Expanded metal filters
Expanded metal sheets ( 5 ) are used to produce tubular filters ( 13 ). The expanded metal sheet ( 5 ) has a multiplicity of rows of openings arranged to reduce nesting when the sheet ( 5 ) is rolled on itself. In particular, the pitch between the rows of openings, the sizes of the openings, or both the pitch between the rows of openings and the sizes of the openings are varied to reduce nesting when the expanded metal sheet ( 5 ) is rolled on itself. The filters ( 13 ) can include external circumferential grooves ( 3 ), rounded corners ( 19 ) produced by a point loading process, textured surfaces ( 37 ) between openings, and/or torturous internal paths produced by non-perforated areas of an expanded metal sheet. The expanded metal sheet ( 5 ) can be composed of carbon steel coated with a material having a higher heat conductivity, e.g., tin.
1. A tubular filter for use with a housing for an explosive charge of an airbag inflator, said housing having (A) a chamber for receiving (i) the tubular filter and (ii) the explosive charge, and (B) a circumferential ring of apertures for allowing gases generated by detonation of the explosive charge to exit the chamber, said circumferential ring of apertures being offset from the midplane of the chamber, said tubular filter being receivable in the chamber in two possible orientations, said tubular filter comprising expanded metal that has been rolled on itself to form a multi-layered tube having a substantially cylindrical outer surface wherein the expanded metal comprises a multiplicity of openings and the substantially cylindrical outer surface comprises two grooves, each of which is a circumferential groove which does not cut the expanded metal, the two circumferential grooves being offset from the midplane of the tubular filter so that only one of the two circumferential grooves is aligned with the circumferential ring of apertures of the housing when the tubular filter is received in the chamber irrespective of which of the two possible orientations the tubular filter has when received in the chamber, each circumferential groove allowing the apertures of the housing to function as an exit for gases generated by detonation of the explosive charge when the circumferential groove is aligned with the circumferential ring of apertures of the housing, each circumferential groove having a width such that when the circumferential groove is aligned with the circumferential ring of apertures of the housing, the circumferential groove is over the apertures even if all tolerances affecting the location of the circumferential groove are in one direction.
2. The tubular filter of claim 1 wherein each of the two circumferential grooves has an arcuate cross section.
3. The tubular filter of claim 1 wherein each of the two circumferential grooves is formed in the expanded metal before the expanded metal is rolled on itself.
4. An assembly comprising:
(a) a housing for an explosive charge of an airbag inflator, said housing having (A) a chamber for receiving (i) a tubular filter and (ii) the explosive charge, and (B) a circumferential ring of apertures for allowing gases generated by detonation of the explosive charge to exit the chamber, said circumferential ring of apertures being offset from the midplane of the chamber and said tubular filter being receivable in said chamber in two possible orientations; and
(b) a tubular filter according to claim 1 within the chamber in one of the two possible orientations;
wherein, irrespective of which of the two possible orientations the tubular filter has within the chamber, only one of the two circumferential grooves of the tubular filter is aligned with the circumferential ring of apertures of the housing.