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The surface, too, is the key
The condition of the component or tool surface has a decisive influence
on the performance of a coating. The precondition for perfect coating
quality is defined as follows:
A component that is ready to receive a good quality coating is ground or polished, well-cleaned and conserved for transport.
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Ground surfaces may not exhibit grinding cracks, oxide skins or rehardening burns.
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The coolant used during grinding may not contain any calcium
sulphonate, boron or iodine compounds or silicone-based anti-foaming
agent.
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Ground, honed, polished or lapped surfaces must be free of abrasives and residues.
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Cutting edges must be burr-free so that they do not break out on first use.
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In EDM processes, it is recommended that a number of finishing passes are made to reduce the formation of the "white layer".
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The surfaces must be bright metal. Corroded, brown-finished, steam-blued or similarly treated surfaces cannot be coated.
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Blind holes and internal threads must be free of hardening salts and other contamination.
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Chips, wax, adhesive tape, paints and other non-metallic contamination,
grinding dust, cleaning agent residues, fingerprints and the like must
be removed from the components.
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Soldered and brazed joints must be kept free of voids, flux and cadmium.
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The components should be demagnetised.
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The average roughness Rz of the functional surfaces to be coated can be
used as a first, general indicator. This value should lie within the
same order of magnitude as the coating thickness. At higher surface
roughness values, there is a danger that the coating is sheared off at
the roughness peaks or breaks down because local surface pressures are
too
high.
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