DE2536005A1 - Cryogenic type high vacuum pump - UTILISES ABSORPTION PROPERTIES OF ACTIVATED CHARCOAL AND WORKS WITH MODERATE TEMPERATURE - Google Patents

Abstract

A cylindrical case (4) has an end plate (3) bolted to the vessel to be evacuated and an opposite end plate (12) bolted to a first stage ion pump (14). It contains a vessel (18) which is filled with liquid nitrogen and covered with activated carbon. Copper tubes (5) connected to the vessel support a series of copper plates (7) which are covered with activated carbon. The plates are held apart by distance pieces (8). The vessel contains a heater (16) which enables the activated carbon to be heated to 300 deg.C to 400 deg.C. Carbon activated at these temperatures has sufficiently good absorption properties to produce vaccua of 10-9 Torr. at a temperature no lower than 77 deg.K. This enables the pump to work with liquid nitrogen rather than liquid helium.

Description

High Vacuum Pump System The invention relates to a cooking vacuum pump system high suction power, with which it is possible, large vacuum containers within a short space of time eit to pressures of approx. 1x10-7Torr and below to evacuate, with the residual gas atmosphere is completely free of hydrocarbons.

Oil-free residual gas pressures of 1x10-7 Torr or lower can be bisner can only be achieved economically with high pumping speeds with tryo pumps.

These pumps will have residual gas pressures of 10 9 torr or less achieved by condensation of the residual gas on cold surfaces that lead to enlargement the surface are coated with activated carbon.

The working temperatures necessary for condensation are so low that that either with a technically complex fl. Ne-cooling or with an expensive one Refrigerator must be worked.

The invention is based on the object of a pump system homer Specify suction power that allows a vacuum recipient within a short Time to evacuate to about 1x10-7 Torr or lower, with no hydrocarbons in the residual gas and without using temperatures lower than 77 ° K These The object is achieved in that instead of a commercially available Cryopump a cryo-sorption pump operating at 77 O'r is used, the one Ion atomizer pump or titanium evaporator pump is switched on.

While in conventional cryopumps the activated carbon is essentially serves to enlarge the condensation surface, is used in the cryo-sorption pump the high gas absorption capacity of adsorbents, preferably activated carbon, for Reduction of residual gas pressures exploited.

Investigation of the absorption capacity of activated carbon and carbon sorption varnish at 770K showed that the achievable final pressure after heating at 100 ° C was about 10 6Torr, while it is below 10 8 Torr can be lowered.

In contrast, the cooling of the activated carbon or

of the carbon sorption varnish from 77 0K to 25 0K no significant improvement of the final pressure. Only at temperatures between 200 - 15 0K occurs as a result of condensation or adsorption of the neon and hydrogen a further decrease in pressure.

Let us first leave the partial pressures of hydrogen and neon except for eight, it turns out that one is activated with an at approx. 350 ° C. and on 77 0K cooled activated carbon can reach residual gas pressures of 10-7 to 10-9 Torr, which are comparable with the saturation vapor pressures over cooling surfaces of 150 - 200K. Since activated carbons can have surface areas of 1500 m² / g, it is possible to pass through to build corresponding quantities of activated carbon or sorption lacquer cryo-sorption pumps, which have a high pumping speed and a long enough service life to be used in production plants can be used. The activity of the coal can be kept longer obtained, the better the pre-vacuum in the container to be evacuated.

The pump can be activated again and again by heating it out.

With the cryo-sorption pumps, cooling surfaces of 2 Realize up to 4 m2, on which coal amounts of 500 to 1000 g are applied can what an active surface from 0.7x106 to 1.5x106m2. Due to the resulting high pumping speed of several 1031 / sec when printing - 6 range from 10 3 to 10 Torr, the Cryo-Sorptiorssp = s are excellently suited as Additional or start pumps for ion atomizer pumps or titanium evaporator pumps, which reach their maximum pumping speed at 10 6 to 10 8 Torr and at a fore-vacuum pressure from 10-3Torr cannot be started yet.

The combination cryo-sorption pump / ion atomizer pump or titanium evaporator pump is suitable as a UHV pump arrangement for generating propellant-free residual gas pressures from 10 7 to 10 10 torr. With the titanium evaporation pump in particular, a with A pumping speed for hydrogen comparable to that of the refrigerator cryopump is achieved will.

In contrast to the cryopumps, where the is glued to the capacitor Activated carbon is mainly used to enlarge the cold surface and is only used to approx. 800 to 1000 C may be baked out without damaging the system is for a satisfactory puncture of the cryo-sorption pump a good thermal coupling of the Coal to the cooling system (77 ° K) and the possibility of heating the sorbent absolutely necessary for 3000 to 40000. In addition, as much sorbent as possible should be used be applied to the cooling surfaces.

