Presentation on theme: "LIQUID STATE PROCESSES"— Presentation transcript:
1 LIQUID STATE PROCESSES Partial melting and fusion of jointPhysical and mechanical changes taking placeCan be with application of pressure or by addition of filler materialPrior to joining, PREPARATION TO BE DONESTANDARDS- AWS; ASTM-TYPES OF GROOVES, JOINTSNITCDr. 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 applicationThe 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 OPEN ACETYLENE AND IGNITE OPEN OXYGEN AND ADJUST FLAME STEPS for OAWPREPARE THE EDGES AND MAINTAIN PROPER POSITION ………………………….(USE OF FIXTURES, CLAMPS)OPEN ACETYLENE AND IGNITEOPEN OXYGEN AND ADJUST FLAMEHOLD TORCH AT ABOUT 45O AND FILLER METAL AT 30 TO 40 OTOUCH FILLER ROD TO JOINT AND CONTROL MOVEMENTSINGLE BEAD MADEDr. N. RAMACHANDRAN, NITC
9 FOR DEEP JOINTS, MULTIPLE PASSES CLEANING EACH WELD BEAD IS IMPORTANT EQUIPMENT- WELDING TORCH- VARIOUS SIZES AND SHAPESCYLINDERS DIFFERENT THREADS, ANCHORED AND NOT DROPPEDDr. N. RAMACHANDRAN, NITC
10 LOW COST. MANUAL AND HENCE SLOW CAPABILITIESLOW COST. MANUAL AND HENCE SLOWPORTABLE, VERSATILE AND ECONOMICAL FOR LOW QUANTITY AND REPAIR WORKSFOR ALL FERROUS AND NONFERROUS METALSLIMITATIONS THICKNESS < 6 MMSKILL ESSENTIAL---FOR PIPE, PRESSURE VESSELS, LOAD BEARING STRUCTURAL MEMBERSDr. N. RAMACHANDRAN, NITC
11 Oxygen CylindersOxygen is stored within cylinders of various sizes and pressures ranging from 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 Oxygen CylindersCylinders are regularly re-tested using hydrostatic (NDE) while in serviceCylinders are regularly chemically cleaned and annealed to relieve “jobsite” stresses created by handling .Dr. N. RAMACHANDRAN, NITC
13 Cylinder Transportation Never transport cylinders without the safety caps in placeNever transport with the regulators in placeNever 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 CylindersOxygen 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 carefullyDr. N. RAMACHANDRAN, NITC
15 Pressure Regulators for Cylinders Reduce high storage cylinder pressure to lower working pressure.Most regulators have a gauge for cylinder pressure and working pressure.Dr. N. RAMACHANDRAN, NITC
16 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 varyRegulator diaphragms are made of stainless steelDr. N. RAMACHANDRAN, NITC
17 Pressure Regulators Gauges Using a “Bourdon” movement Gas entering the gauge fills a Bourdon tubeAs 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.Dr. N. RAMACHANDRAN, NITC
18 Regulator Hoses 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 itDr. N. RAMACHANDRAN, NITC
19 Check Valves & Flashback Arrestors Check valves allow gas flow in one direction onlyFlashback 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.Dr. N. RAMACHANDRAN, NITC
20 Acetylene GasVirtually 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 CylindersAcetylene 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 Acetylene CylindersCylinders are filled with a very porous substance “monolithic filler” to help prevent from large pockets of pure acetylene formingCylinders have safety (Fuse) plugs in the top and bottom designed to melt at 212° F (100 °C)Dr. N. RAMACHANDRAN, NITC
23 Acetylene ValvesAcetylene cylinder shut off valves should only be opened 1/4 to 1/2 turnThis 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.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 cutting1/4” material Oxy 30-35psi Acet 3-9 psi1/2” material Oxy 55-85psi Acet 6-12 psi1” material Oxy psi Acet 7-15 psiCheck the torch manufactures data for optimum pressure settingsDr. N. RAMACHANDRAN, NITC
25 Regulator Pressure Settings The maximum safe working pressure for acetylene is 15 PSI !Dr. N. RAMACHANDRAN, NITC
26 Typical torch stylesA small welding torch, with throttle valves located at the front end of the handle. Ideally suited to sheet metal welding. Can be fitted with cuttingattachment 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.Dr. N. RAMACHANDRAN, NITC
28 FuelsThe 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.
29 AcetyleneAcetylene 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.
30 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.
31 HydrogenHydrogen has a clean flame and is good for use on aluminum. It can be used at a higher pressure than acetylene and istherefore 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.PropanePropane does not burn as hot as acetylene, and so can only be used for cutting, not for welding.PropylenePropylene is used in production welding.
