Oxyfuel Welding and Cutting Equipment, Setup, and Operation Chapter 30 Oxyfuel Welding and Cutting Equipment, Setup, and Operation

Objectives Describe how to maintain the major components of oxyfuel welding equipment Explain the method of testing an oxyfuel system for leaks Demonstrate how to set up, light, adjust, extinguish, and disassemble oxyfuel welding equipment safely

Introduction Oxyfuel welding, cutting, brazing, hardsurfacing, heating, etc. Use the same basic equipment Cylinders Regulators Hoses Hose fittings Safety valves Torches Tips

Introduction (cont'd.) All oxyfuel processes use a high-heat, high-temperature flame Produced by burning a fuel gas mixed with pure oxygen Gases are supplied in pressurized cylinders Regulators reduce gas pressure from the cylinder Gas flows through flexible hoses Torch controls flow Acetylene is the most widely used fuel gas

Pressure Regulators Reduce a high pressure to a lower working pressure Kept constant over a range of flow rates Various types Low-pressure regulators, high-pressure regulators, single-stage regulators, dual-stage regulators, cylinder regulators, etc. Not interchangeable

Regulator Operation Regulators work by holding the forces on both sides of a diaphragm in balance Gas pressure on back side of diaphragm is reduced Two-stage regulators Keep pressure constant at very low or high flow rates Two sets of springs, diaphragms, and valves

FIGURE 30-1 Force applied to the flexible diaphragm by the adjusting screw through the spring opens the high-pressure valve. © Cengage Learning 2012

Regulator Gauges One or two gauges on a regulator Line drop One regulator gauge shows working pressure Shows pressure at regulator and not at the torch Second gauge shows cylinder pressure Line drop Caused by resistance of a gas flow

Regulator Safety Pressure Release Device Safety release valve or safety disc Prevent excessive pressure from damaging the regulator Safety release valve Made of a ball held against a seat by a spring Safety disc Thin piece of metal held between two seals Must be replaced if used

Cylinder and Regulator Fittings Ensure regulator is not connected to wrong gas or pressure Common adapters Left-hand male acetylene cylinder fitting to a right-hand female regulator fitting Argon or mixed gas male to a female flat washer-type CO2 fitting Considerations Keep fittings free of dirt and oil Screw together freely by hand Replace damaged connections

Regulator Safety Precautions Key points Back off adjusting screw at shut down to prevent damage Creep is rising pressure on working side of regulator If leakage at the seat is severe: maximum safe pressure can be exceeded on working side Results in damage to diaphragm, gauge, hoses, etc. Do not use regulators that creep excessively

Regulator Care and Use Considerations No internal or external moving parts on a regulator or a gauge require oiling Adjusting screw becomes tight and difficult to turn: remove and clean with a dry, oil-free rag Replacing adjusting screw: be sure it does not become cross-threaded Welding is finished and cylinders are turned off: gas pressure must be released and adjusting screw backed out

Welding and Cutting Torches: Design and Service Oxyacetylene hand torches Most common type of oxyfuel gas torch used Combination welding and cutting torches More flexible Straight or dedicated cutting torches Longer than combination torches Most manufacturers make torches in a variety of sizes for different types of work

Mixing the Gases Two methods for mixing oxygen and fuel gas Two gases mixed completely before leaving tip One method uses equal pressures Gases are mixed in a mixing chamber Second method uses higher oxygen pressure Gases are mixed in an injector chamber

FIGURE 30-18 Schematic drawing of an oxyacetylene welding torch. © Cengage Learning 2012

Torch Care and Use Considerations Torch body contains threaded connections for the hoses and tips Wrench should never be used on one nut unless the other connection is protected Hose connections should not leak after they are tightened Valves should be easily turned on and off Bubbles around the valve stem indicates a leaking valve packing

FIGURE 30-22 One hose-fitting nut will protect the threads when the other nut is loosened or tightened. Larry Jeffus.

