High strength cleaning of fasteners

1. Contamination during rinsing

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

2. Improper stacking of fasteners

After tempering, the fasteners show signs of discoloration. After soaking in ether, oil like residue is found after evaporation of ether, which is a high content of lipids. It indicates that the fasteners are polluted by cleaning agent and quenching oil during rinsing period, and melt at heat treatment temperature, leaving chemical burn scar, which proves that the fastener surface is not clean. 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 mesh belt furnace show that the fastener has slight oxidation in quenching oil due to unreasonable stacking during heating, but it is almost negligible. This phenomenon is related to the cleaning process, not to the problem of quenching oil.

3. Surface residue

The white residue on the high strength screw was analyzed by infrared spectrometer and confirmed to be phosphide. If acid cleaning agent is not used for cleaning and the rinsing tank is found to have high carbon solubility, the tank liquid should be poured out regularly and the concentration level of alkali liquor in the rinsing tank should be detected frequently.

4. Alkali burn

The high strength screw is blackened by quenching waste heat and has a uniform and smooth oil black outer surface. However, in the outer ring, there is an area visible to the naked eye. In addition, there are also 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 cleaning agent, dried (not rinsed) and tempered at 550 ℃. The antirust oil is extracted from the tempering furnace under hot state. As a result, red spots are found on the screw thread.

It was found that the red area on the screw was caused by alkali burn. Chloride and calcium compounds contained in alkaline cleaning agent would burn steel fasteners during heat treatment, leaving marks on the surface of fasteners.

The basic substance on the surface of steel fasteners can not be removed in quenching oil, so that the surface of steel fasteners will be burned in high temperature austenite state, and the damage will be aggravated in the next tempering.