Silencer Painting

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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