The black screw production process has various specific technical quality problems due to different Industrial Bolt Factory （https://www.chinaweigao.com/product/bolt/）. These changes will directly affect the quality of multi-station screws.
1. There are three main types of common problems in the use of waste heat blackening agent:
The problem of stainless steel screws during wire phosphating is that the phosphating film is too thick. In severe cases, it will peel off and affect the adhesion of the black film of non-standard screws. Redness and rust on the working surface will appear after tempering during heat treatment. The solution to this problem, such as pretreatment before the fastener is fed into the heat treatment, that is, cleaning with alkali or acid, to remove the phosphate film on the surface of the non-standard screw workpiece.
2. Red rust on the surface of stainless steel screws after heat treatment and tempering. There are several possible causes of this type of situation:
(1) Produced by surface phosphate film; (2) The cleaning liquid in the cleaning tank adheres to the surface of the part after the processing fastener enters the heat treatment, and the furnace mouth temperature is too low when it enters the heating furnace, which is generated during the moisture drying process Rust; (3) After oil quenching, due to the aging of the oil or the high temperature of use, the carbon in the quenching oil will precipitate and be adsorbed on the surface of the workpiece (small workpieces are especially common). After entering the tempering furnace, due to the effect of carbon and temperature, iron oxide is produced, resulting in a red rust color; (4) The water quenching medium is used for a long time, and the anti-rust ability in the medium decreases and the parts rust.
Solution: (1) Remove the phosphating film; (2) Increase the heating temperature of zone 1 of the mesh belt furnace; (3) When using the oil quenching agent, use a reasonable temperature below 60°C to reduce the oil aging process (4) To control the carbon potential in the furnace, reduce the carbon potential as much as possible without decarburization; (5) Check the data of the water quenching medium frequently, and add rust inhibitors if necessary.
3. The blackening agent should be used under the prescribed operating methods. It is strictly forbidden to bring in acid and alkali substances, which will destroy the film-forming performance of the blackening agent. The use temperature should be kept between 40-50℃, and it must be stirred frequently when not in use to keep the blackening agent in good condition. Attention should be paid to the use of post-cleaning liquid, and avoid the use of inorganic salt cleaning agents as much as possible. Since inorganic salts have the ability to reduce the water film after drying, they will bring the salts in the cleaning liquid into the blackening agent, resulting in quantitative changes. The qualitative change will eventually destroy the performance. After using the blackening agent for a period of time, usually half a year, the blackening agent must be replaced throughout the tank.
Therefore, the quality problems caused by the blackening of China Stud Supplier ( https://www.chinaweigao.com/ ) multi-station screws can be solved by the following methods:
(1) Blackened again from the tempering furnace;
(2) Adjust the concentration of blackening agent;
(3) Cleaning fluid after replacement.