DIN 267-26

DIN 267-26:2005-12
Mechanical fasteners—Technical delivery conditions—Part 26: Spring steel lock washers for bolted joints

1. Scope
   DIN 267-26 applies to conical lock washers made of spring steel in accordance with DIN 6796 and DIN 6908, which are used as anti-loosening devices in bolted joints. The objective is to compensate for the loss of preload due to embedding or creeping—but not to prevent loosening under transverse loads.
2. Materials and Surface Requirements
   Permissible materials are spring steels in accordance with DIN EN 10089 or EN 10132-4 with a final hardness of 420–490 HV to prevent hydrogen embrittlement. The surfaces must be smooth, burr-free, and protected against corrosion. Electrolytic coatings in accordance with DIN EN ISO 4042 are permitted; however, caution is advised at high hardness levels due to the risk of brittle fracture.
3. Test Requirements
   a) Dimensional inspection: per DIN EN ISO 3269, AQL 1.5
   b) Hardness test: per DIN EN ISO 6507-1/6508-1; target value: 420–490 HV
   c) Set test: Compressive load for 2 minutes, minimum residual height as per Table 1
   d) Endurance test: 48 h at 100 °C, max. 2% loss of height, no cracks/breaks
   e) Spring force test: Test stroke –20 µm, minimum residual spring force per Table 2
   Spring characteristic curve and contact force in accordance with VDI 2230-1 (for screws ≥ 8.8)
4. Packaging and Marking
   Tension washers must be packaged in a manner that provides mechanical protection. Each package must be labeled with the standard designation, dimensions, quantity, and manufacturer’s identification (e.g., “DIN 6796 – 8 – FSt”).
5. Overall Assessment
   DIN 267-26 establishes mandatory technical delivery requirements for spring steel lock washers. It ensures:
   - Reliable compensation for loss of preload
   - Resistance to embrittlement when the correct material is selected
   - Standard-compliant testing, material quality, and surface protection
   
   The standard thus forms a central basis for the safe and quality-assured use of lock washers in technically demanding bolted joints.