GB2074000A

GB2074000A - Resistance heating elements

Info

Publication number: GB2074000A
Application number: GB8109171A
Authority: GB
Original assignee: Bellinger L H
Current assignee: Bellinger L H
Priority date: 1980-04-02
Filing date: 1981-03-24
Publication date: 1981-10-21
Also published as: GB2074000B

Abstract

The use of electrical resistance heating in pottery kilns hitherto has been inhibited by firstly the need to provide door interlock safety devices and secondly the inability to effect reduction firing without damaging the resistance heaters. The object of the invention is to provide resistance heating means suitable for kilns avoiding these disadvantages, this objective being met in a construction comprising an impervious ceramic tube (1) through which a resistance heating element (12) passes leaving the bore of the tube free for the passage of cooling air. The bore of the tube may be closed during heating by a plug (17). <IMAGE>

Description

SPECIFICATION Resistance heating elements This invention relates to resistance heating means and is particularly, though not necessarily, concerned with resistance heating means for pottery kilns.

Hitherto, electrical resistance heating of pottery kilns has been inhibited by two major parameters.

Firstly, the presence of electrical resistance elements inside the kiln has made it necessary to provide door interlock safety devices, to ensure that an operative cannot enter the kiln with power to the resistance heaters still on, and which would be potentially dangerous to the operative, and secondly, great difficulty is experienced in effecting necessary reduction firing of the pottery in the kiln. Reduction firing of the pottery is frequently a necessary step in pottery production, and with a kiln heated with conventional resistance heaters, the elements are almost invariably damaged during reduction firing, to an extent necessitating their replacement afterthe reduction firing step.

The object of the present invention is to provide a resistance heating means suitable for use in kilns and which avoids the above disadvantages.

According to the present invention, a resistance heating means comprises an impervious ceramic tube through which a resistance heating element passes leaving the bore free for the passage of air.

Preferable, the heating element is a wire coil cemented inside the ceramic tube, the coil having double twisted tails leading to the terminals connecting the coil to a source of electrical supply. It is further preferred that one end of the tube is closed during use of the heating means by a loose fitting plug, which plug can be removed to allow relatively rapid cooling of the ceramic tube. Thus, at each end of the ceramic tube, the tails of the element may surround a second, short, ceramic tube set in the end of the main ceramic tube, and the plug may be a loose fit in one of the second, short ceramic tubes.

Alternatively, a small calibrated hole can be provided in one (upper in use) end of the tube, which avoids the need for a loose plug, and whilst the cooling of the tube is not quite so rapid as is the case when the loose plug is removed, it still avoids all the disadvantages of the known closed tubes.

When used in a pottery kiln, the main ceramic tube can lie in appropriate holes through the top and bottom linings to the kiln, there being a support member below the bottom lining against which the main tube or the, lower, second tube abuts. Preferably, and to assist in the passage of air through the main ceramic tube, it is set in a substantially vertical disposition.

The invention, particularly when used in a reduction firing pottery kiln satisfies the two requirements of being electrically safe, thereby avoiding the need for door interlock safety devices and allows reduction firing of any conventional type without there being the risk of damage to the heating elements. An additional advantage is that with the loose fitting plug removed, a controlled, but relatively rapid cooling of the heating means is achieved without introducing the possibility of imparting thermal shock to the kiln load, this allowing the kiln to be opened much earlier than has been possible hitherto.

One embodiment of the invention will now be described with reference to the accompanying schematic drawings, in which : Figure 1 is a vertical section through part of a pottery kiln having electrical resistance heating means according to the invention; and Figure 2 is a sectional side elevation through the electrical resistance heating means of Figure 1,to a larger sale.

In the drawings, electrical resistance heating means has an impervious ceramic tube 1 extending through holes 2,3 in the top and bottom lining 4, 5 of a pottery kiln 6. The heating means having a generally vertical disposition and being supported by a support member 7 lying below the kiln. Leads 8, 9 from a resistance heating element within the tube 1 extend to terminals 10,11.

As is shown in Figure 2, the resistance heating element is a wire coil 12 cemented within the tube having double twist tails 13, 14terminating in the leads 8, 9. Set within the tube 1 at each end is a secondary tube 15, 16 providing for the passage of air through the bore of the tube 1, the tube 15 being provided with a loose fitting ceramic plug 17, placed in the position shown during heating of the kiln to restrict air flow through the tube 1.

Thus, during heating of the kiln, the resistance heating element 12 is electrically safe, and there is, therefore, no necessity to provide complex and expensive interlock door safety devices. Equally importantly, when reduction firing takes place (using any of the known techniques) there is complete protection afforded the element 12 by the tube 1.

After heating the kiln, and after reduction firing when required, the heating means is switched off, and the plug 17 removed to allow free passage of air through the tube 1. This brings about rapid but controlled cooling of the heating means, and avoids any thermal shock being applied to the kiln load.

1. A resistance heating means comprising an impervious ceramic tube through which a resistance heating element passes leaving the bore free for the passage of air.