Welding and Heating Torch Tips Key points No industrial standard tip size identification system Students must learn various tip sizes Tip sizes: comparable to numbered drill sizes On some torch sets: each tip has its own mixing chamber

Torch Tip Care and Use Considerations Tips may have metal-to-metal seals or an O-ring or gasket between the tip and the torch seat Tighten metal-to-metal seal tips with a wrench Tips with an O-ring or gasket can be tightened by hand Dirty tips can be cleaned with tip cleaners Damaged tips or tips with cleaners broken in them can be reconditioned

Backfires Backfire Flame goes out with a loud snap or pop Causes: Touching the tip against the workpiece Overheating the tip Flame settings are too low Loose tip Damaged seats Dirt in the tip

Flashbacks Flame is burning inside the tip, torch hose, or regulator Produces a high-pitched whistle Close oxygen valve and then close fuel valve Allow torch to cool Usually indicates a serious problem with the equipment

Reverse Flow and Flashback Valves Reverse flow valve Prevents gases from flowing through the torch into the wrong hose If gases are allowed to mix in the hose or regulator they might explode Flashback arrestor Will do the job of a reverse flow valve Will also stop the flame of a flashback

Care of the Reverse Flow Valve and Flashback Arrestor Considerations Both devices must be checked on a regular basis Internal valves may become plugged with dirt Test reverse flow valve: blow air backwards through the valve Test flashback arrestor: follow manufacturer's recommended procedure Replace of not functioning correctly

Hoses and Fittings Characteristics Siamese hoses are molded together as one piece Other hoses may be taped together Fuel gas hoses must be red and have left-hand threaded fittings Oxygen hoses must be green and have right-hand threaded fittings Hoses are available in four sizes

Hose Care and Use Considerations Hoses not in use: gas must be turned off and pressure bled off Hoses are resistant to burns: not burn-proof Hoses should be checked for leaks Hose fitting can be changed if damaged To replace hose end: hose is cut square

Types of Flames Oxyacetylene flame settings Carburizing flame Excess of fuel gas Neutral flame Balance of fuel gas and oxygen Oxidizing flame Excess of oxygen

Leak Detection Leak-detection solution Solution can be: Premixed or concentrate Must be free flowing Good quantity of bubbles without film Solution can be: Dipped Sprayed Brushed

Figure 30-36 Safety chain cylinder. Larry Jeffus.

FIGURE 30-42 Connect the free ends of the oxygen (green) and the acetylene (red) hoses to the welding torch. Larry Jeffus.

FIGURE 30-43 Select the proper tip or nozzle and install it on the torch body. Larry Jeffus.

FIGURE 30-44 Back out both regulator-adjusting screws before opening the cylinder valve. Larry Jeffus.

FIGURE 30-45 Stand to one side when opening the cylinder valve FIGURE 30-45 Stand to one side when opening the cylinder valve. Larry Jeffus.

FIGURE 30-48 Adjust the regulator to read 5 psig (0 FIGURE 30-48 Adjust the regulator to read 5 psig (0.35 kg/cm2g) working pressure. Larry Jeffus.

FIGURE 30-50 Identify any cylinder that has a problem by marking it. Larry Jeffus

Manifold Systems Used when there are a number of work stations or a high volume of gas will be used Must be located at least 20 feet or more from work Rooms used for manifolds can be also used for cylinder storage Piping for high-pressure side of the manifold must be steel, stainless steel, or alloyed copper Should be tested for leaks at a half times operating pressure

Manifold Operation Considerations Clean pipes with oil-free, noncombustible fluid before regulators are attached Install regulators and purge the system with nitrogen Fill pipes with oxygen or fuel gas Set line pressure as low as possible

Summary You will work with experienced welders After you have developed skills and found a welding job These welders have developed many good shortcuts Safe way of setting up and testing a system should always be followed Always refer to the manufacturer's operating instructions and safety recommendations