The manufacturing process of screws mainly includes five core steps: wire preparation, cold heading, thread rolling, heat treatment, and electroplating. The entire process is highly automated and requires precise technology.
Wire Preparation and Treatment: Manufacturing begins with selecting suitable metal wire (such as carbon steel or stainless steel), typically with a diameter between 5-19 mm. First, spheroidizing annealing is performed to reduce hardness and improve plasticity, facilitating subsequent processing. Then, the surface oxide layer is removed by pickling or mechanical descaling, followed by phosphating and saponification treatment to improve lubricity and wear resistance.
Cold Heading: The wire is fed into a cold heading machine, where it is stamped at high speed through a die at room temperature, forming the basic shape of the screw head and shank in one step. This step significantly improves material utilization and ensures strength.
Thread Rolling: Using a moving and a fixed threading plate, pressure is applied to the cold-headed blank, causing plastic deformation of the metal surface to form threads. Compared to thread cutting, thread rolling enhances thread strength and reduces material waste.
Heat Treatment: To improve the hardness and toughness of screws, heat treatment is necessary. The general process includes:
Cleansing surface oil
High-temperature carburizing (for high-strength screws)
Quenching and hardening
Low-temperature tempering to reduce internal stress and prevent brittle fracture.
This process is particularly crucial for high-strength screws of grade 8.8 and above.
Electroplating and Surface Treatment: Finally, zinc, nickel, or other metal layers are electrochemically plated onto the screw surface to provide rust and corrosion protection and improve appearance. Environmentally friendly electroplating also adds a passivation film, further enhancing corrosion resistance. The entire process takes approximately 1.5 to 2 hours.
