GB2128305A - Electrode boiler - Google Patents

Abstract

An electrode shield for an electrode hot water boiler comprises a sheet of inert plastics material such as polytetrafluoroethylene rolled up into a cylinder 10 of appropriate length and diameter and retained in shape by means of screws or bolts 14 of an inert non-conductive material. The screws or bolts 14 are recessed into strips 16, 18 of similar inert non- conducting material so as to prevent fouling during use. <IMAGE>

Description

SPECIFICATION Electrode hot water boiler This invention relates to improvement in electrode hot water boilers, ana in particular to improvements in the electrode shields therefore.

Electrode hot water boilers produce hot water from electricity directly by the emersion of electrodes in the water. In normal operation the boilers are filled with water and the rate of hot water production is controlled by raising and lowering an insulating shield or shields between the live and neutral electrodes thereby adjusting the effective electrode operating area. One common type of electrode hot water boiler has electrodes projecting from the base of the boiler upwardly. The electrodes are generally in the form of cast iron alloy rods, and around each electrode, suspended from a suitable mounting plate, is a cylindrical insulator of porcelain or glass.The supporting plate is mounted on a thread mechanism turned by an electric motor thereby allowing the cylindrical insulators to be moved up and down into and out of register with their associated electrodes thereby controlling the power consumption of the boiler.

The electrode shield must obviously be of an insulating material, and must be durable enough to withstand constant operation in an environment of water which may be superheated to temperatures of up 1 800C. In practice this limits the material from which electrode shields can be made to glass and ceramic materials such as porcelain. These materials are extremely brittle and are easily damaged either in transit, or in service. Indeed our co-pending application No.

8214082 relates to a mechanism for reducing or eliminating one common problem causing damage in service to porcelain or glass electrode shields.

Apart from accidental damage, the very severe condition within such boilers chemically attack glass or porcelain limiting the service life of conventional electrode shields in any case. It is recognised that it would be preferable to employ an inert plastics material such as polytetrafluoroethylene for the manufacture of electrode shields, but this has provided impractical since cylinders of the size and diameter required for normal electrode hot water boiler application are not commercially available and, since it is difficult or impossible to produce a permanent bond in PTFE, cylinders of the necessary length made up from smaller units cannot be employed.

The present invention seeks to provide an improved electrode cylinder which overcomes or reduces many of the above problems.

According to the present invention there is provided an electrode shield for an electrode hot water boiler which comprises a sheet of inert plastics material rolled up into a cylinder of appropriate length and diameter, and retained in shape by means of screws or bolts of an inert non-conducting material.

In order that the screw or bolt heads should not protrude and foul the apparatus during operation of the electrode hot water boiler, the bolt heads, and nuts if employed, should preferably be recessed or countersunk either into the sheet material itself, or where this is of insufficient thickness, into a separate strip of material so as to provide a continuous smooth line.

The inert plastics material will preferably be a fluorocarbon material such as polytetrafluoroethylene, and the screws or bolts used to hold it together will preferably also be of the same material.

One preferred way of making the electrode shields of the present invention is to provide a sheet of inert plastics material skived off a solid cylindrical ingot of the material. Such a sheet will have a natural tendency to roll into a cylinder of substantially regular circular section. It is preferred that the greater portion of the circumference of the cylinder so formed should have a double thickness of the sheet material and the overlapping portion where the bolts or screws are applied, to be of three thicknesses, although other numbers of thicknesses can of course be employed depending on the thickness of the sheet material and the required strength and thickness of the finished cylinder.

The invention will be described further, by way of example, with reference to the accompanying drawing in which: Figure 1 is a transverse section through an electrode shield constructed in accordance with the invention; and Figure 2 is a side elevation, corresponding to figure 1.

