GB2044523A

GB2044523A - Method of, and getter arrangement for, maintaining a vacuum in a container

Info

Publication number: GB2044523A
Application number: GB8000982A
Authority: GB
Original assignee: Messer Griesheim GmbH
Current assignee: Messer Griesheim GmbH
Priority date: 1979-01-24
Filing date: 1980-01-11
Publication date: 1980-10-15
Also published as: SE8000007L; IT8019152A0; FR2447604A1; IT1129963B; DE2902623A1

Abstract

In order to prevent foreign gas from accumulating in the vacuum space of a container by microleakage etc., so-called getter substances are used during evacuation. This is usually effected by means of a complicated getter activation apparatus, by which the getter materials are activated in the vacuum part. The object of the present invention is to provide a method of getter activation which can be performed without great cost. For this purpose, it is proposed that the getter substance is activated by local heating. Thus, the getter substance is received in a tube and is activated by means of a heater element provided on the outside of the external container. Due to this simple arrangement, there is no difficulty, even at a later time, in effecting re-evacuation of the vacuum space by local heating of the getter substance. <IMAGE>

Description

SPECIFICATION Method of, and getter arrangement for, maintaining a vacuum in a container The present invention relates to a method of, and a getter arrangement for, maintaining a vacuum in a vacuum container by means of a getter substance.

It is known that, in container construction, particularly in cryo-container construction, the natural heat convection from the external container towards the deep cooled internal container is reduced by vacuum insulation. The value of said heat convection is, over a wide range, a function of the residual gas pressure which still exists in the vacuum space between the external and internal containers even after evacuation has been effected. Due to unavoidable microleakage and gas desorption, the residual gas pressure in said vacuum space increases in the course of time. However, heat convection from the external to the internal container inevitably also increases, which leads to an undesirable increase in the evaporation of the liquefied deep cooled gas present in the internal container.

In order to avoid an undesirable increase in said residual gas pressure, physical adsorbents and getters are introduced into the vacuum space before its evacuation, in order to consume the residual gases still remaining after evacuation of the foreign gases freshly accumulating due to the microleakage and aftergases, and thus to maintain the vacuum, or even to improve it. In this case, the getter substance is present in an activated state in the vacuum space.

The getter substance was hitherto packed in glass ampoules which were melted down after the activation process. The glass ampoules were then inserted into a tube sold red onto the container and crushed in the high vacuum after the container had been annealed, so that the getter substance was freely present in the vacuum space.

To enable this to be achieved, it was necessary to employ a complicated getter activation apparatus (high vacuum apparatus combined with glass melting apparatus). Moreover, a socalled "crushing tube was necessary on the container in order to enable the glass ampoule present inside the vacuum space to be destroyed so as to free the getter substance.

It is therefore an object of the present invention to provide a method of maintaining a vacuum in a vacuum container by means of a getter substance, which can be performed simply and cheaply.

According to the present invention, there is provided a method of maintaining a vacuum in a vacuum container, by means of a getter substance, characterised in that the getter substance is introduced openly into the vacuum space of the container, and that the getter substance is activated by local heating during evacuation of the vacuum space.

Thus, by open introduction of the getter substance into the vacuum space of the containter, and by effecting activation of the substance simultaneously with the evacuation of said space, the hitherto customary complicated introduction and activation process is considerably simplified, whilst furthermore no additional measures, such as the destruction of a glass ampoule and corresponding devices for the purpose, are required.

In order to perform this method, advantageously a getter arrangement is used in which an open tube accommodating the getter substance is arranged on the inside of the external container.

It is further advantageous if the tube is covered by a sieve. This ensures that the getter substance remains in its intended position, namely in the tube, during the assembly of the two containers.

According to a further feature of the invention, zirconium is provided as getter substance. It is obviously also possible, and lies within the scope of the invention, to use magnesium, or barium, or another chemically active alkaline metal or alkaline earth metal instead of zirconium.

A preferred embodiment of the invention will now be described with reference to tha accompanying drawing.

As illustrated in the sole figure of the drawing, a vacuum container 10 comprises an external container 1 2 and an internal container 14, which are arranged concentrically one inside the other in spaced relationship so as to provide a vacuum space 1 6.

