Steel strand and belt reinforced with steel strand

Abstract

The utility model relates to a steel wire strand and a belt reinforced by using the same. A steel strand and a belt comprising a steel strand, the belt being particularly designed for use as an elevator belt. Such a belt is very long and must withstand multiple cycles. The utility model solves the problems that when a steel wire strand is combined into a belt, the belt cannot run well on a crown-shaped pulley, and the belt is wave-shaped after a load is removed. This problem is solved by a steel strand having a core, a first layer of steel filaments and a second layer of steel filaments, wherein the total angle spanned by the second layer of filaments with an apex at the center of the strand is less than 270 DEG. In this manner, the contact surface between the polymer and the steel strand is greatly increased compared to the prior art steel strand, resulting in better mechanical anchoring, and the adhesive force is greatly increased when using an adhesive.

Description

TECHNICAL FIELD

[0001] The present utility model relates to a steel strand and a belt reinforced by such a steel strand. The steel strand is designed to reinforce a belt used in an elevator. BACKGROUND

[0002] It was not until the turn of the century that there was an increase in the use of polymer belts in elevators for the transportation of people or goods. These 'elevator belts' offered many advantages over the traditional steel wire ropes used to drive elevators up and down the elevator shaft. Elevator belts have a predictable life span that far exceeds that of steel wire ropes. For the same strength, they are much lighter than steel wire ropes. In addition, due to the use of polymers, they offer excellent traction to the running pulleys. One of the main advantages of using belts is that they allow for smaller diameter drive pulleys compared to conventional steel wire ropes. Small diameter drive pulleys allow for compact direct drive units that can be installed at the top of the elevator shaft, eliminating the need for a rooftop machine room.

[0003] Many of the above advantages, particularly strength, predictable fatigue life, small diameter drive pulleys, are made possible by the use of cords made from high strength, fine diameter steel filaments as the strength member of the polymer. Other advantages of using steel cords compared to organic fibers (such as polyaromatic, carbon or high density polyethylene fibers) are their fire resistance and creep resistance. In particular, steel cords made from a plurality of strands twisted together (the strands themselves being composed of steel filaments twisted together) are highly preferred due to their favorable elongation properties and good anchorage into the sheath polymer. One typical construction is a 7x7 construction, which includes a primary strand around which six outer strands are twisted. The primary and outer strands are composed of a primary wire around which six sheath wires are twisted. Another construction is 19+8x7, in which the primary strand includes a primary wire around which the first six filaments are twisted, followed by the subsequent twelve filaments being twisted in a subsequent operation. Clearly, the production of such steel cords with many different steel filament diameters is complex and labor intensive.

[0004] A considerable number of attempts have been made (for a review see the applicant's WO 2019 / 002162 Al) to replace the steel cords with steel strands. Such steel strands will obviously have less filaments and therefore the steel filaments are thicker to achieve the same strength, but this is acceptable from a fatigue point of view. While the problem of core migration is fully addressed in WO 201 / 002162 Al, other problems arise in the implementation. More particularly, the higher modulus and Hookian character of the steel strands make the use of strands in the belt challenging. In particular, the elongation at low load is less than in the case of steel cords, reflecting the higher modulus of the strands. Now when using a crown pulley, the tracking of the belt is due to the elongation of the steel cords in the belt: when forced off the crown pulley, the belt bends in the plane and thereby climbs back onto the top of the crown pulley. The elongation characteristic is therefore essential to make the steel strands in the belt work.

[0005] Due to the low elongation, the behavior of the belt becomes more sensitive to small differences in the strand performance. If some strands or certain lengths in a single strand are stretched during use, the elongation can become permanent. And when the load is removed from the belt, the obtained elongation results in a non-uniform, irregularly wavy, sometimes curled belt: the belt wrinkling problem. When the used belt is taken out of the elevator, the used belt, while remaining generally flat, cannot be laid flat on a surface. After many efforts, the inventors propose now a solution to solve the belt wrinkling problem, which will be described in detail. Utility model content

[0006] The main object of the utility model is to solve the 'belt wrinkling' problem. Since the origin of the problem is related to the tensile members in the belt, a steel cord construction is also proposed to solve the problem.

[0007] According to a first aspect of the utility model, a steel strand is provided.

[0008] The steel strand comprises a core and a number 'N' of first layer steel filaments twisted around the core with a lay length and a lay direction. The first layer filaments have a diameter designated 'dl', the core has a diameter designated 'do' hereinafter.

