Gas separation – Specific media material – Ceramic or sintered
Patent
1995-03-07
1996-08-20
Spitzer, Robert
Gas separation
Specific media material
Ceramic or sintered
55524, 55DIG5, B01D 3916, B01D 4624
Patent
active
055474810
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a filter element, in particular for separating solid particles from air.
BACKGROUND OF THE INVENTION
The document EP-B-0 177 521 discloses a filter element whose substantially inherently stable, permeably porous shaped body is made of fine-grained polyethylene with a higher molecular weight, and polyethylene which is fine-grained in the initial state with a lower molecular weight, these polyethylene components being combined into the shaped body by the action of heat, and a surface-pore coating of fine-grained polytetrafluoroethylene being provided. In actually produced filter elements of this kind the higher-molecular polyethylene has a molecular weight of more than 10.sup.6. Due to the surface-pore coating, the filter element can filter on the principle of surface filtration. Even fine and extremely fine particles of the medium to be filtered are already held on the afflux surface of the filter element and can be cleaned off of this surface very easily, for example by the backflow principle.
These filter elements were hitherto produced using an ultrahigh-molecular polyethylene starting material, in which just under 10% of grains are larger than 250 microns and smaller than or equal to 63 microns. These filter elements are used quite successfully in practice. However the invention achieves a further improvement in known filter elements.
It is an object of the invention to solve the technical problem of developing a permeably porous filter element having a substantially inherently stable shaped body made substantially of polyethylene and bearing a fine-pored coating on its afflux surface, so as to reduce flow resistance and improve the formation of the coating.
SUMMARY OF THE INVENTION
The above is fulfilled by the instant invention, according to a first embodiment of which a filter element has a permeably porous, substantially inherently stable shaped body, wherein:
(a) the shaped body is made substantially of polyethylene;
(b) the shaped body is built up of ultrahigh-molecular, fine-grained polyethylene with an average molecular weight of more than 10.sup.6 and a further polyethylene component which is fine-grained in the initial state and has an average molecular weight of less than 10.sup.6 ;
(c) the grains of ultrahigh-molecular polyethylene and the further polyethylene component are combined into the shaped body by the action of heat;
(d) the shaped body is provided on its afflux surface for the medium to be filtered with a fine-pored coating of a fine-grained material having a smaller average grain size than the shaped body and filling at least a considerable depth of the surface pores thereof on the afflux surface; and
(e) the ultrahigh-molecular polyethylene has in the initial state a grain-size distribution with at least 95% by weight of grains in the range of>63 to .ltoreq.250 microns.
This first inventive solution and novel sharp definition of the grain-size range of the ultrahigh-molecular polyethylene for the shaped body to be coated means that the uncoated shaped body has a very uniform pore distribution in which particularly very small pores which increase flow resistance are virtually fully absent. The surface pores of the uncoated shaped body also have a very uniform pore-size distribution. The coating therefore also has a very uniform pore-size distribution with a smaller average pore size, based on the same coating material. This results in a virtually uniform filter load and a virtually perfect surface filtration over the total afflux surface of the filter element.
According to a second embodiment, the present invention relates to a filter element, in particular for separating solid particles from air, which has a permeably porous, substantially inherently stable shaped body, together with the abovementioned features (a) to (d),
wherein:
the ultrahigh-molecular polyethylene has in the initial state a grain-size distribution with at least 60% by weight of grains in the range of>125 to.ltoreq.250 microns.
This second in
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Bethke J urgen
Herding Walter
Rabenstein Klaus
Herding GmbH Entstaubungsanlagen
Spitzer Robert
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