1、 WORLDWIDE FASTENER STANDARD Date: 2001-07-09 WD 950 Material and Performance Requirements for Spaced Thread Tapping Screws and Thread Cutting Screws Printed copies are uncontrolled. Page 1 of 3 Copyright 2001, Ford Global Technologies, Inc. 1. SCOPE This standard covers material and performance req
2、uirements for heat-treated carbon and stainless steel tapping screws and carbon steel thread cutting screws. In normal use, these screws produce mating threads in materials into which they are driven without deforming their own threads or breaking during assembly or in service. For details of other
3、requirements affecting thread cutting screws only see the Appendix. 2. REFERENCES ISO 1502 General purpose metric screw threads - Gauging. ISO 6507 Metallic materials - Hardness test - Vickers test. 3. GENERAL REQUIREMENTS Carbon steel screws shall be made from cold heading quality, killed steel wir
4、e suitable for case hardening. Stainless steel screws shall be made from Type 304 or similar material. NOTE: Stainless steel tapping screws need only meet the material requirements specified in Clause 3. Clauses 4 and 5 apply to carbon steel screws only. 4. METALLURGICAL REQUIREMENTS CARBON STEEL SC
5、REWS ONLY 4.1. CORE HARDNESS The Core Hardness shall be 270-390 HV5 for all types of tapping screws up to and including ST3.9, and 270-390 HV10 for ST4.2 and larger. Core hardness shall be determined at mid-radius of a transverse section through the full minor diameter. 4.2. SURFACE HARDNESS The Sur
6、face Hardness shall be 450 HV0.3 minimum for all types of tapping screws. For routine quality control purposes, surface hardness may be measured on end, shank or head of the screw after suitable preparation, in cases of dispute surface hardness shall be determined by: - Sectioning the specimen at th
7、e center of the longitudinal axis. - Metallurgically mounting and polishing the specimen. - Determining HV0.3 in accordance with ISO 6507, or Knoop (Tukon-500 gram load) hardness at a distance of 0.05mm below the root diameter. 4.3. TOTAL CASE DEPTH A microhardness test shall be carried out at the t
8、hread flank midpoint between crest and root or, in the case of smaller screws up to No. 7 or M4, in the root of the thread. The case depth shall be at the point where the hardness exceeds the actual core hardness by HV25 and shall be in accordance with the following. (Note: For thread cutting screw
9、requirements see the Appendix.) Tapping Screw Size Total Case Depth (mm) Sizes 2.2 and 2.6mm Sizes 2.8 and 3.5mm Sizes 4.2 to 5mm Sizes 6.3mm and larger 0.04 - 0.1 0.05 - 0.18 0.1 - 0.23 0.15 - 0.28 COPYRIGHT Ford Motor CompanyLicensed by Information Handling ServicesWORLDWIDE FASTENER STANDARD Date
10、 2001-07-09 WD 950 Material and Performance Requirements for Spaced Thread Tapping Screws and Thread Cutting Screws Printed copies are uncontrolled. Page 2 of 3 Copyright 2001, Ford Global Technologies, Inc. 4.4. MICROSTRUCTURE The microstructure shall show no band of free ferrite between case and
11、core, as determined by metallographic examination. 5. PERFORMANCE REQUIREMENTS CARBON STEEL SCREWS ONLY 5.1. DRIVE TEST Sample screws (coated or uncoated, as received) shall, without deforming their own thread, produce a mating thread in a test plate described below until a thread of full diameter i
12、s completely through the test plate. 5.1.1. TEST PLATE The test plate shall be made of low carbon steel with a carbon content not exceeding 0.23%, having a hardness of 130-170HV, and thickness as specified in Table 1. Test holes shall be drilled, or punched and redrilled, or reamed, to diameters spe
13、cified in Table 1 for the size of tapping screw being tested. NOTE: Thread cutting screw hole diameters are specified in the Appendix. Table 1. Standard test plate thickness and hole sizes for drive test inspection of tapping screws Dimensions in mm Tapping Screw Plate Thickness Hole Diameter ST Ref
14、 NR Min. Max. Min. Max. 2.2 2.5 2.9 3.3 3.5 3.9 4.2 4.8 5.5 6.3 8 2 3 4 5 6 7 8 10 12 14 16 1.17 1.17 1.17 1.17 1.85 1.85 1.85 3.1 3.1 4.67 4.67 1.3 1.3 1.3 1.3 2.06 2.06 2.06 3.23 3.23 5.05 5.05 1.905 2.185 2.415 2.68 2.92 3.24 3.43 4.015 4.735 5.475 6.885 1.995 2.235 2.465 2.73 2.97 3.29 3.48 4.06
15、5 4.785 5.525 6.935 COPYRIGHT Ford Motor CompanyLicensed by Information Handling ServicesWORLDWIDE FASTENER STANDARD Date: 2001-07-09 WD 950 Material and Performance Requirements for Spaced Thread Tapping Screws and Thread Cutting Screws Printed copies are uncontrolled. Page 3 of 3 Copyright 2001, F
16、ord Global Technologies, Inc. 5.2. TORSIONAL STRENGTH TEST The shank of the sample screw (coated, or uncoated, as received) shall be clamped in mating, split, blind-hole die (Figure 1) or other means, such that the clamped portion of the thread is not damaged and at least two full threads project ab
17、ove the clamping device and at least two full form threads exclusive of point and end slot are held within the clamping device. (A blind hole may be used in place of the clamping device, providing the hole depth is such to ensure that breakage will occur beyond the point, or the full length of the f
18、lute(s) or end slot(s). By means of a suitable calibrated torque measuring device, apply toque to the screw until failure occurs. The torque required to cause failure shall equal or exceed the minimum value shown in Table 3 for the type and size of screw being tested. Torsional strength requirements
19、 for Thread Cutting Screws are specified in the Appendix. Figure 1. Typical test device for torsional tests Table 3. Torsional strength requirements for tapping screws Nominal Size of Screw Minimum Torsional Strength ST Ref NR NM 2.2 2.5 2.9 3.3 3.5 3.9 4.2 4.8 5.5 6.3 8 2 3 4 5 6 7 8 10 12 14 16 0.45 0.9 1.5 2 2.7 3.4 4.4 6.3 10 13.6 30.5 COPYRIGHT Ford Motor CompanyLicensed by Information Handling Services
