Development of Quenchant in vacuum furnace
Release date： 2014-02-09 00:00 source： http://www.bkktraining.com Click：
Oil based quenchant
The earliest used oil is animal and vegetable oil, which has weak cooling capacity, but still has enough cooling capacity, and when the oil temperature rises, it has little effect on the quenching capacity, so it is an ideal quenching medium. Due to the limitation of price and raw material source, mineral oil is widely used in industry, such as 0 × diesel oil, 15 ~ 32 × viscosity grade mechanical oil, etc. With different viscosity and flash point, the cooling capacity and service temperature of mineral oil are different. Because of its slow cooling rate, it is not easy to harden the carbon steel and low alloy steel with large section, and the surface of the material is easy to stain, so the use of oil is limited. In order to improve the cooling capacity of the oil, the methods of properly increasing the oil temperature (usually within the range of 80 ℃), strongly stirring circulation and adding additives can be adopted. Additives such as sodium sulfonate, barium sulfonate, calcium sulfonate and calcium naphthenate are added into the oil. During quenching and cooling, the additives stick to the surface of the workpiece and become the mass point of the second-class domestic product Zeng steam bubble, which makes the stable steam film difficult to form and improves the cooling capacity in the high temperature area. This oil is called "fast quenching oil". In addition, adding heat stabilizer, ash free surfactant and 1% sodium mizoline oleate and 0.3% T501 to light oil and quench oil extracted by solvent refining method can make the surface of workpiece quickly covered by oil film after quenching without carbon black deposition on the surface, thus making the surface of workpiece bright and clean after quenching. This kind of oil is called "bright quench oil". In addition, the addition of surfactant in mineral oil can make the metal quenched evenly, and is conducive to the cleaning of mineral oil after quenching. For example, add 2% ~ 5% non-ionic emulsifier such as nonylphenol polyoxyethylene (6) ether to the quenching mineral oil, and wash the metal products with water after quenching to remove the mineral oil.
Water based quenchant
Water is the most economical quenching medium. Its chemical stability is very high and its heat capacity is large. However, the cooling capacity of pure water is not strong in the high temperature zone, but it is very large near 300 ℃. Therefore, the cooling characteristics of pure water is exactly the opposite of the ideal quenching medium, which is the reason why pure water is rarely used. The commonly used water-based quenchants are brine, alkaline water, saturated calcium chloride, trinitrate solution (NaNO3, NaNO2, KNO3), organic polymer solution, etc.
In the late 1950s, the United States put forward a non-toxic, odorless, non combustible and cooling performance in water and oil, adjustable polyvinyl alcohol (PVA), water solution quenching medium, and later developed into polyalkylene glycol (PAG), polyoxyethylene glycol (Gly), polyvinylpyrrolidone (PVP) and other organic polymer water-based quenchants. At the end of 1970s, ACR, a non martensitic quenchant suitable for bainite quenching, was developed. Its characteristic viscosity is high. It is suitable for isothermal quenching, forging hot forging quenching, high speed steel and martensitic stainless steel quenching. In addition, there are some new quenchants, such as polyacrylamide (PAM), methylcellulose (CMC) and high molecular weight soap aqueous solution.
Polyether prepared by ring opening polymerization of ethylene oxide and propylene oxide has inverse solubility, which makes it play an excellent lubricating role in water-based metal processing fluid (such as cutting fluid, grinding fluid and quenching fluid). When the polyether solution is brought into the cutting area and meets the hot metal surface, the liquid temperature quickly rises to higher than the cloud point of polyether. At this time, polyether is separated from water to form tiny droplets like oil, which form a thin lubricating oil film on the metal surface and play a role of fluid lubrication. The results show that when the temperature is higher than the cloud point, the concentrated solution of 5% polyether solution has the same lubricity. At room temperature, polyether is easily soluble in water, and its aqueous solution has many excellent properties required by quenchants, so it is widely used in quenchants. The monomer used in the preparation of "traditional polyether" must include ethylene oxide, and the content of its mass fraction in the whole molecule is preferably 70% - 90%, at least 10%. It is also possible to use only one monomer, ethylene oxide. Other monomers contain low-level epoxides of C3 ~ 4, such as two isomers of propylene oxide, tetraoxofuran and sulfobutane. The molecular weight of traditional polyether is about 20000, which belongs to the category of medium and high molecular weight. The "step synthesis" method is usually used for its preparation, that is, the polyether with a relative molecular weight of several hundred to several thousand is synthesized with propylene oxide and ethylene oxide according to the general method, and then the polyether with a higher relative molecular weight is prepared by continuous polymerization with the monomer using the polymer as the initiator. Repeat the above steps several times to get the desired relative molecular weight product. The hybrid copolymers and mosaic copolymers of ethylene oxide with another monomer can be called "traditional polyether". Alcohols and amines are commonly used in the preparation of "traditional polyether" initiator. A large number of patents on the synthesis and application of polyether for water-based quenchant have been reported abroad, and it has entered the stage of industrial production and application. The research in this field in China started late, and many products still need to be imported. In recent years, time modified polyether has been widely studied.
PAG quenchant is a kind of water widely used in industry
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