Shelf for a vacuum-drying cabinet

A removable shelf for a vacuum-drying cabinet is machanically expandable so that it comes into thermal contact under pressure over a large area with the heated walls of the cabinet interior. The shelf can be inserted into a supporting framework which can be freely positioned in the cabinet interior and can be removed for cleaning. A baffle plate on the supporting framework protects the material to be dried from strong air currents when the cabinet interior is evacuated.

The present invention relates to a shelf for a cabinet and particularly but 
not exclusively to removable shelves for vacuum-drying cabinets. 
Vacuum-drying cabinets are used for the rapid and efficient drying of 
temperature-sensitive substances, powders, porous material, small parts, 
etc. The material to be dried is disposed on removable shelves in the 
vacuum-drying cabinet. The shelves are removably inserted in the interior 
of the vacuum-drying cabinet so that on the one hand the material to be 
dried can easily be introduced into the cabinet and on the other hand the 
shelves can be removed for cleaning. The drying of the material in the 
vacuum-drying cabinet is performed by evacuating the cabinet interior and 
then heating the material. The heating of the material is nearly always 
effected by thermal conduction. Heating by convection does not occur in 
practice, as the cabinet interior is evacuated at a pressure of up to 
10.sup.-2 mbar (hPa). In practice the material is not heated by radiation 
either, as no substantial radiation occurs in the temperature range used 
of up to a maximum of 200.degree. to 300.degree. C. 
Essentially two possible techniques for heating the material carried by the 
shelf by thermal conduction are known, i.e. shell heating and plate 
heating. 
In shell heating, the walls of the interior of the vacuum-drying cabinet 
are heated. The heat is conducted from these walls via the shelves to the 
material to be dried. In this case the shelves lie loosely on support 
devices, such as, for example, bearing rails or bearing bars, which are 
mounted on the walls of the cabinet interior. As the shelves only lie 
loosely on the support devices, a relatively poor thermal contact is 
produced between the heated walls and the shelf, so that the material is 
only heated slowly. The support devices mounted on the walls obstruct the 
cleaning of the cabinet interior when the shelves have been removed. 
In plate heating, the shelves are themselves electrically heated. As a 
result the material positioned on the shelves can be quickly and 
efficiently heated. However the heatable shelves are considerably more 
expensive to manufacture. It is more difficult to remove the shelves 
because of the electrical connections required. The contacts for the 
electrical heating of the shelves, which are located in the cabinet 
interior, constitute an explosion hazard, e.g. if small parts cleaned with 
easily flammable solvents are dried. Finally, thorough cleaning of the 
cabinet interior is impeded by the support devices for the shelves. 
According to one aspect of the present invention, there is provided a shelf 
suitable for removable insertion into a vacuum-drying cabinet having 
heatable walls, which shelf can be mechanically expanded in at least one 
dimension so that in the expanded state it maintains heat-conducting 
contact with the heated walls of the cabinet interior. 
Preferably, the shelf is maintained in contact with the heated walls under 
pressure. 
According to another aspect of the present invention, there is provided a 
cabinet having at least one shelf in accordance with the present 
invention, including a plurality of supports for removably supporting the 
at least one shelf, the supports being arranged on a removable supporting 
frame which can be freely positioned in the interior of the cabinet. 
For insertion into the cabinet interior and removal from the cabinet 
interior the shelf may be compressed contrary to the expansion direction, 
so that it has sufficient clearance with respect to the walls of the 
cabinet interior. When the shelf is located in the cabinet interior, it 
may be expanded and come into contact with the walls of the cabinet 
interior under pressure. As a result there is good thermal contact between 
the heated walls and the shelf, so that the heat of the heated walls can 
quickly be transmitted to the shelf in order to heat the material to be 
dried. 
