WO2007085869A1

WO2007085869A1 - Freeze dryer shelf

Info

Publication number: WO2007085869A1
Application number: PCT/GB2007/050022
Authority: WO
Inventors: Ivan Haynes Lanaway
Original assignee: BOC Group Ltd; IMA Life SRL
Current assignee: BOC Group Ltd; IMA Life SRL
Priority date: 2006-01-27
Filing date: 2007-01-17
Publication date: 2007-08-02
Anticipated expiration: 2008-07-27
Also published as: GB0601680D0; GB2434633A

Abstract

A freeze dryer shelf has opposed, parallel first and second plates (12, 14) 5 spaced apart from one another by a corrugated sheet (16) attached to the plates and defining at least one flow channel (18) for conveying a diathermic fluid between the plates.

Description

FREEZE DRYER SHELF

The present invention relates to a freeze dryer shelf and to a method of assembling a freeze dryer shelf.

Freeze dryer shelves are located within a freeze drying chamber of a freeze dryer for receiving a plurality of containers or vials containing the product to be freeze dried. The chamber usually includes a number of shelves, each of which can be raised and lowered within the chamber. To load the shelves, the shelves are initially collapsed in the lower portion of the chamber, and the uppermost shelf is first moved into a loading position. After that shelf has been loaded, the mechanism automatically raises the loaded shelf to enable the next shelf to be moved to the loading position. This moving sequence continues until the chamber loading has been completed. To unload the chamber, the loading sequence is reversed, with the lowermost shelf being unloaded first.

The shelves also serve to transfer heat between a diathermic fluid such as alcohol, glycol, or silicone oil, and the products to be freeze-dried. During the freeze drying process, moisture present within the products is frozen. An external refrigeration circuit cools diathermic fluid circulating within the freeze dryer shelves in order to cause heat to be transferred from the products to the diathermic fluid and thereby cause the freezing of the moisture contained within the products. After freezing, the chamber is evacuated to a pressure typically below 1 mbar, and the diathermic fluid is heated by an external heater to cause the ice within the samples to sublimate into water vapour.

The shelves of a freeze dryer are also commonly used to press stoppers into the containers. During the freeze drying process, the stoppers are loosely located on the mouths of the containers to enable the water vapour to sublimate from the samples. Upon completion of the freeze drying process, the shelves are moved relative to each other so that the upper surfaces of the stoppers of the containers located on one shelf contact the lower surface of the next shelf up. Continued relative movement of the shelves depresses the stoppers into the containers to form air-tight seals.

Freeze dryer shelves are typically formed by two opposed stainless steel plates having stainless steel ribs located between the plates in order to form both a space, typically between 10 and 20 mm in height, between the plates and flow channels for the diathermic fluid. The ribs serve to provide the necessary strength for the shelf to support its own weight and the weight of the containers placed thereupon. In addition, the ribs must enable the shelf to withstand the forces placed upon the plates during the depression of the stoppers, which can be up to 1 .5 kg/cm². The four edges of the plates are capped with solid bars continuously welded to the top and bottom plates.

A vacuum brazing technique used to assemble such a freeze dryer shelf is described in US patent 5,519,946. In this method, a nickel brazing substance is sandwiched between the bottom plate and the ribs (preferably in the form of hollow rectangular tubes), and between the tubes and the top plate. The sub- assembly is placed inside a vacuum induction furnace, which is ramped up to the melting point of nickel and the crystallisation temperature of stainless steel. The temperature is stabilised to stress relieve the sub-assembly, and then the furnace is gradually cooled to around 200O. The sub-assembly is then quenched with inert gas and allowed to cool to room temperature. Solid bars are then welded to the plates to cap the edges of the plates.

A freeze dryer shelf manufactured using this method typically comprises at least forty individual stainless steel tubes which need to be correctly positioned between the plates prior to the vacuum brazing to create a serpentine flow channel for the diathermic fluid flowing between the plates. The location of the tubes needs to be robust enough to prevent their movement during the vacuum brazing process, and must allow for some differential expansion between the tubes and the plates during the vacuum brazing process. Therefore, a jig is commonly used to assist the correct location of the tubes relative to the plates. Due to the number of tubes that are typically used in the assembly of the shelf, the location of the tubes can nonetheless be a time consuming process.

Furthermore, as the shelves require a high level of flatness to aid heat transfer, reliable stoppering and interfacing with automatic loading equipment, the rectangular tubes must be manufactured with high degrees of flatness and straightness. Stainless steel rectangular tubes having such qualities tend to be expensive, and not readily available in the market place.

