Industry News

Analysis of six common problems in fastener cleaning

2021-06-18
In order to better use fasteners, when we use fasteners, we need regular maintenance, such as regular cleaning of fasteners, which can improve the efficiency of fasteners. But when we clean the fasteners, we often find some problems, mainly there are six common problems.
1. Pollution generated during rinsing
After the fasteners were quenched, they were cleaned with silicate cleaning agent and then rinsed. Solid materials appeared on the surface. The infrared spectrometer was used to analyze this material and it was confirmed to be inorganic silicate and iron oxide. This is caused by the incomplete rinsing and residual silicate on the surface of the fastener.

2. Unreasonable stacking of fasteners
Fasteners show signs of discoloration after tempering. Use soaking to allow oily residue to remain after volatilization, which is a high content of lipids. It shows that the fastener is contaminated by cleaning agent and quenching oil during the rinsing period, and it melts at the heat treatment temperature, leaving chemical burn scars. Such substances confirm that the surface of the fastener is not clean. Analyzed by infrared spectrometer, it 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 confirmed that the fasteners are slightly oxidized in the quenching oil due to unreasonable stacking when heating, but it is almost negligible. This phenomenon is related to the cleaning process, not the quenching oil. The problem.


3. Surface residues

There is a white residue on the high-strength screw, which was analyzed by infrared spectrometer and confirmed to be phosphide. No acidic cleaning agent cleaning was carried out, and the inspection of the rinsing tank found that the tank liquid had a higher carbon solubility. The tank liquid should be poured out regularly, and the concentration level of the lye in the rinsing tank should be checked frequently.

4. Alkali burns
High-strength screws are blackened by quenching heat and have a uniform and smooth oil-black outer surface. However, there is an area visible to the naked eye with orange XX in the outer circle. In addition, there are areas that are slightly light blue or light red. The original bar and wire rod are coated with phosphating film to facilitate cold heading and tapping. They are directly heat treated without rinsing, cooled in quenching oil, cleaned with alkaline detergent, blow-dried (not rinsed), tempered at 550°C, hot After removing the anti-rust oil from the tempering furnace, red spots were found on the screw threads.
It has been tested 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 scars on the surface of the fasteners.
Iron and steel fasteners cannot remove surface alkalis in the quenching oil, so that the surface burns in the high-temperature austenite state and aggravates the damage during the next step of tempering. The recommendation is to thoroughly clean and rinse the fasteners before heat treatment to completely remove the alkaline residues that cause the fasteners to burn.


5. Improper rinsing

For large-size fasteners, polymer aqueous solution is often used for quenching, and alkaline cleaning agent is used to clean and rinse before quenching. After quenching, the fasteners have rusted on the inside. Analysis with infrared spectrometer confirmed that in addition to iron oxide, there are sodium, potassium and sulfur, indicating that there is an alkaline cleaning agent on the inside of the fastener, which is likely to be potassium hydroxide, sodium carbonate or similar substances, which promotes its rust. Rinse the fasteners to check whether there is excessive contamination, and it is also recommended to change the rinse water frequently. In addition, adding rust inhibitors to the water is also a good way.

6. Excessive corrosion
Some black stripes are often seen in high-strength fasteners. It has also been seen in the test that the fasteners before the heat treatment have been rinsed with inorganic and organic cleaning agents. After quenching, there are still black stripes and even careful cleaning before heat treatment. , Will also leave streaks after heat treatment. Infrared spectrometer was used to analyze the residual pollutants on the surface, and it was found that there were higher concentrations of sulfur and calcium. With a small amount of acetic acid and isopropanol, fold a small piece of test filter paper on the dark spot and wipe it firmly, leaving the dark spot on the filter paper. Analysis of the 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 quenching oil that has dried out, and it is also the evolution of vapor phases during the quenching process. Because the quenching oil is excessively aging, it is recommended to pour out the old oil, add new oil, and implement process supervision and quenching oil maintenance during the entire process cycle.


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