Cleaning problems of high strength fasteners

1. Pollution caused during rinsing   After quenching, the fasteners were cleaned with silicate cleaning agent, and then rinsed. XX solid substances appeared on the surface. The substances were analyzed with infrared spectrometer and confirmed to be inorganic silicates and iron oxide. This is caused by incomplete rinsing and residual silicates on the surface of the fastener. 2. Unreasonable stacking of fasteners   The fasteners showed signs of color change after tempering. Soak them in ether and allow the ether to evaporate, leaving oily residues. These substances are high levels of lipids. It shows that the fasteners were contaminated by cleaning agents and quenching oils during the rinsing period, and melted at the heat treatment temperature, leaving chemical burn scars. Such substances confirmed that the surface of the fasteners was not clean. Analysis was carried out using an infrared spectrometer and was a mixture of base oil and ether in the quenching oil. Ether may come from additives to quenching oil. The analysis results of the quenching oil in the mesh belt furnace confirmed that due to unreasonable stacking of the fasteners during heating, the fasteners were slightly oxidized in the quenching oil, but it was almost negligible. This phenomenon was related to the cleaning process rather than the quenching oil. problem. 3. Surface residues   There was white residue on the high-strength screws, which was analyzed by infrared spectrometer and confirmed to be phosphide. No acid cleaning agent was carried out, and the rinsing tank was inspected and found that the tank liquid had a high carbon solubility. The tank liquid should be poured out regularly and the concentration level of alkali in the rinsing tank should be frequently tested. 4. Alkali burn   High-strength screws are blackened by quenching residual heat and have a uniform and smooth oil-black outer surface. But there is an area visible to the naked eye on the outer ring. In addition, there are slightly light blue or light red areas visible. The original bar stock and wire rod are coated with a phosphating film to facilitate cold heading and tapping. They are directly heat treated without rinsing, cooled in quenching oil, cleaned with alkaline cleaning agent, dried (without rinsing), tempered at 550 ° C, and removed from the tempering furnace in a hot state to soak in anti-rust oil. As a result, red spots were found on the screw threads.   After testing, the red areas on the screws were caused by alkali burns. Alkaline cleaning agents containing chloride substances and calcium-containing compounds will burn the steel fasteners during heat treatment, leaving spots on the surface of the fasteners.   Steel fasteners cannot remove surface alkalis in quenching oil, which burns the surface in the high-temperature austenite state and exacerbates the damage during the next tempering process.