Pressure device and seal for filter belt machines

A pressure device for machines for dewatering or filtering of suspensions, sludges or the like or for material to be pressed for the exertion of surface pressure on at least one circulating pressure belt which can be provided for supporting an equally circulating filter belt, which pressure device consists of an essentially completely hollow pressure bladder in the form of a closed frame in particular of essentially quadrangular shape viewed in top view of the pressure belt, which pressure bladder is subjectable to pressure medium and forms a very small, self-adjusting gap on the edge.

The invention relates to a pressure device for machines and to machines 
provided therewith for dewatering or filtering of suspensions, sludges, in 
particular fibrous material or pulp suspensions or the like, or for 
material to be pressed, for exerting pressure on at least one circulating 
pressure belt which can be provided for supporting at least one also 
circulating filter belt, preferably screen belt. 
For the further processing or the disposal of various sludges or fibrous 
suspensions accumulating in industry or community facilities, prior 
dewatering is necessary. It is important in this to obtain high dry matter 
contents, either for further use or the disposal of this material or for 
the subsequent drying of the product. In the latter case, the energy 
required for mechanical pressing is essentially lower than that required 
for thermal drying, so that one aim of dewatering is to obtain the highest 
possible contents of dry matter by mechanical means. 
For dewatering according to the principle of the double screen belt press, 
two values, above all, are determining for the dewatering result, namely, 
the dewatering time and the dewatering pressure, both having to be adapted 
to the material to be dewatered, and moreover, the highest possible values 
for pressing time as well as pressing pressure are aimed at. 
In conventional belt presses, the pressing power is applied to the two 
filter belts either via looped rollers as a result of screen tension or 
socalled press nips, with a linear support of the press belts by means of 
press rollers. There are also supports of the filter belts in the form of 
perforated plates, although sliding friction occurs between these plates 
and the moving screen belts, so that the pressing forces are limited, on 
the one hand, and high frictional forces with corresponding stress and 
abrasion of the screen belts and high driving power requirement result, on 
the other hand. 
Similar problems also result when circulating pressure belts are interposed 
between the screen belts and stationary pressure plates or the like, in 
this case, however, between the pressure belts and the pressure plates or 
the like. 
It is the object of the invention to avoid these disadvantages and to 
provide a pressure device or a machine provided therewith which permits 
the exertion of a continuous pressing power over the entire or a larger 
surface of the press cake at low energy requirement. 
This object is achieved according to the invention in a pressure device of 
the type initially mentioned if at least one, very largely, conveniently 
completely, separate, essentially closed, deformable and essentially 
completely hollow pressure bladder of flexibly elastic material having 
tensile strength in the form of a closed frame conveniently adapted to the 
surface facing it or the surface abutting it of the supporting or pressing 
device and thus abutting this surface, in particular of quadrangular, for 
instance rectangular shape viewed in top view onto the filter belt or 
pressure belt, conveniently with rounded corners, is arranged, a gap, 
advantageously a small gap in relation to the height of the pressure 
bladder, being independently adjustable between pressure bladder and 
pressure belt, at least by admitting pressure medium into the pressure 
space formed by the frame-shaped pressure bladder and the inner space of 
the pressure bladder. The hollow pressure bladder has an essentially 
closed cross section. 
By the arrangement according to the invention, it is achieved that even at 
fluctuating thickness of the material to be pressed, an automatic 
adjustment takes place and the pressing power thus remains unchanged. 
According to an embodiment of the invention, it is provided that the hollow 
pressure bladder is at least partially a component of a wall of an 
essentially completely enclosed pressure space to which pressure medium, 
in particular pressure fluid (liquid) can be admitted and which is 
arranged on one side of the pressure belt, the hollow pressure bladder 
being arranged at a distance from the wall at least on exertion of 
pressure by the admission of pressure medium, thus forming a gap through 
which pressure medium can escape for lubricating. In this embodiment, 
fluid friction without contact of solid parts is obtained between the 
moving belts and the stationary parts, so that friction forces and thus 
wear and driving power are kept very low. The gap formed between the 
hollow pressure bladder and the pressure belt, which gap is very small in 
relation to the thickness of the pressure belt, adjusts itself 
independently on being subjected to pressure by the pressure medium. In 
the inactive position, i.e. when the machine is not in operation, this gap 
optionally need not be present. 
