GB2198825A

GB2198825A - Furnace for continuously heat treating wire

Info

Publication number: GB2198825A
Application number: GB08630165A
Authority: GB
Inventors: Gerald Frank Ward; Warren Starbuck
Original assignee: MELTECH ENG
Current assignee: MELTECH ENG
Priority date: 1986-12-17
Filing date: 1986-12-17
Publication date: 1988-06-22
Anticipated expiration: 2006-12-17
Also published as: GB8630165D0; GB2198825B

Abstract

A tubular furnace for continuously heat treating wire comprises at least one furnace section having at least one electrically-operated heating surface 22, 23 constituting one wall of a relatively narrow furnace chamber along which extends a metal tube or a horizontal array of metal tubes 25 supported adjacent the heating surface on a bridge structure 26 at the input side and output side of the section. A control means including thermo couples 38, and 39 is provided for the or each furnace section to provide and maintain the electrical power input at a predetermined optimum value to ensure that the heat energy input is used to maximum effect and efficiency. In use, the wire is passed through the tube(s). <IMAGE>

Description

A FURNACE FOR USE IN HEAT TREATING ELONGATE ELEMENTS This invention relates to a furnace for use in heat treating elongate elements. In particular, the invention relates to a tubular furnace for continuously heat treating metal wires.

Conventionally a tubular furnace for continuously heat treating metal wires comprises a horizontal array of small-diameter metal tubes disposed longitudinally of an elongated configuration furnace heated, for example, by electricity or gas to temperatures up to 12000C. The metal wires to be heat treated are drawn through the metal tubes, one wire to each tube.

This known furnace has its heat energy input generally along the furnace length and this is neither the most effective or most efficient heat energy input due mainSy to the differential furnace temperature resulting from the wire coming in cold and leaving at a too-high temperature caused by heat transter along the furnace length as a consequence of the wire moving longitudinally through the furnace.

It is an object of the present invention to obviate or mitigate this drawback and to provide a tubular furnace whereof the heat energy input is used to maximum effect and efficiency.

According to the present invention there is provided a tubular furnace for continuously heat treating wire comprising at least one furnace section having at least one electrically-operated heating surface constituting one wall of a relatively narrow furnace chamber along which extends a horizontal array of metal t-ubes supported adjacent the heating surface on a bridge structure at the input side and output side of each section, and a control means for the or each furnace section to provide and maintain the electrical power input at a predetermined optimum value.

Preferably, the or each furnace section has upper and lower electrically-operated heating surfaces defining the relatively narrow furnace chamber and between which the horizontal array of metal tubes is supported.

Preferably, each bridge structure comprises a support pillar on which is mounted a rail bridge plate and between the input and output bridge structures of a furnace section rails for supporting the metal tubes.

The support pillar is preferably of a flattened inverted U-configuration.

The rail bridge plate is preferably coupled to a support pillar by a tongue-and-slot connection.

The rail bridge plate is preferably of horizontally-castellated configuration at and along its upper end to receive the metal tube supporting rails Each rail is preferably of T-configuration with a grooved upper surface for receiving and supporting a metal tube.

The support pillars, rail bridge plates and supporting rails are preferably formed of reaction bonded silicon nitride.

The metal tubes are preferably thin walled and formed of high temperature resistant alloy material.

The horizontal array of metal tubes may be disposed in exact horizontal alignment or be vertically staggered.

While in practice there is likely to be an array of metal tubes as referred to above the present invention does not preclude a furnace section containing only one metal tube.

Due to the flattened grooved top support surface of the metal tube supporting rail, metal tubes of different diameters are supportable on such a rail.

The metal tubes are preferably supported by the bridge structures between and relative to the upper and lower heating surfaces so as to ensure uniform and complete symmetry of thermal distribution (vertically and horizontally) throughout the or each furnace section.

Preferably, the upper and lower heating surfaces are defined by identical heater panels each constituted by resistance wires embedded in a ceramic mass, the pair of heater panels being coupled to their own electrical control means as mentioned above. Preferably, per furnace section, the control means comprises a control thermocouple, temperature controller and solid state relay means. Preferably each furnace section has a limit thermocouple.

