Expanded metal filters

Abstract

Expanded metal sheets are used to produce tubular filters. The expanded metal sheet has a multiplicity of rows of openings arranged to reduce nesting when the sheet 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 is rolled on itself. The filters can include external circumferential grooves, rounded corners produced by a point loading process, textured surfaces between openings, and/or torturous internal paths produced by non-perforated areas of an expanded metal sheet. The expanded metal sheet can be composed of carbon steel coated with a material having a higher heat conductivity, e.g., tin. Among other things, the filters can be used in automobile airbag inflators to capture slag and absorb heat produced by the inflator's explosive charge.

What is claimed is: 
     
         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 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 a circumferential groove which does not cut the expanded metal, the tubular filter being receivable in the chamber with the circumferential groove aligned with the circumferential ring of apertures,   wherein:   (a) the circumferential groove allows 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, and   (b) the circumferential groove has 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 the circumferential groove has an arcuate cross section. 
     
     
         3 . The tubular filter of  claim 1  wherein the circumferential groove 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; and   (b) a tubular filter according to  claim 1  within the chamber with the filter's circumferential groove aligned with the circumferential ring of apertures of the housing.