Fluid filter element

Details Fluid filter element Fluid filter element

2001-09-20

2004-02-03

Drodge, Joseph (Department: 1723)

Liquid purification or separation

Filter

Supported, shaped or superimposed formed mediums

C210S493300, C210S493500, C210S506000, C055S521000, C055S497000, C055SDIG005, C428S181000, C428S182000

Reexamination Certificate

active

06685833

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention concerns a fluid filter element and method for forming same.
2. Description of Prior Art
Fluid filter elements are well known and are widely used in fluid filters for varying areas of use, including hydrodynamic machines and air-conditioning engineering. Their meander-shaped or zig-zag structure provides a substantially increased filter area, in relation to a fixed afflux flow cross-section. In order to fix the fold walls of such a structure relative to each and to support them with respect to each other, various different kinds of design configurations have been developed. Filters with depressions which are embossed into the flat filter material and which, when the material is folded, bear against each other and support each other are known.
In the case of earlier fluid filter elements of that kind the embossings of the fold walls were simply laid against each other when executing the folding operation and the filter element which was finished as a kind of “fold pack” was externally fixed by being clamped in a box or frame. While such particularly simple fluid filter elements certainly operate satisfactorily at the beginning of their period of use and in areas of use without involving fluctuating pressure loadings worth mentioning, critical stability problems are found to occur in relation to certain degrees of filling with deposited dust particles, or dust loading, and in particular when used in relation to fluid-dynamic machines.
A relatively long time ago, therefore, the inventor proposed a filter structure in which the mutually facing embossings of the filter material are glued to each other, in the folded condition, on their respective top sides. The gluing operation is implemented by a selective thin application of adhesive or suitable impregnation of the filter material in the region of the embossings. Such a filter structure is described for example in U.S. Pat. No. 5,290,447.
In connection with rising demands on the part of users in terms of performance and service life of the fluid filter elements, there was a trend for an increase in the fold height, which at the same time results in an increase in the maximum spacing of the filter material surfaces from each other. In that respect, difficulties arose in regard to implementing those increasing spaces solely by increasing the depth of the embossing regions which support the fold walls relative to each. In particular, with embossings which are of an increasing depth, there is an increased risk of through-embossings or piercings, holes or at least very thin areas in the filter material. Fluid filter inserts with such piercings are rejects.
Therefore, in a further stage in development, the proposal was made that, instead of an application of adhesive without a thickness worth mentioning on the top sides of the embossings, adhesive threads of considerable thickness should be applied, which together with the embossings afford the required maximum spacing between the fold walls from the filter material. That structure is described for example in U.S. Pat. No. 5,804,014.
In a next step in development—the inventor proposed to use a structure which is controlled variably in respect of its height (specifically rising linearly towards the opening of the folds), in particular also entirely without any embossing or at any event without embossing which is variable in respect of its depth, in the filter material. This therefore involves fluid filter elements in which the spacing function and the supporting function as between the fold walls of a zig-zag fold configuration is achieved substantially solely by adhesive threads which are variable in height. That structure is described for example in DE 197 55 466 A1.
In the above-mentioned fluid filter structures, depressions and raised portions are embossed into the filter material alternately in the widthwise direction of the filter material and in a direction perpendicularly to the fluid flow direction and parallel to the material surface, so that (in the folded condition of use) support regions are disposed alternately at both sides of the filter medium. In a situation involving long-term use of those filter structures under high levels of loading, in particular in fluid filters for fluid dynamic machines which entail a pronounced fluctuating pressure loading, and also in the case of filters for suspended matter or mechanical filters which can be cleaned off, problems arose with reliability.
In particular, it is observed that the filter medium in such devices can be torn away from the adhesive threads under a high loading. The filter medium can also be delaminated in a layer-wise fashion. The reason for this is that the boundary layer between the adhesive thread and filter medium is subjected to a heavy tensile loading on the feed air or upstream side. In the regions where the filter medium has come away from the adhesive thread, it begins to “flutter”. The entire filter element then becomes unstable from the fluid dynamics point of view, the folds on the discharge air or downstream side collapse, and enormous pressure difference rises occur which can reach a level practically involving local air impermeability of the filter. As the ultimate effect, the filter is destroyed.
Therefore, in an unpublished German patent application, the inventor proposed a specially reinforced structure for high-efficiency fluid filters of that kind. It is provided in that structure that, in all embossing regions, the filter material fold walls are not only glued to each other on the mutually facing raised portions, but in addition a particularly high adhesive thread is provided in lateral orientation with those adhesive means—that is to say in the depressions on the rearward surface of the filter material, which depressions correspond to the raised portions. In that structure the filter material is therefore “clamped in position” on both sides between adhesive threads in all gluing regions.
A technological problem of this last-mentioned arrangement however is that the adhesive threads must be formed of very great height, in the depressions in the filter material. When using conventional hot melt adhesives and manufacturing installations, relatively wide adhesive threads are also formed in that situation, which detrimentally reduce the usable filter area. In particular the amounts of adhesive become so great that, in the case of the adhesive threads which are to be applied on the underside of the web of filter material, the hot melt adhesive drips out before it hardens. The usual application of adhesive to the horizontal disposed filter material, which is advantageous from the point of view of the apparatus configuration, is thus no longer possible. In addition, the application of controlled adhesive threads to both sides of a filter medium is in any case technologically demanding and presupposes the use of metering devices which operate precisely and which are correspondingly expensive.
FIGS. 1-6
further illustrate various prior art structures and problems.
Referring to
FIG. 1
, shown therein is an isometric view of a part of a filter material
10
in a lying condition, for the production of a fluid filter element in accordance with the prior art; embossed into the filter material
10
on both sides of the plane of the material are depressions and raised portions respectively as indicated at
11
, which are approximately triangular in longitudinal section, that is, they extend longitudinally at an angle with respect to the plane of the material, and between approximately trapezoidal and rectangular in cross-section, typically in a soft curve, which extends in the longitudinal direction of the filter material web. Reference numeral
13
denotes fold edges which extend perpendicularly thereto and which are also embossed into the filter material. The embossings
11
extend virtually over the entire spacing “a” between adjacent fold edges
13
and embossing height is illustrated at “b
1
”.
FIG. 2
is a diagrammatic isometric view of a

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