GB2158893A - A shaft seal for an oven air circulator - Google Patents

Abstract

An airtight oven for sterilizing objects comprises an air circulator 2 mounted on a shaft 20 which is sealed by a sealing chamber 22. A pair of spring loaded P.T.F.E. gaskets 28 form a tight seal around the shaft and filtered air is supplied to the chamber 22 through an inlet 32 so that if any leakage occurs at the shaft seal, only clean air enters the oven. <IMAGE>

Description

1

SPECIFICATION

An oven The invention relates to an airtight oven corn- 70 prising at least two doors separating two chambers, and further, more comprising a filter arrangement, through which the air within the oven is circulated in a closed circuit by means of a circulator, said closed circuit optionally including means for adjusting the temperature of the circulating air.

The filters must be placed in such a manner that the air cannot pass during its circulation.

Furthermore, the filters must be replaceable, and the filter frame should be capable of expanding in proportion to the oven shell. In addition it should be possible for the air to circulate through the filters without the pump in question introducing impurity particles into 85 the circuit in which the air circulates.

These objects are according to the invention obtained by the filter arrangement comprising a frame loosely secured to a resilient, trumpet like, airtight suspension arrangement which in 90 turn is secured to the rim of a channel passed by the circulating air, whereby the major por, tion of said rim may be formed by the oven shell.

The trumpet-like, tubular suspension arrangement may advantageously be secured to the parts of the oven shell during the assembling thereof, preferably through welding.

In order to facilitate the replacement of the filters, the supporting frame with the filters may rest on one or more rails by means of wheels and be displaceable along said rails upon release from the trumpet or tube-like suspension arrangement. In this manner the supporting frame is easily moved to the oppo- 105 site side of the oven, whereby the filters oppose the door. Subsequently, it is easy to pull out the filters from the supporting frame, to remove them from the oven, and to insert new filters.

The invention also relates to a shaft seal about a rotating shaft, e.g. the rotating shaft of a circulator, which extends through an opening in the plate wall such as an oven shell separating two chambers which contain their respective media or their respective qualities of the same medium such as air, water or oil, and whereby at least one medium must not be mixed or polluted by the other me- dium. The shaft seal is characterised by the shaft being received in two spring-loaded gaskets displaceable in the longitudinal direction of the shaft and co-operating with a sealing chamber, in which an inlet nozzle is provided which feeds a small amount of an appropriate medium of a sufficiently high quality such as thoroughly filtered air, at an overpressure, whereby this medium may penetrate into and be mixed with the two first- mentioned media without lowering the quality GB 2 158 893A 1 of said two media. In this manner a shaft seal is obtained which makes it possible to situate the driving motor of the circulator outside the oven without penetration of polluted air through the inlet opening of the rotating shaft.

It is according to the invention an advantage to situate the sealing chamber on the outside of the plate wall and to define said chamber by the plate wall as well as by a preferably circular plate portion pressed outwards, e.g. of stainless steel, said plate portion being shaped with a circular surface and situated at a distance from and parallel to the plate wall, whereby said circular surface continues into and is defined by a short circularcylindrical surface which in turn continues into a surface extending radially outwards from the cylindrical surface parallel to the plate wall and being hermetically secured thereto and e.g. screwed thereon by means of intermediary gaskets.

The spring-loaded gaskets may advantageously be made of a heat-resisting material such as teflon, and each gasket may be shaped with a central, circular hole being exactly so great that the shaft can be received therein in an easy, sliding fitting. In this manner a complete seal is obtained between the gaskets And the shaft.

The spring-loaded gaskets may advantageously abut their respective walls in the sealing chamber and be mutually spaced by a compression spring. In this manner a good sea[ between the gaskets and the sealing chamber is obtained. It is therefore only necessary to feed relatively small amounts of air in order to maintain an overpressure within said sealing chamber.

The compression spring may either be a spiral spring or a conical spiral spring.

The invention deals especially with the case where the media mentioned in the introduction are common atmospheric air and filtered, sterilised air, respectively, having a more specified maximum content of particles, e.g. of the magnitude 100 particles per cubic foot corresponding to class 100 for sterilising ovens. The medium fed to the shaft seal through the nozzle of the sealing chamber may then suitably be purified filtered air fed by a pressure corresponding to a water column of about 5 mm.

