gases in welding

Gases in welding

Introduction

Welding processes include various gases used for different purposes. Some of them are combustible and some are inert, some gases are also rich in oxygen. These gases are described here based on their usage.


Use of flammable gases by weld

Flammable gases are commonly used by a gas welding process in which oxygen is added to obtain the desired heat. The most commonly used gases in gas welding are as follows :
Acetylene +oxygen = 3100 °C to 3300 °C (Oxyacetylene)
 Hydrogen + oxygen = 2500 °C       (Oxyhydrogen)
Propane +Oxygen  = 2500 °C      ( Oxypropen) 

See detail  Gas welding

Use of Shielding gases by weld

Shielding gases are used to protect the weld pool from harmful atmospheric gases, among these the gases mainly used in the welding process are as follows :
Argon, Helium, Carbon dioxide, Nitrogen, Hydrogen and propane, etc.
See detail- Shielding gases

Absorption of gases by weld

A very important metallurgical change resulting from the creation of molten weld pools is the absorption of gases by it. These gases are absorbed into the molten metal and react with each other, resulting in welding defects such as porosity, cracks, oxide inclusions. etc.
This category contains gases such as hydrogen, oxygen and nitrogen, which often cause problems.
There are three major sources of gases such as an electrode, the atmosphere and the patent metal.

 Electrodes

The electrode wire may contain considerable amounts of dissolved oxygen as well as some hydrogen and nitrogen. Which can develop carbon monoxide (CO), carbon dioxide (CO2) etc. gases at the time of welding.
See Detail -Welding electrodes,       Electrodes     

The atmosphere

Shielding gases are used to protect the molten metal from atmospheric contamination. If there is no adequate shielding protection, these gases such as oxygen, nitrogen and water vapour can come into contact.

The patent metal.

The amount of hydrogen, oxygen, and nitrogen in the plate material is also in a limited proportion, and the hydrogen content of the plate material is, in general, fairly low, being of the order of 1 ml/100grms.If this amount becomes too much, then a problem can occur. The oxygen content may range from 0.001% to0.03 %. The Nitrogen content may vary from 0.001% to0.004% or higher if Bessemer quality plate is considered 
See Detail- The Material

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