US3088219A

US3088219A - High-vacuum plants

Info

Publication number: US3088219A
Application number: US20790A
Authority: US
Inventors: Kraus Thaddaus Josef
Original assignee: Balzers Patent und Beteiligungs AG
Current assignee: Balzers Patent und Beteiligungs AG
Priority date: 1959-04-07
Filing date: 1960-04-07
Publication date: 1963-05-07
Anticipated expiration: 1980-05-07
Also published as: NL105775C; GB883376A; CH367269A

Description

May 7, 1963 T. (JOSEF) KRAUS 3 0 219 HIGH-VACUUM PLANTS Filed April 7, 1960 2 Sheets-Sheet 1 H 5 774/100 44/8 (dasEF) Kmrus May 7, 1963 T. (JOSEF) KRAUS 3,088,219

HIGH-VACUUM PLANTS Filed April 7. 1960 2 Sheets-Sheet 2 28 g g m 25 H 4 32 be/l0w: 5 38 37 Bell Valve I fiwv-Q-viw f re /400 905 (40551 mmus United States Patent Mad stein Filed Apr. 7, 1960, Ser. No. 20,790 Claims priority, application Switzerland Apr. 7, 1959 7 Claims. or. 34-15 The present invention relates to a high vacuum plant comprising a recipient having an access aperture to be opened for the insertion of the articles to be treated in vacuo and for the withdrawal of said articles after treatment.

The invention has the main object of providing a high vacuum plant of the kind referred to and a method of its operation capable of substantially reducing the pumping time required for evacuating said recipient after the same has been opened for the insertion or withdrawal of the articles treated therein, and more particularly for shortening the pumping time for establishing a high vacuum after a previous part-evacuation to a preliminary vacuum.

It is another object of the invention to achieve the aforesaid saving in pumping time without the use of sluice devices as hitherto used for keeping the recipient proper constantly under vacuum, even while inserting and withdrawing the articles undergoing treatment.

The purpose of such devices is naturally to save pumping time: with many processes the treatment of the articles in vacuo takes only a fraction of the time required for pumping. For example a thin reflexion-reducing layer may be deposited on a lens from the vapor phase easily within a minute, while it takes at least half an hour or longer to reach the high vacuum required for the operation after preliminary evacuation by previous pumping.

The aforesaid sluice devices, which accordingly serve for saving pumping time, are however costly in construction, and are at present not sufiiciently developed for many articles to be treated in vacuo, for example for lenses, so as to find use in industrial production. Accordingly the use of high vacuum plants, the recipient of which can be opened for the insertion and the withdrawal of the articles to be treated, has been continued and the losses in time involved thereby have been accepted.

It has now been found that even in such plants quite a considerable proportion of the pumping time, namely up to 99% and even more, can be saved at least for the high vacuum evacuation, by operating according to a new method of operation forming the subject of the invention described hereinafter.

With the objects as aforesaid and other objects in view, which will become apparent later from this specification and the accompanying drawings, I provide a method for the operation of a high vacuum plant comprising the steps of opening the recipient, inserting the articles to be treated in vacuo into the said recipient and introducing simultaneously into same a flow of dried gas of a humidity below that of the surrounding space, closing said recipient, evacuating said recipient, carrying out the treatment of the articles in vacuo, re-opening said recipient while introducing simultaneously into the same a flow of said dried gas, and withdrawing the treated articles.

A high vacuum plant according to my present invention comprises in combination: a recipient having an access aperture, a closure member capable of closing said aperture, evacuating means operatively connected to said recipient, and at least one dry gas introducing orifice arranged inside said recipient and directed towards said access aperture, said orifice being connected to an exter- 3,088,219 Patented May 7., 1963 nal source of dried gas while said closure member is open.

Although it has been known that water vapour constitutes a considerable proportion of the gases or vapours which have to be pumped ofi when establishing a high vacuum in a conventional recipient, whether made of glass or of metal, it is nevertheless quite surprising that such enormous savings in pumping time can be attained by the simple measure mentioned.

For example it may be mentioned that a metal vacuum recipient having a capacity of about litres required a regular high vacuum pumping time of 88 minutes with existing pumps, in order to reach a vacuum of 4 l0- mm. Hg after preliminary evacuation to 10' mm. Hg. When however proceeding by the method according to the present invention, i.e. when constantly blowing a gas sharply dried by phosphorus pentoxide into the recipient,

.while in the opened condition in communication with the external atmosphere, then with the same pumps and without any other provisions for the high vacuum pumping (after a preliminary evacuation), pumping times were attained amounting to fractions of a minute, for example of 50 seconds for the range from 10- mm. Hg to 2X10- mm. Hg. These observations have been confirmed on numerous other plants. It should be remarked that these achievements were attained not only in cases when the air of the external atmosphere was extraordinarilymoist, but quite generally, i.e. with the air of the external atmosphere having a relative humidity, lying between 20 and 60% of saturation.

