Overview
ISO 2951:2019 specifies a practical test method for determining the insulation resistance of vulcanized and thermoplastic rubbers. The method measures total insulation resistance without distinguishing between volume and surface contributions and is intended for test pieces with relatively high resistance (see the standard for the applicable resistance threshold). ISO 2951:2019 is an empirical, rapid quality-indication test: simple to prepare and useful when extreme precision is not required.
Key topics and requirements
- Scope and applicability: Applies to vulcanized and thermoplastic rubber test pieces above the resistance threshold indicated in the standard; alternative methods (ISO 1853, ISO 2878) are referenced for lower-resistance materials.
- Test equipment: Resistance is determined by measuring current and voltage; a stable d.c. supply of (500 ± 10) V is specified. Measuring equipment should have the sensitivity and an accuracy of ±5 %. (See IEC 62631-3-x references for measurement principles.)
- Electrodes:
- Conducting-paint electrodes (conductive silver or colloidal graphite) for flat plates, tubes and rods - applied as ~1 mm strips spaced 10 ± 0.5 mm.
- Bar electrodes for thin sheets and tapes - metal bars (≈10 × 10 × 50 mm) spaced ~25 mm with guarding arrangements.
- Test pieces and preparation:
- Dimensions specified for plate, rod/tube, tape and thin-sheet formats.
- Electrodes must be attached before conditioning.
- Cleaning guidance (alcohol/ether or other suitable solvent) and handling precautions are provided in Annex A.
- Conditioning: At least 16 h at controlled environments - (23 ± 2) °C & (50 ± 5)% RH or (27 ± 2) °C & (65 ± 5)% RH; use same conditions throughout comparable tests.
- Procedure and results:
- Measure each test piece individually while still in the conditioning atmosphere.
- Electrification time typically 1 min at the specified voltage.
- Results are normalized to standard electrode lengths (formulas given for 100 mm and 25 mm reference lengths) and reported in megaohms; at least three test pieces required and the median value should be reported.
- Calibration and reporting: Calibration schedule is normative (Annex B); test reports must include sample details, test conditions, electrode type, cleaning, test voltage/time, individual results and median value.
Applications and users
ISO 2951:2019 is used for:
- Quality control and routine inspection in rubber manufacturing
- Incoming material verification for component suppliers
- Materials testing laboratories and R&D when screening insulating rubbers
- Comparative assessments of insulation performance where a quick, reproducible indication is needed
Primary users: materials engineers, QA/QC technicians, test lab managers, rubber compounders and product developers.
Related standards
- ISO 1853, ISO 2878 - methods for lower-resistance test pieces
- ISO 18899 - guide to calibration of test equipment
- IEC 62631-3-1 / -3-2 / -3-3 - general principles and resistance measurement methods
Keywords: ISO 2951:2019, insulation resistance, vulcanized rubber, conducting-paint electrodes, bar electrodes, rubber testing, test method, calibration, conditioning.
