Due to different enterprises, there will be a variety of specific technical quality problems in the production process of screw blackening. These changes will directly affect the quality differences of multi position screws.
1. There are three common problems in the use of waste heat blackening agent
The problem of stainless steel screw in phosphating is that the phosphating film is too thick, and if it is serious, flake will fall off, which will affect the adhesion of blackening film of non-standard screw. In the process of heat treatment, the working surface will be red and rusty after tempering. The solution to this problem is that the fasteners are pretreated before heat treatment, that is, cleaning with alkali or acid, and removing the phosphating film on the surface of non-standard screw workpiece.
2. After heat treatment and tempering, red rust on the surface of stainless steel screws may occur
(1) (2) the cleaning solution in the cleaning bath sticks to the surface of the parts after heat treatment, and the temperature of the furnace mouth is too low when entering the heating furnace, resulting in corrosion in the process of water drying; (3) after oil quenching, carbon in quenching oil is precipitated due to aging of oil or too high service temperature, which is adsorbed on the surface of workpiece (especially for small workpieces). After entering the tempering furnace, iron oxide will be produced due to the effect of carbon and temperature, resulting in red rust color; (4) the anti rust ability of water quenching medium decreases after long-term use, resulting in rust of parts.
The solutions are as follows: (1) remove the phosphating film; (2) increase the heating temperature of zone 1 of the mesh belt furnace; (3) when using the oil quenchant, it is necessary to reasonably use the temperature below 60 ℃ to reduce the aging process of the oil; (4) to control the carbon potential in the furnace and reduce the carbon potential as far as possible without decarburization; (5) frequently detect the data of water quenching medium and add antirust agent if necessary.
3. The blackening agent should be used under the specified operation method. It is strictly prohibited to bring in acid or alkali substances, which will damage the film-forming performance of blackening agent. The operating temperature should be kept between 40-50 ℃, and the blackening agent should be stirred frequently when not in use. At the same time, attention should be paid to the use of post cleaning solution, and inorganic salt cleaning agent should be avoided as far as possible. Since inorganic salt has the performance of reducing after drying water film, it will reduce the content of Salt into the blackening agent, produce a change from quantitative change to qualitative change, and ultimately destroy the performance. After using blackening agent for a period of time, it is generally half a year, and the blackening agent must be replaced in the whole tank.
Therefore, the quality problems in the process of multi position screw blackening can be solved by the following methods:
(1) Blackening again from the tempering furnace;
(2) Adjust the concentration of blackening agent;
(3) Replace the cleaning fluid.
