F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL-COMBUSTION ENGINES
F01N1/00—Silencing apparatus characterised by method of silencing
F01N1/16—Silencing apparatus characterised by method of silencing by using movable parts
F01N1/165—Silencing apparatus characterised by method of silencing by using movable parts for adjusting flow area
B—PERFORMING OPERATIONS; TRANSPORTING
B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
B21D—WORKING OR PROCESSING OF SHEET METAL OR METAL TUBES, RODS OR PROFILES WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
B21D51/00—Making hollow objects
B21D51/02—Making hollow objects characterised by the structure of the objects
B21D51/10—Making hollow objects characterised by the structure of the objects conically or cylindrically shaped objects