| 摘要 |
A layered filtering structure ( 10 ) comprises at least a first layer ( 12 ) and a second layer ( 13 ). Each layer comprises a web of metal fibers which has been sintered. The two layers ( 12, 13 ) are in contact with each other. The first layer, most close to the filter inlet side has a porosity below 55%, and the second layer, closer to the filter outlet side has a porosity which is at least 20% greater than the porosity of the first layer. The first layer is compacted in a separate manufacturing step. The layered filtering structure combines the advantage of a small filter rating with a low pressure drop.
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