{"id":2323,"date":"2023-03-07T16:43:43","date_gmt":"2023-03-07T15:43:43","guid":{"rendered":"http:\/\/haertha.dev.neuekommunikation.de\/wordpress\/?post_type=verfahren&p=2323"},"modified":"2023-05-17T11:08:41","modified_gmt":"2023-05-17T09:08:41","slug":"phosphating","status":"publish","type":"verfahren","link":"https:\/\/haertha.de\/en\/process\/phosphating\/","title":{"rendered":"Phosphating"},"content":{"rendered":"
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The process<\/h2>\r\n \r\n <\/div>\r\n \r\n
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\nThe objective of phosphating is to form a phosphate layer on the metal surface<\/strong>. The process begins with pickling the component to remove the natural oxide layer from the metal. This step leads to cations going into solution, with the evolution of hydrogen.
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\nThe component is afterwards immersed in a phosphate solution<\/strong> to precipitate barely soluble phosphates. Depending on the composition of the solution, an iron, manganese or zinc phosphate layer now forms. The process can be repeated if necessary. Phosphating is sub-categorised into layer-forming and non-layer-forming phosphating.\n\u00a0
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Non-layer-forming phosphating<\/span><\/h3>\n


\nNon-layer-forming phosphating is designated as such because no metal cations pass from the phosphate solution into the treated metal. Instead, all cations which form the layer originate from the material itself.<\/strong> Although providing great dimensional stability, this process provides less corrosion protection compared with layer-forming phosphating.
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\nLayer-forming phosphating<\/span><\/h3>\n

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\nIn this variant of phosphating, cations from the base metal may also be involved in the layer formation, but the majority of the positive metal ions originate from the phosphate solution.<\/strong> For fitted components, it is necessary to take account of the additional layer, which can range in thickness between hundreds of nanometres to a few micrometres.
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\nMetals and types<\/span><\/h3>\n

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Another distinguishing feature of phosphating is the metal that contributes to forming the layer structure<\/strong> \u2013 the most common are iron, zinc or manganese. Depending on the desired properties, two or three of these metals can be applied at the same time.<\/p>\n

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Iron<\/h4>\n

Iron phosphating is used to provide corrosion protection and to form the basis for the painting of components such as metal sheets. It is regarded as the simplest and cheapest option<\/strong>, because surface activation and phosphating take place in the same work step. Iron phosphating requires temperatures from 25 \u00b0C to 65 \u00b0C and a pH value between 4 and 6. Iron phosphate layers weigh between 0.2 and 0.8 g\/m2<\/sup>. Iron phosphating is suitable for workpieces made from iron, aluminium, or zinc.<\/p>\n

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Zinc<\/h4>\n

For zinc phosphating, the metal surface must be pre-treated in order that a fine-crystalline zinc phosphate layer<\/strong> can be achieved. For this purpose, the process begins with a titanium salt bath. Nickel is added to the subsequent bath at 35 \u00b0C to 80 \u00b0C and pH values range from 2.2 to 3.2. This process causes pores to form on the metal surface, which absorb oils particularly well and thus increase corrosion protection. It also results in improved paint adhesion on blank and galvanised steels. The zinc phosphate layer has a matt appearance, and a light grey to medium grey colour. It weighs 1.5 to 30 g\/m2<\/sup>.<\/p>\n

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Manganese<\/h4>\n

Manganese phosphating takes place at temperatures from 90 \u00b0C to 95 \u00b0C and at a pH value between 2.2 and 2.4. Manganese phosphate layers weigh between 10 and 25 g\/m2<\/sup>. They provide friction-reducing properties, good corrosion protection<\/strong>, and high absorption capacity for oil \u2013 ideal for use in transmissions or slide bearings. Since it produces a dark grey to black colour combined with a silky-matt look, manganese phosphating is also used for the visual enhancement of small arms.<\/p>\n

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INFO: Coating thickness
\nThe composition of the phosphate solution determines the thickness of the conversion layer.<\/strong>While phosphating with manganese or zinc can produce layers having a thickness of up to 2 \u03bcm, iron phosphating layers are usually only a few hundred nanometres thick.<\/span><\/p>\n

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Other metals and types<\/h4>\n

Trication phosphating<\/strong> is a phosphating process that involves zinc, nickel, and manganese. Other additives frequently used for phosphating are sodium nitrate, sodium nitrite, sodium fluoride, and calcium. Less common is the use of titanium, zirconium, and copper sulphate. Nickel is largely avoided because it is dangerous to health.<\/p>\n

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Features and advantages<\/span><\/h3>\n
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  • Adhesion promoter<\/strong>: the phosphate layer is firmly anchored in the base metal<\/li>\n
  • High level of corrosion protection<\/strong>: Pores and capillaries ensure a high capacity for absorbing oils and paints that provide corrosion protection<\/li>\n
  • High lubricity<\/strong>: Reduction of friction and wear<\/li>\n
  • Appearance can be adjusted via the process: fine crystalline to coarse crystalline structure, light grey to black<\/li>\n
  • Insulation<\/strong>: Phosphate layers offer high insulation resistance<\/li>\n
  • Rust resistance<\/strong>: damaged layers are nearly insusceptible to rust<\/li>\n<\/ul>\n

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