Belt reinforced with steel strands

Abstract

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.

Claims

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.

Description

BRIEF DESCRIPTION OF FIGURES IN THE DRAWINGS

(1) FIG. 1 shows a cross section of the inventive elevator belt with the steel strands.

(2) FIG. 2 shows the cross section of a preferred steel strand of the type 3+6+6|6 at final lay length that is particularly preferred to reinforce the inventive belt;

(3) FIG. 3 shows the cross section of an alternative embodiment of the steel strand of the type 3+7+7|7 at final lay length that is particularly preferred to reinforce the inventive belt;

(4) FIG. 4 shows the cross section of another alternative embodiment of the steel strand of the type (1+6)+7+7|7 that is particularly preferred to reinforce the inventive belt.

(5) FIG. 5 shows a cross of an embodiment of a steel strand wherein the core is of an equal lay construction.

(6) In the figures like elements over various embodiments carry the same unit and tens digit. The hundred digit refers to the number of the figure.

MODE(S) FOR CARRYING OUT THE INVENTION

(7) When reducing the invention to practice account has to be taken of the following limitations: The arrangement of the steel strands in the belt is to be determined on a perpendicular cross section of the belt, perpendicular meaning perpendicular to the length dimension of the belt; The arrangement of the filaments is determined on a cross section of the belt. A ‘construction’ of a steel cord comprising steel filaments is solely determined by the filament diameters, lay lengths and how the filaments are arranged in a cross section; The diameter of steel filaments can be measured up to the micrometer (μm). The diameter of a round filament is the average of the largest and smallest calliper diameter. Filaments whereof the difference between the largest and the smallest calliper diameter is below 7 μm are considered ‘round’; The tolerance on the diameters of the steel filaments is set to −4 to +4 micrometer (μm) from the nominal diameter. Hence, two filaments that show a difference in diameter that is smaller 8 μm (8 μm not included) will be treated as having the same diameter; The tolerance on lay lengths is between −5% to +5% of the nominal value. Lay length is determined as per the ‘Internationally agreed methods for testing steel tyre cord’, Chapter E4 ‘Determination of Length and Direction of Lay’ as published by BISFA, “The International Bureau for the Standardisation of Man-made Fibres”. The closing lay length is calculated as per the formula {1} based on the measured diameters of the core and the diameter and number of intermediate layer filaments.

(8) FIG. 1 shows a perpendicular cross section of the inventive belt 100 showing the main features of the belt. The thickness ‘t’ is the smallest dimension of the belt. Perpendicular to the thickness T and the length dimension is the width ‘W’ of the belt. A number of steel strands 104—in this case 10—are embedded in a polymer jacket 102. The steel strands have an indicated diameter ‘D’ and the centres of the steel strands are separated by a pitch ‘p’. The lens 106 shows the steel strand dW21 as further explained in FIG. 2.

(9) Such a belt is made by the techniques known in the art such as extrusion of parallel arranged steel strands through a single extrusion head or by laminating parallel unwound steel strands in between two sheets, the former method being more preferred over the latter method.

(10) FIG. 2 shows a steel strand 200 (‘dW21’) particularly suited for use in the inventive belt. It has a core 203 that comprises three filaments 202 of size 120 μm diameter twisted together at a lay of 3.8 mm in Z direction. The core 203 has thus a diameter ‘do’ of 259 μm. The intermediate layer steel filaments 204 have a first diameter of 210 μm. The number N has been set to 6. The intermediate layer is surrounded by an outer layer consisting of 12 steel filaments: 6 second steel filaments 206 and 6 third steel filaments 208. The second diameter is 223 μm. The third diameter is 170 μm. The first radius 205 is 130 μm. The second radius 212 is 500 μm, the third radius 210 is 510 μm. The first, second and third radius can be calculated by simple trigonometry from the measured filament sizes and/or from a cross section. The gap between the filaments of the outer layer at final lay length is 11 μm. The diameter of the strand is 1.02 mm.

(11) It follows from formula {1} that the closing lay length CL is 2.56 mm. At this lay length the gap between the intermediate filaments is closed. The final lay length with which core, intermediate layer filaments and outer layer filaments are twisted together in the final product is 10 mm. Hence the final lay length is between 2×CL i.e. 5.12 mm and 6×CL i.e. 15.36 mm.

(12) This reinforcement strand turned out to be a large improvement to the multi strand cord 7×3×0.15 that is well known to reinforce synchronous belts. The latter is composed of 7 strands twisted together at a lay of 8 mm in S (alternatively Z) direction of which each strand consists of three filaments twisted together a 9 mm in Z direction (alternatively S). Note that both dW21 and 7×3×0.15 have the same number of filaments.

