Categories and Application metallurgy gearbox is very extensive, mainly through the mesh with the drive gears to achieve the role of acceleration, deceleration, change the transmission direction, changing rotational torque or the distribution of power, in order to meet a variety of metallurgical equipment, power transmission needs. Metallurgical gearboxes for a variety of host devices, the main drive gear box as wire rod, roughing profile or plate, finishing and vertical roll, etc., but also a number of auxiliary equipment for transmission, flying shear, coiling machine, punching machine, slitting machine and roller conveyor and so on. As one of the most critical metallurgical equipment, metallurgical gearbox can run stably and reliably related to the whole production line can work properly, if it fails to lead to serious consequences. Metallurgy gearbox usually in heavy load, impact load, high or low speed, high temperature or high pollution and other harsh operating environment, it is precisely because of the special nature of the work environment and the continuous demand for reliable work, metallurgy gearbox is equipped with a bearing on the proposed more stringent requirements. High-performance bearings, the correct choice of bearing selection, tolerance, and the initial clearance and mounting dimensions is a prerequisite to ensure continuous reliable operation of the gearbox.
Bearing selection
1. Select the appropriate bearing type
Metallurgy gearbox bearings generally use double row roller bearings powertrain combinations to meet the needs of heavy loads and high power. Roller bearings with tapered roller bearings, cylindrical roller bearings and spherical roller bearings based. Metallurgy gear box with what type of gear shaft bearings by the force conditions and determine the characteristics of various types of bearings. Double row tapered roller bearings have a good radial and axial load capacity of the composite bearing internal clearance adjustable, but also helps to enhance the rigidity of the transmission system, and therefore the tapered roller bearing is designed to give priority to the metallurgical gearbox bearing type. But tapered roller bearings are also inadequate, such as higher prices and do not have self-aligning capability and anti-eccentric, so metallurgy gearbox is also a large selection of other types of bearings, such as spherical or cylindrical roller bearings.
Metallurgy gearbox often mix different types of bearings to achieve the most optimal design purposes. Compared with tapered roller bearings, spherical roller bearings low cost, under certain stress conditions that can withstand radial bearing axial combined loads. Spherical roller bearings have the biggest advantage is the ability to self-aligning, can work under eccentric conditions. When the bearing dimensions are similar, the choice of double row cylindrical roller bearings achieve higher radial load capacity, but can not afford this type of bearing axial load. Usually in radial and axial load conditions chosen composite cylindrical roller bearings, thrust bearings need to use or add other types of bearings to withstand axial loads.
2. Double row tapered roller bearings combination
When double row tapered roller bearing assemblies, bearing end usually set to "fixed end", that is the end face of the bearing inner and outer rings are top tight without leaving gaps, play axial positioning and axial load effects; the other end bearings " Floating end "to absorb thermal expansion and accumulation gear shaft tolerances. "Locating" bearing only the radial load bearing outer face and the bearing cap and retaining shoulder should allow sufficient clearance to offset gear shaft axial displacement occurred after the thermal expansion, the detailed structure shown in Figure 1. To improve the transfer of torque, metallurgy gearbox large selection of engagement for helical gears. Under heavy load conditions, the helical gear is not easy to produce shock and vibration noise, smooth operation and a large carrying capacity, and therefore superior to spur bevel gear drive transmission under heavy load conditions.
