This standard specifies the mechanical properties and test methods for self-drilling tapping screws. Below is a structured outline to guide through the key sections:<\/p>\n
The standard outlines precise requirements for self-drilling tapping screws to ensure reliability in fastening applications. These screws are designed for drilling and tapping in a single operation, commonly used in construction, automotive, and machinery industries.<\/p>\n
Self-drilling tapping screws must be manufactured from case-hardening steel or heat-treated steel. This selection ensures the necessary balance between ductility in the core and hardness on the surface, critical for drilling through materials like steel or aluminum without pre-drilling.<\/p>\n
Metallurgical properties are essential for the screw’s performance under stress. Proper heat treatment prevents failures such as cracking or brittleness.<\/p>\n
After heat treatment, the surface hardness of self-drilling tapping screws shall be at least 530 HV 0.3. This high surface hardness enables effective drilling and tapping, reducing wear on the screw tip during installation.<\/p>\n
The core hardness after treatment is specified as follows:<\/p>\n
A recommended minimum tempering temperature is 330\u00b0C. Avoid the tempering range of 275\u00b0C to 315\u00b0C to minimize the risk of tempered martensite embrittlement, which could lead to premature failure under load.<\/p>\n
The case depth must comply with the values in Table 1. This depth ensures sufficient hardened layer for drilling while maintaining core toughness.<\/p>\n
| Thread Size<\/th>\n | Min (mm)<\/th>\n | Max (mm)<\/th>\n<\/tr>\n<\/thead>\n | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| ST 2.9 and ST 3.5<\/td>\n | 0.05<\/td>\n | 0.18<\/td>\n<\/tr>\n | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| ST 4.2 to ST 5.5<\/td>\n | 0.10<\/td>\n | 0.23<\/td>\n<\/tr>\n | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| ST 6.3<\/td>\n | 0.15<\/td>\n | 0.28<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\nMicrostructure<\/h4>\nIn the heat-treated microstructure, no banded ferrite shall appear between the surface hardened layer and the core. This ensures uniform strength and prevents weak zones that could cause shear failure.<\/p>\n Hydrogen Embrittlement<\/h4>\nElectroplated self-drilling tapping screws are at risk of hydrogen embrittlement-induced fracture. Manufacturers and platers must implement measures, including testing per GB\/T 3098.17, to control this risk. Additionally, consider the hydrogen embrittlement relief requirements in GB\/T 5267.1 for electroplated fasteners to enhance long-term durability.<\/p>\n Mechanical Properties<\/h3>\nMechanical properties define the screw’s ability to perform under operational conditions, including drilling, tapping, and load-bearing.<\/p>\n Drilling Performance<\/h4>\nThe drilling portion of the screw must drill a prefabricated hole suitable for extruding mating internal threads under the test conditions specified in section 4.2.1. This ensures efficient installation without additional tools.<\/p>\n Thread Forming Performance<\/h4>\nIn the prefabricated hole drilled per 3.3.1, the screw shall extrude mating internal threads without deformation when screwed into the test plate as per 4.2.1.1. This property is vital for secure fastening in thin materials.<\/p>\n Torsional Strength<\/h4>\nWhen tested per 4.2.3, the torsional strength shall ensure the failure torque equals or exceeds the values in Table 4. High torsional strength prevents breakage during tightening.<\/p>\n Test Methods<\/h2>\nStandardized test methods verify compliance with the requirements, providing reproducible results for quality assurance.<\/p>\n Metallurgical Performance Tests<\/h3>\n |
| Thread Size<\/th>\n | Test Plate Thickness (mm)<\/th>\n | Axial Force (N)<\/th>\n | Max Screwing Time (s)<\/th>\n | Screw Speed (rpm)<\/th>\n<\/tr>\n<\/thead>\n | ||||||||||||||||||||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| ST 2.9<\/td>\n | 0.7 + 0.7 = 1.4<\/td>\n | 150<\/td>\n | 3<\/td>\n | 1800\u20132500<\/td>\n<\/tr>\n | ||||||||||||||||||||||||||||||||||||||||||
| ST 3.5<\/td>\n | 1 + 1 = 2<\/td>\n | 150<\/td>\n | 4<\/td>\n | 1800\u20132500<\/td>\n<\/tr>\n | ||||||||||||||||||||||||||||||||||||||||||
| ST 4.2<\/td>\n | 1.5 + 1.5 = 3<\/td>\n | 250<\/td>\n | 5<\/td>\n | 1800\u20132500<\/td>\n<\/tr>\n | ||||||||||||||||||||||||||||||||||||||||||
| ST 4.8<\/td>\n | 2 + 2 = 4<\/td>\n | 250<\/td>\n | 7<\/td>\n | 1800\u20132500<\/td>\n<\/tr>\n | ||||||||||||||||||||||||||||||||||||||||||
| ST 5.5<\/td>\n | 2 + 3 = 5<\/td>\n | 350<\/td>\n | 11<\/td>\n | 1000\u20131800<\/td>\n<\/tr>\n | ||||||||||||||||||||||||||||||||||||||||||
| ST 6.3<\/td>\n | 2 + 3 = 5<\/td>\n | 350<\/td>\n | 13<\/td>\n | 1000\u20131800<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n Test plate thickness may consist of two steel plates. These values are for acceptance inspection only.<\/p>\n Test Procedure<\/h5>\nScrew the coated or uncoated specimen into the test plate until one full thread passes through. Apply axial force and speed per Table 2 throughout drilling and tapping.<\/p>\n Drilling Inspection<\/h4>\nBy agreement, perform drilling inspection using test plates per 4.2.1.1 with thickness per Table 3. Pre-punch a locating point. After drilling through, the maximum hole size shall not exceed Table 3 limits.<\/p>\n \n
|