Filter device

A filter device with a preferably hollow-cylindrical, pleated filter element which is arranged concentrically around a cylinder axis and through which a medium to be filtered passes. Seals are necessary on the filter device so that the medium to be filtered will not be able to leak out and so that the filter element, which typically is constructed of filter paper, must be fixed in place together with its pleats. Advantageously, an elastic composition can be disposed as a seal on at least one of the ends of the filter element, and after curing the elastic composition will fix the pleats of the filter element and will have sufficient residual elasticity to seal the filter element with respect to a central mounting tube on which it is to be mounted.

BACKGROUND OF THE INVENTION 
This invention relates to a filter device with a, preferably 
hollow-cylindrical, pleated filter element which is arranged around a 
cylinder axis and through which a medium to be filtered passes, and a seal 
arranged on at least one end of said filter element and extending radially 
inwardly of said filter element so as to contact a central tube on which 
the filter element may be mounted. 
A filter device of this kind is disclosed in published German Patent 
Application No. DE-OS 4,206,519, in which a pleated, hollow-cylindrical 
filter element is provided with plates which sealingly cover the ends, 
made of metal for example, or with sealing materials in the form of foils. 
These seals in plate or foil form extend radially inward by a certain 
amount into the interior cylinder, so that sealing to a central tube can 
be achieved. 
As soon as this known filter device is inserted into the circulation system 
for motor oil or diesel fuel or gasoline, these seals are exposed to large 
tearing stresses, so that there is always a danger that the filter element 
will tear when inserted into the filter housing and thus not only will the 
sealing material be damaged, but also the filtering action will be 
defeated. Furthermore, these seals are exposed to great stress during 
operation due to the relatively high temperatures of the medium being 
filtered, especially in the case of motor oil, which can result in a 
reduction of the effectiveness of the entire filter device. 
SUMMARY OF THE INVENTION 
It is therefore an object of the invention to provide an improved filter 
device such that a lasting functionality will be assured. 
Another object of the invention is to provide a filter device in which a 
reliable seal is produced by a simple manufacturing procedure. 
These and other objects have been achieved in accordance with the present 
invention by providing a filter device comprising a pleated filter element 
which is arranged around a cylinder axis and through which a medium to be 
filtered passes, and a seal on at least one end of the filter element and 
extending radially inwardly of the filter element so as to contact a 
central tube on which the filter element is to be mounted; in which the 
seal is formed from a curable elastic composition disposed on the end so 
as to fix the pleats of the filter element and seal the end of the filter, 
the composition after curing retaining sufficient residual elasticity to 
seal the filter element with respect a central tube on which it is to be 
mounted. 
The filter device of the invention advantageously adapted to solve the 
problem of tearing or damage of the end seals of hollow cylindrical, 
pleated filter elements mounted on central mounting tubes. 
It is a particular advantage of the present invention that a measure that 
is necessary for fixing the pleats of the hollow cylindrical filter 
element can be combined with the production of the sealing surfaces. The 
residual elasticity of the elastic mass that remains after the curing or 
hardening or setting process is capable of assuring a sufficient sealing 
action for a long period of time, even in the case of filtered media which 
have relatively high temperatures, such motor oil at 170.degree. C. Also, 
the filter devices can be replaced, as is necessary after a certain period 
of operation, in a simple manner because the elastic connection makes it 
possible to remove the filter element without any need for an expensive 
tool. Due to the simple construction of the filter device using only a few 
materials, the used filter devices can easily be recycled without any need 
to separate their materials. 
Additional advantageous embodiments of the filter device according to the 
invention which make it easy to form the radially inner sealing surfaces, 
are described hereinafter. An optimal residual elasticity can be achieved 
by using appropriate mixing ratios of nitrile rubber and phenolic resin to 
produce the elastic composition from which the seals are made. Preferred 
mixing ratios of nitrile rubber to phenolic resin range from 1:0.8 to 
1:1.5.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
FIG. 1 shows a hollow cylindrical filter device 1 in which the filter 
element 3, made for example of filter paper folded in pleats, is situated 
in a filter housing 2. At the end of the filter device 1 there is a 
sealing closure 4 which forms a seal against a connecting piece (not 
shown). 
Such filter devices can be employed, for example, for filtering motor oil, 
fuel or air in the operation of a motor vehicle with an internal 
combustion engine. The apparatus in which the filter device is used is 
omitted from the drawing to facilitate better understanding of the 
drawing. As a rule the medium to be filtered is delivered from the outside 
to the surfaces of the pleated filter element 3, and the filtered medium 
is discharged through a central tube which is sealingly inserted into an 
inner, concentric opening 5 of the closure 4. Filter devices of this 
general type are known in the art, for example from German Utility Model 
No. DE-U 18 51 221. 
In the embodiment of the filter device 1 according to the invention which 
is shown in FIG. 1, it can be seen from the upper closure piece 4, how an 
elastic composition 6, which serves as the seal, has flowed, prior to a 
curing or hardening procedure, into the pleated folds of the filter 
element 3, and thereafter fixes the pleated structure in place. This means 
that the elastic composition 6 at temperatures above 90.degree. C. first 
softens and then sets (melt-reaction adhesive). In the described 
embodiment, the elastic composition 6 is formed of nitrile rubber and 
phenolic resin, the mixing ratio of rubber to resin being from 1:0.8 to 
1:1.5. Use of an appropriate thermal curing process assures that 
sufficient residual elasticity remains to provide an adequate sealing 
effect at the points of connection between the filter element and the 
device in or on which it is mounted. If desired, additional sealing means, 
such as paper rings for example, can be embedded in the elastic 
composition 6 in order to improve the sealing properties. 
In the illustrated embodiment, the elastic composition is distributed over 
the entire end surface of the filter device and is extended with an inner 
region 7 into the concentric opening 5. For optimum sealing, however, it 
may be sufficient if only those portions of the closure piece 4 which lie 
opposite a connection piece are provided with the elastic composition 6. 
FIG. 2 shows a sectional view of the end of the filter device 1. Here it 
can be seen how the elastic composition 6 extends into the pleated filter 
element 3 and is sealingly in contact via an inner region 7 with a central 
tube 8 through which the filtered medium is discharged. Sealing to an end 
connecting piece, not shown here, is likewise achieved by the end face 
surface of the elastic composition 6. 
The introduction of the elastic composition 6 into the filter element 3 
thus assures an outstanding sealing action and fixation of the filter 
element in a simple manner due to its remaining residual elasticity. 
In one preferred embodiment, the elastic composition is rolled into a foil 
and punched out as a disk having a diameter corresponding to the end of 
the filter element prior to being applied to an end of the filter element. 
After application of the elastic composition to the filter element, the 
elastic composition preferably is cured by application of heat. In a 
particularly preferred embodiment, the elastic composition is applied to 
both ends of the filter element and cured simultaneously. 
The foregoing description and examples have been set forth merely to 
illustrate the invention and are not intended to be limiting. Since 
modifications of the described embodiments incorporating the spirit and 
substance of the invention may occur to persons skilled in the art, the 
invention should be construed broadly to include all variations falling 
within the scope of the appended claims and equivalents thereof.