Introduction to precision steel pipes and advantages of precision steel pipes
What is precision steel tube
Precision steel tube is a high-precision steel tube material processed by cold drawing or hot rolling. Because the inner and outer walls of precision steel pipes have no oxide layer, high pressure without leakage, high precision, high smoothness, cold bending without deformation, flaring, flattening without cracks, etc., they are mainly used to produce pneumatic or hydraulic components, such as cylinders or The oil cylinder can be a seamless tube or a welded tube.
Basic use of precision steel pipe
Precision steel pipes are widely used in automobiles, motorcycles, electric vehicles, petrochemicals, electric power, ships, aerospace, bearings, pneumatic components, seamless steel pipes for medium and low pressure boilers, etc., and can also be applied to steel sleeves, bearings, hydraulics, machining, etc. field!
Precision steel pipe production process
The production process of precision steel pipes is the same as that of ordinary seamless pipes, with the addition of a final pickling and cold rolling process.
Precision steel pipe process
Tube billet——inspection——peeling——inspection——heating——piercing——pickling passivation——grinding——lubrication and air drying——cold rolling——degreasing——cutting——inspection——marking——Product packaging
Steel pipe difference
1. The main feature of seamless steel pipe is that it has no welded seam and can withstand greater pressure. The product can be rough cast or cold drawn parts.
2. Precision steel pipe is a product that has appeared in recent years, mainly because the inner hole and outer wall dimensions have strict tolerances and roughness.
Features of precision steel pipe
1. The outer diameter is smaller.
2. High precision can be produced in small batches.
3. The cold-drawn finished product has high precision and good surface quality.
4. The horizontal area of the steel pipe is more complicated.
5. The performance of the steel pipe is superior, and the metal is denser.
3. The cold-drawn finished product has high precision and good surface quality.
4. The horizontal area of the steel pipe is more complicated.
5. The performance of the steel pipe is superior, and the metal is denser.
The calculation formula of precision steel pipe: [(outer diameter-wall thickness)*wall thickness]*0.02466=kg/m (weight per meter)
Heat treatment process
Prelude
Vacuum annealing high-quality spring steel, tool steel, precision steel pipe wire, stainless steel products and titanium alloy materials, can be vacuum treated for bright annealing. The lower the annealing temperature, the higher the degree of vacuum required. In order to prevent the evaporation of chromium and accelerate the heat transfer, the carrier gas heating (heat preservation) method is generally used, and attention should be paid to the use of argon instead of nitrogen for stainless steel and titanium alloys.
process
Vacuum quenching vacuum quenching furnace is divided into oil quenching and gas quenching according to the cooling method. According to the number of stations, it is divided into single-chamber and double-chamber. Vacuum oil quenching furnaces are all double-chambers, with electric heating elements in the back chamber and an oil tank under the front chamber. After the workpiece is heated and insulated, it is moved into the front chamber. After closing the middle door, fill the front chamber with inert gas to approximately 2.66%26times; 10～1.01%26times; 10 Pa (200～760mm Hg), and then oil. Oil quenching can easily cause surface deterioration of the workpiece. Due to the high surface activity, significant thin-layer carburization can occur under the action of a short-term high-temperature oil film. In addition, the adhesion of carbon black and oil on the surface is not good for simplifying the heat treatment process. The development of vacuum quenching technology mainly lies in the development of an air-cooled quenching furnace with excellent performance and a single station. The aforementioned double-chamber furnace can also be used for gas quenching (jet cooling in the front chamber), but the double-station operation makes it difficult to produce large quantities of furnaces, and it is also easy to cause deformation of the workpiece during high temperature movement or change the orientation of the workpiece to increase quenching Deformed. The single-station air-cooled quenching furnace is air-jet cooled in the heating chamber after the heating and heat preservation are completed. The cooling rate of air cooling is not as fast as that of oil cooling, and it is also lower than the molten salt isothermal and staged quenching in the traditional quenching method. Therefore, continuously increasing the pressure of the spray cooling chamber, increasing the flow rate, and using the inert gases helium and hydrogen whose molar mass is smaller than that of nitrogen and argon are the mainstream of the development of vacuum quenching technology today. In the late 1970s, the pressure of nitrogen spray cooling was increased from (1～2)%26times;10Pa to (5～6)%26times;10Pa, making the cooling capacity close to oil cooling under normal pressure. Ultra-high pressure gas quenching appeared in the mid-1980s, using (10～20)%26times; 10Pa helium, the cooling capacity is equal to or slightly higher than oil quenching, and has entered industrial application. In the early 1990s, 40% 26times; 10Pa hydrogen was used, which was close to the cooling capacity of water quenching, and it was still in its infancy. Industrial developed countries have progressed to high pressure (5 ~ 6)%26times;10. Pa gas quenching is the main body, while the relationship between vapor pressure (theoretical value) and temperature of some metals produced in China is still in the general pressure gas quenching (2%26times; 10Pa) stage.
The result of vacuum carburizing is a vacuum carburizing-quenching process curve. After heating to the carburizing temperature in a vacuum and keeping it warm to purify and activate the surface, pass in a thin carburizing enriched gas (see Controlled Atmosphere Heat Treatment), infiltrate under a negative pressure of about 1330Pa (10T0rr), and then stop the gas (depressurization) ) To spread. The precision steel pipe quenching after carburizing adopts one-time quenching method, namely, power off first, and nitrogen to cool the workpiece to below the critical point A, so that the internal phase change occurs, then stop the gas, turn on the pump, and raise the temperature to between Ac1 and Accm. The quenching method can be air-cooled or oil-cooled. The latter is austenitized and moved into the front chamber, filled with nitrogen to normal pressure, and filled with oil. The temperature of vacuum carburizing is generally higher than that of ordinary gas carburizing. Infiltration and diffusion are often used at 920～1040℃. The infiltration and diffusion can be divided into two stages as shown. Pulse ventilation and gas stop can also be used. . Due to the high temperature, especially the surface is clean and active, the vacuum carburizing layer is formed faster than ordinary gas, liquid and solid carburizing. If the carburized layer is required to be 1mm, it only takes 5h at 927℃ and 1h at 1033℃.
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Reference source: Internet
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Post time: Sep-02-2021