6.5 Soldering Techniques It is important to apply heat properly in any soldering operation. A number of heat sources are available, such as soldering irons, soldering guns, and a variety of torches, but this text addresses only the air-acetylene torch and open- flame technique. Torch selection is determined by the type and size of the soldering job. Large tips providing high heat, or even an oxyacetylene torch, may be used by skilled operators. Less-skilled operators should use the air-acetylene torch, with its soft flame and lower temperatures, to avoid over- heating the base metals. A variety of tips may be used with an air-acetylene torch. Pro Tip Heat and Torch Tip Relationship More heat is obtained with larger torch tips. The smaller the torch tip, the lower the heat. The larger the torch tip, the higher the heat. Selecting the proper size tip (or flame) requires experience. In general, small tubing requires a small flame, and large tubing requires a large flame. See Figure 6-15. Dirty tips or faulty adjustment may produce a sooty flame that deposits carbon on the work- piece. This carbon deposit will prevent the alloy from flowing properly and result in a poor joint. For consistently good soldering, keep in mind that the alloy will flow properly only when the joining pieces are heated equally and evenly to the solder’s flow point. Do not apply the flame directly to the alloy. U0se the flame to heat the base metals to the solder’s melting point. Then, back off the flame just far enough to maintain the proper temperature until melted alloy fills the joint. Apply only enough°C alloy to form a bright shiny bead at the point1083here w th1981ecesCopper e pi meet.tubing solders will usually melt in the range of 400°F to 500°F (204°C to 260°C). Avoid overheating the base metals. 6.4.7 Shutting Off the Torch The torch can be shut down temporarily by merely closing the handle valve to turn off the flame. It can then be laid aside until it is needed again. However, if the unit is not going to be used for a long time, it should be completely shut down as follows: 1. Close the valve on the torch handle, using finger-tip pressure only. This will kill the flame. 2. Tightly close the cylinder valve. 3. Reopen the torch handle valve to bleed off (release) any acetylene trapped between the hose and regulator. Bleeding should con- tinue until both gauges read zero. 4. Turn the adjusting screw on the regulator all the way out (counterclockwise) to close the regulator. This will help to avoid gas loss if the cylinder or torch valves leak. 5. Rewind the hose and place the unit in safe storage. Goodheart-Willcox Publisher Figure 6-14. The flame can be adjusted with a knob on the handle. The hottest area of the flame is just in front of the inner cone’s tip. Chapter 6 Soldering 91 Copyright Goodheart-Willcox Co., Inc. Ch06.indd 91 10/24/2014 9:24:52 AM cylinder will hold. The cylinder sizes are desig- nated by a letter/number combination. The table in Figure 7-7 matches oxygen and acetylene cylinders by size. HVACR service technicians seldom use the large fuel gas cylinders common in welding opera- tions. Technicians prefer smaller cylinders that can be easily transported to rooftops, basements, and other locations where heating, ventilation, and air conditioning equipment is installed. See Figure 7-8. The small oxyacetylene units perform the same duty as the large units, except the oper- ating pressures are different, and the supply of oxygen and acetylene does not last as long in the small units. To overcome the supply problem, technicians stock one or two extra cylinders for additional capacity. Carrying stands and two-wheel carts are available to hold the small cylinders. An oxyacetylene outfit that uses small cylin- ders, regulators, hoses, and torches is called a light-duty, or aircraft-type, unit. It is preferred by many service technicians because of its portability. All the components are matched and have ⅜ ″ (size “A”) fittings at the regulator, hoses, and torch handle. The small oxyacetylene outfits also require small brazing and cutting tips. These, in turn, require small operating (work or flow) pressures. Follow the manufacturer’s recommendations for the type of equipment available. 7.5.1 Cylinder Pressures Oxygen cylinders are charged to 2200 psi at 70°F (15 169 kPa at 21°C), but the actual pressure in the cylinder will vary with the temperature. All gases expand when heated and contract when cooled. If the temperature exceeds 70°F (21°C), the pressure in a full cylinder will rise above Caution Avoid Excess Flux Special care must be exercised when using fluxes to braze copper tubing or brass fittings in a refrigeration system. Fluxes are harmful contaminants inside the tubing of a refrigeration system. Avoid excess flux. Apply only the amount necessary. 