Why does the Stainless Steel Tube Turn Yellow or Black after Bright Annealing?

  • By:At present, the application of stainless steel pipes in the market is very extensive, and it has a very important role in many industries. In order to ...
  • Date:2021/09/18

At present, the application of stainless steel pipes in the market is very extensive, and it has a very important role in many industries. In order to reduce the hardness of the pipe and improve the plasticity; refine the grains and eliminate the internal stress, so it must be annealed.

However, many users report that the annealed stainless steel tube is yellow or blue, and the expected brightening effect is not always achieved. How to solve this problem?

As a proffesional supplier of online tube type induction heating bright annealing furnace, the technical engineers of Hangao Tech (SEKO Machinery) will discuss with you:

1. The yellowing of the surface is due to the unstable heating temperature. That is, the surface temperature of the pipe is high, and the temperature in the pipe is low.

The reason is that the annealing temperature control, or the design of the annealing furnace temperature zone is problematic. The tube-type annealing furnaces on the market are mixed, and the price difference is also very large. It is difficult for users to distinguish good from bad. Some users simply pursue the low price but ignore the actual working quality of the bright annealing furnace. As a result, the quality of the annealed pipes cannot meet customer requirements. Moreover, not long after the equipment, various maintenance problems began to appear. Not only drags down the production schedule, but also spends a lot of money and manpower for maintenance.

2. Find the reason from the process flow and technology, which are related to the user's temperature setting, the cleanliness of the surface of the stainless steel tube, and the material of the stainless steel tube.

In order to solve the above problems and make the stainless steel tube bright after annealing, the main points are as follows:

1. The air tightness of the heating furnace, heat preservation section and cooling water jacket. This is the key factor for whether the stainless steel tube is bright.

2. Whether the structure of the annealing furnace, the distribution of the temperature zone, and the thermal field of the annealing furnace are reasonable. This directly affects the uniformity of heating of the stainless steel tube. The stainless steel tube must be heated to an incandescent state, but it cannot soften and sag.

3. The stainless steel pipe itself has excessive oil or water stains. In this way, the atmosphere in the furnace is destroyed, and the purity of the protective gas cannot be achieved.

4. Ensure the slight positive pressure of the atmosphere in the furnace, so that the air will not be sucked back like in the furnace. If it is ammonia decomposition mixed gas, it usually needs more than 20kBar.

I hope users pay attention to the above points. If the annealed stainless steel tube still does not achieve the expected results, please contact our company's technical department. We are happy to discuss solutions with you.




Guangdong Hangao Technology Co., Ltd.

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