Train wheel construction is entirely determined by wheel diameter, rim, hub size, hub rim pitch, spoke plate shape, and rim tread profile. Each size or shape has its special significance.
Wheel diameter has a large impact on itself and the whole vehicle. On the one hand, the larger the wheel diameter, the higher the centre of gravity of the vehicle, the worse the dynamic performance of the vehicle. On the other hand, increasing the diameter of the wheel, can reduce the contact stress of the wheel and rail, reduce the wheel wear rate, increase the heat capacity of the wheel, and improve the ability to withstand the braking thermal load on the tread. Therefore, the size of the wheel diameter should be determined according to the vehicle situation. But in general, the larger the axle weight of the vehicle, the larger the wheel diameter should be, to increase the heat capacity of the wheel and increase the contact area of the wheel and rail, reduce tread damage and wear. In addition, the value of wheel diameter should also pay attention to the standardisation of specifications of the series of issues, to facilitate the wheel manufacturing and maintenance.MTJ can be customised to produce a diameter of 400 mm-1250 mm rail wheels, there are purchasing needs welcome to find us inquiries!
Rim width size depends mainly on the amount of wheel and rail carriage. When the wheels are running on the curve, the outer wheel rim is close to the rail, and the inner wheel rim is far away from the rail. Only the inner wheel tread on the rail carries enough to ensure that the wheelset is not derailed.
The difference between the new rim thickness and the rim limit is the effective wear thickness of the rim. The thicker the rim, the greater the effective wear thickness. But the wheel weight is also large. The thicker the effective wear thickness, the longer the service life of the wheel, and the larger the difference between the old and new wheel diameters.
Vehicle maintenance, to meet the requirements of the suspension between the vehicle, often needs to increase the levelling plate in the heart of the disc, side bearing and other positions. If the difference in diameter between the old and new wheels is too large, the increased plate is correspondingly thicker. Thus, the heart disc bolt is easy to break, but also increases the workload of maintenance.
The quality of the rim accounts for a large proportion of the wheel quality, i.e. the quality of the rim determines the quality of the wheel to a large extent. Especially for cast steel wheels, due to the casting process, the larger the rim mass, the thicker the spoke plate is required, and the larger the wheel mass will be. Wheel for the unsprung mass, the increase of its mass on the wheel track vertical action force has a greater impact.
To improve the hardness of the rim to increase its service life, the wheel tread is quenched in production. Due to the characteristics of the hardening process, the depth of hardening is limited. The thicker the rim is, the lower the internal hardness is, and the wear resistance is getting worse. Although the service life of the wheel is extended with the increase of rim thickness, the proportion of extension is getting smaller and smaller.
From the point of view of the service life of the wheel, the thicker the rim, the better. However, from the point of view of wheel weight and diameter difference between old and new wheels, the rim thickness should be as small as possible. Rim thickness size has its advantages and disadvantages, and should be based on the specific conditions of use of vehicles and the above factors affecting the comprehensive determination.
The wheel and axle are assembled by the interference fit, the main role of the wheel hub is the wheel is firmly fixed to the axle, and its size is mainly by the wheel and axle with the fastening force required by the decision. The thickness of the hub varies with the axle weight. In the hub length size and axle with a certain amount of interference between the case, the thicker the hub thickness, the greater the wheel mass, and the greater the fastening force between the wheel and axle. Reasonable hub thickness should be: to meet the requirements of the axle fastening force under the premise of the thickness as small as possible, to reduce the mass of the wheel.
Hub rim distance refers to the inner side of the rim and the hub of the axial distance between the inner side, the value of the wheel with the inner distance, and the axle distance between the two wheelbases, so in the selection of the hub rim distance can not be considered from the perspective of the wheel alone, should be based on the inner distance of the wheel and the axle to coordinate the consideration.
The strength of the spoke plate is directly related to the safety of driving, so the spoke plate of the wheel should have enough strength. The spoke plate shape of the wheel has a greater impact on the structural strength and stiffness. Smaller radial stiffness can make the wheel have greater elasticity, improve the brake thermal load under the action of the wheel stress state and reduce the wheel and rail power force, so the radial stiffness of the spoke plate should be moderately small. Spoke plate axial stiffness should be as large as possible, otherwise the wheel will produce a large axial deformation. Axial deformation is too large to change the normal contact position of the wheel and rail and rim angle, affecting the performance of the vehicle, and increasing the possibility of track climbing. A good shape of the spoke plate can greatly improve the structural rigidity of the wheel without increasing the deadweight, and improve the stiffness of the wheel, so the spoke plate is the key part of the wheel structure design and optimisation.
