SILENCER PAINTING By, Jojo.G.D’Cruz Roll no. :21 S7 Mech

SILENCERS Silencers are provided in automobiles to condition and remove exhaust gases. Silencer or muffler is a device to absorb and damp out high pressure surges of gases introduced into the exhaust of an engine, when exhaust valves open, to a smooth, quiet flow which will emerge into the outer atmosphere without undue noise. It helps in improving the engine performance

Parts of a Silencer A silencer is a combination of tuning chambers, baffle partitions and perforated and solid tubes designed to create reflected waves that interfere with each other or cancel each other out and thus dissipate noise pulses while moving exhaust gases and vapor from all the cylinders and thereby preventing an undesirable roar.

CAUSES OF SILENCER FAILURE When the engine runs, the transmitted hot air has a temp 100°C to 400°C in various zones. The function of the silencer works better under the hot condition as there is hardly any accumulation and condensation of flue gases. However, after the engine stops and the silencer cools to normal ambient temperature there is condensation of the residual fumes and this initiates the corrosion on the internal surface of the silencer. The water vapor (H 2 O) and oxides of sulphur SO/SO 2 from the flue gasses react forming low concentrated sulphuric acid (H 2 SO 4 ) which is highly corrosive and attacks the welded areas first. This weakens the welding strength and affect the steel material causing the pit marks, which leads to formation of holes or clear apertures.. At the same time the initial corrosion accelerate further due to more attacks during the heating and cooling cycles of the condensation of the acid fumes. Moisture can also come from the outside in the form of rain.

Need Of Internal Painting For The Silencers When the vehicle is not running the acid droplets formed by the chemical reaction of the exhaust gases, starts condensing or accumulating on the inner side of the silencer. So the metal surface of the silencer starts rusting in the absence of any protective layer. This weakens the welds and causes pits and holes and ultimately the baffle breaks away indicating complete silencer failure. The protective layer of paint will prevent this due to its anti corrosion properties. Noise muffling capacity of the silencer is reduced by corrosion because it causes prominent holes and pits in the welded areas which causes the leakage of sound wave without destructive interference. Sometimes the weld becomes so weak that the baffles and pipes inside the silencers become loose and starts vibrating under the impact of gases. This causes unpleasant noise and failure of silencer. Owing to corrosion in the silencer, the perforations of pipes inside it may get chocked and prevent smooth passage of gases which will increase back pressure on the engine reducing its efficiency.

CHALLANGES IN PROPER INTERNAL PAINTING PROCESS Improper De-greasing and surface cleaning Air entrapment Protection of Catalytic Converter (CAT)

Requirements of the Heat Resistant Paint to be Utilized for Painting: Good etching properties. (So that paint adheres to surface quickly and firmly.) Resistant to acid attacks. Sufficient resistance to alkali attacks. Good heat resistance to avoid being affected by hot flue gases and to prevent the peel off effect. Uniform film coating. Better penetration of gaps and crevices.

Pretreatment Of Internal Surface Before Applying Paint Degreasing and Cleaning Acid Cleaning Phosphate Coating

DIFFERENT METHODS OF PAINT APPLICATION Spray painting Electro less Plating (EN) Dipping Flow Coating

DESIGN MODIFICATION IN SILENCERS TO ACHIEVE SATISFAC TORY INTERNAL PAINT COATING 1. In a silencer, after assembly, only tail pipe is available for paint filling and there is no air vent if CAT is masked. To achieve this, a modification is done in silencer in the form of a drilled hole on the cover plate near inlet pipe. It serves the purpose as an air vent as well as helps in proper circulation of air to remove solvent fumes while baking. This hole can also be used for sending in compressed air for fast draining of paint instead of using gravity. After painting has been done this can be closed by nut with asbestos washer or by welding. The diameter of vent hole if required can be reduced

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. This may affect the silencer performance but this is yet o be proved experimentally.

3. To ensure proper attachment of paint filling nozzle to the tail pipe, a cone shaped structure may welded to it as shown.

CONSTRUCTION OF SPM 1. Upper paint tank 2. Collection tank 3. Pump 4. Agitator 5. Over flow Pipe 6. Distribution Pipe 7. Painting Nozzle 8. Silencer holding fixture 9. Drain off channel

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

DRYING OF PAINT 1. Baking 2. Hot air ovens

FUTURE SCOPE FOR THIS CONCEPT The concept of internal painting of silencers has just seen the light development. Earlier this field was not even in the agenda of automobile makers. Development of efficient methods of painting internal parts and reduction in draining period is going on. Simultaneously the development of low cost heat resistant paint is being done for better flow and setting characteristics. Besides this, modification in design of silencers is tried out to suit internal painting without sacrificing its basic function. In the current scenario, the SPM developed for this concept has limited painting capability as well as specific to a particular silencer design. Efforts are going on to make fully automated SPM with higher painting rate as well as adaptable to various silencer designs. As the benefits of this concept are proven by experimental results, it gains ground in the fact of providing better silencer functioning and customer satisfaction. The success of initial experiments have developed confidence in minds of Auto industry giants who are enthusiastic in further development in this field to incorporate this concept in their regular production schedule. Bajaj Auto Ltd. Has adopted this concept for it new models like Pulsar and Caliber 115.

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