Specific surface functionality Protect your tools: coatings for almost every application
Tools, regardless of the industry, are sometimes exposed to extreme conditions during operation. The tools, in particular their surfaces, have to withstand temperature changes, sometimes enormous pressures and the effects of the processed materials — certain coatings can help counteract these issues.
Coatings can be applied to the tool surfaces to protect them. Various application methods are currently available on the market. The non-profit KIMW Forschungs-GmbH (KIMW-F) based in Lüdenscheid has specialised in chemical vapour deposition (CVD). In this process, the use of metal-organic precursor compounds (MO-CVD) makes it possible to reduce the coating temperatures to values between 200°C and 500°C. This makes it possible to produce even complex and difficult materials. In this way, it is possible to coat even complex and customised tools without changing the dimensional accuracy and the mechanical properties. In addition, the coatings applied in this way are highly crevice-resistant and have a high 3D capability. The application of homogeneous and contour-conform coatings is thus possible even on very demanding and complex geometries. The coating properties (thickness, crystallinity, density) depend on the process parameters. The inflow of precursor compounds and other reactants, the gas supply, the pressure and temperature in the reactor as well as the evaporator temperature can be precisely controlled. By selecting the process parameters, the 3D conformity and gap mobility of the coatings can be varied in a targeted manner. In contrast to plasma-based processes, very high aspect ratios (depth of a hole / diameter of a hole) can be homogeneously coated in the thermal CVD process.
KIMW-F operates five CVD hot-wall reactors
Over the last few years, KIMW-F has been able to greatly expand its CVD coating technology and currently has five CVD hot-wall reactors of different sizes. In this type of reactor, the entire volume of the coating chamber is brought to the required temperature by an external heating source. The associated system periphery was specifically adapted to the reactor volume and the applied coating systems and associated precursor compounds. The liquid, solid or dissolved chemicals used for layer deposition are fed into the reactors by computer-controlled dosing systems. The patented mini-extruder used to convey powder precursors was developed and built at the KIMW-F.
In the smallest of the plants, which is used for layer redevelopment and optimisation of layer deposition depending on the process parameters, sample coins of 20 mm diameter can be coated. The reaction chamber of the pilot plant is deliberately kept small in order to achieve fast process control with high layer growth rates and minimal material turnover at the same time. This allows a massive reduction in the time and cost of coating development. Thanks to the same precursor conveyor system, a simple upscaling of the processes is possible using the next larger CVD system with a reactor diameter of 90 mm. Multilayer coatings of precursors brought into solution, which can be conveyed alternately, are applied to the substrates in a system with a volume of 70 litres and a diameter of 208 mm. The coating structure achieved in this way ensures high media resistance and corrosion protection. Another plant of the same size is operated with the patented solids delivery system. The largest of the five reactors, with a diameter of 540 mm, also offers space for the coating of larger tool inserts.
In addition to a wide range of oxide coatings (modifications of zirconium oxide, aluminium oxide, chromium oxide, copper oxide and silicon oxide), hard material coatings such as chromium carbide and tungsten carbide as well as metallic copper coatings can be applied to various tool surfaces. KIMW-F has extensive know-how in the production of multi-layer coatings, whose individual layers in combination can both reinforce a property and have different properties in the layer structure, thus enabling the desired functionality.
By optimising the process parameters and the reactor design, it has already been possible to improve the functionalities of thermally and electrically insulating coatings, coatings for corrosion protection, coatings for demoulding improvement and coating reduction in the injection moulding process, as well as wear protection coatings and electrically conductive coatings.
Coating analysis closely linked to optimisation of coating performance
The optimisation steps are closely linked to the layer analysis. This has also recently been expanded so that the KIWM-F can now examine the layer properties and layer performance directly on site using digital microscopy, scanning electron microscopy (SEM (incl. EDX detector)), X-ray fluorescence analyser, micro-nano-mechanical measuring device and impedance spectrometer and analyse layer properties such as hardness, layer thickness, composition, wear resistance, adhesion, porosity, tribology and media density.
In addition to the application of tribological coating systems and the use of remote plasma to improve adhesion and the coating of plastic components, the KIMW-F will also focus on the targeted use of functional coatings in other industries in the future.