- Slides: 42
Oxyacetylene Welding (OAW) The oxyacetylene welding process uses a combination of oxygen and acetylene gas to provide a high temperature flame.
Oxyacetylene Welding (OAW) • OAW is a manual process in which the welder must personally control the torch movement and filler rod application • The term oxyfuel gas welding outfit refers to all the equipment needed to weld. • Cylinders contain oxygen and acetylene gas at extremely high pressure.
Typical Oxyacetylene Welding (OAW) Station
Oxygen Cylinders • Oxygen is stored within cylinders of various sizes and pressures ranging from 20002640 PSI. (Pounds Per square inch) • Oxygen cylinders are forged from solid armor plate steel. No part of the cylinder may be less than 1/4” thick. • Cylinders are then tested to over 3, 300 PSI using a (NDE) hydrostatic pressure test.
Oxygen Cylinders • Cylinders are regularly re-tested using hydrostatic (NDE) while in service • Cylinders are regularly chemically cleaned annealed to relieve “jobsite” stresses created by handling.
Cylinder Transportation • Never transport cylinders without the safety caps in place • Never transport with the regulators in place • Never allow bottles to stand freely. Always chain them to a secure cart or some other object that cannot be toppled easily.
Oxygen Cylinders • Oxygen cylinders incorporate a thin metal “pressure safety disk” made from stainless steel and are designed to rupture prior to the cylinder becoming damaged by pressure. • The cylinder valve should always be handled carefully
Pressure Regulators for Cylinders • Reduce high storage cylinder pressure to lower working pressure. • Most regulators have a gauge for cylinder pressure and working pressure.
Pressure Regulators for Cylinders • Regulators are shut off when the adjusting screw is turn out completely. • Regulators maintain a constant torch pressure although cylinder pressure may vary • Regulator diaphragms are made of stainless steel
Pressure Regulators Gauges Using a “Bourdon” movement • Gas entering the gauge fills a Bourdon tube • As pressure in the semicircular end increases it causes the free end of the tube to move outward. • This movement is transmitted through to a curved rack which engages a pinion gear on the pointer shaft ultimately showing pressure.
Regulator Hoses • Hoses are fabricated from rubber • Oxygen hoses are green in color and have right hand thread. • Acetylene hoses are red in color with left hand thread. • Left hand threads can be identified by a grove in the body of the nut and it may have “ACET” stamped on it
Check Valves & Flashback Arrestors • Check valves allow gas flow in one direction only • Flashback arrestors are designed to eliminate the possibility of an explosion at the cylinder. • Combination Check/ Flashback Valves can be placed at the torch or regulator.
Acetylene Gas • Virtually all the acetylene distributed for welding and cutting use is created by allowing calcium carbide (a man made product) to react with water. • The nice thing about the calcium carbide method of producing acetylene is that it can be done on almost any scale desired. Placed in tightly-sealed cans, calcium carbide keeps indefinitely. For years, miners’ lamps produced acetylene by adding water, a drop at a time, to lumps of carbide. • Before acetylene in cylinders became available in almost every community of appreciable size produced their own gas from calcium carbide.
Acetylene Cylinders • Acetylene is stored in cylinders specially designed for this purpose only. • Acetylene is extremely unstable in its pure form at pressure above 15 PSI (Pounds per Square Inch) • Acetone is also present within the cylinder to stabilize the acetylene. • Acetylene cylinders should always be stored in the upright position to prevent the acetone form escaping thus causing the acetylene to become unstable.
Acetylene Cylinders • Cylinders are filled with a very porous substance “monolithic filler” to help prevent large pockets of pure acetylene forming • Cylinders have safety (Fuse) plugs in the top and bottom designed to melt at 212° F (100 °C)
Acetylene Valves • Acetylene cylinder shut off valves should only be opened 1/4 to 1/2 turn • This will allow the cylinder to be closed quickly in case of fire. • Cylinder valve wrenches should be left in place on cylinders that do not have a hand wheel.
Oxygen and Acetylene Regulator Pressure Settings • Regulator pressure may vary with different torch styles and tip sizes. • PSI (pounds per square inch) is sometimes shown as PSIG (pounds per square inch -gauge) • Common gauge settings for cutting – 1/4” material Oxy 30 -35 psi Acet 3 -9 psi – 1/2” material Oxy 55 -85 psi Acet 6 -12 psi – 1” material Oxy 110 -160 psi Acet 7 -15 psi • Check the torch manufactures data for optimum pressure settings
Regulator Pressure Settings • The maximum safe working pressure for acetylene is 15 PSI !
