GB2094960A

GB2094960A - Electrical resistance furnaces

Info

Publication number: GB2094960A
Application number: GB8207871A
Authority: GB
Original assignee: PLUME A E Ltd
Current assignee: PLUME A E Ltd
Priority date: 1981-03-18
Filing date: 1982-03-18
Publication date: 1982-09-22
Also published as: GB2094960B

Abstract

An electrical resistance furnace includes a number of electrical resistance heating elements (11) arranged around the sides and surrounding a space (12) containing a crucible (13) or similar container to be heated. The elements (11) are supported at least at their ends by fire- brick material 19 and are surrounded by heat insulation (21, 22, 23, 33). Both ends of each resistance element (11) extend through apertures in the fire-brick material (19) so that by removing part of the heat insulation (23, 33) access may be gained to both ends of the element (11) from the exterior of the furnace to permit removal and repair or replacement. <IMAGE>

Description

SPECIFICATION Electrical resistance furnaces This invention relates to electrical resistance furnaces of the type which include a number of electrical resistance heating elements arranged around a space for a crucible or similar container to be heated, the elements being surrounded by fire-brick material which in turn is surrounded by various forms of heat insulation and usually an external metal casing is provided around the heat insulation.

One difficulty encountered with such furnaces is that when it becomes necessary to replace a faulty heating element a considerable delay, possibly a matter of days, is encountered due to the need to let the furnace cool before access can be gained to the element in the interior space.

It is an object of the present invention to alleviate this difficulty.

The present invention consists in an electrical resistance furnace which includes a number of electrical resistance heating elements arranged around the sides and surrounding a space containing a crucible or similar container to be heated, the elements being supported at least at their ends by fire-brick material and being surrounded by heat insulation, wherein both ends of each resistance element extend through apertures in the firebrick material so that by removing part of the heat insulation access may be gained to both ends of each element from the exterior of the furnace to permit removai and repair or replacement of the element.

in the accompanying drawings:- Figure 1 is a diagrammatic plan view of a part of one form of electrical resistance furnace according to the present invention; Figure 2 is a diagrammatic vertical part-section; Figure 3 shows a detail of a corner fire-brick; and Figure 4 shows a detail of one end of an electrical resistance heating element.

In carrying the invention into effect according to one convenient mode by way of example, an electrical resistance furnace includes a lumber of electrical resistance heating elements 11 arranged with their axes horizontally around a space 12 containing a crucible 1 3 resting upon fire-bricks 14.

Each resistance element consists of a ceramic tube 15 upon which is wound a conductor 1 6 welded at each end to a plate 17, having holes 20 for bolts 37, so that in the region of the plate 1 7 the current-carrying capacity of the conductor 16 is greatly increased to insure that the minimum of heat is generated in this region.

The elements 11 are supported at each end by corner fire-bricks 19, stacked one upon each other with the end wound turns of the conductors 1 6 resting in U-shaped grooves 1 8 in the fire-bricks 1 9. The ends of the tubes 1 5 extend beyond the end wound turns of the conductors 16 but do not extend through the fire-bricks 1 9 to the exterior.

Beyond the end wound turns the conductors extend to the exterior where they are connected to the plates 1 7. Normally the elements have a 3phase star or delta connection formed by means of links 35 and one or two of the four corners of the furnace are arranged for external connection to the electrical power supply. At the other two or three corners, adjacent ends of the elements are interconnected by links 31 as in Figure 1.

The elements 11 are surrounded by heat insulation in the form of pre-formed calcium silicate boards 21 extending between the corner fire-bricks 19 and these are backed up by further calcium silicate boards 22.

In turn, these components are encased in a metallic outer casing 24 having removable corner covers secured by screens 32 and corner calcium silicate boards 33 are provided inside the corners 25 to complete the heat insulation. The casing is completed by top cover 36 having a removable lid 38.

Inside the corner boards 33 there is provided ceramic wool fibre 23 which is also inserted in the grooves 19 around the ends of the conductors 1 6 and tubes 1 5. A heat insulating fillet 34 rests upon the top of the corner fire-bricks 1 9 and the top of the boards 21 and engages the side of the crucible 13 so as to provide a reasonable seal for space 1 2 assisted by the fibre 23 in the grooves 1 8.

It will be appreciated that with this arrangement, should any element 11 need replacing then all that is necessary is to let the furnace cool for a short while and then remove the appropriate two corner covers 25 and corner heat insulation 33 and 23.

This will permit access to the electrical connections at both ends of the faulty elements so that the element can be disconnected and withdrawn from the furnace and repaired or replaced without needing to gain access to the interior of the furnace. This operation may thus be performed and the furnace started up again in a much shorter period of time when compared with conventional furnaces, thus saving possibly a number of days interruption in the use of the furnace.

In some cases, if appropriate electrical connections can be provided, it may be sufficient to gain access to only one end of each resistance element.

