CHAPTER  5 GAS   WELDING This chapter discusses equipment and materials used in gas welding. Information is provided on the operation and maintenance of oxyacetylene and oxy- MAPP  equipment.  Included  are  welding  techniques  and safety  precautions  associated  with  gas  welding. Oxyacetylene  and  oxy-MAPP  (methylacetylene- propadiene) welding are two types of gas-welding proc- esses.  They  require  a  gas-fueled  torch  to  raise  the temperature of two similar pieces of metal to their fusion point that allows them to flow together. A filler rod is used to deposit additional metal. The gas and oxygen are mixed to correct proportions in the torch, and you can adjust the torch to produce various types of flames. A properly made gas weld is consistent in appear- ance,  showing  a  uniform  deposit  of  weld  metal.  Com- plete fusion of the sidewalls is necessary to forma good joint.  Some  of  the  factors  you  must  consider  when making a gas weld are as follows: edge preparation, spacing and alignment of the parts, temperature control (before,  during,  and  after  the  welding  process),  size  of the  torch  tip,  size  and  type  of  the  filler  rod,  flame adjustment, and rod and torch manipulation. In some cases, fluxes are needed to remove oxides and slag from the molten metal and to protect the puddle from atmos- pheric  contamination. When you join sections of plate by gas welding, the edges of the plate at the joint are uniformly melted by the heat from the torch. When welding heavier sheets and plates, you have to use filler metals. The edges of the heavier plate are beveled to permit penetration to the base of the joint. Both the filler metal and the base metal are melted, and as they solidify, they form one continu- ous piece. For welding light sheet metal, filler metal is usually not necessary. The edges of light sheet metal are flanged at the joint so they flow together to form one solid piece when you melt them. OXYGAS WELDING EQUIPMENT An  oxygas  welding  outfit  is  basically  the  same  as an oxygas cutting outfit with the exception of the torch. The  welding  outfit  usually  consists  of  a  cylinder  of acetylene  or  MAPP  gas,  a  cylinder  of  oxygen,  two regulators, two lengths of hose with fittings, and a welding torch with tips (fig. 5-1). An oxygas welding outfit also is called a welding rig. In addition to the basic equipment mentioned, you also use the same auxiliary equipment that was dis- cussed in chapter 4. This equipment consists of tip cleaners,  cylinder  trucks,  clamps,  and  holding  jigs. Safety  apparel,  which  includes  goggles,  hand  shields, gloves, leather aprons, sleeves and leggings, is essential and should be worn as required. Information on safety apparel is contained in chapter 3. Oxygas  welding  equipment,  like  cutting  equipment, may be stationary or portable. A portable oxygas outfit, as shown in figure 5-2, is an advantage when it becomes necessary  to  move  the  equipment. To perform your welding duties, you must be able to set up the welding equipment and make the adjust- ments  required  to  perform  the  welding  operation.  Thus it is important that you understand the purpose and function of the basic pieces of equipment that makeup the welding outfit. The gases, cylinders, regulators, hoses, and safety equipment are covered in chapter 4. If you have any questions, you should review chapter 4 before  continuing. WELDING  TORCHES The oxygas welding torch mixes oxygen and fuel gas in the proper proportions and controls the amount of the mixture burned at the welding tip. Torches have two needle valves: one for adjusting the oxygen flow and the other for adjusting the fuel gas flow. Other basic parts include a handle (body), two tubes (one for oxygen and another for fuel), a mixing head, and a tip. On some models the tubes are silver-brazed to the head and the rear end forgings, which are, in turn, fitted into the handle. Welding tips are made from a special copper alloy and are available indifferent sizes to handle a wide range of uses and plate thicknesses. Two general types of welding torches are used: l Low pressure l Medium pressure 5-1