GB/T 39693.3-2021 in English
VALIDRubber, vulcanized or thermoplastic—Determination of hardness—Part 3:Dead-load hardness using the very low rubber hardness (VLRH) scale
- Issued on:2021-03-09
- Implemented on:2021-10-01
- File Format:PDF
- Delivery:Via email within 1~3 business days
$214.00
《GB/T 39693.3-2021硫化橡胶或热塑性橡胶 硬度的测定 第3部分：用超低橡胶硬度（VLRH）标尺 测定定试验力硬度》由TC35（全国橡胶与橡胶制品标准化技术委员会）归口，TC35SC2（全国橡胶与橡胶制品标准化技术委员会通用试验方法分会）执行，主管部门为中国石油和化学工业联合会。
Introduction
Analysis of the core content of the standard
GB/T39693.3-2021 is equivalent to the ISO483:2018 international standard, which is specifically designed for the hardness determination of ultra-soft rubber below 35IRHD. The standard innovatively introduces the VLRH scale, which measures the indentation depth difference ΔD of a 2.50mm spherical indenter under a contact force of 8.3mN and a total force of 100mN, to achieve a 0-100VLRH linear calibration.
Comparison of key test parameters
| Parameters | VLRH method | Traditional IRHD method | Shaw AO method |
|---|---|---|---|
| Applicable hardness range | 0-35IRHD | 10-100IRHD | 20-90AO |
| Indenter diameter | 2.50±0.01mm | 2.5/5.0mm | Cone |
| Total test force | 100.0±1.0mN | 5.4-8.3N | 8.06N |
Technology Evolution Background
The standard solves the problem of insufficient resolution of traditional methods in testing ultra-soft rubber (such as printing rubber rollers and shock-absorbing supports). By reducing the pressing force to 100mN and using precise displacement measurement (±0.001mm), the hardness resolution reaches 0.5VLRH, which is more than 4 times higher than the IRHD method.
Key points for implementation
- Specimen requirements: Thickness ≥6mm (thinnest layer ≥2mm), distance between measuring point and edge ≥3mm
- Environmental control: Adjustment is required at standard laboratory temperature for ≥3h
- Test process: Contact force maintained for 5s → Apply indentation force for 30s → Read VLRH value directly
- Surface correction: Compensation is required through the difference between Hflat and Hcurved
Key items for calibration
Take Borui hardness tester as an example, regular calibration is required:
- Spherical indenter diameter error ≤±0.01mm (N grade)
- Pressing force 91.7mN±0.5mN (S grade)
- Pressing force 235±30mN (U grade)
It is recommended to establish a calibration plan according to ISO489:2018, in which the displacement sensor needs to be calibrated every 6 months.
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