[0009] Around the first layer, a second layer of steel filaments is provided with the same lay direction and lay length. The strand is thus an 'equal lay' strand, having a single lay length and lay direction. The second layer filaments have a second diameter designated 'd2' hereinafter. The second diameter d2 is equal to or greater than dl (d2 > dl).

[0010] When considering a perpendicular cross-section of the steel cord, each of the second layer filaments will subtend an angle, with the side of the angle being tangent to the cross-section of the filament, when considered from the center of the steel cord (also the center of the core), wherein the sum of those angles of all filaments of the second layer is less than or equal to 270°.

[0011] The sum of all angles of the apexes subtended by the second layer filaments at the center of the steel cord can also be less than 260°, or even less than 250°. In any case, the sum of the angles must be greater than 200°, otherwise the second layer will hardly increase the breaking load of the cord. The breaking load of the cord is the tension (in N) at which the cord fails catastrophically.

[0012] When the second layer of steel filaments covers less than 270° of the circle, the second layer is open by 90° and wherein the first layer filaments are present. This has a number of advantages:

[0013] - The first layer filaments are also retained by the polymer, since the first layer filaments can now come into contact with the polymer (see below).

[0014] - The steel cord is better mechanically anchored in the polymer, since the gap between the second layer filaments is very large.

[0015] - The contact surface per unit length between the steel filaments and the polymer is also increased compared to the semi-Walton cords as proposed in WO 2019 / 002162 Al.

[0016] - This results in a more adhering surface in case an adhesive is used, so the adhesion between the steel cord and the polymer is higher. Since the steel cord carries all the forces in the belt when the torque of the drive sheave or pulley interacts with the polymer, a good force transfer between the steel cord and the polymer is required. The present invention increases both the mechanical anchoring and the chemical adhesion.

[0017] - Since the second layer of steel filaments is very open, the contact pressure of the belt when running on the sheave of an elevator is also transferred to the first layer of steel. In this way, the core is better retained.

[0018] The total angle subtended by the second layer filaments is proportional to the number of filaments in the second layer, proportional to the diameter d2 of the second layer filaments, and inversely proportional to the distance of the second layer filaments to the center of the core. Furthermore, the cord lay has an influence on it, since the angle that the filaments make with the axis of the cord increases as the lay is shortened. Therefore, in the perpendicular cross-section, a circular cord will appear as an ellipse. Therefore, the side of the angle subtended by the filaments must be tangent to this ellipse.

[0019] The number of second layer filaments is equal to or greater than the number 'N' of first layer filaments, but not greater than '2N - 1'. When there are '2N' filaments, the second layer is considered'saturated', meaning that no more filaments can be added to the layer. In this case, a compact cord type cord can be obtained, which is a single twist cord, all filaments being identical. Thus, the second layer can be called 'unsaturated'.

[0020] However, in order to allow all second layer filaments to be accommodated as well as possible in a configuration with the lowest potential energy, i.e. a stable configuration, it is most preferred that the filaments of the second filament layer nest in the crevices, recesses, valleys formed by the twisted first layer filaments. This means that the number of second layer filaments is preferably 'N'. A special case of this configuration is called the Seale configuration, wherein the number of second layer filaments is equal to the number of first layer filaments, and the diameter of the second layer filaments is such that the second layer is completely closed, or in other words: the total span angle of the second layer filaments is 360° or at least very close to 360°.

[0021] The number 'N' can be equal to 5, 6, 7, 8 or 9. Particularly preferred numbers are 6, 7 and 9, because they result in a filament diameter that is small enough, while the number of filaments in the strand remains limited. The diameter of the filaments has a large influence on the fatigue life expectancy thereof. A smaller diameter sustains a smaller bending stress for the same bending diameter of the strand itself or of the belt in which the strand is incorporated.

[0022] The diameter of the second layer filaments can be equal to the diameter of the first layer filaments. Alternatively, the diameter of the second layer filaments is greater than the diameter of the first layer filaments, for example more than 5% or more than 10% or even more than 20% of the diameter of the first layer filaments. Thereby, d2 is larger than 1.05 x di, 1.10 x di or 1.20 x di. Preferably, the diameter d2 is kept smaller than 2.00 x di, or smaller than 1.75 x di, even more preferably smaller than 1.50 x di. This in turn improves the fatigue life.

