GB2181466A - Blocking of strand and rope - Google Patents

Abstract

An enclosed or sheathed strand or rope is filled with a blocking material in a fluid state and the strand or rope is heated. The preferred blocking material comprises a fluid suspension of a solid (e.g. a wax) in a liquid (e.g. a polyolefin), the solid dissolving in the liquid on heating to form a solution which transforms to a gel on cooling. The strand or rope wires may be electrically heated.

Description

SPECIFICATION Blocking of strand and rope The present invention relates to the blocking of strand and rope, i.e. the filling of voids between the component filaments or wires of the strand or rope in order to prevent the ingress of foreign matter such as corrosives and abrasives. In particular the invention is concerned with strand or rope which is enclosed, e.g. being sheathed with plastics or metal or wrapped with plastics or metal tape.

The conventional method of blocking strand or rope involves applying a blocking material during stranding or closing. Conventional blocking materials have to be heated above their melting point to achieve a sufficiently low viscosity for ease of application.

A requirement has arisen for the blocking of finished strands and ropes, particularly large strands for structural applications, such strands being enclosed in a sheath which may be tubular.

The present invention provides a method of blocking an enclosed strand or rope, comprising filling the enclosed strand or rope with a blocking material in a fluid state and heating the strand or rope.

In one aspect, the invention provides a method of blocking an enclosed strand or rope, in which the enclosed strand or rope is filled with a blocking material which has been heated to a temperature at which it is fluid, and, during filling, the strand or rope is heated to a temperature at which the blocking material is fluid.

For example, a sheathed strand' or rope is heated, and a blocking material which has been heated to a temperature at which it is fluid is pumped along the strand or rope.

However, it is very difficuit to impregnate such strand or rope with conventional blocking materials, since unavoidable heat losses tend to cause the material to solidify while the strand or rope is being filled with the heated material. To achieve effective penetration it is necessary to heat the strand or rope uniformly over a considerable length. The strength of the sheathing may be much reduced at elevated temperature, and there is therefore a risk that the hot sheathing may burst under pressure from the material being pumped in.

Accordingly, in another aspect, the invention provides a method of blocking an enclosed strand or rope, in which the enclosed strand or rope is filled with a fluid blocking material comprising a solid in suspension in a liquid, and the strand or rope is heated to a temperature at which the solid dissolved in the liquid, the said material becoming a gel when the strand or rope cools.

The invention also provides a material for blocking strand or rope, comprising a fluid suspension of a solid in a liquid, the solid dissolving in the liquid on heating to form a solution which transforms to a gel on cooling.

Such a material may be pumped into a sheathed strand or rope at a lower temperature than with a conventional blocking material.

The fluid blocking material preferably comprises a mixture of polyolefin liquid and a solid wax additive. The polyolefin base may have a molecular weight of up to 3000 and will typically be a polybutene (such as "HYVIS" [RTM]) or polyisobutene. The solid additive may be a high melting point wax such as a paraffin wax or polyethylene wax or other olefinic waxes. Small quantities of additional additives may be included to enhance the corrosion protection properties, improve adhesion, or change the colour of the material.

A preferred supply form of the material will be a relatively low viscosity fluid with the solid additives finely dispersed and held in suspension, so that when heat is applied to the mixture during processing, the solid particles are dissolved into the solution and the material is transformed into a reversible thermoplastic state, i.e. becomes solid on cooling below a defined melting point and vice versa.

The advantages of this type of blocking compound are: a) The constituent materials are commercially available with a wide range of properties.

b) The transformation temperature can be varied to suit the process parameters by the selection of appropriate materials.

c) The melting point and physical properties, e.g. penetration, of the mixture can be changed to suit the operating temperature range by material selection and by varying the wax content or type.

d) Prior to transformation the mixture may be handled and pumped in a cold fluid state without the need for heating. This is particularly advantageous during the actual blocking operation since the strand may be filled at substantially lower temperatures than conventional blocking materials (which must be heated above their melting point to achieve a sufficiently low viscosity for ease of pumping and effective penetration), or even at ambient temperature. The safety hazards are thereby much reduced. The viscosity of the base material (e.g. polybutylene) at ambient temperature may be selected with lower temperature injection in mind, without prejudice to the properties of the final (transformed) mixture.

e) The ability to pump the blocking material in a cold condition or heated only to a low temperature enables much longer lengths of sheathed strand to be filled in a single operation, since time, temperature, and pressure are limiting factors from a sheathing viewpoint.

