PHOSPHATE CONVERSION COATINGS

 

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SPRAY APPLICATION IRON PHOSPHATING

Spray iron phosphate coating is the newest method. Spray pressure plays effective role on the surface reaction. Although first investment of this process is costly, it has various advantages;  improved quality, high speed of production and low chemical consumption.

 

Two types of degreasing can be employed. One is alkaline degreasing prior to phosphating. Other one is the combination of neutral degreasing chemical and phosphating chemical in the same working bath.

 

Important parameters of spray iron phosphating process are;

*   Temperature,

*   pH,

*   Concentration,

*   Application time. 

 

Operating temperature is between 55 – 65 °C with 2 – 5 minutes of application time. Spray pressure must be in the range of 1.5 - 2.0 bar. With low pressure insufficient coating, at high temperatures dusty coating can be seen on the surface. pH of the coating solution must be in the range of 4 – 6. Optimum pH value is obtained by pH reducer or by main component phosphating product. Concentration of the iron phosphate conversion coating solution is between % 1.5 – 3.0. Phosphated metal workpieces are rinsed and then brought to passivation treatment. At the next stage, drying temperatures must not pass over 110 °C. At excessive temperatures water particles which are located between phosphate crystals evaporate, thus quality of the coating reduces, corrosion protection cannot be effective any longer.