GB2073301A - Electric immersion heaters - Google Patents

Abstract

The head of an immersion heater has a screw-threaded portion (10), for securing it in place, with a circular end plate (11) at one end for supporting heating elements and an outwardly directed shoulder (13) at the other end. A polygonal flange (14) stems from the shoulder and has an inturned strengthening lip (15) with diametrically opposed lugs (16 and 17), the larger of which (16) carries a screw-threaded rod (18). The cover has a top (20) and a depending skirt (21). A marginal portion (23) of the skirt is of polygonal shape and fits within the lip (15) to make it difficult to insert a tool for levering off the cap. The smaller lug (17) projects through a hole (24) in the skirt to anchor the cap in place, while a hole (25) in the top of the cap enables a retaining nut to be screwed onto the rod (18). <IMAGE>

Description

SPECIFICATION Electric immersion heaters This invention relates to electric immersion heaters and in particular to the construction of heads and covers for immersion heaters. The invention is concerned with immersion heater heads of the kind (hereinafter referred to as the kind specified) comprising an externally screw-threaded tubular portion which a circular end plate at one end and an outwardly directed annular shoulder at the other end, a flange of polygonal outline stemming from the outer edge of the shoulder and extending in an axial direction away from the tubular portion. In use the heating element or each heating element of an immersion heater is mounted on the head, so as to project from that side of the end plate facing away from the flange.At the other side of the end plate are disposed, in use, various components such as electrical connections for the element or elements, and a thermostatically controlled switch. A removable and replaceable cover is provided which, when in position on the head, protects those components and prevents accidental access being obtained to the components.

Immersion heaters with heads of the kind specified and with covers of the kind outlined above are described and illustrated in British Standard 3456: Section A8: 1963, and while it is envisaged that immersion heaters embodying the present invention will usually be designed so as to comply with that British Standard (or any subsequent revision or revisions thereof) it is to be understood that the invention includes within its scope immersion heaters that do not so comply.

It was at one time the usual practice to form immersion heater heads of the kind specified as hot brass stampings. More recently, however, it has become relatively expensive to form heads in that manner and alternative methods of manufacture have been sought. With this in mind it has been proposed to form the heads from sheet metal by drawing or pressing operations, and it is with heads formed in this manner that the present invention is concerned.

According to the present invention there is provided in combination an immersion heater head of the kind specified and a cover, the head being formed from sheet metal, and that edge part of the flange further from the shoulder being formed with an inturned strengthening lip having two integral extensions directed towards each other from opposite sides of the head, one extension constituting a support for attachment means for the cover, and the other extension comprising a retaining lug for cooperation with a complementary formation on or in the cover, the arrangement being such that the head and cover can be assembled together so that the retaining lug co-operates with said complementary formation at one side of the cover, and the attachment means releasably retains the other side of the cover, it being necessary for the attachment means to be released and the cover to be partially removed from the head before said complementary formation can be released from the lug and the cover wholly removed from the head.

The attachment means may be releasably engageable with said support, and the arrangement may be such that it must be disengaged from that support before the cover can be removed from the head. In a preferred arrangement, however, the attachment means comprises a first part secured to the support and a second part releasably connectable to the first part, the arrangement being such that the cover can be removed when the first and second parts are disconnected from each other.

The complementary formation may comprise an indentation, a shoulder or the like formed on the cover, but in a preferred construction the complementary formation comprises a hole, in the cover, which is entered by the retaining lug when the cover is in place on the head.

The cover preferably includes a marginal portion which is lodged inside the strengthening lip and the flange when the cover is in place. The strengthening lip is preferably of substantially uniform width so that its inner edge is of a generally polygonal shape similar to the shape of the flange, the marginal portion of the cover preferably being of substantially the same shape so that there is only a narrow clearance between the marginal portion and the inner edge of the strengthening lip, the clearance being narrower than that which would occur if the marginal portion were of circular shape.

An embodiment of the present invention will now be described in more detail, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a plan view of an immersion heater head, Figure 2 is a section through the head, along the line 2-2 of Fig. 1, Figure 3 is a plan view of a cover for the head shown in Figs. 1 and 2, and Figure 4 is an elevation of the cover as viewed in the direction of the arrow 4 in Fig.

3.

The head shown in Figs. 1 and 2 is made from sheet brass and is intended to form part of an electric immersion heater in accordance with British Standard 3456: Section A8: 1963. The head comprises an externally screw-threaded tubular portion 10 with a circular end plate 11 at one end thereof. It is intended that a heating element should be mounted on the head, and to this end holes 1 2 are formed in the plate 11; the element projects from that side of the plate 11 facing away from the tubular portion 10, while at the other side of the plate are disposed various components such as electrical connections for the element and a thermostatically controlled switch. At the other end of the tubular portion 10 the head is formed with an outwardly directed annular shoulder 1 3 of planar form.A flange 14 of octagonal outline stems from the outer edge of the shoulder 1 3, and extends in an axial direction away from the tubular portion 10.

That edge part of the flange 1 4 further from the shoulder 1 3 is formed with an inturned strengthening lip 1 5 which is integral with the flange. The lip has two integral extensions 1 6 and 1 7 directed towards each other from opposite sides of the head. At one stage during the formation of the head the material from which the lip and extensions are to be formed constitutes an axial extension of the flange 1 4 and is aligned with the flange.

