GB2136098A

GB2136098A - Hot water cylinders

Info

Publication number: GB2136098A
Application number: GB08306041A
Authority: GB
Inventors: John Barry Bryant; John Robert Bryant
Original assignee: Bryant & Sons Ltd Barry
Current assignee: Bryant & Sons Ltd Barry
Priority date: 1983-03-04
Filing date: 1983-03-04
Publication date: 1984-09-12
Also published as: GB2136098B; GB8306041D0

Abstract

A hot water cylinder 10 is moulded, without seams, from a plastics material. The top 12 of the cylinder is domed outwardly, whilst the bottom 14 of the cylinder 10 is domed inwardly. The bottom 14 may have a complex surface, formed of portions of different curvatures, at the intersections of which are formed strengthening ribs. An indirect heating coil 26 passes through externally threaded connectors 22, 24, which are formed integrally in the side walls of the tank 10, and which serve as parts of compression fittings around the coil 26. The wall thickness of the cylinder 10 is greater at the top 12 than at the bottom 14, which in turn is of greater thickness than the side walls. <IMAGE>

Description

SPECIFICATION Hot water cylinders This invention relates to hot water cylinders, and is concerned particularly although not exclusively with domestic hot water cylinders.

According to a first aspect of the invention, there is provided a seamless hot water cylinder of plastics material.

Preferably, the cylinder is formed with at least one connector of plastics material, for connection to external pipework. Indeed, it is preferred that every connector on the cylinder, for connection to external pipework, is of plastics material.

The cylinder preferably has an indirect hot water heating coil within the cylinder, the coil having an inlet pipe and an outlet pipe each of which passes through a plastics tube projecting outwardly of the wall of the cylinder, each tube being formed on the cylinder and forming at least part of a seal around the respective pipe.

Preferably, each tube is externally threaded and co-operates with an internally threaded nut of a compression fitting which forms a seal around the respective pipe.

The wall of the cylinder may advantageously be thickened adjacent each point where a connection is made to the tank. The cylinder wall is preferably thicker at the top and bottom of the cylinder than at the sides of the cylinder. The cylinder wall may be thicker at the top of the cylinder than at the bottom.

The top of the cylinder is preferably domed outwardly, and the bottom of the cylinder is preferably concave. Advantageously, the bottom of the cylinder may be formed with a plurality of adjacent recesses projecting into the cylinder. At least some of the recesses may have different curvatures.

The cylinder is preferably a domestic hot water cylinder, and may be of polyethylene, which may advantageously be translucent.

According to a second aspect of the present invention, there is provided a method of manufacturing a hot water cylinder, comprising the steps of charging a mould with particles of a thermoplastic plastics material, heating the mould to cause the particles to melt, spinning the mould to distribute the molten material within the mould, and allowing the mould to cool whilst continuing to spin it, thereby to form a seamless plastics hot water cylinder within the mould.

Preferably, the mould has a removable lid, and the cylinder is withdrawn through the top of the mould when the lid has been removed. The lid may contain mould portions which mould plastics connectors on the cylinder, which connectors are for connection to external pipework.

The rest of the mould may also contain mould portions which mould plastics connectors on the cylinder, which connectors are for connection to external pipework. The mould portions preferably afford local thickening of the cylinder wall.

Preferably, at least some of the mould portions are removable.

The mould may be spun at a speed substantially in the range 50 to 60 r.p.m.

The mould may be heated to a temperature substantially in the range 2000 C to 4000 C.

The plastics material may comprise polyethylene.

The mould is preferably spun about 2 orthogonal axes. The respective speeds of rotation of the mould about the 2 orthogonal axes may be different. Preferably, the mould is spun in such a way as to form a cylinder wall which is thicker at the top and bottom than at the sides of the cylinder.

Preferably, the method in accordance with the second aspect of the invention is employed to provide a hot water cylinder in accordance with the first aspect of the invention.

For a better understanding of the invention and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying diagrammatic drawings, in which: Figure 1 is a side elevation of a domestic hot water cylinder embodying the invention; Figure 2 is a plan view of the cylinder; Figure 3 is a detail view showing, in section, a fitting on the cylinder for an immersion heater; Figure 4 shows in plan the bottom of a modified cylinder; Figure 5 is a part sectional view on the line V-V of Figure 4, and Figure 6 is a sectional view on the line VI--VI of Figure 4.

