What Is a Screw Nut?
Screw nuts are components used in conjunction with a rotary shaft, enabling the rotation of the screw part for conveyance and precise positioning of objects.
Constructed from die-cast metal, screw nuts offer durability and cost-effectiveness compared to ball screws. However, they tend to be less efficient due to the higher friction in the screw threads. Selecting the appropriate screw nut is crucial, considering the load they will move and the desired accuracy.
Uses of Screw Nuts
Screw nuts find applications in transporting objects within a specified range and in lifting and lowering equipment. When integrated with an automatic device on the rotary shaft, they facilitate precise, electrically controlled movement of equipment.
Examples of applications include:
- Lifting and lowering parts in FA (Factory Automation) equipment
- Motion applications in amusement equipment
- Movable jacks
Principle of Screw Nuts
The principle behind screw nuts is straightforward: a threaded rotary shaft drives the movement of the screw nut. Made from high-strength zinc alloy, screw nuts exhibit excellent friction properties and high load capacity. The mechanical properties include:
- Tensile strength: 275-314 N/mm^2
- Tensile strength (0.2% yield): 216 to 245 N/mm^2
- Compressive strength: 539 to 686 N/mm^2
- Compressive strength (0.2% yield): 294-343 N/mm^2
- Fatigue strength: 132 N/mm^2×10^7 cycles
- Charpy impact value: 0.098 to 0.49 N-m/mm^2
- Elongation: 1 to 5%
- Hardness: 120～145 HV
When selecting screw nuts, consider the following safety factors based on the type of load:
- Static loads used infrequently: Safety factor of 1 to 2
- General unidirectional loads: Safety factor of 2 to 3
- Loads with vibration or impact: Safety factor of 4 or more