| 摘要 |
<p>PURPOSE: To hold the stable shape of a duct in the extending and contracting states by providing grooves on valley parts and one shoulder part of a duct wall in the duct longitudinal section, attaching a spiral reinforcing coil as a synthetic resin material capable of fusing-stuck to the duct wall material on the duct mountain part, and satisfying the specified condition in the extending state. CONSTITUTION: As resin for forming a wall of an extending and contracting bellows duct l, polypropylene can be mentioned, and its modulus of elasticity in bending is set to the range of 2500 to 10000kgf/cm<2> . A material having the high modulus of elasticity in bending is required as a material, and the modulus of elasticity in bending in the range of 10000 to 3000kgf/cm<2> is preferable. In the longitudinal section of the duct wall for forming the duct valley parts, the ratio of the inclined side in which a groove 7 is provided on the shoulder part and the other inclined side is set to the range of 3:7 to 7:3. The pitch/wave height is set to the range of 1.8 to 3.2, the wave height/duct outside diameter is set to the range of 0.02 to 0.1, and the wave height/coil core diameter is set to the range of 1.5 to 5. Therefore, suspending in the extending state or the contracting state is decreased, the weight can be decreased, and cutting properties can be improved.</p> |
