How to choose the temperature of bearing grease?

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In the process of equipment design, installation and use, the selection of bearing grease temperature is very important. For motors, the commonly used lubricating medium is grease.

Generally, grease suppliers will mark some data on the technical parameters of grease, including dropping point, operating temperature range, etc.

On the other hand, there are many temperature calculations in different technical data.

Occasionally, the results of various calculations, as well as the temperature limits of other parts of the bearing, are not quite the same as those specified for the grease. Numerous concepts and calculations lead engineers into a puzzle when choosing.

Next, we will sort out these concepts to help engineers have a clearer idea when selecting grease temperature.

Grease temperature selection
Grease is usually selected to provide adequate lubrication to the bearing under a given operating condition. At this time, it is necessary to check the “given operating conditions” and “meet the lubrication performance”. This is the usual lubrication selection check calculation.

It has been said in the past (you can also refer to “Motor Bearing Application Technology”, “Motor Bearing Fault Diagnosis and Analysis”, “Gearbox Bearing Application Technology”, and other articles in this public number), the selection and check calculation of lubricating grease is essentially Check Kappa coefficient. When the Kappa coefficient is between 1 and 4, it means that the selected lubrication meets the lubrication requirements.

During the calculation, it can be noticed that there are many temperature effects. For example, the viscosity change curve is actually the change curve of viscosity against temperature.

The essence of this check calculation is to check whether the selected grease can meet the Kappa coefficient falling between 1-4 at the current temperature. If the answer is yes, then the choice is appropriate, otherwise it needs to be adjusted.

Diagnosis and Analysis of Improper Bearing Installation

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The bearing itself is a precision mechanical part. When the bearing is running, only a very thin lubricating oil film is separated between the rolling element and the raceway of the bearing. The thickness of this lubricating film is only one hundred and two hundredths of a sheet of paper. The lubricating film is an important factor for the normal operation of the bearing. If the lubricating film is damaged, it will cause direct contact between the bearing metal and the metal. Generally, the diameter of dust particles is much larger than the thickness of the lubricating oil film. Therefore, when there is contamination inside the bearing, the contamination particles will pierce the lubricating film and affect the lubricating performance of the bearing, which is an important factor leading to the premature failure of the bearing.

In addition, if liquid contaminants enter the bearing, it may cause problems such as corrosion of the bearing and degeneration of the grease, which will also cause the lubrication failure of the bearing.

Therefore, one of the most important factors in bearing installation is cleanliness. This cleanliness includes the cleanliness of the bearing installation environment, the cleanliness of the bearing installation tools, the cleanliness of the shaft and the bearing chamber, etc. These all require cleaning work before bearing installation.

In addition, it is also necessary to avoid contamination of bearings, lubrication, etc. during the bearing installation process.

Failure Analysis and Prevention Methods of Rolling Bearings in Plate Mill

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There are many types of rolling bearings used in plate rolling mills, and each type of bearing has its own suitable application occasions. In actual work, there are many cases of bearing failure or early damage due to improper bearing selection. Therefore, the selection of bearing type and the correct installation and use play a […]

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Motor bearing load and heat generation

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When the motor bearing temperature is not significantly higher than the motor base temperature, the overall heating of the motor bearing is not the main component of the motor heating, and the temperature distribution at this time is in line with the normal temperature distribution. Therefore, from the perspective of temperature distribution, the possibility of determining that the bearing is faulty can be roughly reduced. When the temperature of the motor bearing is significantly higher than the temperature of the surrounding motor end cover and frame, the bearing as a main heating element as a whole obviously affects the overall temperature distribution of the motor. This is different from the temperature distribution that should be between the motor bearing and the frame. At this time, there is reason to doubt whether the motor bearing has some faults.

The temperature of the motor bearing is significantly higher than the temperature of the machine base. At this time, the temperature sources of the bearing include the inside of the bearing and the outside of the bearing. The heat outside the bearing comes from adjacent parts such as the shaft and the bearing chamber. The internal temperature of the bearing comes from various frictions inside the bearing. When the bearing temperature is higher than the base temperature, it means that the friction inside the motor bearing occupies the mainstream of heat generation and becomes the main part that affects the temperature rise.

