The process of fastener screw manufacturing includes: plate element-annealing-pickling-cold heading-thread rolling-heat treatment-electroplating-packaging.
1. Plate Element
Refers to the original wire rod (raw material) purchased from the manufacturer.
Heat the wire to an appropriate temperature, keep it for a certain period of time, and then cool it slowly to adjust the crystal structure, reduce the hardness, and improve the wire processability at room temperature.
Purpose: Remove the oxide film on the wire surface and form a layer of phosphate film on the metal surface to reduce the scratches on the tool and die during the wire drawing and cold forging or forming processes.
1) Pickling: Immerse the entire raw material into three hydrochloric acid tanks with a concentration of 20-25% at room temperature for several minutes. The purpose is to remove the oxide film on the surface of the wire.
2) Clean water: remove the hydrochloric acid corrosion products on the wire surface.
3) Oxalic acid: increase the activity of metals to make the film produced in the next process more dense.
4) Coating treatment: the raw material is immersed in the phosphate, the steel surface is in contact with the chemical conversion treatment solution, the steel is dissolved to form insoluble compounds (such as Zn2Fe (Po4) 2.4H2o), which adhere to the steel surface to form a coating.
5) Clean water: remove the residue on the surface of the film.
6) Lubricant: Because the friction coefficient of the phosphate film is not very low, it can not give sufficient lubricity during processing, but it reacts with metal soap (such as sodium soap) to form a hard metal soap layer, which can increase its lubricating performance.
4. Cold heading
Cut the wire, upset it into a screw blank, form the head, make a cross groove (or other head type) thread blank diameter and rod length, and fillet under the head.
5. Thread rolling
6. Heat treatment
Strengthen the strength, hardness and bremsstrahlung of its screws. A good screw can't be too hard, it will break easily if locked. And it can't be too soft, for it's easy to slip and it won't lock tightly. So if the screw has the characteristics of outer steel and inner flexibility, it must be heat treated.