Seamless pipes are manufactured by punching a steel ingot or solid pipe, followed by hot rolling, cold rolling, or cold drawing processes. In China's steel pipe industry, seamless pipes hold a significant position. According to incomplete statistics, there are approximately 240 production enterprises dedicated to seamless pipes, with around 250 sets of production units. The annual production capacity reaches about 4.5 million tons. In terms of size distribution, pipes with diameters less than φ76 account for 35%, while those between φ159 and φ650 make up 25%. Regarding product types, general-purpose pipes amount to 1.9 million tons, representing 54% of the total. Petroleum pipes reach 760,000 tons, or 5.7%, while hydraulic props and precision pipes together account for 150,000 tons, or 4.3%. Stainless steel pipes, bearing pipes, and automobile pipes collectively reach 50,000 tons, making up 1.4% of the market.
The raw material used in the production of seamless tubes is a round billet. This billet is cut to a length of approximately one meter using a cutting machine and then transported via conveyor belt into a furnace for heating. The billets are heated to around 1,200 degrees Celsius, typically using hydrogen or acetylene as fuel. Maintaining precise temperature control in the furnace is critical for ensuring consistent quality. Once heated, the billets are fed into a piercing machine, with the most common type being the conical roller piercer. This machine offers high efficiency, excellent product quality, and can handle a wide range of steel types with large perforation diameters.
After piercing, the round billet undergoes rolling, rolling, or extrusion through three rolls. Following this, the sizing process begins. A sizing machine drills into the steel die at high speed, forming the final shape of the steel pipe. The inner diameter of the pipe is determined by the outer diameter of the sizing tool. Once sized, the pipe is sent to a cooling tower, where it is cooled by water spraying. After cooling, the pipe must be straightened to ensure uniformity.
Once straightened, the pipe is conveyed to a metal detector or undergoes a hydraulic pressure test for internal inspection. Any defects such as cracks or air bubbles will be detected during this stage. After passing the quality inspection, each pipe undergoes manual sorting to ensure only top-quality products proceed. Finally, the pipe is marked with its serial number, specifications, and production batch number before being lifted into the warehouse by a crane.
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