{"id":279,"date":"2022-05-23T06:38:00","date_gmt":"2022-05-23T06:38:00","guid":{"rendered":"https:\/\/mewelding.com\/?p=279"},"modified":"2024-03-18T10:38:05","modified_gmt":"2024-03-18T10:38:05","slug":"oxyfuel-gas-welding-ofw-procedures","status":"publish","type":"post","link":"https:\/\/mewelding.com\/oxyfuel-gas-welding-ofw-procedures\/","title":{"rendered":"Oxyfuel Welding (OFW)"},"content":{"rendered":"
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\"Oxygas<\/figure><\/div>\n\n\n

Oxyfuel welding is a welding process in which metals are joined by heat of the flame emanating from the tip of an oxyfuel welding torch<\/a>. The pressure may or may not be applied and filler rod may or may not be used.<\/p>\n\n\n\n

As the name suggests, any oxy-fuel welding process involves two gases. One is oxygen, which enables combustion of the fuel gas. The second is a fuel gas, which is stored in a separate cylinder, and may be acetylene gas, MAPP gas, or any other hydrocarbon gas with a high calorific value. The two gases re mixed in the mixing head of the welding torch, in proper proportions.<\/p>\n\n\n\n

The flame emanating from the torch produces a puddle of molten metal, by melting the surface of the base metal. In this puddle, the tip of a filler rod is dipped progressively such that fresh weld metal gets deposited. The freshly deposited weld metal fuses and becomes one with the base metal.<\/p>\n\n\n\n

Oxyfuel welding can be used in most welding positions. The various positions in oxyfuel welding<\/a> include \u2013 flat, horizontal, vertical, and overhead; although right technique and skill is required on welder\u2019s part to get quality welds in vertical and overhead positions. Further, oxyfuel welding can be used in both forehand and backhand methods.<\/p>\n\n\n\n

Also, oxyfuel welding can be used for making fillet welds<\/a> and butt welds both, in a wide variety of base metal grades. Gas welding of aluminum can be done by using hydrogen as well as acetylene as the fuel gas.<\/p>\n\n\n\n

Oxy-acetylene welding of aluminum is an important and viable process, however special care is required to contain warpage and breakage. Therefore steps which enable slow heating and slow cooling are required when welding aluminum with oxy-acetylene welding process.<\/p>\n\n\n\n

Advantages Of Oxy-fuel Welding<\/h2>\n\n\n\n

One of the main advantages of oxy-fuel welding is that the welder can control the size of the weld puddle easily. The welder can exercise control over the heat input, temperature of the weld zone, and shape and size of the weld bead. This is because the filler rod is added separately to the weld puddle by the welder\u2019s hand. The welder can manipulate the rate of feeding of the filler rod to control the size of the bead.<\/p>\n\n\n\n

Another advantage is that this process can be used for welding in almost all positions. Thin sheets, pipe welding, repair welding, etc. can all be done satisfactorily with this process. It is, however, not best suited for welding of thick sections.<\/p>\n\n\n\n

Gases<\/h2>\n\n\n\n

Acetylene is the most commonly used fuel gas in oxy-acetylene welding process. However, any gas that is used as a fuel gas in this process must meet the following properties:<\/p>\n\n\n\n

    \n
  1. High calorific value.<\/li>\n\n\n\n
  2. High temperature of the flame.<\/li>\n\n\n\n
  3. Minimum reaction of the gas with the base metal and filler rod.<\/li>\n\n\n\n
  4. High flame propagation rate.<\/li>\n<\/ol>\n\n\n\n

    Acetylene meets all requirements expected from a fuel gas. Hence it finds a widespread usage. Other than acetylene, MAPP gas, propane, propylene, natural gas, etc. are also used as a fuel gas in oxy-fuel welding. These gases have good calorific value, but exhibit low flame propagation tendency.<\/p>\n\n\n\n

    The problem with other gases is that the flames produced by these gases are excessively oxidizing at oxygen-to-fuel ratios high enough for usable heat transfer rates. High flame temperatures are obtained only at high oxygen to fuel ratios. So, use of special flame holding devices is necessary for stable operation and adequate heat transfer.<\/p>\n\n\n\n

