WELDING FLAMES

Neutral Flame:
-A neutral flame is produced when approximately equal volume of oxygen and acetylene are mixed in the welding torch and burnt at the torch tip.
-The temperature of the neutral is of the order of about 3260 degree Celsius.
-The flame has a nicely defined inner core which is light blue in color. It is surrounded by an outer flame envelop produced by the combination of oxygen in the air and superheated carbon monoxide and hydrogen gases from the inner cone.This envelop is usually a much darker blue than the inner cone.
-A neutral flame is named so because it effects no chemical change in the molten metal and therefore will not oxidize or carburize the metal.
-The neutral flame is commonly used for the welding at:
1) mild steel
2) stainless steel
3) Cast steel
4) Copper
5) Aluminum
Oxidizing Flame:
-If after the neutral flame has been established the Oxygen supply is increased to produce Oxidizing flame.
-Oxidizing flame can be observed by the small white cone which is shorter,more bluer and more pointed than the neutral flame.
-An oxidizing flame burns making a roaring sound.and is much hotter than the neutral flame due to excess of oxygen supply causing the temperature to rise up to 6800 degree  Celsius
-A slightly Oxidizing flame.is helping welding most metals like  (1) Copper-base metal  (2) Zinc-base metals
(3) A few types of ferrous metals such as manganese steel and cast iron.
-The Oxidizing atmosphere in these cases creates a base metal oxide that protects the base metal.
Reducing Flame:
If the volume of Oxygen supplied in the metal flame is reduced the reducing flame will be a carburising flame
rich in acatylene.
-A reducing flame can be observed by acetylene feather which exists between the inner cone and the outer envelope.The outer flame envelope is longer than neutral flame an is usually much brighter in color
-A reducing flame does not completely consumes the available Carbon, therefore the burning temperature is
lower and the left over carbon is forced into the molten metal. With iron and steel it produces very hard  and brittle substance known as iron carbide.This chemical change makes the metal unsuitable for many applications in which the weld may need to be bent or stretched. Metal that tend to absorb Carbon should not be welded with reducing flame.
-A reducing flame has an approximate temperature of 5500 degree Fahrenheit.A reducing flame may be distinguished from a carburizing flame in the fact that a carburizing  flame contains more acetylene than a reducing flame.
-A carburizing flame is used in the welding of lead  and for surface hardening process.
-A reducing flame on the other hand does not carburize the metal rather it ensures the absence of oxidizing condition. It is used for welding of low alloy steel and for those metals ( e.g non-ferrous) that do not tend to absorb carbon. This flame is very well used for welding high carbon steels.      
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TYPES OF WELDING FLAMES

To Ignite a Flame
Open the acetylene control valve of the welding torch and after the system has been flushed to clean the torch nozzle the gas is ignited. At this stage enough oxygen is drawn in from the atmosphere to burn acetylene partially.
The acetylene control valve is then adjusted until the flame ceases to smoke. The oxygen control valve of the welding torch is then opened in order to adjust the proportion in which acetylene and oxygen are required to mix and burn.
Types of Flame:

                                                                     fig-1

                                                                         fig-2

1-Neutral flame (Acetylene Oxygen in equal proportions)
2-Oxidising flame (Excess of Oxygen)
3-Reducing flame (Excess of Acetylene)

In oxy-acetylene welding flame is the most important tool.All the welding equipment simply serves to maintain and control the flame.The correct type of flame is essential for the production of satisfactory welds.
The flame must be of proper size,shape and condition in order to operate with maximum efficiency. 

GAS WELDING PROCESS AND EQUIPMENTS

Gas welding is a fusion welding processes which joins metals using the heat oh combustion of an oxygen/air and fuel gas (i e. acetylene,hydrogen,propane or butane ) mixture. The intense heat (flame) thus produced melts and fuses together the edges of the parts to be welded, generally wit the addition of filler metal.

OXY-ACETYLENE WELDING

When acetylene is mixed with oxygen wit appropriate proportion in the welding torch and ignited, the flame resulting at the tip of the torch is sufficiently hot to melt and join the parent metal.
The oxy-acetylene flame reaches a temperature of about 3200 degree Celsius and thus can melt all commercial metals during welding,actually flow together to form a complete bond. A filler metal rod is generally added to the molten metal pool to build up the seam slightly for greater strength.
Oxy-Acetylene welding does not require the components to be forced together under pressure until the weld forms and solidifies.