The required properties of a blocking material for structural strands may be defined by reference to flexibility and penetration/viscosity over a range of temperatures. Typically it is required to remain solid but flexible up to about 60"C, and to melt at 80-90"C, although higher temperatures may be specified for hot climates. The degree of stiffness in the climatic temperature range may be controlled to resist migration of the blocking material in service.

The preferred operating procedure is to pump the material into a tubed rope or strand in its initial fluid state at normal ambient temperature or heated somewhat to reduce its viscosity. After or during filling, heat is applied to the rope or strand until the transformation temperature is attained and then (natural) cooling is allowed to occur. Uniform, economic, and controllable heating can be most effectively achieved by using the electrical resistance method, i.e. applying a low voltage current to the strand itself via suitable end connections. For example, with a steel wire strand 85mm in diameter (excluding the sheathing) and 1 50m long, by applying a heating current of 3000 A at a D.C. voltage of 22V, a temperature of 100"C can be achieved in 1 to 1.5 hours.

The blocking material is preferably pumped in at one end. For long strands it may be necessary or advantageous to pump the material in at both ends or at an intermediate position or at positions spaced along the strand.

Example A typical formulation would consist of a polybutene with a molecular weight of 780 (HY VIS 5) and a polyethylene wax with a molecular weight of 3000 (Hoechst Wax PA130).

After intimate mixing of the components and injection of the mixture into the strand, the product would be heated to 130"C. The wax component would dissolve in the polybutene and on cooling would form a solid gel. With a wax content of 10% by weight, a penetration (IP50) of 95-105 1/10 mm at 25"C and a drop point (IP31) of 117"C (melting point approx. 1200C) could be achieved in the final gel.

Alternative waxes or wax like materials could be employed to vary the hardness of the gel and the melting point. Such materials are: a) mineral oil wax such as micro-crystalline wax, paraffin wax, etc; b) synthetic hydrocarbon/wax produced by synthesis of cracked coal gas; c) other olefin derivatives; d) aliphatic acid derived wax such as polyamide or ketone; e) natural or animal waxes such as montan, beeswax, and carnauba wax.

The grade of polybutene can also be used to vary the properties of the fixed gel but more importantly to vary the properties of the untransformed (fluid) mixture.

The range of materials/properties presently considered useful are: Polybutene base : M.wt. 300-3000 Solid wax : M.wt. 200-20000 Solid wax content : 5-50% by weight Transformation temperature : 70-170"C Melting point range : 50-150"C

Claims (16)

1. A method of blocking an enclosed strand or rope, comprising filling the enclosed strand or rope with a blocking material in a fluid state and heating the strand or rope.

2. A method as claimed in claim 1, in which the strand or rope is heated during the filling step.

3. A method as claimed in claim 2, in which the strand or rope is additionally heated before the filling step.

4. A method as claimed in any of claims 1 to 3, in which the strand or rope is heated after the filling step.

5. A method as claimed in claim 1, in which the enclosed strand or rope is filled with a blocking material which has been heated to a temperature at which it is fluid, and, during filling, the strand or rope is heated to a temperature at which the blocking material is fluid.

6. A method as claimed in claim 1, in which the enclose strand or rope is filled with a fluid blocking material comprising a solid in suspension in a liquid, and the strand or rope is heated to a temperature at which the solid dissolves in the liquid, the said material becoming a gel when the strand or rope cools.

7. A method as claimed in any preceding claim, in which the strand or rope is heated by passing an electric current through it.

8. A material for blocking strand or rope, comprising a fluid suspension of a solid in a liquid, the solid dissolving in the liquid on heating to form a solution which transforms to a gel on cooling.

9. A material as claimed in claim 8, in which the liquid is a polyolefin.

10. A material as claimed in claim 9, in which the polyolefin has a molecular weight of 300 to 3000.

11. A material as claimed in claim 9 or 10, in which the polyolefin is a polybutene or polyisobutene.

12. A material as claimed in any of claims 8 to 11, in which the solid is a wax.

13. A material as claimed in claim 12, in which the wax is an olefinic wax.

14. A method as claimed in claim 12 or 13, in which the solid has a molecular weight of 200 to 20,000.

15. A method of blocking an enclosed strand or rope, substantially as described with reference to the Example given.

16. A material for blocking strand or rope, substantially as described with reference to the Example given.