Ten major achievements in the history of tribology and lubrication technology（2）
author: Leila
2024-10-22
6.1877~Now: Synthetic oil takes lubrication technology to a new level:
Humans are pursuing better things in all fields, including lubricants. Although mineral oil has brought better lubricants to humans, humans began to seek better oils before the development of the petroleum industry was 20 years old. The research and development of synthetic oils began.
Human research on synthetic oils can be traced back to 1877, when French chemist Charles Friedel and American chemist James Mason Crafts jointly discovered the Friedel–Crafts reaction, also known as the Friedel–Crafts reaction, and produced hydrocarbons for the first time through artificial synthesis.
In 1913, German chemist Friedrich Bergius used hydrogenation to turn coal into oil, realizing the artificial synthesis of coal to oil. However, it was not until 1929 that Standard Oil of Indiana (the predecessor of ExxonMobil) in the United States made a technological breakthrough, and synthetic oil technology really matured to the level of commercialization. However, due to the high cost, it was not truly commercialized at that time. In 1937, PAO came into being and became a leader in the field of synthetic oil, especially in the field of engine oil.
Germany's research on synthetic oil also started very early, dating back to before World War I and during World War II. In 1923, Germans Frans Fischer and Hans Tropsch invented natural gas to oil technology (Fischer-Tropsch synthesis), which can convert methane into high-quality synthetic oil. Fischer-Tropsch synthesis makes the production of high-quality synthetic oil commercially possible.
In 1939, the Fischer-Tropsch synthesis method was commercialized in Germany. In the 1930s and 1940s, synthetic fuels, rubber, lubricants, and paraffin produced by Fischer-Tropsch synthesis began to emerge in Germany.
During the two world wars, the research on synthetic oil mainly benefited from the support of the US and German armies. During this period, another synthetic oil, PAG (water-soluble), appeared. To be precise, PAG is not an oil, but a synthetic liquid. PAG is one of the earliest synthetic oils to be tried in the transportation field. Although they have strong water absorption, PAG has excellent low-temperature performance and good thermal stability. In 1944, under severe cold conditions in the north (Canada, Alaska and other northern regions), the US military used PAG for aircraft engine lubrication. After accumulating 150,000 flight hours, the engine still had no problems.
In the late 1940s, scientists began to study ester oils, initially diesters, and then polyester oil (POE). With the further development of synthetic oil research, synthetic oils now include many types, including PAO, PAG and other types, as well as silicone oil, alkyl naphthalene, perfluoropolyether and other varieties. Among them, PAG is not limited to traditional water-soluble PAG, but also oil-soluble PAG (OSP).
Human research on synthetic oils can be traced back to 1877, when French chemist Charles Friedel and American chemist James Mason Crafts jointly discovered the Friedel–Crafts reaction, also known as the Friedel–Crafts reaction, and produced hydrocarbons for the first time through artificial synthesis.
In 1913, German chemist Friedrich Bergius used hydrogenation to turn coal into oil, realizing the artificial synthesis of coal to oil. However, it was not until 1929 that Standard Oil of Indiana (the predecessor of ExxonMobil) in the United States made a technological breakthrough, and synthetic oil technology really matured to the level of commercialization. However, due to the high cost, it was not truly commercialized at that time. In 1937, PAO came into being and became a leader in the field of synthetic oil, especially in the field of engine oil.
Germany's research on synthetic oil also started very early, dating back to before World War I and during World War II. In 1923, Germans Frans Fischer and Hans Tropsch invented natural gas to oil technology (Fischer-Tropsch synthesis), which can convert methane into high-quality synthetic oil. Fischer-Tropsch synthesis makes the production of high-quality synthetic oil commercially possible.
In 1939, the Fischer-Tropsch synthesis method was commercialized in Germany. In the 1930s and 1940s, synthetic fuels, rubber, lubricants, and paraffin produced by Fischer-Tropsch synthesis began to emerge in Germany.
During the two world wars, the research on synthetic oil mainly benefited from the support of the US and German armies. During this period, another synthetic oil, PAG (water-soluble), appeared. To be precise, PAG is not an oil, but a synthetic liquid. PAG is one of the earliest synthetic oils to be tried in the transportation field. Although they have strong water absorption, PAG has excellent low-temperature performance and good thermal stability. In 1944, under severe cold conditions in the north (Canada, Alaska and other northern regions), the US military used PAG for aircraft engine lubrication. After accumulating 150,000 flight hours, the engine still had no problems.
In the late 1940s, scientists began to study ester oils, initially diesters, and then polyester oil (POE). With the further development of synthetic oil research, synthetic oils now include many types, including PAO, PAG and other types, as well as silicone oil, alkyl naphthalene, perfluoropolyether and other varieties. Among them, PAG is not limited to traditional water-soluble PAG, but also oil-soluble PAG (OSP).
