Extrusion method refers to the metal billet is placed in a "closed" container composed of an extrusion cylinder, an extrusion die and an extrusion rod, and the pressure exerted by the extrusion rod forces the metal to flow out of the extrusion die hole, and the metal plastic forming method is obtained, which is a time-rich seamless steel pipe manufacturing method. According to the relative relationship between the direction of force applied by the extrusion rod and the direction of metal flow, the extrusion method can be divided into two kinds: positive extrusion and reverse extrusion. The direction of force applied by positive extrusion is consistent with the direction of metal flow, and the reverse extrusion is opposite. Reverse extrusion has the advantages of small extrusion pressure, large extrusion ratio, fast extrusion speed, reducing extrusion temperature, improving extrusion conditions, easy to achieve isothermal/isobaric/isobaric extrusion, improving product microstructure and dimensional accuracy, reducing metal pressure margin at the end of extrusion, improving metal yield, etc. However, its operation is relatively inconvenient, and the section size of the product is limited by the size of the extrusion rod.
The application of metal extrusion technology in industry has more than 100 years of history, but the use of steel hot extrusion technology in production was gradually developed after the invention of glass extrusion lubricant in 1941, especially the development of non-oxidation heating, high-speed extrusion technology, mold materials, and advances in tension reduction technology, making the production of seamless steel pipes more economical and reasonable. The output and quality have been greatly improved, and the range of varieties has been further expanded, thus attracting the attention of all countries.
At present, the product range of seamless steel pipe produced by extrusion method is generally: outer diameter: 18.4 ~ 840mm, the minimum wall thickness can reach 2mm, the length is about 15m, and the small diameter pipe can get 60m steel pipe. The capacity of the extrusion machine is generally 2000 ~ 4000 tons, and the maximum is 12000 tons.
Extruded seamless steel pipe production has the following advantages over other hot rolling methods:
Because the extruded metal is in a state of three-way compressive stress, it can produce materials that are difficult or unrollable and forging, such as nickel-based alloys.
Due to the large amount of metal deformation during extrusion (extrusion ratio is large), the complete deformation is completed in a short time, so that the organization of the product is uniform and the performance is good.
The internal and external surface defects are less, and the geometric size accuracy is higher.
Flexible organization and production, suitable for small batch, multi-variety production.
Can produce complex section pipe and bimetal composite pipe.
For the production of special purpose steel pipe products, such as nuclear industry, aerospace and so on
The disadvantages are:
1) High requirements for lubricants and heating, resulting in increased production costs.
2) Low tool life, large consumption, and expensive.
3) The qualified rate of finished products is low
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