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The Link Between Mirror Processing and Surface Roughness of Stainless Steel Tubes


Stainless steel pipes are usually required to achieve a certain brightness, that is, a higher surface roughness.

Most of the mirror processing methods for stainless steel tubes are mechanical polishing.

If high precision requirements are required in the polishing process, we generally use mirror processing or electrolytic polishing.

It can be divided into internal surface polishing and external surface polishing.

These two polishing methods are actually different to a certain extent.

What are the methods used in the polishing process?

1. Mechanical polishing

One is to use a polishing machine to polish the internal surface: use a polishing rod to stretch into the pipe to drive a thousand impellers or a self-made abrasive belt wheel to rotate at a high speed, and polish with the rotation of the stainless steel polishing pipe itself, and slowly move forward the polishing rod while rotating.

Generally speaking, rough polishing shall be carried out with 60 # – 80 # impeller or belt pulley, and then fine polishing shall be carried out with high precision gradually according to the requirements of finish.

Large-size pipes above 6 generally use thousand impellers, and small size pipes can use self-made abrasive belt wheels, which can reduce costs.

If you feel that the mechanical polishing is not bright enough, you can apply the polishing paste properly to increase the brightness.

One is to use the mirror processing equipment for processing: put the initially processed stainless steel tubes on the lathe, and use the mirror processing equipment for high-frequency impact processing, which has high efficiency and good effect, and can obtain a higher surface roughness than the traditional polishing machine.

The key is that this processing method has no dust and chips, and is clean and environmentally friendly.

2. Electropolishing

Electrolytic polishing takes the workpiece to be polished as the anode and the insoluble metal as the cathode.

The two poles are immersed into the electrolytic cell at the same time, and the DC current is used to generate selective anodic dissolution, so as to increase the brightness of the workpiece surface of the internally polished stainless steel polishing tube.

After polishing, because the surface oxide layer is damaged, it is better to passivate the surface with acid solution, otherwise it is easy to rust.

The mirror effect of stainless steel pipe is actually a form of stainless steel pipe fittings, because its surface roughness level is relatively high, the surface quality level can be as high as “8K“, which is as bright as the mirror, so it is called stainless steel mirror tube, and its surface roughness value is generally the following levels:

  • Mirror grinding: 0.01 ~ 0.08;
  • Super finishing: 0.01~0.04 of mirror surface;
  • Polishing, fine (mirror) polishing: 0.02 ~ 0.16.

The surface roughness of stainless steel mirror tube refers to the roughness of the machined surface with small spacing and small peaks and valleys.

The distance (wave distance) between two wave peaks or two wave troughs is very small (below 1mm), which belongs to micro geometric shape error.

The smaller the surface roughness, the smoother the surface.

Stainless steel tubes are mainly made of austenitic stainless steel, such as 0Cr18Ni9, 1Cr18Ni9Ti and so on.

Stainless steel mirror tubes are polished after the processing of these stainless steel tubes.

The processing technology is generally bright annealed.

It can be divided into seamless stainless steel bright annealed tubes and welded bright annealed tubes.

Seamless tubes are generally used in aviation, sensors, nuclear power instruments, etc.

Welding is usually used for decoration.

The stainless steel mirror tube is usually used on the oil pipe of the power plant, such as the EH oil pipe of the steam turbine.

Stainless steel mirror tube is mainly made of stainless steel.

It is a product with 8K surface quality different from other stainless steel tubes after many times of polishing by different processes.

Therefore, we need to pay special attention to it in daily use and purchase.

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