What should be paid attention to when cleaning fasteners

Update:29 Dec 2020
Summary:

In order to better use fasteners(https://www.yyjfhardwa […]

In order to better use fasteners(https://www.yyjfhardware.com/), regular maintenance is required during use, such as regular cleaning, to improve its efficiency. However, when we clean, we often find some problems. Here are the six major problems for everyone:

1. Surface residue

There is a white residue on the high-strength screw, and the infrared spectrometer is used to analyze and check that the residue is phosphide. No acidic detergent was used for cleaning, and the rinse tank was checked to find that the tank liquid had carbon solubility. The bath should be poured out regularly, and the concentration level of the lye in the rinse tank should be checked frequently.

2. Unreasonable stacking of fasteners

After the fastener is tempered, there are signs of discoloration. Soak them in ether. After the ether had evaporated, an oily residue was found. These substances are high in lipids. The results showed that it was contaminated by detergent and quenching oil during rinsing, and melted at the heat treatment temperature, leaving traces of chemical combustion. The surface of these materials is 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 and inspection of the quenching oil in the mesh belt furnace confirmed that it would stack up unreasonably during heating, and there were traces of slight oxidation in the quenching oil, which were almost negligible. This phenomenon is related to the cleaning process, not the quenching oil. problem.

3. Alkali combustion

The high-strength screw has a uniform and flat oil-black outer surface after the heat of quenching. However, there is a visible area of ​​the courseware in the outer circle. In addition, there are some 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. They are directly heat treated without rinsing, cooled in quenching oil, cleaned with alkaline cleaning agent, blow-dried (not rinsed), and returned at 550°C. When heating, take out the immersed anti-rust oil from the tempering furnace and find red spots on the threads.

It was detected that the red area on the screw was caused by alkali burning. Alkaline cleaners containing chloride substances and calcium compounds burn steel fasteners during heat treatment, leaving marks on the surface.

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

4. Contamination during flushing

After quenching, wash the fasteners with silicate cleaner and then rinse. Unidentified solid matter appeared on the surface. The substance was analyzed by infrared spectrometer and proved to be inorganic silicate and iron oxide. This is due to the incomplete rinsing, and the silicate remains on the surface.

5. Improper flushing

For large fasteners, aqueous polymer solutions are usually used for quenching. Before quenching, they are washed and rinsed with alkaline detergent. After quenching, the inside has rusted. Analysis with infrared spectroscopy confirmed that in addition to iron oxide, there are sodium, potassium and sulfur, indicating that the alkaline cleaner adhered to the part, it may be potassium hydroxide, sodium carbonate or similar substances, which promotes its rust. Check whether it is contaminated, it is recommended to replace the flushing water frequently. In addition, adding rust inhibitors to the water is also a good method.

6. Excessive corrosion

High-strength fasteners often see some black stripes. In the test, it can also be seen that the inorganic and organic cleaners were rinsed before the heat treatment. Streaks will be left after heat treatment, and even careful cleaning before heat treatment will leave streaks. Analyzing the residual contaminants on the surface with an infrared spectrometer, it was found that the concentration of sulfur and calcium was higher. Using a small amount of acetic acid and isopropanol, fold a small piece of test filter paper firmly on the dark spot, leaving the dark spot on the filter paper. Analysis of 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 the substance is an oil that has been baked and quenched, and it is also a gas phase released during the quenching process. Due to the excessive aging of the quenching oil, it is recommended to pour out the old oil, add new oil, and conduct process supervision and quenching oil maintenance during the entire process cycle.