Lubricating Oil: The Basics You Should Know

Basic properties of lubricating oil

Lubricating oil is a technology intensive product, which is a complex mixture of hydrocarbons, and its real performance is the comprehensive effect of complex physical or chemical change processes.

The basic properties of lubricating oil include general physical and chemical properties, special physical and chemical properties and simulation bench test.

Lubricating Oil: The Basics You Should Know 1

General physical and chemical properties

Each type of lubricating grease has its common general physical and chemical properties to indicate the internal quality of the product.

For lubricating oil, these general physical and chemical properties are as follows:

Appearance (chromaticity)

The color of an oil product can often reflect its refining degree and stability.

For base oil, the higher the refining degree is, the cleaner the hydrocarbon oxides and sulfides are removed, and the lighter the color is.

However, even if the refining conditions are the same, the color and transparency of base oils produced by crude oils from different oil sources and base genera may also be different.

For new finished lubricating oil, due to the use of additives, color as an indicator to judge the refining degree of base oil has lost its original significance.


Density is the simplest and most commonly used physical performance index of lubricating oil.

The density of lubricating oil increases with the increase of the amount of carbon, oxygen and sulfur in its composition.

Therefore, under the same viscosity or the same relative molecular weight, the lubricating oil with more aromatics, more colloids and asphaltenes has the highest density, the one with more cycloalkanes is in the middle, and the one with more alkanes is the lowest.


Viscosity reflects the internal friction of oil products and is an indicator of the oiliness and fluidity of oil products.

Without any functional additives, the higher the viscosity, the higher the oil film strength and the worse the fluidity.

Flash point

Flash point is an indicator of oil evaporation.

The lighter the fraction of oil, the greater the evaporation, and the lower the flash point.

On the contrary, the heavier the fraction of oil, the smaller the evaporation, and the higher the flash point.

At the same time, the flash point is an indicator of the fire risk of petroleum products.

The danger level of oil products is divided according to the flash point.

Inflammables are those whose flash point is below 45 ℃ and inflammables are those whose flash point is above 45 ℃.

It is strictly forbidden to heat the oil products to its flash point temperature during the storage and transportation of oil products.

With the same viscosity, the higher the flash point, the better.

Therefore, the user should choose the lubricating oil according to the operating temperature and working conditions of the lubricating oil.

It is generally believed that the flash point is 20 ~ 30 ℃ higher than the operating temperature, which can be used safely.

Freezing point and pour point

The freezing point refers to the maximum temperature at which the oil stops flowing under the specified cooling conditions.

The solidification of oil products is very different from that of pure compounds.

There is no definite solidification temperature for oil products.

The so-called “solidification” only loses fluidity as a whole, and not all components become solids.

The freezing point of lubricating oil is an important quality index indicating the low temperature fluidity of lubricating oil.

It is of great significance for production, transportation and use.

Lubricating oil with high freezing point cannot be used at low temperature.

On the contrary, it is unnecessary to use lubricating oil with low freezing point in areas with high temperature.

Because the lower the freezing point of lubricating oil, the higher the production cost, resulting in unnecessary waste.

Generally speaking, the freezing point of lubricating oil should be 5~7 ℃ lower than the minimum temperature of the operating environment.

However, it should also be mentioned that when selecting low-temperature lubricating oil, it should be comprehensively considered in combination with the freezing point, low-temperature viscosity and viscosity temperature characteristics of the oil.

The low temperature viscosity and viscosity temperature characteristics of oil with low pour point may also not meet the requirements.

Freezing point and pour point are indicators of low-temperature fluidity of oil products.

There is no principle difference between them, but the determination method is slightly different.

The pour point and pour point of the same oil are not completely equal.

Generally, the pour point is 2 ~ 3 ℃ higher than the pour point, but there are exceptions.

Acid value, alkali value and neutralization value

Acid value is an index indicating that there are acidic substances in lubricating oil, and the unit is mgKOH/g.

Acid value can be divided into strong acid value and weak acid value, and the combination of the two is the total acid value (TAN for short).

What we usually call “acid value” actually refers to “total acid value (TAN)”.

The alkali value is an index indicating the content of alkaline substances in lubricating oil, and the unit is mgKOH/g.

