Quality Testing of Rubber Materials

Ensuring Rubber Product Integrity

Rubber materials and products must adhere to strict quality standards, encompassing tensile strength, elastic modulus, elongation, and aging resistance. These parameters are critically important for rubber products used in high-precision applications.

Authority: Rubber Products Committee

In the early days of rubber development in China, the Rubber Products Committee was founded. It serves as a vital body responsible for rubber research and development, academic studies, and quality supervision.

1. Solvent Swell Test (Media Resistance)

Objective and Procedures

This test identifies rubber types by measuring weight and hardness changes after immersion in a solvent.

Method

Samples are taken from the finished product and immersed in a selected medium (or combination of media) at a specified temperature for a set duration. Afterward, the samples are weighed, and the durometer is tested. The type of material is then inferred based on changes in weight and hardness.

Example: Immersion in 100°C motor oil for 24 hours.

• Minimal Changes: NBR (Nitrile Butadiene Rubber), FKM (Fluorocarbon Rubber), and CR (Chloroprene Rubber) exhibit minimal changes in mass and hardness.

• Significant Changes: NR (Natural Rubber), EPDM (Ethylene Propylene Diene Monomer Rubber), and SBR (Styrene-Butadiene Rubber) show mass increases of over 100%, significant hardness alterations, and substantial volume expansion.

After media testing, we can test thermal age testing to tell what materials are in the product.

2. Hot Air Aging Test

Accelerated Degradation Analysis

This test projects long-term material behavior through controlled thermal oxidation.

Method

Samples from the finished product are aged in an aging chamber for a specific duration at elevated temperatures. Post-aging, the samples are evaluated for changes. The test can be conducted in stages, gradually increasing the temperature.

Example:

• 150°C: CR (Chloroprene Rubber), NR (Natural Rubber), and SBR (Styrene-Butadiene Rubber) become brittle. NBR (Nitrile Butadiene Rubber) and EPDM (Ethylene Propylene Diene Monomer Rubber) retain some elasticity.

• 180°C: Standard NBR becomes brittle.

• 230°C: HNBR (Hydrogenated Nitrile Butadiene Rubber) becomes brittle, while FKM (Fluorocarbon Rubber) and silicone rubber maintain elasticity.

Comparing the change of the material with the heat, flammability helps determine the class of polymer.

3. Burning Method

Qualitative Analysis via Combustion

Observing combustion characteristics provides clues about rubber composition.

Method

A small sample is burned in open air, and its behavior is closely observed.

Observations:

• Self-Extinguishing Materials: FKM (Fluorocarbon Rubber) and CR (Chloroprene Rubber) tend to be self-extinguishing once the ignition source is removed. If they do burn, the flame is typically smaller than that of NR (Natural Rubber) or EPDM (Ethylene Propylene Diene Monomer Rubber).

• Detailed Examination: Careful observation of the burning state, flame color, and odor can further refine the analysis. For example, NBR/PVC blends may exhibit sputtering flames (as if water is present), self-extinguish upon removal of the ignition source, and produce a dense smoke with an acidic odor.

Note: Halogen-free flame retardants can also cause self-extinguishing behavior. Additional tests may be required for definitive identification.

Once flammability rating is set, let's determine the density the rubber with density testing.

4. Density Measurement

Determining Material Class Through Density

This test is a reliable way to classify materials by the weight.

Method

An electronic scale or analytical balance precise to 0.01 grams is used. A beaker of water and a fine hair-like thread are also required.

Guidance:

• High Density: FKM (Fluorocarbon Rubber) typically has the highest density, exceeding 1.8. CR (Chloroprene Rubber) often has a density above 1.3. High density materials can strongly support that the material class if these polymers.

We can also tell a lot from the glass transition temperatures. Let's touch on glass transition determination by exposing the rubber to cold temperatures.

5. Low Temperature Test

Understanding Glass Transition

This test can detect glass transition of material, and what materials they contain.

Method

Samples are submerged in a suitable low-temperature environment created using dry ice and alcohol. After soaking for 2-5 minutes, the hardness and flexibility of the samples are assessed at the selected temperature.

Example:

• -40°C: Comparing silicone rubber and FKM (Fluorocarbon Rubber), silicone rubber remains relatively soft, while both exhibit good high-temperature and oil resistance. Low-temperature properties can further clarify the nature of the polymer.

With material property, it is important to determine the properties. Here's a wrap up of understanding rubber with hardness testers and low and high temperatures.

Conclusion: Comprehensive Material Analysis for Rubber Products

Quality Control is Vital

Each analysis is useful in getting insights on rubber materials. This knowledge confirms that product design has been maintained.

All the tests are critical for the right designs for electrical cables. Safe reliable quality can be measured through quality testing.