The hollow pressure bladder can consist of flexibly elastic material having 
tensile strength, in particular of fabric-reinforced plastic material or 
rubber. The hollow pressure bladder can also be formed double-walled, for 
instance of an inner skin of compression-proof elastic material and an 
outer skin of material having tensile strength. 
It is convenient if the pressure space adjacent the pressure belt is 
jointly defined on all sides by the pressure belt and the hollow pressure 
bladder which is shaped frame-like for this purpose, with the marginal 
zones of the pressure space being particularly closed against the hollow 
pressure bladder. The hollow pressure bladder is preferably formed 
auto-adjustingly in its marginal zones. 
It is convenient to form the hollow pressure bladder viewed in plan view 
onto the filter belt or pressure belt essentially quadrangular, preferably 
rectangular or square, with the corners preferably being rounded off. 
It is further convenient to fasten the hollow pressure bladder by means of 
at least one frame on a stationary support, this frame also preferably 
being formed essentially quadrangular, for instance rectangular or square. 
The frame can be at least partially hollow. For fastening the hollow 
pressure bladder on the support of the machine, it is convenient to clamp 
the hollow pressure bladder between two frames. For maintaining a constant 
pressure or for compensating pressure, it is convenient if the pressure 
space adjacent the pressure belt and the pressure space in the interior of 
the hollow pressure bladder are connected to one another by means of at 
least one opening. 
In order to be able to adjust different pressures in the pressure space and 
in the interior of the hollow pressure bladder, it is convenient to close 
the pressure space adjacent the pressure belt and the pressure space in 
the interior of the hollow pressure bladder against each other and make 
them suitable for the admission of pressure medium, optionally of 
different pressures, through separate inlets or bores. 
In order to prevent friction between the hollow pressure bladder and the 
pressure belt in the event of breakdown, for instance at failure of supply 
with pressure medium, it is convenient to provide the hollow pressure 
bladder in the gap between it and the pressure belt with at least one 
wear-protection sleeve abutting the pressure belt and made of abrasion 
proof, well gliding material, in particular plastic material, for instance 
polytetrafluorethylene or polyurethane. 
In order to prevent loss of pressure medium, it is convenient to provide at 
least one seal of rubber or plastic material gliding along the pressure 
belt outside of the hollow pressure bladder preferably in circulating 
direction of the pressure belt and transversely thereto spacially behind 
or laterally of the hollow pressure bladder, i.e spacially behind or 
laterally of the gap formed between the hollow pressure bladder and the 
pressure belt at least on admission of pressure medium or in operation, 
with at least one opening for the discharge of pressure medium escaping 
through the gap being provided between the hollow pressure bladder and the 
seal. The gliding seal advantageously completely encloses the outside of 
the pressure bladder. 
It is also possible to provide two or more hollow pressure bladders 
spacially or tightly adjacent in circulating direction of the pressure 
belt, in which case it is convenient for the gliding seal to enclose the 
entire group of pressure bladders.

The dewatering machine of compact construction shown diagrammatically in 
FIG. 1 comprises a lower endless filter belt 1 and an upper endless filter 
belt 2 between which the material to be dewatered is made to pass. The 
lower filter belt 1 is formed as a supporting screen and is passed over a 
plurality of rollers, i.e. a screen regulating roller 11, a reversing 
roller 14 and a tensioning roller 13. The upper filter belt 2 is formed as 
a cover screen and is passed over guide rollers 14', a tensioning roller 
13' as well as over a regulating roller 11'. 
The material to be dewatered is charged by a charging means 7 onto the 
lower filter belt 1 so that a cake of approximately uniform thickness is 
formed to be dewatered between the two filter belts 1,2. 
