First, the main performance indicators of grease

①, Dropping point: It refers to the temperature when heating under specified conditions to reach a certain fluidity. It can roughly determine the operating temperature of the lubricating fingers (dropping point is 15 ~ 30 degrees higher than the use temperature)

② Cone penetration: refers to the depth (unit: 1 / 10mm) that the test cone penetrates into the grease freely and vertically within 5s under the specified temperature and load. It is a measure of consistency and softness.

③. Colloidal stability (oil separation): Refers to the ability to lubricate oil in the skeleton of its thickener under the action of external force, which is determined by the amount of oil. When the amount of grease released exceeds 5% -20%, this grease cannot be used basically.

④, oxidation stability: refers to the ability to resist oxidation during storage and use.

⑤, mechanical stability: refers to the ability to resist changes in consistency under mechanical working conditions. Poor mechanical stability can easily cause the consistency of the grease to decrease.

⑥. Evaporation loss: refers to the percentage of the total loss under the specified conditions. It is an important factor affecting the service life of grease.

⑦.Water resistance: refers to its ability to be insoluble in water, absorb water from surrounding media, and not be washed off by water.

⑧.similar viscosity: refers to the ratio of the shear stress to the shear rate of non-Newtonian fluid flow. When the speed is high, the viscosity is low, otherwise the viscosity is large.

II. Failure analysis of grease

① Failure caused by physical factors

In use, the grease will be subjected to mechanical shear and centrifugal force at the same time. Under the effect of grease, the grease will be thrown out of the friction interface to separate the oil, resulting in reduced grease oil content, reduced penetration and hardening. After a certain degree of grease It will completely fail; under the action of mechanical shear, the grease structure loves to be destroyed (such as soap fiber disengagement or orientation), causing its softening, consistency decrease, and oil growth, etc., which eventually leads to failure. Under normal circumstances, if the grease transfer speed is increased by 2000r / min, its life will be reduced by about half. Under high shear stress, the speed is doubled, and the service life is only 1/10 of the original life.

②, failure caused by chemical factors

The chemical reaction between the grease and the oxygen in the air produces acidic substances. It is the first to consume the antioxidant additives in the fat, but to a certain extent, the organic acids generated will corrode metal components and destroy the structure of the fat, causing it to drip. Decrease, increase in base oil viscosity and poor fluidity. Numerous tests have shown that the higher the temperature, the more pronounced the decline in grease life. For example, if the temperature is between 90 and 100 degrees, every 19 degrees of temperature increase, the life of the fat will be reduced by half, and at 10 to 150 degrees, every 15 degrees of temperature will increase the life of the fat by half.

In addition, moisture, dust, and harmful gases in the environment in which the grease is used are also important factors that cause deterioration. For example, the wear particles of copper, iron, lead and bronze mixed with grease can catalyze the oxidation of terrestrial grease. In short, there are many reasons for the failure of grease, and sometimes it may be caused by a certain cause, but it is more the result of the same effect of multiple factors, or one cause as a breakthrough, and then other reasons work together.

Three, reasonable choice of grease

When selecting the grease, the working conditions (load, speed, temperature) of the friction pair, the working state (continuous operation, intermittent operation, presence of vibration and shock, etc.) and the working environment (humidity, temperature, air pollution, etc.) should be considered. ).

①The operating temperature of the grease should be at least 20 ~ 30 degrees below its dropping point.

When the temperature is high, a grease with good oxidation resistance, low evaporation loss and high drop point should be selected; when the temperature is low, a low starting moment and a similar viscosity should be selected, such as a grease based on a synthetic oil .

② The selected grease should be suitable for the use speed of the lubricated friction pair.

At high speeds, a grease with a large cone penetration made from a low viscosity base oil should be selected; for low speed greases, a grease with a high cone penetration grade made from a high viscosity base oil should be selected.

③ The selected grease should be suitable for the load.