The hot water cylinder 10 illustrated in Figures 1 and 2 is of translucent polyethylene material. It has an outwardly domed top 12, and a concave recessed bottom 14. The wall thickness of the cylinder is thicker at the top 12 than at the base 14, which in turn is of a greater thickness than the side walls of the cylinder.

A cold water inlet connector 1 8 is formed integrally with the tank 10, towards the bottom thereof. A hot water outlet connector 20 is formed integrally with the tank 10, at the top 12 thereof.

An inlet connector 22 and an outlet connector 24 for an indirect heating coil 26 are also formed integrally in the side walls of the hot water tank 1 0. The side walls of the tank are provided with thickened portions 1 6, at each of the connections 18, 22 and 24. The top 12 of the cylinder is provided with a larger thickened portion 30, at one side of which the hot water outlet connector 20 is provided.

To the side of the connector 20 there is provided a further connector 28, which is also formed in the thickened part 30 of the lid 12, and is adapted to receive an immersion heater 34, as illustrated in Figure 3.

The connector 28 is formed integrally with the thickened portion 30, of plastics material, and is provided with an internal screw-thread 36. This mates with an external screw-thread 38 provided on the immersion heater 34, which is therefore simply screwed into place, within the connector 28. A metal band 32 is fitted closely around the connector 28, to strengthen the same.

The illustrated hot water cylinder 10 is manufactured as follows.

Firstly, there is provided a mould which is of a cylindrical shape, and has a detachable lid. The lid is formed with mould units for forming the thickened portion 30 and the connectors 20 and 28 in the top 12 of the cylinder. The sides of the mould are provided with a plurality of detachable mould units, for forming the connectors 18, 22 and 24, and their respective thickened wall portions 16.

The two detachable mould units that are for forming the connectors 22 and 24 are adapted to hold the indirect heating coil 26. With this in position in the mould, and the remaining detachable mould unit for the connector 1 8 also in position, the mould is charged with a predetermined quantity of polyethylene particles - for example, the powder sold under the trade name MICROPOL powder - and the lid of the mould is placed in position. The mould is then heated to about 3500 C, and the mould is caused to spin, at a speed of between 30 and 40 r.p.m.

The mould is caused to spin about 2 orthogonal axes. The polyethylene powder melts at about 1300 C, and due to the spinning action on the mould, is distributed around the walls, top and bottom of the mould. The speeds of rotation of the mould about the two different axes may be made different if desired, to give a differential distribution of the molten polyethylene, around the mould. However, this may not be necessary for a cylinder having a shape approximately as illustrated. This is because the top and bottom of the mould have a smaller surface area than the walls of the mould, so that there is a natural tendency for a greater amount of molten polyethylene to accumulate at the top and bottom, than on the sides.Also, as the top of the mould is concave (from within) whilst the bottom of the mould is convex, the top will naturally tend to retain somewhat more molten polyethylene than the bottom.

When the mould had been heated to its desired temperature for the required amount of time, it is allowed to cool, whilst the spinning is maintained.

As the mould cools, the polyethylene solidifies, to form within the mould the hot water cylinder 10.

Due to the differential distribution of the molten polyethylene, as mentioned above, the top of the cylinder is somewhat thicker than the bottom, which in turn is somewhat thicker than the base.

By way of example, the top 12 may have a wall thickness of about 12 mm, the bottom 14 may have a wall thickness of about 11 mm, and the side walls may have a thickness of about 8 to 9 mm. The top 12 needs to be thickest because this is generally the hottest part of the cylinder 10 in use, whilst the bottom 14 also needs sufficient strength to bear and distribute the weight of the full cylinder 10, in use. The side walls do not generally need to have quite so much strength.

As the mould is cooling and the polyethylene is setting, the finished hot water cylinder 10 tends to shrink somewhat, away from the walls of the mould. Therefore, when the hot water cylinder 10 is fully set, the detachable mould units are removed from the walls of the mould, the lid of the mould is removed, and the tank 10 may be simply lifted out of the mould. The resilience of the walls of the cylinder 10 permits a small deflection thereof, is this should be necessary for the connectors 1 8, 22 and 24 to clear the walls of the mould.

When the cylinder 10 had been removed from the mould, it is finished off by removing flashings, boring out the connectors where necessary, and threading and tapping the connectors where necessary. If desired, the tank 10 can be dipped in an antistatic fluid.

