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
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;
* 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.