Analysis of six common problems in the cleaning of

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Analysis of six common problems in fastener cleaning

in order to better use fasteners, we need to maintain fasteners regularly, such as cleaning fasteners regularly, which can improve the efficiency of fasteners. But when we clean the fasteners, we often find some problems. 1. 2. Regularly check the transmission of the sprocket. There are six common problems

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. Soak them and let them volatilize to find oily residues, which are high content 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. Analyzed by infrared spectrometer, it 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, not 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 liquid had high carbon solubility through inspection. The tank liquid should be poured out regularly. The alkaline liquid in the rinsing tank and the concentration level that Zikai environmental reliability and electromagnetic compatibility experimental center can also do experiments 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), tempered at 550 ℃. They are taken out of the tempering furnace in hot state and soaked in antirust oil. As a result, red spots are found at the screw threads

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, which will burn the surface in the state of high temperature austenite and aggravate the damage in the next tempering step. It is recommended to thoroughly clean and rinse fasteners before heat treatment to completely remove alkaline residues that cause fastener burns

5. Improper rinsing

for large-scale fasteners, polymer aqueous solution quenching is often used. Before quenching, alkaline detergent is used to clean and rinse, and the quenched fasteners have rusted on the inside. The infrared spectrometer was used to analyze, and it was confirmed that in addition to iron oxide, there were sodium, potassium and sulfur, indicating that there was an alkaline cleaning agent adhered to the inside of the fastener, which was likely to be potassium hydroxide, sodium carbonate or similar substances to promote its rusting. Most of the existing universal testing machines install Force Sensors between the upper pressing plate and the beam to check whether there is excessive pollution in the rinsing of fasteners, and it is also recommended to often change the rinsing water. In addition, adding antirust agent to water is also a good method

6. Excessive corrosion

some black stripes are often seen on high-strength fasteners. It is also seen in the test that the fasteners before heat treatment have been rinsed with inorganic and organic cleaning agents, and black stripes are still found after quenching. Even the fine cleaning before heat treatment will leave stripes after heat treatment. The residual pollutants on the surface were analyzed by infrared spectrometer, and higher concentrations of sulfur and calcium were found. Use a small amount of isopropyl alcohol of acetic acid, fold and wipe a small piece of test filter paper at the black spot, and leave the black spot on the filter paper. By analyzing the filter paper with infrared spectrometer, it is confirmed that calcium, sulfur, iron, manganese and chromium are the main elements

the presence of calcium and sulfur in rust spots indicates that this material is a dried quenching oil, which is also the evolution of vapor phase during quenching. Because the quenching oil is over aged, it is recommended to pour out the old oil, add new oil, and implement process supervision and quenching oil maintenance in the whole process cycle

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