The tensile test (stretch performance test) of rubber hot water bags is based on HG/T 2011-2009 (product standard) and GB/T 528-2009 (method standard). The main measurements include tensile strength and elongation at break, to determine whether the bag is prone to cracking or aging and whether it becomes brittle.
I. Standards and Qualification Indicators (Key)
- Standard - Method: GB/T 528-2009 (dumbbell specimen, 500mm/min)
- Product: HG/T 2011-2009
- Qualification Requirements (at room temperature) - Tensile strength ≥ 14.0 MPa
- Elongation at break ≥ 450%
(The recommended content of natural rubber should be ≥ 45% to meet the requirements)
II. Sample Preparation (Cutting Samples from the Hot Water Bag)
- Shape: 2-type dumbbell shape (working width 6mm, gauge length 25mm)
- Location: Cut from the flat part of the hot water bag (avoiding patterns, seams, and areas with uneven thickness)
- Quantity: 5 samples per group (one group for longitudinal direction and one group for transverse direction)
- State adjustment: Place at 23℃ ± 2℃, relative humidity 50% ± 5% for ≥ 3 hours
III. Testing Equipment
- Electronic tensile testing machine (accuracy 1 grade, automatic recording of force/ displacement)
- Clamping device: pneumatic/manual, with corrugated inner liner/sandpaper (anti-slip)
- Thickness gauge (accuracy 0.01mm), standard cutting knife
IV. Test Procedures (Standard Process)
1. Measure dimensions
Measure the thickness/width at 3 points within the gauge length and calculate the average to obtain the cross-sectional area.
2. Clamping
The sample should be vertical, centered, and without distortion; apply an initial tension of 0.1 to 0.5 N (just to straighten it).
3. Parameters
Speed: 500 mm/min; Select GB/T 528-2009; Automatic stop.
4. Breakage
Record the maximum force Fb and the elongation at break; - Valid: Break occurs in the middle of the gauge length
- Invalid: Breaks at the fixture, slips, or skips (re-test)
5. Calculation - Tensile strength (MPa) = Fb (N) / Original cross-sectional area (mm²)
- Elongation at break (%) = ((Breakage gauge length - Original gauge length) / Original gauge length) × 100%
6. Results
Take the average of 5 valid samples and retain 1 decimal place.
V. Common Causes of Nonconformity
- Low strength: Insufficient rubber content, insufficient vulcanization, excessive fillers, uneven rubber mixing
- Low elongation: Excessive vulcanization, aging, hard rubber compound, presence of bubbles/impurities
- Large data fluctuations: Defects in the sample, skewed clamping, slipping of the fixture, uneven thickness
VI. Important Notes
- The hot water bag is made of thin rubber sheet (0.8 - 1.5mm). During cutting and clamping, handle with care to avoid damage.
- The test environment's temperature and humidity are strictly controlled (a 1℃ difference in temperature can result in a 2 - 5% difference in results).
- Aging test: Regularly conduct hot air aging (70℃ × 24 hours / 48 hours) and then measure the tensile strength to check the retention rate.