During a subsequent stage that material is subjected to the action of rollers which, in moving radially inwards, engage the material and cause it to bend inwards and so assume the desired shape. One of the extensions, 16, is larger than the other and constitutes a support. It is of generally triangular shape and is formed with a tapped hole near its free end.

This hole receives one end part of a rod 1 8 which is formed with a complementary thread and is secured in place by a lock nut 1 9. The rod extends in a direction parallel with the axis of the head. The other extension, 1 7, is smaller than the extension 1 6 and constitutes a retaining lug. The extension 1 7 is of rectangular shape, as illustrated.

The head is provided with a removable cover which is shown in Figs. 3 and 4. The cover is made from sheet steel with a wallthickness considerably less than that of the head. The cover has a circular top 20 and a depending skirt 21 stemming from its periphery. That portion 22 of the skirt adjacent to the top 20 is of circular cross-section, but of the marginal portion 23 of the skirt, adjacent to the rim of the cover, is of substantially octagonal shape.

At one side of the cover the marginal portion 23 is formed with a hole 24 of rectangular shape. The hole 24 is just sufficiently large to enable it to receive the lug 1 7. At the diametrically opposite side of the cover the tip 20 is formed with a circular hole 25, and the marginal portion is cut away as indicated at 26. Another part of the side wall 21 is also cut away as indicated at 27, to afford an opening for the entry of electrical leads when the immersion heater is installed.

The cover can be assembled with the head in the following manner. The cover is tilted, so that its axis is inclined to the axis of the head, and that part of the marginal portion 23 of the cover adjacent to the rectangular hole 24 is introduced into the hollow interior of the head close to the lug 1 7. The cover is then moved laterally so that the lug enters the hole.The cover is tilted back again so that it is co-axial with the head, the marginal portion 23 becoming lodged inside the strengthening lip 1 5 and the flange 1 4 and abutting the shoulder 1 3. The cut-away 26 is of a size just large enough to receive the support 1 6. The rod 1 8 is now aligned with the hole 25 in the top of the cover, and the cover is releasably secured in place by a cap nut (not shown) which is screwed onto the rod 1 8. The nut has a cylindrical sleeve, which enters the hole 25 and engages the top part of the rod 18, and a head of larger diameter than the sleeve and which engages that part of the top 20 of the cover bordering the hole 25. The head is formed with a transverse screwdriver slot.

When the cap nut is tightened it is found that the cover is held in place very securely.

For example any normal attempt to knock the cover off the head or to lever it off the head by means of a tool inserted between the cover and the strengthening lip is strongly resisted by the engagement between the lug 1 7 and the edges of the hole 24, between the cap nut and the top 20 of the cover, and between the marginal portion 23 of the cover and the adjacent parts of the head. It will be understood that there is only a narrow gap or clearance between the marginal portion 23 of the cover and the inner edge of the strengthening lip 15, that clearance being less than the clearance would have been if the marginal portion 23 had been of circular outline.

The cover can be removed by unscrewing the cap nut, tilting the cover so that that part thereof adjacent to the hole 26 is removed from the head, and then shifting the cover laterally so as to detach the cover from the lug 17.

Claims (9)

1. Immersion heater head of the kind specified and a cover, the head being formed from sheet metal, and that edge part of the flange further from the shoulder being formed with an inturned strengthening lip having two integral extensions directed towards each other from opposite sides of the head, one extension constituting a support for attachment means for the cover, and the other extension comprising a retaining lug for cooperation with a complementary formation on or in the cover, the arrangement being such that the head and cover can be assembled together so that the retaining lug co-operates with said complementary formation at one side of the cover, and the attachment means releasably retains the other side of the cover, it being necessary for the attachment means to be released and the cover to be partially removed from the head before said comple mentary formation can be released from. the lug and the cover wholly removed from the head.

2. An immersion heater head and cover according to Claim 1 of the preceding claims in which said complementary formation in the cover comprises a hole which is entered by the retaining lug when the cover is in place on the head.

3. An immersion heater head and cover according to either one of the preceding claims in which the attachment means extends through a hole in the cover and includes a part external to the cover which can be manipulated to enable the attachment means to release the cover.

4. An immersion heater head and cover according to any one of the preceding claims in which the attachment means comprises a first part secured to the support and a second part releasably connectable to the first part, the arrangement being such that the cover can removed when the first and second parts are disconnected from each other.

5. An immersion heater head and cover according to Claim 4 in which the first part of the attachment means comprises an externally screw-threaded element projecting from the support in a direction away from the tubular portion of the head, and the second part of the attachment means comprises an element with a complementary internal screw-thread.

6. An immersion heater head and cover according to any one of the preceding claims in which the cover is formed from sheet metal.

7. An immersion heater head and cover according to any one of the preceding claims in which the inner edge of the strengthening lip is of generally polygonal shape similar to the shape of the flange, a marginal portion of the cover being of substantially the same shape as that inner edge, the arrangement being such that when the cover is in place on the head there is only a narrow clearance between said marginal portion of the cover and the inner edge of the strengthening lip, the clearance being narrower than that which would occur if said marginal portion were of circular shape.

8. An immersion heater head and cover according to any one of the preceding claims in which the flange is of octagonal outline.

9. An immersion heater head of the kind specified and a cover, substantially as hereinbefore described with reference to the accompanying drawings.