GB2366710A - Tubular heater - Google Patents

Abstract

A tubular heater for an electric shower has a spirally-wound heating element on the outer surface of the tube 10. The heating element comprises a plurality of print lengths 20, 20.1, each of which corresponds to one complete wrapping of the spiral and each of which has a start point 22, 22.1 and a finish point. The start point 22, 22.1 of each print length is of reduced width relative to the rest of the print length. The print lengths are applied to the outer surface of the tube as wet screen prints, with the reduced width starting point of the second 20.1 and all subsequent print lengths overlapping the finish points of their respective previous print lengths 20 to create an overlap area 24. The arrangement ensures that there is no full width overlapping between adjacent print lengths and so reduces the risk of smudge or creep.

Description

TUBU LAR.WPD 2366710 TITLE: TUBULAR HEATER The present invention relates

to a tubular heater and in particular to a circular heating tube having a spirally wound heating element printed on its outer side.

A tubular heater is known in which a continuously wound heating element is provided on the 5 outside surface of a tube and a voltage applied to the heating element. A liquid, normally water, is passed through the tube. In this way, as the water passes through the tube its temperature is raised by heat generated by the heating element.

It is also known to apply the heating element to the outside surface of the tube by applying the element as a wet screen print which is then dried and fired. The print is wrapped around 10 the tube in a plurality of equal print lengths each of which corresponds to one wrapping of 3600. The start point of one print length is applied in overlapping relationship with the end point of a previously applied print length so as to build up progressively the required electrically continuous spiral element.

A difficulty which has arisen in carrying out the above described method lies in the fact that 15 the start point of a print length is applied in overlapping relationship with a wetted area created by the application of the previously applied print length which tends to cause smudging and creep of the print in the overlapped area, thus damaging the electrical contact between print lengths.

The invention seeks to overcome the above problem 20 In the drawing:

Figure I illustrates part of the length of a tubular heater to which a continuous spirally wound heating element has been applied by a known method, and TUBULAR.WPD 2 Figure 2 illustrates part of a tubular heater in accordance with the present invention to which a spirally wound heating element has been applied by the new method.

In Figure I the tubular heater body is designated 10. As indicated previously a plurality of print lengths 12 are applied sequentially to the body 10 as wet screen prints. The start point 5 of the first print length is designated 14 and the end point of the same print length is designated 16. Hence, each print length wraps around the body 10 by an angle somewhat in excess of 3600.

The second print length is designated-2 I.1.' The start point of this length is designated 14.1 so that an overlapping area 18, shown hatched, occurs between the beginning of this print 10 length and the end of the previous print length 14. Hence, the length 14.1 is applied over an area previously wetted by the application of the print length 14 and it is this which tends to cause smudging and creep of the print.

In Figure 2 the heater body is again designated 10, and, as can be seen, a spiral heating element is once more built up on the outside of the body. However, the start point 22 of each 15 print length 20 is of reduced area, i.e. narrower than the remaining width of the rest of the print length. The narrowed part 22 provides a lead-in to the leading edge or start point of the print length 20.

The second print length is designated 20.1 and its narrowed start point 22.1 is applied to the central region of the length 20 so that no overlapping of the fall widths of the two lengths 20 20 and 20.1 occurs. In this way the central region of the length 20 to which the narrowed start point 22.1 is applied creates a smaller overlapped area 24 with little or no risk of smudge or creep.

NEW151O.UK 3 1. A tubular heater having a spirally-wound heating element on the outer surface of the tube, the heating element comprising a plurality of print lengths each of which corresponds to one complete wrapping of the spiral and each of which has a start point and a finish point, characterised in that the start point of each print length is of reduced width relative to the rest of the print length.

2. A tubular heater as claimed in claim I in which the area of reduced width lies centrally of the print length and consists of a parallel-sided finger.