Phosphate conversion coatings are applied to metals both as a final finish and as an intermediate layer for subsequent coatings.
They are used to:<\/p>\n\n\n\n
At first glance, zinc and manganese phosphate layers may appear equivalent when considered as non-metallic crystalline separating layers, but there are significant differences.<\/p>\n\n\n\n
MANGANESE PHOSPHATING, compared to zinc phosphating, is characterized by a stronger etching action. This results in deeper penetration of the phosphate layer into the metallic substrate, providing higher wear resistance. The manganese phosphating process improves performance during the running-in phase of mechanical parts, increasing the transmittable power and reducing noise.<\/p>\n\n\n\n
During the running-in process, it is the coating that becomes polished through the mutual sliding of the mating surfaces. This ensures the initial adaptation necessary for the proper functioning of any mechanism, at the expense of the coating rather than the base metal. Moreover, practical experience has shown that, regarding the limit load for seizure, manganese phosphating is the preferred method for reducing wear in sliding friction conditions.<\/p>\n\n\n\n
PHOSPHATE CONVERSION TREATMENTS<\/strong> by themselves provide only short-term corrosion protection. To achieve more effective protection, suitable additional treatments are required, depending on the intended use of the phosphated surface \u2014 for example, with the application of protective oils or waxes. The phosphate layer, firmly anchored to the base metal, absorbs lubricant and retains it effectively thanks to its absorbent properties. Such post-treatments should preferably be carried out on phosphated components immediately after treatment to prevent the onset of corrosion.<\/p>\n\n\n\n Phosphate conversion coatings are produced by immersion in baths containing the appropriate solutions, with continuous agitation. During processing, the bath becomes enriched with iron, which results in the deposition of a mixed iron\/manganese or iron\/zinc layer on the surface. The presence of iron, in addition to influencing the chemical conversion of the phosphate layer, also affects the initial rate of attack on the base metal and the nucleation of the crystals. The chemical attack on the base metal, necessary to form the phosphate conversion layer, mainly occurs on the micro-roughnesses created by mechanical processing, so that the material simultaneously acquires both the coating and an improved surface finish.<\/p>\n\n\n\n It is not possible to establish in advance a minimum or maximum limit for the thickness and weight of the phosphate layer, as these vary depending on:<\/p>\n\n\n\n The company standard specifies a thickness not less than 3 microns and not greater than 6 microns, unless otherwise required by the customer. In this case, the tolerance for the specified thickness is \u00b12 microns.<\/p>\n\n\n\n THE THICKNESS IS DETERMINED BY THE MAGNETIC METHOD ACCORDING TO UNI ISO 2178.<\/strong><\/p>\n\n\n\n The coating weight, expressed in mg\/dm\u00b2, divided by the factor 1.4, approximately corresponds to its thickness in microns as measured by the magnetic method. When designing the part, it must be considered that the phosphate deposit forms partly at the expense of the base metal and that, for a fraction varying between \u00bd and \u2154 of the layer thickness, it protrudes beyond the original dimensions of the part.<\/p>\n\n\n2 \u2013 APPLICATION METHODS<\/h3>\n\n\n\n
3 \u2013 PHOSPHATE LAYER THICKNESS<\/h3>\n\n\n\n
\n