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. Due to unreasonable stacking of fasteners, lye remains on the surface, resulting in surface rust and alkali burns or improper selection of quenching oil to rust the surface of fasteners.


1. Pollution caused by rinsing

After quenching, the fasteners were cleaned with silicate cleaning agent, and then rinsed. XX solid material appeared on the surface. The material was analyzed by infrared spectrometer, and it was confirmed that it was inorganic silicate and iron oxide. This is due to incomplete rinsing and residual silicates on the fastener surface.


2. Unreasonable stacking of fasteners

The fasteners show signs of discoloration after tempering. Soak them in ether. After the ether is volatilized, an oily residue is found, which is a high content of lipids. It means 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 confirm that the surface of the fasteners is not clean. Analysis by infrared spectrometer is a mixture of base oil and ether in quench oil. The ether may come from the addition of the quenching oil. The analysis results of the quenching oil in the mesh belt furnace confirmed 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 quenching oil. The problem.


3. Surface residue

There was a white residue on the high-strength screw, which was analyzed with an infrared spectrometer and confirmed to be phosphide. No acid cleaning agent cleaning was carried out, and the rinsing tank was inspected and found that the tank liquid had a high carbon solubility.


4. Alkali burn

High-strength screw quenching residual heat blackening has a uniform and flat oil-black outer surface. But there are orange XX visible areas in the outer ring. In addition, there are slightly bluish or reddish areas visible. The original bar and wire rod are coated with phosphating film to facilitate cold heading and tapping, direct heat treatment without rinsing, cooling in quenching oil, cleaning with alkaline cleaning agent, drying (without rinsing), tempering at 550°C, heat treatment The rust-preventive oil was removed from the tempering furnace in the state of

It has been tested that the red area on the screw is caused by alkali burns. Alkaline cleaning agents containing chloride substances and calcium compounds will burn the steel fasteners during heat treatment, leaving marks 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 aggravates the damage in the next tempering. The recommendation is to thoroughly wash and rinse fasteners prior to heat treating to completely remove alkaline residues that can cause fastener burns.


5. Improper rinsing

Large-sized fasteners are often quenched by polymer aqueous solution. Before quenching, they are cleaned and rinsed with alkaline cleaning agent. After quenching, the fasteners have been rusted on the inside. Analysis with an infrared spectrometer confirmed that in addition to iron oxide, there were sodium, potassium and sulfur, indicating that there was an alkaline cleaning agent on the inside of the fastener, probably potassium hydroxide, sodium carbonate or similar substances, which promoted its rusting. Fastener rinses are checked for excessive contamination and frequent rinse water changes are also recommended. In addition, adding a rust inhibitor to the water is also a good method.


6. Excessive rust

High-strength fasteners often see some black streaks. It is also seen in the test that the fasteners before heat treatment have been rinsed with inorganic and organic cleaning agents. After quenching, black streaks are still found even after careful cleaning before heat treatment. , will also leave streaks after heat treatment. Analysis of residual contaminants on the surface with an infrared spectrometer revealed higher concentrations of sulfur and calcium.

Using a small amount of acetic acid in isopropanol, fold a small piece of test filter paper firmly on the black spot, leaving 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 spots indicates that the substance is a dried quenching oil, and it is also the evolution of the gas phase during the quenching process. 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 during the entire process cycle.