PHOSPHATING AND CHROMATING

1. DONE BY,
ABDULLAH
ABISHEK

2.  Understanding of phosphating, chromating and
its applications.
 Identifying the process of plating.
 Study the process.

4.  Its used on steel parts for corrosion resistance, lubricity
or as a foundation for subsequent coating or painting.
 Its serves as a conversion coating in which dil.Phosphoric
acid and phosphate salts is applied via spraying or
immersion and chemically reacts with the surface of part
being coated to form a layer of insoluble ,crystalline
phosphates.
 It can also be used on aluminium, zinc, cadmium, silver
and tin.

5. A.Manganese.
B. Iron.
C. Zinc.

6. 1. Cleaning the surface.
2. Rinsing.
3. Surface Activation.
4. Phosphating.
5. Rinsing.
6. Neutralizing Rinse(optional).
7. Drying.
8. Application of supplemental coating.

7. Cleaning
the surface
Rinsing
Surface
Activation
Phosphating
Rinsing
Neutralizing
Rinse(optional)
Drying
Applications of
supplemental
coating
End of process
Process-

8.  Corrosion Resistance.
 Zinc and Manganese coatings helps prevent
galling.
 Adhesion and Electric Isolation.
 Porosity mechanically interlock the additional
materials after dying.
 Zinc phosphate coatings are used in conjunction
with sodium stearate(soap) to form a lubricating
layer in cold and hot forging.

9. FINISHED PRODUCT OF PHOSPHATING-

11.  Its used to passivate steel, aluminium , zinc,
cadmium, copper, silver ,magnesium, and tin alloys.
 The chromate conversion coating is named after the
chromate found in chromic acid, also known as
hexavalent chromium, the chemical most widely used
in immersion bath process whereby the coating is
applied.
 Chromate conversion coatings are commonly applied
to everyday items such as hardware and tools they are
greenish-yellow colour.

12. 1. Aluminium.
2. Magnesium.
3. Ferrous.
4. Zinc.

13.  Chromate conversion coating on an aluminium
substrate are known by: chemical film, iridite,
alodine.
 Iridite NCP is non-chromium type of conversion
coating for aluminium substrates.
 The most commonly referred –to standard for
applying chromate conversion coating to
aluminium is MIL-DTL-5541.

14. Alodine may also refer to chromate-
coating magnesium alloys.

15. Chromate conversion
coatings can be applied over
phosphate conversion coatings used
on ferrous substrates. The process is
used to enhance the phosphate
coatings.

16.  Chromating is often performed on galvanized parts
to make them more durable.
 The chromate coating acts as paint, protecting the
zinc from white corrosion.
 The protective effect of chromate coatings on zinc
is indicated by colour, progression from clear/blue
to yellow, gold, olive drab and black.
 Darker coating provides more corrosion resistance.

17. 1. CRONAK Process for Zn-cd consists of 5-10 seconds
of immersion in room-temp solution of 182 g/l
sodium dichromate crystals(Na2Cr2O7.2H2O) and
6ml/l con.sulfuric acid.
2. Iridite 14-2, a chromate conversion coating for
aluminium, contains chromium(iv) oxide, barium
nitrate, sodium silicofluoride and ferricyanide.
3. Chromate coatings are soft and gelatinous when first
applied, but harden and become hydrophobic as the
age. Curing can be accelerated by heating up to 70°C,
but higher temperatures will gradually damage the
coating.

18.  Corrosion Inhibitor.
 Primer.
 Decorative Finish.
 Retain electrical conductivity.
 Coating Hardware tools….

19. FINISHED PRODUCT OF CHROMATING-

20. ZINC PHOSPHATING PROCESS-