All of these requirements can most easily be met by coating fill the cooling surfaces with a carbon sorption varnish (Pat.NTr .: P 2451 717.7).

The advantages achieved with the invention are in particular: that with a pumping speed comparable to that of conventional cryopumps, residual gas composition and final pressure, the combination cryo-sorption pump / ion atomizer pump or

Titanium evaporator pump is cheaper because it is on the refrigerator can be dispensed with. When using an ion atomizer pump, there is also no need the vacuum measuring arrangement, as this Function taken over by the power supply unit will. Due to the favorable working pressure of 10 .5 to 10 9 Torr, you get n> it relatively weakly dimensioned power supply units for the ion atomizer pump or titanium evaporator pump the end. In addition, these pumps achieve their maximum pumping speed in this pressure range with a long service life. The arrangement is still vibration-free, noiseless and not prone to failure. The heat development is insignificant, since only with liquid N2 is worked and the power consumption of the ion atomizer pump is negligible is. Also in the case of the titanium vaporizer, the energy consumption is due to the good Vacuum low.

It is also advantageous that the carbon sorption varnish at temperatures from 300 to 4000C d. H. may be baked out under UHV conditions. With the same Suction opening, the effective pumping speed of the cryo-sorption pump is also higher than that of the refrigerator cryopump because no baffle is required.

Finally, another advantage is that the cryo-sorption pump can be used in several variants.

1. Cryo-sorption pump alone for evacuating recipients without additional hydrogen build-up.

2. Cryo-sorption pump with ion atomizer pump for systems with hydrogen accumulation and low ultimate pressure.

3. Cryo-sorption pump with additional titanium evaporation pump or Refrigerator cooling for very high levels of gas, especially hydrogen.

Due to the construction of the pump according to the modular principle, ee is possible, optionally converting from one pump arrangement to another if necessary.

With a suitable construction of the liquid N2 feed, it is possible to the pump can be installed in any position.

An embodiment of the invention is shown in Fig. 1 and is explained in more detail below.

The outer pump body consists of a cylindrical vessel (4) made of VA steel, which is closed at the end by means of two flanges (3) and (12) is. The upper cover (3) has a hole for connection to a vacuum apparatus (1) and provided with threaded rods (2). The lower flange cover (12) contains a Central bore (is) for connecting an ion atomizer pump (14) or a titanium evaporator or a refrigerator. A backing pump can be connected via an opening (13) will. The actual pump part consists of a coated with carbon sorption varnish fl. N2 storage vessel (18) with fl. l-T2 inlets (17) and a heating cartridge (16). The copper plates (7) coated with carbon sorption lacquer sit on four with the fl. N2 reservoir (18) soldered copper rods (5), which ensure good cooling of the Plates guarantee. The alstands of the individual plates are four each Spacer rings (8) that are soldered to the plates are determined using the entire plate system pressed together by four screws (9). Serves to reduce the liquid N2 consumption a radiation shield (5) and (19) surrounding the dzc plate system.

The one in Pig. 2 version shown is suitable for use a titanium evaporator (24) or refrigerator, which through the opening (45) to the Base plate (12) can be flanged. Part of the ('ryo sorption surfaces is shaped in such a way that a free space (21) is created, which is upward (2Q) and laterally (25) (26) is closed by a kind of baffle.

Both for the capacitor area of the refrigerator and for the Titanium evaporator (24), this optically sealed design is necessary. When using of a titanium evaporator (24) are the surfaces delimiting the free space (20) (22) (23) (25) and (26) are not coated with Kohffie-3orptionslack because they serve as a catcher for the evaporating titanium.

As an application example, a steaming system is shown in FIG. 3, whose function will be explained below.

With closed valves (29) and (39) and open valves (32) and (34), the cryo-sorption pump is first activated via the fore-vacuum line (31) (38) and the ion atomizer pump (37) evacuated. The backflow of oil vapors A coaxial trap (35) or a liquid N2 trap from the backing pump (36) prevents it (33), which is also coated with sorbent varnish. After reaching the final pressure both the cold trap (33) and the cryo-sorption pump (38) are filled with fl. N2 cooled down. The valves (32) and (34) can remain open. During the Cooling of the sorption surface previously heated to 3500 G decreased to 770K the pressure in the pump body increases from initially 10 3 Torr to 10-7 to 10 8 Torr. To The ion atomizer pump or titanium evaporator pump can end the cooling process be switched on. The pump system is now ready for operation.

To evacuate the recipient (27) is initially closed Valves (32) and (34) and open valve (29) a fore vacuum of approx. 10 3 Torr generated, which can be checked on the measuring cell (30). Now valve (29) closed and the high vacuum valve (39) opened. The pressure drops suddenly in the recipient (27) to approx. 1x10 6 to 5x10 7 Torr and decreases further Values from 10 -7 to 10 9 torr, depending on the nature of the recipient and the pumping speed the ion atomizer pump or the titanium evaporator pump.

