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Producing stainless steel tubes requires a tube mill designed with specific considerations for the material's unique properties, namely its higher strength, work-hardening tendency, and need to preserve its corrosion resistance. Shijiazhuang Faith Machinery Co., Ltd offers tube mills configured to meet these challenges for grades like 304, 304L, 316, and 316L.
The forming section of a stainless steel tube mill must be more robust than one for mild steel. The rolls are designed to apply forming pressure gradually to minimize work hardening, which can make the material brittle and difficult to weld. The mill stands are often built with greater rigidity to withstand the higher forces required to form stainless steel. To prevent surface scratches and contamination that could compromise corrosion resistance, the forming rolls are typically made from high-quality materials and may have polished surfaces.
The welding process for stainless steel often differs from that used for carbon steel. While HF welding is possible, Tungsten Inert Gas welding is a common choice, especially for applications where the integrity and corrosion resistance of the weld are paramount. In TIG welding, an electric arc between a non-consumable tungsten electrode and the workpiece generates the heat. The weld zone is shielded from atmospheric contamination by an inert gas, such as argon. This produces a clean, high-quality weld with excellent metallurgical properties. The welding speed for TIG is generally slower than for HF welding, which is a key factor in production planning.
A critical step unique to many stainless steel tube mills is post-weld annealing and pickling. Annealing involves heating the entire tube or just the weld zone to a high temperature to relieve stresses and restore the corrosion-resistant microstructure, which can be altered by the heat of welding. This is often followed by pickling, a chemical process that removes oxide scale (heat tint) from the weld area and restores the passive layer on the stainless steel surface. Some advanced mills may incorporate inline solution annealing systems that use induction heating followed by a controlled quench.
The finishing processes are also crucial. Stainless steel tubes often require a specific surface finish, such as a bright annealed finish or a polished finish. The mill may include polishing units or belt grinders to achieve this. Cutting is typically done with cold saws to avoid generating heat that could discolor the tube or affect the material properties at the cut end. Throughout the process, handling must be careful to avoid marring the surface. The design of a stainless steel tube mill from Shijiazhuang Faith Machinery therefore prioritizes material preservation and surface quality at every stage.
