Materials (cont'd) & Noise
steel used in exhaust applications. Type 409 is stronger than aluminized but exhibits cosmetic problems at exhaust system temperature. At first exposure to high temperature it discolors. Over time it develops a nondestructive coating of surface rust. After an extended time in the field a 409 product will display external discoloration and look worse than a similar part made from aluminized steel, but will last much longer. Another choice is 409 stainless steel with an aluminum coating. Aluminized 409 is used on diesel catalytic converter mufflers due to its excellent high temperature resistance and the corrosion protection of the aluminized coating. Aluminized 409 is found primarily on emission products or high temperature gasoline applications. Series 300 stainless steels are also utlized in exhaust systems. The most common material is Type 304. This material has excellent corrosion resistance and very good high temperature strength and is used in some muffler applications where very high stresses occur. This is a premium material and is also used in many for gasoline applications. The most prevalent use of the material in heavy duty diesel applications is for flex pipe. Flex pipe produced from light gauge 304 stainless steel is an excellent choice considering all the factors of cost, durability, and service life. Often chrome plated cold rolled steel parts are found on exhaust system parts. This material is a reasonable choice for cosmetic applications where a bright mirror finish is desired. Corrosion from the inside of the product can still occur. Chrome parts may be very challenging to produce. It is important to produce the parts with a high level of quality because surface irregularities are very visible to the end user. An alternate choice for chrome parts is bright annealed stainless steel. This material provides a bright mirror like finish with excellent exhaust service life. Bright stainless steel is typically used for muffler heat shields and generally an expensive material choice.
Noise Sources
Five Major Sources of Noise in Trucks
Fan Noise Air Intake 2 1
Exhaust System
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Mechanical Noise
Tires
Easy Maintenance Tips Reduce Exhaust Noise
Check the exhaust tubing. Repair or replace worn or leaking components. Make sure your exhaust system is properly supported. Installing a resonator or wye connector muffler is an economical way to reduce noise. Modify a single exhaust system to a dual. Check stack and tailpipe position. A straight stack will be quieter than a curved stack on vertical exhaust systems. Turn your horizontal tailpipes toward the center of the road.
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