Basic uses of precision tube

Precision tube is widely used in automobiles, motorcycles, electric vehicles, petrochemicals, electricity, ships, aerospace, bearings, pneumatic components, medium and low pressure boiler seamless steel pipes, etc. It can also be used in steel sleeves, bearings, hydraulics, mechanical processing and other fields!
 

Precision tube production process

The production process of precision steel pipe is the same as that of ordinary seamless pipes, except that there is an additional final pickling and cold rolling procedure.
 

Precision tube process flow

Pipe blank - inspection - peeling - inspection - heating - perforation - pickling and passivation - grinding - lubrication and air drying - cold rolling - degreasing - cutting - inspection - marking - finished product packaging
 

Differences between steel pipes

1. The main feature of seamless steel pipes is that they have no welding seams and can withstand greater pressure. The product can be a very rough cast or cold-drawn part.

2. Precision steel pipes are products that have appeared in recent years, mainly with strict tolerances and roughness for the inner hole and outer wall dimensions.
 

Features of precision tubes

1. Smaller outer diameter.

2. High precision can be produced in small batches.

3. Cold-drawn finished products have high precision and good surface quality.

4. The cross-sectional area of the steel pipe is more complex.

5. The steel pipe has better performance and the metal is denser.

Precision steel pipe calculation formula: [(outer diameter-wall thickness)*wall thickness]*0.02466=kg/m (weight per meter)
 

Heat treatment process

Prelude

Vacuum annealing of high-quality spring steel, tool steel, precision steel pipe wire, stainless steel products and titanium alloy materials can all be vacuum treated for bright annealing. The lower the annealing temperature, the higher the vacuum degree required. In order to prevent the evaporation of chromium and accelerate heat conduction, the carrier gas heating (insulation) method is generally used, and it is noted that nitrogen should not be used for stainless steel and titanium alloys but argon should be used.

Process

Vacuum quenching Vacuum quenching furnaces are divided into oil quenching and gas quenching according to the cooling method, and are divided into single-chamber and double-chamber types according to the number of workstations. 904 is a periodic operation furnace. Vacuum oil quenching furnaces are all double-chamber, with electric heating elements in the rear chamber and oil tanks at the bottom of the front chamber. After the workpiece is heated and insulated, it is moved into the front chamber. After closing the middle door, the inert gas is filled into the front chamber to about 2.66%26times;10～1.01%26times;10 Pa (200～760mm mercury column), and oil is added. Oil quenching can easily cause the surface of the workpiece to deteriorate. Due to the high surface activity, significant thin layer carburization can occur under the action of a short high-temperature oil film. In addition, the adhesion of carbon black and oil on the surface is very unfavorable to simplify the heat treatment process. The development of vacuum quenching technology mainly lies in the development of gas-cooled quenching furnaces with excellent performance and single stations. The aforementioned double-chamber furnace can also be used for gas quenching (jet cooling in the front chamber), but the double-station operation makes the production of large-scale furnace loading difficult, and it is also easy to cause workpiece deformation or change the orientation of the workpiece during high-temperature movement to increase quenching deformation. The single-station gas-cooled quenching furnace is jet-cooled in the heating chamber after heating and insulation. The cooling rate of gas cooling is not as fast as oil cooling, and is also lower than the molten salt isothermal and graded quenching in the traditional quenching method. Therefore, the mainstream of vacuum quenching technology development today is to continuously increase the pressure of the spray chamber, increase the flow rate, and use inert gases helium and hydrogen with smaller molar mass than nitrogen and argon. 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 that of oil cooling under normal pressure. In the mid-1980s, ultra-high pressure gas quenching appeared, using (10-20)%26times;10Pa helium, with a cooling capacity equal to or slightly higher than that of oil quenching, and has entered industrial practical use. In the early 1990s, 40%26times;10Pa hydrogen was used, which was close to the cooling capacity of water quenching and was still in its infancy. Industrially developed countries have progressed to high-pressure (5-6)%26times;10. Pa gas quenching as the main body, while the relationship between the vapor pressure (theoretical value) and temperature of some metals produced in China is still in the general pressurized gas quenching (2%26times;10Pa) stage.

Results Vacuum carburizing is a vacuum carburizing-quenching process curve. After heating to the carburizing temperature in a vacuum and keeping the temperature to purify and activate the surface, a rarefied carburizing enriched gas (see controlled atmosphere heat treatment) is introduced, and the infiltration is carried out under a negative pressure of about 1330Pa (10T0rr), and then the gas is stopped (pressure reduction) for diffusion. The precision steel pipe after carburizing is quenched by a single quenching method, that is, the power is turned off first, and the workpiece is cooled to below the critical point A, through nitrogen to make the internal phase change, and then the gas is stopped and the pump is turned on to raise the temperature to between Ac1, and Accm. The quenching method can be air cooling or oil cooling. The latter is to move into the front chamber after austenitization, fill nitrogen to normal pressure, and then add oil. The temperature of vacuum carburizing is generally higher than that of ordinary gas carburizing, and 920-1040℃ is often used. Infiltration and diffusion can be divided into two stages as shown, or pulse ventilation, gas stop, and multi-stage infiltration and diffusion can be used, which has a better effect. Due to the high temperature, especially the clean and active surface, the vacuum carburizing layer is formed faster than ordinary gas, liquid and solid carburizing. For example, if the carburizing layer is required to be 1mm, it only takes 5 hours at 927℃ and only 1 hour at 1033℃.