The spoke plate shapes commonly used at home and abroad are: straight spoke plate, S spoke plate, wavy spoke plate, and basin-type spoke plate.
Compared with other shapes of straight spoke plates, the advantage is the small mass, the disadvantage is that the radial stiffness is too large, and the axial stiffness is small. It is not a good spoke plate shape. Nevertheless, a straight-spoke plate must be used in the case of disc brakes to mount the brake disc.
S-shaped and tub-shaped spoke plates give the wheel reasonable stiffness and low thermal stresses. The main purpose of designing a spoke plate in the shape of an S or basin is to reduce thermal stresses. These two spoke shapes are generally used for tread braking. However, because the S-shaped spoke plate is not favourable to the flow of steel, it is not suitable for cast steel wheels, cast steel wheels are mostly basin-shaped spoke plates.
The wavy spoke plate and the S-shaped spoke plate structure of the difference is mainly the eccentricity of the spoke plate (close to the rim at the centre line of the spoke plate and close to the hub of the spoke plate between the centre line of the axial distance) is different, resulting in this difference is mainly due to the wheel hub rim distance. Wavy spoke plate wheels have less radial stiffness, and wavy spoke plate wheels have higher axial stiffness and stresses compared to the S-shape.
The spoke plate shape can be designed by either the preferred method or the optimisation method, whatever the method, good spoke plate performance is the only goal. In addition, in the wheel spoke plate design, check whether the spoke plate and the lower boundaries of the vehicle interfere.
Rim tread profile design should be considered with the rail head profile with the ideal wheel-rail profile with the state can effectively reduce the contact stress and wear, help to improve the performance of the train through the curve, and effectively improve the critical speed of the train destabilisation. At the same time, the new tread should be designed to be as close as possible to the shape after abrasion, to reduce the amount of metal cutting when correcting the tread. The design principles of the rim tread profile are:
(1) If the rim tread and rail two-point contact occurs, then there must be a point of sliding, sliding point will occur serious wear, so should try to avoid the rim tread and rail two-point contact. In addition, if the wheel is in any position, the wheel and rail contact point at the wheel and rail transverse interface radius of curvature difference should not be too large, to increase the contact surface between the wheel and rail, reducing contact stress, thereby reducing the wheel and rail wear and fatigue damage to the wheel and rail.
(2) Ensure that the wheelset has a high critical speed when running on a straight track, which requires the wheelset in the traverse amount is not too small, the equivalent slope of the wheel tread contact point is small, that is, the difference between the radius of the left and right wheel contact point is small so that the wheelset is not easy to run in a straight line when the serpentine movement occurs.
(3) Curve through the performance is good, that is, when the wheelset runs on the curve, between the wheelset and the track should maintain a small angle of impulse, which requires the wheelset in the traverse amount of the wheel tread contact point at the equivalent slope should be large, that is, the left and right contact point at the radius difference should be large, so that is conducive to the recovery of the position of the wheelset, which can reduce the wheel rim abrasion, trackside wear and the wheel to the curve of the impact.
(4) in use, due to wear, peeling, abrasion and other reasons, the rim tread needs to be often rotary repaired, if the shape after wear and the rim tread initial difference is large, then rotary repair when spinning off the amount of metal will be more, which will reduce the service life of the wheel, so in the design of the rim tread, not only to take into account the above factors of performance but also to consider the economic factors.
The wheel rim needs to have a certain height, too low easy to derail; if the rim design is too high, the tread wear depth is larger when the top of the rim may touch the rail fishtail plate bolts and fishtail plate shoulder. The height of the wheel rim is generally between 26~30mm. Considering the safety through the turnout, the smaller the wheel diameter, the higher the wheel rim should be. The wheel rim has the function of preventing wheel offline, to prevent low-speed wheel climbing and high-speed wheel jumping, wheel rim between the outer side of the rim and the horizontal plane has enough rim angle, generally around 70 °, too small and easy to climb the rail, can not guarantee safety; too large Ambassador repair shape when the amount of cutting increased, and when the wheel pair has a punching angle of the top of the wheel rim is easy to contact with the rails.
Wheel rim tread shape depends mainly on the line conditions and train speed, but the structure of the wheel itself has nothing to do. When the operation of the route and the train speed do not have large changes, even if the wheel structure changes, the tread shape does not need to change. Normally, the tread adopts the standard shape. Wheel design calculation standards generally do not include rim tread shape design calculations.