Preferably the control thermocouple is mounted centrally between the upper and lower heating surfaces and serves to ensure the required temperature profile within its respective furnace section.

Preferably the temperature limit thermocouple is disposed at the top of each furnace section cent rally of the furnace section i.e. the hottest part of the latter.

The or each furnace section is preferably surrounded by ceramic fibre insulation contained within an inner mild steel skin or casing.

The furnace is preferably openable about a horizontal axis for access purposes.

The furnace preferably has an openwork outer skin or casting spaced from an inner skin or casing.

An embodiment of the present invention will now be described by way of example with reference to the accompanying drawings, in which: Fig. 1 is a cross sectional view through a tubular furnace according to the present invention; and Fig. 2 is an exploded perspective view of the metal tube supporting bridge structure; Referring to the drawings, the furnace comprises an inner skin or casing 20 with an outer skin or casing 21 of open work configuration spaced from the inner skin or casing 20. The furnace usually comprises a number of end to end sections, each of which as previously mentioned is individually and independently thermally controlled.

Each section (see Pig. 1) comprises upper and lower panel heaters 22 and 23 which are constituted by resistive wires encased in ceramic fibre. These upper and lower heater panels 22, 23 define a narrow furnace chamber 24 within which are supported tubes 25 along which the wire to be heat treated passes with very low tension due to the completely free straight horizontal path provided by each tube 25.

Each furnace section has at its inlet and outlet a bridge structure which can be best seen in Fig. 2.

This bridge structure serves to support the tubes 25 within the furnace chamber 24.

In the present example the bridge structure comprises two side by side relatively flat inverted U-shaped support pillars 26 adapted to mount a rail bridge plate 27 or 27A by means of a tongue-and-slot connection 28, 29.

The difference between the rail bridge plate 27 and 27A is that the rail bridge plate 27 ensures that the tubes 25 are mounted in horizontal alignment (see the lefthand side of Fig. 1) while rail bridge plate 27A (see righthand side of Fig. 1) permits the tubes 25 to be mounted in vertical staggered array.

Each rail bridge plate 27 or 27A is of castellated construction on its upper surface as indicated at 30.

The support pillars 26 and associated rail bridge plates 27 or 27A at the inlet and outlet to each furnace section are bridged by tube supporting rails 31 of T-configuration with upper relatively flat V-shaped grooves or recesses 32 on which are supported the tubes 25.

The support pillars 26, rail bridge plates 27 or 27A and supporting rails 31 are formed of reaction bonded silicon nitride or similar high temperature resistant ceramic material. The furnace chamber 24 is surrounded by an insulation mass 33 (top, bottom and sides) and between the top and bottom insulation 33 and. the inner skin or casing is a layer of aluminium foil 34.

The heater panels 22 and 23 are identical and this together with the central location of the metal tubes 25 within the furnace chamber 24 surrounded by the insulating mass 33 ensures total uniform symmetry (vertically and horizontally) of thermal distribution within the furnace chamber 24.

Each furnace section is controlled individually and a control thermocouple 38 extends upwardly into the furnace chamber to the central horizontal plane thereof.

A temperature limit thermocouple 39 is located at the top of the furnace chamber 24 centrally of the sides thereof.

The control means for each furnace section in addition to these thermocouples 38 and 39 comprises a temperature controller with solid state relay means (not shown). The ceramic tube limit thermocouple 39 is located inside a stainless steel tube 40 and is held by a bracket 41 in a relatively wide hole or space within the furnace structure.

It can be seen that the control temperature thermocouple 39 is similarly mounted within a stainless steel tube 42 supported by a bracket 43.

The terminals for the heaters 22 and 23 are indicated at 44 are ambient cooled as are those of the thermocouples 38 and 39.

The upper heater panels 22 and associated insulation and equipment are carried in a lid or cover 45 carried by a supporting arm structure 46 pivotally mounted on a shaft 47. This shaft 44 is rotatably supported in brackets 48 forming part of the furnace structure.