7. Additives improve the performance of lubricants
The birth of the petroleum industry also brought about the prosperity and development of the chemical field, triggering the research of chemical additives, and additives can improve the performance of oils, including the optimization of lubricant performance. Before the birth of additives, the composition of lubricants was refined petroleum fractions (i.e. base oils), and no additives were used. The earliest additive was oiliness agent, which appeared around 1918. The birth of additives marked that people used chemical means to solve and optimize lubrication problems. Since then, people have begun to develop additives and add them to base oils to improve the performance of lubricants.
Many discoveries were made in the early stages of additive research and development, but the first major achievement was ZDDP, which was produced in the 1930s. Between the 1930s and 1940s, many additives began to appear: antioxidants, rust inhibitors, extreme pressure agents, dispersants, pour point depressants, viscosity index improvers - these are all important additives, and anti-wear agents were produced in the 1940s. The emergence of additives was mainly stimulated by the automobile industry. The prosperity of the automobile industry has driven the demand for high-quality motor oils, as well as brake fluids and other automotive oils and greases.
In the development history of additives, ZDDP additives containing sulfur and phosphorus deserve our special attention. In the late 1930s, the earliest ZDDP appeared and was used as a metal corrosion inhibitor and also as an antioxidant. In fact, ZDDP is a multifunctional additive that also has anti-wear function, but research in this area was not successful until the 1940s. In the 1950s, ZDDP had become an indispensable additive for engine oils. In addition, transmission oils and some industrial lubricants also began to use ZDDP as an additive. To this day, ZDDP is still a major anti-wear agent for lubricants.
ZDDP is an important additive with the advantages of low cost, good performance and multiple functions. With the development of additive technology, there will definitely be better additives, but ZDDP, as an important additive with good quality and low price, has indeed brought huge benefits to the lubricant industry.
In the development history of additives, ZDDP additives containing sulfur and phosphorus deserve our special attention. In the late 1930s, the earliest ZDDP appeared and was used as a metal corrosion inhibitor and also as an antioxidant. In fact, ZDDP is a multifunctional additive that also has anti-wear function, but research in this area was not successful until the 1940s. In the 1950s, ZDDP had become an indispensable additive for engine oils. In addition, transmission oils and some industrial lubricants also began to use ZDDP as an additive. To this day, ZDDP is still a major anti-wear agent for lubricants.
ZDDP is an important additive with the advantages of low cost, good performance and multiple functions. With the development of additive technology, there will definitely be better additives, but ZDDP, as an important additive with good quality and low price, has indeed brought huge benefits to the lubricant industry.
8. 1920s-1960s: Testing makes tribology a real science
Before the 20th century, tribology was still in the technical field. When problems arose in practical applications, solutions were sought from physics, chemistry or materials science. Tribology had not yet become an independent science.
In the late 19th century, the situation changed with the emergence of hydrodynamic lubrication and elastic hydrodynamic lubrication theories. The deepening of the industrial revolution led to the emergence of new machines, and the emergence of new machines brought new challenges to lubrication. How to predict lubrication problems theoretically became increasingly important.
The earliest friction and wear testing can be traced back to the Renaissance. The testing equipment at that time was very simple: a slider was placed on the table, and a rope was tied to the slider. The rope hung a heavy object and hung from the edge of the table. This experimental instrument only proved that if animal oil was added between the slider and the table, the force required to drag the slider to start moving would be smaller.
Since the Renaissance, there have been some studies on tribology, but they are relatively scattered. Scientists such as Amonton, Newton, and Coulomb have studied friction. In the past 100 years, friction and lubrication have formed scientific testing theories and testing methods to evaluate and predict the performance of lubricants under certain test conditions. This trend has promoted the development of tribology and gradually formed an independent science.
The first commercial lubricant testing instrument was the Falex PIN and VEE friction and wear tester, which was launched in 1927. Its function is to quantitatively measure the anti-wear and extreme pressure properties of liquid and solid lubricants. This tester has a far-reaching impact. Without it, there would be no technical data and quantitative analysis, and tribology would not be scientific.
Today, there are many professional oil testing laboratories that can perform oil testing and analysis. They have professional testing instruments that can analyze the chemical composition of oil products, helping equipment maintenance personnel and lubrication engineers to accurately understand the oil quality and the operating conditions of the equipment.
The first commercial lubricant testing instrument was the Falex PIN and VEE friction and wear tester, which was launched in 1927. Its function is to quantitatively measure the anti-wear and extreme pressure properties of liquid and solid lubricants. This tester has a far-reaching impact. Without it, there would be no technical data and quantitative analysis, and tribology would not be scientific.
