Meal and compound feed: where the problem actually is in agricultural unloading

Grain pours out of a railcar by itself. Meal, oil cake, and feed made from them behave differently from the start. They retain oil and moisture, their particles cling to one another and to metal, and even fresh product discharges poorly. Many sites still unload these railcars with sledgehammers and poles.

Grain usually causes no trouble

Grain is dry, hard, and round enough to flow by gravity at a normal slope. Open the hatches and a grain railcar almost empties itself. This is the baseline. Meal does not behave this way.

How transport rules define meal

The IMSBC Code, the international rules for carrying solid bulk cargoes by sea, defines seed cake and meal as "residue remaining after oil has been expelled mechanically from oil-bearing seeds." The entry covers soya bean, sunflower seed, rape seed, palm kernel, cotton seed, corn gluten, rice bran, oil cake, meal oily, and expellers.

The entry is based on composition: mechanically expelled seeds containing more than 10% oil or more than 20% oil and moisture combined. Oil and moisture are part of the cargo definition. The rules also require operators to keep it as dry as practicable and not handle it during precipitation.

Meal flows poorly from the start

A 2013 Dry Cargo International article on soybean meal handling calls it a poor-flowing, mildly abrasive product. It contains more moisture and oil than grain and flows less readily than most grain cargoes. Grain flows on a 40–45° slope, while meal needs at least 55°. Meal has a bulk density of about 0.6 t/m³, compared with roughly 0.75 for grain.

The article also notes the "stickiness" of meal and its tendency to compact and bridge above an outlet. Once material compacts above a hopper discharge screw, the authors say it is almost impossible to reach.

Researchers have also measured soybean meal flowability in the laboratory. Wang, Chung, and Behnke discharged meal from a round model hopper in a 1995 Applied Engineering in Agriculture study. Storage temperature, moisture content, and particle size had a marked effect on flowability. Reducing the bed height, adding 1% FLO-FRE-GA, and adding 2% sawdust improved discharge.

Meal does not become difficult during transit. It is cohesive and oily from the time it is produced and discharges poorly even from a hopper. It cannot be unloaded like grain.

How these railcars are unloaded in practice

American dry distillers grains (DDG), a residue from corn ethanol production, provide a useful example. Holden International patent US8844852 (2014) says railcars with tenaciously caked product are common, especially in summer, and side-mounted railcar vibrators are not enough. Workers then break the product through the bottom hatch by hand, strike the hopper sides with sledgehammers from outside, and use poles from platforms above.

The patent authors state that sledgehammer blows inevitably cause severe railcar damage and leave large dents.

Pneumat Systems, a US maker of railcar unloading equipment, lists the same cargo group: DDG, wheat bran, soybean meal, corn gluten, other meals, and powders. Without specialist equipment, crews use sledgehammers, air lances, improvised tools, and vibrators. The work takes hours and is unsafe.

The U.S. Grains Council DDGS Handbook identifies poor flowability and material hanging up during discharge from railcars, containers, and vessels as a major handling problem. According to the handbook, railcars were not used regularly for these shipments for a long time. Some facilities place stationary devices above the pit to break the mass with a steel lance before unloading.

Where product remains in the railcar

Even free-flowing cargo leaves residue in the corners and on the internal beams of the railcar body. Meal holds more firmly than grain. Collecting it by hand in a covered railcar is almost impossible because workers cannot see where it hangs and have little room to move. Only a powerful external impact removes residue from the internal baffles.

Why an external impact works

The product grips the metal and itself, and an open hatch does not break that bond. It needs an external impulse. The VH-500 vibratory unloader strikes the railcar frame from outside with up to 550 J per impact. The force travels through the steel into the load, separating it from the walls and baffles so it moves toward the hatch. Crews no longer need to strike the sides with sledgehammers or work from above with poles.

There are no cargo-specific modes: the machine uses the same force for every material. The installation is adapted to the customer through its mounting, geometry, and approach to the railcar. Working pressure is 7 bar. Air consumption is 2.8 m³/min for the VH-500 and VH-500T and 1.8 m³/min for the VH-200.

In routine work, unloading falls from 15–20 minutes per railcar to 5 minutes with the machine plus 2 minutes for cleaning. Global Technics equipment has operated at more than 50 terminals since 2015.

In winter

In freezing weather, oil and moisture may be joined by a slightly frozen layer. A powerful external impact releases it. The VH-500 operates down to −40 °C with special oil and dried air.

Impact will not release cargo frozen solid throughout the railcar body. It must be thawed first.

Where the equipment does not pay

At two or three railcars a day, the purchase usually does not pay. Difficult cargo that takes hours to remove from one railcar is the exception. In that case, the standstill alone justifies the machine.