The main factors that cause heating of motor bearings include the following points:

Motor bearing load

Motor bearing speed

Lubrication of motor bearings

Sealing of motor bearings

Related contamination in the bearing

Damage inside the bearing

Factors Influencing the Service Life of Rolling Mill Bearings

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The rolling mill bearing is an important part of the rolling mill stand. Its main function is to support the rotating roll, bear the rolling force transmitted by the roll, and maintain the correct position of the roll in the stand. The working conditions of rolling mill bearings are very bad and are affected by factors such as high temperature, heavy load, water and dust. Although the consumption of bearings only accounts for about 5% of the total consumption in production consumption, the impact on the output of rolled steel is as high as 20%. Therefore, special attention must be paid to the use and performance indicators of rolling mill bearings.

Rolling mill bearings are precision parts, which have large load-bearing capacity and poor working environment. Common rolling mill bearing failure forms include: fatigue spalling, wear, corrosion, etc. of the working surface. The failure causes are complex and often appear in one or more forms. There are many factors that are difficult to use quantitative expressions to show the existence of bearing failure. contact directly. The factors affecting the service life of rolling mill bearings are mainly divided into internal factors and external factors. The internal factors include bearing material, structural design, processing and manufacturing, etc., and external factors include bearing speed, load, lubrication, and cooling.

What should we pay attention to when oiling motor bearings

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Generally speaking, the amount of grease added for the supplement lubrication of horizontal internal rotating motor shall be:

-For bearings without intermediate fill holes:

G = 0.005BD

Where D is the outer diameter of the bearing and B is the bearing width, in mm. These two data can be retrieved from the bearing type record. G is in grams.

-For bearings with intermediate oil filling holes:

G = 0.002BD

The units in the formula are the same as the previous formula.

For continuous grease injection equipment, the corresponding injection speed is often required. Generally speaking, the corresponding data can be provided from the manufacturer of lubricating equipment. If this data cannot be obtained, the supplementary lubrication amount can be obtained according to the calculation results of the above formula. Then, the time interval of grease supplement lubrication can be determined as the length of time. The grease injection speed is to add the lubricating grease with the added lubricating amount into the bearing within the lubrication time interval.

The grease injection speed is too fast, which can easily lead to excessive grease inside the bearing, which leads to high temperature and other problems. Too slow grease injection will cause poor lubrication of bearings and other problems. Therefore, it needs to be selected properly.

When the motor is working, the temperature of the bearing should be close to the temperature of the motor end cover, which is higher than the ambient temperature due to the influence of the motor heat source. Especially in the northern winter, the ambient temperature is often 0 degrees or even lower. If the grease is kept at room temperature, the temperature of the grease in the warehouse is the same as that of the room temperature. At this time, the grease in the motor bearing works at the working temperature.

From the knowledge of grease, we know that even the same kind of grease has different consistency at different temperatures. If two kinds of grease with different consistency are mixed, the lubrication performance will be affected（ To make an informal analogy, at this time, the lubrication performance of the two temperature grease is different, which can be used as the mixture of two lubricants with different lubrication properties, which is obviously unreasonable).

Improve the service life of rolling mill bearings

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The failure of the work roll bearing of the cold rolling mill causes the rolling line to stop, reducing the operating rate of the rolling mill, and reducing the output; causing damage to the bearing, the bearing seat and its accessories. Therefore, while absorbing the successful experience of other manufacturers, combined with the actual working conditions of the site, starting from the causes of bearing failure and control measures, bearing quality, bearing management, rolling state of the rolling mill, etc., a set of conclusions is drawn to reduce the consumption of work roll bearings. , An effective measure to improve the service life of the bearing.

 

Peel off

When the bearing rotates under a load, the raceway surface or rolling element surface of the inner and outer rings exhibits scale-like peeling due to rolling fatigue, as shown in Figure 2. The peeling of work roll bearings is generally caused by the following factors: excessive load; poor installation (non-linearity), foreign matter intrusion, water ingress; poor lubrication, lubricant discomfort, improper bearing clearance; rust, erosion points, scratches and Development caused by indentation.

Methods to prevent peeling of work roll bearings: check the size of the load and re-study the bearings used; improve the installation method, improve the sealing device; use a lubricant of appropriate viscosity, improve the lubrication method; check the accuracy of the shaft and the bearing box; check the travel Gap.

