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BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to apparatus for producing wire conductors for cables, and in particular to improved heat treating apparatus for such wire conductors.
2. Description of the Prior Art
In the manufacture of plastics coated telephone cable the metallic conductor wires are normally drawn, and then annealed, before being coated with plastics insulation. Sometimes these three processes are carried out entirely separately and independently of each other, but a preferred method of manufacture involves a tandem arrangement of the drawing and annealing process stages, or alternatively a tandem arrangement of all three stages, so that there is an uninterrupted flow of wire through the stages that are arranged in tandem.
For tandem operation an annealing method is required which will operate in a continuous mode of operation on the wire as it emerges at line speed from the drawing process. A common method of on-line annealing involves passing a large electrical current through the wire as it moves on between a system of two or more electrically conductive contact pulleys, which are connected to a current source, and so act as rolling contacts. Using this annealing method with the known type of phosphor-bronze pulleys, or alternatively, pulleys with tyres or contact faces of phosphor-bronze, copper wire is easily produced in an annealed condition suitable for further processing into telephone cables. In order to minimize wire breakage the contact pulleys are driven at a rate providing a small amount of slip ensuring that the peripheral speed of the pulleys is never allowed to be exceeded by the line speed of the wire passing over them. The slip is prone to produce sparking at points of contact, but in practice causes minimal damage, and the wear on the contact pulleys, although significant, can be tolerated. If however the same apparatus is used to anneal wire of other materials, such as aluminum, much less satisfactory results are produced. In particular there is excessive wear of the contact pulleys and sparking which results in a poor surface finish and a much higher incidence of wire breaks. The known apparatus also generally uses driven guide pulleys which may result in excessive tension in the wire. The use of free-running electrical contact pulleys for wire annealing is also known, such as shown in U.S. Pat. No. 2,109,555 issued Nov. 5, 1935. These provide some reduction of the wire tension, but still further reductions are desirable.
SUMMARY OF THE INVENTION
It is therefore the primary object of the present invention to provide an improved annealing process utilizing electrical contact pulleys that can be employed with various wire conductor materials, and using low friction structures to reduce wire tension.
These and other objects and advantages are achieved by novel apparatus for annealing bare work-hardened wire conductors including two or more electrically conductive pulleys over which the wire passes and between which an electric current is established via the wire. The pulley surfaces coming in contact with the wire are faced with, a high-melting point electrically conductive material having a melting point of not less than 1200.degree. C. Examples of suitable materials include two-phase tungsten-copper and tungsten-silver materials, and tungsten, titanium, tantalum and their carbides. Where a high melting point surface layer is to be used this layer may comprise for example a layer of chromium, a cobalt-chromium-tungsten composition, or a boride, nitride or carbide layer.
According to another aspect of the invention there is provided apparatus for annealing or thermal conditioning of bare wire conductors including two or more electrically conductive pulleys over which the wire passes and between which an electric current is established via the wire wherein the pulleys are free-running being driven solely by the passage of the wire. In order to avoid excessive tensioning of the wire, such pulleys are supported in low friction bearings which have a small moment of inertia and are equipped with low torque electrical contact gear.
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There follows a description of an annealer embodying the invention in a preferred form as taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic diagram of the general layout of the annealer suitable for use with wire of various materials such as copper or aluminum.
FIG. 2 depicts a section through one of the contact pulleys, and
FIG. 3 depicts a molten metal contact arrangement optionally replacing the carbon brush contact arrangement depicted in FIG. 2.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to FIG. 1, wire 1 issuing from a drawing machine (not shown) passes over a first electrical contact pulley 2, over electrically insulated guide pulleys 3 and 4, over second and third electrical contact pulleys 5 and 6, and finally over guide pulley 7 to emerge from the annealer at 8. Pulleys 2 and 6 are connected to the ground or earthed side of an electrical current supply 9, while pulley 5 is connected to the live side of the supply. This use of three contact pulleys is designed to restrict the current flow provided by the supply 9 to the region of wire within the annealer irrespective of any electrical connection that may be established between portions of the wire before and after the annealer. The length of wire between pulleys 2 and 5 is made much longer than that between pulleys 5 and 6 so that the former forms a pre-heater section which precedes the main annealing which occurs between pulleys 5 and 6. Pulley 6 is cooled by directing a jet of air or water at it. This cooling reduces the plasticity of the wire at this point thereby permitting a greater tension to be applied to the wiring to draw it through the annealer. If desired, the wire may be wrapped right round this pulley so that it executes a turn and a half before leaving it.
The electrical contact pulleys 2, 5 and 6 are all of substantially the same construction shown in greater detail in FIG. 2. The preferred material for the electrical contact surface of the pulley to the wire is a tungsten-copper two-phase material sold under the name "Elkonite" having a melting point of at least 1200.degree. C. Other suitable materials include tungsten-silver, tungsten, titanium, tantalum and their carbides. In addition, high melting point surface layers of chromium, a cobalt-chromium-tungsten composition, or a boride, nitride or carbide layer, may be used. The contact takes the form of a replaceable tyre or annular ring 20 on a split pulley composed of portions 21 and 22. The pulley rotates on a shaft 23 supported by low friction bearings 24 of the precision ball journal type.
An alternative type of tyre or ring 20 consists of a steel ring with a facing of titanium carbide produced, for example, by a surface chemical reaction with a volatile titanium salt. An alternative construction for the low friction bearings 24 uses a bearing of the air supported type.
The pulley is electrically connected with the power supply by the carbon brush 25 of brush gear 26 bearing on the end of a boss 27. An alternative form of electrical contact is depicted in FIG. 3. The boss 27a is longer and carries a flange 28 at its end dipping into molten metal 29 contained in a heated vessel provided with a gland or system of baffles 30 preventing the splash of metal out through the aperture 31 accommodating the boss 27a.
It should be understood that the invention is applicable to the annealing of various wire conductor materials such as copper and aluminum, as well as nickel and tinned copper. The apparatus has uses other than that of annealing and may also be uesd for thermal conditioning wire to raise it to a suitable temperature for encasing it in plastics insulation. The wire in this case may already be fully annealed. Use of such high melting point materials as tungsten-copper for annealing aluminum wire has increased the lifetime of the pulley faces by a factor of more than five. A similar modification of apparatus for preheating aluminum wire before coating with plastics insulation has increased lifetime by a factor of more than 10.
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