Analysis of 6 common problems in fastener cleaning

In order to better use of fasteners, we need to regularly maintain them when using fasteners, such as regularly cleaning the fasteners, which can improve the efficiency of the fasteners. However, when cleaning the fasteners, we often find some problems, mainly 6 common problems.

1. Contamination caused during rinsing

After the fastener is quenched, cleaned with a silicate cleaner and then rinsed. XX solid substance appears on the surface. This substance is analyzed with an infrared spectrometer and confirmed to be inorganic silicate and iron oxide. This is caused by incomplete rinsing. Silicate remains on the surface of the fastener.

2. The fastener stacking is unreasonable

There are signs of discoloration after the fastener is tempered. Soaked to make oily residues remain after evaporation. This type of substance is a high-content lipid substance. It means that the fastener is contaminated by cleaning agents and quenching oils during the rinsing period, melting at the heat treatment temperature, leaving chemical burning scars. Such substances confirm that the surface of the fastener is unclean. Analysis with an infrared spectrometer is a mixture of base oil and ether in the quenching oil. The ether may come from additives of quenching oil. The analysis results of the quenching oil in the mesh belt furnace confirm that due to unreasonable stacking of the fastener, the fastener has slight oxidation in the quenching oil, but it is almost negligible. This phenomenon is related to the cleaning process, rather than the problem of quenching oil.

3. Surface residues

There is a white residue on the high-intensity screw. It is analyzed with an infrared spectrometer and confirmed that it is a phosphide. There is no acid cleaning agent cleaning. The rinsing tank is not cleaned. It is found that the tank liquid has a high carbon solubility. The tank liquid should be poured out regularly and the concentration level of the alkali liquid in the rinsing tank is often detected.

4. Alkali burns

The quenching waste heat of high-strength screws has a uniform and flat outer surface with an oil-black surface. However, there are areas visible to the outer rings of orange XX. In addition, there are areas with a slightly light blue or light red visible. The original bar material and the strip are coated with phosphated film to facilitate cold heading and tapping. They are heat-treated without rinsing, and are cooled in the quenching oil, cleaned with alkaline cleaning agent, blow-dry (not rinsed), and tempered at 550 degrees Celsius. The anti-rust oil is taken out from the tempering furnace in a hot state, and red spots are found at the screw threads.

The red area on the test screw is caused by alkali burns. The alkaline cleaning agent contains chloride substances and calcium-containing compounds will burn the steel fastener during heat treatment, leaving spots on the surface of the fastener.

Steel fasteners cannot remove surface alkaline substances in quenching oil, thereby burning the surface in high temperature austenite state and aggravating the damage during the next step of tempering. It is recommended to thoroughly clean and rinse the fasteners before heat treatment to completely remove alkaline residues that cause the fasteners to burn.

5. Improper rinsing

Large-sized fasteners are often quenched by polymer aqueous solution. Before quenching, they are cleaned and rinsed with alkaline cleaning agent. After quenching, the fasteners have rusted on the inside. An infrared spectrometer is used for analysis and confirmed that in addition to iron oxide, there are also sodium, potassium and sulfur, which means that an alkaline cleaning agent is adhered to the inside of the fastener, which is likely to be potassium hydroxide, sodium carbonate or similar substances to promote rust. Check the fastener rinsing for excessive contamination. It is also recommended to change the rinsing water frequently. In addition, adding anti-rust agent to the water is also a good method.

6. Excessive rust

High-strength fasteners often see some black stripes. In the experiment, they were also seen that they used inorganic and organic cleaning agents to rinse the fasteners before heat treatment. After quenching, they still found that there were still black stripes or even carefully cleaned before heat treatment. They would leave stripes after heat treatment. An infrared spectrometer was used to analyze the pollutants remaining on the surface and found that there was a higher concentration of sulfur and calcium. Use a small amount of isopropanol of acetic acid to wipe a small piece of test filter paper hard on the dark spots to leave the dark spots on the filter paper. The filter paper was analyzed with an infrared spectrometer to confirm 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 a dried quenching oil, which is also the evolution of the gas phase during the quenching process. Because the quenching oil is over-aging, it is recommended to pour out old oil, add new oil, and perform process supervision and quenching oil maintenance during the entire process cycle.

Source: Quick Information)