In the pressing zone, the two filter belts 1, 2 are supported by 
circulating, endless pressure belts 3 and 4. The lower pressure belt 3 as 
well as the upper pressure belt 4 are passed over reversing rollers 9, 9', 
tensioning rollers 10, 10' and regulating rollers 11", 11'". The drive can 
be effected, for instance, by means of rollers 8, 8'. At the beginning and 
at the end of the press line, smaller reversing rollers 12, 12' are 
arranged. The pressure belts 3, 4 are made of elastic material which is 
impermeable to water and liquids, such as rubber or plastic material. The 
supports 5, 6 serve for exerting the required pressing power on the 
pressure belts 3,4 and further on the filter belts 1,2 and thus on the 
press cake lodged therebetween. These supports 5,6 take up the entire 
pressing force and are therefore of very stable construction. On either 
side of the dewatering machine, the upper and lower supports are connected 
to one another in order to achieve a transmission of the entire forces by 
a short way. This has the advantage that the very high pressing forces do 
not have to be transmitted to the machine frame, so that this machine 
frame can be of comparatively lightweight and inexpensive construction. A 
special hydrostatic pressure device shown in detail in FIG. 2 serves for 
the transmission of the forces from the supports 5,6 to the moving 
pressure belts 3,4. 
FIG. 2 diagrammatically shows the pressure device in section along line 
II--II in FIG. 3. For this purpose, a pressure bladder 15 is bent in 
U-shape and made of elastic material having tensile strength, such as a 
web of fabric-reinforced plastic material or rubber, and provided on the 
stationary support 6; this pressure bladder 15 is attached by means of an 
intermediary frame 16 and a clamping frame 16' in such a way that an 
interior space 18 sealed all around and kept at a certain superpressure is 
formed. 
The surface pressure is exerted on the moving pressure belt 4 in such a 
manner that a pressure medium, such as, for instance, water, is pumped 
through an inlet 20 into a pressure space 17 adjacent the pressure belt 4. 
A small portion of the amount of water introduced escapes through the very 
small, circumferentially extending gap 21. This amount, however, is 
constantly replaced through the inlet 20 by means of a pump not shown in 
detail so that a constant pressure of the desired value is maintained in 
the pressure space 17. 
A connection between the pressure space 17 adjacent the pressure belt 4 and 
the interior space 18 of the pressure bladder 15 is established by a bore 
22. By this bore 22, the pressure in the interior space 18 of the pressure 
bladder 15 and in the pressure space 17 is kept equal, so that the elastic 
pressure bladder 15 is kept in equilibrium. The result of this special 
arrangement is that the width of the gap 21 automatically adjusts itself 
to a very small value in the order of magnitude of a few hundredths of 
millimeters. This keeps the volume of escaping pressure medium, for 
instance water, very low, which also requires very little energy for 
supplementing the pressure medium, for instance water, by means of the 
pump. 
The distance between the support 6 and the moving pressure belt 4 is not 
constant, but changes according to the thickness of the press cake to be 
dewatered and also due to the compression of the material under the 
influence of the pressing force. The embodiment described has the 
advantage that the pressure bladder 15 automatically adapts itself to such 
fluctuations of thickness, so that in this case, the gap 21 also remains 
very small and that the pressure in the pressure space 17 is maintained. 
This makes it possible to maintain a constant surface pressure over the 
entire pressing surface although the material to be pressed is not level 
and shows differences in thickness. 
FIG. 3 diagrammatically shows the configuration of the pressure bladders 15 
according to FIGS. 2, 4 and 5 in reduced scale as compared to FIGS. 2, 4 
and 5, in plan view, the seal according to FIG. 5 not being shown. The 
exemplary shape shown here is a rectangular one, with the clamping frame 
16' fastened, for instance, by means of suitable, spaced screws. The 
pressure bladder 15 is formed, for reasons of production, not with sharp, 
but with slightly rounded corners. 
FIG. 4 shows in sectional view along line IV--IV in FIG. 3 a special 
arrangement of a pressure device. In addition to the inlet 20 for the 
pressure space 17, there is a separate inlet 20' for the interior space 18 
of the pressure bladder 15. This makes it possible to obtain slightly 
different pressures in the pressure space 17 and in the interior space of 
the pressure bladder 15, so that a special adaptation of the pressure 
bladder 15 is possible, which is of advantage in some cases of use. 