[0023] The diameter of the first layer filaments is chosen in combination with the twist pitch of the strand to have at least a gap between the first layer filaments. The total angle of all gap angles measured from the center of the core, i.e. the total angular gap span, is at least 20 degrees and at most 50 degrees. The angular gap between adjacent first layer filaments does not need to be equal for all gaps, but is more preferred if it is. If the core is extended, the presence of a gap between the first layer filaments prevents the first layer filaments from blocking each other. The total angular gap should not be larger than 50 degrees, because then the manufacturing of the cord becomes difficult.

[0024] The core can be a single steel wire rod or even can be an organic fiber, like polyarylate, nylon, polyethylene or even high molecular weight polyethylene. However, these are less preferred because they result in an unacceptable increase of elongation and creep.

[0025] More preferably the core is made of twisted together steel filaments, i.e. the core itself is a steel strand. Even more preferably the core is in an equal twist construction with non-zero level helically deformed filaments, i.e. there are no straight undeformed filaments in the whole core. Instead the core comprises full steel filaments with a helical shape ('level one helical deformation'). Zero level helix or straight filaments cannot absorb compression. Therefore they wick out from the core of the steel strand under repeated loading and unloading of the steel strand during use and should therefore be avoided.

[0026] At least the core lay length is different from the strand lay length. The lay direction of the core and the strand can be the same or opposite. Preferably the core lay length is smaller than the strand lay length. Preferably the core lay length is smaller than one third, one fourth, one fifth or even one tenth of the strand lay length.

[0027] Alternatively the core lay length is smaller than ten, eight, five or even three times the diameter 'do' of the core. The core has the shortest length in the strand compared to the first layer of steel filaments and the second layer of steel filaments, the core has to be able to elastically stretch, extend, therefore the short lay length of the core is important.

[0028] The core can simply be two, three, four or five steel filaments twisted together. Most preferred is three as this forms a robust construction.

[0029] Alternatively a 12 wire half-Walton construction can be envisaged which comprises a core-core consisting of 3 filaments twisted together. 'Core-core' should be interpreted as 'core of a core strand'. In a recess formed by the filaments, 3 larger outer filaments are nested. Between each pair of the 3 larger outer filaments a pair of smaller filaments is provided. An example is given in US 4829760, which is hereby incorporated by reference in its entirety. Another equally preferred embodiment is a 9 wire half-Walton construction which comprises a core-core consisting of 3 fine wires and a sheath consisting of six wires with alternating medium and large size. Such a cord is described in US 3358435.

[0030] To impart greater elongation to the core it is helpful to use crimped steel filaments. Crimped steel wires show a bend with straight sections in between. 'Straight' means that the bend has a radius of curvature which is larger than 100 times the wire diameter. There is already a crimped steel filament which influences the elongation properties of the core. More preferably all core steel filaments are crimped.

[0031] In another preferred embodiment, the core is pre-coated with a polymer. Preferably, this polymer is the same as the polymer of the jacket of the belt. Furthermore, during the production of the steel cord, the core polymer enters the gaps between the first layer of steel filaments. The polymer forms an elastic cushion between the first layer of steel filaments. The polymer of the core also helps to prevent the movement of the first layer of steel filaments: it fixes the steel filaments in place.

[0032] In another preferred embodiment, the steel cord is coated with an organic primer that promotes adhesion between the steel filaments and the polymer.

[0033] The primer is chosen to improve adhesion to the polymer, where a reinforced cord is intended. Typical organic primers are phenol-formaldehyde resins, epoxy resins, cyanoacrylates or acrylic-based (for example the primers sold under the trade name Sikafloor®).

[0034] However, these coatings are relatively thick (more than 1 micron) and can require a considerable processing time. Therefore, a nanoscale organic coating is preferred, chosen from the group comprising or consisting of organofunctional silanes, organofunctional zirconates and organofunctional titanates. Preferably, but not exclusively, the organofunctional silane primer is chosen from the group of compounds of the following molecular formula:

[0035] Y-(CH2) n -SiX3

[0036] wherein:

[0037] Y represents an organic functional group chosen from -NH2, CH2=CH-, CH2=C(CH3)COO-, 2,3-epoxypropoxy, HS- and CI-;

[0038] X represents a silicon functional group chosen from -OR, -OC(=0)R', -CI, wherein R and R' are independently chosen from C1 to C4 alkyl, preferably -CH3 and -C2H5; and

[0039] n is an integer between 0 and 10, preferably 0 to 10, most preferably 0 to 3.

