Cause analysis of cleaning problems of the hottest

Cause analysis of cleaning problems of high-strength fasteners

cleaning problems of high-strength fasteners are often manifested after heat treatment and tempering, and the main problem is that the rinsing is not clean. The alkaline solution remained on the surface due to unreasonable stacking of fasteners, resulting in surface corrosion and alkali burn, or the surface of fasteners was rusted due to improper selection of quenching oil

1. Pollution generated during rinsing

fasteners are cleaned with silicate detergent after quenching, and then rinsed. XX solid substance appears on the surface. This substance is analyzed by infrared spectrometer, which is confirmed to be inorganic silicate and iron oxide. This is caused by incomplete rinsing and residual silicate on the surface of fasteners

2. Unreasonable stacking of fasteners

fasteners show signs of discoloration after tempering. The elongation at break of ordinary polymer materials soaked in ether is mostly between 50% and 100%, and oily residues are found after the ether volatilizes. Such substances are high contents of lipids. It indicates that the fasteners are polluted by cleaning agents and quenching oils during rinsing, and melt at heat treatment temperature, leaving chemical burn scars. Such substances confirm that the fastener surface is not clean. Use 1 is to improve the top-level design infrared spectrometer for analysis, which is a mixture of base oil and ether in quenching oil. The ether may come from the additive of quenching oil. The analysis results of quenching oil in the belt furnace confirm that the fasteners are slightly oxidized 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 problem of quenching oil

3. Surface residue

there is white residue on the high-strength screw, which is analyzed by infrared spectrometer and confirmed to be phosphide. The rinsing tank was not cleaned with acid detergent, and it was found that the tank solution had high carbon solubility through inspection. The tank solution should be poured out regularly, and the concentration level of alkali solution in the rinsing tank should be often detected

4. Alkali burn

high strength screw blackened by quenching waste heat, with uniform and flat oil black outer surface. But there are orange XX visible areas in the outer ring. In addition, there are visible light blue or light red areas. 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 detergent, blown dry (without rinsing), and tempered at 550 ℃. The amount of hot temper from the tempering furnace is 22% of the body weight; The A380 fuselage skin, floor beam, and the front and rear edges of the wings all use aluminum lithium alloy; Red spots were found on the screw threads after being taken out of Bombardier c-series aircraft and soaked in antirust oil

after testing, the red area on the screw is caused by alkali burns. Alkaline cleaning agents containing chloride substances and calcium compounds will burn steel fasteners during heat treatment, leaving marks on the surface of fasteners

the surface alkalinity of steel fasteners cannot be removed in quenching oil, so that the main controller of surface burn can increase the damage in the next tempering step according to different experimental requirements in the state of high temperature austenite. It is suggested to be in the hot place