09/10/2018

Durit Hartmetall GmbH

About the benefit of variety

Tungsten carbide begets ingenuity.
Wear – no, thanks. All producing industrial sectors agree on this demand and that is why they prefer tungsten carbide as a highly resilient material. Since virtually all users are constantly concerned with increased efficiency and profitability by extended service lives, this raises one question: Is it possible to universally achieve this aim by means of standard solutions?

“No, certainly not according to our experience“, says Stefan Grötschel from the construction department at DURIT Hartmetall GmbH in Wuppertal. “More than 90 per cent of all applications require customized products for optimized wear protection. Only those tungsten carbide components individually adjusted to the respective production conditions feature exactly the desired properties required in each case. This cannot be achieved with catalogue standards. On that account, our company offers more than 60 different sorts of tungsten carbide, which were developed in-house. We are sure: Variety creates advantages.”

So it won’t work without a broad basis. According to the experts from Wuppertal, this is absolutely necessary for designing and producing the best suited component in the right material composition, precision, and shape for each requirement. Ultra-fine to coarse grain sizes, different degrees of hardness, complex geometries and sizes, bore diameters of 0.5 mm to outer diameters of up to 500 mm.

It’s the composition that counts
There are numerous possibilities of differentiation within this range. The versatile sintered material made of tungsten carbide and a suitable binder can be specifically adjusted to certain operating conditions by the use of corresponding additives or mixtures. For example, if a good corrosion resistance in addition to wear resistance is required, the commonly used cobalt binder should be replaced by nickel. Another advantage: The residual magnetism is reduced to the minimum. If there is an extreme risk of corrosion, a nickel-chrome binder should be preferred. The share of chrome ensures improved chemical resistance and electrolytic stability. Generally one thing needs to be considered: The higher the binder share, the higher the toughness, while the wear resistance decreases adequately.

Performance down to the last grain
There’s a lot more to the modification of tungsten carbide. In addition to the grain size, there are some more aspects for improving the performance in some respects. Stefan Grötschel explains: “Fine or ultra-fine grain is characterized by even structure and hardness, by exceptional edge stability, and ideal suitability for purely abrasive wear applications. On the contrary, medium-sized grain proves to be the best choice where increased impact resistance is required. If the tungsten carbide needs to absorb particularly heavy shocks and strokes, coarse grain provides the required fracture toughness. So we are able to individually respond to practical challenges and to develop solutions ideally complying with the users’ requirements.”

The positive effects of the carbide’s variety may be illustrated by some distinctive examples in valve technology.

A cage of resistance
The task of reducing cages in valves is to decrease the discharge pressure in the system. In this context, there was a practical problem associated to wear, which resulted from previously used components made of tempered steel. Since the required service lives could not be attained due to quickly occurring wear effects, the involved company was looking for a substitute material featuring an essentially higher wear resistance and a consistently good chemical resistance. GD08NC, a special sort of tungsten carbide by DURIT with a specific nickel/chrome binder perfectly complied with this demand. The service life of the reducing cage could thus be extended by several weeks. This change incidentally paid off within a short period of time – by a remarkably improved service life as well as by reduced effort and expenditure of time and maintenance costs.

The material that progress is made of.
This flexible sintered material also features a broad potential for innovative developments. Due to proven competence in tungsten carbide and long-term cross-sector experience, DURIT is able to produce complex inner contours made of tungsten carbide. A process which was only possible by means of casting techniques. For many users, this new production process implies real progress. For instance, this trend-setting method resulted in an immediate benefit for a company previously struggling with excessively heavy wear in its production processes. The initial situation: The company used to work with chilled cast iron valves extremely strained by abrasion, which lasted only for three weeks on average. This was reflected in correspondingly high maintenance costs. It got even more complicated since those valves were not only supposed to control the flow rate, but also to execute a 45 degree turn of the flow and to pass into a subsequently installed expansion stage. Accordingly, there were increasingly high wear effects in the deflection area.

The experts at DURIT solved this problem by their newly developed process, which enabled a production of valve inserts made of tungsten carbide GD10. By this means, the service life of this component was 15 times higher.

Ready for opposing various kinds of wear
The well-known advantages of tungsten carbide include resistance to abrasion and corrosion. But it also proves successful against damaging effects induced by cavitation, which often occurs in connection with rotodynamic pumps and valve components and which causes increased wear. Depending on specific requirements, special sorts of fine grain as well as corrosion-resistant qualities are applied in this context. The textural composition of these sorts of tungsten carbide prevents any damage of the component by the release of single particles during the implosion of vapour bubbles. The attack by aggressive media is effectively arrested as well.

These few application examples plainly show the importance of a careful on-site analysis of the production conditions. Even if it is eventually all about attaining an ideal ratio of material input, costs, and service life: The right choice of material and fully meeting the user’s desires should always be based on a detailed knowledge of the current difficulties in production.   And: Variety makes it possible.

Exhibitor Data Sheet