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T-LAYER® e TiN CVD
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Fig.1: Mould
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Why choosing a surface coating against corrosion and stuck weld?
The corrosion in die-casting moulds, particularly for steel die-casting, is defined as a damage caused by the chemical affinity between steel and the injected melted metal. The corrosion is caused by the formation of intermetallic layers between the metal and the steel made by the Al-Fe and Si. This phenomenon is sensible to different external factors above all the temperature, which plays a fundamental role in the solubility of the present elements.
Like the corrosion, the stuck weld seems to be governed by the formation of intermetallic layers Al-Fe. Moreover the presence of pyrocracks on the surface offers numerous clutch points.
Each die-caster knows the practical consequences: the melted steel, inserted at high speed and pressure, goes inside the cavities gluing to the mould. Soon after there is a progressive growth of the glued material which transforms the produc into an unacceptable one for finishing, section variation and geometry. Sometimes it's necessary an extraction strength higher than the elastic limit in printed material, causing permanent deformations.
The problem is particularly evident on the cores where it is not possible to cool because, beyond producing wastes, they may seize or even break the same core. |
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What is a PVD coating?
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What is a CVD coating?
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• The acronym P.V.D. (Physical Vapour Deposition) indicates a deposition process obtained by evaporating a metal under vacuum.
• In the industrial practice the coatings used are made up of very strong materials (2000 HV and beyond). The most widespread is titanium nitride (TiN), whose color is golden yellow.
• Some millimeters thick, it is deposited on the final pieces and doesn't influence the tool.
• The principal usage is against the abrasive wear. It is mostly used for the tools but it is used also in other fields: from cold deformation of sheet to moulds and plastic extrusion to the food industry.
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• The acronym C.V.D. (Chemical Vapour Deposition) indicates a deposition process obtained by triggering a chemical reaction only with the temperature.
• The coatings used are TiN, titanium carbide (TiC) and titanium carbonitride (TiCN)
• Compared to PVD, it has the advantage of 2-3 times bigger thickness, a better adhesion and the possibility to reach the most complicated geometry.
• The disadvantages are: the need of a further hardening and tempering process, a polish process and the deformation due to the high temperature of the treatment.
• The best choice must be evaluated according to the specific case, together with our technicians.
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