Solution to the deformation of seamless black steel pipe during the production process

Seamless black steel pipe is uncoated steel, also known as black steel. The dark color comes from iron oxides that form on its surface during the manufacturing process. When steel pipe is forged, a black oxide scale forms on its surface, giving it the finish seen on this type of pipe.

Causes

The main reason for the deformation of the black steel pipe during the production process is that the quality of the pipe material is not good, there is deformation in itself, or there are inclusions, serious scratches and cracks on the surface, there are edges and corners at the grinding place, and deformation occurs after drawing and stretching. In order to avoid deformation, the quality of pipe material should be improved and attention should be paid to inspection and grinding.

 Solution

1. Free correction and mold correction

Free correction is to place black steel pipe fittings on a flat plate or a special simple tire mold, and beat them with a hammer until the size and shape meet the requirements. Mostly used for small and medium pieces. Large castings are generally corrected on designated correcting equipment. Before rectification, the deformation law of the casting should be mastered, and the necessary correcting molds suitable for the geometric shape and size of the rectified part of the casting should be equipped. Mold correction is to place the casting in the forming mold (generally divided into upper and lower molds), and use the selected pressure on the selected straightening machine to correct the casting as a whole. During overall correction, lifting equipment or manipulators are generally used to load or remove castings from the correction mold. The straightening mold for overall straightening needs to be specially designed and manufactured, with high precision requirements, suitable for mass assembly line production, high production efficiency, low labor intensity, and small dimensional deviation of the straightened castings.

2. Cold straightening and hot straightening

Cold straightening is the straightening of normal temperature castings by hammering, manual presses, jacks, friction presses or hydraulic presses. It is suitable for medium and small thin-walled castings with simple geometric shape and small deformation, or as-cast aluminum alloy castings with large deformation but good plasticity, and quenched aluminum alloy castings with large deformation. When the casting structure is complex, it can be corrected with the help of a correcting mold. Thermal correction is divided into local heating and overall heating. When it is difficult to straighten some black steel pipe fittings by cold, it can be corrected by hammering or pressing after local heating. Thick-walled large castings should be rectified by overall heating. Before rectification, measure the amount of deformation that needs to be corrected, and then place them on the pad iron in the heat treatment furnace, and place appropriate pads on them. Appropriate load is applied on the part to be corrected, and the deformation is corrected by the action of load during heat treatment

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