GAS WELDING[.ppt (Size: 564 KB / Downloads: 216)
It is a metal joining process in which the ends of pieces to be joined are heated at their interface by producing coalescence with one or more gas flames (such as oxygen and acetylene), with or without the use of a filler metal.
Process of heating metal surfaces to be joined to melting point with gas flame
Fusing metal into homogeneous mass
Letting it solidify into a single unit
Flame in cone reaches temperatures as high as 5800º to 6300ºF
Filler rod may or may not be used to intermix with molten pool.
Oxygen is stored within cylinders of various sizes and pressures ranging from 2000- 2640 PSI. (Pounds Per square inch)
Oxygen cylinders are forged from solid armor plate steel. No part of the cylinder may be less than 1/4” thick.
Cylinders are then tested to over 3,300 PSI using a (NDE) hydrostatic pressure test.
Acetylene is stored in cylinders specially designed for this purpose only.
Acetylene is extremely unstable in its pure form at pressure above 15 PSI (Pounds per Square Inch)
Acetone is also present within the cylinder to stabilize the acetylene.
Acetylene cylinders should always be stored in the upright position to prevent the acetone form escaping thus causing the acetylene to become unstable.
There are three distinct types of oxy-acetylene flames, usually termed:
Carburizing (or “excess acetylene”)
Oxidizing (or “excess oxygen” )
The type of flame produced depends upon the ratio of oxygen to acetylene in the gas mixture which leaves the torch tip.
The neutral flame (Fig. 4-1) is produced when the ratio of oxygen to acetylene, in the mixture leaving the torch, is almost exactly one-to-one. It’s termed ”neutral” because it will usually have no chemical effect on the metal being welded. It will not oxidize the weld metal; it will not cause an increase in the carbon content of the weld metal.
The excess acetylene flame (Fig. 4-2), as its name implies, is created when the proportion of acetylene in the mixture is higher than that required to produce the neutral flame. Used on steel, it will cause an increase in the carbon content of the weld metal.
The oxidizing flame (Fig. 4-3) results from burning a mixture which contains more oxygen than required for a neutral flame. It will oxidize or ”burn” some of the metal being welded.