GB2312939A - Control cables - Google Patents

Abstract

A multifilament control cable, which may be located within a sheath, comprises three or more filaments of a thermoplastic aromatic polyketone. At least seventy percent of these filaments are twisted at a twist level of at least 15 turns per metre, and the cable has a chord modulus which exceeds 440cN/tex at 20{C and 330cN/tex at 100{C. Such control cables are suitable for push/pull operation in applications such as remote photographic shutter actuation, robotics and control and sensing of tool position. The cables may have excellent recovery and creep performances, as well as very good flex fatigue and abrasion characteristics.

Description

"Control Cables" This invention relates to a control cable, and is concerned more particularly, but not exclusively with control cables of the type used to tension and release fabric structures, or for the operation of robotics or artificial limbs, or of the type referred to as a Bowden cable for use in applications such as the remote opening of engine compartments of vehicles, and the actuation of throttle devices of carburettors.

Bowden cables, which are usually of steel, are protected from rusting and abrasion damage by being encased, and guided through the vehicle body work, inside a flexible spring steel coil covered with a polymer sheath.

The requirements of control cables dictate that the load bearing fibres used should be high in modulus and have very low levels of creep in repeated use situations.

Also they are required to have good flexibility while exhibiting very low levels of friction and wear as the cable moves inside the sheath at temperatures which, in certain automotive and robotic situations, can be as high as 100" C.

In general, thermoplastic fibres have not been considered to be suitable for the construction of the majority of control cables especially those which are required to operate at high temperature because of the likelihood of creep in the fibres which causes a change of length.

However European Patent Application 198,567A describes a cable composed of at least aramid fibre yarns, and preferably also containing carbon fibre yarns, encased in a braided sheath containing aramid yarns and carbon fibre yarns. Although such cables are capable of actuating devices by pulling they are not suitable for control by pushing, as in applications such as remote photographic shutter actuation and in robotics for the control and sensing of the position of tools, because they have insufficient stiffness to resist bending.

It is an object of the invention to provide a novel control cable exhibiting a number of advantageous features in use.

According to the present invention there is provided a multifilament control cable, possibly located within a sheath, said cable comprising three or more filaments of a thermoplastic aromatic polyketone, at least seventy percent of said filaments being twisted at a twist level of at least 15 turns per metre, said cable having a chord modulus as herein defined exceeding 440cN/tex at 20"C and 330cN/tex at 100"C.

A control cable according to the invention has, at 100"C, a residual extension when cycled once between 2cN/tex and 6cN/tex which is preferably 0.55%, and most preferably 0.45%, and, at 100"C, a residual extension when cycled 10 times between 2cN/tex and 6cN/tex which is preferably s0.75%, and most preferably s0.65%, and after cycling for 10 times in such a manner, and allowing relaxation for one minute at a tension of O.lcN/tex, a permanent set, measured under 2cN/tex tension which is preferably s0.35%, and most preferably 10.20%.

The high modulus polyketone filaments used in the cable of the invention may be combined by means of a twisting/tensioning process to provide a cable which not only has excellent recovery and creep performances but also possesses very good flex fatigue and abrasion characteristics.

The control cable of the invention has a diameter which is preferably between 0.20mm and 20mm, and most preferably between 1.5mm and 4.0mm.

If the control cable is provided with a sheath, this is advantageously not adhered in any way to the cable but merely acts as a conduit within which the cable can freely move. Examples of polymeric materials from which the sheath may be made are polytetrafluoroethylene, polyetheretherketone or Nylon 6.6 (Nylon is a Registered Trade Mark).

A further advantage of using high melting point thermoplastic polyketones is that end stop connections can conveniently be provided by over extruding identical polymers over the ends of the cables whilst still retaining substantially all of the fibre integrity.

In order that the invention may be more fully understood, reference will now be made to the following examples.

EXAMPLE 1.

