Fuelsaver: coated ploughshares

Sunday 31st July 2011
Left: Experimental DLC-coated tools after use. Top: Initial test results; the improved coatings after the same plowing distance are shown in the bottom of the picture. Right: DLC-coated plowshare for test purposes. (© Felizitas Gemetz/Fraunhofer IWM; Martin Hörner/Fraunhofer IWM

Tribology hold the key to less friction, less power, less fuel – and ploughshares coated with diamond-like carbon (DLC) slide through the soil like a hot knife through butter. As a result, the tractors pulling them need less power and fuel. In some tests the power required has been reduced by more than 30%. Now Fraunhofer reearchers are testing nitriding steel, glass-fiber-reinforced plastic and tungsten carbide as best ploughshare material for DLC.

Extremely hard, diamond-like carbon coatings are used to protect hard disks in computers and ensure that sliding bearings remain smooth. They could also help farmers save fuel while ploughing, making it easier to till the soil.

Farmers in Germany consume  close on 1bn liters of fuel  yearly to work the land. Around 50% of that energy used  plowing or harrowing is lost as a result of friction between  ploughshare and soil.

To change this, scientists at the Fraunhofer Institute for Mechanics of Materials IWM in Freiburg and their partners in the RemBob project are working on DLC coated plowshares and already halved the friction. Power required by the tractor has been reduced, by more than 30% in some tests.

For farmers, smoothly cutting plowshares means either a time gain because they can use wider equipment or lower costs for fuel, machinery and maintenance. Tractors can be smaller or operate in partial load, with longer repair and maintenance intervals.

“From an environmental point of view it would be better if the tractors were smaller,” says physicist and trained fruit farmer Martin Hörner from Fraunhofer IWM. "They would not only need less fuel but would also be lighter. Lighter machines mean less soil compaction, and the looser the soil, the less power is needed to work it. The quality of the soil would also be better.

"In highly compacted ground there are hardly any worms and other small creatures which help to turn the soil and enrich it with nutrients. Compacted soils are less able to absorb water and dry out more quickly.

“In Germany we are relatively advanced as far as protecting soil resources is concerned, but even in this country more soil is lost by compaction and erosion than is created by natural processes,” he explains.

A further advantage of DLC coatings on groundworking equipment is the protection they provide against corrosion and wear. Plowshares have to be hard and sturdy but  resilient, not breaking if they hit a rock. High durability steels are used, but these suffer visibly if they are used for a prolonged length of time in the ground.

“A tine on a circular harrow can lose 50 % of its mass through wear every season,” states Hörner. But soil, sand and stones also wears down conventional coatings within a very short time. This is why plowshares have not been coated up to now.

"DLC coatings, however, can withstand the extreme stresses and strains. The problem is that the tough steel on the groundworking equipment deforms too easily and is therefore unsuitable as a substrate for the much more rigid diamond-like coating – it would quickly spall.

Project partners are thus testing plowshares made of different materials, including nitriding steel, glass-fiber-reinforced plastic and tungsten carbide, out in the field.

The next project goal is to plow at least 20kms of ground before the coating fails. “If we achieve that, the wear-free plowshare will be within touching distance,” concludes Hörner.

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