M. Burak Toprakoğlu - 030070082 - 9th week

Catalytic Converter: (01:12 - 10.04.2011)

A catalytic converter (Figure) is part of the exhaust system and is a very important part of the emission control system. Because the converter is part of both systems, it has a role in both. As an emission control device, it is responsible for converting undesirable exhaust gases into harmless gases. As part of the exhaust system, it helps reduce the noise level of the exhaust. A catalytic converter contains a ceramic element coated with a catalytic. A catalytic is a substance that causes a chemical reaction in other elements without actually becoming part of the chemical change and without being used up or consumed in the process.

Catalytic converters may be pellet type of monolithic type. A pellet-type concerter contains a bed made from hundreds of small beads. Exhaust gases pass over this bed. On a monolithic-type converter, the exhaust gases pass through a honeycomb ceramic block. The concerter beads or ceramic block are coated with a thin coating of cerium, platinum, palladium, and/or rhodium and are held in a stainless-stell container. Modern vehicles are equipped with three-way catalytic converters which means the converter reduces the three major exhaust emissions: hydrocarbons (HC), carbon monoxide (CO), and oxides of nitrogen (NO_x). The converter oxidizes HC and CO into water vapor and carbon dioxide (CO₂), and reduces NO_x to oxygen ad nitrogen.

(TechOne: Basic automotive service and maintenance, D. Knowles, J. Erjavec, p.162)

Porosity Sealing: (22:36 - 07.04.2011)

Most castings and powdered metal parts have porosity, inherent in the powder metal compacting and sintering process and caused by volatilization of organic impurities in castings. With castings such as iron or aluminum, this porosity allows fluid leakage and with powdered metal parts, can cause severe plating problems. Pores can be quite large, designated as macroporosity, or very small, called microporosity. Sealing of the pores is a routine necessity and is carried out by impregnation with a liquid sealant followed by a curing step. The modern way of sealing this porosity is to use anaerobic impregnants. They are low viscosity impregnants and have revolutionized porosity sealing because of their ability to penetrate microporosity and cure very quickly at room temperature.

(Manufacturing Engineering Handbook, H. Geng, p. 50.10 - 50.11)

Oxyacetylene Welding: (23:38 - 07.04.2011)

Oxyacetylene Welding (OAW) is a fusion-welding process performed by a high-temperature flame from combustion af acetylene and oxygen. The flame is directed by a welding torch. A filler metal is sometimes added, and pressure is occasionally applied in OAW between the contacting part surfaces. A typical OAW operation is sketched in figure. When filler metal is used, it is typically in the form of a rod with diameters ranging from 1.6 t0 9.5 mm (1/16 - 3/8 in). Composition of the fiiler must be similar to that of the base metals. The filler is often coated with a flux that helps to clean the surfaces and prevent oxidation, thus creating a better weld joint.

Acetylene (C₂H₂) is the most popular fuel among the oxyfuel gas welding (OFW) group because it is capable of higher temperatures than any of the others – up to 3480 ^oC (6300 ^oF). The flame in OAW is produced by the chemical reaction of acetylene and oxygen in two stages

C₂H₂ + O₂ → 2CO + H₂ + heat

The products of which are both combustible, which leads to the second-stage reaction

2CO + H₂ +1.5O₂ → 2CO₂ + H₂O + heat

The two stages of combustion are visible in the oxyacetylene flame emitted from the torch.

(Fundamentals of Modern Manufacturing: Materials, Processes, and Systems, Mikell P. Groover, p. 723)

Flexible Overlay Process: (00:15 - 08.04.2011)

The flexible overlay process is capable of depositing a very hard coating material, such as tungsten carbide (WC), onto a substrate surface. This is an important advantage of the process compared to other methods, permitting coating hardness up to about 70 Rockwell C. The process can also be used to apply coatings only to selected regions of a workpart. In the flexible overlay process, a cloth impregnated with hard ceramic or metal powders and another cloth impregnated with brazing alloy are laid onto a substrate and heated to fuse the powders to the surface. Thickness of overlay coatings is usually 0.25 - 2.5 mm (0.010 – 0.100 in). In addition to coatings of WC and WC – Co, cobalt-based and nickel-based alloys are also applied. Applications include chain saw teeth, rock drill bits, oil drill collarsi extrusion dies, and similar parts requiring good wear resistance.

(Fundamentals of Modern Manufacturing: Materials, Processes, and Systems, Mikell P. Groover, p. 685)