The expansion of the shelf can take place in various ways, provided that 
the shelf comes into contact with the walls of the cabinet interior by 
this expansion. It is possible to provide grooves for the introduction of 
the shelf in the vertical side walls and to construct the edge of the 
shelf to be guided in these grooves so that it can be expanded in the 
vertical direction, so that it abuts the upper and lower edge of the 
grooves under pressure. It is also possible to make the shelf expandable 
in the direction of insertion, so that in the expanded state it abuts the 
vertical rear wall and the door of the cabinet interior. However a lateral 
expansion of the shelf is advantageous. As a result the shelf can abut the 
vertical side walls of the cabinet interior. 
In order to obtain the best possible: thermal contact between the walls of 
the cabinet interior and the shelf, the contact between the shelf and the 
walls of the cabinet interior may be constructed with the largest possible 
surface area. For this purpose the shelf expediently has an edge having a 
large surface area parallel to the walls of the cabinet interior, with 
which it abuts the walls. In the design in which the shelf expands 
laterally, this edge may be a marginal strip bent by 90.degree. at the 
longitudinal edges of the shelf. 
The expansion of the shelf is preferably performed by spring action. This 
has the advantage on the one hand of ensuring that the shelf fully abuts 
the walls of the cabinet interior with a large surface area independently 
of manufacturing tolerances. On the other hand, the shelf abutting the 
walls of the cabinet interior under spring action may also follow 
deformations in the walls, which occur when the walls are heated and in 
particular when the cabinet interior is evacuated. 
If the shelf is expandable by spring action, a possibility is expediently 
provided of locking the shelf in its contracted state, so that it can be 
easily inserted into the cabinet interior and can be removed therefrom. 
The locking can be effected by a catch, by cams, by a jointed link 
mechanism or similar devices. 
The shelves can be produced at an advantageous cost. The production costs 
are only slightly higher than the production costs of conventional shelves 
of shell-heated vacuum-drying cabinets and are substantially lower than 
the production costs of shelves in plate-heated vacuum-drying cabinets. As 
the shelves are not directly heated, no electrical connections are 
provided in the cabinet interior, so that the vacuum-drying cabinet is 
explosion-proof. The thermal conduction between the heated walls of the 
cabinet interior and the shelves of conventional shell-heated 
vacuum-drying cabinets are considerably improved, so that rapid heating of 
the material to be dried and thus clearly shorter process times can be 
achieved. The good thermal contact with the heated walls also improves the 
accuracy with which the temperature of the material to be dried can be 
observed. 
As the thermal contact between the shelves and the heated walls of the 
cabinet interior is effected by the expansion of the shelf, thermal 
contact between the walls of the cabinet interior and the shelf via the 
supporting devices is no longer necessary. Therefore the supporting 
devices no longer have to be mounted on the walls of the cabinet interior. 
As a result the support devices can be constructed on a supporting 
framework which is freely inserted into the cabinet interior and can be 
removed from the cabinet interior for cleaning. The cabinet interior can 
therefore be constructed with completely flat-surfaced walls, whereby 
thorough cleaning of the cabinet interior is facilitated. 
In an advantageous embodiment the supporting framework may in addition be 
provided with a baffle plate, which is disposed between the opening of the 
vacuum connection and the material to be dried positioned on the shelves. 
The baffle plate protects the material to be dried from a direct suction 
effect and air movement during suction, so that swirling of the material 
is avoided even with a dusty or powdery material.

FIG. 1 shows the interior of the vacuum-drying cabinet. The cabinet 
interior is formed by a pressure-resistant, cuboid housing made from thin 
steel plate with side walls 10, a rear wall 12, a ceiling 14 and a floor 
16. The housing is surrounded by an outer housing (not shown), so that an 
air jacket is formed, in which heating elements, which heat the walls 
10,12,14,16 of the cabinet interior, are disposed. The open front side of 
the cabinet interior is sealed in vacuum-tight manner by a door, which is 
not shown. A vacuum connection 18, via which the cabinet interior can be 
evacuated and through which dry air or an inert gas can also be supplied 
if necessary, opens through the ceiling 14 into the cabinet interior. The 
walls of the cabinet interior formed by the side walls 10, the rear wall 
12, the ceiling 14 and the floor 16 are completely smooth and have no 
projections or depressions, so that it is possible to clean the cabinet 
interior simply and thoroughly. 
