To use fasteners better, we need regular maintenance […]
To use fasteners better, we need regular maintenance when using China 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 generated during rinsing
After quenching, the fasteners were washed with a silicate cleaning agent and then rinsed. XX solid substance appeared on the surface. The substance was analyzed by an infrared spectrometer and proved to be inorganic silicate and iron oxide. This is because 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 results of the quenching oil in the mesh belt furnace confirm that the fasteners are unreasonably stacked when heated, and the fasteners are slightly oxidized in the quenching oil, but they are almost negligible. This phenomenon is related to the cleaning process, not quenching oil. The problem.
3. Surface residues
There were white residues on the high-strength screws, which were analyzed by the infrared spectrometer and confirmed to be phosphides. No acidic cleaning agent was used for cleaning, and the rinsing tank was inspected and found that the bath liquid had a high carbon solubility. The bath liquid should be drained 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. Also, there are slightly visible areas of light blue or light red. The original bar stock 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 the alkaline cleaning agent, blow-drying (no rinsing), tempering at 550℃, heat Remove the impregnated rust-proof 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 burns. The chloride-containing substances and calcium-containing compounds of the alkaline cleaning agent will burn the steel fasteners during the heat treatment, leaving marks on the surface of the fasteners.
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 rinses the fasteners before heat treatment to completely remove the alkaline residues that cause fastener burns.
5. Improper rinsing
For large-size fasteners, polymer aqueous solution is often used for quenching. Before quenching, it is cleaned and rinsed with an alkaline cleaning agent. 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 the alkaline cleaning agent is stuck on the inside of the fastener, which is likely to be potassium hydroxide, sodium carbonate, or similar substances, which promotes its rust. Check whether the fasteners are rinsed for excessive contamination, and it is also recommended to change the rinse water frequently. Adding rust inhibitor to the water is also a good way.
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. The infrared spectrometer was used to analyze the remaining contaminants 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 vigorously folded on the black spots, leaving the black spots on the filter paper. The analysis of the filter paper by 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 roasted and quenched oil, and the evolution of the 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.