Hot Extrusion Technology of Seamless Steel Tube
With the emergence of glass lubricants, the hot extrusion technology of seamless steel pipes has developed rapidly. At the same time, the problems of non-oxidative heating and service life of tools and dies have also been effectively solved with the development of seamless steel pipe hot extrusion technology. In recent years, my country has successively introduced and independently built a number of hot-extruded seamless steel pipe production lines for the production of high-end seamless steel pipes, which has greatly improved the hot-extrusion technology level of seamless steel pipes in my country.
［Key words］ glass lubricant; hot extrusion; seamless steel pipe; production line
Metal extrusion is a pressure forming method, which is to place a metal blank in a pressure-resistant container, and apply an external force to cause the metal to undergo plastic deformation under a three-dimensional compressive stress state. The metal is in a state of three-dimensional compressive stress during extrusion processing, so it can obtain larger plastic deformation than rolling and forging. According to different materials and extrusion methods, the extrusion coefficient can reach 5~500, or even higher [1] . Due to the characteristics of high dimensional accuracy, dense metal structure and stable mechanical properties of extruded products, hot extrusion technology is widely used in nuclear power, thermal power, petrochemical, aviation, aerospace, transportation and other fields.
- Current status of hot extruded steel pipe industry
In the 1950s , with the invention of glass lubricants, the extrusion technology of ferrous metals developed rapidly. The use of hot extrusion technology to produce seamless steel pipes has the advantages of stable product quality, flexible replacement of varieties, and low cost of tools and molds. It is suitable for the processing of stainless steel, special steel, and low-plasticity and difficult-to-deform materials. For high-temperature corrosion-resistant alloy pipes, stainless steel oil well pipes, duplex stainless steel pipes, urea-grade stainless steel pipes, high-parameter austenitic thermal power boiler pipes, etc., hot extrusion is a necessary production method. At present, there are more than 70 sets (sets) of steel extrusion units in the world , most of which are used to produce high-quality pipes. In the early 1970s in our country , Sichuan Jiangyou Great Wall Steel Works introduced a 31.5MN extrusion machine production line from the former West Germany, which is specially used to produce stainless steel and special alloy pipes and bars. At the beginning of the 21st century, Zhejiang Jiuli Group imported a 35MN extruder from the Italian company Danieli , and became the first private enterprise in China to specialize in the production of stainless steel pipes with an extruder. So far, several extrusion press production lines have been built and put into production, see Table 1 for details .
Hot extrusion process of steel pipe
- Support pad
- mold support
3. Die pad
4. Extrusion die
5. Extrusion cylinder lining
6. Perforating needle
7. Squeeze pad
8. Squeeze rod
9. Pin connector
1 0. Squeeze barrel lining
11. Outer lining of extrusion barrel
12. Blank
13. Glass mat
14. Mold set
15. Products
Hot extrusion process of steel pipe
Billet preparation f ring furnace preheating f vertical induction furnace heating f glass powder lubrication f vertical press punching (expanding) holes f dephosphorization f vertical induction furnace reheating f glass powder lubrication f extrusion f cutting and pressing f cooling The hot extrusion billet of steel pipe can be forging billet, rolling billet, continuous casting billet, centrifugal casting billet, etc. The long billet or short billet enters the extrusion production line after peeling, sawing off, drilling deep holes, turning end faces and chamfering in the processing workshop [2] .
The processed blanks must be degreased by a washing machine before being heated in an annular heating furnace, and then heated in an annular furnace. Generally, the blank is heated to within 9oor in the ring furnace . However, it can be directly heated to the hot extrusion temperature of steel according to the process requirements (suitable for direct extrusion of blanks that do not require hole expansion). Then enter the vertical induction heating furnace to heat up to the hot extrusion temperature of the material . After the heated billet is coated with glass powder on the outer circle on the powder spreading platform, the billet is put into the punching (expanding) hole cylinder by the manipulator, and then the glass powder is added into the "bell mouth" at the end of the billet, and then the Punching (expanding) holes on a punching machine. After punching (expanding) holes, the temperature drop of the hollow blank due to contact with the mold should be reheated, that is, reheated, but the glass powder on the surface of the blank affects the temperature detection during reheating, so that the heating temperature deviates, so generally in Before reheating, dephosphorization is carried out to remove the glass film on the surface of the billet, and then heating is carried out. After the heated billet is coated with glass powder on the inner and outer surfaces, it is sent to the center of the extruder by the ingot feeder for extrusion. After the extrusion is completed, the product and the excess are separated by a separation saw. Articles and tools require appropriate cold treatment.
In the whole extrusion production process, the non-oxidative heating of the billet, lubrication and the life of the tool and die are three important process problems affecting the steel extrusion technology.
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