Tubular articles and method of making same

摘要: A perforate, thin-walled, tube structure of surprisingly high strength, having a tightly-clenched lock seam and generally helical wall corrugations, manufactured by continuous rolling process in which the stock is first put through piercing corrugating stage then fed number complementary-shaped pairs rollers progressively change shape from basically flat to circular cross-section with progressively-formed joining edges tightly clenched manner, use an arbor extending inside tubular roller bears against provide for tight clenching latter external and, at same time, helping pull various stages, all initially-formed corrugations are maintained intact unflattened condition.