As can be seen, there is fixed, for example by welding, to the inside 1 8 of the base of the container 12, a tube 20, the end of which pointing towards the internal container 1 4 is open.

The tube 20, which is welded in situ during the production of the external container 12, serves to accommodate a getter substance 22, which in the present embodiment is zirconium.

In order to prevent, during the assembly of the two containers 12, 14, the getter substance 22 from falling out of the open end of the tube 20 and settling anywhere in the vacuum space 1 6 and thereby changing its position, the tube section 20 is covered with a sieve 24, for example of stainless steel wire.

The mesh size of the sieve is chosen so that the getter substance is prevented from falling out of the tube section in any position of the container.

Before assembly of the two containers 12, 14, the getter substance 22 is packed into the tube 20 and the tube is then blocked by the sieve 24. After assembly of the containers 12, 14 the vacuum space 1 6 is evacuated and the getter substance 22 is activated simultane ously. Activation is effected by local heating of the getter substance by means of a heater element 28 arranged on the outside 26 of the external container 1 2. Since the position of the tube 20 is known, the heater element 28, for example, a mushroom-shaped radiator, can be arranged in the corresponding region of the outside 26, and after it is switched on the getter substance is activated by said heating.

As stated, the presence of the sieve 24 prevents the possibility of the getter substance falling out of the tube 20 and thus ensures that activation of said getter substance by the heater element 28 actually occurs. It is sufficient to activate the getter substance under these conditions if it is exposed to a temperature of approximately 2004C during simultaneous evacuation of the container.

After activation of the getter substance has occured, the heater element 28 is removed. It is obvious and lies within the scope of the invention, also to provide the heater element fixed on the outside 26 of the external container 12, i.e. opposite the tube 20, if convenient.

Should it prove necessary in the course of time to re-evacuate the vacuum container 10, then no new getter substance is required in such a case, since the latter can be activated afresh by local heating as hereinbefore described.

CLAI MS 1. A method of maintaining a vacuum in a vacuum container by means of a getter substance, characterised in that the getter substance is introduced openly into the vacuum space of the container, and that the getter substance is activated by local heating during evacuation of the vacuum space.

2. A getter arrangement for carrying out the method according to claim 1 in a container comprising an internal and an external container providing therebetween a vacuum space, characterised in that an open ended tube accommodating the getter substance is arranged on the inside of the external container.

3. A getter arrangement according to claim 2, characterised in that the open end of the tube is covered by a sieve.

4. A getter arrangement according to claim 1 or claim 2, characterised in that zirconium is provided as getter substance in the tube.

5. A getter arrangement according to any one of the foregoing claims, characterised in that a heater element is arranged, opposite the tube, on the outside of the external container.

6. A method of maintaining a vacuum in a vacuum container, substantially as hereinbefore described.

7. A getter arrangement, substantially as hereinbefore described with reference to the accompanying drawing.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. ously. Activation is effected by local heating of the getter substance by means of a heater element 28 arranged on the outside 26 of the external container 1 2. Since the position of the tube 20 is known, the heater element 28, for example, a mushroom-shaped radiator, can be arranged in the corresponding region of the outside 26, and after it is switched on the getter substance is activated by said heating. As stated, the presence of the sieve 24 prevents the possibility of the getter substance falling out of the tube 20 and thus ensures that activation of said getter substance by the heater element 28 actually occurs. It is sufficient to activate the getter substance under these conditions if it is exposed to a temperature of approximately 2004C during simultaneous evacuation of the container. After activation of the getter substance has occured, the heater element 28 is removed. It is obvious and lies within the scope of the invention, also to provide the heater element fixed on the outside 26 of the external container 12, i.e. opposite the tube 20, if convenient. Should it prove necessary in the course of time to re-evacuate the vacuum container 10, then no new getter substance is required in such a case, since the latter can be activated afresh by local heating as hereinbefore described. CLAI MS

1. A method of maintaining a vacuum in a vacuum container by means of a getter substance, characterised in that the getter substance is introduced openly into the vacuum space of the container, and that the getter substance is activated by local heating during evacuation of the vacuum space.