The material of rubber end gaskets can be initially identified using five common methods: combustion method, specific gravity measurement, media resistance weight gain test, hot air aging test, and low temperature method.
1. Combustion Method: Take a small sample and ignite it in air, observing the combustion state, flame color, and odor:
- Nitrile rubber (NBR): The flame is yellow when burning, with black smoke and a pungent odor, similar to burning plastic.
- Fluororubber (FKM): Self-extinguishing after being removed from the flame, producing dense smoke with a sour smell, and a small flame.
- Silicone rubber: Leaves a white powdery residue after burning, with no obvious flame.
- Ethylene propylene diene monomer (EPDM): Burns continuously with a bright flame, and shows softening and dripping.
2. Specific Gravity Measurement: Measure the sample density using an electronic scale:
- Fluororubber has the highest specific gravity, typically above 1.8;
- Chloroprene rubber (CR), ECO, etc., also mostly have specific gravities above 1.3;
- A significantly higher specific gravity can be preliminarily identified as fluororubber or chloroprene rubber.
3. Weight Gain Test: Immerse the sample in a specific medium (such as 100℃ machine oil) for 24 hours and then weigh it:
- NBR, fluororubber, CR, and ECO show little change in mass and hardness;
- NR, EPDM, and SBR, however, will more than double in weight, with a significant volume expansion.
4. Hot Air Aging Test: Place the samples in an aging chamber and heat for one day, gradually increasing the temperature and observing the changes:
- At 150℃, natural rubber (NR), chloroprene rubber (CR), and SBR will become brittle, while NBR and EPDM will remain elastic;
- At 180℃, ordinary NBR will become brittle;
- At 230℃, hydrogenated nitrile butadiene rubber (HNBR) will also break, but fluororubber and silicone rubber will maintain good elasticity.