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.

1 - 4 . (canceled) 
     
     
         5 . A method of making a filter comprising:
 (a) providing a sheet of metal having a width and an axis;   (b) forming slits in the sheet and stretching the slits in the direction of the sheet's axis to form a multiplicity of rows of openings;   (c) cutting a smaller sheet from the sheet produced in step (b);   (d) rolling the smaller sheet of step (c) on itself to form a tube; and   (e) securing the tube of step (d) with a weld;   wherein in step (b), the multiplicity of rows of openings are arranged to reduce nesting when the smaller sheet is rolled on itself to form the tube.   
     
     
         6 . The method of  claim 5  wherein 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 smaller sheet is rolled on itself to form the tube. 
     
     
         7 . The method of  claim 6  wherein the pitch between rows of openings is varied as a function of the circumference defined by a given portion of the rolled up smaller sheet so that radially adjacent openings do not nest. 
     
     
         8 . The method of  claim 6  wherein in step (b) the sheet is fed at a rate which varies so as to vary the pitch between the rows of openings. 
     
     
         9 . The method of  claim 5  wherein the smaller sheet includes areas that do not include openings. 
     
     
         10 . The method of  claim 5  wherein the filter is an automotive airbag filter. 
     
     
         11 - 28 . (canceled) 
     
     
         29 . A method of making a filter comprising:
 (a) providing a sheet of expanded metal having a multiplicity of openings;   (b) cutting a smaller sheet from the sheet of step (a);   (c) rolling the smaller sheet of step (b) on itself to form a tube having multiple layers; and   (d) securing the tube of step (c) with a weld;   wherein the openings are arranged in rows and, for adjacent layers of the rolled up filter, the pitches of the rows are different.   
     
     
         30 . The method of  claim 29  wherein the pitches are varied as a function of the circumference defined by a given portion of the expanded metal in the rolled up filter so as to reduce nesting of radially adjacent openings. 
     
     
         31 . The method of  claim 29  wherein the smaller sheet includes areas that do not include openings. 
     
     
         32 . The method of  claim 29  wherein the smaller sheet has long sides and short sides and in step (c), the smaller sheet is rolled on itself about an axis connecting the long sides. 
     
     
         33 . The method of  claim 29  wherein the smaller sheet has long sides and short sides and in step (c), the smaller sheet is rolled on itself about an axis connecting the short sides. 
     
     
         34 . The method of  claim 29  comprising the further step of using the filter for an inflator of an airbag device. 
     
     
         35 . A method of making a filter comprising:
 (a) providing a sheet of expanded metal having a multiplicity of openings;   (b) cutting a smaller sheet from the sheet of (a);   (c) rolling the smaller sheet of step (b) on itself to form a tube having multiple layers; and   (d) securing the tube of step (c) with a weld;   wherein the openings are not all of the same size and the openings are arranged so that for adjacent layers in the rolled up filter, the sizes of the openings are different.   
     
     
         36 . The method of  claim 35  wherein the sizes are varied so as to reduce nesting of radially adjacent openings in the rolled up filter. 
     
     
         37 . The method of  claim 35  wherein the smaller sheet includes areas that do not include openings. 
     
     
         38 . The method of  claim 35  wherein the smaller sheet has long sides and short sides and in step (c), the smaller sheet is rolled on itself about an axis connecting the long sides. 
     
     
         39 . The method of  claim 35  wherein the smaller sheet has long sides and short sides and in step (c), the smaller sheet is rolled on itself about an axis connecting the short sides. 
     
     
         40 . The method of  claim 35  comprising the further step of using the filter for an inflator of an airbag device. 
     
     
         41 . A method of making a filter comprising:
 (a) providing a sheet of expanded metal having a multiplicity of openings;   (b) cutting a smaller sheet from the sheet produced in step (a);   (c) rolling the smaller sheet of step (b) on itself to form a tube having multiple layers; and   (d) securing the tube of step (c) with a weld;   wherein the openings are not all of the same shape and the openings are arranged so that for adjacent layers in the rolled up filter, the shapes of the openings are different.   
     
     
         42 . The method of  claim 41  wherein the shapes are varied so as to reduce nesting of radially adjacent openings in the rolled up filter. 
     
     
         43 . The method of  claim 41  wherein the sizes are varied so as to reduce nesting of radially adjacent openings in the rolled up filter. 
     
     
         44 . The method of  claim 41  wherein the smaller sheet includes areas that do not include openings. 
     
     
         45 . The method of  claim 41  wherein the smaller sheet has long sides and short sides and in step (c), the smaller sheet is rolled on itself about an axis connecting the long sides. 
     
     
         46 . The method of  claim 41  wherein the smaller sheet has long sides and short sides and in step (c), the smaller sheet is rolled on itself about an axis connecting the short sides. 
     
     
         47 . The method of  claim 41  comprising the further step of using the filter for an inflator of an airbag device.