49% in weight with respect to total final copolymers,
wherein said resistant layer contains no anti-friction material, and,
wherein said resistant layer consists essentially of said second elastomeric material.
2. The toothed belt according to claim 1 , wherein said second elastomeric material is HNBR or XHNBR.
3. The toothed belt according to claim 2 , wherein said HNBR has an unsaturation level lower that 1%.
4. The toothed belt according to claim 1 , wherein said unsaturated carboxylic acid salt is a zinc salt of polymethacrylate or polyacrylate acid.
5. The toothed belt according claim 1 , wherein said second elastomeric material is formed by a mixture of one or more copolymers, obtained from a dien monomer and a nitrile-group containing monomer in which the nitrile group-containing monomers are in a percentage in the range between 39 and 44% in weight.
6. The toothed belt according to claim 1 , wherein said first elastomeric material is formed by a mixture of one or more copolymers obtained from a dien monomer and a nitrile group-containing monomer in which the nitrile group-containing monomers are in a percentage in the range between 33 and 49% in weight with respect to total final copolymers.
7. The toothed belt according to claim 2 , wherein said resistant layer has a weight in the range between 50 and 80 g/m2.
8. The toothed belt according to claim 1 , wherein it comprises a peroxide as a vulcanisation agent.
9. A process for the manufacture of a toothed belt according to claim 1 , wherein said resistant layer is formed separately from said fabric.
10. The process for the manufacture of a toothed belt according to claim 9 wherein it comprises a step in which said resistant layer is calendered in a first pair of rollers.
11. The process for the manufacture of a toothed belt according to claim 10 , wherein it comprises a step in which said resistant layer is joined to said fabric in a second pair of rollers.
12. A resistant layer for covering the fabric of a toothed belt, said resistant layer totally adhering to the fabric and forming in use the working surface of the toothed belt, and wherein said resistant layer comprises a vulcanization agent and more than 85% of an elastomeric material formed by the at least one copolymer modified with an unsaturated carboxylic acid salt and obtained from dien monomer and a nitrile group-containing monomer,
wherein said elastomeric is formed by a mixture of one or more copolymers obtained from a dien monomer and a nitrile-group containing monomer in which the nitrile group-containing monomers are in a percentage in the range between 33% and 49% in weight with respect to the total final copolymers,
wherein said resistant layer contains no anti-friction material, and wherein said resistant layer consists essentially of said elastomeric material.