The development status of high temperature grease
With the continuous development of our country's economy and the continuous improvement of the level of industrialization, the use of advanced equipment is increasing. The working temperature of many lubricating parts is getting higher and higher, and the requirements for the high temperature resistance of the grease are also increasing. The lubricating grease commonly used in our country is metal soap base grease with mineral oil as the base oil, and the service temperature does not exceed 300 ℃. Research on high temperature grease is of great significance to meet the high temperature lubrication requirements of certain equipment. Grease is composed of base oil and thickening agent. This article mainly discusses the current situation and development trend of high temperature grease from this aspect.
The development status of high-temperature grease is inseparable from the basic knowledge of base oil and saponifier. The prospect of high-temperature grease is very impressive. Modern machinery and equipment are developing in the direction of miniaturization, high speed, and high load, which puts forward higher and higher requirements for the high performance and anti-oxidation stability of grease. Base oil is the main component of grease, accounting for 70% to 90% of the grease content.The performance of the base oil directly affects the performance of all aspects of the grease. At present, the base oil of the grease is mainly mineral oil. The price of mineral oil is low, and it can meet the requirements of use within a certain temperature range, but the composition of mineral oil is complex and contains more. Unsaturated olefins and aromatic hydrocarbons are easy to oxidize and deteriorate. Generally, they cannot be used as base oils for high-temperature greases. However, synthetic oils have better high-temperature stability, oxidation stability, better viscosity-temperature performance, and lower volatility. It can meet various requirements under high temperature conditions and has become the main base oil for high temperature grease. As the base oil of high-temperature grease, there are mainly the following synthetic oils.
Ester oil and polyolefin have similar chemical properties, high flash point, good thermal stability and oxidation stability, and very high service temperature. Ester oil is very polar, making it less volatile and increasing lubricity. At the same time, ester oil has a good adsorption effect on metals, especially iron and steel, and can greatly reduce the wear of high-load bearings, gears, metal cutting and other equipment. Most inorganic and organic thickeners can thicken ester oils to prepare high and low temperature greases. The use temperature range varies with the types of thickeners and ester oils. When making lubricating grease, one or two ester oils can be selected as the base oil according to the requirements of the product, or a mixture of ester oils and other synthetic oils can be selected. For example, high-temperature sealing grease is made of silica gel after surface treatment to thicken ester oil, and added with polyolefin and solid fillers. It has good high-temperature stability, tightness, and resistance to water vapor, ammonia, weak acids and natural gas. The medium has good adaptability. Used for the sealing and lubrication of commercial temperature and high pressure regulating valve and valve stem.
A class of oils containing carbon and hydrocarbons prepared by chemical synthesis methods are collectively referred to as synthetic hydrocarbon oils. Including poly. Hydrocarbons, polybutenes, alkanes, benzenes and synthetic cycloalkanes. The synthetic hydrocarbon used as the base oil of the grease is poly. Hydrocarbon, olefin synthetic oil is a kind of oil with more comprehensive performance, the main advantages are wide viscosity range, good viscosity-temperature, high viscosity index, good thermal oxidation stability, not easy to oxidize and deteriorate at high temperature, good lubricity, less wear in the four-ball test. It has good compatibility with mineral oil and other synthetic oils, and has good sensitivity to additives. Adding a proper amount of antioxidants can greatly improve the oxidation stability. It has strong hydrolysis resistance and good stability under water conditions. Due to the relatively low price of polyhydrocarbon performance, its application is more and more extensive. Non-soap grease based on polyolefin as a base oil has a wide range of uses. Experiments in the bearing show that the grease using general base oil is significantly reduced, and the loss at high temperature is significantly reduced. The grease must be changed every time the equipment is stopped using ordinary grease. Grease using polyolefin only needs to be changed every six months. In addition, due to the reduction of evaporation, the friction parts can always be better lubricated, and the bearing life is greatly increased.
Silicone oil has good high-temperature thermal stability, low evaporation, good low-temperature properties, low freezing point, excellent viscosity-temperature characteristics, and silicone oil has good shear stability. It is non-toxic, water-repellent, flame-retardant, and chemical Inert. The main disadvantage of silicone oil is poor boundary lubricity and poor sensitivity to ordinary lubricating additives. It can be mixed with other synthetic oils to improve its performance. The smaller the hydrocarbon group attached to the silicon atom, the lower the viscosity, and the better the viscosity-temperature performance. , The better the thermal stability. For example, methyl silicone oil starts to oxidize at around 200 degrees. In order to improve its high temperature performance, the introduction of benzene into the silicone oil molecule has the general properties of methyl silicone oil in addition to its properties. The high temperature performance is second only to toluene-based silicone oil and can be used alone as the base oil for medium-duty grease. For example: grease formed by special soap-based thickened silicone oil, suitable for bearing lubrication working under wide temperature conditions.
