Painting

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27-03-2014

Painting

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PRE – TREATMENT PROCESS






PRE – TREATMENT PROCESS
ELECTRO - COAT PROCESS
SEALER PROCESS
SPRAY BOOTH PROCESS
WAX OPERATIONS






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Before the Pre-treatment Process , all bodies are fitted
with specially designed load bars to enable the body to
get loaded in Overhead conveyor and Slave tools
which avoids contact damage of panels during the
Paint process and enables operators to open and
close panels.
Pre-treatment provides the basis of corrosion and
adhesion of Primer coat.
It is a 11 stage automatic immersion – dip/spray
process, gives full protection to all box sections.

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VARIOUS STAGES IN PRE-TREATMENT PROCESS :


Stage 6 : Phosphate dip where the car body is coated with a layer
of Zinc phosphate at 49°C bath temperature for 3 min.
Phosphate coating prepares the basis for corrosion
protection and better adhesion for Electro coat.



Stage 7 : Dip rinse – 2 cleans the excess phosphate solution using
fresh DI water.
Stage 8 :Spray rinse further cleans the car body using DI water recycled
from Stage 10.
Stage 9 : Passivation rinse uses a chrome free Passivation chemical for
filling the gaps between the phosphate crystals and provides a
smooth , uniform phosphate coating finish.
Stage 10 : DI water dip cleans the car body after passivation.

Stage 1 : Pre wash spray rinse in which a chemical (surface active agent surfactant) is
used to loosen oil and wash of contaminants on the body in white .
Cleaner spray rinse – 1 where Pressurized hot water (45°C) spray loosens the
oil left over in the Pre wash stage and pre-heat the car
body for further processes .
Stage 2 : Cleaner spray – 2 containing a Pressurized hot solution(52°C) of Factory water
and Degreasing chemical further cleans the car body .




Stage 3 : Cleaner dip containing a hot solution (50°C) of Factory water and Degreasing



chemical cleans all the interior portions and box sections of the car body
thoroughly.


Stage 4 : Dip rinse – 1 in which factory water is used for removing the Degreasing
chemicals used in the previous two stages.



Stage 5 : Activation dip containing Gardolene ZM solution prepares the surface of the car
body for refined phosphate coating.

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Stage 11 : DI water spray rinse cleans the car finally before E-coat using
new DI water.

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ELECTRO - COAT PROCESS








Electro-coating provides comprehensive water based
paint coating by Electro deposition.
Electro-coating is a fully automatic total immersion
process for maximum coverage and performance and
allows uniform, run free coating for optimum quality.
Electro-coating provides good basis for all subsequent
processes.
Electro-coat bath contains 82% DI water , 17% EC
solids and 1% Solvent.
The process time is 4 to 5 min for a car body. Electrocoat is the first layer of paint in a car body .
The Dry Film thickness of Electro-coat thickness ranges
from 16 to 23 microns.
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In the ED-system the electrically conductive car body
is coated by applying DC-Voltage.
The product acts as cathode on which the paint is
deposited.
The residual acid migrates to the anodic cells kept
inside the sides of the tank through the ED solution
which acts as anode system.
The coated product passes through the subsequent
ultra-filtrate and DI water rinse zones, in which the
loosely adhering paint is rinsed off.

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ADVANTAGES










ELECTRO-COAT CURING

The formation of protective films in highly recessed areas such
as flanges and box sections provides critical corrosion
protection.
Use of water as practically the only carrier virtually eliminates
fire hazard, materially reduces water and air pollution, and
markedly reduces the cost of facilities for controlling these
conditions.
Unlike spray coating, electrodeposited paint will not sag during
baking.
Unlike dip coating, electrodeposited paint is not washed off in
enclosed areas by hot vapors during curing.
Freshly deposited paint is insoluble in water, permitting
complete rinsing and recovery of dragged-out material.
Since the process is automated, direct labor costs are
markedly reduced.
Transfer efficiencies of better than 95% result in reduced paint
waste, especially when compared with spray-applied coatings.





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SEALER PROCESS


The very last stage of Electro-coat process is to cure
the paint in the Electro-coat oven at a temperature of
171°C for 15 minutes.
This gives a smooth and resilient finish.

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TYPES OF SEALERS AND INSULATORS

Purpose of Sealers and Insulators:
 Sealers and insulators are used to eliminate
water, block out fumes, reduce wind and
road noise, reduce the vibration and to
improve the aesthetics on clinches.

