Text-only reference. Published from the recorded official FAA Airframe Chapter 5 PDF. Diagrams, photographs, and figure artwork are not reproduced here; use the official FAA PDF for those materials.
Wire Drill #0 1 2 3 4 5 6 7 8 9 10 13 #000 #00 #0 1 2 3 4 5 6 Decimal Inch Metric Equiv. (mm) Smiths™ AW1A Harris 15 Henrob/ Dillion Victor J Series #00 #0 0.5 1 1.5 2 2.5 3 4 4.5 5 5.5 6 6.5 7 Meco N Midget™ Foil .025 .040 .050 .063 .100 .188 .25 Aluminum Thickness (in) Foil .015 .032 .046 .062 .093 .125 .187 .250 .312 .375 Steel Thickness (in) #00 #0 0.5 1 1.5 2 2.5 3 AW200 AW20 AW201 AW202 AW203 AW204 AW205 AW206 AW207 AW208 AW209 AW210 0.150 0.279 0.343 0.508 0.559 0.572 0.610 0.635 0.660 0.711 0.742 0.813 0.864 0.889 0.940 1.016 1.041 1.067 1.092 1.181 1.321 1.397 1.511 1.613 1.702 1.854 1.930 1.981 2.083 2.184 2.261 2.362 2.489 2.692 2.794 0.0059 0.0110 0.0135 0.0200 0.0220 0.0225 0.0240 0.0250 0.0260 0.0280 0.0292 0.0320 0.0340 0.0350 0.0370 0.0400 0.0410 0.0420 0.0430 0.0465 0.0520 0.0550 0.0595 0.0635 0.0670 0.0730 0.0760 0.0780 0.0820 0.0860 0.0890 0.0930 0.0980 0.1060 0.1100 97 85 80 76 75 74 73 72 71 70 69 67 66 65 63 60 59 58 57 56 55 54 53 52 51 49 48 47 45 44 43 42 40 36 35 Welding Tip Size Conversion Chart All fuel cylinders have a limited capacity to deliver gas to the tip. That capacity is further limited by the gas contents remaining in the cylinder and the temperature of the cylinder.
The following provides some recommended procedures to guard against overheating and flashbacks: • Refer to the manufacturer’s recommendations for tip size based on the metal’s thickness. • Use the recommended gas pressure settings for the tip size being used. • Provide the correct volume of gas as recommended for each tip size. • Do not use an excessively long hose, one with multiple splices, or one that may be too small in diameter and restrict the flow of gas. Note: Acetylene is limited to a maximum continuous withdrawal rate of one-seventh of the cylinder’s rated capacity when full. For example, an acetylene cylinder that has a capacity of 330 cubic feet has a maximum withdrawal of 47 cubic feet per hour. This is determined by dividing 330 5-11 (cylinder capacity) by 7 (one-seventh of the cylinder capacity).
As a safety precaution, it is recommended that flashback arrestors be installed between the regulators and the gas supply hoses of all welding outfits. Figure 5-21 shows recommended tip sizes of different manufacturers, for welding various thickness of metals. Adjusting the Regulator Working Pressure The working pressure should be set according to the manufacturer’s recommendation for the tip size that is being used to weld or cut. This is a recommended method that works for most welding and cutting operations. In a well ventilated area, open the acetylene valve on the torch and turn the adjusting screw on the acetylene pressure regulator clockwise until the desired pressure is set. Close the acetylene valve on the torch. Then, set the oxygen pressure in the same manner by opening the oxygen valve on the torch and turning the adjusting screw clockwise on the oxygen regulator until desired pressure is set. Then, close the oxygen valve on the torch handle. With the working pressures set, the welding or cutting operation can be initiated.
Lighting & Adjusting the Torch With the proper working pressures set for the acetylene and oxygen, open the torch acetylene valve a quarter to a half turn. Direct the torch away from the body and ignite the acetylene gas with the flint striker. Open the acetylene valve until the black sooty smoke disappears from the flame. The pure acetylene flame is long, bushy, and has a yellowish color. Open the torch oxygen valve slowly and the flame shortens and turns to a bluish-white color that forms a bright inner luminous cone surrounded by an outer flame envelope. This is a neutral flame that should be set before either a carburizing or oxidizing flame mixture is set.