It is an aim of at least the preferred embodiment of the invention to seek to solve these and other problems.

In a first aspect, the present invention provides a freeze dryer shelf having opposed, parallel first and second plates spaced apart from one another by a corrugated sheet attached to the plates and defining at least one flow channel for conveying a diathermic fluid between the plates.

By replacing the rectangular tubes with a corrugated sheet to perform the dual functions of spacing the first and second plates and defining one or more flow channels for conveying the heat transfer, or diathermic, fluid through the shelf, the time taken to assemble the shelf can be significantly decreased. For example, one corrugated sheet may replace at least four of the ribs, preferably at least six of the ribs, and more preferably all of the ribs, of the earlier design. The use of a corrugated sheet can increase the stability of the shelf prior to the attachment of the plates to the sheet, and can reduce the tolerances of the flatness and straightness of the ribs. Standard, readily available stainless steel sheet material may be used to form the corrugated sheet, further reducing costs and potentially also the overall weight of the shelf. - A -

The sheet preferably comprises a plurality of sidewalls between the peaks and troughs of the sheet and forming a series of parallel flow channels between the plates. One of the first and second plates is attached to the peaks of the corrugated sheet, and the other plates is attached to the troughs of the corrugated sheet. The peaks and troughs are preferably provided by flat surfaces, and so the corrugated sheet preferably has one of a rectangular or a square profile. Alternatively, the sheet may have a triangular or other profile which presents flat surfaces for attachment to the plates.

The corrugated sheet may be shaped so that the end sidewalls of the sheet provide end walls for the shelf, reducing the number of edge bars required to complete the shelf assembly. Alternatively, each plate may have a sidewall provided on each of the four sides thereof, thereby completely eliminating the requirement to attach end plates or bars to the shelf to seal the shelf.

In one embodiment, at least some of the sidewalls each comprise an aperture for conveying diathermic fluid between adjacent flow channels. The diathermic fluid may then flow along a serpentine flow path between the plates of the shelf. The apertures may be formed in the corrugated sheet either before or after the attachment of the plates to the sheet. For example, notches may be formed in alternate ends of adjacent sidewalls to permit the diathermic fluid to flow along the serpentine path. If required, first and second end plates may then be secured to opposing ends of the first and second plates to peripherally seal the shelf.

In another embodiment, the end plates comprise means for conveying diathermic fluid between adjacent flow channels. For example, each end plate may comprise a series of channels each for conveying fluid between adjacent flow channels. The channels may be formed in the end plates by machining, or by securing spaced flow restrictors to the end plate. Fluid inlet and outlet ports are preferably located in the end plates for introducing and discharging diathermic fluid to and from the shelf. If no end plates are required, the fluid inlet and outlet ports may be located in the sidewalls of the first and second plates.

The shelf may comprise means integral with at least one of the plates for locating the sheet between the plates. The locating means are preferably located at opposing sides of the shelf for retaining the sheet therebetween. The locating means are preferably integral with one of the first and second plates, and preferably comprise sidewalls at opposing sides of said one of the first and second plates. The presence of the locating means can simply assembly of the shelf prior to the attachment process.

Each plate may comprise means for locating that plate relative to the other plate. For example, each plate may comprise sidewalls at opposing sides thereof, each sidewall of one plate being located adjacent a sidewall of the other plate. To facilitate assembly, the sidewalls of one plate are preferably external to the sidewalls of the other plate. Each plate may be bent to define the sidewalls. With this configuration of the plates, again the number of end bars can either be reduced to two, or, where each plate has four sidewalls, the end bars can be completely eliminated.

Each corrugation of the corrugated sheet preferably has a width in the range from 10 to 25 mm, and preferably has a height in the range from 10 to 15 mm. The corrugated sheet preferably has a thickness in the range from 0.5 to 1 .5 mm.

Whilst it is preferable to locate just a single sheet between the plates, depending on the size of the first and second plates the shelf may comprise a plurality of said corrugated sheets, arranged side by side or lengthways. The plates may be attached to the sheet using an adhesive, or by brazing, preferably by vacuum brazing.

In a second aspect the present invention provides a method of assembling a freeze dryer shelf having opposed, parallel first and second plates spaced apart from one another, the method comprising the steps of locating a corrugated sheet between the plates to define at least one flow channel for conveying a diathermic fluid between the plates, and attaching the corrugated sheet to the plates.

Features described above in relation to the first aspect of the invention are equally applicable to the second aspect of the invention, and vice versa.

