Nitrile rubber-metal composite sealing material is based on a metal plate, and the two sides of the metal plate are coated with nitrile rubber foaming coating to form an elastic rubber coating. The composite material not only has the high elasticity, excellent compressibility, and oil resistance of rubber but also has the excellent mechanical strength and hardness of a metal plate. Therefore, nitrile rubber-metal composite sealing materials can play the role of sealing, shock absorption, solvent resistance, and leakage prevention on different occasions, especially in the field of sealing.
1. Preparation and research progress of nitrile rubber metal composite sealing materials
Before preparing the NBR metal composite sealing material, the stainless steel plate must be pretreated. The purpose of matrix pretreatment is mainly two: one is to increase the bonding strength between rubber coating and metal plate (i.e. increase rubber adhesion); Another purpose is to increase the anti-corrosion and anti-wear performance of foamed rubber coating. The combination between nitrile rubber coating and stainless steel plate is mainly mechanical force, which requires that the plate should not only remove oil and rust but also roughen the surface. Roughening the surface is to increase the contact area between the coating and the substrate and increases the chimeric effect between the coating material and the substrate surface. Although the plate is pretreated, the adhesion between nitrile rubber and it is still poor and easy to fall off, which can not meet the requirements of sealing plate. An appropriate process is needed to improve this shortcoming.
The adhesion between nitrile rubber and stainless steel plate is poor. To increase the adhesion between them, the primer process is adopted. Apply hemlock glue on the metal plate to increase the adhesion between the rubber and the metal plate. Hemlock adhesive has excellent adhesion to metal and can also be well combined with nitrile rubber. The bonding between nitrile rubber and hemlock rubber is diffusion bonding, that is, the mutual diffusion between the rubber coating and the substrate surface. Nitrile rubber and hemlock rubber are “intertwined” to form a diffusion layer so that the interface between them disappears, to closely connect the rubber coating with the metal plate.
Nitrile rubber-metal composite sealing material is mainly used in automobile engine parts, which should be in long-term contact with various oils in the process of use. At this time, the oil can diffuse with the internal molecules of the rubber, so that the network structure of the vulcanizate changes and swelling occurs. The strength and mechanical properties of rubber swelled by oil are greatly reduced. The oil resistance of rubber depends on the polarity of rubber and oil. Nitrile rubber contains a polar group nitrile group, which has a high polarity, while oil belongs to a non-polar solvent. According to the selection principle of polymer-solvent, nitrile rubber is not easy to swell due to the large difference in polarity. Generally, the oils contacted by automobile engines are fuel oil and mineral oil, which belong to non-polar oils. The oil resistance of nitrile rubber-metal composite sealing materials also refers to non-polar oils. In recent years, to save oil resources, gasolin e added with ethanol and methanol is being used in industry. According to the development trend of this fuel, a new type of foamed rubber-metal composite sealing material may be developed in the future.
Nitrile rubber-metal composite sealing material was first used in the gasket of the automobile engine cylinders. The gasket used in the early stage was an asbestos board. This kind of gasket has poor performance and is harmful to the human body. Most foreign enterprises produce asbestos nitrile rubber sheets, but the service temperature of pure NBR is low and can not be used in automobile engine cylinders. With the progress of science and technology and the enhancement of human awareness of environmental protection, people have higher and higher requirements for industrial production . They not only require the practicability and beauty of sealing materials but also focus on whether environmental pollution is harmful to the human body. Based on the above problems, researchers at home and abroad have carried out a lot of research in the field of NBR metal composite sealing plates.
2. Application of nitrile rubber metal composite sealing materials
Successfully prepared NBR metal composite sealing products with nitrile rubber as a matrix through the coating process. The NBR metal composite sealing material has both the stability of metal and the high elasticity of rubber. The rubber and metal can be firmly bonded .It is an ideal sealing material.
Introduced the best formula for preparing NBR metal composite sealing material with nitrile rubber dn219 as the matrix and peroxide as the main vulcanization system. The main additives in the formula are zinc oxide 5 phr, stearic acid 1 phr, antioxidant 4010nal phr, and plasticizer dop4 phr. The main filler is thermosetting phenolic resin and N330 carbon black. The modified formula has been put into production in many enterprises and has been applied to motorcycle cylinders, water pumps, air compressors, and other related fields.
To solve the problems of uneven foaming and poor sealing of NBR metal composite sealing materials, we explored the effects of vulcanization time, vulcanization temperature, amount of foaming agent, and filler on the foaming rate of foamed rubber composites. The results show that the performance of NBR metal composite sealing material is the best when the curing time is 20 min, the curing temperature is 140 ℃, the amount of foaming agent is 10% of the total mass of vulcanizate and the amount of filler is 30% of the total mass of vulcanizate. At this time, the foaming rate of foamed rubber is 172%, and the average cell diameter is about 68.35 μm.
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