Different Flames The three types of flame commonly used for welding are neutral, carburizing, and oxidizing. Each serves a specific purpose. [Figure 5-22] Neutral Flame The neutral flame burns at approximately 5,850 °F at the tip of the inner luminous cone and is produced by a balanced mixture of acetylene and oxygen supplied by the torch. The neutral flame is used for most welding because it does not alter the composition of the base metal. When using this flame on steel, the molten metal puddle is quiet and clear, and the metal flows to give a thoroughly fused weld without burning or sparking.
Carburizing Flame The carburizing flame burns at approximately 5,700 °F at A. Neutral flame B. Carburizing (reducing) flame C. Oxidizing flame the tip of the inner core. It is also referred to as a reducing flame because it tends to reduce the amount of oxygen in the iron oxides. The flame burns with a coarse rushing sound, and has a bluish-white inner cone, a white center cone, and a light blue outer cone. The flame is produced by burning more acetylene than oxygen, and can be recognized by the greenish feathery tip at the end of the cone. The longer the feather, the more acetylene is in the mix. For most welding operations, the length of the feather should be about twice the length of the inner cone.
The carburizing flame is best used for welding high-carbon steels, for hard facing, and for welding such nonferrous alloys as aluminum, nickel, and Monel. Oxidizing Flame The oxidizing flame burns at approximately 6,300 °F and is produced by burning an excess of oxygen. It takes about two parts of oxygen to one part acetylene to produce this flame. It can be identified by the shorter outer flame and the small, white, inner cone. To obtain this flame, start with a neutral flame and then open the oxygen valve until the inner cone is about one-tenth of its original length. The oxidizing flame makes a hissing sound, and the inner cone is somewhat pointed and purplish in color at the tip.
The oxidizing flame does have some specific uses. A slightly oxidizing flame is used for bronze welding (brazing) of steel and cast iron. A stronger oxidizing flame is used for fusion welding of brass and bronze. If an oxidizing flame is used on steel, it causes the molten metal to foam, give off sparks, and burn. 5-12 Soft or Harsh Flames With each size of tip, a neutral, carburizing, or oxidizing flame can be obtained. It is also possible to obtain a soft or harsh flame by decreasing or increasing the working pressure of both gases (observing the maximum working pressure of 15 psi for acetylene gas).
For some work, it may be desirable to have a soft or low velocity flame without a reduction of thermal output. This can be achieved by reducing the working pressure using a larger tip and closing the torch valves until the neutral flame is quiet and steady. It is especially desirable to use a soft flame when welding aluminum to avoid blowing holes in the metal when the puddle is formed. Handling of the Torch It should be cautioned that improper adjustment or handling of the torch may cause the flame to backfire or, in rare cases, to flashback. A backfire is a momentary backward flow of gases at the torch tip that causes the flame to go out.
A backfire may be caused by touching the tip against the work, overheating the tip, by operating the torch at other than recommended pressures, by a loose tip or head, or by dirt or slag in the end of the tip, and may cause molten metal to be splattered when the flame pops. A flashback is dangerous because it is the burning of gases within the torch. It is usually caused by loose connections, improper pressures, or overheating of the torch. A shrill hissing or squealing noise accompanies a flashback, and unless the gases are turned off immediately, the flame may burn back through the hose and regulators causing great damage and personal injury. The cause of the flashback should always be determined and the problem corrected before relighting the torch. All gas welding outfits should have a flashback arrestor.
