Why Screw Three Turns and Back Half?

Years ago, a TV program showcased a detail in the construction of a nuclear power plant in China: foreign experts guiding Chinese workers to tighten a screw three times and then back off half a turn. What is the scientific principle behind this operation? Some viewers might wonder, why not just tighten it two and a half turns? But it's not that simple.

In the assembly of high-end mechanical equipment, screwing is a task that requires precise control. The operation manual clearly specifies the torque to be applied to ensure the screw has an appropriate pre-tension force. After tightening, to prevent loosening, an additional pre-tension force is needed. Backing off half a turn eliminates this force, preventing the screw from creeping and deforming plastically under long-term pressure in high-temperature and vibrating environments, thus reducing the risk of strength loss and failure. This "elastic control" ensures that the screw maintains its structural integrity and reliability under long-term loads.

In the construction of nuclear power plants, every screw is crucial. They are not only the bonds that connect components but also the key to ensuring the safe and stable operation of the entire system. Reasonable control of the pre-tension force can prevent the screw from fatiguing and damaging due to excessive force, balance stress distribution, reduce component damage, and extend service life. Additionally, considering the material's coefficient of thermal expansion, proper adjustment of the pre-tension force ensures the screw's stability during temperature changes.

This meticulous operation reflects a responsibility to engineering quality. In the construction of nuclear power plants, any small mistake can lead to severe consequences, so each step must be executed strictly according to specifications. With the advancement of technology, the requirements for nuclear power plant construction are increasingly stringent, and engineers and workers need to combine theoretical knowledge with practice to ensure that every detail meets the highest standards.

In summary, what seems like a simple task of screwing is of great significance in the construction of nuclear power plants. It not only demonstrates the application of material science and mechanical principles but also reflects a high level of responsibility for engineering quality. Such operations ensure the safe, stable, and efficient operation of nuclear power plants, contributing significantly to national energy security and the well-being of the people. In the future, we will continue to explore and improve, driving the healthy development of the nuclear power industry with higher standards and more refined management.