TECHNICAL FIELD

The present invention relates to a method of manufacturing an interiorly insulated tank which has an outer shell or casing with a port, comprising the steps: that a bag or sack is produced from flexible, non-tensible and liquid-tight material, that the sack is passed into the outer casing via the port and the interior of the sack is filled with a fluid under pressure, that a foam-forming and setting insulating material is introduced in a space between the filled sack and the inside of the outer casing.

The present invention also relates to a tank with an outer casing with a port and an inner insulation.

BACKGROUND ART

In the manufacture of water heaters and storage tanks for pleasure craft and camper vehicles etc., it is the traditional technique to produce an inner casing of stainless steel of high quality which is dimensioned to withstand the pressure and those pressure variations for which the water heater is dimensioned. Further, the stainless steel must be selected from such a quality that, during a lengthy period of time and at the prevailing temperatures, it may come into contact with drinking water without the water being contaminated or discoloured or that the steel or its welds corrodes.

On the outside of the inner casing there is traditionally disposed a thermal insulation whose purpose is to reduce the thermal losses from hot water stored in the water heater. Such heat losses are important, since on many occasions access to electric power may be limited aboard a pleasure craft or in a camper vehicle. Alternatively, the water can only be heated when the engine is running. In order to protect the thermal insulation, there is an outer layer which possesses the requisite mechanical strength to afford the protection which the insulation may require in order to prevent mechanical damage, for example during handling of the water heater.

It is also previously known from DE 198 18 662 to produce, interiorly in a configurationally stable outer shell, an insulation of an expanded foam material. In such instance, an inflatable or expandable bag is inserted in the outer shell and which, in the expanded state, leaves a gap to the inside of the outer shell. An expandable foam material is introduced in this space and is allowed to expand and set, in which event the bag acts as a mould core. When the foam material is set and substantially completely fills out the gap, the bag is removed.

On manufacture of water heaters, regardless of the choice of materials and positioning of the insulation, a pressure-tight container is required. Such containers as a rule display dome-shaped or spherical end pieces and a cylindrical centre section positioned therebetween. Since the compression tools which are used in the manufacture of the end pieces are extremely costly, it is common practice that water heaters of different volumes possess the same diameter, and hence different lengths, which complicates the application of an internal insulation.

PROBLEM STRUCTURE

The present invention has for its object to obviate the drawbacks inherent in the prior art technology and, in particular, in an extremely simple manner, to provide a tank with an inner insulation despite the fact that the tank may be of varying length.

SOLUTION The objects forming the basis of the present invention will be attained in respect of the method if this is characterised in that the sack is wholly or partly passed so far into the outer casing that the sack, in the filled state, is largely equidistant to the inside of the outer casing, and that the end of the sack facing away from the port is positionally fixed.

The objects forming the basis of the present invention will be attained in respect of the tank if this is given the characterising features as set forth in appended Claim 10.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

The present invention will now be described in greater detail hereinbelow, with reference to the accompanying Drawings. In the accompanying Drawings:

Fig. 1 shows a section through an outer shell or casing formed into a tank and a sack or bag applied interiorly therein; Fig. 2 is a corresponding section through the outer shell or casing once the sack has been partly evacuated and an insulation applied interiorly in the outer casing; and

. 3 shows one embodiment where the sack or bag is of greater length than the outer casing, for which reason a portion of the sack or the bag in the filled state is disposed outside the casing.

DESCRIPTION OF PREFERRED EMBODIMENT The present invention will be described hereinbelow with reference to a water heater, but the described technique has a considerably broader field of application and may be employed in, for example, hot water boilers, accumulator tanks, storage tanks for hot water etc., etc.

Referring to the Drawings, in Fig. 1 reference numeral 1 refers to an outer shell or casing which may be manufactured from an economical plastic or sheet metal material, hence not necessarily stainless steel material. The dimensioning of the outer casing is such that it withstands the working pressure with relevant safety margins for which the water heater is intended, and in addition also such pressure hammers as may be generated on opening and closing of taps, starting and stopping of pumps etc. It should be observed that the outer casing 1 may be of different length in one and the same diameter so that, as a result, the need for water heaters of different volumes is satisfied.

