When the creep exceeds acceptable limits and it becomes challenging to secure the A size using the adjustment lining, the product must be replaced. For metal-rubber composite conical springs, typically 8 or 4 units are installed per bogie. To ensure the vehicle's height balance, a load-based height measurement test is essential.
The elastic properties of these springs can vary with temperature, so the test samples must be kept at a stable temperature (20–25°C) for over 24 hours before testing. Additionally, since rubber is a polymer material, each sample should be pre-pressed five times under the specified load to relieve internal stresses before any formal testing begins.
The load-based height measurement test involves measuring the spring height when a vertical load of 18,175 kN is applied. The target height is 205 mm, with an allowable tolerance of ±0.6 mm, meaning the measured value should fall between 204.4 mm and 205.6 mm. If the measured height is outside this range, spacers can be added to bring it within specification. This measurement must be performed on 100% of the samples.
During the test, the height is measured at four points, and the average of these measurements is taken as the final result. The individual measurements were: H1 = 205.113 mm, H2 = 205.164 mm, H3 = 205.172 mm, and H4 = 205.136 mm. The average height was calculated as H = (H1 + H2 + H3 + H4) / 4 = 205.146 mm.
The normal temperature static test is conducted using a CSS55100 microcomputer-controlled universal testing machine. The product is first preloaded vertically with 0.11 kN, where the displacement is set to zero. Then, the load is increased at a constant rate of no more than 30 mm/min, compressing the spring from 0 to 75 mm, followed by unloading. This process is repeated three times without any time gap between cycles, ensuring consistent conditions.
After preloading, there is a 15-minute waiting period before conducting the actual test. At this stage, the vertical load is applied again, starting from 0.11 kN at the 12 o'clock position. The spring is compressed from 0 to 65 mm, and the load-deformation curve is recorded. The vertical stiffness is calculated during the rising phase of the load-deformation curve (i.e., the compression cycle). The vertical static performance parameters include a stiffness of 0.175 kN/mm in the deformation range of 0–65 mm, with a tolerance of -11% to +9%, resulting in a valid stiffness range of 0.167 kN/mm to 0.182 kN/mm. It is also required that the stiffness remains nearly linear up to a deformation of 30 mm.
Once the data processing is complete, the computer generates the load-deformation hysteresis curve. For lateral stiffness determination, the absolute values of the load at the +5 mm and -5 mm deformation points are summed and divided by 10 mm to obtain the transverse stiffness value for the given deformation range.
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