[0040] The organofunctional silanes described above are commercially available products. These primers are particularly suitable to obtain adhesion to polyurethane. The thickness of the organic coating is less than 1 micron, preferably less than 500 nanometers, for example between 5 nm and 200 nm. Thin coatings of this size are preferred because thin coatings conform in a conformal manner to the outer surface of the reinforced cord and, due to their thinness, do not hinder the polymer from filling in the valleys between the outer filaments. This is important in the case of the cord of the present invention, because the outer surface of the steel cord exhibits a very curved surface.

[0041] For all embodiments of the present utility model, whether preferred or not, whether substituted or added, the following are valid:

[0042] Whenever in this application reference is made to'steel filaments', it is meant to steel wire material of substantially circular shape with a diameter between 0.02 mm and 0.40 mm, more preferably between 0.04 mm and 0.35 mm or between 0.10 mm and 0.30 mm. The high tensile strength of these filaments, i.e. the breaking load of the filaments (in N) divided by their cross-sectional area (in mm 2 ), is higher than 2000 N / mm 2 , preferably higher than 2350 N / mm 2 , for example higher than 2700 N / mm 2 . At present, the upper limit of the tensile strength is 4000 N / mm 2 , while the upper limit of the tensile strength of ordinary carbon steel (see below).

[0043] By'steel' is meant any type of steel. Preferably, ordinary carbon steel is used. Such steel typically comprises a minimum carbon content of 0.40 wt% C or at least 0.70 wt% C, but most preferably at least 0.80 wt% C, a maximum of 1.1 wt% C, a manganese content ranging from 0.10 wt% to 0.90 wt% Mn, and the sulphur and phosphorus content is each preferably kept below 0.03 wt%; additional micro-alloying elements such as chromium (up to 0.2 wt% - 0.4 wt%), boron, cobalt, nickel, vanadium (non-exhaustive) can also be added. Such carbon steel filaments can be produced at strengths above 2000 MPa, preferably above 2700 MPa, while now strengths above 3000 MPa are common and a move towards strengths above 3500 MPa is being made. Stainless steel is also preferred. Stainless steel contains a minimum of 12 wt% Cr and a significant amount of nickel. More preferred is austenitic stainless steel, which is itself more suitable for cold forming. The most preferred compositions are known in the art as AISI (American Iron and Steel Institute) 302, AISI 301, AISI 304 and AISI 316 or as duplex stainless steel under EN 1.4462.

[0044] Preferably, the steel filaments have a metallic or metal alloy coating. Such an alloy can be used to impart corrosion protection to the steel or to adhere the filaments to the polymer or a combination of both: corrosion protection and adhesion. A corrosion resistant coating is for example zinc or a zinc-aluminium alloy. Most preferred is a low-zinc hot dip coating as described in EP 1280958. The thickness of such a zinc coating is below 2 microns, preferably below 1 micron, for example 0.5 microns. An alloy layer zinc-iron is present between the zinc coating and the steel.

[0045] When steel cords are used to reinforce rubber, other preferred metal adhesion coatings are for example brass coatings (copper-zinc alloys). So-called 'ternary brasses' can also be used, such as copper-zinc-nickel (e.g. 64% by weight / 35.5 wt.% / 0.5 wt.%) and copper-zinc-cobalt (e.g. 64 wt.% / 35.7 wt.% / 0.3 wt.%), or copper-free adhesion systems, such as zinc-nickel or zinc-cobalt.

[0046] According to a second aspect of the application, a belt is provided.

[0047] The belt comprises a polymeric jacket and a plurality of steel cords, which are oriented along the length dimension of the belt and held in parallel relationship by the polymeric jacket. For the purposes of this application, 'parallel relationship' means that the steel cords are arranged within a single surface, such as a planar surface.

[0048] The belt differs from prior art belts in that the steel cords are steel cords according to the first aspect of the application. By using such steel cords, the polymer fills the openings between the second layer of filaments up to the first layer of filaments.

[0049] In order to quantify the degree of contact surface per unit length of steel cord and polymer, this can be compared to the surface of an imaginary cylinder surrounding the steel cord. In a perpendicular cross-section, a smallest circumscribed circle with diameter 'D' can be identified. This circle thus has a circumference of 'πD', π being the Archimedes constant. The surface of the imaginary cylinder is thus 'πD' times the length of the cylinder.