Today, there are many professional oil testing laboratories that can perform oil testing and analysis. They have professional testing instruments that can analyze the chemical composition of oil products, helping equipment maintenance personnel and lubrication engineers to accurately understand the oil quality and the operating conditions of the equipment.
9. 1922~Present: Elastic fluid dynamic lubrication theory helps modern machinery
In the mid-20th century, humans began to recognize two completely different lubrication states: boundary lubrication and hydrodynamic lubrication.
In 1922, W.B.Hardy and Doubleday proposed the definition of boundary lubrication. Boundary lubrication is a "boundary" state of lubrication, a boundary state of transition from hydrodynamic lubrication to dry friction. When boundary lubrication occurs, the relative motion between objects is slow and hydrodynamic lubrication cannot be formed. In the boundary lubrication state, the chemical composition of the lubricant is crucial. When boundary lubrication occurs, it mainly relies on the reaction between the friction surface and the chemical composition in the oil to form a lubricating protective film. In hydrodynamic lubrication, a layer of liquid film between the two contact surfaces is relied on to separate the friction surfaces to avoid direct contact between them, thereby achieving the purpose of lubrication protection. To form hydrodynamic lubrication, the mechanical size, speed, and viscosity of the lubricating oil must meet the requirements in order to successfully form a hydrodynamic lubricating film, allowing the equipment to "ride" on this thin layer of liquid to avoid dry friction. Between hydrodynamic lubrication and boundary lubrication is mixed lubrication. More than 50 years ago, we began to study mixed lubrication. Hydrodynamic lubrication is the ideal state of lubrication, which requires mechanical size, appropriate lubricating oil viscosity, and certain speed and load conditions to achieve together. To understand mixed lubrication, let's look at a scenario like this: for a device, it is in a hydrodynamic lubrication state at the beginning, and the lubricating oil film is in a full film lubrication state, completely separating the objects. However, if any one or more of the following situations occur - the speed decreases, the load increases, and the viscosity of the lubricating oil decreases, then the lubricating film may be incomplete in some parts, that is, in some local areas, some raised peaks on the surface of the object come into contact, resulting in mixed lubrication. When the speed is further reduced, there is almost no relative motion, and it reaches the boundary lubrication state. In 1902, Richard Stribeck expressed these three states of lubrication with a function graph, which we call the Stribeck Curve.
Full film lubrication is that the lubricating oil film can completely separate the contact surfaces to prevent them from contacting. Full film lubrication is divided into two types - hydrodynamic lubrication and elastohydrodynamic lubrication, abbreviated as EHD. When EHD occurs, the speed is generally very high, and the material of the contact surface undergoes elastic deformation. Under this condition, the viscosity of the lubricating oil will increase, which helps to form a lubricating oil film. Similarly, EHD also belongs to full film lubrication. As the speed decreases, EHD gradually transitions to mixed lubrication and then to boundary lubrication.
Elastic hydrodynamic lubrication is similar to hydrodynamic lubrication. It also relies on a layer of fluid lubrication film to separate the contact surfaces. The difference is that the relative motion between the contact surfaces of EHD is rolling. The pressure of the lubricating film formed is greater than that of hydrodynamic lubrication, and the lubricating film produced is thinner than that under hydrodynamic lubrication.
The study of elastic hydrodynamic lubrication and the Strybeck curve has brought people's research into the field of rolling bearings. The invention of rolling bearings is a major breakthrough in modern machinery, making the speed and load capacity of bearings more diverse and wear-resistant.
In 1922, W.B.Hardy and Doubleday proposed the definition of boundary lubrication. Boundary lubrication is a "boundary" state of lubrication, a boundary state of transition from hydrodynamic lubrication to dry friction. When boundary lubrication occurs, the relative motion between objects is slow and hydrodynamic lubrication cannot be formed. In the boundary lubrication state, the chemical composition of the lubricant is crucial. When boundary lubrication occurs, it mainly relies on the reaction between the friction surface and the chemical composition in the oil to form a lubricating protective film. In hydrodynamic lubrication, a layer of liquid film between the two contact surfaces is relied on to separate the friction surfaces to avoid direct contact between them, thereby achieving the purpose of lubrication protection. To form hydrodynamic lubrication, the mechanical size, speed, and viscosity of the lubricating oil must meet the requirements in order to successfully form a hydrodynamic lubricating film, allowing the equipment to "ride" on this thin layer of liquid to avoid dry friction. Between hydrodynamic lubrication and boundary lubrication is mixed lubrication. More than 50 years ago, we began to study mixed lubrication. Hydrodynamic lubrication is the ideal state of lubrication, which requires mechanical size, appropriate lubricating oil viscosity, and certain speed and load conditions to achieve together. To understand mixed lubrication, let's look at a scenario like this: for a device, it is in a hydrodynamic lubrication state at the beginning, and the lubricating oil film is in a full film lubrication state, completely separating the objects. However, if any one or more of the following situations occur - the speed decreases, the load increases, and the viscosity of the lubricating oil decreases, then the lubricating film may be incomplete in some parts, that is, in some local areas, some raised peaks on the surface of the object come into contact, resulting in mixed lubrication. When the speed is further reduced, there is almost no relative motion, and it reaches the boundary lubrication state. In 1902, Richard Stribeck expressed these three states of lubrication with a function graph, which we call the Stribeck Curve.
