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How to Choose Sealing Material of Transformer Bushings

PropertyNBR (Nitrile)Silicone RubberViton (FKM)Cork Rubber
Temperature Range-30°C to 100°C (up to 120°C)-60°C to 200°C-20°C to 250°C-20°C to 100°C
Oil ResistanceExcellent (good with mineral oils)Moderate (less resistant to oils)Excellent (resistant to oils, fuels, chemicals)Moderate (may degrade with oils)
Chemical ResistanceGood with hydrocarbons, oilsGood with ozone, weather, waterExcellent with acids, chemicals, solventsModerate
ElasticityGoodExcellent (flexible, soft)Moderate to goodGood but less elastic
Aging ResistanceModerateExcellent (resistant to ozone, UV)Excellent (very resistant to aging and weathering)Poor to moderate (can dry, crack)
Compression SetModerate (some permanent deformation)Low (recovers well)Low to moderateModerate (compressible but may harden)
CostLow to moderateModerateHighLow
Typical UseGeneral purpose sealing in oil-filled equipmentHigh temp and weather resistance sealingHarsh chemical and high temp sealingLow cost, moderate sealing in less demanding applications

Summary:

  • NBR: Best for oil resistance, general-purpose sealing, good balance of cost and performance.
  • Silicone: Excellent for extreme temperatures and flexibility, but weaker against oils.
  • Viton: Premium sealing, outstanding chemical, oil, and heat resistance for harsh environments.
  • Cork Rubber: Low cost, good compressibility, but less durable and lower resistance to oils and aging.

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