GB2174485A - Annealing furnaces - Google Patents

Abstract

A furnace for use in continuously annealing wire comprises at least one hollow tube (1) constructed of a thermally insulating material, through which a wire to be annealed is passed. The surface of each tube (1) is coated with a heat resistant, electrically non-conductive material (5) e.g. silica, on or within which an electrical heating resistance wire is wound. A thermally insulating mass (9) surrounds the or each tube (1). Thus the tube (1) can be electrically heated as and when required, optimising the cost of running the wire annealing furnace. <IMAGE>

Description

SPECIFICATION Improvements relating to furnaces The present invention relates to a furnace for use in continuously annealing wire.

A known furnace for continuously annealing wire comprises an elongate chamber defined by brick walls, the wire to be annealed being passed con tinuousiy through this chamber inside heat resistant tubes; radiant heat being provided within the chamber by gas burners or electrical heaters fixed at spaced apart locations along the length of the chamber.

Such a brick furnace has a relatively high thermal mass and to both maintain the brick structure of the furnace and achieve the temperatures required to anneal a wire, the furnace has to be heated continuously at a predetermined level and then when the furnace is to be used, the temperature has to be increased to the desired value for annealing. Clearly, a large amount of energy is consumed by such a furnace and it has to be used as often, if not continuously, as possible to make its operation economic.

The aim of the present invention is to provide a furnace which can be used as and when required with the optimum usage of the heat energy available, and which does not require to be continuously heated.

According to the present invention there is provided a furnace comprising at least one hollow tube constructed of a thermally conducting material, through which a wire to be annealed can be passed, the surface of each tube being contained within a heat resistant, electrically non-conductive material on or within which an electrical heating resistance wire is wound, a thermally insulating mass surrounding the tube or tubes.

In a preferred embodiment of the present invention eight elongate tubes are arranged parallel to each other, the tubes extending within an outer elongate casing of desired transverse cross-section, and projecting out from each end of the casing. The tubes are each of circular cross-section and are made of a heat resistant nickel/chromium alloy, e.g. INCONEL. The tubes are silica coated and an electrical heating wire is spirally wound therearound along the length of each tube. Surrounding the tube arrangement and virtually filling the casing is a thermally insulating mass. This is preferably in laminate form, with such laminate being cut from sheets of expanded aluminium oxide fibre.

Whilst the tubes are described hereabove as having a circular transverse cross section, thus providing for the focussing of the radiant heat from the spirally wound electrical heating wire, onto the wire passing through the centre of the tube, the tube may have any desired alternative cross-section, e.g. oval or rectangular.

The present invention thus provides a furnace of low thermal mass which can easily be heated to the desired annealing temperature quite quickly, as and when required, and which uniformly heats a wire passing along the centre of a tube with the radiant heat being substantially focussed on the wire. If desired, individual wire heaters can be wound on different sections of the length of a tube, so that the option exists for heating the different sections to different degrees.

Whilst the ends of the tubes may be open to the atmosphere, they can, of course, sealingly connect with a cooling environment with a controlled atmosphere of a required gas being maintained within the tubes. The selected gas depends upon the coating required on the surface of the annealed wire.

The present invention will now be further described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a cross-sectional, perspective view of a preferred embodiment of the present invention; and Figure 2 is a perspective view of part of one of the tubes used in the furnace of Figure 1.

The furnace constructed according to the present invention and illustrated in the accompanying drawings, basically comprises a number of elongate hollow tubes (1) which are of circular crosssection and which are arranged generally parallel to each other and to the longitudinal axis of a casing (3) within which they are located.

Each tube (1) is made of a heat conducting material such as a nickel/chromium alloy, e.g. Incanel (Registered Trade Mark) and has a silica coating (5) i.e., an electrically insulating coating. An electrical heating resistance wire (7) is spirally wound around the silica coating (5), though alternatively the resistance wire (7) can be embedded within the silica coating (5).

Surrounding the arrangement of tubes (1) is a thermally insulating mass (9) which fills the remainder of the casing (3). This thermally insulating mass (9) is of laminated construction, with the laminates being cut out of expanded aluminium oxide fibre sheet. Alternatively, this thermally insulating mass can be made of any other suitable material.

To allow for access to the tube arrangement for servicing, the laminates are formed in two halves, as in the casing (3). Thus, the casing (3) and the thermally insulating mass (9) can be split as and when required.

Whilst the tubes (1) can be open at each end, the wire to be annealed being merely passed therethrough, the ends of the tubes (1) can alternatively be sealingly connected to a wire feed and a cooling apparatus, with the tube atmosphere being controlled. For example, the tubes can be filled with a selected gas to provide a desired coating on the wires passing through the tubes.

In the above described embodiment, the tubes (1) have a circular cross-section. However, they can alternatively have any desired transverse crosssection, e.g. oval or rectangular, to cater for, say, wire strip passing therethrough.

Whilst the above described embodiment uses an arrangement of eight tubes (1), any number of tubes can be provided, the tubes being supported in the casing (3) by transversely extending supports (not shown). Further, any number of furnaces constructed according to the present invention can be stacked on top of each other and/or located side-by-side.

The present invention thus provides a furnace suitable for continuously annealing wire, the furnace being energy efficient and having a low thermal mass so that it can be raised to the required temperature quite quickly, as and when required.

Claims (14)

1. A furnace comprising at least one hollow tube constructed of a thermally conducting material, through which a wire to be annealed can be passed, the surface of each tube being coated in a heat resistant, electrically non-conductive material on or within which an electrical heating resistance wire is wound, a thermally insulating wire surrounding the tube or tubes.

2. A furnace as claimed in claim 1, in which a number of hollow tubes are mounted parallel to each other within an outer elongate casing.

3. A furnace as claimed in claim 1, or claim 2, in which the electrical heating resistance wire is wound spirally around the or each tube along the length of each tube.

4. A furnace as claimed on claim 1 or claim 2, in which the electrical resistance wire is wound around part of the length of a tube and a further electrical resistance wire is wound around another part of the length of the tube.

5. A furnace as claimed in any one of claims 1 to 4, in which the or each tube is of circular crosssection.

6. A furnace as claimed in any one of claims 1 to 5, in which the or each tube is made of a heat resistant nickel/chromium alloy.

7. A furnace as claimed in any one of claims 1 to 6, in which the electrically non-conductive material coating the or each tube is silica.

8. A furnace as claimed in any one of claims 1 to 7, in which the atmosphere within the or each tube is controlled.

9. A furnace as claimed in claim 8, in which a selected gas dependent upon the coating required on the surface of the annealed wire, fills the or each tube.

10. A furnace as claimed in any one of the preceeding claims, in which the thermally insulated mass is of laminated construction.

11. A furnace as claimed in any one of the preceding claims, in which the thermally insulated mass is made in sections to allow for access to the or each tube.

12. A furnace as claimed in any one of the preceeding claims, in which the thermally insulated mass is made of expanded aluminium oxide fibre.

13. A furnace as claimed in any one of the preceeding claims, when stacked with one more other furnaces as claimed in any one of the preceeding claims.

14. A furnace constructed substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.