GB/T 3098.5-2016 specifies the mechanical properties of self-tapping screws, ensuring their reliability in fastening applications across industries such as automotive, construction, and electronics. This standard outlines requirements for surface hardness, case depth, core hardness, test plate thickness and hole diameter for tapping tests, and minimum torsional strength. Compliance with these parameters guarantees that self-tapping screws perform effectively in forming their own threads without pre-drilling, while maintaining structural integrity under load.
Key Mechanical Properties
The standard defines properties for self-tapping screws with thread designations from ST2.2 to ST9.5. These include minimum surface hardness, case depth ranges, core hardness ranges, dimensions for standard test plates used in tapping performance tests, and minimum breaking torque values. The data ensures screws can withstand installation stresses and operational demands.
| Property / Thread | ST2.2 | ST2.6 | ST2.9 | ST3.3 | ST3.5 | ST3.9 | ST4.2 | ST4.8 | ST5.5 | ST6.3 | ST8 | ST9.5 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Surface Hardness (min) | 450 HV0.3 | 450 HV0.3 | 450 HV0.3 | 450 HV0.3 | 450 HV0.3 | 450 HV0.3 | 450 HV0.3 | 450 HV0.3 | 450 HV0.3 | 450 HV0.3 | 450 HV0.3 | 450 HV0.3 |
| Case Depth (min, mm) | 0.04 | 0.04 | 0.05 | 0.05 | 0.05 | 0.1 | 0.1 | 0.1 | 0.1 | 0.15 | 0.15 | 0.15 |
| Case Depth (max, mm) | 0.1 | 0.1 | 0.18 | 0.18 | 0.18 | 0.23 | 0.23 | 0.23 | 0.23 | 0.28 | 0.28 | 0.28 |
| Core Hardness (range) | 270 HV5 ~ 370 HV5 | 270 HV5 ~ 370 HV5 | 270 HV5 ~ 370 HV5 | 270 HV5 ~ 370 HV5 | 270 HV5 ~ 370 HV5 | 270 HV5 ~ 370 HV5 | 270 HV10 ~ 370 HV10 | 270 HV10 ~ 370 HV10 | 270 HV10 ~ 370 HV10 | 270 HV10 ~ 370 HV10 | 270 HV10 ~ 370 HV10 | 270 HV10 ~ 370 HV10 |
| Standard Test Plate Thickness (min, mm) | 1.17 | 1.17 | 1.17 | 1.17 | 1.85 | 1.85 | 1.85 | 3.1 | 3.1 | 4.67 | 4.67 | 4.67 |
| Standard Test Plate Thickness (max, mm) | 1.3 | 1.3 | 1.3 | 1.3 | 2.06 | 2.06 | 2.06 | 3.23 | 3.23 | 5.05 | 5.05 | 5.05 |
| Standard Test Plate Hole Diameter (min, mm) | 1.905 | 2.185 | 2.415 | 2.68 | 2.92 | 3.24 | 3.43 | 4.015 | 4.735 | 5.475 | 6.885 | 8.27 |
| Standard Test Plate Hole Diameter (max, mm) | 1.955 | 2.235 | 2.465 | 2.73 | 2.97 | 3.29 | 3.48 | 4.065 | 4.785 | 5.525 | 6.935 | 8.33 |
| Breaking Torque (min, N·m) | 0.45 | 0.9 | 1.5 | 2 | 2.7 | 3.4 | 4.4 | 6.3 | 10 | 13.6 | 30.5 | 68 |
Note: Hardness values are measured using Vickers method with specified loads (e.g., HV0.3 indicates 0.3 kgf load). Case depth refers to the carburized layer, essential for thread-forming capability. Test plate specifications ensure consistent evaluation of tapping performance.
Alternative Standards
For international compatibility, GB/T 3098.5-2016 aligns closely with ISO 2702:2011, which provides equivalent requirements for heat-treated steel tapping screws.
Soalan Lazim (FAQ)
- What is the purpose of surface hardness in self-tapping screws?
- Surface hardness, set at a minimum of 450 HV0.3, ensures the screw can cut and form threads in the mating material without deformation, enhancing durability in applications like sheet metal assembly.
- How does case depth affect screw performance?
- Case depth, ranging from 0.04 mm minimum to 0.28 mm maximum depending on size, provides a hardened outer layer for thread-forming while maintaining a tougher core, preventing brittle failure during installation.
- Why are core hardness ranges specified?
- Core hardness (270 to 370 HV with varying loads) balances strength and ductility, ensuring the screw resists torsional stresses without cracking, critical for reliable fastening in dynamic environments.
- What do the test plate dimensions indicate?
- These dimensions standardize tapping tests, simulating real-world materials. For example, for ST4.8, the plate thickness ranges from 3.1 to 3.23 mm with hole diameters from 4.015 to 4.065 mm, verifying screw performance consistency.
- How is breaking torque tested and why is it important?
- Breaking torque, with minimum values up to 68 N·m for ST9.5, is tested by applying torque until failure. It ensures the screw can handle installation forces without breaking, vital for safety in structural applications.
- Is GB/T 3098.5-2016 compatible with international standards?
- Yes, it is harmonized with ISO 2702:2011, allowing for global interchangeability in design and procurement of self-tapping screws.
