Paint application techniques

SEMINAR
ON
PAINT APPLICATION TECHNIQUES
PRESENTED BY-
 MR. MAYUR MANIK KHANDAIT
 B.TECH. VIITH SEMESTER C.T.
 SURFACE COATING TECHNOLOGY
 LAXMINARAYAN INSTITUTE OF
TECHNOLOGY , NAGPUR

Sr. No. Contents
1 Brush application
2 Roller Coating
3 Spray Painting
4 Flow Coating
5 References

Brush Application
The brushes are available in various sizes:
1) 1 to 2 inches- for small spaces, tight trim
areas, touch-ups and detail work
2) 2.5 to 3 inches- for any trim and corner work
3) 4 to 5 inches- for larger areas likes walls or
side panelling

Types of brushes used
1. Foam Brush
2. Wall Brush
3. Radiator Brush
4. Stain Brush
5. Trim Brush
6. Varnish and enamel brush

1)Pick up of paint on brush is controlled by paint viscosity at low shear
rate, shear rate of dipping & removing brush from paint
2)If viscosity is too high too much paint is brought out with brush
3)Ease of brushing requires low viscosity
4)Fim thickness is affected by viscosity at high shear rate
5)Brush marks results from splitting the wet film between the brush &
substrate as the paint is applied
6)Film thickness increases with increase in viscosity
Properties

1. The operator is in complete control of its movements and
quantity of paint being applied
2. It is the best method for painting large complex objects under
outside conditions or in large paint shops
3. It can be used where not practicable to build spray-booth
equipment around the object
4. Wastage of paint is relatively low
5. Contamination of other equipment in the vicinity is negligible
Advantages

1. It is relatively slow operation.
2. Costly in labour.
3. It is more lengthy procedure training a brush hand
than an operator for many of the other alternative
methods of paint application.
Disadvantages:

ROLLER COATING
1. Roller coating machines are used to apply
coating one or both sides of flat materials such as
tin plates, strip metals, wood boards & fiber
boards
2. Roller coaters are also used to coat collapsible
metal tubes & to apply wood graining & or flat
metal surfaces

1. Roller coaters are available in 21 standards sizes roll length
ranging from 8-122 inches
2. Applicator rolls have outside dia. From 5 to 11 inches depending
on the length of rolls
3. Coating material is contained in the angular spaces between
doctor & applicator roll
4. Coating speed depends on the type of coating, speed of conveyor
and other factors
5. Thickness of coating is determined by clearance between doctor
and applicator rolls
SPECIFICATIONS

1. Doctor rolls are steel tubes ground to near-perfect
surface then Chromium coated & polished
2. Hard rubber rolls also may be used as doctor rolls
3. Applicator rolls covered with solvent resistant type of
synthetic rubber but for special cases they may be of
composition of Glue & Glycerine
MATERIALS

1. Smooth, even, dust and ―fat edge free films can be
produced
2. Films dry relatively quickly
3. No excessive solvent or paint losses due to evaporation
occur
4. There is no fire hazard
Advantages of Roller Coating

Disadvantages of Roller Coating
1)Limited to thin sheet stock
2)Not able to apply the variety of finishes
used in spray coating

SPRAY APPLICATION OF PAINT
Basic principle
To atomize the paint into a fine spray & to
direct the spray onto the object to be coated

1. Compressed air spraying
2. Electrostatic spraying
3. Hot spraying
4. Two component spraying
5. Airless spraying
6. Aerosol spraying
TYPES OF SPRAY PAINTING

COMPRESSED AIR SPRAYING
Type of material feed
a) Suction Feed
b) Gravity Feed
c) Pressure Feed
Classification of air spray guns
Type of air cap used
a) External mix
b) Internal mix
Air valve used
a) Bleeder spray gun
b) Non-bleeder spray gun

Bleeder type
1. The spray gun designed without air valves
2. Air is continuously passing through the gun & therefore no
pressure build-up in the lines
3. The trigger controls only the flow of paint.

Non-bleeder type
1. Gun fitted with an air valve which shuts off the air supply
when the trigger is released
2. The trigger controls both the air and the paint supply
3. Gun is used in all the cases where the compressed air
supply can be regulated.

