GB2252774A

GB2252774A - Reinforced transmission belt

Info

Publication number: GB2252774A
Application number: GB9202549A
Authority: GB
Inventors: Marc Eggermont
Original assignee: Bekaert NV SA
Current assignee: Bekaert NV SA
Priority date: 1991-02-06
Filing date: 1992-02-06
Publication date: 1992-08-19
Anticipated expiration: 2012-02-06
Also published as: DE4200736A1; IE914457A1; BE1004469A3; GB9202549D0; GB2252774B; JPH04307146A; IE66749B1

Abstract

The invention relates to a toothed transmission belt reinforced with cord in which the cord lies essentially in the longitudinal direction of the transmission belt and consists of at least four and at most twenty-eight filaments having a diameter of between 0.04mm and 0.20mm. The cord displays a geometrically regular structure in cross-section, this structure consisting of a central core of one or more filaments, surrounded by at least one layer of filaments.

Description

2 2 5 2774 1 - REINFORCED TRANSMISSION BELT This invention relates to a

transmission belt that is reinforced with cord and particularly, but not exclusively, to a toothed transmission belt reinforced with steel cord.

Because of the absence of creep, steel cord is a suitable material for reinforcing transmission belts. Such steel cord usually has the following composition: a minimum carbon content of 0.65%, for example 0.75 or 0.80%; a manganese content varying between 0.40 and 0.70%; a silicon content varying between 0.15 and 0.30%, and a maximum sulphur and phosphorus content of 0.03%, respectively. Micro-alloying with elements such as copper, chrome, nickel, vanadium and boron is also possible. Because of the small diameters (see below), the chosen material should display a rather high degree of purity: the number and size of the non-metallic inclusions is preferably limited (e.g. size < 0.10 gm).

Transmission belts run under an axial tension varying between 10 and 100 Newtons. Furthermore, transmission belts must be capable of undergoing a great number of rotations. With each rotation the transmission belt bends around a guide wheel or around a drive wheel. For certain applications the radius of curvature of this bending is relatively small. Another requirement is that the transmission belt must run in the middle of the guide wheels and must show no tendency to rub against either of the upright edges of the guide wheels. If the guide wheels have no edges, the transmission belt must have no tendency to slip off the wheels. Consequently, the properties required of steel cord reinforcement are: the steel cord must have good tensile strength, good flexibility, a high bending fatigue level and, finally, it must be torsion-free.

This last requirement is for the purpose either of making the transmission belt run in the middle of the grooves of the guide wheels or to prevent the transmission belt from slipping off the wheels.

Up to the present, the so-called strand constructions of the m x n type have been utilised for steel cord reinforcement. Such a steel cord consists of m strands, and each strand consists of n filaments. If the strands, as such, have been twisted in the Sdirection, then these strands are twisted together into a cord in the Z-direction in order to obtain the desired torsion balance. Examples of such cords include a 3x3 construction, a 7x3 construction, a 7x4 construction and a 7x7 construction.

The existing stranded constructions are flexible and torsion-free, but for applications in which transmission belts have to work under extreme conditions, the tensile strength and the bending fatigue level are sometimes less than desired.

An object of the present invention is to improve upon the disadvantage of the current state of the art.

According to a first aspect of the invention, there is provided a transmission belt reinforced by cord in which the cord lies substantially in the longitudinal direction of the transmission belt and comprises at least four and at most twenty-eight filaments with a diameter of between 0.04mm and 0.20mm, the cord exhibiting a layered structure in crosssection, this structure comprising a central core of one or more filaments, surrounded by at least one layer of filaments.

According to a second aspect of the invention there is provided a cord for reinforcing a transmission belt comprising at least four and at most twenty-eight filaments with a diameter of between 0.04 and 0.20mm, the cord exhibiting a layered structure comprising a central core of one or more filaments surrounded by at - 3 least one layer of filaments.

Preferably, in cross-section the cord, which advantageously is made of steel, displays a geometrically regular structure. By geometrically regular structure is meant that the cross-sections of the filaments lie in a nearly symmetrical arrangement. Preferably, the filaments have a diameter of between 0.04mm and 0.15mm.

The number of filaments must be at least four, because otherwise it is difficult to obtain a geometrically stable core layer structure. With more than twenty-eight filaments it is difficult to control the geometry of the cross-sections and to obtain regularly formed cross-sections. The diameter must be limited to at most 0.2omm because of the required flexibility.

The core filaments are usually all of equal diameter. The filaments of each layer are also usually of equal diameter. The diameter of the core filaments can be equal to the diameter of the layer filaments. However, this is not a necessity. It depends mainly on the number of filaments in the core and in the layers. The direction of twist in the core and in the layers can be the same or different.

By preference, a number of steel cords will lie in a plane alongside one another, though without touching one another.

If the transmission belt consists of a polymer such as polyurethane, then the steel cord is preferably covered with a corrosion-resistant coating such as zinc or a zinc alloy, for example zinc-aluminum or zincnickel.