In use, a connection is made to the hot water outlet connector 20 by means of a compression fitting. To this end, a length of hot water pipe (usually of copper) is brought adjacent the connector 20, and a compression nut and olive are fitted on the end of the pipe. The end of the pipe is then pushed through the bore in the connector 20, and the compression nut screw-threadedly engages the connector 20. As the compression nut is tightened, the olive is tightened between the connector 20 and the compression nut, to provide a water tight compression seal. A joint is made at the cold water inlet connector 18, in a similar fashion. Seals are also made at the connectors 22 and 24 in a similar manner, except that it will be appreciated that the pipes constituting the ends of the coil 26 already pass through the connectors 22 and 24.All that is required is to introduce an olive and a compression nut over the end of each of these pipes, and make the compression fittings at the connectors 22 and 24. Thereafter, joints may be made to the copper pipes constituting the ends of the coil 26, in any desired manner.

Jointing paste or tape may be used at each of the connectors 18,20, 22, 24 and 28, if desired.

Indeed, its use is desirable at the connector 18. At the remainder of the connectors, however, it will be appreciated that the plastics will be subjected to a considerable degree of heating, and we have found that, after a considerable period of time, the plastics tend to flow very slowly such that the screw-threads of the plastics connectors become firmly bedded into the screw threads of the compression nuts (or of the immersion heater 34, in the case of the connector 28), such that the joint may become so good that it will break upon a later attempt to unmake it.

Thus, the illustrated hot water cylinder 10 may have a number of advantages over previous cylinders of which we are aware. Being of plastics, it is much lighter than copper or other metal cylinders. As the connectors 18, etc are themselves of plastics, the weight of the cylinder 10 is further reduced. In fact, some initial experiments of our own showed that the use of metal connectors instead of the plastics connectors 18, etc led to gradual leakage at the respective locations on the cylinder 10, after a considerable period of time, due to the small but accumulative effects of the differential rates of thermai expansion of the metal connectors and the plastics cylinder. It will be appreciated that forming the connectors 18, etc integrally with the cylinder 10 gives a great improvement in this respect.It is a particular advantage of the illustrated hot water cylinder 10 that, being seamless, it is very much less prone to leakage than previous hot water cylinders.

A further advantage of the cylinder 10 is that, being translucent, both the level of water in the cylinder and any sediment or deposits within the cylinder may be observed, and if necessary, a decision can be taken as to when the cylinder should be cleaned or replaced, based on the condition of the internal surfaces as viewed through the walls of the cylinder.

Yet another advantage of the illustrated hot water cylinder 10 is that, being of a plastics material, the loss of heat through the cylinder walls is very much reduced, compared with a conventional copper cylinder. It will also be appreciated that the plastics material of the cylinder 10 is considerably tougher in certain respects than copper. This is particularly useful where the cylinder 10 has to be drilled after the initial moulding operation, as the likelihood of damage to the cylinder 10 is minimal. By contrast, damage can often occur to a copper cylinder, when being handled and subjected to manufacturing operations such as drilling. In addition to being lighter than conventional hot water cylinders, the illustrated cylinder 10 may be made relatively cheaply.

The above described manufacturing operation lends itself readily to automation, and we envisage that hot water cylinders 10 as illustrated may readily be produced at a rate of 24 per hour. This compares extremely favourably with the manufacture of copper cylinders, which have a typical production rate of 1 per hour by hand, or at the most, 6 per hour with a semi-automated system. As discussed above, the mould units which form the connectors 1 8, 22, 24 are detachable. They may be made interchangeable with alternative mould units, which may, if desired, be movable about the mould to different positions, so as to provide numbers and types of fittings in different desired configurations, for differing customers' requirements.

In Figure 1, the bottom 14 of the tank 10 is shown as being a simple concave shape, and this can be quite adequate, for strength. However, experiments have shown that, under certain conditions, the concave bottom 14 may be blown out outwardly, by pressure within the cylinder 10.

Therefore, it is preferred to provide a cylinder such as 10 with a bottom which has a plurality of adjacent recesses, rather than one simple one.

Figures 4 to 6 show one such arrangement.

In Figures 4 to 6, the bottom 40 of a cylinder is formed as four separate identical recesses 41, each of which comprises two portions 42 and 43 of different curvatures. This arrangement defines ribs 44 and 45 at the intersections of the portions of different curvature, thus considerably strengthening the bottom 40 of the cylinder.