Referring to the drawings, it can be seen that a cylindrical tube for use as an electrode shield for an electrode hot water boiler comprises a sheet of PTFE 10 rolled into a double thickness over the greater part of its circumference, and a triple thickness at the portion 1 2 where it is fixed together. The fixing is achieved by means of a series of PTFE screws 14 passing through holes bored in the sheet 10 and entering tapped holes within a strip of PTFE material 16. In order to prevent the heads of the screws 14 protruding, they are countersunk into holes in a second strip 1 8 also of PTFE material.Although the two strips 16, 1 8 protrude in the radial direction, they form a smooth line in the axial direction, which is the direction of movement of the cylinder in use which prevents the screw heads from fouling the apparatus. The thickness of the strips 16 and 18 can easily be accommodated in the space within an electrode hot water boiler for the electrode shields and thus forms no disadvantage in service.

In a particular example, a cylinder of approximately three feet in length and internal diameter of four inches was produced by skiving a 1/1 6" thick sheet 10 from a solid ingot of PTFE and producing a tube of double thickness as described above. This tube was fixed by means of conventional clips and/or bracket within an electrode hot water boiler in place of the conventional glass or porcelain electrode shield.

The electrode shield so made was approximately as cheap to produce as the conventional glass or porcelain shield it replaced, that was much less brittle and much more chemically resistant therefore giving a very much greater service life.

In order to prevent the possibiiity of the screws 1 4 coming loosened in service, the ends of the threads in the strip 16 may be burned over so preventing unscrewing.

While the invention has been described with reference to a type of electrode hot water boiler in which the electrodes project upwardly, it is of course equally applicable to types of boiler in which the electrodes are suspended downwardly.

Claims (Filed on 22.6.83.) 1. An electrode shield for an electrode hot water boiler which comprises a sheet of inert plastics material rolled up into a cylinder of appropriate length and diameter, and retained in shape by fixing means of an inert non conductive material.

2. A shield as claimed in claim 1 in which the plastics material is a fluorocarbon material.

3. A shield as claimed in claim 2 in which the material is polytetrafluoroethylene.

4. A shield as claimed in any one of claims 1 to 3 in which the fixing means are made of the same material as the cylinder.

5. A shield as claimed in any one of claims 1 to 4 in which the sheet is skived off a solid cylindrical ingot of the material.

6. A shield as claimed in any one of claims 1 to 5 in which the greater portion of the circumference of the cylinder has a double thickness of sheet material.

7. A shield as claimed in any one of claims 1 to 6 in which the fixing means are screws or bolts.

8. A shield as claimed in any one of claims 1 to A 7 in which the fixing means are countersunk into a strip of non-conductive material.

9. An electrode hot water boiler having an electrode shield as claimed in any one of claims 1 to 8.

10. An electrode shield substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

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

Claims (10)

**WARNING** start of CLMS field may overlap end of DESC **. The electrode shield so made was approximately as cheap to produce as the conventional glass or porcelain shield it replaced, that was much less brittle and much more chemically resistant therefore giving a very much greater service life. In order to prevent the possibiiity of the screws 1 4 coming loosened in service, the ends of the threads in the strip 16 may be burned over so preventing unscrewing. While the invention has been described with reference to a type of electrode hot water boiler in which the electrodes project upwardly, it is of course equally applicable to types of boiler in which the electrodes are suspended downwardly. Claims (Filed on 22.6.83.)

1. An electrode shield for an electrode hot water boiler which comprises a sheet of inert plastics material rolled up into a cylinder of appropriate length and diameter, and retained in shape by fixing means of an inert non conductive material.

2. A shield as claimed in claim 1 in which the plastics material is a fluorocarbon material.

3. A shield as claimed in claim 2 in which the material is polytetrafluoroethylene.

4. A shield as claimed in any one of claims 1 to 3 in which the fixing means are made of the same material as the cylinder.

5. A shield as claimed in any one of claims 1 to 4 in which the sheet is skived off a solid cylindrical ingot of the material.

6. A shield as claimed in any one of claims 1 to 5 in which the greater portion of the circumference of the cylinder has a double thickness of sheet material.

7. A shield as claimed in any one of claims 1 to 6 in which the fixing means are screws or bolts.

8. A shield as claimed in any one of claims 1 to A 7 in which the fixing means are countersunk into a strip of non-conductive material.

9. An electrode hot water boiler having an electrode shield as claimed in any one of claims 1 to 8.

10. An electrode shield substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.