A supporting framework 20 is freely inserted into the cabinet interior. The 
supporting framework 20 comprises a front frame 22 and a rear frame 24. 
Frames 22 and 24 have an open rectangular cross-section, the width of 
which is almost equal to the width of the cabinet interior, while the 
height of the frames 22 and 24 is somewhat less than the height of the 
cabinet interior. Frames 22 and 24 are manufactured from circumferential 
flat strip steel. A baffle plate 26 made from steel plate is attached on 
top of the frames 22 and 24 by spot welding. A corresponding plate 54 made 
from steel plate is mounted on the bottom of the frames 22 and 24 to 
stabilise the supporting framework 20. The baffle plate 26 and the plate 
54 connect the front frame 22 with the rear frame 24 and keep these frames 
at such a distance part that when the framework 20 is inserted the rear 
frame 24 is disposed directly in front of the rear wall 12 and the front 
frame 22 is disposed at the open front side of the cabinet interior. The 
width of the baffle plate 26 is chosen so that on both sides it maintains 
a spacing from the side walls 10. The baffle plate 26 thus protects the 
cabinet interior and in particular the space inside the supporting 
framework 20 from the vacuum connection opening in the centre into the 
ceiling 14. However the vertical distance of the baffle plate 26 from the 
ceiling wall 14 and the lateral distance of the baffle plate 26 from the 
side walls 10 guarantees a sufficient passage area for the suction of air 
out of the cabinet interior through the vacuum connection 18. 
Bearing rails 28, which are equidistantly and inwardly directed, are welded 
to the vertical posts of frames 22 and 24. The bearing rails 28 form a 
support for a shelf 30, as is represented in FIGS. 2 to 5. 
Each shelf 30 consists of an upper support plate 32 and a backing plate 34, 
which abuts the lower surface of said upper plate and has its surface 
parallel thereto. The support plate 32 and the backing plate 34 are made 
from a sheet of a metal which is a good conductor of heat. The surface 
dimensions of the support plate 32 are chosen so that it substantially 
fills the entire interior of the supporting framework 20. The upper 
support plate 32 supports the material to be heated. 
When the shelf 30 is inserted into the supporting framework 20, one 
longitudinal edge of the support plate 32 extending in the direction of 
insertion (in FIGS. 2 to 4 this is the right longitudinal edge) engages 
between the vertical post of the frames 22 and 24 and laterally beyond 
them and is bent downwardly at right angles as a marginal strip 36 having 
a large area. The support plate 32 lies with an inwardly bent edge 56 with 
lateral clearance on the bearing rails 28 and can be displaced in the 
transverse direction until the marginal strip 36 comes to abut the lateral 
wall 10 of the cabinet interior with its entire area. 
The backing plate 34 is displaceably guided in the transverse direction on 
the under side of the support plate 32. For this purpose dowel pins 38, 
which engage in slots 40 in the backing plate 34 extending in the 
transverse direction, are attached to the under side of the support plate 
32. The length of the slots 40 determines the travel of the reciprocal 
transverse movement of support plate 32 and backing plate 34. At both its 
longitudinal edges extending in the direction of insertion, the backing 
plate 34 is bent downwardly at right angles in the form of marginal strips 
42 and 44 respectively. The backing plate 34 protrudes with one marginal 
strip 42 (in FIGS. 2 to 4 the left edge-strip) past the corresponding 
longitudinal edge of the support plate 32, whereby the travel determined 
by the dowel pins 38 and the slots 40 determines the amount by which the 
backing plate 34 with the marginal strip 42 protrudes past the 
longitudinal edge of the support plate 32. The region of the backing plate 
34 which protrudes past the support plate 32 has dimensions in the 
direction of insertion such that the backing plate 34 which the downwardly 
bent marginal strip 42 can engage in the transverse direction between the 
frames 22 and 24 of the supporting framework. The marginal strip 42 lies 
with one inwardly bent edge 58 on the bearing rails 28. 
