The Art of Welding. William Galvery

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TOOL TIP

       Adjusting the Torch to a Neutral Flame

      Open the acetylene valve no more than 1/16 turn and use a spark lighter to ignite the gas coming out of the tip. A smoky orange flame will be the result, Figure 3-28 (A).

      Continue to open the acetylene valve until the flame stops smoking (releasing soot). Another way to judge the proper amount of acetylene is to open the acetylene valve until the flame jumps away from the torch tip, leaving about 1/16 inch gap (1.6 mm), Figure 3-28 (B). Then close the valve until flame touches the torch tip.

      Open the oxygen valve slowly. As the oxygen is increased, the orange acetylene flame turns purple and a smaller, white inner cone will begin to form. With the further addition of oxygen, the inner cone goes from having ragged edges, Figure 3-28 (C), to sharp, clearly defined ones. The flame is now neutral and adding oxygen will make an oxidizing flame, Figure 3-28 (D).

      If a larger flame is needed while keeping the same tip size, the acetylene may be increased and the oxygen further increased to keep the inner cone’s edges sharp. This process of increasing the acetylene, then the oxygen is usually done in several cycles before the maximum flame available from a given tip is achieved. Adjusting the flame below the minimum flow rate for the tip orifice permits the flame to ignite inside the nozzle. This is flashback and makes a popping sound. If you need a smaller flame, use a smaller torch tip. See the section on flashback.

Figure 3-28 Shows flame adjustments from carburizing to a neutral flame

       Flame Temperatures

      The tip of the inner cone is the hottest part of the flame. The inner cone is where the optimum mixture of oxygen and acetylene burn. The outer envelope where any unburned acetylene burns with oxygen from the atmosphere. A neutral flame is when enough oxygen is present in the flame to be burning all of the acetylene gas and is used for most welding processes. See Figure 3-29.

Figure 3-29 Graph of an oxyacetylene flame temperature profile

       TOOL TIP

       Lighting a Multi-Flame (Rosebud) Tip

      This type of tip produces a large flame for heating metal prior to welding, bending, or brazing. When using a multi-flame tip you first set the acetylene pressure at or just below 15psi (1 bar) and the oxygen pressure at 30psi (2 bar); open the acetylene torch valve far enough to light the acetylene flame. Once the flame is ignited, open the acetylene valve until you have full flow of gas; now you can open the oxygen torch valve and adjust the flame to slightly carburizing. You may now use the multi-flame (rosebud) to heat materials but keep the sharp inner cone flame away from the material and only touch the carburizing flame to the material being heated. A heat sensing device such as a pyrometer or temperature sensing stick can be applied to the material to indicate the temperature of the material being heated.

       Figure 3-30 A rosebud tip is often used to preheat materials prior to welding

       Photo courtesy of Hobart Welders

       How is the equipment shut down?

      First turn off the oxygen and then the acetylene with the torch handle valves. Turning off the acetylene first can cause a flashback.

      Turn off the oxygen and acetylene cylinder valves at the upstream side of the regulators.

      Separately, open and reclose the oxygen and acetylene valves on the torch handle to bleed the remaining gas in the hoses and regulator into the atmosphere. Verify that both the high-pressure and low-pressure gauges on both regulators indicate zero.

      Unscrew the regulator pressure adjustment screws on both cylinders in preparation for the next use of the equipment. The regulator screws should be loose but not about to fall from their threads.

What are the joint preparations for welding?

      Refer to Figure 3-31.

Figure 3-31 Preparation for OAW butt welds

How are welds judged?

      For butt welds, here are examples of a correct weld, poor penetration weld, excessive reinforcement, undercutting, and excessive root reinforcement. See Figure 3-32.

Figure 3-32 Correct and defective butt weld profiles

       Producing a good weld bead is a combination of four main factors: the distance between the torch tip and the work, the angle at which you hold the torch, your speed when moving the torch along the weld area, and the heat produced by the torch. Getting everything right takes practice, so always test your technique on scrap metal first.

      Figure 3-33 Create a puddle at the start of the bead. Keep the tip steady until a puddle begins to form. Begin making a circular motion with the torch, slowly moving the torch tip in the direction of the bead. Keep the distance to the work and the speed of your movements consistent.

      Figure 3-34 Now try it with a filler rod. The goal is to intermittently dip the end of the rod into the puddle to add material to the weld. Dip the end of the rod into the puddle while making a circular motion with the torch. This will help blend the filler material into the weld. Withdraw the rod from the puddle, but keep it close to the end of the torch to keep it preheated. Don’t directly heat the end of the rod with СКАЧАТЬ