[0050] In the same perpendicular cross-section, a contact profile or contact curve is identified, in which the polymer contacts the filaments of the first layer of filaments and the filaments of the second layer of filaments. The total length along this curved interface is referred to as 'C'. In the belt of the application, the length 'C' of the contact profile is greater than 1.5 times the circumference 'πD' of the circumscribed circle. The ratio C / πD can even be greater than 1.6 or 1.7 or even 1.8.

[0051] This means that the contact area between the polymer and the steel cords of the belt is at least 50%, or 60% or 70%, or even 80% greater than the contact area of a smooth cylindrical surface of the same diameter. The adhering surface is thus also much greater, so that the total adhesion of the steel cords to the polymer is greatly increased.

[0052] The polymeric jacket encloses, surrounds, holds the steel cords in place. The actually usable polymers are thermosetting polymers (such as rubbers) and thermoplastic polymers, the latter being preferred because they are easy to process and enable easy modification of the mechanical properties of the polymer. The most preferred thermoplastic materials are thermoplastic polyurethanes (TPU) and thermoplastic polyolefins (TPO).

[0053] TPUs derived from polyether polyols are well resistant to hydrolysis but have low mechanical properties. TPU derived from polyester polyols have better mechanical properties but are less resistant to hydrolysis. TPU derived from polycarbonate have intermediate resistance to hydrolysis and mechanical properties. Most preferred are TPU based on polyether polyols and TPU based on polycarbonate polyols. BRIEF DESCRIPTION OF DRAWINGS

[0054] Figure 1 A first embodiment of a belt according to the present utility model is shown.

[0055] Figure 2 A first embodiment of a steel cord according to the present utility model is shown.

[0056] Figure 3 A second embodiment of a belt according to the present utility model is shown.

[0057] In the reference numerals, the hundreds digit refers to the figure number, while the units and tens digits refer to the equivalent feature in the figure. DETAILED DESCRIPTION

[0058] Figure 1 A first embodiment of a belt 100 according to the present utility model is shown. The belt comprises steel cords 102 arranged in parallel. Typically, 5 to 15 steel cords can be arranged in a single belt like this, but usually 8 to 10 are sufficient to impart sufficient strength to the belt. The sheath 110 is a polycarbonate polyol based polyurethane. Also shown in the steel cord 102 are the core 108, the first layer filaments 106 and the second layer filaments 104.

[0059] Figure 2 A detailed view of the steel cord 102 of Figure 1 is shown. The steel cord 202 comprises a core 208 made of three filaments of diameter 0.28 mm twisted together in the S direction with a lay of 5.1 mm. The lay of the core is just short of 10 times the 0.60 mm core diameter. This is the core diameter 'do'. The core is covered with PU 216 of diameter up to 0.70 mm. Subsequently, 9 first layer filaments 206 and 9 second layer filaments 204 are added to the core in a single operation in the S direction with a lay of 14 mm. The diameter dl of the first layer filaments 206 is 0.31 mm and the diameter d2 of the second layer filaments 204 is 0.33 mm. The total gap angle in the first layer is then 38.3°. In a subsequent operation, an organo-functional silane adhesive is applied and during drying, the polyurethane of the core melts into the gap shown at 214. Thus, the polyurethane fills the gap between the first layer filaments.

[0060] The angle indicated as 'a' has its apex at the center of the core and the sides are tangent to the second layer filaments. By multiplying by N (in this case 9), a total angle of 243° is obtained, which is less than 270°.

[0061] In practice, the sum of the angles spanned by the filaments in the second layer of the strand can be determined by forming a vertical cross-section of the steel wire strand, for example by casting in epoxy, followed by vertical sawing and polishing; determining the center of the core, which is also the center of the strand; and then analyzing the cross-section with an optical microscope (for example Zeiss Axio Imager.A1m), preferably done with an image processing program such as ImageJ (available from the Optical and Computational Instrumentation Lab at the University of Wisconsin).

[0062] Subsequently, a belt is produced having 12 cords arranged parallel to each other. Figure 2 The belt is made by techniques known in the art, for example by extruding the parallel arranged steel wire strands through a single extruder head or by laminating the parallel unwound steel wire strands between two sheets, the former method being more preferred than the latter.