Preferred features of the present invention will now be described with reference to the accompanying drawings, in which:

Figure 1 is a perspective view of part of a freeze dryer shelf according to the present invention;

Figure 2 is a cross-sectional view of a first embodiment of a freeze dryer shelf, illustrating the flow path for diathermic fluid;

Figure 3 is a cross-sectional view of a second embodiment of a freeze dryer shelf, illustrating the flow path for diathermic fluid;

Figure 4 is a plan view of the sheet of the shelf of Figure 3 prior to corrugation;

Figure 5 is a cross-sectional view of a third embodiment of a freeze dryer shelf, illustrating the flow path for diathermic fluid; Figure 6 is a plan view of the sheet of the shelf of Figure 5 prior to corrugation; and

Figure 7 is perspective view of part of another freeze dryer shelf according to the present invention.

With reference first to Figure 1 , a freeze dryer shelf 10 comprises a pair of first and second plates 12, 14. Both plates are flat, parallel and spaced apart from one another by a corrugated sheet 16 located within the space formed between first and second plates 12, 14. The first and second plates 12, 14, and the corrugated sheet 16 are preferably formed from stainless steel. The corrugated sheet 16 defines at least one flow channel 18 for diathermic fluid conveyed between the first and second plates 12, 14.

The corrugated sheet 16 is preferably folded to form a plurality of corrugations comprising peaks 22, troughs 24 and sidewalls 26 extending between the peaks 22 and troughs 24 of the sheet 16. The corrugations of the sheet 16 preferably have either a substantially rectangular, or a substantially square profile, so that the peaks 22 and troughs 24 of the sheet 16 provide elongated flat surfaces for attachment to the first and second plates 12, 14 respectively . With such a profile, the sheet 16 defines a plurality of substantially parallel flow channels 18 between the first and second plates 12, 14. As illustrated in Figure 1 , the extreme sidewalls 26a, 26b of the sheet 16 can provide side walls of the shelf 10.

Each corrugation of the sheet 16 preferably has a width in the range from 10 to 25 mm, and a height in the range from 10 to 15 mm. In one preferred configuration, the sheet 16 has a length of 200 mm. Depending on the sizes of the first and second plates 12, 14, a plurality of sheets 16 may be arranged side by side, and/or end to end, so that the sheets 16 fill the space formed between the first and second plates 12, 14. The sheets may comprise the same number of corrugations, or a different number of corrugations, in order to fill the space between the first and second plates 12, 14. For example, sheets having between four and eight peaks 22, or troughs 24, may be provided. The sheets may have the same number of peaks 22 and troughs 24, or different numbers of peaks 22 and troughs 24. The, or each, sheet 16 preferably has a thickness in the range from 0.5 to 1 .5 mm.

With reference to Figure 2, which illustrates a first embodiment of a freeze dryer shelf 10 including a corrugated sheet 16, first and second end plates 30, 32 are secured to opposing ends of the first and second plates 12, 14 to peripherally seal the shelf 10. The end plates 30, 32 are preferably provided by bars or rods each having a substantially square or rectangular transverse cross-section. A fluid inlet 34 and a fluid outlet 36 are formed in the end plates 30, 32 to permit diathermic fluid to flow into, and to be subsequently discharged from, the shelf 10. In use, the fluid inlet 34 and fluid outlet 36 are connected to hoses which are, in turn, connected to an external circuit for the diathermic fluid which conventionally includes a pump to circulate the diathermic fluid, a refrigerant circuit for cooling the diathermic fluid during the freezing phase of the freeze drying process, and an electrical heater for heating the diathermic fluid during the sublimation phase of the freeze drying process.

In this first embodiment, the end plates 30, 32 are shaped or otherwise configured to convey diathermic fluid between adjacent flow channels 18 to define a serpentine flow path within the shelf. For example, as illustrated the end plates 30, 32 may be machined to define a series of channels 38 spanning adjacent fluid channels 18 to transfer fluid from one fluid channel 18 to another, and thereby define a serpentine flow path for fluid through the shelf 10. The channels 38 in the end plates 30, 32 may be alternatively defined by any other suitable technique, for example by attaching a series of flow restrictors 40 to the end plates 30, 32. Support blocks may be provided on the outer periphery of the shelf 10 for receiving support rods for connecting the shelf 10 to other shelves within a chamber of a freeze dryer.

