Weldcare Oxy-Gas Welding

Oxy-Gas Processes

Oxy-Acetylene welding relies on the heat of a flame to melt the material being welded. Fusion can either be autogenous or with the addition of a filler material.

Safety

The high flame temperature required for oxy-fuel welding and cutting processes is obtained by combining oxygen with a fuel gas to produce flame temperatures of approximately 2500°C to 3000°C. There are certain precautions to be taken when using gases and these are described below:-

Oxygen Fig.1 OXYGEN (black, right hand thread) should be handled carefully and must not be stored in warm areas. The pressure of oxygen in cylinders when full is 2500lbs.per square inch (200 bar) at normal temperature and any rise in surrounding temperature will cause an increase in cylinder pressure above 2500lbs.Oil or grease should never be allowed to come into contact with oxygen cylinders as an inflammable mixture will be formed, which may ignite spontaneously.

Fig. 2 ACETYLENE (maroon, left hand thread) should be stored in a separate fuel compound as acetylene and air form an explosive mixture, these cylinders should also be chained when either in use or in storage. No alloy containing more than 70% copper should be used on any part of the equipment as a highly explosive compound is formed. Cylinders must always be stored upright and away from high temperatures.

Propane Fig 3. PROPANE (red, left hand thread). Storage as for acetylene, a fuel gas. Highly inflammable and can form explosive mixtures with air or oxygen (2% to 10%). With propane being heavier than air it can flow easily in still air some considerable distances therefore care must be exercised when using this gas.

Oxy-Gas Cutting

Oxygen cutting is more partial disintegration than cutting. It relies on the fact that when steel is heated in the presence of oxygen it will combine with the oxygen to form a magnetic oxide (slag).

Equipment

Fig. 1 Oxy-Flame Equipment

Regulators

Regulators for cutting must allow a higher outlet pressure than the equivalent welding regulator:-

Oxygen regulators, for cutting, should read up to 14 bar.
Acetylene regulators, for cutting, should read up to 2 bar

(14.505 psi = 1 bar)

Fig. 2 A Single Stage Regulator

Brazing

Brazing is the joining of two materials by means of another which has a melting point lower than that of either of the two parent metals. There are three types of brazing:

Soldering, where the melting temperature is less than 450°C.
Low Temperature Brazing, where the temperature of melting is between 450°C and 1000°C.
High Temperature Brazing, where the melting temperature is greater than 1000°C

The accepted method of introducing the molten filler material is to apply the brazing alloy to the outer surface of the joint and to allow it to flow in and through the joint. There are three mechanisms that promote the flow of the brazing alloy - capillary attraction, temperature gradient and gravity.