The alkali value is also divided into strong alkali value and weak alkali value.

The combination of the two is the total alkali value (TBN).

What we usually say “alkali value” actually refers to “total alkali value (TBN)”.

Neutralization value actually includes total acid value and total base value.

However, unless otherwise noted, “neutralization value” generally refers to “total acid value”, and its unit is mgKOH/g.

Water content

Water content refers to the percentage of water content in lubricating oil, usually by weight.

The existence of water in the lubricating oil will destroy the oil film formed by the lubricating oil, deteriorate the lubrication effect, accelerate the corrosion of organic acids on metals, rust equipment, and make the oil prone to sediment.

In short, the less water in the lubricating oil, the better.

Mechanical impurities

Mechanical impurities refer to the precipitates or colloidal suspensions in lubricating oil that are insoluble in solvents such as gasoline, ethanol and benzene.

Most of these impurities are sand and iron filings, as well as some organic metal salts that are difficult to dissolve in solvents brought by additives.

Generally, the mechanical impurities of lubricating oil base oil are controlled below 0.005% (mechanical impurities below 0.005% are considered as none).

Ash and sulphated ash

Ash refers to the non combustible substances left after burning under specified conditions.

The composition of ash is generally considered to be some metal elements and their salts.

Ash has different concepts for different oil products.

For base oil or oil products without additives, ash can be used to judge the refining depth of oil products.

For oil products (new oil) with metal salt additives, ash has become a means to quantitatively control the amount of additives added.

Sulfuric acid ash is used to replace ash in foreign countries.

The method is to add a small amount of concentrated sulfuric acid after the oil sample is burned and before it is burned and ashed, so that the metal elements of the additive can be converted into sulfate.

Residual carbon

Under the specified experimental conditions, the coke black residue formed after heated evaporation and combustion of oil products is called carbon residue.

Carbon residue is an important quality index of lubricating oil base oil, and it is an item specified to judge the nature and refining depth of lubricating oil.

The amount of carbon residue in lubricating oil base oil is not only related to its chemical composition, but also related to the refining depth of the oil.

The main substances that form carbon residue in lubricating oil are gum, asphaltene and polycyclic aromatic hydrocarbons in the oil.

Under the condition of insufficient air, these substances are subject to strong thermal decomposition and condensation to form carbon residue.

The deeper the refining depth of the oil, the smaller the carbon residue value.

Generally speaking, the smaller the carbon residue value of blank base oil, the better.

Now, many oil products contain additives of metal, sulfur, phosphorus and nitrogen elements, and their residual carbon value is very high.

Therefore, the residual carbon of additive oil has lost the original significance of residual carbon determination.

Mechanical impurities, moisture, ash and carbon residue are quality indicators that reflect the purity of oil products and the refining degree of lubricating base oil.

Special physical and chemical properties

In addition to the above general physical and chemical properties, each lubricating oil should also have special physical and chemical properties that characterize its use characteristics.

The higher the quality requirements, or the stronger the specificity of the oil, the more prominent its special physical and chemical properties.

The test methods reflecting these special physical and chemical properties are briefly introduced as follows:

Oxidation stability

Oxidation stability indicates the anti-aging performance of lubricants.

Some industrial lubricants with long service life have this index requirement, which has become a special performance required by these types of oils.

There are many methods to determine the oxidation stability of oil products.

Basically, a certain amount of oil products are oxidized at a certain temperature for a certain time in the presence of air (or oxygen) and metal catalysts, and then the acid value, viscosity change and sediment formation of oil products are measured.

All lubricants have different automatic oxidation tendencies according to their chemical composition and external conditions.

Oxidation occurs with the use process, so some aldehydes, ketones, acids, colloids, asphaltenes and other substances are gradually generated.

Oxidation stability is the performance of inhibiting the formation of the above substances that are not conducive to the use of oil products.

Thermal stability

Thermal safety quality refers to the high temperature resistance of oil products, that is, the resistance of lubricating oil to thermal decomposition, that is, the thermal decomposition temperature.

Some high-quality anti-wear hydraulic oils and compressor oils have put forward the requirements of thermal safety.

The thermal stability of oil products mainly depends on the composition of base oil.

