You ask – we answer

What are the critical factors for coating success? What does KOMET RHOBEST have to know for the coating and what does the user have to know?

    • Carbide composition:
      Specification of the carbide manufacturer and the carbide designation as well as specification of the share of WC/binding material/mixed carbide and grit size.
    • Specification of the material used and machining process
    • Specification of the desired coating length
    • Suitability of the tool for coating:
      If the tool is soldered, the solder must be able to resist a coating temperature of at least 750°C. This requires technical clarification in advance. Does the tool have cooling channels? If these cooling channels contain dirt or sintering residue, this could evaporate during coating, with a negative effect on the coating results. Is the tool geometry suitable? Technical clarification is necessary before certain forms can be coated. If tolerances have to be kept, we recommend clarifying the possibility of coating with us in advance on the basis of a tool drawing with exact tolerance specifications.
    • Packaging: The tools should always be dispatched in their original packaging, surrounded by bubble wrap in a suitable box, filled with sufficient foam filling material in order to avoid damage during transport.



    Why does KOMET RHOBEST need the exact composition of the carbide?


    The binding material contained in the carbide (usually cobalt or nickel) prevents the growth of pure diamond and/or converts the discharged diamond to graphite phase. This makes it necessary to remove these elements from the zone near the surface of the tool by wet-chemical preliminary treatment before coating. This depletion zone differs for each carbide, depending on the composition. To guarantee optimum diamond coating, the cobalt-free zone must be just large enough for the carbide not to become brittle in this area and not to disturb diamond growth. For this reason, the exact share of all elements (particularly cobalt) must be known.
    Thanks to our long years of expertise and constant development we have managed to coat even carbides with a high cobalt content (up to 20%) as standard.


    What are the advantages of the KOMET RHOBEST diamond layer compared with other CVD layers?

    The main difference is the nano-crystalline structure of the KOMET RHOBEST diamond layer. The small size of the crystals leads to outstanding layer adhesion (even with ultra-fine grit carbide types), smoothness and the achievement of sharp cutting edges.


    What are the main differences between the KOMET RHOBEST diamond layer and DLC layers?


    With DLC ("diamond-like-carbon") layers, part of the carbon sp2 is hybridised, in other words the material contains shares of graphite or amorphous carbon. Depending on the type, only parts of the carbon is crystalline, the rest is amorphous. This makes DLC layers softer than the KOMET RHOBEST layer (which is made up 100% of sp3 hybridised carbon) and thus only of limited value as protection against abrasive wear.


    Which materials can be coated?

    See our current carbide list. Carbides which are not included in this list are subjected to optimisation through preliminary treatment before "regular" coating. During this process, the principle suitability of the carbide type is checked on the basis of an exactly defined procedure, and the optimum preliminary treatment variant is prepared. Trial tools are required for this purpose. These must have the same surface and cut properties as the "original tool" (quantity according to agreement). The optimisation process takes about 4 to 6 weeks and is a free service for our customers against provision of the tools and test results.


    What criteria are used to prepare the carbide list? Why is the list changing all the time?

    The carbide list contains all those carbide types sent to KOMET RHOBEST in large quantities for diamond coating which have proved their optimum suitability in practical use in customer applications. We update this list once a month on the basis of the current frequency distribution. If you cannot find the carbide you are looking for on this list, please contact us. We have long years of experience in coating more than 100 carbide types and will be happy to advise you.


    Can a tool that has already been used and re-ground be coated again?


    In principle, it is possible to coat re-ground tools. However, optimum layer adhesion can only be guaranteed for those surfaces which are 100% free of previous coats.


    It is possible to remove the KOMET RHOBEST diamond layer completely from tools which have already been coated?

    So-called complete layer removal without damaging the carbide structure of the tool is not possible at present due to the perfect adhesion of the diamond layer.


    Which layer thicknesses are usually achieved?


    The standard layer thickness of the KOMET RHOBEST diamond layer is usually 5 µm depending on the diameter of the tool. On account of the nano-crystalline structure – the individual diamond crystals have edge lengths of a few nm (=0.000001 mm) – the layer is closed from a thickness of only around 100 nm. From an order volume where the coating line is completely filled, the layer thickness can be set to an accuracy of +/- 10%. On customer request, special layers can be produced, the thickness of which deviates from the usual thickness.


    How high is the friction coefficient of the KOMET RHOBEST diamond layer?

    The friction coefficient of the KOMET RHOBEST diamond layer was determined during a bearing treatment application, the values measured were 10% lower than the friction coefficient of Teflon. Friction coefficient is defined as the ratio between two forces. The force required to move one body against another is set in relation with the force required to press this body against the surface. This value is 0.04 for Teflon (dimensionless value).


    How are the costs calculated?

    For cost calculation, the are the tool takes up in the coating line is the factor which is mainly relevant. In the case of rotating tools, the respectively largest diameter is decisive. A milling cutter with blade diameter 3 mm and shank diameter 6 mm is calculated using the price for a 6 mm diameter. In addition, the coating prices also depend on the length to be coated, which means that the coating length must be quoted with every order. Please note that the overall length of the tool is not used to calculate the coating price.