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Thumbable Sealer
Flowable Sealer or Duplex sealer
 Plugs and tapes:
 Deadner Pads
 Roof Ditch Sealer



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Thumbable Sealer :
Thumbable sealer is a vinyl product which is very
malleable.
It is used to fill the gaps where panels are joined.
Flow able Sealer or Duplex sealer :
Duplex Sealer is used to seal hem
flanges and other similar joints. It’s made of very soft vinyl. It is
applied with a Sealer gun to seal various joints in Clinches, Car
body interiors etc. and is applied to the undersides of body using
sealer spray gun to protect them from stone chipping and water
spray.
Plugs and tapes:
Plugs and tapes are used to seal the holes which
were needed during body construction and for drainage in the
Phosphate and Electro-coat processes.

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SEALER CURING




Deadner Pads :
Deadner pads are used to stiffen panels
and therefore reduce vibration and to act as insulators
and absorb noise.
Roof Ditch Sealer :
Roof Ditch Sealer is used to seal
joints between body sides the Roof panel.
It increases the aesthetic effect of the car body.
It is applied with a Special Roof Ditch Sealer gun and
the excess sealer is taken off by using a vacuum
machine which absorbs the excess sealer.

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SPRAY BOOTH PROCESS

Once the Plugs and Pads are fitted and all the sealers
are applied, the units leave the sealer deck and pass
through the Sealer Gel Oven at 90 Deg C for 7
minutes.
This fuses the pads into place and partially hardens
the sealers so they are less prone to damage in
subsequent operations.

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All industrial products have to be protected in
some way or another against corrosion.
The most common protection against corrosion
is the application of paint materials.
The paint can be applied onto the work piece by
dipping or spraying.
The spray procedure has to take place in
specially designed paint spray enclosures (paint
spray booths).
The requirements have to be met according to
the paint systems (Solvent-borne paints, Waterborne paints, 2-components paints) which are
very different from each other.
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In order to make the object resistant to corrosion, and
to minimize the paint spread, Gloss, etc. a certain
minimum paint coat thickness is required.
This coat thickness is achieved by application in 2 or 3
steps.
For best results some basic application techniques
has to be followed as per specifications for different
paint types and colours.

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The Spray booth is designed for Primer, Basecoat and
Clear coat application on car bodies.
Processing of Topcoat paint is only allowed after prior
thorough cleaning of the spray booth.

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There are some important aspects in Spray booth to
achieve product quality:
Filtered supply and re-circulated air
Air conditions
- Temperature
- Humidity
Regular air distribution
Constant air balance
Regular downdraft velocity
No dust or dirt in spray booth
Optimum lighting
Suitable clothing for workers and visitors
No materials containing silicone shall be used
Keep doors of spray booth and clean room closed
Regular cleaning of plant equipments (Flooding
trays, Flooding plates,Floor grids, Spray guns, Booth
walls)
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DOWNDRAFT


The air supplied from the air supply units through
filters in the spray booth with a specified velocity in a
downward motion is Downdraft.



It controls paint over spray raised out of spray
painting , increases fresh air circulation inside the
spray booth and prevents accumulation of paint on the
operators and structures.

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HUMIDITY



TEMPERATURE

The amount of water content in air is humidity.
The spray booth should be maintained in a specified
humidity (71% +/- 6%) for preventing the solvent from
drying fast.






Maintaining of temperature is vital in spray booth since
the evaporation of solvent rate also depends on the
temperature.
Temperature is maintained at 27+/-3 deg C inside
spray booth.
Temperature and Humidity is measured twice a day
using a Digital Temperature Gauge.

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Primer




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Primer coat is applied between the E-coat and
Topcoat to minimize the surface roughness problems
and adhesion problems.
Types of Primer :
1. Colour compatible Primer
2. Colour matched Primer

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Basecoat

CLEAR COAT

Basecoat gives the colouring to a car body.
It is also called as color coat.
 Basecoat is applied after Primer coat and before
Clear coat.
 Types of Basecoat :
1. Solid
2. Metallic
3. Pearlescent

Clear coat is the colourless, topmost
layer of paint on a car body.
 Clear coat gives gloss effect and it also
protects the paint layer from harmful UV
rays.







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SURFACE PREPARATION




Surface Preparation is a vital function of Paint shop in
getting the units ready for both Primer and Topcoat.
All traces of contaminations such as oil, dirt etc. must
be removed since they will affect the final Paint finish.
Sanding:



Types of sanding
Scuff Sanding
Detail Sanding
 Orbital Sanding



Sanding is done for finding as well as identifying the defects.
It is necessary to sand the paint surface after application of
each layer.
Sanding can only be done after the unit has been cured in the
ovens when the paint is hardened.

