The hardness of the oil seal on the market is about 70 degrees, the higher the hardness, the smaller the shrinkage of the rubber, the larger the inner diameter of the oil seal produced, and the smaller the compression change; however, in some special occasions, the oil seal products with hardness lower than 70 degrees may be used. At present, many oil seal manufacturers use NBR to replace a certain proportion of NBR to produce oil seal and reduce the cost of raw materials. Can NBR produce low hardness oil seal? How to design the low hardness oil seal production formula with NBR?
1. Reference formula of low hardness oil seal containing NBR
50 parts of NBR, 60 parts of NBR reclaimed rubber, 5 parts of zinc oxide, 2 parts of stearic acid, 50 parts of carbon black, 15 parts of plasticizer, 1 part of antioxidant, 3 parts of accelerator, 0.5 parts of sulfur, total 186.5 parts. Curing temperature: 155 ℃; curing time: 10min; oil seal hardness: 50 degrees (Shore hardness).
When using NBR reclaimed rubber instead of NBR 1jlyy1031 to produce low hardness oil seal, rubber product manufacturers need to select the low hardness NBR reclaimed rubber which is close to the hardness value according to the hardness of the used NBR raw rubber and the hardness demand of the oil seal.
2. Selection of low hardness NBR oil seal matching agent
When NBR and NBR are used together to produce rubber oil seal, in order to adjust the hardness of oil seal, it is necessary to select reinforcing carbon black and rubber plasticizer reasonably. In general, the quick press furnace black belongs to the medium strength carbon black, which can improve the rubber material stiffness and the rubber material extrusion performance; the fine particle hot cracking carbon black can give the rubber material high elasticity, high elongation, low constant elongation strength and low hardness; the high wear furnace black, medium ultra wear carbon black and other reinforcement carbon black can significantly improve the rubber material hardness, which should be avoided in the formulation of low hardness nitrile oil seal. 。
Adding a proper amount of plasticizer to NBR / NBR compound can reduce the intermolecular force of rubber, improve the plasticity and fluidity of rubber compound, reduce the hardness and constant elongation stress of rubber compound, improve the elasticity and reduce the heat generation of rubber compound; adding a proper amount of DOP when using NBR to produce low hardness oil seal can better coordinate the technological performance, hardness and other mechanical indexes of rubber compound Relationship.
When NBR is used to reduce the production cost of low hardness oil seal, the rubber products manufacturers should choose the vulcanization system with low sulfur and high acceleration, such as the combination of accelerator CZ and accelerator TMTD, with a small amount of sulfur, which is more favorable for the balance of mechanical index of rubber compound. In order to improve the aging resistance of the NBR reclaimed oil seal, the rubber manufacturer can also add a suitable amount of rubber antioxidant OD to improve the protective effect of low hardness oil seal on heat, oxygen, flexing and cracking.