Reasonable lubrication is the key factor to ensure the reliable operation and prolong the service life of rolling bearings. Most of the rolling bearing Right Grease faults are directly or indirectly related to improper lubrication. This includes the use of inappropriate lubricants, lubricant aging and insufficient lubrication.
Causes of rolling bearing failure: ① insufficient lubrication, ② Right Grease inappropriate lubricant, ③ aging lubrication, ④ failure of materials and production, ⑤ wrong bearing selection, ⑥ secondary injury, ⑦ installation failure, ⑧ liquid impurities and ⑨ solid impurities.
Most bearing manufacturers Right Grease recommend the use of grease, except that rolling bearings in extreme operating environments (such as high temperature and radiation) use lubricants (such as mineral oil and synthetic oil). The following is to share the selection of rolling bearing grease.
Choose the right grease
When selecting suitable grease for rolling bearings, the following factors usually need to be considered: Right Grease bearing type, speed, operating temperature and load, as well as installation position, seal, impact and vibration, as well as the requirements of regulations and environmental protection.
The characteristics of grease fundamentally depend on the Right Grease following three aspects:
1) Base oil type & viscosity
The viscosity of base oil affects the formation of lubricating film. The Right Grease common base oils are mineral oil and synthetic oil. The former is a low-cost base oil because its production process and cost are much simpler and cheaper than synthetic oil.
Synthetic oil includes synthetic hydrocarbon, synthetic ester, Right Grease polyglycol, silicone oil, fluorinated oil, phosphate ester, polyether and so on, which have different characteristics.
Thickener is an important part of lubricating grease. The thickener is dispersed in the base oil and forms the structural skeleton of lubricating grease, so that the base oil is Right Grease adsorbed and fixed in the structural skeleton.
The water resistance and heat resistance of lubricating grease are mainly determined by thickener. There are two kinds of thickeners used to Right Grease prepare lubricating grease: soap based thickeners (i.e. fatty acid metal salts) and non soap based thickeners (hydrocarbons, inorganic and organic).
All greases contain additives. However, some additives improve the performance of the base oil itself (antioxidants, viscosity regulators, Right Grease detergents, etc.), while others act on the bearing and metal surface (such as anti-wear additives, corrosion inhibitors, antifriction agents).
The composition of thickener and base oil divides lubricating grease into different types, and different Right Grease consistencies are represented by nlgi consistency number. The consistency represents the solid state of the grease. The original consistency data is that the metal cone is placed on the surface of a tank of grease,
and the sinking depth within 5 Right Grease seconds is measured at 25 ° C, which is called penetration or coning. The data is 0.1mm (for example, if the sinking is 25mm, record 250). The recognized test standards are DIN ISO 2137 and ASTM D 217.
Due to the inconvenient performance of penetration, the national lubricating grease Association (nlgi) has formulated the consistency grade system (nlgi grade), which sets the high consistency (penetration 85-115) as No. 6 and the low consistency (penetration 445-475) as No. 000. The higher the number, the harder and thicker the grease is.
Rolling bearings are suitable for nlgi No. 1, 2 or 3 grease.
Factors affecting grease selection
1) Bearing type
It is necessary to distinguish between point contact (ball bearing) and line contact (needle roller bearing and cylindrical bearing).
For ball bearings, the contact area of ball movement is relatively small. Generally, grease with base oil viscosity ISO VG 68 to 100 is sufficient.
Line contact rolling bearings have higher requirements for grease. Not only does the contact surface need more grease, but also sliding and friction.
This is not conducive to the formation of lubricating film, which is easy to cause wear. Grease with higher base oil viscosity (ISO VG 150 to 460 or higher) should be selected. It may also be necessary to add anti-wear additives with consistency No. nlgi 2.
The grease should match the speed parameters of the bearing. This mainly depends on the type and proportion of thickener and base oil. The speed parameter of grease is not a material parameter, but depends on the type of bearing and the required short running time.
Generally speaking, the rolling bearing with high speed or low starting torque needs to choose the grease with higher speed parameters. For low speed rolling bearings, it is recommended to select the grease with lower speed parameters.
In order to obtain good lubrication effect and long service life, it is generally recommended to select grease according to the temperature of the bearing in the standard operating range.
The working temperature range and stability of grease at high temperature depend on the type and proportion of thickener and base oil, production quality and production process.
Other factors to be considered include high applicable temperature, drip point (the temperature at which the grease is heated under specified conditions to reach a certain fluidity, called drip point), and low applicable temperature.
Since the cone penetration of grease is related to the load that can be borne during use, the grease with small cone penetration (high consistency) should be selected for heavy load; If bearing both heavy load and impact load, grease containing extreme pressure additives, such as grease containing molybdenum disulfide, shall be selected.
5) Environmental humidity
If the working environment is humid, water vapor is easy to invade the bearing. If the temperature is suddenly cold and hot, water is also easy to condense. This problem is particularly prominent when there are large holes in the bearing or housing.
Water can cause serious damage to grease or bearings, usually caused by aging, hydrolysis, lubricating film failure and corrosion.
Composite barium based and composite calcium based greases can provide good waterproof performance, which has been certified in practice. The anti-corrosion effect of grease is also affected by additives.
6) Oscillation, shock and vibration
Oscillating load can have a great influence on the structure of thickener in grease. If the mechanical stability of the grease is not high, the lubrication effect will be affected.
This leads to softening, degreasing, or hardening of the grease, reducing the lubricating capacity. Therefore, it is recommended to select grease with corresponding mechanical stability test.
If hard impurity particles penetrate into the bearing, it will not only increase the noise, but also cause wear. Proper sealing of the bearing can prevent this from happening. The grease can enhance the sealing effect by adding a layer of protection on the seal. In this case, a stronger grease type should be selected.
8) Installation position and adjacent parts
Even if the rotating shaft is vertical or inclined, the lubricant must be maintained 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 greases may occur. Therefore, attention must be paid to the compatibility between greases. However, where possible, the solution is to use only one grease, which should also be compatible with the sealing material.
9) Regulations and environmental protection
In different industrial sectors, legal and environmental factors should also be considered when selecting oils and fats. For example, in the food processing industry, grease with relevant authorization is specified. For details, refer to a global standard NSF (National Health Foundation) certified H1 or H2 level.
H1 grade food grade lubricant is a harmless lubricant used in machinery and equipment such as food production, production, packaging, treatment, transportation and storage, which has the chance of accidental contact with food.
This means that the grease must be non-toxic, biodegradable and neutral in smell and taste. Such lubricants are usually made of composite aluminum matrix and poly α It is composed of olefin or medicinal white oil as base oil.
H2 grade lubricant is a lubricant that does not contact with food in food production. It can be used for lubrication or antirust film of equipment and components.