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News

High strength steel is gentle on the crops

SSAB Tunnpl : 17 June, 2006  (Company News)
As wide as an airliner, but now lighter than ever. When a Hardi Evrard self-propelled sprayer runs across a field, it does so without damaging the crops. With a width of about 30 metres, these vast machines resemble giant birds with outstretched wings as their long lattice booms extend freely out at the sides. The high stresses that they create are carried by an advanced chassis manufacturered from high strength steel. The structure is light but stable, reliable and durable. France-based Hardi Evrard , where the development work was carried out.
As wide as an airliner, but now lighter than ever. When a Hardi Evrard self-propelled sprayer runs across a field, it does so without damaging the crops. With a width of about 30 metres, these vast machines resemble giant birds with outstretched wings as their long lattice booms extend freely out at the sides. The high stresses that they create are carried by an advanced chassis manufacturered from high strength steel. The structure is light but stable, reliable and durable. France-based Hardi Evrard , where the development work was carried out.

Hardi Evrard has used an advanced high strength steel for the design of its strong, resilient chassis which is now 500 kg lighter than if it had been made of a standard steel. Additionally, the use of high strength steel in the new design enables it to better withstand very high fatigue stresses in the long spray booms created when the sprayer is travelling. The company uses laser cutting and riveting, which also contributes to the improved properties.

The lower weight means that the machines are more gentle on the fields and cause less damage to the crops. The lighter machine does not compact the soil as much and can be designed with a higher ground clearance, so that it travels well clear of the crops.

Lower weight also allows for a larger spray tank and more liquid, which makes operation more efficient and reduces the number of topping-up stoppages. Time is almost always of critical importance in spraying as large areas must be sprayed quickly when the weather is right. As a result the driver often has to work long shifts, and a lighter machine is more comfortable for him to operate.

Riveting for sturdiness and flexibility
Hardi Evrard began producing this type of chassis in the mid-1990s, and since then has gradually refined and developed the design. The chassis is now made of Domex 650 MC, which has a minimum yield strength of 650 N/mm2. Sheet steel between 3 and 10 mm thick is used for the various components.

The chassis consists of two longitudinal channel-section members to which the cross-members are riveted. The components are cut by laser and are painted before assembly. The surface treatment must be of a very high quality in order to prevent corrosion which could be created due to the environments in which the machines have to operate.

The long spray booms are secured well back on the chassis, which is where the loads are highest.

The decision to use riveting for the chassis is based on experience gained from truck manufacturers. Riveting is much quicker than welding and eliminates sensitive welded joints. In addition to faster production, riveting ensures higher strength and better durability of the machines.

Much of the design is dictated by customer's individual requirements, and riveting then makes it simpler to adapt the chassis to suit various types of equipment.

Strength allows for continual development
The basic design utilising a strong chassis was an essential prerequisite for the advanced suspension and springing system recently introduced by Hardi Evrard on the machines. The track of each pair of wheels can be varied while the machine is travelling, to suit the ground conditions and the way that the crop has been planted. Due to the introduction of new springing, the machines are more stable and can be run at a higher speed, which results in higher efficiency.
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