The invention will be described below with reference to the accompanying drawing, in which Fig. 1 illustrates an oven according to the invention, Fig. 2 is a sectional view parallel to the plane of the paper of the oven in Fig. 1, Fig. 3 is a sectional view of the oven taken along the line X-X of Fig. 1, and Fig. 4 illustrates the shaft seal of Fig. 3 in connection with the circulator of the oven.

The oven illustrated in the drawings is air- 2 GB2158893A 2 tight. It comprises at least two airtight doors indicated by dot-and-dash lines and preferably situated in a partition between a sterile chamber and an impure chamber. These two doors cannot be opened simultaneously. In one side of the oven a filter to be passed by the air is mounted, said air being circulated by a circulator in a closed circuit consisting of channels. Means 3 for adjusting the temperature of the air are provided in the closed circuit. The filter 1 is mounted in a supporting frame 4. The technical problem is that it should be possible for the supporting frame to expand in response to the changes of the temperature and the channels should be tight. According to the invention the frame 4 is loosely secured to a resilient, trumpet or tube-like, airtight suspen sion arrangement 5 which in turn is secured to the rim of a channel 6 passed by the circulating air. In this manner it is possible for the frame 4 to expand irrespective of the remaining part of the oven without the circulating channel 6 bypassing the filter. When parts of the circulating channel 6 are formed by the oven shell 7, the trumpet-like, tubular suspension arrangement 5 may advantageously be secured to said parts of the oven shell 7 during the assembling thereof, as indicated at 8, preferably through welding. In this manner a very reliable and completely airtight construction is obtained.

According to the invention the supporting frame 4 with the filters 1 rest one one or more rails 11 by means of wheels. After release from the trumpet-like suspension arrangement, the supporting frame 4 with the filters 1 are displaceable along the rails. The rails 11 extend through the oven and are situated above the doors of the oven in such a manner that a replacement of the filters may take place through the doors. Therefore the oven need only be idle for a very short time in connection with a replacement of the filters 1.

The filters are made of wavy fibre glass folded zig-zag in a steel frame and packed and sealed by a mass of silicon. Such filters become more and more efficient. Upon use for a long period, the drop in pressure across the filters becomes too great and the filters must be replaced.

Fig. 2 furthermore illustrates how the air circulates within the oven.

A slight overpressure may optionally exist in the oven.

Fig. 3 is a sectional view of the oven taken 120 along the line X-X of Fig. 1. The objects to be sterilised are situated in the oven chamber 40. The circulator 2 driven by a motor 50 circulates the air, said air being sucked up wards from the oven chamber 40 and into the 125 circulator 2 through a channel in one side of the oven and subsequently further into the other side of the oven and forced through the above filter situated in the left side of the oven in Fig. 1. From this filter, the filtered air 130 again enters the oven chamber 40. Thus the circuit is closed and it is consequently the same air that circulates all the time. Adjacent the circulator 2, a heating surface and a cooling surface are provided, e.g. an electrically heated heating coil and a water-cooled tube coil for adjusting the temperature of the circulating air. Since the circulating air due to the filtration has and must have a very small content of particles, it is essential that the oven is very tight. The oven is as mentioned situated in a partition between an---impureand a--pure-chamber.

Therefore the oven comprises a first door 37 to the impure chamber, whereas a second opposing door 38 may open to the pure chamber. The two doors cannot be opened simultaneously. The doors are sealed by dou ble sealing strips 39.

Fig. 4 illustrates an embodiment of a shaft seal according to the invention. A shaft 20 extends through the oven shell 7. At one end the shaft is connected to the circulator 2 of the oven and at the opposite end to a motor 50 (not shown), which is usually situated immediately opposite thereto. A cooling disc 48 is mounted below the motor, and this disc is provided to ensure the motor against overheating. A circular plate portion 24 pressed outwards and the plate wall 23 of the oven form a sealing chamber 22 about the shaft 20. The plate portion 24 is fixedly screwed onto the oven plate 23. The connection is sealed by a gasket. The shaft 20 is loosely packed with two spring-loaded teflon gaskets 28 sealing between the shaft 20 and the sealing chamber 22, cf. Fig. 3. The two teflon gaskets are made in such a manner that they seal tightly to the shaft. After use for a short period, a minimum leak has, however, occurred, which may cause oozing therein of impurities. The risk of oozing is increased by the circulator usually producing an underpressure at the shaft. In order to avoid impurities penetrating along the shaft, the sealing chamber 22 may be provided with a nozzle 32, through which carefully filtered air is fed by a pressure corresponding to a water column of about 5 mm. The filtered air is then fed from a pump 34 through a filter 42, cf. Fig. 1. All additional components such as pump, filter, driving motor, relays controlling the closing of the doors, measuring equipment controlling the air resistance of the filter and consequently the operational acitivity etc. are as far as possible situated either on top of the oven or at a closed control panel. Such a control panel is situated in Fig. 1 in the left side of the oven since it is essential to keep the oven doors and the oven front smooth in order to facilitate the cleaning.