It is obvious that the new method constitutes a big jump forward in the technical progress. Its application is recommended everywhere, where articles giving off comparatively little gas, such as glass or metal components, are to be treated for short periods of time under a high vacuum, and subsequently the plant has at once to be charged anew. In these cases of application the efliciency and availability of an existing high vacuum plant is enormously improved by the new method.

For carrying out the new method the following indications may be useful:

The blowing in of the dry gas is conveniently effected from a point in the interior of the recipient in the direction towards the aperture, through which the recipient in the opened condition is in communication with the external atmosphere. It appears that thereby the ingress of moist ambient air is prevented more effectively. In order to make savings in the rinsing gas blown into the recipient it is advisable to throttle the outflow into the surrounding atmosphere by obstacles arranged outside of the aperture of the recipient. Such obstacles which can be readily provided as a make-shift arrangement on existing plants may be constituted e.g. by curtains, which close the means of access to the recipient from all sides except for small slots serving for the insertion, the withdrawal and other manipulations required when the recipient is opened.

As regards the kind of the dry gas to be blown in, the following has to be stated: in principle naturally all sufiiciently dry gases may be utilised insofar as they are chemically compatible with the articles to be treated and with the components of the plant. It suifices, to use previously dried air. Dry CO has the advantage that it is readily compressible so that even large quantities require only relatively small, handy containers for storage.

The choice of the rinsing gas is often determined by the technological process being performed. For example dry 0 may be blown into plants wherein oxidizing processes are to be carried out. In other plants, dry N argon or other known inert gases will be used. The use of an inert gas for the protection of articles treated, for example in furnaces, is known in itself, but for protecting the articles from high temperatures or from chem ical activity, while the use of such gases in the dried state for the purpose of shortening the evacuation periods has been proposed for the first time by the'present invention.

The method according to the invention may also be carried out in several stages, i.e'. the recipient may be surrounded'by an outer shell, and the atmosphere in the enclosed-space may be kept at a lower humidity than that corresponding to the external atmosphere. This may be done in that the enclosed-space is supplied with dry gas .(e.g. by constantly blowing in dry air), or by setting up conventional drying agents therein or by building-in .a drying apparatus. Drying agents and drying apparatus may naturally also be arranged in the recipient proper, if desired.

When calling the aforesaid enclosed space the 1st enclosed space, one could say that the method according to the invention may be carried out by surrounding the recipient with a 1st, 2nd, etc. enclosed space, and by supplying all or some of said enclosed spaces with dry gas while the recipient is in the opened state. In the simplest case, the dry gas, which is blown into the recipient proper, is made to flow through the consecutive enclosed spaces in succession.

These and other features of my said invention will be clearly understood from the following description of some embodiments of my new and improved vacuum plant given by way of example and not of limitation with reference to the accompanying diagrammatic drawings, in which:

FIGURE 1 is a diagrammatic longitudinal part section of a first embodiment of a vacuum recipient with a device for blowing a dried gas into the surrounding enclosed space;

FIGURE 2 is a diagrammatic representation on a smaller scale of a first modification; and

FIGURE 3 of a second modification of the embodiment according to FIGURE 1, also on a smaller scale than FIGURE 1;

FIGURE 4 is a diagrammatic representation of another embodiment.

In FIGURE 1 the vacuum recipient 1 is formed by the bell 2 and the platform 3. This recipient 1 can be evacuated through the pipe 4 by means of a pump 5. 6 denotes an annular seal, 7 denotes a hydraulic hoisting device, by means of which the bell 2 can be raised and the recipient can be opened. The position of the raised bell is indicated in this figure in dotted lines.

The recipient described, which rests on a base 8, is totally enclosed in a casing 9, which may be formed either of rigid walls or of a gas-tight synthetic plastic material, e.g. a thin sheet of synthetic material. The casing 9 is connected in a gas-tight manner, to the base 8 by means of the flange 10 with annular seal 11, buthas one or several flaps or movable resilient sleeves 13, through which articles can be inserted into the recipient 1 (when the same is opened) or any other manipulations can be carried out. When for example the recipient contains a device for the deposition from the vapor phase of thin layers on lenses, the lenses may be introduced by hand through the sleeve 13.

FIGURE 1 moreover shows a blower 14 for aspirating atmospheric air, a drying device 15 for this aspirated air adjoining downstream of the blower and a pipe 16 leading into the interior 17 of the casing 9. Moreover a valve 18 is provided on the bell 2, through which air can be let into the recipient from the interspace between the casing 9 and the bell 2.

