MELT-BLOWN DEPTH FILTER ELEMENT AND METHOD OF MAKING IT

A tubular depth filter element has one or more concentric zones. Each zone includes layers of a melt blown filament. An additional filament oscillates through the depth of the element, traversing through part of the depth of the filament with each oscillation but traversing through substantially all of the depth of the element over multiple oscillations. The traversing filament is preferably biased towards the outside of the element. The depth filter element may be made by spraying filaments onto a rotating mandrel. The filaments of the concentric zones are sprayed from fixed nozzles spaced apart along the length of the mandrel. The traversing filament is sprayed from a nozzle assembly that moves laterally or has compound motion relative to the mandrel. For example, the nozzle assembly may oscillate relative to the mandrel while an air attenuator of the nozzle assembly oscillates relative to the remainder of the nozzle assembly.