The cleaning problem of high strength fasteners is often manifested after heat treatment and tempering, and the main problem is that the rinsing is not clean. As a result of unreasonable stacking of fasteners, lye remains on the surface, forming surface rust and alkali burn, or improper selection of quenching oil makes the fastener surface rust.
1. Pollution produced during rinsing
After quenching, the fasteners were cleaned with silicate cleaning agent and then rinsed. Solid material appeared on the surface. The material was analyzed by infrared spectrometer and confirmed to be inorganic silicate and iron oxide. This is due to the residue of silicate on the fastener surface after rinsing incomplete.
2. The stacking of fasteners is not reasonable
After tempering fasteners show signs of discoloration, soak with ether, let ether volatilize and find the remaining oily residue, such substances are high content of lipids. It indicates that fasteners are contaminated by cleaning agents and quenching oils during the rinsing period, which melt at heat treatment temperature and leave chemical burning scars. Such substances prove that the fastener surface is not clean. Analyzed with 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 confirm that the fasteners have slight oxidation in the quenching oil due to unreasonable stacking during heating, but it is almost negligible. This phenomenon is related to the cleaning process, rather than the quenching oil problem.
3. Surface residue
The white residue on the high strength screw was analyzed by infrared spectrometer and confirmed to be phosphide. No acid cleaning agent was used to clean the rinse tank, and the inspection of the rinse tank found that the tank had a high carbon solubility. The tank should be emptied regularly, and the concentration level of lye in the rinse tank should be checked frequently.
4. Alkali burn
High strength screw quenching residual heat blackening has a uniform, smooth oil black outer surface. But in the outer ring there is an orange visible area. In addition, there are areas of light blue or light red.
It has been detected that the red area on the screw is caused by alkali burn. Alkaline cleaning agent containing chlorides and calcium compounds will burn steel fasteners during heat treatment, leaving spots on the surface of fasteners.
The surface alkalinity of steel fasteners cannot be removed in the quenching oil, so that the surface burns at high temperature austenite and aggravates the injury in the next step of tempering. It is recommended to wash and rinse fasteners thoroughly prior to heat treatment to completely remove alkaline residues that cause burns to fasteners.
5. Improper rinsing
For large size fasteners, polymer aqueous solution quenching is often used. Before quenching, alkaline cleaning agent is used to clean and rinse the fasteners. After quenching, the fasteners have rusted on the inside. Analysis with infrared spectrometers confirmed that in addition to iron oxide, there are sodium, potassium and sulfur, indicating that the fastener is stuck to the inside of the alkaline cleaning agent, probably potassium hydroxide, sodium carbonate or similar substances, promote rust. Fastener rinsing is checked for excessive contamination and frequent replacement of rinsing water is also recommended. In addition, adding rust inhibitor to the water is also a good way.
Post time: Dec-30-2022