All of the aforementioned components of the freeze dryer shelf 10 are preferably fabricated from stainless steel. The plates 12, 14 may be attached to the sheet 16 using an adhesive, or by brazing, preferably vacuum brazing. In order to assemble the shelf 10 using a brazing process, a nickel or copper- based powder on a self-adhesive backing or brazing tape is sandwiched between first plate 12 and the peaks 22 of the, or each, corrugated sheet 16, and between the second plate and the troughs 24 of the, or each, corrugated sheet 16. The assemblage is sandwiched between graphite blocks or any heat conductive material and placed within a vacuum induction furnace. The assemblage is heated in the furnace at a temperature that ramps from room temperature to within approximately 10°C of the melting of nickel, approximately 482O. The temperature is then stabilized and then again ramped up to the melting point of nickel and the crystallization temperature of the stainless steel. This temperature is stabilized for between 15 and 20 minutes in order to stress relieve the assemblage of components. Thereafter, the furnace is cooled down for about 12 hours to 204 °C, at which point the entire assemblage is quenched with an inert gas, such as nitrogen. Thereafter, the assemblage is allowed to cool to room temperature. The end plates 30, 32 are then welded to the plates 12, 14, and preferably ground, smoothed, and polished.

Figures 3 to 6 illustrate second and third embodiments of a freeze dryer shelf 10, in which notches or apertures 50, 60 are formed in the side walls 26 of the sheet 16 prior to corrugation to permit fluid to pass from one of the fluid channels 18 to a downstream adjacent fluid channel 18. Alternatively, in the third embodiment illustrated in Figures 5 and 6, the notches 60 may be readily formed in the sheet 16 following corrugation, or following the attachment of the first and second plates 12, 14 to the sheet 16. Figure 7 illustrates a modification to the freeze dryer 10 illustrated in Figure 1 , in which each of the first and second plates 12, 14 comprises sidewalls 70, 72 respectively located on opposing sides of the plates. The sidewalls 70 are integral with the first plate 12, and the sidewalls 72 are integral with the second plate 14. The sidewalls are preferably formed by bending each of the plates 12, 14 so that the sidewalls extending substantially orthogonal to the plates 12, 14. As illustrated in Figure 7, one of the first and second plates 70, 72 is slightly larger than the other so that each sidewall of one of the plates is located adjacent a sidewall of the other plate. The sidewalls 70, 72 serve to locate the plates 12, 14 relative to each other prior to the brazing process, and to provide two side walls for the shelf 10. The sidewalls 72 of the second plate 14 also serve to locate the corrugated sheet 16 between the first and second plates 12, 14, with the sides of the sheet 16 abutting the inner surfaces of the sidewalls 72. The sidewalls 70, 72 may be attached together using an adhesive or by brazing.

Any of the features of the shelves illustrated in Figures 2 to 6 may be provided with the shelf illustrated in Figure 7. Furthermore, as well as having sidewalls 70, 72 located on the sides of the first and second plates 10, 12, each plate 12, 14 may also have additional sidewalls, having a similar shape and size to the sidewalls 70, 72, located on the ends thereof. Fluid inlet and outlet ports may be located in these additional sidewalls to convey diathermic fluid into, and away from, the shelf 10. Consequently, no separate end plates or bars may be required to peripherally seal the shelf 10.

Claims

1. A freeze dryer shelf having opposed, parallel first and second plates spaced apart from one another by a corrugated sheet attached to the plates and defining at least one flow channel for conveying a diathermic fluid between the plates.

2. A shelf according to Claim 1 , wherein the sheet comprises a plurality of sidewalls between the peaks and troughs of the sheet and forming a series of parallel flow channels between the plates.

3. A shelf according to Claim 2, wherein at least some of the sidewalls each comprise an aperture for conveying diathermic fluid between adjacent flow channels.

4. A shelf according to Claim 3, wherein the aperture comprises a notch formed in the end of the sidewalk

5. A shelf according to Claim 3 or Claim 4, comprising first and second end plates secured to opposing ends of the first and second plates to peripherally seal the shelf.

6. A shelf according to Claim 2, comprising first and second end plates secured to opposing ends of the first and second plates to peripherally seal the shelf, the end plates comprising means for conveying diathermic fluid between adjacent flow channels.

7. A shelf according to Claim 6, wherein each end plate comprises a series of channels each for conveying fluid between adjacent flow channels.

8. A shelf according to any of Claims 5 to 7, wherein fluid inlet and outlet ports are located in the end plates for introducing and discharging diathermic fluid to and from the shelf.

9. A shelf according to any preceding claim, comprising means integral with at least one of the plates for locating the sheet between the plates.