FIG. 4 also shows the arrangement of a wear-protection sleeve 24 of 
abrasion-proof, well gliding material, in particular plastic material, for 
instance polytetrafluor ethylene or polyurethane. This serves for 
preventing wear of the pressure bladder 15 at failure of the supply of 
compressed water or other breakdowns where it comes into contact with the 
circulating pressure belt 4. This also offers the advantage that the 
materials for the impermeable pressure belt 4 and the wear-protection 
sleeve 24 can be optimally matched to one another in respect of gliding 
behavior and no consideration need be given to abrasion in the selection 
of the material of the pressure bladder 15. An additional advantage 
resides in the fact that in case of damage, for instance by faulty 
operation, only the comparatively inexpensive wear-protection sleeve 24 
need be exchanged, while the pressure bladder 15 remains undamaged. 
FIG. 5 shows as a further variant a sectional view along line V--V in FIG. 
3 through the pressure bladder 15 with the pressure space 17 and the 
interior space 18 of the pressure bladder 15. This shows a further seal 25 
also fixed to the support 6. This seal 25 glides on the moving pressure 
belt 4 and serves for trapping the pressure medium escaping from the gap 
21, so that this medium can be discharged via bores 26 and returned to the 
pressure space 17 via a pump in the cycle which is not shown. This 
prevents a loss of pressure medium or pressure water which results in 
substantial advantages in respect of operation and cost. 
The seal 25 consists of rubber or plastic material, for instance 
thermoplastic material, and is arranged in circulating direction and in 
transverse direction of the pressure belts 3,4 spacially behind these, 
i.e. spacially after the gap 21 between the hollow pressure belts 3,4 as 
well as spacially laterally next to the pressure bladder 15. 
FIG. 6 shows as a further example a different embodiment of the pressure 
device in sectional view. In this the interior space 18 is defined partly 
by the pressure bladder 15 and partly by the fixed support 6. The 
fastening of the pressure bladder 15 is effected by means of the clamping 
frames 16 and 16' which are formed essentially quadrangularly and results 
in a tight connection. 
FIG. 7 shows an alternative embodiment in which pressure bladder 15 has an 
outer wall 30 and an inner wall 31. Inner wall 31 is formed from an 
elastic material, and outer wall 30 is formed from a material having a 
higher tensile strength than the material used for inner wall 31. Pressure 
bladder 15 is attached to the device in the same manner as the pressure 
bladder of FIG. 2. 
FIG. 8 shows another alternative embodiment in which a second hollow 
pressure bladder 40 is disposed around the first hollow pressure bladder 
15. Bladder 40 has the same frame-like shape as bladder 15 and completely 
encircles and encloses bladder 15. Bladder 40 is a attached to the device 
in the same manner as bladder 15, i.e., by a frame 43 and a clamping frame 
44. Frame 43 has a bore 46 which communicates the interior space 41 of 
bladder 40 with the pressure space 45. Pressure space 45 is bounded by 
bladder 40, bladder 15, belt 4, and stationary support 6. If a seal 25 is 
used with this double bladder arrangement, seal 25 is disposed beyond 
bladder 40 so as to encircle and enclose both bladders. 
In a machine with an upper pressure belt and a lower pressure belt, such as 
it is shown in FIG. 1, the hollow pressure bladder described can be 
associated with the upper and the lower pressure belts. The pressure belts 
are formed smooth on their sides facing the pressure bladder. 
The pressure device or a machine provided therewith can also be used for 
material to be pressed, in which case only pressure belts, but no filter 
belts or screen belts are used. The pressure bladders or hollow frames 
filled with pressure medium can be subjected to the action of pressing or 
supporting means with plane or concavely curved plates or surfaces facing 
them., the pressure pads or hollow frames can also be arranged in hollow 
chambers open towards the pressure belt. The belts could also pass over 
one or a plurality of roller(s), which results in a convex support. In 
this case, the closed frames formed of the hollow pressure bladders would 
have to be convexly curved accordingly. The material to be pressed could 
also be dry material. 
According to the invention, a pressure space proper is only present in the 
space enclosed by the hollow frame or pressure pad and in the interior of 
the frame or pad., after the zone surrounding the frame or pad, only 
leakage water or the like escapes through the lubricating gap 21.