A polyetheretherketone of intrinsic viscosity 0.98, measured at 250C in a solution of 0.1 gram ofthe polymer in 100 ml of 98% sulphuric acid, was melted in an extruder at 375"C and spun from a 2.0mm spinneret as a circular filament at 18 grams/min. The extruded monofilament was immediately cooled by an air quench set at a velocity of 60 metres per minute, hot roll drawn at 1600C with a draw ratio of 3.58, and relaxed at 25"C by 0.5% before being wound up at 120 metres per minute as 0.40mm diameter filament.

Nineteen such filaments were combined together to make a cable with one central core filament, 6 filaments twisted around the core filament in an S direction at 40 turns per metre, and 12 filaments twisted over the top of the previous 7 filaments in a Z direction at 40 turns per metre, the cable being continuously heat set at 230"C under a tension equivalent to 6.5cN/tex.

The chord modulus and residual extension after cycling between two loads were then measured on the cable using an Instron tester (Model 4302) for room temperature testing, and an Instron tester (Model 6025, Chamber F 7581-300) for 100"C testing.

The test methods used and methods of calculation of the four key parameters associated with the cable of the invention are set out in Appendix A.

Results for Example 1 are shown in Table 1, together with the results for comparable cables constructed from 19, 0.40mm diameter polyetheretherketone monofilaments. These include: EXAMPLE 2 Example 1 was repeated in its entirely except that (1) the spinneret was provided with a pack extension of 200mm below the spinneret which served to maintain the temperature of the filament after extrusion and prior to quenching, and (2) a draw ratio of 3.87 and a relax ratio of 1.2% were used.

The chord modulus and residual extension after cycling were measured on the cable as in Example 1. The results are recorded in Table 1.

EXAMPLE 3 Example 1 was repeated in its entirety except for a few alterations. More particularly the conditions were set to produce a 0.7mm monofilament. The filament was spun from a 2.00mm spinneret as a circular filament at 36 grams/min with a draw ratio of 3.80 and the filament was relaxed at 3650C by 1.1% before being wound up at 76 metres per minute as a 0.7mm product.

Seven 0.7mm monofilaments of this type were combined together to make a cable with one central core filament and 6 filaments twisted in a Z direction at 30 turns per minute as an outside wrap, the cable then being heat set at a temperature of 23 00C under a tension of 5.2cN/tex.

The chord modulus and residual extension of the cable after recycling were measured as in Example 1. The results are given in Table 2.

EXAMPLE 4 In this example, the polyketone polymer used was polyetherketone of intrinsic viscosity 0.90, measured at 25"C in a solution of 0.1 gram of the polymer in looms of 98% sulphuric acid. The polymer was melted in an extruder at 3950C and spun from a 2.0mm spinneret as a circular filament at 17 grams/minute in the manner of Example 1.

The extruded monofilament was immediately cooled by an air quench set at a velocity of 60 metres per minute, hot roll drawn at 2100C with a draw ratio of 3.40 and relaxed at 25"C by 1.1% and then wound up at 80 metres per minute as a 0.27mm product.

Seven such 0.27mm monofilaments were combined together to make a cable with one central core filament and 6 surrounding filaments twisted in a Z direction at 50 turns per minute, the cable being continuously heat set at 21 50C under a tension equivalent to 2.70cN/tex.

The chord modulus and residual extension after cycling were measured on the cable as in Example 1. The results are recorded in Table 3.

EXAMPLE 5 In addition to heat setting as used in the previous examples, it is also possible to introduce a resin into the cable structure in order to provide an additional degree of cohesion to the cable and to impart modified surface characteristics to the cable.

In this example, seven monofilaments as produced in Example 2 were coated with a thermosetting liquid polyurethane at a pick up on the filaments of about 35% w/w, prior to twisting and heat setting.

The twist level was 40 turns per minute and heat setting was carried out at 2300C under 1 .9cN/tex. The chord modulus and residual extension after cycling were measured on the cable as in Example 1. The results are recorded in Table 4.

