Bearing is a highly accurate machine part, there are many reasons for its fatigue limit, which leads to unpredictable harm, in which overheating is the main cause. So why are bearings and bearings overheating?
Overheating in bearings - bearings are its abnormal warming in active condition. There are many causes for this heat, behind the wire are the main causes:
Recognize the bearing - the bearings are too hot to burn
• Choose the type of lubricant that is not suitable
Lubricants have a lubricating role, reducing friction wear, and they also have efficient heat transfer and transmission functions. Therefore, depending on the type of bearings, the manufacturer recommends which type to use. There are many people who use lubricants for bearings without knowing what kind they are? This is a mistake right from the beginning. Because each type of lubricant has viscosity and operates in different conditions. Therefore, to use the right type, consult the manufacturer's recommendations.
• Use too much grease
Some types of bearings, bearings manufacturers have oil, or lubricant grease. They calculated this amount of grease in accordance with the life cycle of the bearing. We buy and install and use it without further investigation. There are some people who often open the bearings and look more. This is not recommended because additional investigation if not the same type is already extremely dangerous. When operating, they can react because they do not work in the same mode, which will create a cohesive residue that directly affects the bearing. If this type of grease is of the same type as the available one, it is also not good to reduce the viscosity, reduce the heat transfer, thus, more or less affect the operation of the bearing.
• Lubricants lubricate contaminants
Contaminated lubricants are a direct agent to the overheating of bearings. Because when the impurities are mixed, it can cause a chemical reaction that affects the viscosity and completely loses the lubrication of grease. Therefore, it will obstruct the operation, more precisely, produce large friction, to enjoy the machine's success. There are many cases of long-term contaminated grease and grease that are turned into inert glue to the point that the machine cannot operate.
• Wrong selection and assembly of bearings or wrong design
There are many types of bearings that are manufactured to accommodate the different parts of each machine. We cannot replace bearings in large load cranes fitted to motor systems. Each type of bearing is generally defined by the manufacturers of specifications such as: size, speed, load-bearing level ... A person who understands the parameters of the bearing to compare with the operating system It is a smart job to choose the most suitable bearings for your machinery. But if you are not familiar with either of the above, please consult the expert's opinion, or the manufacturer's recommendations. In addition, you should choose genuine bearings and original bearings to make your apparatus more stable.
• Extreme operating conditions or bearings are overloaded.
Operating conditions or working conditions of bearings are its operating environment. This condition may be the operation of excessive limit revolutions, high load bearing level, operating in polluted air, hot, chemical environment ...
The most important cause is loss of concentric hole when installing. I will focus on this issue the most.
In general, there are two types of bearings: ball bearings and roller bearings. Each of these types has many different types of structures, but basically, ball bearings are contact point ball bearings and roller bearings are the contact type. Roller bearings provide better load bearing capacity so they can withstand higher loads than ball bearings, but they generate more heat than ball bearings.
Road contact forms, geometry of chopsticks, production methods and many other factors play an important role in minimizing the amount of heat generated. For a single-row, eccentric roller bearing (note that we do not mention the concentric loss between the pump shaft and the motor shaft but the concentricity of the supporting chamber holes) only about 1 minute is allowed. (1/60 of 1 degree), the bearing can compensate for this deviation. Some bearings manufacturers use logarithmic profiles that increase the eccentricity value to 3 minutes (3/60 of 1 degree) of an arc. This is good, but not much.
Let us take a look at the following example, Figure 1 is a vertical centrifugal pump, with a 24-inch distance between two bearings of two bearings and a diameter of 4 inches.
Let's have a feel for the numbers, assuming the inner diameter of the bearing bearing hole is 8 inches. In order to maintain the eccentricity of bearings in about 1 minute (1/60 of 1 degree), we need to solve the simple geometric relationship:
tan (1 minute) = c / L
Inside:
c: the concentric
L: the distance between 2 bearings 2 bearings
Inferred C=12 inch x tan(1/60 degree)= 0,003 inch (1mil=0,01 inch = 0,025mm = 25,4 micron)
If the pillow holes in this example have a concentricity of about 3 mils (not much!), The bearings can work in allowable eccentricity. If higher eccentricity allows, it will lead to overheating at bearings and lead to failure.
Self-aligning roller bearings, drum bearings, tapered ball bearings
Normally new pumps reach the required eccentricity value, but after many years of operation, it is necessary to check the concentricity of the pillow holes when removing the repair.
In order to reduce the effect of concentric loss, one has to design a tapered roller bearing at one end of the shaft instead of a cylindrical roller bearing. As shown in Figure 1, cylindrical roller bearings face up face to face, and the lower pillow is a pair of tapered roller bearings (capable of self-balancing).
