Method for achieving a heat insulation for refrigerators or freezers

Abstract: This invention relates to a heat insulation for a refrigerator or freezer. The insulation comprises a material, which is placed in a hermetically closed space (13) surrounded by a diffusion tight shell, and which does not achieve its full insulating properties until the refrigerator has been used for a long time.

Description: This invention relates to a method for achieving a heat insulation for a wall or a door for a refrigerator or freezer wherein an insulation material, comprising closed cells and being provided with a gas having such properties that the gas can diffuse from the cell structure with a velocity which is at least five times faster than that of the air gases, during the manufacturing process is placed in an hermetically sealed space which is surrounded by a diffusion-tight shell. US-A-1898977 describes an insulation for a refrigerator of the type mentioned above and utilizes vacuum in conjunction with powered or closely spaced, finely divided or foraminous filling material. The filling materials are for instance silocel powder, closely spaced sheets of paper, attenuated fibrous material, cork or similar porous material. GB-A-760942 describes a vacuum insulation structure for a refrigerator wherein passages are provided between the insulation material and the surrounding walls in order to assist in evacuating the gases within the insulation material during the manufacturing process. Previously several different materials and material combinations have been suggested in order to increase the heat insulating caracteristics for walls and doors in refrigerators and freezers as well as it has been suggested to use so called vacuum panels. Conventional insulations usually comprise foamed polymeric materials whereas for vauum panels an evacuated shell of diffusion tight material - for instance plastic or sheet metal - which is filled with powder or celluar material is used. This lastmentioned arrangement is descirbed for instance in SE 90937, EP 188806, JP 63135694, US 5066437. The arrangement has however certain drawbacks since it is difficult to maintain sufficiently low pressures during the complete life time, which is 15-20 years, of the cabinet since also a minor leakage decreases the heat insulating caracteristics. Further it is difficult and expensive to carry on the evacuation process as far as should be desirable in massproduction since such an evacuation process takes a very long time. Thus, because of the long and narrow evacuation passages it takes at least 15 hours to reduce the pressure to 1 mbar independently of the capacity of the vacuum pump whereas the production time for a refrigerator is abt 20 min. In order to make it possible to evacuate slightly faster, as appears from some of the abovementioned publications,polymeric materials with open cell structure have been used. The disadvantage with an open cell structure both with regard to conventional insulations and vacuum insulations is however that it with such a structure is difficult to fulfil the demands for mechanical strength at lower densities. In practice it has been necessary to use comparatively high densities which means that the heat conductivity in the solid state increases considerably as well as price and weight. A closed cell structure in combination with adherence to the surrounding shell gives mechanical stability also at comparatively low densities but demands for small cells in order to minimize the heat transportation by radiation and in order to get superinsulation (which means that the free length of movement of the molecyles should be of the same magnitude as the size of the cell) at as high pressures as possible. The abovementioned desires regarding closed and open cells are thus contradictory which means that the properties which have been regarded as most important, i.e. mechanical strength or the possibility to evacuate the insulation quickly, have determined what kind of cell structure that should be used. It is also known, see US 4448041, to use vacuuminsulated wall elements for large mobile cold storage rooms the wall elements communicating with a vacuum pump. These vacuum pumps are however of conventional type and hence comparatively power demanding and expensive and their use can with regard to costs and energy consumption only be motivated at the type of larg construction which is described in the abovementioned publications. Further FR 2628179 describes hermetically sealed wall elements which in a manner not shown in detail are connected to some kind of vacuum source the pressure of 50-100 mbar which is created being comparatively high and being in such an interval that it can not in any higher degree contribute to increase the heat insulation capability. GB-A-865391 describes a thermal insulator which consists of multi-celluar material being contained within a gas-tight envelope which is evacuated. The multi-celluar material is inpregnated with a gas and the envelope is sealed. The gas within the material will be condensed and create a high degree of vacuum. US-A-1550961 describes a box shaped refrigerator having first and second walls forming a space for a cooling fluid and there also are third walls which together with the second walls form a vacuum space surrounding the cooling space. There is however no fill material within the vacuum space. The purpose of this invention is to create a method by means of which it is possible to get a permanent vacuum insulation with very good heat insulating caracteristics for refrigerators and freezers in up-to-date massproduction and which in principle reduces the energy consumption with 50% compared to the refrigerators and freezers of today the arrangement not having the drawbacks which are desribed above with reference to the vacuum panels described. The basis of the invention is that the cabinet during the production is equipped with a cheap and energy saving vacuum pump which communicates with hermetically sealed spaces in the walls and/or doors of the cabinet these spaces being provided with a heat insulating material with particular properties these properties appearing from the following claims. The method is characterized by the features of the characterizing portion of claim 1. The invention will now be descibed in detail with reference to the accompanying drawing in which the figure schematically shows a section through a refrigerator or freezer with an insulation which has been produced in accordance with the invention. In the figure several wall parts 10 which surround a cold room are shown the wall parts having an outer and an inner shell 11 and 12 resp. which are joint to each other and which therebetween form an hermetically sealed space 13 which is filled with heat insulating material. This material at least partly consists of closed cells which are produced by foaming for instance poyol/isocyanate with a gas having such properties that it can diffuse through the cell structure with a velocity which is at least five times faster than the air gases. A suitable gas is for instance carbon dioxide. By foaming with small molecules, type carbon dioxide, a closed cell structure can achieve such a high diffusion velocity that the evacuation is possible during a reasonable time period such a period in this context being a 24-hour period up to some months. The evacuation process goes very far which means that a final pressure which is less than 0,1 mbar is maintained in the evacuation conduit 17 this level being achieved in the insulation not before a long time use of the cabinet 18. Each space 13 via an evacuation channel 14, 15, 16 communicates with an evacuation conduit 17 which is connected to a vacuum pump 18. The vacuum pump is driven by an electric motor having a very low power consumption. The pressure in the evacuation conduit 17 is sensed by a sensor 19 which is connected to an electric control means 20 deactivating the pump when a certain underatmospheric pressure has been achieved in the evacuation conduit. The control means 20 can also be used to activate or deactivate the compressor 21 in the cabinet from the thermostate. In the material which is provided in the space 13 distribution channels 22 are made which connect remote parts of the insulation with the evacuation channels 14, 15, 16 the distribution channels being produced by means of plastic pipes, by thermal shock for instance by putting a thin unisolated conduit in the material after which a current is allowed to flow through the conduit so that the heat burns a channel or by using focused light for the same purpose. It is also possible to create distribution channels by putting a fibre material 23 in the insulation preferably on its outside. By a suitable choice of material also a spontaneous cracking of the cells can be achieved during the evacuation because of the pressure difference between the outside and inside of the cell. It should be mentioned that it is possible to place the insulating material free in any diffusion tight material for instance plastic the diffusion tight material forming a surrounding cover which after evacuation is placed in the shell which forms the walls of the refrigerator or freezer. This creates mechanical stability and also a slot between the shell and the insulating material the slot being used for the evacuation.