Many additives with low decomposition temperature often have adverse effects on the stability of oil products;

Antioxidants can not significantly improve the thermal stability of oil products.

Oiliness and extreme pressure

Oiliness refers to that the polar substances in lubricating oil form a solid physical and chemical adsorption film on the metal surface of the friction part, thus playing the role of high load resistance and friction and wear resistance.

Extreme pressure refers to that the polar substances in lubricating oil decompose on the metal surface of the friction part under high temperature and high load, and react with the surface metal to form a soft (or plastic) extreme pressure film with low melting point.

Thus, it has the lubrication function of impact resistance, high load and high temperature resistance.

Corrosion and rust

Due to the oxidation of oil or the action of additives, it often causes the corrosion of steel and other non-ferrous metals.

Generally, the corrosion test is to put the red copper bar into oil, place it at 100 ℃ for 3 hours, and then observe the change of copper;

The corrosion test is that the steel surface will rust under the action of water and steam.

The determination of rust resistance is to add 30ml distilled water or artificial seawater to 300ml test oil, and then place the steel bar in it, stir it at 54 ℃ for 24 hours, and then observe whether the steel bar is corroded.

The oil product should have the function of resisting metal corrosion and rust. In the industrial lubricant standard, these two items are usually required to be tested.

Anti foaming property

During the operation of lubricating oil, due to the existence of air, foam will often be produced, especially when the oil contains additives with surface activity, it is easier to produce foam, and foam is not easy to disappear.

The generation of foam in the use of lubricating oil will destroy the oil film, cause the friction surface to sinter or increase wear, promote the oxidation and deterioration of lubricating oil, and also make the lubrication system air resistance, affecting the circulation of lubricating oil. Therefore, anti foaming is an important quality index of lubricating oil.

Hydrolytic stability 

Hydrolytic stability characterizes the stability of oil under the action of water and metals (mainly copper).

When the oil has a high acid value or contains additives that are easy to decompose into acidic substances when encountering water, this index is often unqualified.

Its measurement method is to add a certain amount of water to the test oil, mix and stir the copper strip at a certain temperature for a certain time, and then measure the acid value of the water layer and the weight loss of the copper strip.


Industrial lubricating oil is often inevitably mixed with some cooling water in use.

If the anti emulsifying property of the lubricating oil is not good, it will form an emulsion with the mixed water, making it difficult for the water to be discharged from the bottom of the circulating oil tank, which may cause poor lubrication.

Therefore, demulsibility is a very important physical and chemical property of industrial lubricants.

Generally, 40ml of test oil and 40ml of distilled water are stirred violently at a certain temperature for a certain time, and then the separation time of oil layer water layer emulsion layer into 40-37-3ml is observed;

Industrial gear oil is to mix the test oil with water, stir it for 5 minutes at a certain temperature and 6000 rpm, and place it for 5 hours, and then measure the milliliters of oil, water and emulsion layer.

Air release value

The hydraulic oil standard has this requirement, because in the hydraulic system, if the air dissolved in the oil cannot be released in time, it will affect the accuracy and sensitivity of hydraulic transmission, and in serious cases, it will not meet the use requirements of the hydraulic system.

The method of measuring this property is similar to that of anti foaming, but it is to measure the release time of air (MIST) dissolved in the oil.

Rubber tightness

In the hydraulic system, most people use rubber as seals.

The oil products in machinery inevitably contact with some seals.

The oil products with poor rubber sealing can make the rubber swell, shrink, harden and crack, affecting its sealing.

Therefore, it is required that the oil products have good adaptability to rubber.

The hydraulic oil standard requires the rubber sealing index, which is measured by the change of a certain size of rubber ring after soaking in oil for a certain time.

Shear stability

During the use of the oil with tackifier, due to the effect of mechanical shear, the high molecular polymer in the oil is cut off, which reduces the viscosity of the oil and affects the normal lubrication.

Therefore, shear stability is a special physical and chemical property that must be tested for this kind of oil.

There are many methods to determine the shear stability, including ultrasonic shear method, nozzle shear method, Vickers pump shear method, FZG gear wheel shear method.

These methods ultimately determine the viscosity decline rate of oil products.


Solubility is usually expressed by aniline point.

