What to pay attention to when buying bearing grease? BENOY decomposition

The characteristics of grease are fundamentally determined by the following three aspects:

1.Base oil type and viscosity

The viscosity of the base oil affects the formation of a lubricating film. The most common base oils are mineral oil and synthetic oil. The former is the lowest cost base oil. Its production process and cost are much simpler and cheaper than synthetic oil.

2.Thickener

Thickener is an important component of grease. The thickener is dispersed in the base oil and forms the structural skeleton of the grease, so that the base oil is adsorbed and fixed in the structural skeleton. The water resistance and heat resistance of grease are mainly determined by the thickener.

3.Additives

All greases contain additives. However, some additives are used to improve the performance of the base oil itself (antioxidants, viscosity modifiers, detergents, etc.), while others are effective on bearings and metal surfaces (such as antiwear additives, corrosion inhibitors, antifriction agents).

The composition of thickener and base oil divides grease into different types, and different consistency is indicated by NLGI consistency number. The consistency represents the solid state of the grease. The original consistency data is a metal cone placed on the surface of a can of grease. The depth of sinking within 5 seconds is measured at 25 ° C. It is called penetration or cone penetration. The data is 0.1 mm (for example: sinking 25 mm, the record is 250), the recognized test standards are DIN ISO 2137, ASTM D 217.

Due to the inconvenient expression of penetration, the National Grease Association (NLGI) has developed a consistency number system (NLGI Grade), which sets the highest consistency (penetration 85-115) to No. 6 and the lowest consistency (penetration) 445-475) as 000. The higher the number, the harder and thicker the grease.

Rolling bearings are suitable for NLGI No. 1, 2 or 3 greases.

9 factors that influence grease selection

When selecting the right grease for rolling bearings, the following factors usually need to be considered: bearing type, speed, operating temperature and load, as well as mounting position, seals, shocks and vibrations, and consideration of regulatory and environmental requirements.

1.Bearing type

A distinction needs to be made between point contacts (ball bearings) and line contacts (needle bearings and cylindrical bearings).

For ball bearings, the contact area of the ball movement is relatively small, and usually a grease with a base oil viscosity of ISO VG 68 to 100 is sufficient.

Linear contact rolling bearings place higher demands on grease. Not only because the contact surface requires more grease, but also sliding and friction. This is not conducive to the formation of a lubricating film, which is liable to cause wear. A grease with a higher base oil viscosity (ISO VG 150 to 460 or higher) should be selected. An anti-wear additive may also be required, with a consistency number of NLGI 2.

Speed

The grease should match the speed parameters of the bearing. This depends mainly on the type and proportion of thickener and base oil. The speed parameter of the grease is not a material parameter, but depends on the type of bearing and the minimum operating time required.

Generally speaking, rolling bearings with high speed or low starting torque need to choose grease with higher speed parameters. For low-speed rolling bearings, it is recommended to choose grease with lower speed parameters.

3.Temperature

In order to obtain good lubricating effect and long working life, it is usually recommended to choose the grease according to the temperature of the bearing in the standard operating range. The working temperature range of the grease and its stability at high temperatures depend on the type of thickener and base oil and their proportion, production quality and production process.

Other factors that need to be considered include the maximum applicable temperature, the dropping point (the temperature at which the grease is heated under specified conditions to reach a certain fluidity, called the dropping point), and the minimum applicable temperature.

4.Load

Since the size of the grease penetration is related to the load that can be used during use, grease with a small penetration (large consistency) should be used for heavy loads; if it is subjected to both heavy and shock loads, Greases such as those containing molybdenum disulfide.

5.Ambient humidity

If the working environment is relatively humid, water vapor can easily invade the bearings. If the temperature is quenched and heated, the water will easily condense. This problem is particularly acute when there are large cavities in the bearing or housing.

Water can cause serious damage to grease or bearings, usually caused by aging, hydrolysis, failure of the lubricant film and corrosion. Composite barium-based and composite calcium-based greases provide good water resistance, which has been certified in practice. The anticorrosive effect of grease is also affected by additives.

6.Oscillation, shock and vibration

The oscillating load can have a large effect on the structure of the thickener in the grease. If the mechanical stability of the grease is not high, the lubrication effect will be affected. This results in softening, degreasing, or hardening of the grease, reducing the lubricity. Therefore, it is recommended to choose a grease that has been tested for mechanical stability.

7.Sealing

If hard foreign particles penetrate the bearing, it will not only cause increased noise, but also wear. Proper sealing of the bearings can prevent this from happening. Grease can enhance the sealing effect by adding a layer of protection to the seal. In this case, a more robust grease type should be selected.

8.Installation position and adjacent components

Even if the axis of rotation is vertical or inclined, the lubricant must remain at the lubrication point. In addition to proper sealing, choosing a more viscous grease can also prevent it from flowing away.

If multiple lubrication points are located close to each other, accidental contact between the grease may occur. Therefore, attention must be paid to the compatibility of greases with each other. However, when possible, the best solution is to use only one type of grease, which should also be compatible with the sealing material.

9.Regulations and environmental protection

Different industrial sectors should also consider legal and environmental factors when selecting grease. In the food processing industry, for example, the use of greases with relevant authorizations is specified. For details, please refer to a global standard NSF (National Health Foundation) certification H1 or H2 level.

H1 food-grade lubricant is a safe and harmless lubricant used in food production, production, packaging, processing, transportation, storage and other machinery and equipment, which has the opportunity of accidental contact with food.

H2 lubricants are lubricants that do not come into contact with food in food production. They can be used for the lubrication of equipment and components or anti-rust films, etc. These components are not in contact with food.

Tips: Proper lubrication and maintenance are very important, and proper installation and use are also indispensable. During assembly or installation, if the internal clearance of the bearing is too large or too small, or in some cases, the preload is too high, which may cause early damage and shorten the bearing life. In addition to causing downtime and costly maintenance, improper bearing assembly and installation may have more negative effects, such as affecting the operation of other parts and shortening their service life.