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In order to use fasteners better, we need to maintain them regularly when using them, such as cleaning them regularly, 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 the fastener is quenched, it is cleaned with silicate cleaner, then rinsed, and XX solid substance appears on the surface. The substance is analyzed by infrared spectrometer, and it is confirmed that it is inorganic silicate and iron oxide. This is due to the residual silicate on the fastener surface due to incomplete rinsing.
2. Unreasonable stacking of fasteners
There is discoloration sign after tempering of fasteners. Soak the fasteners to make them volatilize and find the remaining oily residues. These substances are high content lipids. It indicates that the fastener is polluted by cleaning agent and quenching oil during the rinsing period, and melts under the heat treatment temperature, leaving chemical burn scars, which proves that the fastener surface is not clean. The mixture of base oil and ether in quenching oil is analyzed by infrared spectrometer. The ether may come from the addition of quenching oil. The analysis results of quenching oil in the mesh belt furnace show that there is slight oxidation in the quenching oil due to unreasonable stacking of fasteners during heating, but it can be almost ignored. This phenomenon is related to the cleaning process, rather than the problem of quenching oil.
3. Surface residue
There is white residue on the high strength screw, which is proved to be phosphide by infrared spectrometer. No acid cleaner cleaning was carried out, and the rinsing tank was found to have high carbon solubility through inspection. The tank solution should be regularly poured out, and the concentration level of alkali solution in the rinsing tank should be regularly detected.
4. Alkali burn
The blackening of high-strength screws after quenching has a uniform and flat oil black outer surface. But in the outer circle there is a visible area of orange XX. In addition, light blue or light red areas can be seen. The original rod and wire rod are coated with phosphating film to facilitate cold heading and tapping. They are directly heat-treated without rinsing. They are cooled in quenching oil, cleaned with alkaline detergent, dried (without rinsing) and tempered at 550 ℃. The hot state is taken out of the tempering furnace and soaked with antirust oil. As a result, red spots are found on the screw threads.
It is found that the red area on the screw is caused by alkali burn. The alkali cleaner containing chloride and calcium compound will burn the steel fastener during heat treatment, leaving marks on the fastener surface.
The surface basicity of iron and steel fasteners can not be removed in the quenching oil, so that the surface burns in the high temperature austenite state, and the damage is aggravated in the next step of tempering. It is recommended that fasteners be thoroughly cleaned and rinsed before heat treatment to completely remove the alkaline residues that cause burns to fasteners.
5. Improper rinsing
For large-scale fasteners, polymer water solution is often used for quenching. Before quenching, alkaline detergent is used for cleaning and rinsing. After quenching, the fasteners are rusted inside. It is confirmed that there are sodium, potassium and sulfur in addition to iron oxide by infrared spectrometer. It is indicated that there is alkaline cleaner on the inside of fastener, which is likely to be potassium hydroxide, sodium carbonate or similar substances to promote its rust. Check whether there is excessive pollution in the rinsing of fasteners. It is also recommended to change the rinsing water frequently. In addition, it is a good way to add antirust agent into water.
6. Excessive rusting
Some black stripes are often seen in high-strength fasteners. It is also seen in the test that the fasteners before heat treatment were rinsed with inorganic and organic cleaning agents. After quenching, it is still found that there are still black stripes, even the fine cleaning of the pre heat treatment, which will leave stripes after heat treatment. The residual pollutants on the surface were analyzed by infrared spectrometer. It was found that sulfur and calcium were in high concentration. Using a small amount of isopropanol acetate, fold and wipe a small piece of test filter paper at the black spot, and leave the black spot on the filter paper. The main elements of filter paper are calcium, sulfur, iron, manganese and chromium.
The presence of calcium and sulfur in the rust spot indicates that the substance is a dried quenching oil and the evolution of the gas phase in the quenching process. Because the quenching oil is over aged, it is recommended to pour out the old oil, add new oil, and implement process supervision and quenching oil maintenance in the whole process cycle.