Why Is The Stainless Steel Tube Not Bright After Continuous Bright Gas Shielded Annealing Furnace Treatment

Some customers have asked questions about the non-brightness of stainless steel after annealing in the process of using stainless steel tube continuous bright annealing furnace.

Foshan Huichengsheng Mechanical Equipment Co., Ltd. specializes in industrial heat treatment industry and has more than 20 years of production experience. We have a wealth of experience with such issues.

Then the factors affecting the brightness of the stainless steel tube annealing furnace are as follows:

First, whether the annealing temperature reached the specified temperature. Stainless steel annealing furnace generally adopt solid solution heat treatment, which commonly called "annealing", and the temperature rang is 1040~1120 ℃ (Japan standard). It can through the observation hole of the annealing furnace, the stainless steel tubes in the annealing zone should be in an incandescent state, but no softening and sagging occurred.  

Second, the annealing atmosphere. Generally the ammonia decomposition gas (NH3) is used for annealing atmosphere, and the purity of the atmosphere is preferably 99.99% or more. If another part of atmosphere is an inert gas, the purity may be low, but it is absolutely impossible to contain too much oxygen and water vapor. 

Third, the seal ability of the furnace, the bright annealing furnace should be closed and isolated the outside air, if hydrogen is used for protection gas, the only one exhaust port is open(used to ignite the discharge hydrogen). The method of inspection can be applied to the gaps of the joints of the annealing furnace with soapy water to see if the gas is running. The most easy place to run the gas is the place where the annealing furnace enters the pipe and the place where the pipe is discharged. The sealing ring in this place is particularly prone to wear, thus should always check and change frequently.

Forth, the pressure of protection gas, in order to prevent the micro-leakage, the protection gas should maintain a positive pressure, if hydrogen is used for protection gas, the general demand is 20kBar or more. 

Fifth, water vapor in the furnace. On the one hand, check whether the material of the furnace body is dry. When the furnace is first installed, the material of the furnace body must be dried. Second, whether the stainless steel pipe entering the furnace has excessive water stains. If there is a hole in the pipe, do not leak water. Otherwise, the atmosphere of the furnace will be completely destroyed.

If these types of problems do not occur, the stainless steel pipe that should be annealing after about 20 minutes will start to illuminate, which is the kind of reflective bright.

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