Different grades of oil have different aniline points for the dissolution limit of composite additives. The limit value of low ash oil is greater than that of peralkaline oil, and the limit value of single-stage oil is greater than that of multi-stage oil.


The volatility of base oil is related to fuel consumption, viscosity stability and oxidation stability.

These properties are particularly important for multi-stage oils and energy-saving oils.

Rust resistance

This refers specifically to the special physical and chemical properties of antirust grease.

Its test methods include humidity test, salt spray test, lamination test, water displacement test, in addition to shutter box test, long-term storage test, etc.

Electrical performance

Electrical performance is the unique performance of insulating oil, mainly including dielectric loss angle, dielectric constant, breakdown voltage, pulse voltage, etc.

The refining depth, impurities and moisture of base oil have a great impact on the electrical performance of oil products.

Special physical and chemical properties of lubricating grease

In addition to the general physical and chemical properties of lubricating grease, special-purpose grease has its special physical and chemical properties.

For example, grease with good water resistance requires water drenching test;

Low temperature torque shall be measured for low temperature grease;

Multi effect grease should be tested for extreme pressure wear resistance and rust resistance;

Bearing life test shall be carried out for long-life grease.

There are also corresponding test methods for the determination of these properties.

Other special physical and chemical properties

In addition to the general performance, each oil product should have its own unique special performance.

For example, the cooling rate of quenching oil should be measured;

Emulsion stability should be determined for emulsified oil;

Anti creep coefficient shall be measured for hydraulic guide rail oil;

Spray lubricating oil should be tested for oil mist diffusivity;

Measure the coagulation point of refrigerant oil;

Low temperature gear oil shall be measured to form groove point, etc. These characteristics need special chemical composition of base oil or some special additives to ensure.

Instructions for using lubricating oil:

Lubricating Oil: The Basics You Should Know 2

Oil storage:

1. Do not put it upright in the open air to prevent the invasion and pollution of water and debris.

2. Indoor storage can be placed vertically, with the barrel face up for easy extraction.

3. Tighten the sealing cap to keep the oil barrel sealed.

4. Keep the barrel surface clean and clear.

5. Keep the ground clean so that oil leakage can be found in time.

6. Do a good job of warehousing registration, first come, first use.

7. Place the frequently extracted oil on the oil barrel rack and control the discharge with a switch.

8. New oil and waste oil shall be placed separately.

Containers filled with waste oil shall not be filled with new oil to prevent pollution.

Oil safety:

1. Oil products shall be stored separately, and combustible products shall not be placed around.

2. No fireworks, no kindling into the oil depot.

3. At least two fire extinguishers shall be equipped.

4. The tarpaulin or oil dirt removed after wiping the machine shall not accumulate to avoid combustion support.

5. Inflammable special oil products or chemical solvents shall be separated and stored, and inflammable signs shall be placed.

Usage notes:

1. Consult with lubrication experts and use lubricants of appropriate specifications to minimize the types of oil used.

2. Each kind of machine shows the parts that need to be refueled, the name of the oil product, the refuelling cycle, etc. in a simple drawing, and a special person is responsible for it to avoid using the wrong oil product.

3. Clean and wipe containers and tools such as oil pump and oil kettle before refueling each time.

4. Each kind of special container for oil, and the name of the oil contained in the container shall be marked to prevent pollution.

5. Before oil change, the machine must be washed with solvent, and water-soluble cleaning agent must not be used.

6. Make mechanical maintenance records after adding or changing lubricating oil every time.

7. If abnormal oil products are found or the oil change cycle has expired, samples should be taken and submitted to a professional company for testing and verification.

Environmental protection and health:

1. It is strictly forbidden to discharge waste oil directly into ditches and soil to prevent environmental pollution.

2. Waste oil and waste liquid are collected in special barrels, and then handed over to the recycler approved by the government for recycling.

Do not dump them randomly.

3. People with skin allergies or scratches should avoid direct contact with lubricating oil.

4. Do not wear clothes with oil stains, and do not put rags contaminated by oil into bags.

5. Do not wipe the oil stains on the skin with dirty rags to prevent metal debris hidden in the rags from abrading the skin and causing infection.