Claims: Method for achieving a heat insulation for a wall or a door for a refrigerator or freezer wherein said insulation during the manufacturing process is placed in an hermetically sealed space surrounded by a diffusion-tight shell and wherein said space is connected to a vacuum pump (18) permanently mounted in the refrigerator or freezer and wherein the insulation is provided with distribution channels (22,23) connected to the vacuum pump characterized in that the insulation material comprises closed cells which during the manufacturing process are filled with a gas having such properties that the gas can diffuse from the cell structure into the channels with a velocity which is at least five times faster than that of the air gases, that the vacuum pump is driven by an electric motor and that the gas is gradually evacuated from the cell structure by means of the vacuum pump when the refrigerator or freezer has been installed by the customer such that the final pressure in the space is reached within some months from the time of installation. Method according to claim 1 characterized in that the insulation material consists of a foamed material such as polyol/isocyanate said gas is a drive gas in the foaming process. Method according to claim 1 or 2, characterized in that said gas is carbon dioxide. Method according to any of claims 1-3, characterized in that a fibre material is used as distribution channels (23) this material preferably being placed in touch with the shell. Method according to any of claims 1-3, characterized in that the channels are formed along the boarder line between the material and the shell by not allowing the material to adhere to the shell. Method according to any of the preceding claims, caracterized in that the shell is a plastic material.

Inventors: ROSEEN RUTGER ARVID, ROSEEN, RUTGER ARVID
Applicants: ELECTROLUX RES & INNOVATION, ELECTROLUX RESEARCH & INNOVATION AB
Application year: 1993
Main classification: F25D23
IPC codes: F16L59, F25D23