(13) Table 1 shows a comparison of the main parameters of both:

(14) TABLE-US-00001 TABLE 1 Parameter dW21 7 × 3 × 0.15 Diameter (mm) 1.02 0.91 Actual breaking load (N) 1750 950 Metallic cross section (mm.sup.2) 0.59 0.37 Fill factor (%) 72 57 Axial stiffness between 2 to 10% 978 563 of MBL (N/%) Modulus in linear region (N/mm.sup.2) 187000 175000

(15) With ‘MBL’ is meant the ‘Minimum Breaking Load’. This is the lowest breaking load that can be expected based on 6-sigma statistical variations. For the purpose of this application it is set to 7% lower than the actual breaking load.

(16) With ‘Axial stiffness between 2 to 10% of MBL’ (EA) is meant the ratio of load difference ΔF between 2 to 10% of the MBL (in N) divided by Δε the difference in elongation (in %) between these points. It is an important measure for the elongation in the working region of the reinforcement strand. In formula: ΔF=(EA)Δε.

(17) The ‘modulus in the linear region’ is taken in a region of the load elongation curve that is linear e.g. in a region above 10% of the MBL.

(18) When used in a belt such as an elevator belt or a synchronous belt the reinforcement strand according the invention shows the following advantageous features: The strength per diameter is much higher, implying that for the same pitch of reinforcement cords in the belt, a much higher strength can be obtained! Indeed, the strength of the dW21 is almost the double compared to that of 7×3×0.15. This is due to the line contacts in the reinforcement strand rather than the point contacts in the multi strand cords. This also opens the possibility to use higher tensile strength filaments. In the working region of the belt the axial stiffness is larger in the reinforcement strand compared to that of the multi strand cord. This is an important improvement in that the belt will elongate less for the same number of cords.

(19) Much to the surprise of the inventors, the reinforcement strand did not show any core migration in extended tests in belts. Indeed, prior trials with belts comprising true Warrington strands in belts inevitably showed core migration.

(20) The inventors attribute this to two major features: The use of a core existing out of a 3×1 strand. The helical shape of the filaments accepts more compression than a single straight filament; The presence of gaps in the intermediate layer allows the steel filaments present therein to take slightly different positions thereby absorbing compression without wicking out.

(21) A particular comparison of a belt with a width ‘W’ of 25 mm and a thickness ‘t’ of 5 mm with the inventive cord and the prior art cord can be found in Table 2:

(22) TABLE-US-00002 TABLE 2 dW21 7 × 3 × 0.15 Reinforcement (invention) (prior art) Belt width (in mm) 25 25 Number of cords (number) 16 16 Pitch ‘p’ (in mm) 1.56 1.56 Diameter cord ‘D’ (in mm) 1.02 0.91 D/p (ratio) 0.65 0.58 Breaking load belt (in N) 28000 15200 Steel mass per area (kg/m.sup.2) 2.97 1.86

(23) By using the inventive strand the breaking load of the belt increases with 84% while the steel mass per unit area only increases with 60%. The axial stiffness of the belt in the working region also increases due to the use of the inventive strand in combination with the increased steel mass.

(24) Although the reinforcement strand dW21 does have some surface roughness due to the different second and third radii this surface roughness is much less than that of for example a 7×7 type of cord. While for a 7×7 cord the use of an adhesive is not absolutely necessary, it does turn out to be beneficial to use an organic primer to promote the adhesion between the reinforcement strand according the invention and the polymer jacket. For the described case an organo functional silane was used. It took 650 N to pull out a length of 12.5 mm of steel strand dW21 out of the belt. The adhesion force per unit length is thus 52 N/mm that is larger than 30 times the diameter of the reinforcement strand i.e. 39 N per mm of embedded strand.

(25) FIG. 3 shows another implementation ‘dW24’ of the steel strand 300 with N equal to 7. It is described by the following formula (brackets denote different twisting steps, numbers represent diameters of filaments in millimetre; subindices indicate laylength in mm and lay direction):
[(3×0.18).sub.5.6s+7×0.26+7×0.285|0.18].sub.15s

(26) The core 303 is a 3×1 strand of three 0.18 filaments 302 twisted together at lay 5.6 mm in ‘s’ direction. Around the core 303 an intermediate layer of 7 steel filaments 304 with first diameter 0.260 mm is present. In the outer layer 0.285 mm filaments 306 alternate with 0.18 mm filaments 308. The mirror image is equally well possible (all lay directions reversed).

(27) The important geometrical features are identified in the Table 3 below:

(28) TABLE-US-00003 TABLE 3 Core 303 diameter ‘d.sub.0’ (μm) 388 First diameter ‘d.sub.1’ 304 (μm) 260 N 7 Closing lay length CL (mm) 4.46 2 × CL 8.92 4 × CL 17.84 Final lay length FL (mm) 15 First radius 305 (μm) 454 Second radius 312 (μm) 634 Third radius 310 (μm) 656 Relative difference Second to Third radius (%) 3.3 Gap between filaments of outer layer (μm) 1

(29) The mechanical properties of this reinforcement strand are compared to that of a 7×7 construction of diameter 1.6 mm that is very popular to reinforce elevator belts (See U.S. Pat. No. 6,739,433): Table 4.

