GB1588771A - Furnace heating elements - Google Patents

Description

(54) IMPROVEMENTS IN OR RELATING TO FURNACE HEATING ELEMENTS (71) We, FHD FURNACES LI MITED, a British Company of, 124a/130, Edinburgh Avenue, Trading Estate, Slough SL1 4SW, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to furnace heating elements of the tape type.

A conventional tape-type heater element consists of a length of resistance material formed with a series of return bends so as to have substantially parallel spaced lengths to give reasonably uniform heating over an area, e.g. 2 feet square. The lengths of tape have to be kept spaced apart and the element needs to be supported in use.

Where an element is used in a furnace from which it is not removable without complete access, e.g. by opening a hinged roof of the furnace, or dismantling some part of the furnace, it may be supported on a tile or beams of refractory insulating material (such as Sillimanite) and held in place by so-called cleats recessed in the slots in the tile or beams and locked in position e.g. by jamming rods which also serve to stop the element tape from rising above the cleats. In other cases resort has been had to combtype spacers in which spacer beams are formed as combs, with slots into which the tape is introduced and then retained in position by wire staples. In either case, the tape is under considerable stress and the assembly of the element is beset by many practical difficulties in force the tape into the required position and holding it.Also, when the element is used, considerable thermal expansion (followed by contraction on cooling) takes place, and the tightly fitted tape and comb or cleats cause mechanical stress, which may damage the tape or the supports, leading to premature failure.

According to the invention, there is provided a tape-type resistance furnace heating element comprising a length of resistance tape formed into a series of spaced substantially parallel lengths joined by return bends, a series of insulating refractory spacer beams extending transversely to the parallel lengths, each spacer beam having a series of longitudinally spaced apertures each aperture receiving two adjacent lengths of the tape so that during assembly the return bends at one side of the element may be threaded through the apertures of the beams which may then be slid relative to the element to the required positions thereon, the spacer beams being free for limited longitudinal movement relative to each other, and means for spacing the spacer beams for each other.

It is preferred to have insulating refractory spacer pins, such as lengths of alumina tubing, located in the apertures to prevent contact between the adjacent lengths passing through a common aperture.

This arrangement of spacer beams means that the spacer beams can conform to the heater tape rather than vice versa and simplifies assembly considerably.

The invention will be further described with reference to the drawing accompanying the provisional specification. The single Figure of drawing is a perspective view of a preferred embodiment of heating element according to the present invention installed as the roof heater on a hooded hearth type of furnace.

Although the element illustrated is shown as installed as a roof heater in a particular type of furnace, it is to be understood that it may be used in other types of furnace and also it is not confined to being used as a roof heater but may also be used as a side or floor heating element.

Attention is drawn to our co-pending patent application No. 13817/77, (Serial No.

1588772) filed simultaneously herewith and entitled "Improvements in or relating to furnaces".

The only parts of the furnace shown, other than the heater element are a hearth 1, a hood 2 and support beams 3.

The heating element consist is of a length of resistance tape having its ends formed as lead-outs 4 adapted to extend out through the sides of the furnace for connection to external circuitry. Between the ends 4, the element is formed into spaced and substantially parallel lengths joined by return bends 5. The return bends are shown in the drawing at one end only, but it will be appreciated that similar return bends will be provided at the opposite side.

The tape is assembled with a plurality of spacer beams 6, each of which has a series of apertures 7 equal to half the number of parallel lengths of tape. The spacer beams 6 are threaded successively and independently onto the tape by threading the return bends at the far side of the element one through each aperture and relatively sliding the tape and spacer beams. The spacer beams are formed of a refractory insulating material such as Sillimanite, which is a refractory material based on a mixture of alumina and silica.

The spacer beams 6 are spaced apart by means of spacers 8, which may be in the form of short lengths of tube, e.g. of alumina, which are loosely retained in position by a loop of wire 9 threaded through holes in the spacer beams 8 and through the tubes. The ends of the wire 9 may be welded or otherwise secured together.

In order to prevent the adjacent lengths of tape from coming into contact. it is preferred to insert spacer pins 10 across the apertures 7 between the lengths of tape therein. For this purpose, the spacer beam is preferably provided at the top with a through hole leading into each aperture and spacer pins themselves, which may for instance be tubes of alumina or other refractory material. are dropped in through these holes. There is no need to anchor the lower ends of these tubes. In many cases, centering of the tube to get it in to a receiving aperture could in fact make assembly much more difficult.

It will be seen that this form of heater element is comparatively easy to assemble in that there is no need to force the lengths of tape into closely predetermined positions, but instead each of the spacer beams is threaded 011 separately and they remain structurally separate although spaced apart by the spacers 8. This means that should the tape have some sort of distortion, this can be accommodated and the tape is also reasonably free to expand and contract in normal use. The tape itself has considerable structural strength so that the assembly of tape and spacer beams may be handled as a unit and introduced to or removed from the furnace in the assembled state.

Although it has been described in a form in which each spacer beam extends the whole width of the tape, it might, if a large number of lengths of tape were used, prove to be easier to assemble such an arrangement in which the spacer beams were not as long as this.

