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 […]
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
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.
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).
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.
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.
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.
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.
Installation of rolling mill bearings
The service life of rolling mill bearings is not only related to the quality of the bearing, but also closely related to its installation and use. To this end, attention should be paid to the technical requirements for bearing installation, and the relevant operating procedures should be followed.
1. Preparation before installation
(1) Before installation, carefully check the mating surfaces of the roll neck, bearing box, bearing ring and bearing box cover, etc., and check whether the size, shape and position accuracy and the mating male cover meet the technical requirements of the design. .
(2) The edges and burrs of the surface that matches the bearing, the roll neck, the bearing box hole, and the oil hole must be removed, cleaned and coated with lubricating oil.
2. Installation of four-row cylindrical roller bearings
(1) Install the labyrinth ring (waterproof cover)
The fit of the labyrinth ring and the roll neck is generally a tighter dynamic fit, and a copper rod must be used to tap lightly during installation. The two ends of the labyrinth ring must be parallel and closely fit the shaft shoulder and the inner ring of the bearing.
(2) Install the inner ring
The inner ring of the four-row cylindrical roller bearing has an interference fit with the roll neck. The inner ring should be heated to 90-100°C before installation. Do not exceed 120°C to prevent incomplete shrinkage of the inner ring after cooling. The heating method can be heating by oil tank or induction heating, and heating with open flame is absolutely prohibited.
The market requirements for various mechanical devices and instruments using rolling bearings have become increasingly stringent, and the conditions and performance required for bearings have become increasingly diversified. In order to select the most suitable bearing from a large number of structures and sizes, it is necessary to study from various angles.
When selecting a bearing, generally, the bearing structure is roughly determined by considering the ease of arrangement, installation, and disassembly of the bearing as a shaft system, the allowable space and size of the bearing, and the marketability of the bearing. Secondly, while comparing and studying the design life of various machinery using the bearing and the various endurance limits of the bearing, the bearing size is determined. When selecting a bearing, it is often biased to consider only the fatigue life of the bearing. The grease life, wear and noise caused by the aging of the grease also need to be fully studied. Furthermore, according to different applications, it is necessary to select specially designed bearings for accuracy, clearance, cage structure, grease, etc. requirements.
However, there is no certain order and rules for selecting bearings. The priority should be the conditions, performance, and the most relevant matters required for the bearing, which is especially practical.
The eighteen-high rolling mill bearings adopt double-row needle roller bearings. When the copper foil is rolled at a high speed of 600m/min, the bearing speed reaches 3550r/min. The working conditions of the bearing are extremely bad, and improper assembly is prone to burns and scratches on the bearing surface. Needle roller fracture, wear, needle roller cage fracture and other problems.
The eighteen-high rolling mill has a total of 8 backing bearing rolls, each with 9 bearings, and a total of 72 bearings. The bearings have no inner ring and are assembled on 8 surface-hardened mandrels.
(1) Bearings should be tested for meat thickness before installation. The bearings should be tested and classified one by one. According to the requirements of the machine, the thickness deviation of the backing bearing on the same shaft should be less than 0.005mm, and they should be divided into 8 groups, especially during use for a period of time. Later, the needle rollers and outer ring of the backing bearing will have a certain degree of wear. Therefore, it is necessary to check the thickness of the bearing regularly.
(2) After the mandrel of the backing bearing is used for a period of time, the bearing surface will also have some wear. The bearing surface of the mandrel should be changed during assembly, which can prolong the use time of the mandrel.
(3) After a long-term use of the backing bearing in the middle part, the load it bears is different from that of the bearings on both sides, and the needle roller wear will be more serious. You can exchange positions with the bearings on both sides regularly to extend the use of the bearings. life.
(4) Regularly clean the oil injection hole on the mandrel to avoid clogging of debris and ensure that the bearing can have sufficient lubricating oil supply. Generally, compressed air can be used to blow out the oil hole at one end of the mandrel, and observe the oil outlet hole. Air pressure and air volume, if necessary, use a probe to clean up.
(5) After the bearing is installed, the side support roller can be used to carry out the pressing test, and the side support roller can be rotated, and more than half of the backing bearing can follow.
