How is the blackening treatment of the slewing bearing made? Methods and process flow
Methods for blackening treatment of slewing bearings
There are many methods for metal anti-rust treatment, including alkaline chemical oxidation, alkali-free oxidation, high-temperature gas oxidation and electrochemical oxidation. Among them, blackening treatment is a kind of surface oxidation treatment. The main method is to put the bearing in a very concentrated alkali and oxidant, and after heating and oxidation at a certain temperature, a uniform and dense ferroferric oxide film is formed on the surface of the bearing, which is firmly combined with the original metal to play an anti-rust effect. Because the color of ferroferric oxide is black, this anti-rust treatment method is also called blackening treatment. Of course, due to the influence of various factors in the operation, the color of the oxide film also has blue, reddish brown and brownish brown. The generated oxide film is beautiful in color, elastic, and thin, usually 0.5-1.5um thick. It has no effect on the overall size and precision of the bearing, and has a certain effect on eliminating the profit deformation caused by heat treatment.
Process flow of blackening treatment of slewing bearings
For slewing bearings made of low carbon steel, medium carbon steel, high carbon steel, alloy steel, and cast steel, the blackening treatment should follow the operating process of preparation → degreasing → cleaning → pickling → cleaning → blackening → cleaning → oil immersion → drying → inspection. The specific process flow is as follows:
(1) Check the quality of the bearing: Before the blackening process, the quality of the bearing should be checked. For parts with decorative requirements, the roughness should be lower than Ral.6um, and generally should reach Ra3.2um. There should be no cracks, bumps, hard scratches or metal plating on the surface, severe surface rust, and thick oxide scale that is difficult to remove. These will affect the effect of the blackening process.
(2) Cleaning and degreasing: To remove oil stains from the bearing surface, place the bearing in a solution of 3%-5% metal detergent and soak it at 70-100 degrees Celsius for 10-30 minutes, depending on the degree of oil stains. Then rinse with clean water until the oil stains and solution on the workpiece are removed.
(3) Pickling and rust removal: Before blackening, rust and oxide scale on the bearing surface should be removed. However, the bearing surface cannot be corroded, so the pickling time of the bearing should be controlled. Use a 60% hydrochloric acid solution and soak for 5-10 minutes. After soaking, rinse with running water to wash off the hydrochloric acid solution remaining on the bearing surface.
(4) Blackening treatment: high temperature immersion, place the bearing in a blackening solution with sodium hydroxide and sodium nitrite as the main components, the solution temperature is controlled at 125-155 degrees Celsius, soak twice, take out and air dry after soaking for 8-10 minutes, observe the coloring on the surface, soak it in the blackening solution for 8-10 minutes again, take it out again to observe the coloring and adjust the solution concentration and temperature in time.
(5) Cleaning and saponification: put the blackened bearing into the saponification solution for saponification, the temperature is controlled at 20-50℃, soak for 3-5 minutes, wash it with clean water and air dry it.
(6) Oil seal sealing: soak it in anti-rust oil and then mechanical oil for ten minutes. The temperature of the oil seal is used according to the requirements of the oil. Under normal circumstances, the heating temperature of ordinary mechanical oil is 105-120 degrees Celsius, and the oil sealing time is 2-5 minutes. Take it out and spin dry.
(7) Appearance inspection: Check the uniformity of the black color of the bearing. Generally, the thickness of the protective film after blackening is 0.6-1.5um
This concludes the sharing of the slewing bearing manufacturer on how the slewing bearing is blackened. In addition to blackening, there are other methods for bearing surface corrosion protection, such as flange, galvanizing, phosphating, zinc spraying, and chrome plating. Among them, the blackening method is relatively simple and practical.
If you encounter other problems during the bearing surface corrosion protection operation, you are welcome to call us at Luoyang Hengguan Bearing Co., Ltd.