Various other modifications may be made within the scope of the invention WHAT WE CLAIM IS: 1. A tape-type resistance furnace heating element comprising a length of resistance tape formed into a series of spaced substantially parallel lengths joined by return bends. a series of insulating refractory spacer beams extending transversely to the parallel lengths, each spacer beam having a series of longitudinally spaced apertures each aperture receiving two adjacent lengths of the tape so that during assembly the return bends at one side of the element may be threaded through the apertures of the beams which may then be slid relative to the element to the required positions thereon, the spacer beams being free for limited longitudinal movement relative to each other, and means for spacing the spacer beams from each other.

2. An element as claimed in claim 1, comprising refractory spacer pins located in the apertures to prevent contact between the adjacent lengths passing through a common aperture.

3. An element as claimed in claim 2, in which the spacer pins are formed by lengths of alumina tubing.

4. An element as claimed in claim 1, 2 or 3. in which the means for spacing the spacer beams comprising lengths of refractory tubing suspended between the spacer beams on a supporting loop passing through the tubing and through alignment holes formed in the spacer beams.

5. An element as claimed in any of the preceding claims in which the spacer beams each extend the whole width of the element.

6. A tape type resistance furnace heating element substantially as hereinbefore described with reference to the drawing accompanying the provisional specification.

7. A furnace including at least one heating element as claimed in any of claims 1 to 5.

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

Claims (7)

**WARNING** start of CLMS field may overlap end of DESC **. entitled "Improvements in or relating to furnaces". The only parts of the furnace shown, other than the heater element are a hearth 1, a hood 2 and support beams 3. The heating element consist is of a length of resistance tape having its ends formed as lead-outs 4 adapted to extend out through the sides of the furnace for connection to external circuitry. Between the ends 4, the element is formed into spaced and substantially parallel lengths joined by return bends 5. The return bends are shown in the drawing at one end only, but it will be appreciated that similar return bends will be provided at the opposite side. The tape is assembled with a plurality of spacer beams 6, each of which has a series of apertures 7 equal to half the number of parallel lengths of tape. The spacer beams 6 are threaded successively and independently onto the tape by threading the return bends at the far side of the element one through each aperture and relatively sliding the tape and spacer beams. The spacer beams are formed of a refractory insulating material such as Sillimanite, which is a refractory material based on a mixture of alumina and silica. The spacer beams 6 are spaced apart by means of spacers 8, which may be in the form of short lengths of tube, e.g. of alumina, which are loosely retained in position by a loop of wire 9 threaded through holes in the spacer beams 8 and through the tubes. The ends of the wire 9 may be welded or otherwise secured together. In order to prevent the adjacent lengths of tape from coming into contact. it is preferred to insert spacer pins 10 across the apertures 7 between the lengths of tape therein. For this purpose, the spacer beam is preferably provided at the top with a through hole leading into each aperture and spacer pins themselves, which may for instance be tubes of alumina or other refractory material. are dropped in through these holes. There is no need to anchor the lower ends of these tubes. In many cases, centering of the tube to get it in to a receiving aperture could in fact make assembly much more difficult. It will be seen that this form of heater element is comparatively easy to assemble in that there is no need to force the lengths of tape into closely predetermined positions, but instead each of the spacer beams is threaded 011 separately and they remain structurally separate although spaced apart by the spacers 8. This means that should the tape have some sort of distortion, this can be accommodated and the tape is also reasonably free to expand and contract in normal use. The tape itself has considerable structural strength so that the assembly of tape and spacer beams may be handled as a unit and introduced to or removed from the furnace in the assembled state. Although it has been described in a form in which each spacer beam extends the whole width of the tape, it might, if a large number of lengths of tape were used, prove to be easier to assemble such an arrangement in which the spacer beams were not as long as this. Various other modifications may be made within the scope of the invention WHAT WE CLAIM IS:

1. A tape-type resistance furnace heating element comprising a length of resistance tape formed into a series of spaced substantially parallel lengths joined by return bends. a series of insulating refractory spacer beams extending transversely to the parallel lengths, each spacer beam having a series of longitudinally spaced apertures each aperture receiving two adjacent lengths of the tape so that during assembly the return bends at one side of the element may be threaded through the apertures of the beams which may then be slid relative to the element to the required positions thereon, the spacer beams being free for limited longitudinal movement relative to each other, and means for spacing the spacer beams from each other.

2. An element as claimed in claim 1, comprising refractory spacer pins located in the apertures to prevent contact between the adjacent lengths passing through a common aperture.

3. An element as claimed in claim 2, in which the spacer pins are formed by lengths of alumina tubing.

4. An element as claimed in claim 1, 2 or 3. in which the means for spacing the spacer beams comprising lengths of refractory tubing suspended between the spacer beams on a supporting loop passing through the tubing and through alignment holes formed in the spacer beams.

5. An element as claimed in any of the preceding claims in which the spacer beams each extend the whole width of the element.

6. A tape type resistance furnace heating element substantially as hereinbefore described with reference to the drawing accompanying the provisional specification.

7. A furnace including at least one heating element as claimed in any of claims 1 to 5.