| 摘要 |
PROBLEM TO BE SOLVED: To maintain excellent silencing performance for a long time by forming a crystalline alumina fiber layer, which exhibits a specificα-alumina crystallization rate value and a specific mullite crystallization rate value, on a metallic cylinder side face of a sound absorbing member in a silencer in which the outside of an inorganic fibrous sound absorbing member is coated by a metallic shell. SOLUTION: In a silencer used for an internal combustion engine and the like, an inorganic fibrous sound absorbing member is arranged around a metallic cylinder, and the outside of the sound absorbing member is coated by a metallic shell. In this case, a crystalline alumina fiber layer exhibiting anα-alumina crystallization rate of 5% or less and a mullite crystallization rate of 80% or less is formed on the metallic cylinder side face of the inorganic fibrous sound absorbing member. Desirably, an alumina content in the crystalline alumina fiber layer is 85wt.% or less, while a content of grain with a diameter of 44μm or more is 10wt.% or less. In this way, heat deterioration of the sound absorbing member due to high temperature emission gas can be prevented, while scattering of the fibrous object to the atmosphere is prevented, so that stable silencing performance can be maintained for a long time.
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