Six major problems in the cleaning of fasteners in the current era
1. Pollution generated during rinsing
After the fasteners were quenched, they were washed with a silicate cleaning agent, then rinsed, and XX solid matter appeared on the surface, and the material was analyzed by an infrared spectrometer to confirm that it was an inorganic silicate and iron oxide. This is due to the fact that the rinsing is not completely caused by the residual silicate on the surface of the fastener.
2. Unreasonable stacking of fasteners
After the fasteners are tempered, there are signs of discoloration. Soaking with ether, and evaporating the ether, the remaining oily residue is found. These substances are high-content lipids. It is indicated that the fastener is contaminated by the cleaning agent and the quenching oil during the rinsing period, and melts at the heat treatment temperature, leaving a chemical burn scar, which proves that the surface of the fastener is not clean. Analysis by infrared spectrometer is a mixture of base oil and ether in the quenching oil. Ether may be derived from the addition of quenching oil. The quenching oil analysis results in the mesh belt furnace confirmed that the fasteners were unreasonably stacked due to the improper heating, and the fasteners were slightly oxidized in the quenching oil, but they were almost negligible. This phenomenon is related to the cleaning process, not the quenching oil. The problem.
3, surface residue
A white residue on the high-strength screw was analyzed by an infrared spectrometer and confirmed to be a phosphide. There is no acid cleaning agent cleaning, and the rinsing tank inspection shows that the bath has a high carbon solubility. The bath should be periodically drained, and the concentration of the lye in the rinsing tank is often detected.
4, alkali burns
High-strength screw quenching residual heat blackening has a uniform, flat oil black outer surface. However, there is an area visible to the naked eye in the outer ring. In addition, there is a slightly light blue or light red area visible. The original bar and wire rod are coated with a phosphate film to facilitate cold heading and tapping. Direct heat treatment without rinsing, cooling in quenching oil, alkaline cleaning agent cleaning, drying (no rinsing), tempering at 550 °C, heat The state was taken out of the tempering furnace and the rust-preventing oil was removed, and as a result, red spots were found at the screw threads.
The red area on the tested screw is caused by alkali burn. The alkaline cleaning agent containing chloride substance and calcium-containing compound will burn the steel fastener during heat treatment and leave marks on the surface of the fastener.
Steel fasteners do not remove surface alkalines in quenching oil, causing surface burns in high temperature austenite and aggravating damage in the next tempering. It is recommended to thoroughly clean and rinse the fasteners prior to heat treatment to completely remove alkaline residues that cause burns to the fasteners.
5, improper rinsing
For large-size fasteners, the polymer solution is often quenched, washed and rinsed with an alkaline cleaner before quenching, and the quenched fasteners are rusted on the inside. Analysis by infrared spectrometer confirmed that in addition to iron oxide, there were sodium, potassium and sulfur, indicating that the inside of the fastener was adhered with an alkaline cleaning agent, which is likely to be potassium hydroxide, sodium carbonate or the like to promote rust. It is recommended to check the rinsing of the fasteners for excessive contamination. It is also recommended to change the rinsing water frequently. In addition, it is also a good idea to add rust inhibitor to water.
6, excessive corrosion
High-strength fasteners often see some black streaks. In the test, it was also seen that the fasteners before heat treatment were rinsed with inorganic and organic cleaning agents. After quenching, it was found that there were still black streaks and even carefully cleaned before heat treatment. It also leaves streaks after heat treatment. The residual particles on the surface were analyzed by an infrared spectrometer and found to have a higher concentration of sulfur and calcium. Using a small amount of acetic acid in isopropanol, a small piece of test filter paper was strongly wiped at the dark spots to leave the black spots on the filter paper. Analysis of the filter paper by infrared spectrometer confirmed that calcium, sulfur, iron, manganese and chromium were the main elements.
Calcium and sulfur in the rust spots indicate that the material is a quenched oil that has been dried and is also an evolution of the gas phase during quenching. Because the quenching oil is excessively aged, it is recommended to pour out the old oil and add new oil throughout the entire process cycle.