For heavy loads, choose a grease with high base oil viscosity and high thickener content. When the load is particularly large, it is necessary to choose a grease with extreme pressure additives or fillers (molybdenum disulfide, graphite); at low and medium loads, generally use a No. 2 consistency soap fiber structure with short, medium viscosity base oil.

④ The selected grease should be suitable for the environmental conditions used

In environments with humid air or contact with water, calcium-based, lithium-based, lithium-based composites and other water-resistant greases should be selected; when there is a lot of dust, thicker (i.e., higher grade) greases should be selected to ensure tightness. Preferably, impurities can be prevented from being mixed into the friction pair. In the environment of strong chemical media, chemical-resistant synthetic oil grease such as fluorocarbon grease should be selected.

⑤The selected grease should be suitable for the lubrication mode of the friction pair.

When it is a centralized grease supply, you should choose 00 ~ 1 grease; for parts that are regularly filled with grease guns, grease cups, etc., you should choose No. 1 ~ 3 grease; for long-term use without changing the grease, you should choose Use No. 2 or No. 3 grease.

⑥ The selected grease should be suitable for the working state of the friction pair

For example, when the vibration is large, apply a grease with high viscosity, good adhesion and vibration damping properties, such as a compound soap-based grease thickened by a high-viscosity cycloalkyl or mixed base lubricating oil.

⑥ The selected grease should be suitable for its purpose

For lubricating greases, specific choices must be made according to the types of friction pairs, working conditions, working conditions, environmental conditions, and methods of supplying grease; for protective greases, metals should be effectively protected from corrosion, such as protection For parts in contact with seawater, aluminum-based greases with strong adhesion and water resistance should be selected; general protective greases can be selected from solid hydrocarbon thickened high-viscosity base oils. For sealing grease, attention should be paid to its resistance to the solvent of the medium to be sealed.

The selected grease should be as far as possible to reduce the variety of grease and improve economic benefits.

In the case of meeting the requirements, try to use lithium-based grease, complex soap-based grease, polyurea and other multi-purpose universal grease. In this way, not only the types of fat are reduced, the management of fat is simplified, but also the cost of grease and maintenance costs are reduced due to the long life of multi-effect fat.

4. Proper use of grease

①, the amount of lubrication should be appropriate

Excessive amount of grease will increase the frictional torque, increase the temperature, and increase the amount of fat; while too small amount of grease, you will not get reliable lubrication and dry friction will occur. In general, the appropriate amount of grease is 1/3 ~ 1/2 of the total void volume in the bearing. However, depending on the circumstances, sometimes the bearing edges should be greased to implement cavity lubrication.

②, pay attention to prevent the use of different types, brands and mixed old and new grease

Avoid the cross-use of grease container and tools, otherwise, it will have adverse effects on the dropping point of fat, increase of cone penetration and decrease of mechanical stability.

③ Pay attention to replacement of new fat

As the types and quality of grease are constantly improved and changed, when the old equipment is changed to new grease, it should be tested before trial use before it can be used formally. When replacing the new grease, the waste grease should be removed and the parts cleaned. clean. When replenishing grease, squeeze out the waste grease until you see new grease at the grease outlet.

④ Pay attention to the management of grease filling process

Before collecting and filling the grease, pay close attention to the cleanliness of the containers and tools. The grease supply port on the equipment should be wiped clean in advance to prevent the mixing of mechanical impurities, dust and sand particles.

⑤, pay attention to the timely replacement of seasonal fats

For example, if the environment where the equipment is located in winter and the temperature difference between summer plums and summer plumes is large, if winter fats are used in summer or vice versa, the results will be counterproductive.

⑥ Pay attention to regularly changing the grease

The time for adding and changing the grease should be determined according to the specific use situation. It is necessary to ensure reliable lubrication without causing grease to be wasted.

Do not pack grease in wooden or paper containers

Prevent oil from becoming hard, mixed with moisture, or contaminated by deterioration, and should be stored in a cool, dry place.