The device described can be used in the following manner according to the method of the invention:

Firstly the hell 2 is assumed to be raised and the recipient to be charged with the articles to be treated in vacuo. Then the bell 2 is closed, evacuated through the components 4 and 5, until the working vacuum is attained,

and subsequently the vacuum treatment is carried out. During this period a flow of dry air is continuously blown into the enclosed space between the casing 9 and the outside of the bell 2. By the excess pressure which consequently prevails in this enclosed space the casing 9 is then kept in shape even when it consists of a thin sheet; moreover the sleeve 13 is pressed against the wall of'the casing so that it is kept closed. The movable flap 12 and collapsible sleeve 13 thus form obstacles against the outflow of dried air. The air introduced into said enclosed space can accordingly flow off to the external atmosphere only through the existing small leaks, so that the consump tion of dry air remains low. The air flowing past the walls of the enclosed space carries along the moisture that would normally adhere to the outside of the bell 2 and to the inside of the casing 9 in the form of an extremely thin film, so that in the course of this operation these walls are practically completely dried. This is, as explained hereinabove, of decisive importance for the shortening of the pumping time. a

After the vacuum treatment in the recipient has been terminated the recipient has to be opened in order to be able to take out the articles treated, and to introduce new ones. For this purpose firstly the valve -18 is opened, so that the dry air from the enclosed space 17 flows into the recipient. Thereafter the bell 2 is raised, the articles are taken out of the bell 2 and casing '9 through the flap 12 or sleeve 13, and any other manipulations which may become necessary, such as the exchange of evaporation sources or the like, are carried out in the recipient. During this stage dry air constantly flows from the pipe 16 into the

spaces

1 and 17, and flows oil? outward through the flap 12 and servicing sleeve 13, which are temporarily opened during the manipulations described. Any penetration of moist air from the external atmosphere and accordingly any condensation on the walls of the bell and casing are prevented by the flow of dry air or gas from pipe v16.

After the recipient has been made ready for renewed evacuation, the bell .2 is lowered, valve 18 is closed again, and the recipient 1 is evacuated through the pipe 4 by the pump 5. In this second and any further evacuation the advantage of the method according to the invention makes itself noted by substantially shortened pumping periods. Any further evacuation cycle is carried out in a similar manner as described; it is essential that the moist air is kept away from the inner wall surface of the recipient and the apparatus components contained therein as well as from those parts outside thereof which are in gas interchange with the inner wall surface when the recipient is opened. It has been found that for example even cm. of an area which had been in contact for a prolonged period with the external atmosphere (relative humidity about 50%) and then came into communication with the recipient, might prolong the pumping period by about 10 to 20 minutes. For this reason it is advisable previously to dry even the articles to be treated before their insertion into the recipient. .For example during the vacuum treatment of one charge, the articles to be treated in the next consecutive charge may be deposited already in the enclosed space 17 so that they are previously dried there in the air'current. In order to attain a uniform flow through the enclosed space 17, the tip 19 of the casing 9 may have a restricted vent through which air can escape outward.

.Modified embodiments for carrying out the method according to the invention are diagrammatically illustrated in FIGURES 2 to 4. In FIGURES 2 and 3, respectively, 21 and 2-1 denote the recipient, 22 and 22' a casing surrounding the recipient, and 23 and 23' a cflap, sleeve or similar means of access for the same purpose. 24 and 124' denote the evacuating line, 25 and 25' the vacuum pump, and 26 and 26 a line, which is in communication with a source 27 and 27' of dried gas. This source may be a drying appliance (like of FIGURE 1) or for example a pressure gas container for extremely dry oxygen, nitrogen or any other suitable gas.

The embodiments according to the FIGURES 2 and 3 difler from that of FIGURE 1 primarily in that the introduction of the dry gas into the

recipient

21 or 21 and into the

casing

22 and 22, respectively, takes place partly at difierent points.

In FIGURE 2 the line 26 is directly connected with the recipient 21 through a valve 28. In this arrangement dry air flows through the enclosed space 2.9 only when the recipient 21 is opened. While the same is closed, the atmosphere in the enclosed space 29 is at rest; if desired, however, a fan may be used for circulating the air therein, which is convenient when in this enclosed space 29 a drying appliance charged for example with phosphorous pentoxide is set up. In the embodiment according to FIGURE 2 the casing 22 (particularly its means of access 23) should be capable of being closed so tightly that no appreciable quantity of the external air can penetrate into it during the treatment period. During the charging and discharging of this plant the danger of penetration of moist air through the means of access 23 is obviated by the outward flow of dry gas through it.

In FIGURE 3 additionally a line provided with a valve 39 is arranged. In this arrangement dry air may be introduced simultaneously into the recipient 2.1 and into the enclosed space 29'. This construction is recommended particularly for large plants; the operation is otherwise analogous to that described hereinabove with reference to the FIGURES 1 and 2.