1. An electrical resistance furnace which includes a number of electrical resistance heating elements arranged around the sides and surrounding a space containing a crucible or similar container to be heated, the elements being supported at least at their ends by fire-brick material and being surrounded by heat insulation, wherein both ends of each resistance element extend through apertures in the fire-brick material so that by removing part of the heat insulation access may be gained to both ends of each element from the exterior of the furnace to permit removal and repair or replacement of the element.

2. An electrical resistance furnace as claimed in

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Electrical resistance furnaces This invention relates to electrical resistance furnaces of the type which include a number of electrical resistance heating elements arranged around a space for a crucible or similar container to be heated, the elements being surrounded by fire-brick material which in turn is surrounded by various forms of heat insulation and usually an external metal casing is provided around the heat insulation. One difficulty encountered with such furnaces is that when it becomes necessary to replace a faulty heating element a considerable delay, possibly a matter of days, is encountered due to the need to let the furnace cool before access can be gained to the element in the interior space. It is an object of the present invention to alleviate this difficulty. The present invention consists in an electrical resistance furnace which includes a number of electrical resistance heating elements arranged around the sides and surrounding a space containing a crucible or similar container to be heated, the elements being supported at least at their ends by fire-brick material and being surrounded by heat insulation, wherein both ends of each resistance element extend through apertures in the firebrick material so that by removing part of the heat insulation access may be gained to both ends of each element from the exterior of the furnace to permit removai and repair or replacement of the element. in the accompanying drawings:- Figure 1 is a diagrammatic plan view of a part of one form of electrical resistance furnace according to the present invention; Figure 2 is a diagrammatic vertical part-section; Figure 3 shows a detail of a corner fire-brick; and Figure 4 shows a detail of one end of an electrical resistance heating element. In carrying the invention into effect according to one convenient mode by way of example, an electrical resistance furnace includes a lumber of electrical resistance heating elements 11 arranged with their axes horizontally around a space 12 containing a crucible 1 3 resting upon fire-bricks 14. Each resistance element consists of a ceramic tube 15 upon which is wound a conductor 1 6 welded at each end to a plate 17, having holes 20 for bolts 37, so that in the region of the plate 1 7 the current-carrying capacity of the conductor 16 is greatly increased to insure that the minimum of heat is generated in this region. The elements 11 are supported at each end by corner fire-bricks 19, stacked one upon each other with the end wound turns of the conductors 1 6 resting in U-shaped grooves 1 8 in the fire-bricks 1 9. The ends of the tubes 1 5 extend beyond the end wound turns of the conductors 16 but do not extend through the fire-bricks 1 9 to the exterior. Beyond the end wound turns the conductors extend to the exterior where they are connected to the plates 1 7. Normally the elements have a 3phase star or delta connection formed by means of links 35 and one or two of the four corners of the furnace are arranged for external connection to the electrical power supply. At the other two or three corners, adjacent ends of the elements are interconnected by links 31 as in Figure 1. The elements 11 are surrounded by heat insulation in the form of pre-formed calcium silicate boards 21 extending between the corner fire-bricks 19 and these are backed up by further calcium silicate boards 22. In turn, these components are encased in a metallic outer casing 24 having removable corner covers secured by screens 32 and corner calcium silicate boards 33 are provided inside the corners 25 to complete the heat insulation. The casing is completed by top cover 36 having a removable lid 38. Inside the corner boards 33 there is provided ceramic wool fibre 23 which is also inserted in the grooves 19 around the ends of the conductors 1 6 and tubes 1 5. A heat insulating fillet 34 rests upon the top of the corner fire-bricks 1 9 and the top of the boards 21 and engages the side of the crucible 13 so as to provide a reasonable seal for space 1 2 assisted by the fibre 23 in the grooves 1 8. It will be appreciated that with this arrangement, should any element 11 need replacing then all that is necessary is to let the furnace cool for a short while and then remove the appropriate two corner covers 25 and corner heat insulation 33 and 23. This will permit access to the electrical connections at both ends of the faulty elements so that the element can be disconnected and withdrawn from the furnace and repaired or replaced without needing to gain access to the interior of the furnace. This operation may thus be performed and the furnace started up again in a much shorter period of time when compared with conventional furnaces, thus saving possibly a number of days interruption in the use of the furnace. In some cases, if appropriate electrical connections can be provided, it may be sufficient to gain access to only one end of each resistance element. CLAIMS

2. An electrical resistance furnace as claimed in claim 1, wherein the regions where the ends of the elements pass through the fire-brick material and the region between the top of the heat insulation and near the top of the crucible are seaied to enclose the space surrounding the crucible.

3. An electrical resistance furnace as claimed in claim 1 or 2, wherein the furnace is provided with an outer casing having four removable corn covers covering removable heat insulation so that both may be removed to gain access to the ends of the elements at each corner.

4. An electrical resistance furnace wherein -he axes of the heating elements are hodzontal.

5. An electrical resistance furnace substantially as described with reference to the accompanying drawin ws.