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LIQUID STATE PROCESSES

LIQUID STATE PROCESSES. Partial melting and fusion of joint Physical and mechanical changes taking place Can be with application of pressure or by addition of filler material Prior to joining, PREPARATION TO BE DONE STANDARDS- AWS; ASTM- TYPES OF GROOVES, JOINTS. NITC.

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LIQUID STATE PROCESSES

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  1. LIQUID STATE PROCESSES • Partial melting and fusion of joint • Physical and mechanical changes taking place • Can be with application of pressure or by addition of filler material • Prior to joining, PREPARATION TO BE DONE STANDARDS- AWS; ASTM- TYPES OF GROOVES, JOINTS NITC Dr. N. RAMACHANDRAN, NITC

  2. OXY ACETYLENE WELDING (OAW) Dr. N. RAMACHANDRAN, NITC

  3. Oxyacetylene Welding (OAW) The oxyacetylene welding process uses a combination of oxygen and acetylene gas to provide a high temperature flame.

  4. Oxyacetylene Welding (OAW) • OAW is a manual process in which the welder must personally control the 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. Dr. N. RAMACHANDRAN, NITC

  5. Typical Oxyacetylene Welding (OAW) Station Dr. N. RAMACHANDRAN, NITC

  6. Oxy acetylene gas welding Dr. N. RAMACHANDRAN, NITC

  7. Compressed gas cylinders containing oxygen and MAPP gas Dr. N. RAMACHANDRAN, NITC

  8. STEPS for OAW • PREPARE THE EDGES AND MAINTAIN PROPER POSITION- ………………………….(USE OF FIXTURES, CLAMPS) • OPEN ACETYLENE AND IGNITE • OPEN OXYGEN AND ADJUST FLAME • HOLD TORCH AT ABOUT 45O AND FILLER METAL AT 30 TO 40 O • TOUCH FILLER ROD TO JOINT AND CONTROL MOVEMENT • SINGLE BEAD MADE Dr. N. RAMACHANDRAN, NITC

  9. FOR DEEP JOINTS, MULTIPLE PASSES • CLEANING EACH WELD BEAD IS IMPORTANT • EQUIPMENT- WELDING TORCH- VARIOUS SIZES AND SHAPES • CYLINDERS DIFFERENT THREADS, ANCHORED AND NOT DROPPED Dr. N. RAMACHANDRAN, NITC

  10. CAPABILITIES • LOW COST. MANUAL AND HENCE SLOW • PORTABLE, VERSATILE AND ECONOMICAL FOR LOW QUANTITY AND REPAIR WORKS • FOR ALL FERROUS AND NONFERROUS METALS LIMITATIONS THICKNESS < 6 MM • SKILL ESSENTIAL---FOR PIPE, PRESSURE VESSELS, LOAD BEARING STRUCTURAL MEMBERS Dr. N. RAMACHANDRAN, NITC

  11. Oxygen Cylinders • Oxygen is stored within cylinders of various sizes and pressures ranging from 2000- 2640 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. Dr. N. RAMACHANDRAN, NITC

  12. Cylinders are regularly re-tested using hydrostatic (NDE) while in service Cylinders are regularly chemically cleaned and annealed to relieve “jobsite” stresses created by handling . Oxygen Cylinders Dr. N. RAMACHANDRAN, NITC

  13. 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. Dr. N. RAMACHANDRAN, NITC

  14. 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 Oxygen Cylinders Dr. N. RAMACHANDRAN, NITC

  15. Reduce high storage cylinder pressure to lower working pressure. Most regulators have a gauge for cylinder pressure and working pressure. Pressure Regulators for Cylinders Dr. N. RAMACHANDRAN, NITC

  16. 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 for Cylinders Dr. N. RAMACHANDRAN, NITC

  17. 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. Pressure Regulators Gauges Using a “Bourdon” movement Dr. N. RAMACHANDRAN, NITC

  18. Hoses are 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 groove in the body of the nut and it may have “ACET” stamped on it Regulator Hoses Dr. N. RAMACHANDRAN, NITC

  19. 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. Check Valves &Flashback Arrestors Dr. N. RAMACHANDRAN, NITC

  20. 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. Dr. N. RAMACHANDRAN, NITC

  21. 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. Dr. N. RAMACHANDRAN, NITC

  22. Cylinders are filled with a very porous substance “monolithic filler” to help prevent from 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 Cylinders Dr. N. RAMACHANDRAN, NITC

  23. 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. Acetylene Valves Dr. N. RAMACHANDRAN, NITC

  24. 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 30-35psi Acet 3-9 psi • 1/2” material Oxy 55-85psi Acet 6-12 psi • 1” material Oxy 110-160psi Acet 7-15 psi • Check the torch manufactures data for optimum pressure settings Dr. N. RAMACHANDRAN, NITC

  25. Regulator Pressure Settings • The maximum safe working pressure for acetylene is 15 PSI ! Dr. N. RAMACHANDRAN, NITC

  26. 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 torch styles Dr. N. RAMACHANDRAN, NITC

  27. Fuels • The most commonly used fuel gas is acetylene. • Other gases used are propylene, liquified petroleum gas (LPG), propane, natural gas, hydrogen, and MAPP gas. • Acetylene and gases that liquify under cylinder pressure should only be used where it can be relied on that the gas cylinder in use will always be vertical with its valve on top. • Note that there is not a single gas called "oxyacetylene"; that misconception is sometimes found among the unknowledgeable.