In the illustrated embodiment the sealing chamber is situated on the outside of the oven shell, but it is within the scope of the invention to situate the chamber in the oven shell 3 or immediately inside said shell.

In the embodiment illustrated, the spring is a compression spring shaped as a cone.

The spring may also be formed as a spiral spring. According to a second embodiment the spring-loaded gaskets may be situated outside the sealing chamber and be retracted towards the walls of the sealing chamber by a tension spring. According to an additional embodiment, the influence of the spring may be provided by two compression springs situ ated outside the sealing chamber. According to a fourth embodiment, the gaskets may be situated inside the sealing chamber and be pulled out towards the walls of the sealing chamber by means of tension springs.

The above should be acceptable to class corresponding to less than 100 particles per cubic foot.

Claims (10)

1. A shaft seal about a rotating shaft, e.g.

the rotating shaft of a circulator, which ex tends through an opening in a plate wall such as the shell of an oven separating an impure and a pure chamber, e.g. a non-sterile cham ber (a working chamber) and a sterile cham ber (sterilising oven), said chambers contain ing their respective qualities of one and the same medium such as atmospberic air, 95 whereby at least one quality (the sterile qual ity) must not be mixed with the other quality, characterised by the shaft being loosely re ceived by a circumferential slip in two spring loaded and displaceable gaskets co-operating with the walls of a sealing chamber about the extension of the shaft through the plate wall, said sealing chamber communicating with a means such as a filter for treating the medium in question, whereby the means in turn is connected to the delivery side of a pump, which on the suction side ends outside the pure chamber, preferably in the impure cham ber.

2. A shaft seal as claimed in claim 1, characterised by the sealing chamber being defined by the plate wall of the oven shell as well as by a preferably circular plate portion pressed outwards and situated at a distance from and parallel to the plate wall, said circular plate portion continuing into a short, circular-cylindrical surface substantially perpendicular thereto and in turn continuing into a surface extending radially from the cylindrical surface parallel to the plate wall and being hermetically secured thereto.

3. A shaft seal as claimed in claim 1 or 2, characterised by the springloaded gaskets abutting their respective walls in the sealing chamber and being mutually spaced by means of an intermediary compression spring, e.g. a spiral spring or a conical spiral spring.

4. A shaft seal as claimed in the preceding claims 1 to 3, whereby the various qualities of the medium in question are common atmo- GB2158893A 3 spheric air and filtered, sterilised air, respectively, having a predetermined maximum content of impurity particles, characterised by the pump feeding purified filtered air to the seal- ing chamber at a pressure corresponding to a water column of about

5 mm. 5. A shaft seal substantially as described above and with reference to the accompanying drawing. 75

6. An airtight oven comprising at least two doors separating two chambers, and furthermore comprising a filter arrangement, through which the air within the oven is circulated in a closed circuit by means of a circulator, said closed circuit optionally including means for adjusting the temperature of the circulating air, characterised by the filter arrangement comprising a frame loosely secured to a resilient trumpet- or tube-like airtight suspension arrangement in turn secured to the rim of a channel permitting passage of the circulating air, whereby the major portion of said rim may be formed by the oven shell.

7. An oven as claimed in claim 6, charac- terised by the trumpet-like suspension arrangement being secured to the parts of the oven shell during the assembling thereof, preferably through welding.

8. An oven as claimed in claim 6, characterised by the supporting frame with the filters resting on one or more rails by means of wheels and being displaceable along said rails upon release from the trumpet-like suspension arrangement.

9. An oven as claimed in claim 8, characterised by the rails extending through the entire oven and being placed above the doors of the oven.

10. An oven substantially as described above and with reference to the accompanying drawing.

Printed in the United Kingdom for Her Majesty's Stationery Office, Dd 8818935, 1985. 4235. Published at The Patent Office. 25 Southampton Buildings, London, WC2A lAY, from which copies may be obtained.