The contour formed by the rim and tread on the radial section of a wheel forging. The selection of the rim and tread shape of the wheel forgings not only affects the wear and service life of the wheel forgings on the track, but is also directly related to the curve passing performance and running quality of the equipment. The rim enables the wheel forgings to pass through curves and switches reliably without derailing.
The tread is conical with a taper of 1:10 near the rolling circle. When passing the curve, the outer wheel rolls on the outer rail with a larger diameter near the rim, and the inner wheel rolls on the inner rail with a smaller diameter, so that on the one hand, the wheel forgings play a guiding role with the change of the direction of the line, and the different rolling distance of the inner and outer wheel can also compensate for the difference in the length of the inner and outer rail.
When running in a straight line, if the wheelset deviates from its center position on the line, the difference in the rolling radius of the two wheels will cause the wheelset to move in the direction of returning to its center position. The outer taper of the wheel is 1:5, which can increase the difference in rolling radius between the two wheels of the wheel pair, making it easier to pass small radius curves. Reducing the tread taper helps suppress snaking motion, but the wheel rim wear is significantly increased, and the wheel rotation period and wheel life are greatly shortened. This method is only used on some high-speed passenger trains.
On the other hand, the tread shape of the wheel forging rim wears quickly in the early stages of operation, and then gradually becomes stable and the wear slows down. The shape restored after rotational repair cannot be maintained for a long time, and the amount of metal cutting is large. Therefore, railways in some countries adopt a wheel tread shape that is close to wear and reaches a relatively stable state, called a concave tread, also known as a wear-shaped tread. Adopting this shape can not only reduce wheel wear and extend the repair cycle, but also reduce the contact stress due to the improved wheel-rail contact state.