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SILENCER PAINTING
By,
Jojo.G.DCruz
Roll no. :21
S7 Mech
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SILENCERS
Silencers are provided in automobiles tocondition and remove exhaust gases.
Silencer or muffler is a device to absorb anddamp out high pressure surges of gasesintroduced into the exhaust of an engine, whenexhaust valves open, to a smooth, quiet flow
which will emerge into the outer atmospherewithout undue noise.
It helps in improving the engine performance
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Parts of a Silencer
A silencer is a combination oftuning chambers, bafflepartitions and perforated andsolid tubes designed to createreflected waves that interferewith each other or cancel eachother out and thus dissipatenoise pulses while movingexhaust gases and vapor from
all the cylinders and therebypreventing an undesirable roar.
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CAUSES OF SILENCER FAILURE
When the engine runs, the transmitted hot air has a temp 100C to400C in various zones. The function of the silencer works betterunder the hot condition as there is hardly any accumulation andcondensation of flue gases. However, after the engine stops and the
silencer cools to normal ambient temperature there is condensationof the residual fumes and this initiates the corrosion on the internalsurface of the silencer. The water vapor (H2O) and oxides of sulphurSO/SO2 from the flue gasses react forming low concentratedsulphuric acid (H2SO4) which is highly corrosive and attacks thewelded areas first. This weakens the welding strength and affect the
steel material causing the pit marks, which leads to formation ofholes or clear apertures. . At the same time the initial corrosionaccelerate further due to more attacks during the heating andcooling cycles of the condensation of the acid fumes.Moisture canalso come from the outside in the form of rain.
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Need Of Internal Painting For The Silencers
When the vehicle is not running the acid droplets formed by the chemicalreaction of the exhaust gases, starts condensing or accumulating on theinner side of the silencer. So the metal surface of the silencer starts rustingin the absence of any protective layer. This weakens the welds and causes
pits and holes and ultimately the baffle breaks away indicating completesilencer failure. The protective layer of paint will prevent this due to its anticorrosion properties.
Noise muffling capacity of the silencer is reduced by corrosion because itcauses prominent holes and pits in the welded areas which causes theleakage of sound wave without destructive interference. Sometimes theweld becomes so weak that the baffles and pipes inside the silencers
become loose and starts vibrating under the impact of gases. This causesunpleasant noise and failure of silencer.
Owing to corrosion in the silencer, the perforations of pipes inside it may getchocked and prevent smooth passage of gases which will increase backpressure on the engine reducing its efficiency.
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CHALLANGES IN PROPER INTERNAL
PAINTING PROCESS
Improper De-greasing and surface cleaning
Air entrapment
Protection of Catalytic Converter (CAT)
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Requirements of the Heat Resistant Paint to be Utilized forPainting:
Good etching properties. (So that paint adheresto surface quickly and firmly.)
Resistant to acid attacks. Sufficient resistance to alkali attacks.
Good heat resistance to avoid being affected byhot flue gases and to prevent the peel off effect.
Uniform film coating.
Better penetration of gaps and crevices.
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DIFFERENT METHODS OF PAINT
APPLICATION
Spray painting
Electro less Plating (EN)
Dipping Flow Coating
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DESIGN MODIFICATION IN SILENCERS TO ACHIEVE
SATISFAC TORY INTERNAL PAINT COATING
1. In a silencer, after assembly,only tail pipe is available for paint fillingand there is no air vent if CAT ismasked. To achieve this, amodification is done in silencer in the
form of a drilled hole on the coverplate near inlet pipe. It serves thepurpose as an air vent as well as helpsin proper circulation of air to removesolvent fumes while baking. This holecan also be used for sending incompressed air for fast draining of
paint instead of using gravity. Afterpainting has been done this can beclosed by nut with asbestos washer orby welding. The diameter of vent holeif required can be reduced
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2. During trials it has been
found that paint accumulates over
the baffles causing non uniformity
in paint coating. This problem is
solved by making two small
diametrically opposite openings
near the edge of the baffles as
shown in figure. Also a slope may
be provided around the openings
to ease the passage of paint. Thismay affect the silencer
performance but this is yet o be
proved experimentally.
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3. To ensure proper
attachment of paint filling
nozzle to the tail pipe, a
cone shaped structure maywelded to it as shown.
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CONSTRUCTION OF SPM
1. Upper paint tank
2. Collection tank
3. Pump
4. Agitator
5. Over flow Pipe
6. Distribution Pipe
7. Painting Nozzle8. Silencer holding fixture
9. Drain off channel
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PROCESS FLOW DIAGRAM OF
SILENCER PAINTING
FULLY ASSEMBLED
SILENCER
AIR DRYING
DEGREASING
SHOT BLASTING OF
EXTERNAL SURFACE
SPRAY PAINTING OF
EXTERNAL PARTS
CLOSING OF INLET AND
TAIL PIPE OF SILENCER
WATER RINSE
COMPLETE DRY OFF
WATER RINSE
MASKING OF CATALYTIC
CONVERTER
INTERNAL PAINTING
OF SILENCER
BAKING
ACID CLEANING
Chromic acid or phosphoric-
chromic acid rinse
PHOSPHATING
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DRYING OF PAINT
1. Baking
2. Hot air ovens
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FUTURE SCOPE FOR THIS
CONCEPT
The concept of internal painting of silencers has just seen the lightdevelopment. Earlier this field was not even in the agenda of automobile makers.Development of efficient methods of painting internal parts and reduction indraining period is going on. Simultaneously the development of low cost heatresistant paint is being done for better flow and setting characteristics. Besides this,modification in design of silencers is tried out to suit internal painting withoutsacrificing its basic function.
In the current scenario, the SPM developed for this concept has limitedpainting capability as well as specific to a particular silencer design. Efforts aregoing on to make fully automated SPM with higher painting rate as well asadaptable to various silencer designs.
As the benefits of this concept are proven by experimental results, it gainsground in the fact of providing better silencer functioning and customer satisfaction.The success of initial experiments have developed confidence in minds of Autoindustry giants who are enthusiastic in further development in this field toincorporate this concept in their regular production schedule. Bajaj Auto Ltd. Hasadopted this concept for it new models like Pulsar and Caliber 115.
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THANK YOU
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