2. Resistance heating means as in Claim 1, wherein the heating element is a wire coil cemented inside the ceramic tube.

3. Resistance heating means as in claim 2, wherein the coil has doubled twisted tails leading to the terminals connecting the coil to a source of electrical supply.

4. Resistance heating means as in any of Claims 1 to 3, wherein one end of the tube is closed during use by a loose fitting removable plug.

5. Resistance heating means as in any of Claims 1 to 3, wherein a small calibrated hole is provided at one end of the tube.

6. Resistance heating means as in any of Claims

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Resistance heating elements This invention relates to resistance heating means and is particularly, though not necessarily, concerned with resistance heating means for pottery kilns. Hitherto, electrical resistance heating of pottery kilns has been inhibited by two major parameters. Firstly, the presence of electrical resistance elements inside the kiln has made it necessary to provide door interlock safety devices, to ensure that an operative cannot enter the kiln with power to the resistance heaters still on, and which would be potentially dangerous to the operative, and secondly, great difficulty is experienced in effecting necessary reduction firing of the pottery in the kiln. Reduction firing of the pottery is frequently a necessary step in pottery production, and with a kiln heated with conventional resistance heaters, the elements are almost invariably damaged during reduction firing, to an extent necessitating their replacement afterthe reduction firing step. The object of the present invention is to provide a resistance heating means suitable for use in kilns and which avoids the above disadvantages. According to the present invention, a resistance heating means comprises an impervious ceramic tube through which a resistance heating element passes leaving the bore free for the passage of air. Preferable, the heating element is a wire coil cemented inside the ceramic tube, the coil having double twisted tails leading to the terminals connecting the coil to a source of electrical supply. It is further preferred that one end of the tube is closed during use of the heating means by a loose fitting plug, which plug can be removed to allow relatively rapid cooling of the ceramic tube. Thus, at each end of the ceramic tube, the tails of the element may surround a second, short, ceramic tube set in the end of the main ceramic tube, and the plug may be a loose fit in one of the second, short ceramic tubes. Alternatively, a small calibrated hole can be provided in one (upper in use) end of the tube, which avoids the need for a loose plug, and whilst the cooling of the tube is not quite so rapid as is the case when the loose plug is removed, it still avoids all the disadvantages of the known closed tubes. When used in a pottery kiln, the main ceramic tube can lie in appropriate holes through the top and bottom linings to the kiln, there being a support member below the bottom lining against which the main tube or the, lower, second tube abuts. Preferably, and to assist in the passage of air through the main ceramic tube, it is set in a substantially vertical disposition. The invention, particularly when used in a reduction firing pottery kiln satisfies the two requirements of being electrically safe, thereby avoiding the need for door interlock safety devices and allows reduction firing of any conventional type without there being the risk of damage to the heating elements. An additional advantage is that with the loose fitting plug removed, a controlled, but relatively rapid cooling of the heating means is achieved without introducing the possibility of imparting thermal shock to the kiln load, this allowing the kiln to be opened much earlier than has been possible hitherto. One embodiment of the invention will now be described with reference to the accompanying schematic drawings, in which : Figure 1 is a vertical section through part of a pottery kiln having electrical resistance heating means according to the invention; and Figure 2 is a sectional side elevation through the electrical resistance heating means of Figure 1,to a larger sale. In the drawings, electrical resistance heating means has an impervious ceramic tube 1 extending through holes 2,3 in the top and bottom lining 4, 5 of a pottery kiln 6. The heating means having a generally vertical disposition and being supported by a support member 7 lying below the kiln. Leads 8, 9 from a resistance heating element within the tube 1 extend to terminals 10,11. As is shown in Figure 2, the resistance heating element is a wire coil 12 cemented within the tube having double twist tails 13, 14terminating in the leads 8, 9. Set within the tube 1 at each end is a secondary tube 15, 16 providing for the passage of air through the bore of the tube 1, the tube 15 being provided with a loose fitting ceramic plug 17, placed in the position shown during heating of the kiln to restrict air flow through the tube 1. Thus, during heating of the kiln, the resistance heating element 12 is electrically safe, and there is, therefore, no necessity to provide complex and expensive interlock door safety devices. Equally importantly, when reduction firing takes place (using any of the known techniques) there is complete protection afforded the element 12 by the tube 1. After heating the kiln, and after reduction firing when required, the heating means is switched off, and the plug 17 removed to allow free passage of air through the tube 1. This brings about rapid but controlled cooling of the heating means, and avoids any thermal shock being applied to the kiln load. CLAIMS

6. Resistance heating means as in any of Claims 1 to 5, wherein at each end of the ceramic tube the tails of the element surround a second short ceramic tube set in the end of the main ceramic tube.

7. Resistance heating means as in Claim 5 or Claim 6, wherein the plug is a loose fit in one of the short ceramic tubes.

8. Resistance heating means substantially as hereinbefore described with reference to the accom panying drawings.