  28. Acetylene • Acetylene is the fuel first used for oxy-fuel welding and remains the fuel of choice for repair work and general cutting and welding. Acetylene gas is shipped in special cylinders designed to keep the gas dissolved. • The cylinders are packed with various porous materials (e.g. kapok fibre, diatomaceous earth, or, formerly, asbestos), then filled about half way with acetone. • Acetylene dissolves into the acetone. This method is necessary because above 207 kPa (30 lbf/in²) acetylene is unstable and may explode. There is about 1700 kPa (250 lbf/in²) of pressure in the tank when full.

  29. Acetylene when burned with oxygen gives a temperature of 3200 °C to 3500 °C (5800 °F to 6300 °F), which is the highest temperature of any of the commonly used gaseous fuels. Its main disadvantage is its comparatively high cost. • As acetylene is unstable at a pressure equivalent to being roughly 33 feet = 10 meters underwater, underwater cutting and welding must use hydrogen instead of acetylene.

  30. Hydrogen • Hydrogen has a clean flame and is good for use on aluminum. It can be used at a higher pressure than acetylene and is • therefore useful for underwater welding. For small torches, hydrogen is often produced, along with oxygen, by electrolysis of water in an apparatus which is connected directly to the torch. • Propane • Propane does not burn as hot as acetylene, and so can only be used for cutting, not for welding. • Propylene • Propylene is used in production welding.

  31. MAPP gas • MAPP gas is a registered product of the Dow Chemical Company. • It is liquified petroleum gas mixed with methylacetylene-propadiene. It has the storage and shipping characteristics of LPG and has a heat value a little less than acetylene. Because it can be shipped in small containers for sale at retail stores, it is used by hobbyists. Other welding gasses that develop comparable temperatures require special procedures for safe shipping and handling.

  32. 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. Dr. N. RAMACHANDRAN, NITC

  33. 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. Dr. N. RAMACHANDRAN, NITC

  34. 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 Dr. N. RAMACHANDRAN, NITC

  35. 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. Dr. N. RAMACHANDRAN, NITC

  36. Neutral-with inner cone(30400C-33000C), outer envelope, (21000C near inner cone, 12600C at tip)- high heating Reducing- Bright luminous inner cone, acetylene feather, blue envelope Low temperature, good for brazing, soldering, flame hardening Hydrogen, methyl acetylene, propadiene also used as fuel. Oxidising- pointed inner cone, small and narrow outer envelope Harmful for steels, good for Cu- Cu based alloys TYPES of FLAMES NITC Dr. N. RAMACHANDRAN, NITC

  37. OXY ACETYLENE WELDING(OAW)Types of Flames Neutral Reducing Oxidising high heating low temperature good for Cu- Cu alloys Dr. N. RAMACHANDRAN, NITC

  38. Pure Acetylene and Carburizing Flame profiles Dr. N. RAMACHANDRAN, NITC

  39. Neutral and Oxidizing Flame Profiles Dr. N. RAMACHANDRAN, NITC

  40. Flame definition • The neutral flame is produced when the ratio of oxygen to acetylene, in the mixture leaving the torch, is almost exactly one-to-one. 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 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 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. Dr. N. RAMACHANDRAN, NITC

  41. Quiz time • The regulator diaphragm is often made from _______? A: reinforced rubber B: malleable iron C: tempered aluminum D: stainless steel Dr. N. RAMACHANDRAN, NITC

  42. 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 groove cut around it. C: may have ACET stamped on it. D: All of the above. Dr. N. RAMACHANDRAN, NITC

  43. Quiz time • An oxygen cylinder must be able to withstand a ________ pressure of 3300 psi (22753 kPa) to be qualified for service. A: atmospheric B: hydrostatic C: hydroscopic D: vapor Dr. N. RAMACHANDRAN, NITC

  44. 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 Dr. N. RAMACHANDRAN, NITC

  45. Quiz time • True or False ? • A flint and steel spark lighter is the generally used to light the oxyacetylene flame. • Answer: True Dr. N. RAMACHANDRAN, NITC

  46. Quiz time • Acetylene cylinder fuse plugs melt at a temperature of ________° F or 100°C • Answer • 212°F Dr. N. RAMACHANDRAN, NITC

  47. Quiz time • What is the maximum safe working gauge pressure for acetylene gas? A: 8 psig (55 kPa) B: 15 psig (103 kPa) C: 22 psig (152 kPa) D: 30 psig (207 kPa) Dr. N. RAMACHANDRAN, NITC

  48. Quiz time • The colour of and oxygen hose on a oxyacetylene welding outfit is ______? • Answer • Green/Blue Dr. N. RAMACHANDRAN, NITC

  49. 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 Dr. N. RAMACHANDRAN, NITC

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