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DETAIL SANDING :

SCUFF SANDING :

Scuff sanding is done on E-coat bodies for
highlighting the defects.
 All the horizontal and upper vertical surfaces
are lightly sanded in a front-to-back motion.


Defects found by scuff sanding are removed
by detail sanding.
 Light, Circular motion should be used for
removing the defects.




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ORBITAL SANDING :

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CLEANING METHODS

Orbital sanding should only be used where
absolutely necessary.
 The Orbital sander uses self-adhesive paper
discs and is powered by compressed air.
 Defects which cannot be removed / difficult
to remove by Detail sanding are removed by
Orbital sanding.




Note : Detail sanding, if done in Front-to-Back motion creates
defect called sanding patch.

Cleaning is one of the most important ways of
keeping defects to a minimum as the units
progress through the Paint shop.



It plays a vital part of the preparation for corrosion
protection, primer and topcoat.



Tack-off
Blow-off
Solvent wipe



Note : After all sanding operations , the sanded area must be
blown off and then cleaned with a Tack-off cloth or wet scotch
brite.
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TACK-OFF :


BLOW-OFF :

Tack-off takes place before the car enters
into the spray booth for Primer and Topcoat.
Tack-off is a special cloth that has a slightly
sticky surface.
When it is used to wipe the unit, it picks up
loose dirt and dust, and because it is lint-free it
doesn’t leave any contamination behind.

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Blow-off takes place after sanding operations.
It is a process for removing loose dirt or dust
with compressed air.
Automatic blowers are fixed at the exit of Primer
sanding and entry of spray booth.

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SOLVENT WIPE :
In some plants a process called solvent wipe
is carried out.
 It also takes place after the sanding.
 Solvent
wipe
is
used
to
remove
Contaminations on the unit before painting.
 A small amount of polishing compound is put
onto the sanded area and spread around with
the pad before it is started.


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The pad is used flat against the surface.
A little pressure is applied for few seconds to
remove the sanding scratches, Finally the
Polished area is wiped with a wet scotch brite.
 Defects which cannot be removed at Polish
Deck are sent to Spot repair or Major repair
according to the severity.



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Spot Repair:

WAX OPERATIONS


Spot Repair is a repair area where defects
are leveled by sanding, painted, baked and
polished.
 Major Repair:
Major Repair is a repair area where the full
body is repainted for any major paint defect.
In major repair, the car body will be fully
sanded and the topcoat layer will be
removed.
Then it is cleaned, blown off, tack-wiped and
sent for re-painting.
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Air dry Blackout:
Air dry Blackout is a cosmetic treatment that’s
applied to the rear wheel housings and certain
other areas of a body.
It’s a black colored paint that dries in
atmospheric heat.
It is usually applied after the final paint
application with an airless spray gun to control
overspray.
After the blackout the wheel arch is finally
visually checked to make sure there is no
overspray on the exterior paint surfaces.
If there is, it is removed by the approved solvent.

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CAVITY WAX:
Cavity wax, which is a paraffin wax, is applied
to add further corrosion protection.
 The wax is injected into cross members and
box sections of the ‘A’ Pillars , Rocker panel ,
Hood interiors , Deck lid interiors , Floor
panel.
 It is also sprayed into the lower parts of the
door using Wax spray gun.
 Different nozzles are used for different
applications and different models.


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The long lance model is used to reach right to
the ends of the box sections.
 With this type of nozzle, the trigger is pulled
continuously while the lance is drawn out
smoothly and evenly.
 The trigger is released just before the end of
the lance reaches the opening.
 An airless spray gun with a long, slightly bent
nozzle to reach the corners is used to spray
paint in the door interior sections.


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COATING THICKNESS MEASUREMENT
Coating thickness is an important variable that plays a
role in product quality, process control, and cost
control.
Measurement of film thickness can be done with many
different instruments.
The issues that determine what method is best for a
given coating measurement include the type of
coating, the substrate material, the thickness range of
the coating, the size and shape of the part, and the
cost of the equipment.

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Non destructive dry film methods
 magnetic,
 eddy current,
 ultrasonic, or micrometer measurement
 Destructive dry film methods
 cross-sectioning or gravimetric


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electrostatic transfer application

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