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Six common problems when cleaning fasteners

        In order for fasteners to be used better, we need to carry out regular maintenance when using fasteners, such as regular cleaning of fasteners, which can improve the efficiency of fastener use. However, when we clean fasteners, we often find some problems. There are six common problems.
 
 
1.Contamination during rinsing
 
After the fastener is quenched, it is washed with a silicate cleaning agent and then rinsed. An XX solid substance appears on the surface. This substance is analyzed with an infrared spectrometer and it is confirmed that it is an inorganic silicate and iron oxide. This is caused by silicate remaining on the surface of the fastener due to incomplete rinsing.
 
2. Unreasonable stacking of fasteners
 
There are signs of discoloration after the fastener is tempered. Soak in ether, and let the ether volatilize, and you will find an oily residue, which is a high content of lipids. It shows that the fasteners were contaminated by cleaning agents and quenching oils during the rinsing period, and melted at the heat treatment temperature, leaving chemical burn scars. Such substances confirm that the surface of the fasteners is not clean. It is analyzed by infrared spectrometer and it is a mixture of base oil and ether in quenching oil. Ethers may come from the addition of quenching oil. The analysis results of the quenching oil in the mesh belt furnace confirmed that the fasteners were slightly oxidized in the quenching oil due to irrational stacking when the fasteners were heated, but it was almost negligible.This phenomenon was related to the cleaning process, not the quenching oil. of
problem.
 
3.Surface residue
 
White residues on the high-strength screws were analyzed by infrared spectrometer and confirmed to be phosphides. No acid detergent was used for cleaning, and the rinsing tank was inspected and found that the bath had a high carbon solubility. The tank solution should be drained regularly, and the concentration of the lye in the rinsing tank should be checked frequently.
 
4. Alkali burns
 
High-strength screw quenching after heat blackening has a uniform, flat oil black outer surface. But there are visible areas of orange XX in the outer circle. In addition, there are areas that are slightly light blue or red. The original bar and wire rod are coated with a phosphating film to facilitate cold upsetting and tapping. They are directly heat treated without rinsing, cooled in quenching oil, washed with an alkaline cleaner, blow dried (no rinsing), tempered at 550 ° C, and heated. Take out the anti-rust oil from the tempering furnace and find red spots on the screw threads.
It was detected that the red area on the screw was caused by alkali burns. The alkaline cleaning agents containing chloride substances and calcium compounds would burn steel fasteners during heat treatment, leaving marks on the surface of the fasteners.
Steel fasteners in the quenching oil can not remove the surface alkalis, which will burn the surface in the high temperature austenite state, and increase the damage during the next tempering. The recommendation is to thoroughly wash and rinse the fasteners before heat treatment to completely remove the alkaline residues that cause the fasteners to burn.
 
5. Improper rinsing
 
For large-scale fasteners, polymer aqueous solutions are often used for quenching. Before quenching, they are washed and rinsed with alkaline cleaning agents. After quenching, the fasteners have rusted on the inside. Analysis by infrared spectrometer confirmed that in addition to iron oxide, there are sodium, potassium and sulfur, indicating that there is an alkaline cleaning agent stuck to the inside of the fastener, which is likely to be potassium hydroxide, sodium carbonate or similar substances, which promotes rust. Check the fastener for rinsing for excessive contamination. It is also recommended to frequently change the rinsing water. It is also a good idea to add rust inhibitors to the water.
 
6.Excessive rust
 
High-strength fasteners often see some black streaks. I also saw in the tests that inorganic and organic cleaning agents were used to rinse the fasteners before heat treatment. After quenching, it was still found that there were still black stripes and even the fine cleaning of the puppets before heat treatment. It will also leave streaks after heat treatment. An infrared spectrometer was used to analyze the residual pollutants on the surface, and it was found that sulfur and calcium were present in higher concentrations. With a small amount of acetic acid in isopropanol, a small piece of test filter paper was strongly folded at the dark spots, leaving the dark spots on the filter paper. Analysis of filter paper with infrared spectrometer confirmed that calcium, sulfur, iron, manganese and chromium are the main elements.
 
The presence of calcium and sulfur in the rust spots indicates that this substance is a dried quenching oil, and it is also the evolution of gaseous materials during the quenching process. Because the quenching oil is excessively aged, it is recommended to pour out the old oil, add new oil, and perform process supervision and quenching oil maintenance during the entire process cycle.
 
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