Glossary of technical terms

Abrasive wear: mechanical wear caused by the relative sliding of two contact surfaces;

Additive: a small amount of substances added to improve lubrication performance;

Adhesion improver: add additives to oil and grease to improve adhesion effect (such as polyisobutylene);

Adhesion lubricant: add adhesion modifier to prevent the lubricant from falling due to centrifugal force;

AF coating, antifriction coating: at present, the most widely used dry film solid lubricant, including room temperature curing and heat curing. The formula contains solid lubricating materials (called “raw materials”) and bonding materials, see “binder”;

Anti aging: aging of materials caused by oxidation, overheating, or containing some metals (such as copper, lead, silver, etc.). The anti-aging ability of materials can be improved by adding some additives (such as antioxidants);

ASTM: American Society for testing and materials;

Base oil: basic components of lubricating oil and grease;

Binder: non-volatile medium or excipient, which is used to enhance the bonding fastness between solid lubricating material particles or enhance the adhesion between solid lubricating film and friction surface;

Loosening torque: the torque required to loosen a bolt connection;

Chemical inertness: (lubricant) does not react with some substances;

Friction coefficient: the ratio of friction force and normal force between two contact surfaces;

Low temperature performance: cloud point, pour point and freezing point are used as indicator values for lubricating oil, and Kesternich flow pressure and low temperature torque test can be used to measure lubricating grease;

Colloid: the particles in the stable liquid (particle size 10-5 ~ 10-7cm) are used as a solution (no particle sedimentation);

Compound grease: lubricating grease with thickener made of metal soap and various acids, especially suitable for high temperature and long-term use;

Consistency: an index of lubricating grease, which is divided into non working cone penetration and working cone penetration, and is measured according to nlgi (American Lubricating Grease Institute) standard.

Simply divide the consistency into nine grades, such as:

Consistency gradeWorking taper (1/10mm)

Density: mass of lubricant per unit volume at 20 ℃ (g/cm3);

Detergents: surfactants that remove surface residues and sediments;

Dispersibility: improve the dispersibility of insoluble substances in liquid;

DN value: reference value of rotating speed to rolling bearing grease, expressed by bearing pitch diameter (mm) multiplied by revolutions per minute;

Drip point: refers to the temperature at which the lubricating grease changes from semi-solid state to liquid state, which is an indicator of the heat resistance of the lubricating grease.

With the increase of temperature, the temperature at which the first drop drops from the container is set as the drip point temperature;

Dynamic viscosity: that is, absolute viscosity, which reflects the internal resistance between fluid molecules when lubricating oil flows.

Measure by lubricating oil flowing through the pipe hole or gap;

EP additive: a chemical substance used to improve the ability to bear heavy loads and high temperatures, so as to enhance the wear resistance of oil and grease;

Emcor: corrosion resistance test of lubricating grease for rolling bearings in water.

At least two grease lubricated bearings are tested after running in water for about a week.

The corrosion resistance value is 0 ~ 5 (0 refers to no corrosion, 5 refers to serious corrosion);

Ester oil: compounds of acids and alcohols, used as lubricating materials and in the production of lubricating grease;

Flash point: the lowest temperature at which the flame will contact the mixture of oil vapor and air and flash;

Fluorosilicone oil: silicone oil containing fluorine atoms in molecules;

Fretting corrosion wear: a kind of mechanochemical wear caused by slight relative sliding of two contact bodies, pitting pits appear on the friction surface and oxide chips are accumulated between the friction surfaces;

Friction: the phenomenon of tangential impedance on the contact interface of two objects when they are in relative motion;

Grease: lubricating medium composed of base oil and thickener;

Inhibitor: an additive used in lubricants to delay aging and corrosion;

Freezing point: the maximum temperature of the oil product when the oil surface of the cooled sample no longer moves under the specified test conditions.

Expressed in ° C.

Pour point: the lowest temperature at which the cooled sample can flow under the specified test conditions.

Expressed in ° C.

It is a conventional index used to measure the low-temperature fluidity of lubricating oil.

The pour point of the same oil is slightly higher than the pour point. In the past, the pour point was commonly used, but now it is internationally used.

Development prospect of lubricating oil

In the next 10 years, the demand for lubricating oil in the Asia Pacific region will reach 15.5 million tons, while China will account for 40% of the demand in the region.