Figure 1 gearbox with double row tapered roller bearing combinations
But will generate additional axial thrust oblique gear and applied to "fixed end" bearings. When the axial thrust is large, the selection of the double row tapered roller bearings as a "fixed end", or add thrust bearings are the ideal solution. When only a single gear shaft helical gear is engaged, and the gear shaft "fixed end" choice-aligning roller bearings, should pay attention to the maximum axial and radial bearing suffered ratio relationship of the force. Spherical roller bearings due to their structural characteristics, when the bearing axial forces suffered more than their radial force suffered 1/3 or 1/4 (depending on the bearing series may be), the bearing will be subject to unilateral roller force, the other sub-roll situations unloaded. Unstressed end roller can not boot during rotation and positioning in the raceway, roller skew occurs, slip and crash cage, etc., may result in severe cage fracture, premature bearing failure. Double row tapered roller bearings with pure rolling and roller end rib-guided design, installation by controlling the bearing clearance can be used to separate a large axial force and roller bearing conditions, characteristics and differences between the two types of bearings can be Referring to Figure 2 shown. "Fixed end" of the bearing radial-axial combined loads, in order to share and improve the life of the bearing force, "fixed end" generally radial force on the smaller side, "floating-side" on the radial force than the Large side. Sometimes the choice of self-aligning roller bearings to increase the axial bearing capacity, will be "fixed end" of the radial force on the larger side, in this case, the "fixed end" Spherical Roller Bearings carrying capacity should be higher than "floating terminal" bearings.
Figure 2 Spherical roller bearings and double row tapered roller bearing difference
3. Consider the actual working conditions and axial load
Cone bevel gear and bevel gear is similar, will have a greater axial load gear meshing, bearing selection should also refer to the actual working conditions and axial load size. Herringbone gears can be used in pairs as a spin but opposite bevel gear applications, no axial thrust herringbone gears, rolling mill gear box wider application. Selection herringbone gear meshing transmission time, the input and output shafts simply set a "fixed end" axial positioning gear to the rest position should be set to "float end." "Locating" bearing can be cylindrical or spherical roller bearings, the "fixed end" should be used in axial load carrying ability of the double row tapered roller bearings. Bearing selection optimization design shown in Figure 3, the "floating end" bearings are single row cylindrical roller bearings. In addition, high-speed wire rod mill gearbox applications, high-speed input shaft is often used a specially designed double row tapered roller bearings to qualified high speed, frequent acceleration, deceleration, forward and reverse bearing applications and other harsh conditions.
Figure 3 herringbone gear bearing optimized selection
4. Consider sufficient carrying capacity
Bearing selection in addition to the correct choice when bearing types, whether the selected key factors bearing sufficient bearing capacity is also to be considered. Calculate bearing force come bearing theory of life is the most common way to measure the bearing load capacity. Metallurgy gearbox depending on the application, the general theory of life will have a minimum bearing requirements, for example, some gearbox bearings require a minimum life expectancy of not less than 50 000 h, some applications require not less than 30 000 h. Usually when calculating bearing life, in order to obtain a conservative bearing life, generally bearing rotation speed average working conditions chosen to replace the maximum speed of the rotation speed. Gearbox under conditions of constant power, the speed will result in lower torque increase, while torque increases will lead to larger bearing force. Bearing life and speed into 1:1 inverse relationship, but with 10 times the force into the relationship, that doubling the force bearing, bearing life will be reduced by 10-fold. For some low speed and heavy load applications, the results of the theoretical bearing life often not truly reflect the bearing performance, generally the primary consideration bearing nominal ratio of equivalents of the bearing force is greater than the safety factor, a more accurate method is the analysis software to calculate the bearing rollers The maximum contact stress.
Bearing tolerances
Metallurgy gearbox bearings are usually in heavy load, impact load, high speed or low speed and other harsh operating environment, properly chosen bearing tolerances only beneficial bearing installation, while ensuring bearing and shock does not occur under heavy load conditions laps situation. Generally, bearing rotating components using an interference fit, loose fit stationary parts. The actual range of bearing interference fit bearing not only on the size of the change, but under heavy load and high speed application conditions should be greater than the conventional application conditions interference fit. In the selection of inch tapered roller bearings, should pay attention to the difference metric bearings inch bearings and their tolerance band corresponding adjustment range fits Shaft and housing tolerances size. Inch bearing inner ring diameter tolerances are "plus tolerance", and metric bearings opposite. If the shaft and housing tolerances are still selected in accordance with the metric bearings, imperial bearing inner and outer rings will appear with the situation of transition, leading to the bearing outer ring and the inner ring is difficult to install and easy laps, affecting bearing life. Inch bearings should refer to specific tolerances size bearings suppliers recommended size. Compared with the imperial bearing, large size bearing tolerances metric selection is relatively simple, for overloading, bearing inner rotating bezel stationary application conditions, diameter size range 320 ~ 500mm large-size spherical or cylindrical roller bearings, shaft using r6 tolerance. For more than 500mm diameter size spherical or cylindrical roller bearings, shaft can r7 tolerance. Spherical or cylindrical roller bearing tolerances can be selected H7 or G7.