1.Gun position
2.Gun distance
3.Gun speed
SPRAYING TECHNIQUE

Gun position (Tilting)
1) Gun speed

Specifications
1) Air pressure at gun ranges from 30-70 psi & from 10-35 psi on
pressure tank
2) Sufficient volume of compressed air to be available is essential
3) Clear finish is atomized more readily than a heavily pigmented
finish
4) Adjustment can made in spraying pressure & consistency of finish
5) Usual spraying consistency is 25-35 sec

ELECTROSTATIC SPRAY
Types of Electrostatic Systems
Automatic Electrostatic System
Manual Electrostatic system

Several types of sprayers or atomizers are available but 2 which
are most widely used are bell & disc shaped
Paint is supplied to the atomizer through a hollow drive shaft &
rotation of atomizers carries the paint uniformly
As paint leaves the sprayer it is atomized by the electrostatic field
& paint particles are bought to the object being sprayed by the
attraction of field
Process

HOT SPRAY APPLICATION
1) It works on fact that viscosity of viscous
liquids is reduced when temp. is increased
2) Normally sprayed at 60-70 deg. Celsius
3) All units equipped with thermostats to
prevent overheating

Advantages
1) Reducing the viscosity & increasing the solid content at application viscosity
2) Higher application temperature improves leveling and reduces orange peels
3) It permits application of same film thickness with fewer coats thus saving
material and manpower also application conditions more uniform
4) Due to elevated temperature of the fluid less energy is required for the
atomization and consequently less compressed air is required
5) Contains less solvent, also much of this solvent evaporates during its passage
to the article
6) More solid material is applied with each pass of the gun & less amount of
expensive solvent is wasted

TWO-COMPONENT SPRAYING
1. Designed to mix two components after they have left the
spray gun & before they reach the surface to be coated
2. One component, usually the base coating material enters
gun near nozzle & expelled through fluid tip
3. Other component, usually the catalyst is admitted into the
atomizing air stream
4. Ratio of base material is controlled uniform by multiple
regulators and flow meter

Advantages
1. Compressed air is not used, therefore there is little or no overspray
2. Gun is designed to be self cleaning which eliminate problem of
having highly reactive materials remain in the gun
3. Two components pumped through separate hoses to spray gun
4. They are premixed in the gun before they are automized by the
pressure which hs been developed
5. Pressure ranges from 100-500 psi
6. Temperature can be controlled from R.T. to 120 deg. Celcius

AEROSOL APPLICATIONS
1. Coating materials packaged in pressurized containers are
referred to as aerosols.
2. In most of the cases pressure is provided by fluorocarbon such as
trichlorofluromethane and diclorodifluromethane (This are gases
at Natural Temperature & Pressure but can be liquefied)
3. This liquefied gases are used in container to provide pressure for
propelling and atomizing the coating.
4. When mixture of paint and propellent is released from container
rapid vaporization of propellent atomizes the paint.

1. Only advantage of aerosol paints is their convenience
2. Principal disadvantage is their high cost
3. Paint can be applied simply “Pushing the button”
4. There are no brushes or other equipment to clean after
application
5. In most cases, equal part of propellent & paint in the container
so that the coverage is much less than that would be expected
from the size of the container
6. Useful for touch-up coatings on wood or metal goods damaged
in handling

FLOW COATING
1. It is useful for open work objects such as metal furniture,
bicycle frames
2. Coating material may be flowed over the objects & excess
caught in container and recycled
3. Automatic flow coating is done in the tunnel
4. To facilitate cleaning of equipment, a strippable coating may
be applied to the inner walls of the tunnel

1. Simple equipment
2. Little labour required
3. Easily automated
4. Dead air spaces can be coated if a stream of paint can be directed
upward into the recess
5. Smaller volumes of paint are required, because the parts need not be
immersed
6. Little paint is wasted if the parts are allowed to drain over the tank
7. When variety of colours must be applied flow coating is to be
preferred to dipping
Advantages of Flow Coating

1. High solvent loss by evaporation. Solvent must be replenished on a regular basis.
2. Possible settling of the paint in the circulation systems.
3. Fire and toxicity hazards associated with the high solvent loss.
4. Inability to coat certain recesses and inside surfaces.
5. Gradual paint contamination if the paint rinses dirt, salts, oils, and so forth from the parts.
6. Film thickness control is a problem. Paint may become trapped in recesses and drain slowly or
not at all. On vertical surfaces, wedging may occur resulting in fatty edges.
7. The drain-off area must be cleaned regularly. Since this is usually done manually, some dried
paint may fall into the circulation system and clog the filters, pumps, and nozzles.
Limitations of Flow Coating

References
1. Payne, H. F. Organic Coating Technology. New York : John
Wiley & Sons, 1954, Vol. 2, 24, pp. 1036-1052.
2. Talbert, Rodger. Paint Technology Handbook. Boca Raton : CRC
Press Taylor & Francis Group, 2007, 6,7, pp. 107-130, 143-150.
3. Krishnan, Dr. S. M. What Is A Paint? Karaikudi : Auro
Consultancy Services, 2012, pp. 114-152.

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