In FIGURE 4 a design is illustrated in which part only of the outside of the wall of the recipient is protected from the moist atmosphere. 31 denotes a bell forming the recipient, 32 a vertical closure wall of this bell, 33 the evacuation line, 34 the vacuum pump, 35 a rail on which the bell 31 is suspended by means of rollers 36 and can be moved horizontally away from the wall 32 in order to open the recipient. The bell 31 is here not fully enclosed by a casing (such as 9, 22, 22 in the other figures), but only over a short stretch at the left hand side margin of the bell 31. This envelope has here the form of an expansible folded bellows 37, which is attached on the one hand to the closure wall 32 (along a circle 38) and on the other hand to the bell 31 (along a circumference 39). When the recipient is to be opened, it is driven away from the wall 32 to the right, while the bellows 37 is stretched. At the same time dry gas is introduced into the recipient through a valve 40, so that it flows through the same and escapes through the means of access 41 into the bellows 37, thus preventing the moist external air from penetrating into the recipient. One of these means of access 41 is indicated in FIGURE 4 as a flap. When the charging is terminated, the bell is closed again. The bellows folds up and forms a small enclosed space around the annular seal 42 between the bell 31 and the wall 32, which space remains filled with dry air and accordingly prevents condensation on the outside of the said seal and of the flange of the bell. Obviously, analogous to FIGURE 3, a separate supply line of dry gas could be provided for this enclosed space in order to make even more sure that no moist air can penetrate into it.

While I have described herein and illustrated in the accompanying drawings what may be considered typical and particularly useful embodiments of my said invention, I wish it to be understood that I do not limit myself to the particular details and dimensions described and illustrated; for obvious modifications will occur to a person skilled in the art.

What I claim as my invention and desire to secure by Letters Patent, is:

l. A method for the operation of a high vacuum plant having an evacuatable recipient comprising the steps of opening the recipient, inserting dry articles to be treated in vacuo into said recipient and introducing simultaneously into the same a flow of dried gas of a humidity below that of the surrounding atmosphere, closing said recipient, evacuating said recipient to a pressure of the order below 10* mm. Hg, carrying out the treatment of the articles in vacuo, re-opening said recipient while introducing simultaneously into the same a flow of the said dried gas from a point in the interior of said recipient towards the opening thereof, and Withdrawing the treated articles.

2. A method as claimed in claim 1, comprising the additional step of maintaining in the space surrounding said recipient an atmosphere of a humidity 'lower than that of the ambient air.

3. A method for the shortening of the pumping time in discontinuously operating vacuum plants having a vacuum recipient repeatedly to be opened and subsequently closed for inserting dry articles to be treated therein and for withdrawing the same after treatment, comprising the consecutive steps of opening an access opening to said vacuum recipient, blowing dry gas of a humidity substantially lower than that of the surrounding atmosphere from the interior of said vacuum recipient outwardly in the direction towards said open access opening, closing said access opening, and evacuating said vacuum recipient to a pressure of the order below 10 mm. Hg.

4. A device for treating articles under high vacuum comprising in combination: a recipient, a casing surrounding said recipient at least at one end thereof, means for moving said recipient from an open to a closed position within said casing, a gas-tight sealing member engaged by said recipient in its closed position, means tor evacuating said recipient, means in said casing providing access to the interior thereof, a flexible closure for said access means, a source of dried gas, and means for injecting said dried gas into the interior of said casing.

5. The device according to claim 4 including valved means for injecting a current of dried gas into the recipient.

6. The device according to claim 4 in which the gas injecting means is located adjacent the access means in the casing.

7. The device according to claim 4 in which the flexible closure is a resilient sleeve.

References Cited in the file of this patent UNITED STATES PATENTS 1,580,957 Chafle et al. Apr. 13, 1926 1,799,248 Reinhardt Apr. 7, 1931 1,866,346 Clark July 5, 1932 2,307,802 Reichel Jan. 12, 1943 2,465,963 Beardslee Mar. 29, 1949 2,858,795 Walker Nov. 4, 1958 2,890,878 Steinherz et al. June 16, 1959

Claims

4. A DEVICE FOR TREATING ARTICLES UNDER HIGH VACUUM COMPRISING IN COMBINATION: A RECIPIENT, A CASING SURROUNDING SAID RECIPIENT AT LEAST AT ONE END THEREOF, MEANS FOR MOVING SAID RECIPIENT FROM AN OPEN TO A CLOSED PORTION WITHIN SAID CASING, A GAS-TIGHT SEALING MEMBER ENGAGED BY SAID RECIPIENT IN ITS CLOSED POSITION, MEANS FOR EVACUATING SAID RECIPIENT MEANS IN SAID CASING PROVIDING ACCESS TO THE INTERIOR THEREOF, A FLEXIBLE CLOSURE FOR SAID ACCESS MEANS, A SOURCE OF DRIED GAS, AND MEANS FOR INJECTING SAID DRIED GAS INTO THE INTERIOR OF SAID CASING.