LYCRH Railway bearings

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Railway rolling stock Bearings 

Railway rolling stock bearings refer to bearings used in locomotives and vehicles. Bearings on locomotives include axle box bearings, traction motor bearings, transmission system bearings, bearings of the power unit and bearings of the cooling system, etc. The bearings in railway vehicles are mainly axle box bearings, and passenger car axle boxes mostly use short cylindrical roller bearings. The axle box of freight car mainly adopts tapered roller bearings. The variety, structure and performance of these vehicle bearings are basically similar to those of locomotive axle box bearings.

Axle box bearing

The locomotive wheel is connected to the locomotive body through the axle box, spring and the bogie frame. The axle box bearing directly bears the gravity on the pressure spring of the locomotive and the radial and axial impact of the steel rail on the wheel. In addition, it also transfers traction and causes Some additional loads are generated, so the axle box bearings must have a higher load-bearing capacity to withstand shock and vibration, that  offer features of longer life, safety and reliability, smaller size and quality, be easy to check and maintain, etc.. Therefore, locomotive bearings are often used non-standard series of bearings to adapt to special bearing technical circumstance. There are three types of rolling bearings commonly used in locomotives.

Cylindrical roller bearings

Cylindrical roller bearings are used in most axle boxes of diesel locomotives and electric locomotives. There are two main types of bearings

1) Four-row cylindrical roller bearings   The earliest used and largest number of four-row cylindrical roller bearings (type 972832) have been installed in axlebox for locomotives bearings in China country. The bearing has a high load carrying capacity and long life, and its rated dynamic load is 1445kN. Since it can only bear radial load and cannot bear axial load, a device for bearing axial force must be provided in the axle box.

2) Double-row cylindrical roller bearings   Double row cylindrical roller bearings(type 982832T) are used in China’s Dongfanghong  type 2, 3, 5, 21 locomotive axle boxes and Beijing locomotive axle boxes which bear radial force ,while the angular contact the ball bearings (type 146132T) bear axial load.

Spherical roller bearings

The advantage of using spherical roller bearings is that it can be designed without a tilt compensation device mounting between the axle box and the bogie frame. The axle box bearing of ND2 diesel locomotive imported from Romania is C-shaped spherical roller bearing produced by SKF Bearing Company. Its model is equivalent to domestic bearing 3G4053736KT. The rollers of this type of bearing are symmetrical, the inner ring has no outer ribs, the middle flat retaining ring can be separated, the roller and the outer ring are in line contact, the effective working length of the roller is longer, and the service life is slightly longer than that the same size of the outer profile of asymmetrical self-aligning roller bearings.

Tapered roller bearings

This type of tapered roller bearing is used double-row tapered roller bearings in locomotive axle boxes. The ND5 diesel locomotive in the United States is equipped with AP type bearings produced by TIMKEN. This type of bearing is in inch size, the commonly used bearings are B, C, D, E, F and G grades, which are used for different grades of axles.

Machining Technology of Super Large Split Three-row Cylindrical Roller Slewing Bearing

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With the increasing maturity of offshore equipment technology, large cranes in the offshore industry have developed to super-large size and super-large tonnage, and the supporting slewing bearing diameter is more than 10 m. The slewing bearing structure of this diameter section is mostly split. Its advantage is that it is easy to transport, store and disassemble. The disadvantage is that it needs to be split and spliced many times, the processing technology is complicated, and the processing accuracy is difficult to ensure, so it is necessary to determine the appropriate processing technology.

 

1. Super large split three-row cylindrical roller slewing bearing structure
The structure of a split three-row cylindrical roller slewing table is shown in Figure 1. It adopts stepped lap joints, and the axial direction is connected by hinged bolts (Figure 2) to form an integral inner and outer ring. After assembly, the inner ring of the bearing The expansion in the inner diameter direction is shown in Figure 3.

Fig.1 Structure diagram of split three – row cylindrical roller slewing bearings

 

Fig.2 Diagram of inner ring connection

 

Fig.3 Diagram of inner ring expanding along inner diameter direction

The maximum outer diameter of the split bearing is 12.3776 m. The height is 0.6 m, the maximum wall thickness is 489 mm, and the inner and outer rings are divided into 18 sections. Technical requirements: The assembly height is (600±2) mm, the axial clearance is 1.2 ~ 1.8 mm, the radial clearance is 0.5 ~ 1.2 mm, the axial runout is not more than 0.6 mm, and the radial runout is not more than 2 mm.