Electric resistance heating devices – Heating devices – Tank or container type liquid heater
Reexamination Certificate
1999-01-19
2001-02-13
Walberg, Teresa (Department: 3742)
Electric resistance heating devices
Heating devices
Tank or container type liquid heater
C220S501000, C220S507000
Reexamination Certificate
active
06188840
ABSTRACT:
The present invention relates to process for the manufacturing of a pressure vessel and a pressure vessel, especially for a water heater, received through the process.
Water heaters in different sizes for both household and industrial purposes normally includes a pressure vessel which without exceptions are made from metal. The heating of the water is achieved by using an electrical heater which normally is constituted by a metal tube containing a heating filament embedded in a mineral or a ceramic material. The heater is guided by a sensor which detects the temperature of the water. The existing pressure of the water supply system is normally used when feeding hot water from the water heater wherein the heater can be placed independently. This is achieved by means of a clack valve which is placed on the cold water inlet of the water heater. This valve will open and replace hot water with cold water as soon as the pressure in the water heater becomes lower as the hot water are drawn from the water heater. The pressure vessel is normally insulated to minimise the energy losses. The temperature range is normally 50-90° C.
One disadvantage with the water heaters of today is that they are manufactured from a metal. It often becomes necessary to provide the pressure vessel with a sacrificial anode to avoid galvanic corrosion since metal is a good conductor. It is possible to use a more noble metal for the pressure vessel to avoid this type of corrosion but that would only move the problem with corrosion to the parts of the water supply system that are made of less noble metals. Metals are also good heat conductors which increases energy losses.
Another disadvantage is caused by the thermal expansion of the water. Most materials expands when the temperature increases, so do most metals, however not enough to compensate for the expansion of the water. This means that the pressure in a water heater completely filled with cold water will increase as the temperature of the water increases. This will cause great stress on the pressure vessel wherein the vessel has to be over-dimensioned in respect to the normal working pressure. This means that the design will be unnecessary heavy and costly.
Yet another disadvantage is the relatively long heating time from completely cold to fully warm water. This problem can of course be rectified by supplying more energy to the water heater. The energy needed to get reasonably short heating times would however be unreasonably lhigh. Such an energy supply would involve a rebuilding of the electrical supply to, for example, a normal household.
Since the heater causes a thermally driven circulation, the temperature of the water in the vessel will be mainly homogenous. The water temperature in the vessel will thereby also decrease mainly homogeneously as cold water are supplied in connection with the use of hot water from the water heater.
Through the present invention the above mentioned disadvantages and inconveniences have been avoided and a pressure vessel for an improved water heater has been achieved. The invention relates to a process for the manufacturing of a pressure vessel made from thermoplastic material or thermosetting resin. The pressure vessel comprises a first and a second vessel end part manufactured through injection moulding or press moulding and possibly an intermediate tube part which preferably is manufactured through extrusion. The vessel end parts include a circumfering shell which form the sides of the pressure vessel and each one dome which form the upper and the lower ends respectively of the pressure vessel when joined. A number of interconnecting and thereby load distributing walls stretch from the domes along the circumfering shell towards the open part of each vessel end part. A corresponding number of matching walls stretch from one open end of the possible intermediate tube part along the circumfering shell of the tube part to the other end of the same so that when two vessel end parts are joined, possibly with an intermediate tube part placed in between, the edges of each of the walls in the different parts meet. A number of cells are hereby formed between the walls. The walls are placed so that a number of crossing areas are formed between intersecting or connecting walls. The invention is characterised in that at least one, preferably all crossing areas are provided with a termination by achieving a hole from the outside of the dome. The hole area is larger than the crossing area and the depth of the hole greater than the goods thickness of the dome part. Communicating openings between the cells in the pressure vessel are hereby prepared.
The possibly intermediate tube parts are preferably manufactured by extrusion. They can however also be manufactured by means of injection moulding possibly assisted by melt core technologies or the like.
The vessel end parts and the possible intermediate tube part are suitably joined by mirror welding, friction welding, pressing or gluing.
The holes are preferably achieved in connection with the manufacturing of the vessel end parts and then by means of peg-like parts placed in one of the halves of a mould. The holes can also be achieved through after-treatment by drilling, milling or the like.
One or more of peg-like parts which is/are placed in one of the mould halves and/or opposite points at the other half of the mould is/are suitably provided with an axially placed long core or cores whose cross-section area are smaller than the cross-section area of the crossing area. At least one channel which is parallel to, and having the full length of the walls are hereby formed in the cross-section of the crossing area.
According to another embodiment of the invention the two halves of the mould are provided with receiving means, placed axially with the peg-like parts. The receiving means are intended to receive a preferably extruded tube. The tube is manufactured of a thermosetting resin or a thermoplastic material. In cases where the tube is manufactured from a thermoplastic material, the melting temperature of the material in the tube should be at least as high as the melting temperature of the material used for the manufacturing of the vessel. The tube is placed in the mould cavity of the mould, after which a fluent plastic material is injected into the mould cavity while the receiving means prevents intrusion of plastic material into the tube through a tight fit between the receiving means and the edges of the tube.
To further prevent the plastic material from entering the tube a gas is suitably injected into the tube simultaneously with the injection of the plastic material. A pressure mainly corresponding to the pressure of the injected fluent plastic material hereby forms within the tube. The tube is hereby also prevented from collapsing under influence of the injection pressure of the plastic material. This will further make use of tubes with very thin walls possible.
As an alternative the tube can be replaced by a so called melt core profile. The two halves of the mould are here provided with receiving means, placed axially with the peg-like parts. The receiving means are intended to receive the melt core profile which is placed into the mould whereupon the fluent plastic material is injected into the mould cavity. The melt core profile is then removed by melting after allowing the plastic material to solidify and removal of the part from the mould. At least one through-hole channel which is parallel to the walls is hereby formed in the cross-section of the crossing area. The mould can as an alternative be provided with means for melting of the melt core profile whereby the profile can be removed while the part is still located in the mould.
According to yet another embodiment of the invention a predetermined amount of fluent plastic material is injected into the mould cavity.
The fluent plastic material is allowed to solidify somewhat, after which a gas is injected into the plastic material through the peg-like parts or the opposite points in the other half of the mould. At le
Norrlöw Olof
Orlowski Witold
Campbell Thor
Perstorp AB
Stevens Davis Miller & Mosher L.L.P.
Walberg Teresa
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