In-Train Dynamics of Freight Car Cushioning
It is typical for railcars to be assembled into a train by coupling individual cars together in a marshalling yard. These yards often use impact ramps or flat switching to accelerate the railcar to a velocity sufficient to roll through a series of switches and tracks to the designated train. Rail operations attempt to keep these velocities to a minimum, but unfortunately at times impact velocities can be higher than desirable. Depending on the type of coupling system (i.e. draft gear or end-of-car cushion unit), damage to the railcar, lading or both can occur at these velocities.
Another source of damage can occur in-train, where relative velocities between railcars can become large. Train length, gross rail load, terrain and the locomotive inputs are sources for these in-train shocks along with automatic couplers and their inherent free-slack. Coupling components must be designed to account for these various inputs to reduce in-train shocks to acceptable levels. Computer simulations validated through over-the-road testing is one of the tools that used to predict the performance of various end-of-car products.
As trains become longer and heavier, it’s critical that coupling component manufactures understand railcar dynamics and focus their efforts on products that can reduce in-train shocks. Products such as active draft cushioning along with improvements to A.A.R. specifications will be instrumental to support global heavy haul operations.