Gas Welding for Copper


Welding of Copper and its Alloys Weldability of Copper and Copper Alloys Welding Characteristics of Copper and its Alloys TIG Welding for Copper MIG Welding for Copper Gas Welding for Copper Brazing for Copper Welding of High Copper Alloys Welding Brasses Welding of Bronzes Welding of Silicon Bronzes Gas Welding of Bronzes Welding of Copper Nickels

Gas Welding for Copper

Gas Welding for Copper - Tough pitch copper, if gas welded, may suffer from hydrogen embitterment due to the effects of time, temperature and atmosphere. Oxygen-free Coppers can be gas-welded satisfactorily provided they are not oxidized. Oxy-acetylene process is employed for welding coppers because of high temperature of oxy-acetylene flame as compared to those of the flames of oxygen and other fuel gases. Neutral flame is recommended when using a flux otherwise a slightly oxidizing flame may be used.
The oxide thus formed serves to protect the molten metal. Because of high conductivity of Copper, the tip size selected should be one to two sizes larger than would be required for an equivalent thickness of steel.

No flux is needed when welding pure copper. However, for welding copper alloys a flux is required. Flux should be such that the metal can be deoxidized properly and the oxides formed in the process should be removed into slag. The flux should not contain sodium phosphate.
Flux constituents are:
Borax, Charcoal, SiO₂ etc.
The ingredients are mixed with soluble glass and the paste is applied to the welding rod which is already pickled in nitric acid and rinsed with water.
Sound welds are produced by a silicon-deoxidized (Cu) filler metal. Blow holes and gas bubbles in the finished weld can be removed if small quantity of phosphorus is added to the filler metal. Lap joints should be avoided as the resultant weld usually lacks in fusion due to high thermal conductivity of copper.

For sheets less than or equal to 1.5 mm thick, a flanged joint is preferred. For thicknesses up to 3 mm, a square butt joint is used with up to 1.5 mm gap. From 3 to 6 mm thicknesses, a single V joint with 60 to 90° included angle and root face equal to about one-fifth of plate thickness may be employed. A gap of up to 3 mm must be maintained during preheating.
Preheating is required when welding large sections. Tack welds should preferably be avoided as they give rise to cracking during welding at the place of tack welds. Instead the parts to be welded should be fitted up in jigs and fixtures. During welding the inner cone of the flame should be 3 to 6 mm away from the surface of the puddle. Backhand technique is generally preferred for flat position welding.

Welding should be carried out with as few interruptions and with the highest possible speed. This will reduce the amount of cuprous oxide forming during welding. For welding arsenical, non-arsenical touch pitch and deoxidized copper; and particularly for welding copper fire boxes and electrical work, the following welding rod of Indian Oxygen Ltd.
After welding, the weld and near weld area may be peened to, make seam dense and to refine grain. For thicknesses up to 5 mm, light peening may be done when the metal is cold. For thicknesses greater than 5 mm, light peening may be done while the metal is hot (200-300°C). After peening, the weld may be heated to 5000C and then quenched in water.

Given below are nominal conditions* for gas welding coppers:

Tip Size	Plate thickness mm	Pressure, kg/cm²				Gas Consumption (lpm)
		O₂		C₂H₂
		Min	Max	Min	Max	Min	Max
2	0.40	0.07	0.105	0.07	0.105	0.25	0.5
3	0.80	0.07	0.105	0.07	0.105	0.5	1.0
5	1.60	0.07	0.21	0.07	0.21	1.0	1.5
7	2.40	0.07	0.28	0.07	0.28	1	2.5
13	4.0	0.21	0.49	0.21	0.49	3	12.5
35	8.0	0.42	0.98	0.42	1.05	18	36
70	19.0	0.77	1.54	0.7	1.05	37.5	70

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