How is cold drawn seamless pipe made?


Cold drawn seamless pipe has a high strength to weight ratio and can be machined to provide a combination of desired properties.This type of tube has a variety of uses, especially where thick walls, specific steel alloys, or both are required. Specific applications include bushings, gaskets, bearings and other mechanical components in automobiles, trucks, aircraft and construction, agricultural and drilling equipment, and hydraulic cylinders. Cold drawn seamless pipes have good dimensional accuracy, surface quality, microstructural uniformity, machinability and high tensile properties. It is also suitable for post-processing such as carburizing, heat treatment, etc.

Manufacturing Process

Cold drawn seamless tubes are produced from solid round billets by rotary piercing and then rolled in rolling mills that allow an extremely wide range of diameter/wall thickness ratios. The tube is then processed through a multi-pass downsizing mill and rotary classifier. Tube sections from the hot rolling mill are slowly air-cooled or moved directly to a unique isothermal annealing furnace to ensure uniform microstructural hardness that promotes excellent machinability. The process contrasts with traditional slow cooling furnaces, where the tube bundles are cooled. This can lead to changes in microstructure and hardness from tube to tube or even within the tube itself.

After cooling, the tubes were pickled in an acid bath to remove scale and inspected. Minor defects are removed by grinding before cold drawing and additional machining. During cold drawing, the tube is drawn in a controlled manner on a mandrel and through a die to reduce diameter and wall thickness. After forming, the tubes are subjected to stress relief annealing, straightening and cutting to length according to customer requirements. Finally, check the tube for dimensional accuracy and surface finish.

Cold working applied to inner and outer surfaces improves surface finish, increases tensile properties, improves machinability in many grades, and produces more precise dimensions.

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