32 MAPP gasMAPP 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.
33 Typical startup procedures Verify that equipment visually appears safe ie: Hose condition, visibility of gaugesClean 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 slowlyOpening the cylinder valve quickly will “Slam” the regulator and will cause failure.Dr. N. RAMACHANDRAN, NITC
34 Typical startup procedures Never stand directly in the path of a regulator when opening the cylinderCheck for leaks using by listening for “Hissing” or by using a soapy “Bubble” solutionAdjust the regulators to the correct operating pressureSlightly open and close the Oxygen and Acetylene valves at the torch head to purge any atmosphere from the system.Dr. N. RAMACHANDRAN, NITC
35 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 flameDr. N. RAMACHANDRAN, NITC
36 Flame SettingsThere are three distinct types of oxy-acetylene flames, usually termed:NeutralCarburizing (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
37 TYPES of FLAMESNeutral- with inner cone(30400C-33000C), outer envelope, (21000C near inner cone, 12600C at tip)- high heatingReducing- Bright luminous inner cone, acetylene feather, blue envelopeLow temperature, good for brazing, soldering, flame hardeningHydrogen, methyl acetylene, propadiene also used as fuel.Oxidising- pointed inner cone, small and narrow outer envelopeHarmful for steels, good for Cu- Cu based alloysNITCDr. N. RAMACHANDRAN, NITC
38 OXY ACETYLENE WELDING (OAW) Types of Flames NeutralReducingOxidisinghigh heatinglow temperaturegood for Cu- Cu alloysDr. N. RAMACHANDRAN, NITC
39 Pure Acetylene and Carburizing Flame profiles Dr. N. RAMACHANDRAN, NITC
40 Neutral and Oxidizing Flame Profiles Dr. N. RAMACHANDRAN, NITC
41 Flame definitionThe 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
42 Quiz time The regulator diaphragm is often made from _______? A: reinforced rubberB: malleable ironC: tempered aluminumD: stainless steelDr. N. RAMACHANDRAN, NITC
43 Quiz timeThe 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
44 Quiz timeAn oxygen cylinder must be able to withstand a ________ pressure of 3300 psi (22753 kPa) to be qualified for service A: atmosphericB: hydrostaticC: hydroscopicD: vaporDr. N. RAMACHANDRAN, NITC
45 Quiz timeWhy is the area above 15 psig often marked with a red band on a acetylene low pressure regulator ?AnswerAcetylene pressure above 15 psig is unstable and should not be usedDr. N. RAMACHANDRAN, NITC
46 Quiz time True or False ? Answer: True A flint and steel spark lighter is the generally used to light the oxyacetylene flame.Answer: TrueDr. N. RAMACHANDRAN, NITC
47 Quiz timeAcetylene cylinder fuse plugs melt at a temperature of ________° F or 100°CAnswer212°FDr. N. RAMACHANDRAN, NITC
48 Quiz timeWhat 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
49 Quiz timeThe colour of and oxygen hose on a oxyacetylene welding outfit is ______?AnswerGreen/BlueDr. N. RAMACHANDRAN, NITC
50 Quiz time The type of safety device is used on a oxygen cylinder. A: A fusible plugB: A check valveC: A pressure safety diskD: A spring loaded plugDr. N. RAMACHANDRAN, NITC
51 Quiz time True or False ? Answer: True The regulator is closed when the adjusting screw is turned out.Answer: TrueDr. N. RAMACHANDRAN, NITC
52 Quiz timeThe colour of acetylene hose on a oxyacetylene welding outfit is ______?AnswerRedDr. N. RAMACHANDRAN, NITC
53 Quiz timeNo 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)Dr. N. RAMACHANDRAN, NITC
54 Quiz timeTo 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.Dr. N. RAMACHANDRAN, NITC
55 Quiz time What type of safety device is used on a acetylene cylinder. A: A spring loaded plugB: A pressure safety diskC: A fusible plugD: A check valveDr. N. RAMACHANDRAN, NITC
56 Quiz time Mixing _______ and water will produce acetylene gas. A: calcium carbideB: potassium carbonateC: carbon dioxideD: acetylene carbideDr. N. RAMACHANDRAN, NITC
57 Cutting For cutting, the set-up is a little different. A cutting torch has a 90-degree angled head with six orifices placed around a central jet.Oxygen Rich Butane Blow Torch FlameFuel Rich Butane Blow Torch FlameThe six outer jets are for oxygen and acetylene (oxy-propane devices use an array of many jets) and the central jet carries only oxygen.Dr. N. RAMACHANDRAN, NITC
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