Melt-blown depth filter element, method and machine 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.
1. A depth filter element comprising,
an outside surface and an inside surface,
one or more first filaments deposited in layers, the one or more first filaments forming a helicoid, and
a traversing filament,
wherein,
the traversing filament is deposited on the one or more first filaments between the layers in a pattern that traverses back and forth across a helix on the helicoid, wherein the helix has an oscillating diameter and wherein more of the mass of the traversing filament is deposited towards the outside surface of the element.
2. The element of claim 1 wherein the traversing filament follows an oscillating path wherein the traversing filament traverses through part of the depth of the element in a single oscillation but traverses through more of the depth of the element over multiple oscillations.
3. The element of claim 1 wherein, in a part of the helix, the diameter of the helix oscillates at a constant rate.
4. The element of claim 1 wherein, in part of the helix, the diameter of the helix is constant.
5. The element of claim 1 wherein the one or more first filaments form a set of concentric zones.
6. The element of claim 5 wherein a first filament of an outer zone overlaps, intersects or intermingles with a first filament of another zone through at least 50% of the other zone.
7. The element of claim 5 having four or more concentric zones or five or more concentric zones.
8. The element of claim 1 having an outside diameter of 2.0 inches or more.