Oxy Acetylene Welding

Oxy-Acetylene (OA) welding

is one of the many types of welding. It is extremely versatile, and with enough skill and practice you can use this type of welding for virtually any metal. In fact, the oxy-acetylene flame burns at 6000 °F, and is the only gas flame that is hot enough to melt all commercial metals. Oxy-acetylene welding is simple in concept - two pieces of metal are brought together, and the touching edges are melted by the flame with or without the addition of filler rod. 

Advantages of Oxy-Acetylene Welding :

·        It's easy to learn.

·        The equipment is cheaper than most other types of welding rigs (e.g. TIG welding)

·        The equipment is more portable than most other types of welding rigs (e.g. TIG welding)

·        OA equipment can also be used to "flame-cut" large pieces of material.

Disadvantages of Oxy-Acetylene Welding :

·        OA weld lines are much rougher in appearance than other kinds of welds, and require more finishing if neatness is required.

·        OA welds have large heat affected zones (areas around the weld line that have had their mechanical properties adversely affected by the welding process)

Materials Suitable for OA Welding

Most steels

Brass

Preparation :

1)      Assemble all of the materials needed to make the weld. This includes parts, OA equipment, fixturing, tools, safety mask, gloves, and filler rod.

2)      Clean the parts to be welded to remove any oil, rust, or other contaminants. Use a wire brush if needed to remove any rust.

3)      Assemble and fixture the parts in place - the parts need to be stable for a good weld line. Ceramic bricks, vise grips, pliers, and clamps are available in a file cabinet in the weld room for fixturing.

4)      Select the nozzle you plan to use for welding. Nozzles come in a variety of sizes, from 000 (for a very small flame - typically used for thin materials) to upwards of 3 (for a large flame - needed for thick materials).  Larger nozzles produce larger flames and, in general, are more appropriate for thicker material. Choosing the right size nozzle becomes easier with more experience.

5)      Clean the nozzle.  Carbon deposits can build up on the nozzles which interfere with flame quality and cause backfiring. The cleaning tool has a  wide flat blade (with a file-like surface) which is used to clean carbon deposits on the exterior of the nozzle.  Use it to scrape any deposits from the flat face of the tip.  Use the wire-like files to clean the interior of the nozzle.  Pick the largest wire which will fit inside the nozzle, and the scrape the edges of the hole to remove any carbon buildup.

6)      Attach the nozzle to the gas feed line by hand.  Don't over-torque - the nozzle and hose fitting are both made of brass which doesn't stand up well to abuse. A snug, finger tight fit is the sufficient.

7)      Check the pressure levels in the oxygen and acetylene tanks.  There should be at least 50 psi in the acetylene tank. The oxygen tank can be used until it is completely empty. . Note: The oxygen used in OA welding in NOT for human consumption.  It contains contaminants that could be unhealthy if taken in large quantities

Adjusting the flame

  The blue flame will be divided into 3 different color regions - a long yellowish tip, a blue middle section, and a whitish-blue intense inner section.  There are three types of flames as described below :

·        Neutral - This type of flame is the one you will use most often in the metalwork room. It is called “neutral” because it has no chemical effect upon the metal during welding. It is achieved by mixing equal parts oxygen and acetylene and is witnessed in the flame by adjusting the oxygen flow until the middle blue section and inner whitish-blue parts merge into a single region. 

·        Reducing / Carburising flame - If there is excess acetylene, the whitish-blue flame will be larger than the blue flame. This flame contains white hot-carbon particles, which may be dissolved during welding. This “reducing” flame will remove oxygen from iron oxides in steel.

·        Oxidizing flame - If there is excess oxygen, the whitish-blue flame will be smaller than the blue flame. This flame burns hotter. A slightly oxidizing flame is used in brazing, and a more strongly oxidizing flame is used in welding certain brasses and bronzes.

Safety features incorporated into oxy-acetylene equipment

The Acetylene tank contains an absorbent substance called Acetone. Acetone can absorb 25 times its own volume of Acetylene. 

Colour coding: oxygen cylinder is black and acetylene is maroon, hoses and regulators are colour coded with oxygen as blue and acetylene as red.

The acetylene connection on the torch has a left hand thread and the oxygen  connection has a right hand thread to prevent interchange.

Flashback arrestors are placed on the acetylene and oxygen lines to prevent  feedback of gases.

Regulators are designed to fit only on acetylene or high pressure oxygen cylinders and cannot be changed