In order to use fasteners better, we need regular maintenance when using fasteners, such as regular cleaning of fasteners, which can improve the efficiency of fasteners. But when we clean fasteners, we often find some problems, mainly six common problems.
1. Pollution during rinsing
After quenching, the fasteners were cleaned with silicate cleaning agent and then rinsed. XX solid substance appeared on the surface. This substance was analyzed by infrared spectrometer and proved to be inorganic silicate and iron oxide. This is due to the fact that silicate remains on the fastener surface due to incomplete rinsing.
2. Unreasonable stacking of fasteners
After the fasteners are tempered, there are signs of discoloration. Use soaking to allow oily residues to be found after volatilization. Such substances are high-content 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. These substances confirmed that the fastener surface was not clean. Infrared spectrometer analysis is a mixture of base oil and ether in quenching oil. The ether may come from the addition of quenching oil. The analysis result of the quenching oil in the mesh belt furnace confirms that the fasteners are unreasonably stacked when heated, and the fasteners are slightly oxidized in the quenching oil, but they are almost negligible. The problem.
3. Surface residue
There were white residues on the high-strength screws, which were analyzed by infrared spectrometer and confirmed to be phosphides. No acidic cleaning agent was used for cleaning, and the rinsing tank was checked to find that the bath liquid had a high carbon solubility. The bath liquid should be poured out regularly, and the concentration level of the lye in the rinsing tank should be regularly checked.
4. Alkali burns
The high-strength screw quenching waste heat blackening has a uniform and flat oil black outer surface. However, there is a visible area of orange XX in the outer circle. In addition, there are slightly visible areas of light blue or light red. The original bar and wire rod are coated with phosphating film to facilitate cold heading and tapping. Direct heat treatment without rinsing, cooling in quenching oil, cleaning with alkaline cleaning agent, blow drying (no rinsing), tempering at 550 ℃, heat Remove the immersion anti-rust oil from the tempering furnace and find red spots on the screw threads.
It has been detected that the red area on the screw is caused by alkali burn. The alkaline cleaning agent containing chloride and calcium compounds will burn steel fasteners during heat treatment, leaving marks on the fastener surface.
Iron and steel fasteners cannot remove the surface alkali in the quenching oil, so that the surface burns in the high-temperature austenite state, and the injury will be increased in the next tempering. The recommendation is to thoroughly clean and rinse the fasteners before heat treatment to completely remove the alkaline residues that cause fastener burns.
5. Improper rinsing
For large-sized fasteners, polymer aqueous solution is often used for quenching. Before quenching, they are washed and rinsed with alkaline cleaning agent. After quenching, the fasteners have rusted on the inside. Analysis with an infrared spectrometer confirmed that in addition to iron oxide, there are sodium, potassium, and sulfur, indicating that the alkaline cleaning agent adhered to the inside of the fastener, it is likely that potassium hydroxide, sodium carbonate, or similar substances, promote its rust. Check whether the fasteners are rinsed for excessive contamination, and it is also recommended to change the rinse water frequently. In addition, adding rust inhibitor to the water is also a good method.
6. Excessive corrosion
High-strength fasteners often see some black stripes.In the test, it was also seen that the fasteners before heat treatment were rinsed with inorganic and organic cleaning agents.After quenching, they still found black stripes and even carefully cleaned before the heat treatment. It will also leave streaks after heat treatment. Infrared spectrometer was used to analyze the residual pollutants on the surface, and it was found that the concentration of sulfur and calcium was higher. With a small amount of isopropyl alcohol in acetic acid, a small piece of test filter paper was foldd firmly on the black spots, leaving the black spots on the filter paper. The analysis of filter paper by infrared spectrometer confirmed that calcium, sulfur, iron, manganese and chromium were the main elements.
The presence of calcium and sulfur in the rust spots indicates that this substance is roasted and quenched oil, and it is also the evolution of gas phase during quenching. Because of the excessive aging of the quenching oil, it is recommended to pour out the old oil, add new oil, and implement process supervision and quenching oil maintenance throughout the entire process cycle.
Link to this article：Analysis Of Six Common Problems In Fastener Cleaning
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