Lubricant knowledge introduction

lubricating oileffect
(1) Lubrication
When the engine is running, if some friction parts are not properly lubricated, dry friction will occur.Practice has proved that the heat generated by dry friction in a short period of time is enough to melt the metal, causing damage to the machine parts or even jamming (many water or oil leaks)carThis is the main reason for failures such as cylinder pulling and shaft holding). Therefore, the friction parts in the engine must be given good lubrication.
When the lubricating oil flows to the friction part, it will adhere to the friction surface to form an oil film to reduce the resistance between the friction parts. The strength and toughness of the oil film are the key to its lubrication effect.
(2) Cooling effect
Only a small part of the heat generated by the combustion of fuel in the engine is used for power output, frictional resistance consumption and driving of auxiliary mechanisms; most of the remaining heat is not only discharged into the atmosphere with the exhaust gas, but also carried by the cooling medium in the engine Walk partly. The excess heat in the engine must be discharged from the body, otherwise the engine will burn out due to excessive temperature. This is done by the engine cooling system, on the other hand, it relies on the lubricating oil from the cylinder,piston,CrankshaftAfter the surface absorbs the heat, it is carried to the oil pan and dissipated.
(3) Washing effect
When the engine is working, a lot of dirt will be produced. Such as inhalation of sand and dust brought by the air, carbon deposits formed after the combustion of the mixed gas, jelly formed after the oxidation of lubricating oil, metal swarf generated by friction between parts and so on. These dirt will adhere to the friction surface of the machine parts, if it is not cleaned, it will increase the wear of the machine parts.In addition, a large amount of gum will makePiston ringThe adhesion is stuck, causing the engine to fail to operate normally. Therefore, these dirt must be cleaned up in time. This cleaning process is completed by the circulation of lubricating oil in the body.
(4) Sealing function
Engine cylinders and pistons, piston rings and ring grooves, andValveThere is a certain gap between the valve seat and the valve seat, which can ensure that the movement pairs will not get stuck. However, these gaps can cause poor cylinder sealing, and the result of combustion chamber leakage is to reduce cylinder pressure and engine output.
The oil film formed by the lubricating oil in these gaps ensures the sealing of the cylinder, maintains the cylinder pressure and engine output power, and prevents the exhaust gas from fleeing downwards.Crankshaftbox.
(5) Anti-rust effect
When the engine is running or stored, the moisture in the atmosphere, lubricating oil, fuel, and the acid gas generated by combustion will cause corrosion and rust to the mechanical parts, thereby increasing the damage to the friction surface. The oil film formed by the lubricating oil on the surface of the machine parts can prevent the machine parts from directly contacting water and acid gases, and prevent corrosion and rust.
(6) Eliminate impact load
At the end of the compression stroke, the air-fuel mixture begins to burn, and the cylinder pressure rises sharply. At this time, the lubricating oil in the bearing gap will alleviate the impact load on the pistons, piston pins, connecting rods, crankshafts and other parts, make the engine work smoothly, and prevent direct metal contact and reduce wear.
Performance requirements that lubricants must meet
(1) Suitable viscosity and good temperature resistance
The viscosity of lubricating oil is related to the startability of the engine, the degree of wear of mechanical parts, the consumption of fuel and lubricating oil, and the size of power loss. The oil viscosity is too high, the fluidity is poor, it takes a long time to enter the friction surface, the fuel consumption will increase, the wear of the parts will increase, the cleaning and cooling performance is poor, but the sealing performance is good; the viscosity is too small, a reliable oil film cannot be formed, and lubrication cannot be maintained , Poor sealing, large abrasion, and power drop. Therefore, it is not good if the viscosity is too large or too small, and it should be appropriate.
The operating temperature range of engine lubricating oil is very wide. It is required to have sufficient viscosity to ensure lubrication at around 300°C; it is required to have sufficient fluidity when it is below 0°C, or even at -40°C, to ensure smooth starting. Therefore, good viscosity characteristics and temperature resistance are required.
(2) Good detergency and dispersion performance
When the sludge and other dirt generated by the lubrication system are too much, it will be precipitated from the oil, causingOil filterAnd the oil hole is blocked, the fluidity of the oil is poor, the piston ring sticks, the fuel consumption increases, and the power decreases. In order to prevent the above failures, it is necessary to add an oil-soluble detergent and dispersant to the lubricating oil.
Detergent dispersants are mainly divided into metallic detergents and ashless dispersants. Among them, the metal type detergent and dispersant can prevent the sludge deposition in the piston ring groove, and has a good cleaning ability on the piston ring area. When used alone, it is called a detergent; the ashless detergent has poor ability to prevent sludge in the ring groove, but It has a strong ability to disperse sludge in oil, sometimes called dispersant alone. The two are best used in combination.
(3) Good lubricity
Most of the engines use sliding bearings, and they have to bear heavy loads. For example, the main bearings are 5-10MPa (steam) and 10-20MPa (diesel), and the connecting rod bearings are 7-14MPa (steam) and 12-15MPa (diesel). ), individual parts can even reach 90MPa. Engine lubricating oil must have good lubricity under high load and high pressure conditions.
(4) Good acid neutralization
Fuel oil, especially diesel, contains a large amount of sulfur, and the acid gas produced after combustion combines with water to form a solution such as sulfuric acid or sulfurous acid. These acids corrode the metals in the engine. Therefore, the lubricating oil is required to have a good ability to neutralize the acid and reduce the damage to the engine caused by the acidic substances produced by combustion.
(5) Good anti-oxidation and thermal oxidation performance
Lubricating oil will combine with oxygen at high temperatures, and its oxidation products make the lubricating oil deteriorate and fail, which is one of the main reasons for many engine failures. Various antioxidant additives should be added to the lubricating oil to avoid its oxidative deterioration.
(6) Good foam resistance
Due to the strong agitation and splash lubrication of the crankshaft, it is easy to generate bubbles in the lubricating oil, reduce the lubrication performance, and cause the oil pump to malfunction. Therefore, a good foam inhibitor product must be added to the lubricating oil to inhibit the generation of foam and maintain the effectiveness of the lubricating oil.