Analysis of six common problems in fastener cleaning

In order to better use fasteners, we need to conduct regular maintenance when using fasteners, such as regular cleaning of fasteners, which can improve the use efficiency of fasteners. However, when we clean fasteners, we often find some problems, mainly including six common problems.

1. Pollution during rinsing

After the fastener is quenched, it is cleaned with silicate cleaner, and then rinsed. XX solid substance appears on the surface, which is confirmed to be inorganic silicate and iron oxide by infrared spectrometer analysis. This is caused by silicate residue on fastener surface due to incomplete rinsing.

2. Unreasonable stacking of fasteners

After tempering, the fasteners show signs of discoloration. Soak the fasteners in order to find oily residues after volatilization, which are high content lipids. It indicates that the fastener was polluted by cleaning agent and quenching oil during rinsing period, melted at heat treatment temperature and left chemical scar, which proves that the fastener surface is not clean. The mixture of base oil and ether in quenching oil is analyzed by infrared spectrometer. Ether may come from additives of quenching oil. The analysis results of the quenching oil in the mesh belt furnace confirmed that the fasteners were slightly oxidized in the quenching oil due to unreasonable stacking during heating, but it was almost negligible. This phenomenon was related to the cleaning process, not the problem of the quenching oil.

3. Surface residues

There was white residue on the high-strength screw, which was confirmed to be phosphide by infrared spectroscopy. The acid detergent was not used for cleaning, and the rinsing tank was inspected and found to have a high carbon solubility. The tank solution should be regularly emptied, and the concentration level of alkali solution in the rinsing tank should be regularly detected.

4. Alkali burn

The quenching waste heat blackening of high-strength screws has a uniform and flat oil black outer surface. But there is an orange XX visible area in the outer circle. 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 and dried with alkaline cleaner (without rinsing), and tempered at 550 ℃. The hot state is taken out of the tempering furnace and dipped with antirust oil. As a result, red spots are found on the screw threads.

It is detected that the red area on the screw is caused by alkali burn. The alkaline cleaner contains chloride substances and calcium compounds, which will burn the steel fasteners during heat treatment and leave marks on the fastener surface.

The surface alkalinity of steel fasteners cannot be removed in the quenching oil, so that the surface will be burned under the high temperature austenite state, and the damage will be aggravated during the next tempering. It is recommended that the fasteners be thoroughly cleaned and rinsed before heat treatment to completely remove alkaline residues that may cause burns to the fasteners.

5. Improper rinsing

For fasteners with large specifications, polymer aqueous solution is often used for quenching. Before quenching, alkaline cleaning agent is used for cleaning and rinsing. The quenched fasteners have rusted on the inside. The infrared spectrometer was used for analysis and it was confirmed that there were sodium, potassium and sulfur in addition to iron oxide, indicating that alkaline cleaning agent was stuck on the inner side of the fastener, which was probably potassium hydroxide, sodium carbonate or similar substances to promote its rusting. Check whether the fastener rinsing is excessively polluted. It is also recommended to change the rinsing water frequently. In addition, it is also a good method to add rust inhibitor to water.

6. Excessive corrosion

High strength fasteners often see some black stripes. It is also seen in the test that the fasteners before heat treatment were rinsed with inorganic and organic cleaning agents. After quenching, it is still found that there are still black stripes, and 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 it was found that there were high concentrations of sulfur and calcium. Use a small amount of isopropyl alcohol of acetic acid to fold and wipe a small piece of test filter paper at the black spot and leave the black spot on the filter paper. The filter paper was analyzed by infrared spectrometer, and it was confirmed that calcium, sulfur, iron, manganese and chromium were the main elements.

The presence of calcium and sulfur in the rust stain indicates that this substance is roasted quenching oil, and is also the evolution of vapor phase substances during quenching. Because the quenching oil is excessively aged, it is recommended to pour out the old oil, add new oil, and implement process supervision and quenching oil maintenance throughout the process cycle.