Claims (9)

Claims 1. High-vacuum pump system d u n g e n g e n e n a l a l t that by using the cryo-sorption effect of activated adsorbents, preferably of activated carbons, which are applied to cooling surfaces and cooled to 770 be, the residual gas pressure in pre-evacuated containers completely oil-free to 10 6 to 10 8 Torr can be reduced, and that by connecting a backing pump via a fl. N2 cold trap also hydrogen can be pumped, and that in particular through an additional ion atomizer pump or titanium atomizer pump even at high temperatures Hydrogen accumulation final pressures below 10 9 torr can be achieved. 2. High vacuum pump system according to claim 1, d a d u r c h g e k e n n z e i h n e t that to achieve a high pumping speed activated carbon in Porm of granules with a suitable binder, preferably nitrocellulose or water glass, if necessary after adding copper powder, on the cooling surfaces, preferably copper or aluminum sheets, glued on and baked at approx. 3000C is activated. 3. High vacuum pump system according to claim 1, d a d u r c h g e k e It is not noted that the cooling surfaces, preferably Eupfer or aluminum sheets, coated with a cryo-sorption lacquer, preferably with an activated carbon sorption lacquer will. 4. High vacuum pump system according to one of the preceding claims, D u r c h e k e k e n n n z e i c h n e t that the cryo-sorption pump is used, depending on the intended use with adsorber pumps or backing pumps and ion atomizer pumps, titanium evaporator pumps, Turbomolecular pumps or a refrigerator can be combined and a rapid Enables lowering the pressure of a connected container. 5. High vacuum pump system according to one of the preceding claims, d u r c h g e k e n n n z e i c h n e t that the cryo-sorption surfaces (7) in a cylindrical vessel (4) closed on one side from a suitable one Material, preferably VA steel, whose end faces (3) and (12) have openings (i) (13) (15) for connecting a recipient, a fore-vacuum system and an ion atomizer pump or a refrigerator or titanium evaporator. 6. High vacuum pump system according to one of the preceding claims, d a d u r c h e k e n n z e 1 c h n e t that the cryo-sorption surfaces (7) according to The modular principle is attached to four copper rods (5) and soldered through Spacer rings (8) are separated from each other, and that by four screws (9) these Plates releasably pressed together with the radiation shield (6) and (19) sina, and that the copper rods (5) are still soldered to the liquid N2 storage vessel (18) and that the latter have openings for the fluid N2 supply (17) and for a heating cartridge (16). 7. High vacuum pump system according to one of the preceding claims, d u r c h e k e nn n n z e i c h n e t that by removing a part or of all cryo-sorption plates and by replacing the ion atomizer pump (14) with a refrigerator with attached capacitor plates, the cryo-sorption pump in a refrigerator cryopump can be converted, and that in particular in this Case a simple baffle can be made that on the copper rod (5) angled metal plates coated with sorption lacquer (20) (25) and (26) are lined up, which are also separated from each other by spacer rings. 8. High vacuum pump system according to claim 7 or one of the preceding Claims, d u r c h e k e n n -z e i c h n e t, that instead of the refrigerator a Titanium evaporator (24) can be flange-mounted, and that for Absorption of the evaporating titanium the closest metal surfaces (20) (22) (23) (25) and (26) are not coated with carbon sorption varnish. 9. High vacuum pump system according to one of the preceding claims, d u r c h g e k e n n z e 1 c h n e t that the cryo-sorption surfaces The part containing it is particularly suitable as an additive to ion atomizer pumps or Titanium evaporator pumps provide the required starting pressure of 10 4 to for these pumps 10 5 Torr can be reached very quickly. 3 signs 1 suction opening 2 threaded bolts 3 front plate 4 cylinder vessel 5 cooling rods 6 radiation shield 7 cryo-sorption surfaces 8 spacer sleeves 9 locking screw 10 Flange 11 O-ring or metal seal 12 Flange cover 13 Pre-vacuum connection 14 Ion atomizer pump 15 -suction opening 16 heating cartridge 17 refill device for fl. N2 18 fl. N2 reservoir 19 radiation shield 20 curved cooling plates (baffle u. Titanium catcher) 21 blank 22 inner cooling plate (titanium catcher) 23 inner Cooling plate (titanium catcher) 24 titanium evaporator 25 curved cooling plate (baffle and Titanium catcher) 26 curved cooling plate (baffle and titanium catcher) 27 recipient 28 Base plate 29 Valve 30 Pre-vacuum measuring cell 31 Pre-vacuum line 32 Valve 33 Cold trap 34 Valve 35 Coaxial trap 36 Backing pump 37 Ion nebulizer pump 38 Cryo-sorption pump 39 High vacuum valve L e r s e i t e