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Swedish mining company LKAB has increased its iron ore deliveries, thanks to stronger wagons that can carry 20 per cent more ore than their predecessors.

The high-strength steel wagons are in service far up in northern Europe, between Lulea 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 lighter wagons have now been rolling on the northern track for some time.

The deadweight of the wagons has been reduced by extra-high-strength, hot-rolled steel, with a minimum yield strength of 650MPa 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 per cent and in terms of volume, by around 25 per cent.

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.

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,” says Jonas Finn, project leader at LKAB for the development of the wagon bodies.

‘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.’ The extra-high-strength steel used for the wagon body is 4mm thick.

The two large hatches at the bottom of the wagon open fully for emptying.

‘In the wagons, we have eliminated the problem of ore sticking to the sides during emptying,’ says 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 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.

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.

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