EXAMPLE 6 Example 5 was repeated except that the filaments in the cable were not coated with a polyurethane and the cable was heat set under a tension of 5.2cN/tex rather than 1.9cN/tex.

COMPARATIVE EXAMPLE A A cable was made using the same polyetheretherketone and according to Example 1 but at a tension of 1.5cN/tex and using, instead of filaments made in accordance with Example 1, 0.40mm diameter filaments type Z1 110 manufactured by Zyex Limited and sold under their Registered Trade Mark "ZYEX" for weaving applications.

The chord modulus and residual extension of the cable were measured in the same way as in Example 1. The results are recorded in Table 1.

COMPARATIVE EXAMPLE B 1. A cable was made according to Example 1 but at a tension of 1.ScN/tex and using, instead of filaments made in accordance with Example 1, 0.40mm diameter filaments type 21130 manufactured by Zyex Limited and sold under their Registered Trade Mark "ZYEX" for coiling applications.

The chord modulus and residual extension values for the cable are recorded in Table 1.

COMPARATIVE EXAMPLE C A cable was made according to Example 3 except that a tension of 1.3cN/tex was applied during heat setting.

The chord modulus and residual extension values for the cable are recorded in Table 2.

COMPARATIVE EXAMPLE D A cable was made by twisting together a 7 filament bundle of polyester monofilaments, each of diameter 0.25mm, commercially available as "MACROFIL" from Shakespeare Monofil UK Limited at a twist level of 50 turns per metre, the cable being heat set at a temperature of 1800C under a tension of 1.0cN/tex.

The chord modulus and residual extension values for the cable are recorded in Table 3.

TABLE 1 Chord Modulus cN/tex Residual Extension % After 20"C 100"C 1 cycle 10 cycles Relaxation Example 1 466 348 0.42 0.52 0.16 Example 2 493 362 0.39 0.48 0.12 Comp Ex A 368 271 0.64 0.97 0.49 Comp Ex B 402 302 0.59 0.79 0.34 TABLE 2 Chord Modulus cN/tex Residual Extension % After 20"C 100 C 1 cycle 10 cycles Relaxation Example3 507 360 0.44 0.52 0.16 Comp Ex C 416 316 0.56 0.71 0.32 TABLE 3 Chord Modulus cN/tex Residual Extension % After 20"C 100"C 1 cycle 10 cycles Relaxation Example 4 552 421 0.39 0.55 0.23 Comp Ex D 710 214 1.57 2.13 0.86 TABLE 4 Chord Modulus cN/tex Residual Extension % After 20"C 100"C 1 cycle 10 cycles Relaxation Example 5 566 410 0.47 0.66 0.25 Example 6 653 513 0.38 0.47 0.18 The cables produced in Comparative Examples A to D were found to be unsuitable for remote opening or actuation in vehicles and in sensing and control applications by push/pull operation due to excessive elongation under tension and after repeated operation ofthe control cable. In contrast those cables produced in accordance with Examples 1 to 6 were found to be ideally suited to these applications.

The test procedures used to determine chord modulus and residual extension of the various cable samples are now set out in detail.

CHORD MODULUS (a) Procedure at 200C A tensile extensometer (Instron Model 4302) operating at a constant rate of extension was used. The testing was carried out in an environment regulated to 200C, 65% relative humidity. Samples were conditioned in this environment for at least 24 hours prior to testing. The gauge length was 200mm, hom grips were used and the cross head speed set to 4mm/min. A load cell of 1KN was employed. Equipment for monitoring the load-extension curve was provided.

(b) Procedure at 100"C A tensile extensometer (Instron Model 6025) operating at a constant rate of extension was employed. The testing was carried out in an environmental chamber (Instron E7581-300) regulated to 100"C. Samples were conditioned in this environment for 1 minute. The gauge length was 200mm, high temperature horn grips were used and the cross head speed was set at 4mm/min. A load cell of IKN was employed.

Equipment for monitoring the load-extension curve was provided.

In order to measure chord modulus a sample cable was inserted into grips under 0. lcN/tex pre-tension and extended under those conditions outlined above.