The outer casing has an assembly flange 2 which, in the finished state of the water heater container, serves for anchoring and enclosing such equipment as must be located interiorly in the water heater, for example, inlet and outlet ports, safety valves, heater loops, electric heating elements etc.

According to the present invention, it is an advantage if the aperture through the assembly flange 2 is made as small as is humanly possible, since the loading on and risk of fatigue of that closure which closes the assembly flange and thereby the outer casing is reduced. The positioning of the port in the centre of the dome-shaped end piece is also advantageous, since this region, on the manufacture of the end piece, has been stretched the least and therefore displays the best mechanical strength.

In Fig. 1, a sack 3 or bag of flexible, non-tensible and fluid-tight material has been inserted in the outer casing 1. The sack 3 has a neck 4 which extends from the interior of the outer casing out to the outside thereof via a port 5 which is defined by the assembly flange 2. In that the sack may be wrinkled together, a small aperture through the assembly flange does not involve any problems. In the embodiment according to Fig. 1 , the sack 3 has been specifically dimensioned concerning its length so as to fit into the relevant outer casing 1.

Since the length of the outer casing 1 may vary in one and the same diameter, the sack 3 may also be manufactured of such length that it fits also into the longest outer casing. This implies that the sack will be "too long" in a shorter outer casing. Such an embodiment is illustrated in Fig. 3. In the illustrated position, it is presupposed that the sack 3 is filled with a pressure medium, so that it is kept taught to an intended, carefully defined configuration. In order to render the material in the sack non-tensible, the material may include high strength fibres, wires of metal or other non-extensible material. PET material may also be employed, since this material is substantially non-tensible. Further, the sack is naturally tight in respect of the fluid which is employed on pressurising of the interior of the sack 3 so that this assumes its intended form.

The space between the pressurised sack 3 and the inside of the outer casing 1 is that space which is to be filled with insulation. If the insulation layer is to be thicker than that which is apparent from the Drawing, the sack is made correspondingly smaller with regard to its diameter and further, it is possible for example to provide the outer casing 1 with a thicker layer of insulation in the upper region of the water heater than is the case at the bottom, since the temperature may be expected to be higher further up in the water heater. In such a case, the sack is given a non-round cross sectional configuration, with, for example, a flattening at the top where the thicker insulation is to be located. Alternatively, a rotation-symmetric sack may be positioned off- centre in the outer casing with its longitudinal centre axis more proximal the bottom of the outer casing.

If the sack 3 is filled with a gas, it is appropriate that this gas has such a powerful excess pressure that the sack is not deformed and collapses in an uncontrolled manner when a foam-forming, expanding and setting material is introduced into the space between the inside of the outer casing 1 and the outside of the sack 3. In that the material in the sack is non-tensible, a quite powerful excess pressure may be employed.

If the sack 3 is instead filled with an incompressible medium, for example water, it is sufficient to prevent the water from running out of the sack 3 when the insulation is applied. In this case, the pressure may be lower, but the sack will be heavier, for which reason its alignment and retention must be better, at least in the recumbent orientation. As was intimated above, for the creation of the intended insulation, use is made of an expanding, foam-forming and setting or hardening material which is introduced into the space 6 intended therefore, for example via an inlet 7 in the end of the outer casing 1 facing away from the port 5. If the sealing between the neck 4 and the assembly flange 2 is not totally and completely perfect, this implies that the air which initially was located in the space 6 may be expelled this way, whereby there is a guarantee that the space 6 is filled completely, in particular if the filling operation takes place with the neck turned to face upwards. One method of ensuring the evacuation of air when the foam-forming material expands with the assembly flange 2 of the outer casing turned to face upwards, which is a preferred orientation for the outer casing 1 , almost tightly wound helical springs or flexible tubes may be clamped in place between the assembly flange 2 and the outside of the sack 3. These springs or tubes are removed on removal of the sack. An evacuation route for air is important, so that all of the available space between the sack and the inside of the outer casing can be filled with completely insulating material.