7.5 Gas Cylinders and Related Equipment Oxygen and acetylene cylinders are sized according to the amount of gas in cubic feet the 1800 1700 1600 1500 1200 1100 800 600 212 982 927 871 816 649 593 427 316 100 melts Tubing changes to red brass color Tubing changes to yellow brass color Flux disappears Plastic range for various alloys Flux turns to clear liquid Flux begins to melt Flux turns milky color Flux dries out (water boils away) °F Goodheart-Willcox Publisher Figure 7-6. Visual signals to important temperatures involved in the brazing process. Goodheart-Willcox Figure 7-7. The different cylinder sizes that can be matched for use in an oxyacetylene brazing and cutting outfit. Cylinder Sizes for Matched Systemst Acetylene Oxygen 10 cu. ft. (MC) 40 cu. ft. (B) 60 cu. ft. (#2) 60 cu. ft. (#2) equalss equalss equalss also equalss 20 cu. ft. (AA or R-Oxy)) 40 cu. (A) 60 cu. (J) 80 cu. (JJ) 1 4 Heating and Cooling Essentials Copyright Goodheart-Willcox Co., Inc.. Ch07.indd 104 10/21/2014 8:06:07 AM a f u ll c y li n d e r w ill ri se ab ove Goodheart-W Willcoox W PPublishererhs o ubli ifferent cy lind er s iz es that ca n be a n oxyacetylene brazin g a n d cutt ting t f ze s f or Matched S Sy s em s Oxygen equa l equa l equa l s o equal 20 cu. f t. f f (AA or R- O xy 40 cu . fft. t. f f (A) 60 cu. fft. t. f f (J) 80 cu. fft. t. f f (JJ) Copyright Goodheart-Willcox C o ., Inc molecules fit in between the acetone molecules. As pressure is relieved during use, the acetylene gas is released to flow out of the torch. Each time the cylinder is refilled, the tare weight should be checked and acetone added as needed. Pro Tip Acetylene Cylinder Position Acetylene cylinders should be used in an upright position to avoid loss of acetone and poor flame quality. Safety Precautions with Acetylene Safety-consciousness is a mark of good crafts- manship and is guided by common sense. Observe the following precautions for using acetylene safely. • Never permit fuel gas to escape and accumulate. Acetylene concentrations ranging from 3% to 90% in air or oxygen are explosive. • Never store acetylene or other fuel cylinders in a closed, unventilated area. • Do not expose fuel gas tanks to high tempera- tures or sources of ignition. • When setting up an air-acetylene torch, check all fittings for leakage by spraying them with a soapy water solution. Leaks will blow bubbles. A soapy solution can be made by mixing concentrated dishwashing detergent and water in a 1:1 ratio. A squirting dispenser is handy for applying the solution. Do not use the torch until all fitting leaks have been eliminated. Never use a flame to detect leaks. • Never use a cylinder that is leaking acetylene. If gas leaks around the valve stem when the valve is opened, close the valve and tighten the packing nut. This will compress the packing around the valve stem and should stop the leak. If the leak does not stop, close the cylinder valve, tag the cylinder a “leaker,” and return it to your supplier. Keep the “leaker” away from all sources of ignition. • Never open the acetylene cylinder valve more than one-half turn. All acetylene cylinders are manufactured to Department of Transportation (DOT) require- ments. Cylinders are thoroughly tested by the DOT Bureau of Explosives before being used commercially. A fusible plug located in the bottom of each cylinder will melt at approximately 212°F (100°C) to relieve dangerous pressure buildup. Safety Note Acetylene Cylinders Acetylene can be unstable, unsafe, and explosive at working pressures above 15 pounds per square inch (psi) or 103 kilo- pascals (kPa). However, the gas can be safely stored in cylinders at a higher pressure by the following method. An acetylene cylinder is filled with a porous substance that absorbs acetone, a liquid solvent. Next, a precisely measured amount of acetone is introduced into the cylinder and absorbed by the porous substance. Then, the cylinder containing the porous material and acetone is weighed. The weight is stamped on the cylinder. This is the tare weight, which is the weight of the container before it is filled with acetylene. Finally, acetylene is pumped into the cylinder where it is absorbed by the acetone. It is thought that the acetylene B MC Uniweld Figure 6-8. Common acetylene cylinder sizes are B and MC. The B cylinder holds 40 lb of acetylene the MC cylinder holds 10 lb. All acetylene cylinders must be tested and approved for use. Chapter 6 Soldering 87 Copyright Goodheart-Willcox Co., Inc. Ch06.indd 87 10/24/2014 9:24:39 AM Pro Tips provide students with advice and guidance that is especially applicable for an on-the-job technician. Caution boxes warn students against practices that could potentially damage equipment or instruments. Safety Notes alert students of potentially dangerous materials and practices. vii Copyright Goodheart-Willcox Co., Inc.