The new high strength steel wagons are in service far up in northern Europe, between Luleå in Sweden and Narvik in Norway. The traffic on this Ore Line is intensive, and there are strict rules for the track loading by the trains. The highest permissible axle load is 30 tonnes, which means that every wagon may weigh a maximum of 120 tonnes when fully laden. The entirely new and appreciably lighter wagons have now been rolling on the northern track for some time.

The change is the product of successful design work, in which high strength steel has played a central role. The deadweight of the wagons has been reduced by extra-high strength, hot rolled steel with a minimum yield strength of 650 MPa being used for the wagon bodies. This has led to more profitable transport, since the payload capacity of the wagons has been increased in terms of both weight and volume. The capacity in terms of weight has been raised by 20 percent and in terms of volume, by around 25 percent. The ore is hauled in the form of pellets or finely crushed ore, known as fines. The relationship between weight and volume is different for pellets and crushed ore, which has made it important to take into account not only the weight but also the volume when the payload capacity was increased.

”We have put to use everything possible within the framework set by the authorities for railway wagons,” explains Jonas Finn, Project Leader at LKAB for the development of the new wagon bodies. ”In the design work, we have also taken into consideration that the wagons must be more efficient and simpler to maintain.”

Takes seconds to unload

LKAB has raised its delivery capacity substantially in recent years, and the trend will continue in the immediate future. In order to succeed, transport must take place without disturbances and at high efficiency. The designers have therefore devoted a great deal of effort to designing the wagons for rapid loading and unloading. The wagons must also be designed for a minimum of service and maintenance time. This is illustrated by the fact that loading and unloading take place while the train is rolling. It takes only a few seconds to unload a wagon.

The continual and frequent loading and unloading imposes high stresses on the wagons. In addition, the climate is very harsh, with biting cold and humid sea air that causes heavy icing.

”We carry out regular de-icing with warm flushing water,” explains Finn. ”It is important for the water to drain away quickly before it freezes. We have therefore provided the new wagon bodies with drain holes and have designed the insides so that there are no pockets in which water could collect.

Efficient design

The extra-high strength steel used for the wagon body is 4 mm thick. The two large hatches at the bottom of the wagon open fully for emptying.
”In the new wagons, we have eliminated the problem of ore sticking to the sides during emptying,” says Jonas Finn. ”There are no corners or folds in which the ore can remain.”

The design of the body is similar to that of a boat hull, so that the body is stayed by ribs that distribute the forces from the load onto the chassis. The design is efficient and requires no external reinforcements. Laser-hybrid welding and laser cutting are used in the production of the wagons. The methods selected are designed to provide wear-resistant joints and a minimum of heat-affected material in the high strength steel.

Maintenance is quick and simple

Every wagon is taken directly from production into operation and everything is thoroughly planned - not least the maintenance. All maintenance work is planned to save time. As an example, the brake pads can be changed in a couple of minutes without the wagon having to be taken to a workshop.

The changeover to high strength steel for the wagons has been successful and has become a valuable cog in the ambitious work at LKAB. Due to the successes on the wagons, the company’s well thought-out design has been nominated for the 2008 Swedish Steel Prize.