The reverse filling sequence is naturally also possible in that the foam-forming material is introduced in, for example, between the neck 4 and the assembly flange 2, the inlet port 7 serving for evacuation of the air which must depart from the outer casing.

Naturally, it is also possible to provide the outer casing 1 with several inlet ports positioned at different places than those intimated above.

Depending upon the quality and properties of the foam-forming material, it may be appropriate to provide, on the inside of the outer casing 1 , some adhesion-promoting material, while, on the other hand, the outside of the sack 3 may suitably be provided with some slippage or release agent or a plastic bag or foil which is then subsequently allowed to remain on the insulation. Many foam-forming insulating materials generate considerable quantities of heat when they set. Consequently, it is important that the sack be manufactured from a material which withstands at least 80°C without its properties being changed, it must thus also still remain non-tensible at elevated temperatures. In such instance, PET material is a good choice, since it can withstand this temperature with a generous margin.

If the foam-forming material requires heat or cooling for hardening or setting, it may be appropriate to supply this heat interiorly in the sack 3 in that the sack is filled with a heated fluid. Alternatively, heat or cold may naturally be supplied on the outside of the outer casing 1, or combinations of both alternatives.

Fig. 2 shows the outer casing 1 with an insulation 8 applied on its inside and consisting of an expanded foam material. It will also be apparent that the sack 3 is no longer under pressure or even has a slight partial vacuum so that it has collapsed and released from the inside of the insulation 8. In this state, the sack may readily be drawn out through the port 5 in order later to be applied as a mould tool in the next tank in series production. In order for the water heater to be able to be finished, a rubber sack or plastic sack of elastic material is fitted interiorly in the insulation 8, where the rubber material is selected from a food standard quality which withstands relevant temperatures or contact with water for lengthy periods of time without contaminating the water. Naturally, this sack need not consist of a non-tensible material, but is preferably elastic, since the insulation 8 transfers the pressure of the elastic sack to the outer casing 1 in a harmonious manner. If the sack is made smaller than the inner configuration of the insulation 8, the elasticity will moreover force out a part of the content when the water heater is to be emptied before winter storage. In order reliably to avoid freezing damage, it is appropriate that the elasticity reduce the volume of the rubber sack by at least 8 % if a tap or faucet is opened in the water system to which the water heater is connected. According to the present invention, the insulation 8 will, in many operations or situations, be affected by pressure from the rubber sack. This naturally also applies to transients. In order for the insulation to withstand such loadings, it is configurationally stable and has a density of at least 100 kg/m ³ , preferably 120 kg/m ³ .

In order to guarantee that the non-tensible sack 3 arrives in the intended position, it is appropriate to use fixing devices or centring devices where such may be pin-shaped and intended for cooperation with the inlet port 7. Further support means may be provided on the outside of the sack or the inside of the outer casing with a view to rendering the space 6 as uniformly thick as possible in order thereby for the insulation 8 to be correspondingly uniform. This is particularly relevant if the sack is filled with water, since the sack will then become heavier and will need better support. Such centring means may possibly be left in place in the insulation if they consist of a material with poor thermal conductivity.

In the above, it was mentioned that the outer casing 1 may be of varying length in one and the same diameter. In order to avoid needing to manufacture one sack 3 per length, it is appropriate to make the sack longer, so that in the expanded state, it is partly located outside the assembly flange 2 if the outer casing 1 is not of maximal length. In such an embodiment, as shown in Fig. 3, the sack 3 is inserted only so far into the outer casing that, in the filled state, it has largely equal spacing to the inside of the outer casing 1 throughout its entire surface. In this case, a part 9 of the sack 3 is left outside the port 5 in the outer casing 1, and it will be apparent from Fig. 3 that, also on filling or pressurisation, it will there expand to the same diameter as interiorly in the outer casing, because of the non-tensible material in the sack. The length 9 of the sack which is left outside the outer casing may vary.

Further modifications to the present invention are conceivable without departing from the scope of the appended Claims.