Expendable folded paper filter - with V-folds at corners giving firmer glued edge seams

摘要

An expandable filter for gas or liquid is made from a transversely folded strip of filter paper, the folds form V-shaped open external pockets and V-shaped closed internal pockets. The internal pockets are formed from two successive fold halves with folds at 45 degrees to the transverse folds, thus giving inward pointing side walls. Firm glued edge seams, which cannot open, are obtained. The filter is open at one side and the area lost by gluing is reduced.