Threaded connection is the most fundamental and critical connection method in mechanical equipment and engineering structures. From precision components in electronic products to main connections in bridge steel structures, thread selection and anti loosening schemes directly determine the safety and service life of equipment operation.
I Thread specification selection
Scientifically selecting thread specifications, deducing parameters from working conditions, rather than just looking at labels. The core logic of thread selection is to first clarify the working condition requirements, then match the corresponding parameters, and finally verify standard compatibility. The performance of threads is determined by three core factors: load, environment, and assembly requirements.
Load type: dynamic alternating load (such as engine connecting rod, vibrating screen); Static overload (such as steel structure beams and columns, fixed supports); Is it necessary to seal (such as hydraulic pipelines, pressure vessels).
Environmental conditions: presence of corrosive media, temperature fluctuation range, high or low vibration frequency.
Assembly requirements: whether frequent disassembly and assembly are needed, and the requirements for assembly space and accuracy.
Based on these three aspects, the core parameters can be preliminarily locked in.
1. Selection and judgment of tooth type and pitch (coarse/fine teeth)
Pitch selection: Under the same nominal diameter, fine thread has a smaller lead angle, stronger self-locking performance than coarse thread, and stronger anti loosening ability, suitable for vibration and dynamic load scenarios; Coarse thread has strong versatility, faster assembly speed, and higher tooth profile strength, making it suitable for static heavy-duty and fast assembly scenarios.
2. Verification of effective length of bolt+engagement length
Specification for screw in depth (to avoid slipping teeth due to insufficient meshing): The screw in depth of steel parts should be ≥ 1d (d is the nominal diameter); Cast iron/aluminum alloy screw in depth ≥ 1.25d~1.5d; Plastic and lightweight concrete should be screwed in to a depth of ≥ 2d, and it is necessary to add a pre embedded nut sleeve.
Extension length: It is best to expose 2-3 teeth of the bolt after tightening the nut. If the exposed length is too long, it is prone to collision and bending, and if it is too short, it cannot be stably locked.
3. Accuracy level, surface treatment adaptation environment
Verify accuracy and processing technology to ensure assembly quality. The thread accuracy directly affects the reliability of the connection, and a complete set of thread ring gauges needs to be used for testing during mass production. The choice of processing technology can also affect strength.
Anti corrosion matching: indoor dry blackening/phosphating; Outdoor galvanizing; Coastal salt spray, chemical environment Dacromet/316 stainless steel.
II Anti loosening method
Scientifically select anti loosening methods, classify them according to principles, and match the requirements of working conditions. Threaded connections can maintain tightness under static load and stable temperature conditions by relying on their self-locking properties. However, in environments with vibration, impact, variable load, or large temperature differences, the frictional force between threaded pairs will disappear, and the pre tightening force will gradually decrease, ultimately leading to loose and ineffective connections. Therefore, the corresponding anti loosening method must be selected according to the working conditions.
1. Friction anti loosening (suitable for conventional scenarios, easy to disassemble)
By maintaining a constant frictional force between the threaded pairs to prevent relative rotation, the advantage is that it does not change the original structure, is easy to disassemble, and is suitable for most conventional working conditions. However, in high-frequency and strong vibration scenarios, the preload force will gradually decrease with the vibration, making it unsuitable for vibration working conditions that require high reliability.
2. Mechanical locking and anti loosening (higher reliability, suitable for dynamic load scenarios)
Mechanical anti loosening relies on stop elements to directly limit the relative rotation of threaded pairs, and will not fail due to a decrease in preload force. The reliability of anti loosening is higher than that of friction anti loosening, and it is suitable for high demand scenarios such as vibration and impact loads. The core advantage is that it is not affected by vibration or changes in preload force. As long as the stop element does not fail, the thread will not loosen, making it the preferred choice for high reliability scenarios such as aerospace and automotive power components.
3. Permanent anti loosening (the most reliable anti loosening effect, but cannot be reused after disassembly)
Permanent anti loosening uses methods such as bonding, punching, welding, etc. to make the threaded pair an irreversible fixed connection, suitable for scenarios that do not require disassembly and have extremely high anti loosening requirements.
Anaerobic adhesive bonding anti loosening: Apply anaerobic adhesive on the surface of the thread, tighten and solidify the adhesive to bond the thread. The anti loosening effect is good, and it can also seal and prevent leakage. It is suitable for scenarios such as pipeline connection and electronic component fixation.
Punch point riveting anti loosening: After tightening the nut, punch points at the edge of the nut to break the motion relationship of the thread pair, making the thread unable to rotate, suitable for permanent connection of small parts.
Thread selection and anti loosening is a system solution based on working conditions. Only by matching the corresponding requirements can the connection be ensured to be stable and reliable in the long run, avoiding major failures caused by small threads.
Post time: 9月-09-2026