(30) TABLE-US-00004 TABLE 4 Parameter dW24 7 × 7/1.6 Diameter (mm) 1.30 1.61 Actual breaking load (N) 3054 3200 Metallic cross section (mm.sup.2) 1.07 1.30 Fill factor (%) 76 64 Axial stiffness between 2 to 10% 1624 1250 of MBL (N/%)

(31) Although the 7×7/1.6 has a larger diameter, the axial stiffness in the working region (2 to 10% of MBL) is lower than for the inventive reinforcement strand. The cord is in test and does not show core migration.

(32) FIG. 4, Table 5 illustrates still another steel strand dW34 that can be used in the inventive belt of the following make:
[(0.24+6×0.23).sub.7.2z+9×0.33+9×0.30|0.21].sub.16.8z

(33) The formula should be read in the same way as with the previous example. The mirror image (all in ‘s’ direction) will have equal properties.

(34) TABLE-US-00005 TABLE 5 Core 403 diameter ‘d.sub.0’ (μm) 700 First diameter 404 ‘d.sub.1’ (μm) 330 N 9 Closing lay length CL (mm) 8.14 2 × CL 16.3 4 × CL 32.6 Final lay length FL (mm) 16.8 First radius 405 (μm) 680 Second radius (μm) 412 901 Third radius (μm) 410 890 Relative difference Second to Third radius (%) 1.2 Gap between filaments of outer layer (μm) 4

(35) A comparison of mechanical data to 7×7 of equal diameter 1.8 mm is shown in Table 6:

(36) TABLE-US-00006 TABLE 6 Parameter dW34 (inv) 7 × 7/1.8 (pa) Diameter (mm) 1.80 1.80 Actual breaking load (N) 5900 3965 Metallic cross section (mm.sup.2) 2.01 1.54 Fill factor (%) 79 61 Axial stiffness between 2 to 10% 2734 1570 of MBL (N/%)

(37) For the same diameter of 1.80 mm a much higher breaking load is obtained. Also the axial stiffness in the working region of between 2 to 10% of the MBL is much higher. This results in an axially stiffer behavior in the region where the reinforcement is used i.e. in the working region of a belt.

(38) Table 7 shows the comparison of two elevator belts reinforced with dW34 strand (dW34 (1) and dW34 (2)), compared to the commonly used 7×7/1.8 prior art (‘pa’) multistrand cord.

(39) TABLE-US-00007 TABLE 7 Reinforcement dW34 (1) dW34 (2) 7 × 7/1.8 (pa) Belt width (in mm) 30 30 30 Number of cords (number) 10 12 10 Pitch ‘p’ (in mm) 3.0 2.5 3.0 Diameter cord ‘D’ (in mm) 1.8 1.8 1.8 D/p (ratio) 0.60 0.72 0.60 Breaking load belt (in N) 59000 70800 39650 Steel mass per area (kg/m.sup.2) 5.26 6.31 4.03

(40) The first version of the inventive belt dW34 (1) is geometrically identical to the prior art belt 7×7×/1.8 (pa). The use of the dW34 reinforcement strands immediately results in an increase of belt breaking load of 49%, with only an increase in areal steel mass in the belt of 30%. The increased steel mass contributes to a higher axial stiffness in the working region.

(41) When decreasing the pitch between strands—by going from 10 to 12 strands—the D/p ratio rises above 0.72: see column dW34 (2). The breaking load of the belt is then 79% higher than that of the prior art with only an increase in steel mass of 57%.

(42) In order to reach the same belt breaking load of 70.8 kN with the prior art 7×7/1.8 construction, one would need an impossible D/p ratio of 1.08 i.e. the cords would be intersect one another.

(43) When using an organic adhesive as the described organofunctional silane, an adhesion value of 120 N/mm could be reached which is well above 20×D of 36 N/mm and also above 30×D i.e. 54 N/mm.

(44) In an alternative of the embodiment the dW34 embodiment (1+6) core is replaced with an equal lay construction of the following type:
[3×0.18+3×0.15|0.22|0.15).sub.7.2z+9×0.33+9×0.30|0.21].sub.16.8z

(45) A cross section of the reinforcement strand with such a core is depicted in FIG. 5. The filaments of the outer layer are as in that of FIG. 4. Only the core is different. The core-core is formed by three filaments 501 of diameter 0.18. The notation 3×0.15|0.22|015 indicates that the outer layer of the core is formed of three groups of each time three filaments: one middle filament of larger size (0.22 mm, indicated 502) that has two neighboring filaments of smaller diameter (0.15 mm, indicated 511). This results in a fairly round core 503 of diameter 0.70 mm.

(46) In all of the above examples the wires are hot dip galvanized with a coating weight of 5 gram per kilogram of strand.

(47) A synchronous belt is built up in much the same way as the belt 100 except that one side of the belt is provided with teeth for engagement with toothed pulley.