The present invention refers to a sterilization chamber for autoclaves and of the type in which the sterilization process incorporates treatment of the goods to be sterilized with alternating temperature and pressure variations, with the pressure varying between overpressure and vacuum suction, and which is provided with a wall structure incorporating an inner wall and an outer wall arranged spaced apart therefrom, whereby an intermediate space is formed between the two walls.

Autoclaves are used for sterilization of different types of goods, e.g. surgical and dental instruments, whereby the goods during a short period of time shall be heated with water steam to a high temperature, usually 134°C and at a pressure of 2.1 bar. The goods shall furthermore be subjected to vacuum.

The sterilization chamber hereby is subjected to two contradictory requirements. It must have low heat capacity (kWs/kg degree), low heat conductivity (W/m degree) and it furthermore shall be strong. Due to the internal subpressure, which must be established in connection with the vacuum treatment of the goods, it is required that the sterilization chamber has thick walls, thus that it can withstand the internal subpressure without buckling.

In order to try to meet these problems it earlier has been arranged an insulation in the intermediate space between the inner and outer walls, which insulation acts as a heat insulation. In connection to vacuum suction of the sterilization chamber situated inside the inner wall, the pressure in the intermediate space is also lowered, which means that the inner wall, which often is manufactured from a high tensile stainless steel, need not be made as thick as it otherwise must have been. As this pressure reduction in

the intermediate space between the two walls is effected in connection to vacuum suction and not during the time the steam pressure is applied in the sterilization chamber, this means that the heat insulation in the intermediate space must be dimensioned to accomplish the entire heat insulation.

The purpose of the present invention is to provide a sterilization chamber of the type mentioned in the introduction, which can have a thinner inner wall of high tensile steel compared to what has earlier been possible, at the same time as the requirement for a thick layer of insulation material is reduced, and this has been achieved in that said space between the walls of the chamber have a constant vacuum, which is lower than the lowest treatment pressure for which the sterilization chamber is intended, in order primarily to ascertain that the inner wall is not subjected to an internal subpressure and secondly for contributing to the heat insulation.

Hereinafter the invention will be further described with reference to an embodiment shown in the accompanying drawing.

The figure shows in cross section a non-limiting embodiment of a sterilization chamber according to the invention, whereby the chamber has been shown without associated connections for vacuum, steam, cooling medium, etcetera.

The sterilization chamber 1 incorporates a strong outer wall 12, e.g. from structural steel, and in the embodiment shown shaped as a cylinder, which is closed off at one end by a dome-shaped portion, an inner wall of stainless, but considerably thinner material than the outer wall, and which inner wall is received inside the outer wall 2, thus that an intermediate space 4 is formed between inner wall 3 and outer wall 2. The open end of the sterilization chamber

rests against a planar, strong end wall 5 of substantially circular form, with a thin planar inner wall 6, provided at a distance from the outer end wall 5 and for increasing the load carrying capacity and the insulating power, the space between the end wall 5 and the inner wall 6, in the embodiment shown, is filled with an insulation 7, which has been subjected to vacuum suction. Between the open end of the two vessels of the very sterilization chamber and the planar end wall 5 there is preferably provided a seal 8, positioned in a groove, here illustrated as a sealing ring having a circular cross section.

In the intermediate space 4 between the inner wall 3 and the outer wall 2 of the chamber prevails a permanent, constant vacuum, which, when this space, in connection with the manufacture of the chamber, is hermetically sealed off, can be set to a level below the lowest pressure ( subpressure) to which the interior of the sterilization chamber will be subjected in connection with the vacuum suction involved in the sterilization process, and this vacuum in the intermediate space will efficiently ascertain that the interior of the inner wall 3 never will be subjected to an overpressure acting from within and outwards in relation to the pressure in the intermediate space 4, i.e. also during vacuum suction of the interior of the sterilization chamber. As this means that the inner wall 3 never will be subjected to an inner subpressure, the risk for this inner wall to buckle inwardly is not at hand, and from strength aspects the inner wall 3 therefore can be made rather thin. The outer wall 2 on the other hand must be made thicker as it will be acted upon from within by the negative pressure difference, which is at hand between the intermediate space 4 and the surrounding atmosphere.

By the fact that the space between the inner and outer walls 3, 2 has a comparatively low subpressure, the entire chamber will operate as a vacuum insulated thermos, preferably at a

pressure below 10 ^"2 mbar, which gives a good heat insulation only as a consequence of this low vacuum.

Even if the two curved inner and outer walls 3, 2 are subjected only to tensile stresses in contrast to the planar end wall, which is also subjected to bending stresses, the intermediate space 4 between these curved wall sections can preferably also be provided with a (not shown) heat insulation. It has proven itself that the insulating materials used reduces their heat conductivity considerably in vacuum of the levels, which are constantly at hand in the space 4.

As appropriate insulating materials can be mentioned, e.g. MICROTHERM, a microporous heat insulating material, or the porous fibre silicate board SUPRATHERM "L", which is marketed by the company Brandenburger Isoliertechnik GmbH % Co K.G.. Another appropriate material can be the hard glass fibre fabric BRA-GLA, which is also marketed by Brandenburger Isoliertechnik.

Due to its ability to withstand high pressures this lastmentioned material, can be designed as a screen pattern, preferably in the form of a honeycomb structure. If this material has a heat conductivity of 0,22 W/mK it is possible to make high strength structures with a heat conductivity of about 0,0022 W/mK if a vacuum is at hand in the cavities of the honeycomb structure.

In this manner and by utilizing vacuum both for preventing that the inner wall casing of the sterilization chamber is buckled and for reaching a good heat insulation, it is obtained a sterilization chamber that fulfils the desiderata of a low heat capacity, a good heat insulation at the same time as it has a thin insulation but yet is strong.

By the fact that the heat capacity is reduced, the power required at heating as well as during cooling is also reduced. Hereby it is possible either to increase the speed of the process and/or to reduce the required size of the associated steam generator and cooler, if any.

Also with a short distance between the walls of a sterilization chamber according to the invention it is possible to reach a good insulation as compared to a chamber of conventional type and without a permanent, hermetically sealed off vacuum, in which the insulation properties are directly proportional to the thickness of the insulation.

The invention is not limited to the embodiment illustrated as an example in the drawing and described in connection thereto but variants and modifications are possible within the scope of the accompanying claims.