As an alternative to the above described arrangement, the mould may be made with a detachable base rather than a detachable lid. This may avoid unsightly "flashings" caused by the mould lid being separate from the mould body. In such a case, the finished cylinder would be removed from the bottom of the mould.

Although the cylinder 10 may be translucent, it may alternatively be of pigmented material, which may give a more attractive appearance, although losing the advantage of translucency.

Heat loss tests have shown that a cylinder such as 10 may have a 'K' value (representing thermal insulation) of 0.22, which is equivalent to a standard sheet of asbestos, and compares most favourably with a K value 1.1, which is typical of a conventional copper cylinder.

Claims

1. A seamless hot water cylinder of plastics material.

2. A hot water cylinder according to Claim 1, formed with at least one connector of plastics material, for connection to external pipework.

3. A hot water cylinder according to Claim 2, wherein every connector on the cylinder, for connection to external pipework, is of plastics material.

4. A hot water cylinder according to Claim 1,2 or 3, having an indirect hot water heating coil within the cylinder, the coil having an inlet pipe and an outlet pipe, each of which passes through a plastics tube projecting outwardly of the wall of the cylinder, each tube being formed on the cylinder and forming at least part- of a seal around the respective pipe.

5. A hot water cylinder according to Claim 4, wherein each tube is externally threaded and cooperates with an internally threaded nut of a compression fitting which forms a seal around the respective pipe.

6. A hot water cylinder according to any preceding claim wherein the wall of the cylinder is thickened adjacent each point where a connection is made to the tank.

7. A hot water cylinder according to any preceding claim, wherein the cylinder wall is thicker at the top and bottom of the cylinder than at the sides of the cylinder.

8. A hot water cylinder according to any preceding claim, wherein the cylinder wall is thicker at the top of the cylinder than at the bottom.

9. A hot water cylinder according to any preceding claim, wherein the top of the cylinder is domed outwardly.

10. A hot water cylinder according to any preceding claim, wherein the bottom of the cylinder is concave.

11. A hot water cylinder as claimed in Claim 10, wherein the bottom of the cylinder is formed with a plurality of adjacent recesses projecting into the cylinder.

12. A hot water cylinder as claimed in Claim 11, wherein at least some of the recesses have different curvatures.

13. A hot water cylinder as claimed in any preceding claim, of translucent material.

14. A hot water cylinder as claimed in any preceding claim, of polyethylene.

1 5. A hot water cylinder as claimed in any preceding claim, being a domestic hot water cylinder.

16. A hot water cylinder substantially as herein before described with reference to Figure 1 and 2 of the accompanying drawings.

17. A hot water cylinder substantially as hereinbefore described with reference to Figures 1 to 6 of the accompanying drawings.

18. A method of manufacturing a hot water cylinder, comprising the steps of charging a mould with particles of a thermoplastic plastics material, heating the mould to cause the particles to melt, spinning the mould to distribute the molten material within the mould and allowing the mould to cool whilst continuing to spin it, thereby to form a seamless plastics hot water cylinder within the mould.

18. A method according to Claim 17, wherein the mould has a removable lid, and the cylinder is withdrawn through the top of the mould when the lid has been removed.

1 9. A method according to Claim 18, wherein the lid contains mould portions which mould plastics connectors on the cylinder, which connectors are for connection to external pipework.

20. A method according to Claim 17, 18 or 19, wherein the mould contains mould portions which mould plastics connectors on the cylinder, which connectors are for connection to external pipework.

21. A method according to Claim 19 or 20, wherein said mould portions afford local thickening of the cylinder wall.

22. A method according to Claim 19, 20 or 21, wherein at least some of said mould portions are removable.

23. A method according to any one of Claims 17 to 22, wherein the mould is spun at a speed substantially in the range 30 to 40 r.p.m.

24. A method according to any one of Claims 17 to 23, wherein the mould is heated to a temperature substantially in the range 300C C to 400C C.

25. A method according to Claim 24, wherein said plastics material comprises polyethylene.

26. A method according to any one of Claims 17 to 25, wherein the mould is spun about two orthogonal axes.

27. A method according to Claim 26, wherein the respective speeds of rotation of the mould about said axes are different.

28. A method according to any one of Claims 17 to 27, wherein the mould is spun in such a way as to form a cylinder wall which is thicker at the top and bottom than at the sides of the cylinder.

29. A method according to any one of Claims 1 7 to 28, wherein the cylinder is in accordance with any one of Claims 1 to 14.

30. A method according to Claim 17 substantially as hereinbefore described.