Overview
ISO 7931:1985 specifies dimensions and requirements for insulated caps (taps) and bushes used in the secondary circuit of resistance welding equipment. Intended particularly for use with electrode back‑ups in accordance with ISO 5827, the standard defines material selection, finish, marking and designation to ensure safety, interchangeability and correct assembly of welding accessories.
Key Topics
- Scope: Dimensions and requirements for insulated caps (C) and bushes (B) in the secondary circuit for resistance welding equipment, with emphasis on use in back‑ups.
- Materials: Insulation parts shall be manufactured from high‑strength insulating material, for example glass fibre reinforced polyamide. Washers used with bushes are steel, e.g. Fe 510.
- Finish: Edges must be chamfered and grooves rounded to avoid stress concentrations and facilitate assembly.
- Marking & Designation:
- Insulation caps are marked with the letter C. Example designation: Insulation cap ISO 7931 - C.
- Insulation bushes are marked with B and the size (e.g., B 10). Example designation: Insulation bush ISO 7931 - B 10.
- Loading & Support: Insulation bushes conforming to ISO 7931 are intended to be loaded only by the torque moment of fixing screws. Additional axial or lateral forces must be taken up by other measures (shoulders, washers or similar supports).
Applications
ISO 7931 components are used as insulating interfaces in resistance welding secondary circuits, for example in electrode holders, back‑ups and clamps. Practical benefits and uses include:
- Safety: Standardized insulating materials and finishes reduce electrical and mechanical risk.
- Interchangeability: Defined dimensions and designation improve compatibility between manufacturers and equipment.
- Procurement clarity: Clear marking and standard reference on orders (e.g., "Insulation bush ISO 7931 - B 10") reduce ambiguity and supply errors.
Practical implementation notes:
- Use a washer to support a bush when the hole diameter is significantly larger than the bush or when slotted holes are used.
- Provide mechanical shoulders or supports to absorb any forces beyond fixing screw torque.
- Reference the ISO 7931 designation on drawings, BOMs and purchase orders for unambiguous specification.
Related Standards
- ISO 5827 - Spot welding: electrode back‑ups and clamps (application context)
- ISO 887 - Plain washers for metric bolts, screws and nuts (general plan)
- ISO 4762 - Hexagon socket head cap screws (product grade A)
This guidance summarizes the practical value of ISO 7931:1985 for designers, manufacturers and maintenance teams working with resistance welding equipment. Use the standard reference to ensure compatibility, safety and maintainability of insulating caps and bushes.