By 2020, the demand for lubricants in the Chinese market doubled, and the consumption already exceed that of the United States.

The rapid growth of domestic demand for automotive oil and the trend of high-grade automotive oil will promote the automotive lubricant industry to enter a period of rapid development.

While the demand for automotive lubricants is increasing year by year, the grade of oil will also achieve leapfrog development, and high-end oil products will be directly in line with international standards.

Does high viscosity of lubricating oil indicate good quality of lubricating oil?

In general, if the running speed of the parts is high, the load on the surface of the parts may be smaller, and the viscosity of the matching lubricating oil will be low (e.g. spindle oil).

On the contrary, the viscosity of the matching lubricating oil will be higher (e.g. gear oil, of course, it must finally comply with the equipment supplier’s regulations on the selection of lubricating oil).

The quality of lubricating oil includes many indicators in addition to the qualified viscosity, so the quality of lubricating oil cannot be evaluated only by viscosity.

Lubricating oil

It is generally the product of fractionated oil, but also refined from driven vegetable oil.

Also known as “grease”.

Non volatile oil lubricant.

According to their sources, they are divided into animal and vegetable oils, petroleum lubricants and synthetic lubricants.

The consumption of petroleum lubricating oil accounts for more than 97% of the total consumption, so lubricating oil often refers to petroleum lubricating oil.

It is mainly used to reduce the friction between the surfaces of moving parts.

At the same time, it has the functions of cooling, sealing, corrosion prevention, rust prevention, insulation, power transmission, cleaning impurities and so on.

It mainly takes the lubricating oil fraction and residue fraction from the crude oil distillation unit as raw materials, and removes or reduces the components such as substances forming free carbon, substances with low viscosity index, substances with poor oxidation stability, paraffin and chemical substances affecting the color of finished oil through solvent deasphalting, solvent dewaxing, solvent refining, hydrofining or acid-base refining, clay refining and other processes, so as to obtain qualified lubricating oil base oil.

After mixing and adding additives, it becomes a lubricating oil product.

The main properties of lubricating oil are viscosity, oxidation stability and lubricity, which are closely related to the composition of lubricating oil fractions.

Viscosity is an important quality index reflecting the fluidity of lubricating oil.

Different service conditions have different viscosity requirements.

Heavy load and low speed machinery should choose high viscosity lubricating oil.

Oxidation stability refers to the antioxidant capacity of oil products in the service environment due to temperature, oxygen in the air and metal catalysis.

After the oil is oxidized, it will produce fine asphaltene based carbon like substances, viscous paint like substances or paint films, or viscous aqueous substances according to the service conditions, thus reducing or losing its service performance.

Lubricity refers to the antifriction performance of lubricating oil.

Function of lubricating oil

Lubricating oil is a liquid lubricant used in various types of machinery to reduce friction and protect machinery and machined parts.

It mainly plays the roles of lubrication, cooling, rust prevention, cleaning, sealing and cushioning.

Lubricating oil accounts for 85% of all lubricating materials, with a wide variety of brands. Now the annual consumption in the world is about 38million tons.

The general requirements for lubricating oil are:

(1) Reduce friction and wear, reduce friction resistance to save energy, reduce wear to prolong mechanical life and improve economic benefits;

(2) For cooling, it is required to discharge the friction heat out of the machine at any time;

(3) Sealing: it is required to prevent leakage, dust and cross gas;

(4) Corrosion resistance and rust prevention, and it is required to protect the friction surface from oil deterioration or external erosion;

(5) Clean and flush, and it is required to clean and remove the dirt on the friction area;

(6) Stress dispersion buffer, load dispersion, impact mitigation and shock absorption;

(7) Kinetic energy transmission, hydraulic system and remote control motor, friction stepless speed change, etc.

Lubricating oil composition

Lubricating oil is generally composed of base oil and additives.

Base oil is the main component of lubricating oil, which determines the basic properties of lubricating oil.

Additives can make up for and improve the shortcomings of base oil performance, give some new properties, and are an important part of lubricating oil.

Storage of lubricating oil

Barreled and canned lubricating oil should be stored in the warehouse as far as possible to avoid the influence of climate.

