Project Solutions

High-Strength Fastener Problems


In the daily maintenance of high-strength fasteners, but also pay attention to some problems, such as the rinse generated by pollution, fasteners stacked unreasonable, surface residues, these problems will affect the high-definition fasteners Performance Use.

1) rinse when the pollution

Fastener after quenching with silicate cleaning agent, and then rinse, the surface appears XX solid material, this material with infrared spectrometer analysis, confirmed that inorganic silicate and iron oxide. This is due to the rinsing is not complete in the fastener surface due to the presence of silicate.

2) fasteners stacked unreasonable

Fastening after tempering signs of discoloration, soaked with ether, so that volatile ether found in the remaining oily residue, such substances are high levels of lipids. Indicating that fasteners in the rinse by cleaning agents and quenching oil pollution, melting temperature in the heat treatment, leaving chemical burn scars, these materials confirmed that the fastener surface is not clean. Analysis by infrared spectrometer, is a quenching oil base oil and ether mixture. The ether may come from the addition of quench oil. The results of quenching oil analysis in the mesh belt furnace show that the fastener is 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 quenching oil The problem.

3) the surface residue

The white residue on the high-strength screw was analyzed by infrared spectroscopy and confirmed to be a phosphide. No acid cleaning agent cleaning, and rinse tank inspection found that the bath has a high carbon solubility, should be regularly drained, often check the rinse tank lye concentration levels.

4) alkali burns

High-strength screw quenching waste heat black with a uniform, flat surface of the oil black. But in the outer ring with orange XX visible to the eye area. In addition, there are visible slightly light blue or light red area. Raw bar and wire rod coated with phosphating film to facilitate cold heading and tapping, direct heat treatment without rinsing, cooling in quenching oil, alkaline cleaning agent cleaning, drying (not rinse), 550 ℃ tempering, heat The rust-removing oil was removed from the tempering furnace, and a red spot was found at the screw thread.
      The red area of the test screw is caused by alkali burns, alkaline cleaning agent containing chloride material, calcium compounds will be in the heat treatment of steel fasteners burns, leaving the scar on the fastener surface.
      Iron and steel fasteners in the quenching oil can not remove the surface of alkaline substances, which in the high-temperature austenitic state of the surface burns, and in step tempered increase the damage. It is advisable to thoroughly rinse and rinse the fastener thoroughly before heat treatment to completely remove the alkaline residues that cause burns to the fastener.

5) rinse properly

On the large-size fasteners are often used in aqueous polymer solution quenching, quenching with an alkaline cleaning agent to wash and rinse, after quenching the fasteners have rust in the inside. Analysis by infrared spectrometer confirmed that in addition to iron oxide, there are sodium, potassium and sulfur, indicating the inside of the fastener sticky alkaline cleaning agent, is likely to be potassium hydroxide, sodium carbonate or similar substances to promote its rust. Rinse the fasteners to check for excessive contamination, it is recommended to regularly exchange rinse water. In addition, the addition of anti-rust agent to the water is also a good method.

6) excessive corrosion

High-strength fasteners often see some black stripes, also seen in the test, had to use inorganic and organic cleaning agent rinse before the fastener after heat treatment, still found after the black stripes or even heat treatment before the careful cleaning , Will also leave stripes after heat treatment. The residual contaminants on the surface were analyzed by infrared spectroscopy and found to be at higher concentrations of sulfur and calcium. With a small amount of acetic acid in isopropanol, put a small piece of test paper filter in the dark spots at the force of the wipe, the spots left on the filter paper. Analysis of filter paper using infrared spectrometer confirmed that calcium, sulfur, iron, manganese and chromium are the main elements. The presence of calcium and sulfur in the rust spot indicates that the material is a dried quench oil and is the evolution of the gas phase during the quenching process. Due to the excessive aging of the quenching oil, it is recommended to pour out the old oil, add new oil, the implementation of the process in the whole process supervision and maintenance of quenching oil.