Access to the interior of the furnace is thus easily and readily gained.

Each furnace section preferably is provided with two upper heater panels 22 and two lower heater panels 23 or with upper or lower heater panels only.

The furnace according to the present invention thus ensures the application of controlled energy within a small volume combustion chamber with minimal loss of heat.

The individual heat control system for each furnace section ensures the attainment of the required temperature profile throughout the length and height of the furnace section and consequently throughout the entire length of the furnace.

Claims

CLAIMS:

1. A tubular furnace for continuously heat treating wire comprising at least one furnace section having at least one electrically-operated heating surface constituting one wall of a relatively narrow furnace chamber along which extends a metal tube or a horizontal array of metal tubes supported adjacent the heating surface on a bridge structure at the ilspUt side and output side of each section, and a control means for the or each furnace section to provide and maintain the electrical power input at a predetermined optimum value.

2. A tubular furnace as claimed in claim 1, in which the or each furnace section has upper and lower electrically-operated heating surfaces defining the relatively narrow furnace chamber and between which the horizontal array of metal tubes is supported.

3. A tubular furnace ace as claimed in claim 1 or 2, in which each bridge structure comprises a support pillar on which is mounted a rail bridge plate and between the input and output bridge structures of a furnace section rails for supporting the metal tubes.

4. A tubular furnace as claimed in claim 3, in which the support pillar is of a flattened inverted U-configuration.

5. A tubular furnace as claimed in claim 3 or 4, in which the rail bridge plate is coupled to a support pillar by a tongue-and-slot connection.

6. A tubular furnace as claimed in any one of claims 3 to 5, in which the rail bridge plate is of horizontally-castellated configuration at and along its upper end to receive the metal tube supporting rails.

7. A tubular furnace as claimed in any one of claims 3 to 6, in which each rail is of T-configuration with a grooved upper surface for receiving and supporting a metal tube.

8. A tubular furnace as claimed in any one of claims 3 to 7, in which the support pillars, rail bridge plates and supporting rails are formed of reaction bonded silicon nitride.

9. A tubular furnace as claimed in any one of claims 1 to 8, in which the metal tubes are thin walled and formed of high temperature resistant alloy material.

10. A tubular furnace as claimed in any one of claims i to 9, in which tne norizontal array of metal tubes is disposed in exact horizontal alignment or De vertically staggered.

11. z tubular furnace as claimed in any one of claims 2 to 10, in which the metal tubes are supported by the bridge structures between and relative to the upper dnd lower heating surfaces so as to ensure uniform and complete symmetry of thermal distribution (xZertically and h9rizontally) throughout the or each furnace section.

12. A tubular furnace as claimed in any one of claims 2 to 11, in which the upper and lower heating surfaces are defined by identical heater panels each constituted by resistance wires embedded in a ceramic mass, the pair of heater panels being coupled to their own electrical control means.

13. A tubular furnace as claimed in any one of claims 2 to 12, in which the control means comprises, per furnace section, a control thermocouple, temperature controller, solid state relay means, and a limit thermocouple.

14. A tubular furnace as claimed in claim 13, in which the control thermocouple is mounted centrally between the upper and lower heating surfaces and serves to ensure the required temperature profile within its respective furnace section.

15. A tubular furnace as claimed in claim 13 or 14, in which the wenlperature limit thermocouple is disposed at the top of each furnace section centrally of the furnace section, i.e. the hottest part of the latter.

16. A tubular furnace as claimed in any one of claims 1 to 15, in which the or each furnace section is surrounded by ceramic fibre insulation contained within an inner mild steel skin or casing

17. A tubular furnace as claimed in any one of claims 1 to 16, openable about a horiontal axis for - Eccess purposes.

18. A tubular furnace as claimed in any one of claims 1 to 17, comprising an openwork outer skin or casing spaced from an inner skin or casing.

19. A tubular furnace, substantially as hereinbefore described with reference to the accompanying drawings.