Oxy-Acetylene Welding
In oxy-acetylene welding, the flame is produced by the combination of the gases Oxygen and Acetylene. The mixed gases pass through a specially designed torch and the required flame is produced by a nozzle, of a specific size on the end of this torch. The heat from the flame, which can reach temperatures in excess of 3000 degrees C, melts the metal faces of the material to be joined. A filler metal alloy is normally added this being a material similar to, or compatible with, the base material.
The most common types are fusion welding [where metal and filler are fused together to form a homogeneous joint, or brazing [where metal is deposited using surface diffusion and not melting the base material]
For the majority of applications a “NEUTRAL” flame is used [fig a]. However when bronze welding, or brazing it is helpful to adjust to flame to obtain a slight increase in the oxygen supplied. This is known as an “OXIDIZING” flame [fig b]. This type of flame can also be used for the depositing of a hard surface, sometimes known by the trade name STELLITEING. When welding, or brazing aluminium a reducing flame, having excess acetylene is used. This is known as a “CARBURIZING” flame[fig c]
Which Oxy-Acetylene Rod?
Oxy-Acetylene [Gas] Welding rods are selected based on their compatibility with the base materials and the more common ones are listed below:-
- A] Mild Steels
- B] Cast Iron
- C] Aluminium
- D] Bronzes
- E] Copper Phosphorous
- F] Silver brazing [silver soldering]
A] Mild Steel
BS:1453 A1
EN 12536: 01
Commonly known as copper coated mild steel, this rod is suitable for the fusion welding of all types of mild steel.
B] Cast Iron
A high silicon content cast iron fusion welding rod is still available to enable cast iron components to be welded in the “old fashioned” way. Whilst this is not a common practice, if facilities are available, this is still the finest way to achieve a high strength, fully machineable weld in grey cast iron.
C] Aluminium
BS:2901 4047A [NG2]
EN ISO 18273 S Al 4047A
A high silicon aluminium alloy which is particularly suitable for aluminium brazing. A high strength joint with a very neat finish can be achieved on tube, plate and other configurations. This product must be used in conjunction with a high quality aluminium brazing flux.
BS:2901 4043A [NG21]
EN ISO 18273 S Al 4043A
An aluminium 5% silicon alloy. Suitable to for the welding of cast and wrought aluminium alloys in the range H9[6063], H20[6061] & H30[6082].
This alloy should not be used if the end product requires anodising. This product must be used in conjunction with a high quality aluminium welding flux
D] Bronzes
BS: 1845 CZ6A
EN 1044: CU 302
Recognised by the trade as a multi purpose alloy for the brazing and bronze welding of steels, cast iron, copper and copper alloys. This product can also be used for the braze joining of galvanised components. [use adequate ventilation with his application]
E] Copper Phosphorous
This range of copper phosphorous alloys is most commonly used by the refrigeration and heating and ventilating trades. The alloys range from 93% copper with the addition of 7% phosphorous to the addition of up to 15% silver. The higher the silver content the more free flowing the particular alloy.
No flux is required hen joining copper to copper, but a high quality brazing flux must be used when joining copper to brass.
F] Silver Brazing [Silver Soldering]
More commonly used for the brazing together of thin section components in sheet, tube and specific light fabrications, in stainless steels, brasses and other copper alloys. Silver brazing alloys are alloys of copper, silver, zinc and tin, in different percentages which directly affect their performance and melting temperature. The higher the silver content, which can range from 15% to 56%, the lower the melting [joining] temperature and the more free flowing the brazing alloy. Some times cadmium is also added to create the same effect as high silver content. However alloys containing cadmium must not be used in the food, drink, pharmaceutical, or similar environments/industries.
Note:
These guidelines only deal with the more common welding rods in the three joining process. There are, of course many more.