© 2012 Delmar, Cengage Learning Chapter 30 Oxyfuel Welding and Cutting Equipment, Setup, and...

© 2012 Delmar, Cengage Learning

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– 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 PressureRelease 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 – 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. Larry Jeffus.


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

© 2012 Delmar, Cengage Learning Chapter 30 Oxyfuel Welding and Cutting Equipment, Setup, and...

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