After the rotary dumper: what stays inside the railcar

A rotary dumper turns an open-top railcar over, and the cargo falls into the hopper under its own weight. Material stuck to the floor and walls stays inside. After the turn, as much as 300 kg of wet coal can remain in the railcar body. There are three ways to remove it: vibrators on the dumper itself, a crew, or a brush machine.

What the dumper does and does not do

A rotary dumper is designed for cargo that pours out when tilted. The open-top railcar is clamped, turned upside down, and the coal drops into the hopper. At high volumes, this is fast and reliable while the cargo flows.

Wet coal flows poorly and sticks to the floor and walls of the railcar body. The amount left behind depends on its moisture and other properties. The dumper itself has no mechanism for removing this layer.

How much remains

In practice, as much as 300 kg of coal can remain in an open-top railcar after it is turned. This is wet coal stuck to the metal, not frozen cargo. Frozen cargo behaves differently, as explained below.

If the residue is not removed, the railcar carries it back out of the terminal. The cargo has completed the journey without being delivered, and the same thing happens with every railcar that passes through the dumper.

Vibrators on the dumper: VH-500R

The easiest time to clean an open-top railcar is while it is still upside down. Implementation of the VH-500R is under way. These vibratory unloaders are built into the rotary dumper structure. One control system operates them according to the same sequence as the dumper.

The sequence works as follows. The railcar is upside down and the main load has fallen into the hopper. The VH-500R strikes the railcar frame or wall from outside. The stuck coal breaks away from the metal, and gravity carries it into the same hopper.

The VH-500R delivers up to 550 J per impact. Its working pressure is 7 bar, and each vibrator consumes 2.8 m³/min of air. There are no cargo-specific modes: the impact force is the same for every material. The mounting and installation geometry are selected for each dumper.

Using vibratory unloading together with a rotary dumper is already established. Some terminals use VH-500 vibratory unloaders with a dumper so that railcars leave fully clean. The VH-500R integrates this work into the dumper cycle itself. Global Technics equipment has operated at more than 50 terminals since 2015.

Winter is different

The 300 kg figure applies to wet coal stuck to the metal. If cargo freezes to the floor and walls of the railcar body, a substantial part of the coal may remain in the open-top railcar. A powerful external impact releases slightly frozen cargo. The VH-500 operates down to −40 °C with special oil and dried air.

A 1981 review prepared for the Electric Power Research Institute found that US coal-handling facilities could not maintain normal unloading rates in bad weather and that most were not designed for frozen coal. Operators used chemical agents, but the same review did not consider them a universal solution.

The practical limit

A 1979 investigation of the winters of 1976 and 1977 describes an extreme case: "An unusual sequence of weather conditions had caused stockpile coal to freeze to depths of several feet. Loaded hopper cars were frozen throughout, effectively creating 100-ton ice cubes."

A railcar frozen solid throughout must first be thawed in a thaw shed. Impact, vibration, and a brush cannot handle cargo in this condition. Cleaning begins only after thawing.

Without vibrators: a crew

Where the dumper has no vibrators, a crew usually removes the residue. Four people can spend up to 20 minutes on one railcar, or 80 person-minutes for every open-top railcar with residue. They work inside the railcar body with shovels.

For those 20 minutes, four people cannot do other work at the site. At high volumes, cleaning becomes a bottleneck.

Without vibrators: the Sweeper GT brush machine

The Sweeper GT offers another way to clean a railcar after the dumper. This brush machine mounts on a standard material handler of the type used to unload coal from open-top railcars. It works from above, passes through the railcar body, and gathers the residue at one end. A grab or the hatches are then used to remove it. Cleaning takes 3–5 minutes, nobody enters the railcar body, and the machine weighs 4000 kg.

The Sweeper GT cannot handle frozen cargo. The railcar is thawed first, after which the brush removes the residue in the same 3–5 minutes.