Oxy-acetylene Cutting Cutting ferrous metals by the oxy-acetylene process is primarily the rapid burning or oxidizing of the metal in a localized area. This is a quick and inexpensive way to cut iron and steel where a finished edge is not required. the conventional oxygen and acetylene valves in the torch handle that control the flow of the two gases to the cutting head. It also has an oxygen valve below the oxygen lever on the cutting head so that a finer adjustment of the flame can be obtained. The size of the cutting tip is determined by the thickness of the metal to be cut. Set the regulators to the recommended working pressures for the cutting torch based on the tip size selected. Before beginning any cutting operation, the area should be clear of all combustible material and the proper protective equipment should be worn by personnel engaged in the cutting operation.
The flame for the torch in Figure 5-23 is set by first closing the oxygen valve below the cutting lever and fully opening the oxygen valve on the handle. (This supplies the high-pressure oxygen blast when the cutting lever is actuated.) The acetylene valve on the handle is then opened and the torch is lit with a striker. The acetylene flame is increased until the black soot is gone. Then, open the oxygen valve below the cutting lever and adjust the flame to neutral. If more heat is needed, open the valves to add more acetylene and oxygen. Actuate the cutting lever and readjust the preheat flame to neutral if necessary.
The metal is heated to a bright red color (1,400 °F–1,600 °F, which is the kindling or ignition temperature) by the preheat orifices in the tip of the cutting torch. Then, a jet of high- pressure oxygen is directed against it by pressing the oxygen lever on the torch. This oxygen blast combines with the red-hot metal and forms an intensely hot molten oxide that is blown down the sides of the cut. As the torch is moved along the intended cut line, this action continues heating the metal in its path to the kindling temperature. The metal, thus heated, also burns to an oxide that is blown away to the underside of the piece.
Proper instruction and practice provides the knowledge and skill to become proficient in the technique needed to cut with a torch. Hold the torch in either hand, whichever is most comfortable. Use the thumb of that hand to operate the oxygen cutting lever. Use the other hand to rest the torch on and steady it along the cut line. Begin at the edge of the metal and hold the tip perpendicular to the surface, preheating until the spot turns bright red. Lightly depress the cutting lever to allow a shower of sparks and molten metal to blow through the cut. Fully depress the cutting lever and move the torch slowly in the direction of the intended cut.
Practice and experience allow the technician to learn how to 5-13 judge the speed at which to move the torch. It should be just fast enough to allow the cut to penetrate completely without excessive melting around the cut. If the torch is moved too fast, the metal will not be preheated enough, and the cutting action stops. If this happens, release the cutting lever, preheat the cut to bright red, depress the lever, and continue with the cut. Shutting Down the Gas Welding Equipment Shutting down the welding equipment is fairly simple when some basic steps are followed: • Turn off the flame by closing the acetylene valve on the torch first. This shuts the flame off quickly. Then, close the oxygen valve on the torch handle. Also, close oxygen valve on cutting torch, if applicable.
• If the equipment is not used in the immediate future (approximately the next 30 minutes), the valves on the acetylene and oxygen cylinders should be closed and pressure relieved from the hoses. • In a well-ventilated area, open the acetylene valve on the torch and allow the gas to escape to the outside atmosphere, and then close the valve. • Open the oxygen valve on the torch, allow the gas to escape, and then close the valve. • Close both the acetylene and oxygen regulators by backing out the adjusting screw counterclockwise until loose. • Carefully coil the hose to prevent kinking and store it to prevent damage to the torch and tip.
Gas Welding Procedures & Techniques The material to be welded, the thickness of the metal, the type of joint, and the position of the weld dictates the procedure and technique to be used. When light-gauge metal is welded, the torch is usually held with the hose draped over the wrist. [Figure 5-24] To weld heavy materials, the more common grip may provide better control of the torch. [Figure 5-25] The torch should be held in the most comfortable position that allows the tip to be in line with the joint to be welded, and inclined between 30° and 60° from the perpendicular. This position preheats the edges just ahead of the molten puddle.
The best angle depends on the type of weld, the amount of preheating required, and the thickness and type of metal. The thicker the metal, the more vertical the torch must be for proper heat penetration. The white cone of the flame should be held about 1⁄8-inch from the surface of the metal. Welding can be performed by pointing the torch flame in the direction that the weld is progressing. This is referred to as 5-14