In the transverse direction the width of the backing plate 34 is less than 
the width of the support plate 32. As a result the marginal strip 44 of 
the backing plate 34, which is bent downwardly at right angles in FIG. 2 
to 4, is spaced from the marginal strip 36 of the support plate 32. Two 
helical compression springs 46 are inserted between the marginal strips 36 
and 44. The helical compression springs 46 are prestressed so that they 
force apart the support plate 32 and the backing plate 34 into the 
position in which the backing plate 34 maximally protrudes past the 
support plate 32. The expansion length is limited by the dowel pins 38 and 
the slots 40. If the shelf 30 is inserted into the cabinet interior and is 
expanded by the helical compression springs 46, the marginal strip 36 of 
the support plate 32 comes to abut one side wall 10 of the cabinet 
interior and the marginal strip 42 of the backing plate 34 comes to abut 
the opposite side wall 10 with a large area under the pressure of the 
helical compression springs 46. As a result good thermal contact is 
produced between the heated side walls 10 and the shelf 30. 
In order to insert the shelf 30 easily into the cabinet interior and to 
remove it therefrom, the support plate 32 and the backing plate 34 can be 
compressed against the pressure of the helical compression springs 46 and 
be locked in this contracted position. Two jointed links 48 are provided 
for this purpose. One end point of the jointed links 48 is coupled to one 
of the dowel pins 38 and thus to the support plate 32. The other end point 
of the jointed links 48 is coupled to the downwardly bent marginal strip 
44 of the backing plate 34, e.g. to a fixing bolt 50 screwed to this 
marginal strip 44, for the helical compression springs 46. A slide 52 
shared by both jointed links 48, which extends up to the front transverse 
edge of the shelf 30 and consequently is accessible from the open front 
side of the cabinet interior when the shelf 30 is inserted, acts on the 
joints of the jointed links 48. If the jointed links 48 are forced by 
means of the slide 52 into their extended position, the support plate 32 
and the backing plate 34 are pushed together against the force of the 
helical compression springs 34 and locked by the extension of the jointed 
links 48 in this contracted position. During this the slide 52 comes to 
abut a downwardly bent rear stop edge 60 of the backing plate 34. In this 
condition the shelf 30 can easily be, inserted into the support framework 
20 or removed therefrom. If the shelf 30 in the cabinet interior is 
inserted into the support framework 20, the marginal strips 36 and 42 lie 
with their edges 56 and 58 on the bearing rails 28 of the support 
framework 20. The slide 52 is now pulled so that the jointed links 48 
travel from their over-extended locking position into a bent position. The 
helical compression springs 46 can now force apart the support plate 32 
and the backing plate 34 so that the marginal strips 36 and 42 come to 
abut the respective side walls 10 under the pressure of the helical 
compression springs 46. If the shelf 30 is to be removed again, the slide 
52 is pushed in the direction of insertion as far as the stop edge 60 and 
brings the jointed links 48 back into the over-extended position, so that 
the shelf 30 is again locked in its contracted condition. 
In order to guarantee that the support plate 32 and the backing plate 34 
are guided without skewing, four dowel pins 38 and slots 40 are provided. 
Two helical compression springs 46, which are spaced in the direction of 
insertion, and jointed links 48 are also provided. 
It can easily be seen that the compression of the support plate 32 and 
backing plate 34 against the force of the helical compression springs 46 
can instead of by the jointed links 48 also be effected by other 
mechanical means, such as single-arm or two-arm links, cams or similar. 
Thus, embodiments of the present invention provide a cost-advantageous 
design which enables the material to be dried to be heated rapidly and 
efficiently.