US2986326A - High vacuum - Google Patents

Description

May 30, 1961 A. A. LAN DFORS HIGH VACUUM Filed March 4, 1959 I I I I I I I I x I %w& ll \v\ t I I I I I S r I I II I I vw mm mw an vn NN\\ q 1 55% N wt Q Q? Uni ed Stat Pat n Q "HIGH VACUUM Arthur A. Landfors, Boston, Mass., assignor to National Research Corporation, Cambridge, Mass., a corporation of Massachusetts ma Mar. 4, 195 9, Ser.No. 797,99 4 c ai s. 01. 230-49 This invention relates to high vacuum pumping and more particularly to gettering-type pumps. This invention is particularly directed to a novel means of supporting the filament around which gettering material is positioned.

A principal object of the present invention is to provide a means of support whereby filaments may be protected from stresses due to expansion.

Another object of the invention is to provide a pumping component for a vacuum system which may be readily and efliciently removed, replaced, and serviced.

A further object is to provide an inexpensive device for getter pumping.

An important object of the invention is to allow for dependability and long life of filaments.

In the use of filaments supporting helically wound gettering materials, the filaments are heated to fairly high temperatures and are thus subject to stresses which cause frequent failures. The present invention provides a means for reducing such stresses and the incidence of such failures by providing for a filament holder fixed at one extremity of the filament and movable along the axial direction of the filament at its opposite extremity so it may expand freely but move only in the axial direction.

Another problem basic to the getter pump is that both filaments and gettering material such as tantalum must be replaced periodically. In the present invention a removable filament holder can be inserted through an aperture in the wall of a vacuum chamber and sealed to the wall by means of a flange and a gasket such as a crush ring seal. The flange is preferably threaded so as to be connectable to a matched thread on the wall of the chamber. Substitution or repair of such units can be completed with little loss of operating time.

Another factor adding to the usefulness of this device is that more than one pumping unit can be installed in the same chamber. The pumping rate will approximate that desired and the system will operate in spite of failure of one unit.

In a preferred form of the invention, a rod or filament of refractory material is arranged to be heated to a high temperature so as to vaporize gettering material. Supports are placed at opposite ends of the rod, one support being rigid and the other being movable axially so that the rod can move axially while being rigidly supported to withstand transverse forces. The supports are electrically insulated from each other. The rod is wound with gettering material such as titanium (or tantalum). The device is sealed to the chamber to be evacuated by use of a flange and a crush ring.

The apparatus for supporting the rod comprises a metal tube with slots through which vaporized gettering material may ditfuse. Preferably the tube also acts as an electrical conductor for one terminal of the refractory filament.

A preferred embodiment of the device is shown in the drawings. Figure 1 is a diagrammatic, schematic, sectional view of the device attached to a portion of the chamber wall. Figure 2 is a diagrammatic, schematic, sectional view 'of the tube shown in Figure 1 along section line A-A of Figure 1.

In Figure '1, the wall 10 of the chamber to be evacuated is arranged with an opening and a threaded lip'so that flange 12 may be screwedtightly to crush ring 14 which is used to seal wall 10 and flange 12. Attached to flange12 is tube 16 which is the support for the other parts of the device. It has an opening 18 at the top and bottom to permit escape of" the getter vapors. Into one I end portion, of tube 16 is placed a sliding block 20.

The filament" r'od'26 is supported 'at one end by sliding block 20 and at the other end by electrode 28. When the filament 26 expands, the block 20 will move and there will be no stress upon the filament rod due to such expansion. Still the filament does not move transversely. Around filament 26 are windings of gettering material 24 such as tantalum or titanium. Windings 24 may be one or more helical windings.

Electrode 28 is supported by insulating material 30 which is carried by tube 16. Tube 16 and shielding 34 are separated electrically. Insulating material 30, electrode 28, and tube 16 are vacuum sealed to each other.

The voltage source 32 is connected to electrode 28 although the actual connection is not shown here. The current path passes through electrode 28, filament 26, support 20, tube 16, and flange 12. The flange 12 is preferably grounded.

When current passes through the circuit above described, filament 26 is heated to a temperature at which gettering material 24 is vaporized. This vaporized gettering material then passes through slits 18 and operates to evacuate the chamber enclosed in part by wall 10.

The reaction which causes pumping is the combination of the metal or gettering material with the gases present in the chamber to be evacuated. Gettering materials include titanium, tantalum, zirconium, and other materials such as barium, magnesium and aluminum. Other modes of using the getter may be employed than a helix. The getter can be merely placed on the filament in single closed loops which are not dislodged due to rotation of the pump.

The spirit of the invention includes other means of removably mounting the pump to the wall of the ion chamber.

Equally the slits in the tube can be replaced by openings of diiferent shape, cross-section or size, and the mounting block can have another shape.

Since certain changes may be made in the above apparatus without departing from the scope of the invention herein involved, it is intended that all matter contained in the above description, or shown in the accompanying drawing, shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

l. A device for producing vacuum comprising a refractory rod capable of being heated electrically to a high temperature, gettering material carried by said rod so as to be vaporized by said high temperature, supports arranged at opposite ends of said rod, one support being rigid and one being movable axially so that said rod is free to extend axially, means for preventing transverse movement of said movable support, means for electrically insulating said supports from each other, and means for connection to a wall of a vacuum chamber for forming a vacuum-tight joint with said rod and supporting said rod within said vacuum chamber.

2. A pump element which is adapted to be inserted through an aperture in a wall of a chamber which is to be evacuated, said element comprising a source of gettering material for mounting on a flange which seals the aperture, said device having a rigid refractory filament Patented May 30, 1,961,

winding of at least onegetteringm'aterial, 'a 'pair of sup ports for said filament arranged so that motion transverse the x s aifi em s l m t Q t aisl fl p t ba mama t w r ea en? in i e t an alongsaid 'axis and the other of, said supports being adapted to be rigidly onnected to said fiangef 3"."A vacuum pump comprising a refractory metalfilamentjwound with gettering material, two supports for said filament, a sealing flange for forming a vacuum-'tightseal with aportion of the walls of the system to be evacuated, afhollow cylindrical tubetwith, openings surrounding said filament," said supports forsaid filament being connected by said hollow cylindrical tube so that, said openings allowniffusion otvapor therethrough, one ofvsaid sup- 15 2,796,555

ports being rigidly connected to said tube, the other of said supports being slid'ably connected to said tube to vaporized gettering material-diffuses when said filament is heated, said hollow cylindrical tube further acting as 10 an electrical lead for current flowing through filament.

References Cited in the file of this patent UNITED STATES PATENTS Connor June 18, 1957

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