If the transmission belt consists of rubber, then the steel cord is by preference covered with a coating that adheres to the rubber, such as brass, copper, bronze, or complex coatings containing copper (binary or ternary copper alloys).

- 4 In an embodiment of the present invention, the steel cord consists of a core surrounded by one layer of filaments. Examples of such embodiments include:

- lxO.15 + 6xO.15 - 3xO.O8 + 6xO.15 - 3xO.O8 + 9xO.O8 - 3xO.15 + 9xO.15 In another embodiment of the invention, the steel cord consists of a core surrounded by two layers of filaments. Examples of such embodiments include:

- lxO.15 + 6xO.15 + 12xO.l5 - 3xO.O8 + 9xO.O8 + 15xO.O8 By preference, all filaments of any given steel cord in the core and in the layer or layers are twisted in the same direction and have the same pitch so that in the longitudinal direction of the steel cord and throughout essentially the total length of the steel cord they have line contacts with one another. The direction of twist of any given steel cord, however, is by preference the opposite of the direction of twist of any neighboring steel cord, the purpose being to compensate for the possible torsion still present in one steel cord by the torsion of a neighboring steel cord and thereby to achieve a torsion-free composite.

An embodiment of the invention will now be described by way of example only with reference to the accompanying drawings in which:

FIGURE 1 is an overall view of a transmission belt and a drive wheel; FIGURE 2 is a cross-section of a steel cord through plane II-II of FIGURE 1; FIGURE 3 is a cross-section of a steel cord intended for reinforcing a transmission belt; FIGURE 4 is a schematic presentation of how the torsion behavior of a steel cord is measured; FIGURE 5 is a schematic presentation of how the bending fatigue level of a steel cord is determined.

Referring to FIGURES 1 and 2, 1 is a transmission belt that is reinforced by several steel cords 2 that lie in a plane alongside one another.

The steel cords 2 are 12xO.O8 cords, consisting of a core of three filaments 22 of 0.08mm diameter, surrounded by one layer of nine filaments 24 of 0.08mm. All the filaments of any given steel cord are twisted in the same direction, with the same pitch of 4.5mm. As is apparent from the arrows 28, the twist direction of one steel cord 21 is opposite to the twist direction of a neighboring steel cord 211, the twist direction of steel cord 211 is opposite to the twist direction of steel cord 2111, etc.

The transmission belt 1 is driven via the teeth 12 by a drive wheel 4 that also has teeth 42. The transmission belt 1 must run in the middle between the upright edges 44 of the drive wheel and must have no tendency to rub against either of the edges 44.

Transmission belts can be manufactured either by means of an extrusion process or by means of a diecasting process.

FIGURE 3 shows another type of steel cord 2 for reinforcing transmission belts. The steel cord 2 consists of one core filament 22, and intermediate layer of filaments 24 and an outer layer of filaments 26. All filaments have a diameter of 0.15mm and have the same twist direction and pitch (10mm). It is not impossible, however, that the core filament 22, for example, can have a diameter that is larger than the diameter of the filaments 24 of the intermediate layer, and that the diameter of the filaments 24 of the intermediate layer is larger than the diameter of the filaments 26 of the outer layer.

1 TEST 1 Table 1 contains a list of steel cords that have been tested with a view to reinforcing transmission belts.

Table 1

1 state of the art 1 invention 1 7X3XO.06 1 3X3XO.08 1 3+9XO.08 i i i i -1 lpitch (MM) 3/3 4.5/4.5 4.5 ltwist direction S/Z Z/S S lcord diameter (mm) 0.34 0.31 0.31 icoating zinc 1 zinc 1 zinc Table 2 shows the breaking load and the tensile strength of the above constructions.

Table 2 state of the art 1 invention 1 i 1 i i 1 7X3XO.06 1 3X3XO.08 1 3+9XO.08 1 Ibreaking load 1 125 1 99 1 161 1 Itensile strength 1 2119 1 2250 1 2729 1 1 (N/mm2) 1 1 1 1 1 1 1 1 It follows from Table 2 that the steel cord according to the invention has a higher tensile strength than the steel cords according to the start of the art.

As explained above, the ideal cord is torsion-free under axial stress. Torsion-free steel cords prevent the transmission belt from slipping off the guide wheel or drive wheel.

FIGURE 4 shows a test setup for measuring the torsion of a steel cord under the influence of an axial stress. The steel cord 2 is fixed between two clamps 62 and subjected to an axial stress by means of a weight 64 that runs over a wheel 66. The recording apparatus 68 records the torsion. Table 3 summarizes the results:

Table 3

1Torsion moment with 1 state of the art la load of:

1 (NMM)) inventionj J7X3XO.06 1 3X3XO.08 1 3+9x0.08 1 kg 0.21 0.23 0.29 2 kg 0.50 0.46 0.50 3 kg 0.80 0.69 0.84 4 kg 1.11 0.92 1.17 The 3x3 construction according to the state of the art produces the smallest increase of torsion with increasing axial stress. However, the increase of the torsion with the 3+9 construction according to the invention is approximately equally large as the increase of torsion with the 7x3 construction. This is unexpected since the 7x3 construction is twisted in Z/S direction in order to be as torsion-free as possible, while the 3+9 construction is twisted in one single direction, and therefore it is a priori to be expected that the torsion increase would be much larger with the 3+9 construction.

