1. Material
Screw material: Self-tapping screws are usually made of carbon steel, stainless steel or alloy steel. Carbon steel has higher strength, but may be slightly less corrosion-resistant; stainless steel has good corrosion resistance and certain strength. The hardness, toughness and other indicators of the material directly affect the tightening force of the screw. Screws with high hardness can better cut into the material and provide stronger tightening force.
Connected materials: Harder materials will make it more difficult for self-tapping screws to penetrate. If the screw strength is insufficient, it may not be able to form a good tightening; and too soft materials may cause the thread to be unable to be effectively formed, reducing the tightening force.
2. Design factors
Thread design: The type, pitch, and pitch of the thread are all crucial. Triangular threads can form greater friction in the substrate, which is conducive to tightening. Self-tapping screws with large pitch can produce higher tightening force on thinner substrates.
Head design: The conical head can form greater pressure with the surface of the substrate to improve the tightening effect.
Size ratio: The length and diameter ratio of the self-tapping screw will also affect its performance. Improper ratio may cause instability during the connection process and affect the tightening force.
3. Installation operation
Torque control: Torque control during installation is crucial. If the torque is too small, the self-tapping screw cannot be fully tightened and is easy to loosen; if the torque is too large, the screw may be excessively deformed or even broken, or the connected material may be damaged.
Drilling quality: If the drilling diameter is too large, the fit between the screw and the hole wall is not tight, the tightening force and anti-loosening performance will decrease; if the drilling is not vertical or regular, the screw will be unevenly stressed.
4. Use environment
Vibration environment: In a vibration environment, the alternating stress on the self-tapping screw will gradually reduce the original tightening force, resulting in loosening.
High temperature environment: It may cause the material to expand and soften, affecting the fit between the screw and the connected material and reducing the tightening force.
Humid or corrosive environment: It will cause the screw to rust and corrode, weaken its strength, and thus affect the tightening and anti-loosening effect.
5. Specific values of tightening force
Self-tapping screws of different specifications: The tightening force will vary depending on the specifications, materials and connected materials of the screws. For example, for metal self-tapping screws, the same specification of "Type I" self-tapping screws has a lower penetration torque than "Type II". "Type I" self-tapping screws have a larger torque selection window and a higher safety factor for installation; the same specification of "Type II" self-tapping screws has a higher torque efficiency than "Type I". With the same clamping force, "Type II" self-tapping screws consume less torque.
Plastic self-tapping screws: The common cause of tightening failure is cracking of the plastic of the connected part, which shows that the tightening force is closely related to the strength of the connected material.
