| 摘要 |
PROBLEM TO BE SOLVED: To prevent the end part of a core pipe from being broken during drawing in a manufacturing process by inserting a plurality of filaments for reinforcement at a specified interval within a specified length range from both ends of an outer pipe, in a refractory double layer pipe consisting of the outer pipe obtained by laminating a plurality of nonflammable material layers and an inner pipe of synthetic resin fitted into the former. SOLUTION: The refractory double layer pipe 10 to be used as a drain pipe or the like in residences of a housing area is of such a construction that an inner pipe 20 of synthetic resin is sheathed by a nonflammable outer pipe 30. The thermal expansion of the inner pipe 20 generated by the drainage of hot water or the like is absorbed by a gap provided between both pipes 20, 30 and thus a stress is prevented from being brought to bear upon the outer pipe 30. In this case, a plurality of filaments for reinforcement or reinforcing nets are inserted at a specified interval across the length of 30-100 mm from both ends, in the lengthwise direction, of the outer pipe 30 in such a manner that the filaments or the nets are located in a single or a plurality of layers in the circumferential direction between the nonflammable material layers of the outer pipe 30. The filaments for reinforcement or the reinforcing nets to be used are formed of fibers of vinylon, nylon, polyethylene or the like as organic fibers, but are not necessarily defined, whether it be an organic or an inorganic substance.
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