[0063] On a vertical cross-section of the belt, the profile length and diameter 'D' of the cords can also be measured. Due to the wide gaps between the second layer steel wire filaments, polyurethane easily flows in between the gaps. The total profile length 'C' measured is about 10.2 mm, while the diameter 'D' of the steel wire strand is 1.75 mm. Hence, the ratio of the profile length to the circumference 'πD' of 5.50 mm is 1.86. It is noted that for a Seale strand with N = 9, this ratio is 1.40, because in a Seale strand the second layer filaments are close to each other.

[0064] Figure 1 The belt of the 12 cords is tested in a test elevator installation for 40-600 cycles. The trajectory on the crown pulley is observed, which is found to be in line with the belt using a 7x7 multifilament belt. After the test, the load is removed from the belt and no wrinkling is observed. After removing the belt and spreading it out along the length on a clean floor, the belt remains completely straight without any curbing effect and is flat on the floor.

[0065] Figure 3Another embodiment of belt 300 is shown having strands 302 where the core 308 is made by a semi-Walton process where three core-core filaments of 0.18 mm are surrounded by three sets of filaments (0.15 | 0.22 | 0.15) resulting in a total core diameter of 0.70 mm. The core is not extruded. The diameter of the first layer of filaments 306 and the diameter of the second layer of filaments 304 are set equal to 0.31 mm. The total angle spanned by the second layer of filaments is 243° which is lower than 270°. The circumscribed circle is represented by 312 and has a diameter of 1.77 mm and a circumference of 5.56 mm. The contact profile is represented by 314 and has a length of 9.74 mm. The ratio C / πD is 1.75.

[0066] Figure 3 Belt 300 is currently under testing.

Claims

1. A steel strand comprising a core and a number 'N' of first layer steel filaments twisted around the core in a first layer with a strand lay and a strand lay direction, the first layer steel filaments having a first diameter 'dl', the core having a core diameter 'do', characterized in that around the first layer, a second layer of steel filaments is provided with the same lay direction and lay length, the second layer steel filaments having a second diameter 'd2', the second diameter 'd2' being greater than or equal to 'dl', the second layer steel filaments spanning a total angle of less than or equal to 270 degrees measured from the center of the steel strand in a perpendicular cross section of the steel strand.

2. The steel strand of claim 1, wherein, The number of the second layer steel filaments is equal to or greater than the number 'N' and less than '2N-1'.

3. Steel strand according to claim 1 or 2, characterized in that, The number N is equal to 5, 6, 7, 8 or 9.

4. Steel strand according to any one of claims 1 to 3, characterized in that, There is a gap between the first layer steel filaments, the gap having a total angular gap span of at least 20 degrees and at most 50 degrees.

5. Steel strand according to any one of claims 1 to 4, characterized in that, The core is a equal lay strand comprising core steel filaments, the core steel filaments being free of zero level spiral deformation and twisted together with a core lay length different from the strand lay length.

6. The steel strand of claim 5, wherein, The core lay length is shorter than one third of the strand lay length.

7. Steel strand according to any of claims 1 to 6, characterized in that, The core comprises two, three, four or five core steel filaments twisted together.

8. Steel strand according to any of claims 1 to 6, characterized in that, The core comprises 9 to 12 core steel filaments, the core steel filaments being arranged in a semi-Warrington arrangement.

9. Steel strand according to any of claims 5 to 8, characterized in that, At least one core steel filament is crimped, the crimped steel filament comprising a bend with a segment therebetween.

10. The steel strand of claim 4, wherein, The core is coated with a polymer, the polymer being present in the gap between the first layer steel filaments.

11. Steel strand according to any of claims 1 to 10, characterized in that, The steel strand is coated with an organic primer promoting adhesion to a polymer.

12. A belt comprising a polymer jacket and a plurality of steel wire strands, the wire strands being oriented along the length dimension of the belt and held in parallel relationship by the polymer jacket, characterized in that, The steel strand is according to any one of claims 1 to 11 and the polymer fills the openings between the second layer steel filaments up to the first layer steel filaments.

13. The belt of claim 12, wherein, The steel strand has a minimum circumscribed circle with a diameter D and a circumference of πD in a perpendicular cross section, the steel strand having a contact profile where a polymer contacts a filament of the first layer steel filaments or a filament of the second layer steel filaments, the contact profile having a length 'C', the length 'C' being greater than 1.5 times the circumference πD.

Images