The opened barrels of lubricating oil must be stored in the warehouse.

The oil barrel should be placed horizontally, and both ends of the barrel must be wedged tightly with wooden wedges to prevent rolling.

In addition, always check whether the oil drum has leakage and whether the mark on the drum surface is clear.

If it is necessary to put the barrel straight, it is advisable to turn the barrel upside down and make the barrel cover downward, or tilt the barrel slightly to prevent rainwater from accumulating on the barrel surface and flooding the barrel tie.

Water has an adverse effect on any lubricating oil.

On the surface, water is not easy to penetrate the complete barrel cover and enter the oil barrel. However, the oil barrel stored outdoors is exposed to the hot sun during the day, and the weather is cooler at night.

This kind of thermal expansion and contraction will affect the pressure of the air in the barrel;

It is slightly higher than atmospheric pressure during the day and close to vacuum at night.

This change of day and night pressure will produce a “breathing” effect.

During the day, part of the air is “exhaled” out of the barrel, and at night, the air is “inhaled” into the barrel.

If the barrel cover is immersed in water, then at night, the water will inevitably enter the barrel with the air.

Over time, the water mixed in the oil is naturally considerable.

When taking oil, the oil barrel should be placed on a wooden frame with appropriate height, a tap should be equipped at the cover of the barrel surface to drain the oil, and a container should be placed under the tap to prevent dripping.

Or put the oil barrel straight, insert the oil pipe from the end of the barrel and take oil through the hand pump.

When bulk oil is stored in the oil tank, it is inevitable that condensed water and dirt will be mixed in, and finally gather at the bottom of the tank to form a layer of sludge, which will pollute the lubricating oil.

Therefore, the design of the tank bottom should be butterfly shaped or inclined, and the drain cock should be installed to discharge the residue on time.

To the extent possible, the interior of the oil tank should be cleaned regularly.

The influence of temperature on lubricating grease is greater than that of lubricating oil.

Long term exposure to high temperature (such as sunlight) can separate the oil components in lubricating grease, so the lubricating grease barrel should be stored in the warehouse first, and the barrel mouth should be placed vertically upward.

The opening of the barrel containing lubricating grease is larger, and dirt and water are easier to penetrate.

The end of the barrel should be closed immediately after taking it.

Too low or too high temperature has adverse effects on the lubricating oil, so it is not suitable to store the lubricating oil in a place that is too cold or too hot for a long time.

Lubricating Base Oil

Lubricating oil base oil is mainly divided into mineral base oil and synthetic base oil.

Mineral base oil is widely used, with a large amount (about 95% or more), but in some applications, products blended with synthetic base oil must be used, so synthetic base oil has developed rapidly.

Mineral oil base oil is refined from crude oil.

The main production processes of lube base oil include atmospheric and vacuum distillation, solvent deasphalting, solvent refining, solvent dewaxing, clay or hydrorefining.

In 1995, the current standard of lubricating base oil in China was revised, the classification method was mainly modified, and two special base oil standards of low pour point and deep refining were added.

The most important thing in the production of mineral lubricants is to choose the best crude oil.

The chemical composition of mineral base oil includes high boiling point, high molecular weight hydrocarbon and non hydrocarbon mixture.

Its composition is generally alkanes (straight chain, branched chain, multi branched chain), cycloalkanes (monocyclic, bicyclic, polycyclic), aromatics (monocyclic aromatics, polycyclic aromatics), cycloalkyl aromatics, oxygen-containing, nitrogen-containing, sulfur-containing organic compounds, colloids, asphaltenes and other non hydrocarbon compounds.

In the past, major foreign oil companies have divided base oil into paraffin base oil, intermediate base oil, naphthenic base oil, etc. according to the nature and processing technology of crude oil.

Since the 1980s, with the development of engine oil as the guide, lubricating oil tends to be low viscosity, multi-level and universal, which puts forward higher requirements for the viscosity index of base oil.

The original base oil classification method can no longer adapt to this change trend.

Therefore, major foreign oil companies are generally classified according to the viscosity index, but there has been no strict standard.

API classified base oil into five categories (API-1509) in 1993 and incorporated them into eolcs (API engine oil licensing and certification system).

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