The initial bearing clearance
Tapered Roller Bearings initial clearance and the ball bearings, spherical and cylindrical roller bearings define different means axial clearance (BEP), other bearings are radial clearance (RIC). The initial decision of the bearing clearance installation and operation of the bearing clearance after work. Bearing clearance determines the size of the bearing load zone, bearing the initial clearance choose too large cause the bearing load zone is small, less the number of forces that bear roller, resulting in reduced bearing life.
Tapered roller bearing clearance selection may also occur much wear or impact roller cage, resulting in the situation cage fracture occurs. The initial bearing clearance choose too small can cause serious bearing fever appeared bearing locking and burned and so on.
Should metallurgy gearbox bearings initial clearance extrapolated based on the interference fit and maximum rotation speed of the shaft bearing. When the gearbox bearing inner ring and the shaft interference fit, the outer diameter of the bearing inner ring will expand and ate part of the initial clearance, the initial clearance minus the interference fit is the loss of the bearing clearance installation clearance (MEP) . Generally no more than 400mm diameter size for the imperial double row tapered roller bearing, range clearance after installation should be less than 0.5mm. For more than 400mm internal diameter of the large size of the bearing, the maximum clearance range of installation can be enlarged to about 0.6mm.
Initial metallurgical gearbox bearing clearance selection generally do not consider the ambient temperature, but only consider the difference between the temperature of the bearing inner and outer rings, because the ambient temperature will cause thermal expansion of the shaft, but the impact of bearing the ambient temperature will cause thermal expansion. After installing the bearing clearance (MEP) minus the difference between the temperature rise of the bearing inner and outer rings eaten clearance to get the final bearing running clearance (OPE). Metallurgy gearbox large tapered roller bearings for security reasons, the final clearance is generally not allowed to run a negative clearance. Metric cylindrical and spherical roller bearings initial clearance selection methods and tapered roller bearing similar but more simple, usually for a large size, the bearing inner ring interference fit with the outer space conditions and heavy-duty applications, the initial bearing clearance using standard C3 clearance range.
Bearing installation dimensions
Installation dimensions of bearings include shaft shoulder and bearing housing shoulder diameter, and the shaft and bearing maximum chamfer radius. For tapered roller bearings, mounting dimensions also includes safety cage gap size. Shaft shoulder and bearing housing shoulder diameter should be strictly selected in accordance with the requirements of bearings, bearing an appropriate size to ensure that the end face has a sufficient contact area, the size is too large or too small will affect the bearings. Gear shaft and housing fillet radius should be less than the maximum bearing chamfer radius own inner and outer rings, shaft and housing fillet radius too large, the bearing can not be installed in place, resulting in skewed inner and outer rings, affect the normal use of the bearing. In short, the design of metallurgical gearbox, you should pay attention to the bearing mounting dimensions should not be increased or decreased by a predetermined size.
Metallurgy gearbox harsh operating environment equipped with bearings made more stringent requirements, using high-performance bearings and bearing is to ensure the proper use of continuous and reliable operation of the gearbox prerequisite. Based on the metallurgical gearbox bearing selection, tolerance, and the initial clearance and mounting dimensions and other elements to make a brief introduction for the metallurgical gearbox design staff and equipment maintenance officers.