Carbon steel flange cleaning problem

2019-03-19 15:30:52 6

Carbon steel flanges tend to have cleaning problems after heat treatment and tempering. Due to the unreasonable stacking of the fasteners, the residual lye on the surface, surface rust and alkali burn or quenching oil are improperly selected to rust the surface of the fastener. Then, the special-shaped pieces are customized to analyze the main problems.


1, alkali burns

The carbon steel flange quenching residual heat black has a flat and even oil black outer surface, but there is a visible area in the outer ring. In addition, there are areas where light red or light blue is visible. The wire rod and the original bar material are coated with a phosphate film to facilitate cold heading and tapping, heat treatment without rinsing, cooling in quenching oil, alkaline cleaning agent cleaning, drying (no rinsing), tempering at 550 ° C, The hot state is removed from the tempering furnace to dip the rust preventive oil, and as a result, red spots are found at the screw threads. After testing, it was found that the red area on the screw was caused by alkali burn. The alkaline cleaning agent contained calcium compound and chloride, which would burn the steel fastener during heat treatment and leave traces on the surface of the fastener. Steel fasteners do not remove surface alkalines in quenching oil, which can cause surface burns in high-temperature austenite and can cause increased damage in the next tempering. The fasteners should be thoroughly cleaned and rinsed prior to heat treatment to clean the alkaline residue from the surface of the fastener.


2, rinse pollution

After the fasteners were quenched, they were washed with a silicate cleaner, then rinsed, and some solid matter appeared on the surface. The solid materials were analyzed by infrared spectrometry and found to be iron oxide and inorganic silicate. This is due to the fact that the rinsing does not completely leave the silicate on the surface of the fastener.


3. Excessive corrosion

Some black streaks are often seen on the carbon steel flange. The fasteners that have been rinsed with inorganic and organic cleaning agents before heat treatment have been found to have black streaks after quenching. Even if carefully cleaned before heat treatment, it will remain after heat treatment. Lower stripes. The surface residue was analyzed by an infrared spectrometer and found to be a higher concentration of calcium and sulfur. Using a small amount of acetic acid in isopropanol, force a small piece of test paper to force the black spots to leave the black spots on the filter paper. The filter paper was analyzed by an infrared spectrometer to confirm that sulfur, calcium, manganese, iron and chromium were the main elements. Calcium and sulfur in the rust spots indicate that the material is a quenched oil that has been dried and has a gas phase evolution during the quenching process. Due to the excessive aging of the quenching oil, it is recommended to pour the old oil, add new oil, and carry out process supervision and maintenance of the quenching oil throughout the entire process cycle.


4, surface residue

The white residue on the carbon steel flange was analyzed by an infrared spectrometer and confirmed to be a phosphide. It is not cleaned with an acidic cleaning agent. Check the rinsing tank to find that the bath has a high carbon solubility. The concentration of the lye in the rinsing tank should be checked frequently, and the bath should be replaced regularly.