The elongations at stresses of 2cN/tex and 6cN/tex were noted at 20"C and 100"C. Hereafter these are referred to as eA and eB respectively. The chord modulus is calculated according to the formula Chord Modulus = 4 x gauge length cN/tex eB - (in each case the gauge length was equal to 200cm).

Cyclic testing was carried out at 1000C according to the procedure outlined in (b) above. Samples were inserted into the horn grips under a pre-tension of 0. lcN/tex.

The sample was then extended from a stress of 0. lcN/tex to 6cN/tex, maintained at 6cN/tex for 30 seconds, and then returned to a 2cN/tex level. This constituted the first cycle.

Second and subsequent cycles consisted of extending the sample from a stress of 2cN/tex to 6cN/tex, maintaining at 6cNltex for 30 seconds, and then returning to 2cN/tex.

This procedure is carried out for a total of 10 cycles. On the return stage of the 10th cycle the sample is brought down to a 0.1cN/tex level, allowed to relax for 1 minute at this level and then extended to 2cN/tex.

If e, is the elongation of the sample cable during extension in the first cycle; e2 is the elongation ofthe sample cable after completing the first cycle; e,0 is the elongation of the sample cable after completing the tenth cycle; and per is the elongation of the sample after the relaxation period has elapsed; then: residual extension after one cycle (x,) = e2 - e1 200 residual extension after ten cycles (x,0) = e10 - e1 200 permanent set after relaxation (xp) = eR- e1 200 (All elongations to be measured for each sample at a stress level of 2cN/tex and in each case the gauge length is equal to 200mm).

For the avoidance of doubt, it should be understood that "tex" is a measure of the linear density ofthe samples. It is the weight in grams per 1000 metres of material.

In the context of this specification "tex" is defined as the weight in grams for 1000 metres of cable, excluding any coatings, resin, adhesive or sheath that may be present.

Claims (13)

1. A multifilament control cable comprising three or more filaments of a thermoplastic aromatic polyketone, at least seventy percent of said filaments being twisted at a twist level of at least 15 turns per metre, and said cable having a chord modulus as herein defined exceeding 440cN/tex at 20"C and 330cN/tex at 100"C.

2. A cable according to claim 1, wherein said filaments are located within a sheath.

3. A cable according to claim 2, wherein the sheath acts as a conduit within which the filaments can freely move.

4. A cable according to claim 1 or 2, wherein the sheath is made from polytetrafluoroethylene, polyetheretherketone or Nylon 6.6 (Nylon is a Registered Trade Mark).

5. A cable according to any preceding claim, which has, at 100"C, a residual extension when cycled once between 2cN/tex and 6cN/tex which is 0.55%.

6. A cable according to claim 5, which has, at 100"C, a residual extension when cycled once between 2cN/tex and 6cN/tex which is 10.45%.

7. A cable according to any preceding claim, which has, at 1000C, a residual extension when cycled 10 times between 2cN/tex and 6cN/tex which is #0.75%.

8. A cable according to claim 7, which has, at 1000C, a residual extension when cycled 10 times between 2cN/tex and 6cN/tex which is < 0.65%

9. A cable according to any preceding claim, which has, at 1000C, after cycling 10 times between 2cN/tex and 6cN/tex, and allowing relaxation for one minute at a tension of O.lcN/tex, a permanent set, measured under 2cN/tex tension, which is < 0.35%.

10. A cable according to claim 9, which has, at 100 C, after cycling 10 times between 2cN/tex and 6cN/tex, and allowing relaxation for one minute at a tension of 0. lcN/tex, a permanent set, measured under 2cN/tex tension, which is < 0.20%.

11. A cable according to any preceding claim, having a diameter which is between 0.20mm and 20mm.

12. A cable according to claim 11, having a diameter which is between 1.5mm and 4.0mm.

13. A multifilament control cable substantially as hereinbefore described with reference to any of Examples 1 to 6.