10. A shelf according to Claim 9, wherein said locating means are located at opposing sides of the shelf for retaining the sheet therebetween.

1 1 . A shelf according to Claim 10, wherein the locating means are integral with one of the first and second plates.

12. A shelf according to Claim 1 1 , wherein the locating means comprise sidewalls at opposing sides of said one of the first and second plates.

13. A shelf according to any preceding claim, wherein each plate comprises means for locating that plate relative to the other plate.

14. A shelf according to Claim 13, wherein each plate comprises sidewalls at opposing sides thereof, each sidewall of one plate being located adjacent a sidewall of the other plate.

15. A shelf according to Claim 14, wherein the sidewalls of one plate are external to the sidewalls of the other plate.

16. A shelf according to any of Claims 12, 14 and 15, wherein each plate is bent to define the sidewalls.

17. A shelf according to any of Claims 12 and 14 to 16, wherein each plate comprises at least two of said sidewalls.

18. A shelf according to any of Claims 12 and 14 to 17, wherein each plate comprises four of said sidewalls.

19. A shelf according to any preceding claim, wherein the corrugations of the corrugated sheet have a substantially rectangular profile.

20. A shelf according to any preceding claim, wherein the corrugations of the corrugated sheet have a substantially square profile.

21 . A shelf according to any preceding claim, wherein each corrugation of the corrugated sheet has a width in the range from 10 to 25 mm.

22. A shelf according to any preceding claim, wherein each corrugation of the corrugated sheet has a height in the range from 10 to 15 mm.

23. A shelf according to any preceding claim, wherein the corrugated sheet has a thickness in the range from 0.5 to 1 .5 mm.

24. A shelf according to any preceding claim, wherein the corrugated sheet is formed from stainless steel.

25. A shelf according to any preceding claim, comprising a plurality of said corrugated sheets.

26. A shelf according to any preceding claim, wherein said at least one flow channel defines, at least in part, a serpentine flow path for the diathermic fluid.

27. A shelf according to any preceding claim, wherein the plates are attached to the sheet using an adhesive or are brazed to the sheet.

28. A method of assembling a freeze dryer shelf having opposed, parallel first and second plates spaced apart from one another, the method comprising the steps of locating a corrugated sheet between the plates to define at least one flow channel for conveying a diathermic fluid between the plates, and attaching the corrugated sheet to the plates.

29. A method according to Claim 28, wherein the sheet comprises a plurality of sidewalls between the peaks and troughs of the sheet and forming a series of parallel flow channels between the plates.

30. A method according to Claim 29, wherein at least some of the sidewalls each comprise an aperture for conveying diathermic fluid between adjacent flow channels.

31 . A method according to Claim 30, wherein the apertures are formed in the corrugated sheet prior to the attachment of the corrugated sheet to the plates.

32. A method according to Claim 30, wherein the apertures are formed in the corrugated sheet following the attachment of the corrugated sheet to the plates.

33. A method according to any of Claims 30 to 32, wherein the aperture comprises a notch formed in the end of the sidewalk

34. A method according to any of Claims 30 to 33, wherein first and second end plates are secured to the first and second plates to peripherally seal the shelf.

35. A method according to Claim 29, wherein first and second end plates are secured to the first and second plates to peripherally seal the shelf, the end plates comprising means for conveying diathermic fluid between adjacent flow channels.

36. A method according to Claim 35, wherein each end plate comprises a series of channels each for conveying fluid between adjacent flow channels.

37. A method according to any of Claims 34 to 36, wherein fluid inlet and outlet ports are located in the end plates for introducing and discharging diathermic fluid to and from the shelf.

38. A method according to any of Claims 28 to 37, wherein the sheet is located between the plates by means integral with at least one of the plate.

39. A method according to any of Claims 28 to 38, wherein the first plate is located relative to the second plate by means integral with at least one of the plate.

40. A method according to any of Claims 28 to 39, wherein the corrugations of the corrugated sheet have a substantially rectangular profile.

41 . A method according to any of Claims 28 to 39, wherein the corrugations of the corrugated sheet have a substantially square profile.

42. A method according to any of Claims 28 to 41 , wherein a plurality of said corrugated sheets are located between and attached to the corrugated sheet.

43. A method according to any of Claims 28 to 42, wherein the plates are attached to the sheet using an adhesive or using a vacuum brazing technique.

44. A method according to any of Claims 28 to 43, wherein said at least one flow channel defines, at least in part, a serpentine flow path for the diathermic fluid.