Belt reinforced with steel strands
A belt for use as for example an elevator belt, flat belt, synchronous belt or toothed belt comprises steel strands held in parallel by a polymer jacket. The steel strands have a diameter ‘D’ and are separated by a pitch ‘p’. The ratio of diameter ‘D’ over pitch ‘p’ is larger than 0.55. Such belt arrangement prevents the cutting of the polymer jacket between strand and pulley and abates the noise generation during use. The belts are best built with a type of parallel lay strands particularly designed for use in a belt. These strands do not show core migration during use of the belt.
1. A belt comprising a plurality of steel strands and a polymer jacket, said belt having a length dimension, a width dimension and a thickness dimension, said steel strands having steel strand centres, said steel strands being oriented along the length dimension and held in parallel relationship by said polymer jacket, wherein said steel strand centres are aligned in the width dimension and wherein neighbouring steel strand centres are separated by a pitch,
wherein said steel strands have an equal steel strand diameter, wherein the ratio of said steel strand diameter to said pitch is larger than 0.55,
wherein each one of said steel strands comprises a core having a core diameter and each one of said steel strands comprises steel filaments, said steel filaments being organised in
an intermediate layer comprising N first steel filaments circumferentially arranged around said core, said first steel filaments having a first diameter, said core diameter and said first diameter being such that a gap forms between said first steel filaments, and
an outer layer comprising 2N steel filaments circumferentially arranged around said intermediate layer,
wherein said steel filaments of said intermediate layer and said steel filaments of said outer layer are twisted around said core with the same final lay length and direction and wherein said final lay length is larger than two times and smaller than six times the closing lay length, said closing lay length being that lay length at which a gap between said first steel filaments of the intermediate layer is closed.
2. The belt according to claim 1 wherein said steel strands are provided with an organic primer that promotes adhesion between the steel strands and the polymer of said polymer jacket.
3. The belt according to claim 2 wherein said organic primer is selected from the group consisting of organo functional silanes, organo functional zirconates, and organo functional titanates.
4. The belt according to claim 2 wherein said steel strands adhere to said polymer jacket with an adhesion axial force per unit length in newton per millimetre that is at least 20 times the steel strand diameter in mm.
5. The belt according to claim 1 wherein there is no gap between the steel filaments of the outer layer of each one of said steel strands.
6. The belt according to claim 1 wherein said outer layer of each one of said steel strands comprises
N second steel filaments of a second diameter, said N second steel filaments being tangent to a second circumscribing circle having a second radius and
N third steel filaments of a third diameter, said N third steel filaments being tangent to a third circumscribing circle having a third radius
said second diameter being larger than said third diameter, said second steel filaments and said third filaments occupy alternating positions in said outer layer, and wherein the second radius is different from the third radius.
7. The belt according to claim 6 wherein the second radius of each one of the steel strands is larger than the third radius.
8. The belt according to claim 1 wherein in each one of said steel strands the number N is equal to 5, 6, 7, 8 or 9.
9. The belt according to claim 1 wherein said core of each one of said steel strands is a single steel filament comprising bends with straight segments in between.
10. The belt according to claim 1 wherein said core of each one of said steel strands is an equal lay strand of core steel filaments free from zero order helical deformations and twisted together with a core lay length different from the final lay length of each of said steel strands.
11. The belt according to claim 10 wherein the number of said core steel filaments is two or three or four and said core steel filaments have an equal diameter.
12. The belt according to claim 10 wherein the number of said core steel filaments is nine or twelve and wherein said core steel filaments are arranged in a semi-Warrington construction.
13. The belt according to claim 1 wherein the core of each one of said steel strands is a strand comprising a core-core and 5, 6 or 7 core outer steel filaments twisted around said core-core with a core lay length different from the final lay length in each of said steel strands.
14. The belt according to claim 1 wherein said steel filaments of each one of said steel strands are provided with a metallic coating or metallic coating alloy.