The failure mechanism and correct application of grease

1. Failure mechanism of grease

During the use of grease, the causes of its failure are rather complex. There are not only chemical reasons, but also physical reasons, environmental influences, and more often than not, it is the result of the combined effect of multiple factors. Overall, the causes of grease deterioration can be divided into two aspects: one is that certain physical and chemical changes occur within the grease itself, leading to deterioration; The second reason is that the lubrication condition deteriorates due to the mixture of foreign substances, leading to failure.

During the use of grease, it is first subjected to mechanical shearing, causing damage to the structure of the grease. This leads to excessive softening, oil separation, and loss, ultimately resulting in failure. Secondly, it will be affected by heat, such as frictional heat generation or high-temperature environments, which will cause the base oil of the grease to evaporate, thereby reducing the oil volume, hardening the grease, deteriorating its lubricity, and eventually losing its lubricating effect. Studies show that for whatever reason, a type of grease cannot function properly when its base oil content is reduced by half. Thirdly, the grease in the bearing is also subjected to the effect of centrifugal force. If the viscosity of the grease is not appropriate, the adhesion is insufficient, the structure is unstable, or the colloid stability is poor, it may be thrown out of the bearing or severely segregated. This will also lead to a reduction in oil content, hardening of the grease, and eventually loss of normal function. Fourth, under the combined effect of heat and air, oils and fats will accelerate oxidation, resulting in the consumption of antioxidants and the subsequent formation of acidic oxidation products. These acidic oxidation products can cause metal corrosion and may damage the structure of oils, reduce the dropping point, increase the viscosity of base oils, deteriorate fluidity, and even form resin-like substances. The extreme case of oxygenation is that the entire lipid layer completely turns into carbon deposits.

In addition to the above-mentioned physical and chemical factors, lubricating grease is also affected by many environmental factors during its operation. For instance, moisture can emulsify certain greases and accelerate their oxidation. Dust or foreign substances can accelerate wear and oxidation. Vacuum can accelerate evaporation and the hardening of oils, increase the coefficient of friction, etc. All of these will deteriorate the performance of the grease and accelerate its failure. It should be pointed out that these influencing factors often do not act in isolation but are interrelated, mutually influential and work simultaneously. However, there is always a main reason for the failure of a certain type of grease under certain conditions. This main reason may be the quality of the grease itself or it may be due to the "catalysis" of some external factors. If a type of grease has poor high-temperature performance or poor chemical stability, it may experience the following when used in high-temperature environments: softening → loss → poor lubrication → excessive temperature rise → accelerated oxidation → hardening and deterioration → failure. Or: oxidation → formation of acidic products → corrosion of bearings → structural damage → loss → poor lubrication → excessive temperature rise → accelerated oxidation → deterioration and hardening → failure; Or: oxidation → formation of acidic products → corrosion of bearings → structural damage → loss → poor lubrication → excessive temperature rise → accelerated oxidation → deterioration and hardening → failure.

2. Correct use of grease

According to the failure mechanism of grease, the following key points should be well grasped when using grease.

2.1 Proper storage

Grease should not be exposed to direct sunlight. It should be stored in a well-ventilated room with a suitable temperature.

When opening the bucket lid, be sure to prevent sand, dust, water and other debris from mixing in. Close the bucket lid immediately after use.

③ Greases or lubricating oils of different brands and models must not be stored or used together.

The storage period of grease is generally one year. If a small amount of oil leakage is found in the grease during storage, it can still be used after being stirred evenly.

2.2 Reasonable Selection

According to the user manual of construction machinery, different types and grades of grease should be reasonably selected based on the requirements of different parts, usage conditions and seasons. Overcome the previous phenomenon of using the same type of grease and the same grease gun for all parts of the body throughout the year.

The most commonly used greases in construction machinery include calcium-based grease, sodium-based grease, calcium-sodium-based grease, graphite calcium-based grease and lithium-based grease, etc. There are several grades of various types of lubricating grease. The higher the grade, the harder the grease and the higher the dropping point. The smaller the grade, the lower the suitable working temperature; conversely, the lower the grade, the higher. When you are not aware of the regulations on grease in the manual, you can refer to the table at the bottom for selection.

2.3 Correct Usage

When adding grease, the oil gun and grease nozzle should be wiped clean to prevent sand and dust from entering the lubricated parts.

When changing the grease, the grease in the bearing and the bearing cavity should be removed and wiped clean. When filling with new grease, generally only 1/2 to 2/3 of the cavity should be filled.

When lubricating the hinge points, it is better to wait until all the old grease has been squeezed out.

After taking the grease out of the bucket, the remaining grease should be scraped flat to reduce the area of oil separation and prevent the grease from hardening.