Fluorine oil is a colorless and odorless liquid. It inserts oxygen atoms in the main chain to improve the flexibility of the molecule. Therefore, its viscosity-temperature performance and low-temperature performance are better. At the same time, the oxygen atoms are shielded by the surrounding fluorine atoms. Under attack, it has outstanding chemical inertness, thermal oxidation stability and good lubricating performance. It will affect the swelling and shrinkage of rubber when it comes in contact with most rubbers.
Thickener is an indispensable solid part of grease, accounting for 5-30% of the total weight of grease. The thickener thickens the base oil to a semi-solid state, which determines the properties of the grease like the base oil. The types of thickeners can be divided into four categories, namely soap, hydrocarbon, organic and inorganic thickeners. Hydrocarbon-based thickeners are generally used at very low temperatures (less than 80 ℃), and high-temperature thickeners are mainly soap-based organic and inorganic. Soap-based grease is currently the most commonly used grease. The use temperature of single-metal soap grease is not high beyond 120 ℃, which cannot meet high temperature conditions. The high-temperature soap-based greases currently in use are mainly composite soap-based, mainly lithium complex and composite Calcium and composite aluminum, of which composite lithium is the most used.
Lithium complex grease:
The high temperature performance of lithium complex grease is superior, the dropping point can reach 283 ℃, which is about 100 higher than that of some lithium grease, and it also has better mechanical stability and high temperature bearing performance. Lithium complex is composed of lithium soap and other lithium salts co-crystallized together.
The composite aluminum-based grease has a high dropping point, excellent water resistance, good thermal stability and oxidation stability. Compared with a certain lithium complex grease, its outstanding advantages are good pumping performance and unique thermal reversibility. After being heated and cooled for a short time, it can restore the original structure, which is especially suitable for centralized lubrication systems.
Complex calcium sulfonate:
Complex calcium sulfonate grease has a high dropping point. Its thickening system is mainly composed of two parts, one is calcium sulfonate and the other is complex calcium soap. They have both physical mixing and chemical association in the system. Together, it is a more complex compound system. The overbased sulfonate complex calcium-based grease not only has good high temperature properties, colloidal stability, water resistance and corrosion resistance, but also has outstanding extreme pressure resistance and mechanical stability, and its low temperature performance is also greatly improved.
The compound titanium grease is a relatively new high-temperature grease, which has not yet been industrialized. Titanium complex grease has good high temperature performance, and has a long service life at high temperature: in addition, it has good extreme pressure wear resistance and water leaching resistance, and its performance exceeds lithium complex grease and aluminum grease. .
Organic thickeners refer to organic substances that have a thickening effect other than metal soaps and solid hydrocarbons, such as aryl ureas, amides, polytetrafluoroethylene, phthalocyanine pigments and indanthrene dyes, etc.: they are mostly some with aromatic rings The compound with good thermal stability: the organic thickener forms a structural skeleton in the base oil under certain process conditions to make grease. Among the organic thickeners, urea-based thickeners are used more and have development potential. Urea-based thickeners contain one or more urea groups in the molecule. The urea-based thickener does not contain metal ions and will not produce oxidation catalysis on the base oil, and has good oxidation stability. This makes it have a long and high working life in the bearing and can be used for a long time. Urea grease based on a certain synthetic mixed oil, urea-based grease is used on motor bearings, and the temperature is lower than before. In addition, the urea resin has good water resistance, stable chemical properties, and is also very stable to acid gases. It can maintain good lubrication under the harsh conditions of friction control ring walls. For example, the biurea type continuous casting machine grease has a greatly extended service life under the conditions of high temperature, water, dust, and heavy load.
Commonly used inorganic thickeners include bentonite, silica gel, boron nitride, carbon black and so on. Inorganic thickeners generally have good high-temperature performance and are ideal thickeners for the manufacture of high-temperature greases. They have good high-temperature performance and high-temperature oxidation stability, but other properties (such as protection, solid residue after base oil volatilization Etc.) Relatively insufficient.
With the development of modern machinery and equipment, there is an increasing demand for high-temperature multi-effect grease. Lubricating greases with high dropping point and multi-efficiency are developing rapidly. Lithium complex grease and polyurea grease are the main directions for the development of high dropping point greases. The proportion of high dropping point grease has increased in recent years, but due to industrial development and mechanical equipment conditions, high temperature grease started late, developed slowly, and the variety is not ideal. Efforts to develop high-temperature grease, especially lithium complex grease and polyurea grease, is the main direction of the development of high-temperature grease.