Processing technology of high-strength anti-theft screw

In addition to the cold heading process, the manufacturing processes of high-strength anti-theft screws include warm forging, cold extrusion and cutting. The high-strength cold heading screw production process of wind power anti-theft screws is: spheroidizing annealing→cold drawing→cold heading forming→threading→quenching and tempering→surface treatment; the production process of high-strength warm forging bolts for wind power fasteners is: cold Drawing → blanking → warm forging forming → hexagonal shaping → quenching and tempering → thread processing → surface treatment. High-strength anti-theft screws for wind power need to undergo two heat treatments, spheroidizing annealing and quenching and tempering, to make the strength level reach 10.9.
For high-strength anti-theft screws of 10.9 and above, the uniformity of the quenched structure is particularly important. In order to ensure that the high-strength anti-theft screw is fully austenitized during quenching, the quenched structure is uniform, and there is no undissolved ferrite and non-martensitic structure, full attention should be paid to the metallographic analysis of the quenched structure. The heat treatment of foreign high-strength anti-theft screws attaches great importance to full austenitization to ensure the uniformity of the structure, to obtain the best combination of strength and toughness, and to ensure the safety of anti-theft screws during service. Domestic manufacturers of high-strength anti-theft screws have not paid attention to this. The common problem is that the anti-theft screws are insufficient in quenching heating and heat preservation and insufficient austenitization, resulting in uneven quenching structure. This non-uniformity cannot be eliminated in the subsequent tempering process; although the strength and hardness of the anti-theft screw can reach the 10.9 performance requirements, due to the poor uniformity of the structure, the screw contains more ferrite areas , Easy to cause early failure. Therefore, the process control should be strengthened in the heat treatment quenching and tempering process.
In recent years, the conversion coating technology in surface treatment has developed rapidly. For high-strength fasteners, screws are mostly phosphate (phosphated) or oxidized (blackened) oiled surface treatment methods, nuts, washers Phosphorus saponification process is generally used, and their durability grade belongs to light protection, and the purpose is to meet the tolerance range of the friction factor.
High-strength anti-theft screws for wind power are used to reduce the risk of hydrogen embrittlement during pickling and electroplating, and to ensure a service life of more than 15 years. Shot peening + non-electrolytic dacromet coating is used for outdoor fasteners. The protective effect includes mechanical shielding effect, self-passivation effect and good surface anticorrosion effect of sacrificial anode electrochemical protection; the coating layer should be larger than 8-12μm, and the salt spray test should be more than 720h.
For anti-theft screws for general steel structures, the surface lubrication is guaranteed by the phosphorus saponification of the nut and washer, and the torque coefficient is also guaranteed by it. The torque coefficient value is usually 0.11 to 0.15; and the high-strength bolt connection pair for wind power, because the surface adopts With Dacromet coating, the torque coefficient is guaranteed by applying MoS2 during installation. According to the current domestic use of MoS2, if the thread surface and the working surface of the washer are evenly coated with MoS2, the torque coefficient value is generally 0.08～0.13 . If only MoS2 is applied to the thread surface, the torque coefficient value will be slightly increased accordingly. The larger the bolt diameter, the more obvious the improvement.