How To Choose The Elasticity Of The Sealing Ring Material For A Waterproof Junction Box? This Article Will Help You Figure It Out.

Many people focus all their attention on the box material and IP rating when purchasing waterproof cable box, but overlook a detail that directly affects the sealing effect - the elasticity of the sealing ring. Simply put, a sealing ring lacking elasticity is useless; when the cap is tightened, the ring's insufficient rebound leaves microscopic gaps invisible to the naked eye at the seams, allowing moisture to slowly seep in over time.

The elasticity of the sealing ring stems from the material's molecular chain structure. Different formulations correspond to different rebound capabilities, which is why simply looking at hardness data is ineffective;

A comparative analysis of the elasticity of several common materials

Currently, the three most commonly used materials for plastic weatherproof electrical box sealing rings on the market are: silicone rubber (VMQ), ethylene propylene diene monomer (EPDM), and fluororubber (FKM).

• Silicone rubber (VMQ): Excellent elastic recovery; remains soft even at low temperatures (-55℃) and will not harden or crack due to cold weather. However, its mechanical strength is relatively low, and it is prone to permanent deformation under prolonged pressure, with a gradual decrease in compression rebound.

• Ethylene Propylene Dioxide (EPDM):

  • Stable overall elasticity, higher tear strength than silicone rubber.

  • Molecular chains are less prone to breakage under outdoor UV radiation, resulting in slow elastic decay.

  • Strongest water resistance among the three, low volume change rate, and minimal deformation after long-term immersion in water.

  • Operating temperature range approximately -50℃ to +150℃, suitable for most outdoor conditions.

• Fluororubber (FKM): Slightly lower elasticity than silicone rubber, but strongest resistance to chemical media, suitable for industrial applications with complex media such as oil and solvents; also the most expensive.

Besides elasticity, "compression set" is also important.

Elasticity alone is not enough. A more practical indicator for selecting seals is "compression set"—the rate at which the seal springs back to its original thickness after being compressed for a period of time.

A lower compression set indicates that the seal remains in contact with the junction box cover even after material aging, resulting in more stable long-term waterproof performance. EPDM performs better than ordinary silicone rubber in this indicator, especially in waterproof junction box applications requiring long-term outdoor use; this difference becomes increasingly apparent over time.