Diamond-like coatings now better suited to industrial applications

Paul Boughton

Diarc-Technology has developed its next-generation 'diamond-like' coating system that enables ta-C (tetrahedral amorphous carbon) structured coatings to be produced in volume quantities for industrial applications. The company's improved process is targeted at companies needing a hard-wearing protective coating that can deliver increased efficiency and reliability of components operating in challenging and critical wear environments in mechanical systems.
This new generation of coatings also offers extremely low friction in the presence of lubricants, thereby reducing in energy consumption. The super-lubricant coating has broad industrial applications for all types of wear parts in engines, hydraulic systems and power transmissions, and also for precision tool applications. Tapani Haikola, vice president of Diarc, comments: "In many cases the coated component or tool ensures a trouble-free operation of the machine and the production process. On tools, for example, the improvement in service life offered by the coating plays a more important role. Also, improved quality and more efficient production gained when using coated tools is in many cases as important as the service life of the tools."
Diarc describes itself as a pioneer in a low-temperature vacuum plasma deposition process that can lay down a thin, tough layer of diamond-like carbon onto a range of materials from metals to plastics. The process is based on a special plasma accelerator technique to create a highly ionised plasma of the coating material. The plasma is electromagnetically accelerated to a high velocity, directed towards the workpiece and targeted onto the surfaces to be coated. This principle makes it possible to process adherent dense coatings at low temperatures; typical deposition temperatures are below 100 degrees C. The temperature can be adjusted by the process parameters so that it is possible to make coatings at even lower temperatures (around room temperature). The thickness of the coating can range from a few nanometres to several micrometres, depending on the application. The coating process has low energy and raw material demands and no hazardous chemicals or gases are used in any phase of the process.
The ta-C structured hydrogen-free diamond-like coating has five key properties of low friction, high hardness, excellent wear resistance, chemical inertness and high thermal conductivity. The Diarc coating process also allows the coating properties and performance to be optimised for specific applications. Haikola says: "The excellent wear resistance the coating protects the surfaces as a thin layer. As a comparison one micrometre layer of amorphous diamond wears out in the same time as 1mm of hardened steel."
On modern machines the wear is, in general, well in control and the main challenges are to prevent unexpected failures such as seizure of moving parts. This may happen in overload conditions or when the lubrication does not work properly or the lubricant supply fails for some reason.
According to Diarc, the coating ensures reliable and trouble-free operation (preventing seizure) of pneumatic components such as valve actuators for process valves in chemical, oil, and the pulp and paper industries, and on plungers of precision pumps for ventilators. In a radial piston hydraulic motor, coating the sliding surfaces of the moving parts increases the efficiency at low speeds by 30 per cent compared with using uncoated parts. In power transmissions, the friction coefficient has been reported to be 25 to 30 per cent less when the gear wheels are coated with Diarc Diamond coating when compared to uncoated steel gear wheels.
The investment the company has made in its coatings process means that there is increased production capability to support customers with volume requirements. Diarc's system is designed for coating small parts in quantity. The maximum dimensions of parts the company can coat are diameter 660mm, length 700mm (up to 1000mm) and weight 250kg.
For more information, visit www.diarc.fi

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