Double-walled structure and method of producing the same

Abstract

A double-walled-structure, such as a silencer for use in a ventilation duct system, has a perforated inner tube, an outer casing which is arranged at a distance from the inner tube and encloses the same, and a tubular, sound-absorbing element which is arranged between the inner tube and the casing. The tubular element has an increasing density radially outwards from the center axis of the inner tube. The silencer is produced by the sound-absorbing element being arranged on the inner tube, and the inner tube with the sound-absorbing element arranged thereon being enclosed in the surrounding outer casing.

What I claim and desire to secure by Letters Patent  
     
         1 . A double-walled structure, comprising an inner tube having a center axis, an outer casing which is arranged at a distance from said inner tube and encloses the same, and a tubular sound-absorbing element which is arranged between said inner tube and said casing, wherein said tubular element has an increasing density radially outwards from said center axis of said inner tube.  
     
     
         2 . The structure of    claim 1   , wherein said tubular element comprises at least two layers of sound-absorbing material.  
     
     
         3 . The structure of    claim 1    or    2   , wherein said tubular element comprises at least one tubular cylinder, which is rigid and sound-permeable and which is arranged between and coaxially with two neighboring layers of sound-absorbing material.  
     
     
         4 . The structure of    claim 2   , wherein at least one of said layers of sound-absorbing material consists of at least one tubular casing.  
     
     
         5 . The structure of    claim 2   , wherein at least one of said layers of sound-absorbing material is wound at least one turn round an outer circumferential surface of said inner tube.  
     
     
         6 . The structure of    claim 1   , wherein said tubular element comprises at least one tubular casing.  
     
     
         7 . The structure of    claim 1   , wherein said tubular element comprises a material which has a density gradient and which is wound round an outer circumferential surface of said inner tube to form a layer of said material.  
     
     
         8 . The structure of    claim 7   , wherein said material is spirally wound.  
     
     
         9 . The structure of    claim 7   , wherein said material is helically wound.  
     
     
         10 . The structure of    claim 1   , wherein said tubular element comprises a material which is wound a plurality of turns round the outer circumferential surface of said inner tube.  
     
     
         11 . The structure of    claim 5    or    10   , wherein said material is spirally wound.  
     
     
         12 . The structure of    claim 5    or    10   , wherein said material is helically wound.  
     
     
         13 . The structure of    claim 1   , wherein said sound-absorbing element essentially is made of a yieldable material.  
     
     
         14 . The structure of    claim 1   , wherein said sound-absorbing element essentially is made of a fiber material, preferably mineral wool.  
     
     
         15 . The structure of    claim 1   , wherein said inner tube essentially is designed to be sound-permeable.  
     
     
         16 . The structure of    claim 1   , wherein said inner tube is provided with perforations.  
     
     
         17 . The structure of    claim 1   , wherein said inner tube essentially is made of sheet metal.  
     
     
         18 . A silencer for ventilation duct systems, comprising a double-walled structure according to any one of the preceding claims.  
     
     
         19 . A method of producing a double-walled structure, which comprises an inner tube having a center axis, an outer casing which is arranged at a distance from said inner tube and encloses the same, and a tubular sound-absorbing element which is arranged between said inner tube and said casing; 
 said method comprising the steps: that said sound-absorbing element is arranged on the outside of said inner tube in such manner that the density of said element increases radially outwards from said center axis of said inner tube; and    that said inner tube with said sound-absorbing element arranged thereon are enclosed in said outer casing.    
     
     
         20 . The method of    claim 19   , wherein said sound-absorbing element is arranged on an outside of said inner tube by said sound-absorbing element first being secured to said inner tube and by said sound-absorbing element being made of a material which is subsequently wound round an outer circumferential surface of said inner tube.  
     
     
         21 . The method of    claim 20   , wherein said material is spirally wound.  
     
     
         22 . The method of    claim 20   , wherein said material is helically wound.  
     
     
         23 . The method of    claim 20   , wherein during said winding a counterforce is applied to said material in such manner that said sound-absorbing element is given a density increasing radially outwards from said center axis of said inner tube.