The document summarizes the key steps in the painting process of a car body: 1. The process begins with pre-treatment which includes degreasing, activating, and phosphating the body to prepare the metal surface for painting. 2. Primer is then applied through both manual and robotic spraying to protect and promote adhesion of subsequent paint layers. 3. The primer is baked and sealed before applying the top coat paint through base coating and clear coating. 4. The painted body undergoes a final baking before cavities are sealed to complete the painting process.

1. UNIT-1: CAR BODY DETAILS
PAINTING PROCESS OF A PASSENGER
CAR BODY

2. Why Painting Is Required in Car

3. Painting Process
• The painting of a car body means protection of sheet
metal, inside and out, underneath as well as on top
besides giving them a coat of bright shiny colour.
• The first stage is a multi-part rust-proofing treatment
by complete immersion of the body shell in a huge
bath of anti-rust alkyd primer.
• This is followed by surface priming. The entire under
body, wheel arches, insides of the body sills, etc. are
treated with multi-coats of epoxy primer followed by
baking in huge high- temperature ovens.

4. PROCESS CHAIN IN A TYPICAL
AUTOMOTIVE PAINT SHOP

5. PRETREATMENT
• Pretreatment consists of the steps of
– Precleaning
– Degreasing
– Activation
– Phosphating

6. Degreasing
• Degreasing solubilizes grease, for example, deep-
drawing greases, oil, wax, and other contaminations
acquired from the earlier working processes.
• The task of degreasing is to remove all kind of
contaminations from the metal surface, to achieve a
water-break free surface, that is, a continuous water
film on the surface after rinsing off excessive
degreasing chemicals with water and to obtain a
reactive surface which is able to buildup the phosphate
coating that is, the conversion layer, within a
reasonable period of time.

7. Degreasing
• This process removes oil; metal and grease
from car body by immersing the entire car
body in a degreasing solution which is a basic
solution of NaOH at a temperature of about 55
to 60’C

9. RINSING
• Here soft water is sprayed to remove
degreasing material (NaOH) from car body.

10. ACTIVATION
• Activation increases the number of crystallization nuclei on
the metal surface. This results in an increased number of
phosphate crystals per unit surface area and a reduced
coating weight for the applied conversion layer.
• As the surface will be uniformly covered with crystals in a
shorter time, activation treatment also has an accelerating
effect in the phosphate process.
• For activation prior to zinc phosphating, aqueous
dispersions of titanium orthophosphates with a pH
between 7 and 11 are typically used
• This process is used to activate car body by freeing all ions
from it before Phosphating

11. SPRAY RINSE ACTIVATION

12. PHOSPATING
• Phosphating following after a purging process,
serves as a temporary corrosion protection,
and improves the adhesiveness of the paint
film when it is applied.
• Phosphating process takes place for rust
prevention and uniform paint concentration

13. ELECTROCOATING
• Electrocoat paints are water soluble (suspensions
of binders and pigments in d.i.(deionized) water)
with only low proportions of organic solvents
(approximately 3%).
• Electrocoating covers all dip painting processes,
where the paint precipitates on the workpiece
owing to chemical conversion and associated
coagulation of the binder.
• These conversions are caused by an electric
current flow from an external electrode via the
conductive paint, to the workpiece.

14. ADVANTAGES & DISADVANTAGES
OF ELECTROCOATING
Advantages:
• complete and uniform coating, also in cavities;
• very good corrosion protection;
• no formation of drops and runners;
• very low paint losses with the corresponding purging techniques;
• very good possibilities of process and quality control;
• electrocoat installations are fully automatic, and are continuously
operated.
Disadvantages
• high installation-specific expenditure with correspondingly high
investment cost;
• relatively high material cost;
• considerable expenditure for the monitoring of the paint bath.

15. BAKING
• After the Electro-Coating process the car is baked in oven to
make the coating bond strongly with the car body
• Oven has five zones: Radiation (190°C), Convection 1 (172°C),
Convection 2, Convection 3 and forced Cooling (60°C)

16. DESIGN OF OVEN AIR

17. Sealing and Undercoating
• The overlapping, spot-welded metal sheets must be
sealed in such a way that no humidity can penetrate
between the metal sheets and water in the vehicle
interior, which may lead to corrosion there.
• On the weld seams, high viscous polyvinylchloride
(PVC) material is mostly sprayed as paths with airless
application or extruded by flat stream nozzles.
• The underbody protection also serves as protection
from corrosion, mostly for areas exposed to a high
strain because of stone chips. It is applied partially two-
dimensionally, for instance, in wheel arches and in the
rocker panel area

18. Application of Under Body
Protection Material

19. PRIMER APPLICATION
• Before applying the final paint,
primer is applied so that the top
coat can adhere strongly
• Initially solvent wiping and tag
rack wiping is done manually so
as to remove all accumulated dirt
prior to paint application
• The inner parts of the car body
undergo primer application
manually using electro static
spray gun
• The outer parts of the car body
are applied with primer by the
help of three robots.
• The last stage is flash off where
the primer is dried and finally
sent to primer oven for baking

20. TOP COAT APPLIACTION
• Top coat is the final colour
that has to be applied on
the car body.
• It consist of two process
Base coat and Clear coat
• Clear coat is basically
varnish is used to give a
shining effect on the body
• The last stage is flash off
where the paint is dried and
then sent to top coat oven
• In case of two coat models
the process is repeated
twice

21. Cavity Preservation

22. Cavity Preservation
• The corrosion protecting measures are
finalized with the sealing of the cavities with
wax materials. For this, two procedures are
usually followed – spraying and flooding.
• For spraying, special nozzles are inserted in
the cavities, and an exactly measured quantity
of material is sprayed inside each cavity.
• For flooding, the cavities are filled with
flooding wax, under pressure.