The hydraulic tension pre-tightening method involves using hydraulic pressure to stretch a bolt to a specific elongation via a specialized tensioning device. This allows the nut to be tightened without any load, ensuring precise and consistent pre-tightening force. The pre-tightening process of multiple bolts is typically analyzed based on their stress conditions. There are generally two main approaches: one involves tightening the nut with a mechanical or hydraulic wrench, where the bolt stretches due to the spiral sliding surface, creating axial tension. The other method uses either electric heating or hydraulic stretching, where thermal expansion or hydraulic force extends the bolt, making it easier to turn the nut. Once the external force is removed, the bolt remains in an elastic deformation state.
The key difference between these methods lies in how the threads are stressed during pre-tightening. In the first case, the threads are constantly subjected to higher tensile and torsional shear stresses than during normal operation. In contrast, the second method separates the process into two stages—elongation and contraction—so that the threads experience no additional stresses during actual use. This makes the latter method more suitable for applications requiring long-term reliability and minimal wear.
Controlling pre-tightening force using a torque wrench or a fixed torque wrench is simple and practical, but it lacks precision. The pre-tightening torque is highly influenced by friction during the process, which can lead to inconsistent results. This method is not ideal for large bolts, where accuracy is critical. Therefore, in recent years, measuring the bolt's elongation has become a preferred method. By calculating the required elongation based on the desired pre-tightening force, engineers can achieve more accurate results. For large-diameter bolts, heating or hydraulic stretching methods are commonly used to achieve the necessary preload.
In the early days, pre-tightening was done manually, relying on human judgment and effort. As technology advanced, various tools were developed to improve efficiency and accuracy. These included torque wrenches, power-assisted wrenches, hydraulic wrenches, and eventually, electric heating and hydraulic stretching techniques. Each step brought greater control over the pre-tightening process, leading to more reliable and safer bolted connections in industrial applications.
Art Roller,Paint Art Roller for Ceiling,Best Painting Art,Paint Roller for Art
Jiangmen Nichiyo Decorative Material Co.,Ltd. , https://www.nichiyopt.com