FIGURE 5 shows a test setup for determining the bending fatigue level of steel cord. A steel cord 2 is fixed between two clamps 82 and bent over a radius of curvature R. The steel cord is then subjected to a great number of rotations. Next the test is redone for a smaller radius of curvature R. The smallest radius of curvature where no fatigue breaks occur for 1.5x106 cycles is recorded. The smaller the radius of curvature, the better is the bending fatigue behavior of the steel cord. Table 4 gives the results.

Table 4

1 state of the art invention 1 7X3XO.06 1 3X3XO.08 1 3+9XO.08 1 Rmin (MM) 1 6.50 1 8.00 1 6.25 Table 4 shows that the steel cord according to the invention is somewhat better with respect to bending fatigue than the 7x3 construction tested and much better than the 3x3 construction. The steel cord according to the invention, however, is clearly better than the 7x3 construction if the filament diameter is taken into consideration (0.08 mm > 0.06 mm).

TEST 2 The tensile strength and the bending fatigue behaviour have been tested for the following steel cord constructions:

state of the art: - 1. 3x3x0.15 S/Z pitch 8.65/8.1; zinc coating - 2. 7x3x0.15 S/Z pitch 8.65/8.1; zinc coating invention:

3. 3+9x0.15 S pitch 9 (in fact, 12x0.15); zinc coating 4. 7+12x0.15 SIS pitch 6/10; zinc coating - 5. 19X0.15 S pitch 10; zinc coating Table 5 summarises the results.

Table 5 state of invention the art 1 H 1 1 2 11 3 4 5 i i i i i i i i 1 Itensile strength 1 Rm 1 (N/11,1112) 1 2564 1 2393 11 2670 1 2573 j 2625 Rmin (MM) j 31.1 1 34 J1 30.7 1 31.4 1 30.7 From table 5 it follows that the tensile strength levels of the steel cord constructions according to the invention are higher than the tensile strength levels of existing steel cord constructions.

The minimum radius of curvature Rmin for the steel cord constructions according to the invention are on average lower than for the steel cord constructions according to the current state of the art, which therefore indicates a better bending fatigue level behavior.

The invention is not limited to a transmission belt reinforced with steel cord consisting only of steel filaments. Steel cord here also means a mixed structure of steel filaments and synthetic filaments such as nylon and aramid.

- claims 1. A transmission belt reinforced by cord in which the cord lies substantially in the longitudinal direction of the transmission belt and comprises at least four and at most twenty-eight filaments with a diameter of between 0.04mm and 0.20mm, the cord exhibiting a layered structure in cross-section, this structure comprising a central core of one or more filaments, surrounded by at least one layer of filaments.

2. A transmission belt according to claim 1 wherein a plurality of said cords lie substantially in a plane alongside one another.

3. A transmission belt according to claim 1 or 2 wherein said cord comprises steel cord.

4. A transmission belt according to claim 3 wherein the transmission belt comprises a polymer such as polyurethane and the filaments are coated with a corrosion-resistant coating.

5. A transmission belt according to claim 3 wherein the transmission belt consists of rubber and the filaments are coated with a coating that adheres to the rubber.

6. A transmission belt according to claims 1 to 5 wherein the cord consists of a central core and one surrounding layer.

7. A transmission belt according to claim 6 wherein the core consists of one filament and the layer consist of six filaments.

S 8. A transmission belt according to claim 6 wherein the core consists of three filaments and the layer consists of nine filaments.

9. A transmission belt according to claims 1 to 5 wherein the cord consists of a central core and two surrounding layers: a middle layer and an outer layer.

10. A transmission belt according to claim 9 wherein the core consists of one filament, the middle layer of six filaments and the outer layer of twelve filaments.

11. A transmission belt according to claim 9 wherein the core consists of three filaments, the middle layer of nine filaments and the outer layer of fifteen filaments.

12. A transmission belt according to claims 2 to 11 wherein for each single cord all filaments are twisted in the same direction and have the same pitch so that the filaments have line contacts between one another in the longitudinal direction of the cord.

13. A transmission belt according to claim 12 wherein the twist direction of any given steel cord is opposite the twist direction of any neighboring steel cord.

14. A transmission belt according to any preceding claim in which the transmission belt is a toothed transmission belt.

15. A cord for reinforcing a transmission belt comprising at least four and at most twenty-eight filaments with a diameter of between 0.04 and 0. 20mm, 1 the cord exhibiting a layered structure comprising a central core of one or more filaments surrounded by at least one layer of filaments..

12 16. A transmission belt substantially as hereinbefore described with reference to Figure 1 and Figure 2.

17. A cord for reinforcing a transmission belt substantially as hereinbefore described with reference to Figure 3.