Full film lubrication is that the lubricating oil film can completely separate the contact surfaces to prevent them from contacting. Full film lubrication is divided into two types - hydrodynamic lubrication and elastohydrodynamic lubrication, abbreviated as EHD. When EHD occurs, the speed is generally very high, and the material of the contact surface undergoes elastic deformation. Under this condition, the viscosity of the lubricating oil will increase, which helps to form a lubricating oil film. Similarly, EHD also belongs to full film lubrication. As the speed decreases, EHD gradually transitions to mixed lubrication and then to boundary lubrication.
Elastic hydrodynamic lubrication is similar to hydrodynamic lubrication. It also relies on a layer of fluid lubrication film to separate the contact surfaces. The difference is that the relative motion between the contact surfaces of EHD is rolling. The pressure of the lubricating film formed is greater than that of hydrodynamic lubrication, and the lubricating film produced is thinner than that under hydrodynamic lubrication.
The study of elastic hydrodynamic lubrication and the Strybeck curve has brought people's research into the field of rolling bearings. The invention of rolling bearings is a major breakthrough in modern machinery, making the speed and load capacity of bearings more diverse and wear-resistant.
10. The emergence of self-lubricating materials in the 1930s and 1940s
Hydrodynamic lubrication relies on a certain speed, suitable lubricating oil viscosity, and certain load conditions to form a layer of liquid lubricating film. However, under some conditions, such as high temperature and pressure, liquid lubrication is not realistic, or cannot provide good rust and chemical corrosion resistance. In these cases, other lubrication methods need to be sought - self-lubricating materials or solid lubricants.
Self-lubricating materials are solid and lubricating in themselves. They can also be coated on other solid surfaces to lubricate and reduce wear. At present, the solid lubricants that have been commercially used mainly include graphite, molybdenum disulfide, and polytetrafluoroethylene (PTFE), also known as Teflon. This type of solid lubricant is generally used in combination with a resin adhesive to prevent it from being worn away, and is also used with other additives and solvents to enhance performance.
As early as 1906, some people had studied carbon as a solid lubricant. In the mid-to-late 1940s, the scientific community conducted in-depth research on self-lubricating materials. In 1939, Cooper Products in the United States applied for a patent for molybdenum disulfide lubricant.
PTFE is probably the most famous self-lubricating material. In 1938, Plunkett, a chemist at DuPont in the United States, applied for a PTFE patent. Plunkett's research was originally to study the performance of PTFE as a refrigerant, but after pressurizing and cooling the tetrafluoroethylene monomer, he found that tetrafluoroethylene underwent a polymerization reaction to produce a white waxy solid that is chemically inert and lubricating.
Solid lubricants are mainly used in situations where liquid lubricants are not suitable, such as vacuum, some areas where refueling is inconvenient, underwater equipment, dirty environments with a lot of dust, high temperatures, etc.
Self-lubricating materials are solid and lubricating in themselves. They can also be coated on other solid surfaces to lubricate and reduce wear. At present, the solid lubricants that have been commercially used mainly include graphite, molybdenum disulfide, and polytetrafluoroethylene (PTFE), also known as Teflon. This type of solid lubricant is generally used in combination with a resin adhesive to prevent it from being worn away, and is also used with other additives and solvents to enhance performance.
As early as 1906, some people had studied carbon as a solid lubricant. In the mid-to-late 1940s, the scientific community conducted in-depth research on self-lubricating materials. In 1939, Cooper Products in the United States applied for a patent for molybdenum disulfide lubricant.
PTFE is probably the most famous self-lubricating material. In 1938, Plunkett, a chemist at DuPont in the United States, applied for a PTFE patent. Plunkett's research was originally to study the performance of PTFE as a refrigerant, but after pressurizing and cooling the tetrafluoroethylene monomer, he found that tetrafluoroethylene underwent a polymerization reaction to produce a white waxy solid that is chemically inert and lubricating.
Solid lubricants are mainly used in situations where liquid lubricants are not suitable, such as vacuum, some areas where refueling is inconvenient, underwater equipment, dirty environments with a lot of dust, high temperatures, etc.
Principles of lubricant selection according to the working conditions of machinery
Main properties of lubricants