Typical torch styles • A small welding torch, with throttle valves located at the front end of the handle. Ideally suited to sheet metal welding. Can be fitted with cutting • attachment in place of the welding head shown. Welding torches of this general design are by far the most widely used. They will handle any oxyacetylene welding job, can be fitted with multiflame (Rosebud) heads for heating applications, and accommodate cutting attachments that will cut steel 6 in. thick. • A full-size oxygen cutting torch which has all valves located in its rear body. Another style of cutting torch, with oxygen valves located at the front end of its handle.
Typical startup procedures • Verify that equipment visually appears safe IE: Hose condition, visibility of gauges • Clean torch orifices with a “tip cleaners” (a small wire gauge file set used to clean slag and dirt form the torch tip) • Crack (or open) cylinder valves slightly allowing pressure to enter the regulators slowly • Opening the cylinder valve quickly will “Slam” the regulator and will cause failure.
Typical startup procedures • Never stand directly in the path of a regulator when opening the cylinder • Check for leaks using by listening for “Hissing” or by using a soapy “Bubble” solution • Adjust the regulators to the correct operating pressure • Slightly open and close the Oxygen and Acetylene valves at the torch head to purge any atmosphere from the system.
Typical startup procedures • Always use a flint and steel spark lighter to light the oxygen acetylene flame. • Never use a butane lighter to light the flame
Flame Settings • There are three distinct types of oxy-acetylene flames, usually termed: – Neutral – Carburizing (or “excess acetylene”) – Oxidizing (or “excess oxygen” ) • The type of flame produced depends upon the ratio of oxygen to acetylene in the gas mixture which leaves the torch tip.
Pure Acetylene and Carburizing Flame profiles
Neutral and Oxidizing Flame Profiles
Flame definition • The neutral flame (Fig. 4 -1) is produced when the ratio of oxygen to acetylene, in the mixture leaving the torch, is almost exactly one-toone. It’s termed ”neutral” because it will usually have no chemical effect on the metal being welded. It will not oxidize the weld metal; it will not cause an increase in the carbon content of the weld metal. • The excess acetylene flame (Fig. 4 -2), as its name implies, is created when the proportion of acetylene in the mixture is higher than that required to produce the neutral flame. Used on steel, it will cause an increase in the carbon content of the weld metal. • The oxidizing flame (Fig. 4 -3) results from burning a mixture which contains more oxygen than required for a neutral flame. It will oxidize or ”burn” some of the metal being welded.
Quiz time • The regulator diaphragm is often made from _______? A: reinforced rubber B: malleable iron C: tempered aluminum D: stainless steel
Quiz time • The hose nuts for oxygen and acetylene differ greatly, because the acetylene hose nut has. A: a left hand thread. B: has a grove cut around it. C: may have ACET stamped on it. D: All of the above.
Quiz time • An oxygen cylinder must be able to withstand a ____ pressure of 3300 psi (22753 k. Pa) to be qualified for service. A: atmospheric B: hydrostatic C: hydroscopic D: vapor
Quiz time • Why is the area above 15 psig often marked with a red band on a acetylene low pressure regulator ? • Answer – Acetylene pressure above 15 psig is unstable and should not be used
Quiz time • True or False ? – A flint and steel spark lighter is the generally used to light the oxyacetylene flame. • Answer: True
Quiz time • Acetylene cylinder fuse plugs melt at a temperature of ____° F or 100°C • Answer – 212°F
Quiz time • What is the maximum safe working gauge pressure for acetylene gas? A: 8 psig (55 k. Pa) B: 15 psig (103 k. Pa) C: 22 psig (152 k. Pa) D: 30 psig (207 k. Pa)
Quiz time • The color of and oxygen hose on a oxyacetylene welding outfit is ______? • Answer – Green
Quiz time • The type of safety device is used on a oxygen cylinder. A: A fusible plug B: A check valve C: A pressure safety disk D: A spring loaded plug
Quiz time • True or False ? – The regulator is closed when the adjusting screw is turned out. • Answer: True
Quiz time • The color of and acetylene oxygen hose on a oxyacetylene welding outfit is ______? • Answer – Red
Quiz time • No part of an oxygen cylinder walls may be thinner than _______? A: 1/4”in (6. 4 mm) B: 3/8”in (9. 5 mm) C: 3/16”in (4. 8 mm) D: 7/32”in (5. 6 mm)
Quiz time • To prevent the occurrence of flashbacks, a ____ should be installed between either the torch and hoses or regulators and hoses. A: a two way check valve. B: flame screen. C: flashback arrestor. D: three way check valve.
Quiz time • What type of safety device is used on a acetylene cylinder. A: A spring loaded plug B: A pressure safety disk C: A fusible plug D: A check valve
Quiz time • Mixing _______ and water will produce acetylene gas. A: calcium carbide B: potassium carbonate C: carbon dioxide D: acetylene carbide
Modern Welding York County School of Technology