January 2005

Hardmetals research gets some biting advice from King Rat

Engineers trying to design tougher ‘ever-sharp’ industrial cutting blades have gone back to nature and taken a lesson from that doughty and resourceful animal - the rat...

Blades grow blunt after cutting for a while. New knives that can sharpen themselves have been modelled on the incisors of rodents. In this way plastics and elastic materials can be ground faster and more effectively without changing blades.

A plastic park bench, a shopping bag or a Lego brick - they all have something in common with most plastic articles: they are manufactured from granulates. But making granulates or powder takes a lot of grinding. A problem of grinding mills has always been that their blades grow blunt within a few hours. This means halting production to remove, sharpen, replace and adjust the knives. The mills stop turning and valuable time is lost.

Researchers at the Fraunhofer Institute for Environmental, Safety, and Energy Technology (UMSICHT) are collaborating with Kennametal Widia to develop permanently sharp blades for grinding mills, inspired by the self-sharpening incisors of rats.

These creatures are notorious for their permanently sharp teeth that can bite through wood, metal or even concrete. Unlike humans and most other mammals, their permanently growing teeth are not fully coated with enamel. The front surface has a hard, horseshoe-shaped, ultra-thin enamel coat, but behind it is the softer dentine, a bone-like material which mechanically stabilizes the tooth. This is worn down through gnawing, leaving a sharp knife-edge of enamel protruding beyond it.

The new cutting knives work in exactly the same way. Their tough body is made of hard metal, an alloy of tungsten carbide and cobalt. Its outer surface is arched and, just like rodents' incisors, covered with a smooth, twice as hard, multiple-ceramic layer consisting mainly of titanium nitride reinforced with nanomaterials.

To prevent this thin layer from splitting away from the body on cutting, the researchers harden its surface and thus increase the bonding between the two materials. "In contrast to traditional cutting tools, our concept provides extremely stable knives that never grow blunt," says Marcus Rechberger of the UMSICHT Advanced Materials department.

"They don't need to be replaced until they have completely worn away. Our motto is: Install and forget!" Sharp cutting edges have another advantage: the sharper the blade, the finer it cuts, and the less energy it takes.

The UMSICHT researchers are now testing prototypes in grinding mills. "It won't be long before our knives are on the market," Rechberger says. "We have already received the first inquiries from industry."

3-D probe scores hit in China

Shanghai University's Institute of Materials has led the way in high-tech micro-measurement in China with the first commercial purchase of a 3-Dimensional Atom Probe (3DAP) from Oxford nanoScience.

The instrument provides materials scientists with the ability to simultaneously determine the spatial position and chemical identity of individual atoms in conducting materials. The Institute will be using it in studies of aluminium alloys and high-strength steels.

Speaking at the company's Milton Keynes, UK, headquarters Oxford nanoScience's managing director, Richard Davies, said: "This first commercial sale of a 3DAP into China highlights the determination of the country to utilise the latest technology and techniques available.

"The 3DAP offers the materials scientist a unique way of being able to correlate structure at the atomic level with properties at the macro level, such as material strength and hardening."

The company has a growing presence in Asia, with six units already sold in Japan. "We are confident that the order from Shanghai is just the beginning and that there will be more to come from China," said Mr Davies. "The level of interest in the product from the country has been exceptional."

Programme finalised

The programme for June's PM2TEC in Montréal includes authors from 29 countries presenting more than 240 papers focusing on new trends in metal powders and particulate materials, PM processes and new products. Special interest programmes include PM's
competitive environment, gears and driveline components and green part defects.

In the opening general session Robert Katsiouleris, senior vice president, sales and marketing, Rio Tinto Iron and Titanium will speak on a theme of "The challenging world of metallics".