additional heat treatment for aluminium lithium alloys

摘要

A face mask (1), covering at least the nose and mouth, has an air-permeable region (holes 9) for extending over the nasal and oral orifices and has means (7, 8) for attaching the mask to the head. A disposable flexible air-permeable filter (2) extends over the nasal and oral orifices, in contact with the face, and is temporarily connected to the face mask (1) by non-return exhalation valves (12).