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Summarize the problems encountered when cleaning stainless steel fasteners

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Summarize the problems encountered when cleaning stainless steel fasteners

Release date:2018-11-05 Author: Click:

In order to better use fasteners, stainless steel fastener manufacturers need to perform regular maintenance when using fasteners, such as cleaning fasteners regularly, which can improve the efficiency of fasteners. However, stainless steel fastener manufacturers often find some problems when cleaning fasteners. There are six major problems.


1. Pollution generated during rinsing


After the fasteners were quenched, they were washed with a silicate cleaning agent, then rinsed, and XX solid matter appeared on the surface, and the material was analyzed by an infrared spectrometer to confirm inorganic silicate and iron oxide. This is caused by the fact that the rinsing does not completely leave silicate on the surface of the fastener.


2. Unreasonable stacking of fasteners


After the fasteners are tempered, there are signs of discoloration, soaked in ether, and the ether is evaporated to find the remaining oily residue. These substances are high-content lipids. It is indicated that the fastener is contaminated by the cleaning agent and the quenching oil during the rinsing period, and melts at the heat treatment temperature, leaving a chemical burn scar, which proves that the surface of the fastener is not clean. Analysis by infrared spectrometer is a mixture of base oil and ether in the quenching oil. Ether may be derived from the addition of quenching oil. The quenching oil analysis results in the mesh belt furnace confirmed that the fasteners were unreasonably stacked due to the improper heating, and the fasteners were slightly oxidized in the quenching oil, but they were almost negligible. This phenomenon is related to the cleaning process, not the quenching oil. The problem.


3, surface residue


A white residue on the high-strength screw was analyzed by an infrared spectrometer and confirmed to be a phosphide. No acid cleaning agent was cleaned, and the bath solution was found to have a high carbon solubility. The bath should be drained periodically, and the concentration of the lye in the rinsing tank was often checked.


4, alkali burns


The high-strength screw quenching residual heat black has a uniform, flat oil black outer surface. However, there is an area visible to the naked eye in the outer ring. In addition, there is a slightly light blue or light red area visible. The original bar and wire rod are coated with a phosphate film to facilitate cold heading and tapping. Direct heat treatment without rinsing, cooling in quenching oil, alkaline cleaning agent cleaning, drying (no rinsing), tempering at 550 °C, heat The state was removed from the tempering furnace and the rust-preventing oil was removed. As a result, red spots were found at the screw threads.


The red area on the tested screw is caused by alkali burn. The alkaline cleaning agent containing chloride substance and calcium-containing compound will burn the steel fastener during heat treatment and leave marks on the surface of the fastener.


Steel fasteners do not remove surface alkalines in quenching oil, causing surface burns in high temperature austenite and aggravating damage in the next tempering. It is recommended to thoroughly clean and rinse the fasteners prior to heat treatment to completely remove alkaline residues that cause burns to the fasteners.


5, improper rinsing


For large-size fasteners, the polymer solution is often quenched. Before quenching, it is cleaned and rinsed with an alkaline cleaner. The quenched fasteners are rusted on the inside. Analysis by infrared spectrometer confirmed that in addition to iron oxide, there were sodium, potassium and sulfur, indicating that the inside of the fastener has an alkaline cleaning agent, which is likely to be potassium hydroxide, sodium carbonate or the like to promote rust. It is recommended to check the rinsing of the fasteners for excessive contamination. It is also recommended to change the rinsing water frequently. In addition, it is also a good idea to add rust inhibitor to water.


6, excessive corrosion


High-strength fasteners often see some black streaks. In the test, it was also seen that the fasteners before heat treatment were rinsed with inorganic and organic cleaning agents. After quenching, it was found that there were still black streaks and even carefully cleaned before heat treatment. It also leaves streaks after heat treatment. The residual particles on the surface were analyzed by an infrared spectrometer and found to have a higher concentration of sulfur and calcium. Using a small amount of acetic acid in isopropanol, a small piece of test filter paper was strongly wiped at the dark spots to leave the black spots on the filter paper. Analysis of the filter paper by infrared spectrometer confirmed that calcium, sulfur, iron, manganese and chromium were the main elements.


Calcium and sulfur in the rust stains indicate that the material is a quenched oil that has been dried and is also an evolution of the gas phase during quenching. Because the quenching oil is excessively aged, it is recommended to pour out the old oil, add new oil, and perform process supervision and quenching oil maintenance throughout the entire process cycle.


The above are the problems encountered by the stainless steel fastener manufacturers in the cleaning process, hoping to take the lead, pay attention to the problems, better do the cleaning work.

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