Square tube quality must control the brightness after annealing. More influential factors are as follows:
1, The annealing temperature reaches the specified temperature.
Stainless steel tube heat treatment is generally taken by solution heat treatment, which is commonly known as the "annealing", the temperature range of 1040 ~ 1120 ℃ (Japanese standard). You can also observe through the annealing furnace observation hole, annealing the square tube should be incandescent, but did not appear softening sagging.
2, Annealing atmosphere. Pure hydrogen is generally used as the annealing atmosphere, the atmosphere is the best purity of 99.99% or more, if the atmosphere is the other part of the inert gas, the purity can be lower, but absolutely can not contain too much oxygen, water vapor.
3, Furnace sealing. Bright annealing furnace should be closed, isolated from the outside air; the use of hydrogen as a protective gas, only one exhaust port is open (used to ignite the discharge of hydrogen). Check the method can use soapy water in the joints of the annealing furnace gap to see whether run gas; where the most easy gas is the place where the annealing furnace into the tube and out of the tube, the sealing ring of this place is particularly vulnerable to wear and tear, always check often change.
4, The protection of gas pressure. In order to prevent the occurrence of micro-leakage, the furnace protective gas should maintain a certain positive pressure, if it is hydrogen gas, generally require more than 20kBar.
5, The water vapor inside the furnace. On the one hand, check the furnace material is dry, the first furnace, the furnace material must be dried; the second is into the furnace tube is too much residual water stains, especially if the tube above the hole, do not leak into it, Otherwise, the atmosphere of the furnace will be completely destroyed.
