Oxy gas cutting Essay Example

of 1% will typically reduce the cutting speed by 25% and increase the gas consumption by 25%. Choice of fuel gas Fuel gas combustion occurs in two distinct zones.

In the inner cone or primary flame, the fuel gas combines with oxygen to form carbon monoxide and hydrogen which for acetylene, the reaction is given by + 20 4C0 + 2H Combustion also continues in the secondary or outer zone of the flame with oxygen 4CO+2H 4C0 Thus, fuel gases are characterized by their flame temperature - the hottest part of the flame is at the tip of the primary flame linner cone) fuel gas to oxygen ratio - the amount of fuel gas required for combustion but this will 'ary according to whether the flame is neutral, oxidizing or reducing heat of ombustion - heat of combustion is greater in the outer part of the flame rhe five most commonly used fuel gases are acetylene, propane, MAPP :methylacetylene-propadiene), propylene and natural gas.

The properties of the gases are given in the Table. The relative performance of the fuel gases in terms of pierce time, cutting speed and cut edge quality, is determined by the flame temperature and heat distribution within the inner and out flame cones.

Acetylene Acetylene produces the highest flame temperature of all the fuel gases. The maximum flame temperature for acetylene (in oxygen) is approximately 3,1600C ompared with a maximum temperature of 2,8100C with propane. The hotter flame produces more rapid piercing of the materials with the pierce time being typically one third that produced with propane. rhe higher flame speed (7. 4m/s compared with 3. m/s for propane) and the

higher calorific value of the primary flame (inner cone) (18,890kJ/m 3 compared with 10,433 kJ/m 3 for propane) produce a more intense flame at the surface of the metal reducing the width of the Heat Affected Zone (HAZ) and the degree of distortion.

Page h20cutting. doc Propane Propane produces a lower flame temperature than acetylene (the maximum flame temperature in oxygen is 2,8280C compared with 3,1600C for acetylene). It has a greater total heat of combustion than acetylene but the heat is generated mostly in the outer cone ( see Table). The characteristic appearance of the flames for acetylene and propane are shown in Figs. 2 and 3 where the propane flame appears to be less focused.

Consequently, piercing is much slower but as the burning and slag formation are effected by the oxygen Jet, cutting speeds are about the same as for cetylene. Propane has a greater stoichiometric oxygen requirement than acetylene; for the maximum flame temperature in oxygen, the ratio of the volume of oxygen to fuel gas are 1. 2 to 1 for acetylene and 4. 3 to 1 for propane. Page 4 of 6 Fig.

2. Oxyacetylene gas let and nozzle design Fig. 3. Propane gas MAP p MAPP gas is a mixture of various hydrocarbons, principally, methyl-acetylene and propadiene. It produces a relatively hot flame (2,9760C) with a high heat release in the primary flame (inner cone) (1 5,445kJ/m 3), less than for acetylene (18,890kJm ) but uch higher than for propane (10,433kJm 3 ).

The secondary flame (outer cone) also gives off a high heat release, similar to propane and natural gas. The combination of lower flame temperature, more

distributed heat source and larger gas flows compared with acetylene results in a substantially slower pierce time. Page 5 of 6 As MAPP gas can be used at a higher pressure than acetylene, it can be used for underwater cutting in deep water as it is less likely to dissociate into its components of carbon and hydrogen which are explosive. Propylene Propylene is a liquid petroleum gas (LPG) product and has a similar flame temperature to MAPP (28960C compared to 2,9760C for MAPP); it is hotter than propane, but not as hot as acetylene.