    The devices such as holder flames, skirts, counter-bores etc enable higher gas speeds before they leave the tip. This improves the heat transfer efficiency of these gases.<\/p>\n\n\n\n

    Oxidizing behaviour is not a problem for cutting operations though. So these gases can be easily used for preheating of the metal during cutting work. These gases can also be used for other joining processes such as soldering, brazing, etc. in which the heat input is not required to be as high as welding.<\/p>\n\n\n\n

    Second to the fuel gas, oxygen is the second gas that must be used for any oxy-fuel welding process. Oxygen is necessary for combustion, and is therefore indispensable. The proportion of oxygen in relation to the fuel gas determines the type of resulting flame. The use of right types of oxyfuel welding flames<\/a> is necessary to obtain the best results.<\/p>\n\n\n\n

    Sometimes one tends to think that oxygen can be replaced with air. Air contains only 20% of oxygen by volume (the remaining 80% being nitrogen). So the degree of combustion with air-fuel mixture is far lower than when pure oxygen is used. The heat generated by the flame is lower, and is only suitable for welding light sections, or for light soldering and brazing applications.<\/p>\n\n\n\n

    Welding Oxyfuel Working Pressure<\/h2>\n\n\n\n

    The use of right pressure of both the oxygen and fuel gas is important to get the best quality of welding. The required working pressure for welding increases as tip orifice diameter goes up. The rating of tip varies between different manufacturers. Usually, a smaller tip orifice diameter is indicated by a smaller number.<\/p>\n\n\n\n

    The following table indicates the right pressure of oxygen and acetylene for different tip sizes. The table 1 below indicates the pressures for a low pressure or injector type torch. <\/p>\n\n\n\n

    Tip Size Number<\/td>Oxygen pressure (psi)<\/td>Acetylene pressure (psi)<\/td><\/tr>
    0<\/td>9<\/td>1<\/td><\/tr>
    1<\/td>9<\/td>1<\/td><\/tr>
    2<\/td>10<\/td>1<\/td><\/tr>
    3<\/td>10<\/td>1<\/td><\/tr>
    4<\/td>11<\/td>1<\/td><\/tr>
    5<\/td>12<\/td>1<\/td><\/tr>
    6<\/td>14<\/td>1<\/td><\/tr>
    7<\/td>16<\/td>1<\/td><\/tr>
    8<\/td>19<\/td>1<\/td><\/tr>
    10<\/td>21<\/td>1<\/td><\/tr>
    12<\/td>25<\/td>1<\/td><\/tr>
    15<\/td>30<\/td>1<\/td><\/tr><\/tbody><\/table>
    Table 1: Oxygen and acetylene pressures for a low pressure or injector type torch<\/figcaption><\/figure>\n\n\n\n

    The table 2 below indicates the pressures for a balanced pressure type torch.<\/p>\n\n\n\n

    Tip Size Number<\/td>Oxygen pressure (psi)<\/td>Acetylene pressure (psi)<\/td><\/tr>
    1<\/td>2<\/td>2<\/td><\/tr>
    3<\/td>3<\/td>3<\/td><\/tr>
    4<\/td>3<\/td>3<\/td><\/tr>
    5<\/td>3.5<\/td>3.5<\/td><\/tr>
    6<\/td>3.5<\/td>3.5<\/td><\/tr>
    7<\/td>5<\/td>5<\/td><\/tr>
    8<\/td>7<\/td>7<\/td><\/tr>
    9<\/td>9<\/td>9<\/td><\/tr>
    10<\/td>12<\/td>12<\/td><\/tr><\/tbody><\/table>
    Table 2: Oxygen and acetylene pressures for a balanced pressure type torch<\/figcaption><\/figure>\n\n\n\n

    Base Metal Preparation<\/h2>\n\n\n\n

    Like in any other welding process, preparation of base metal is important for obtaining a quality weld. The right kind of joint design, right bevel angle, and proper cleaning are important.<\/p>\n\n\n\n