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1、Oxyfuel Cutting and Welding,Oxyfuel:the process of combining pure oxygen with a combustible fuel gas to produce a flameCan be used for welding,brazing,cutting,and heating metalsOxygen&fuel gases are stored under pressure in cylinders and are released as individual gases through valves,regulators,and
2、 hoses.Mixed as they flow through torch assembliesBurn as they are discharged through special tips,Fuel gases:Propane,natural gas,propylene&acetyleneVary in their chemical compositionReact with the metal in different waysFactors to consider in selecting a gas:Availability&costWelding process or oper
3、ation to be performedThickness of metal&type of welded joint to be producedPhysical properties of metalsChemical properties of metals,Propane(C3H),Supplied in a liquid form under positive pressure,which varies with temperatureMost oxyfuel cutting torches can use LP gas,but special hoses and cutting
4、tips are required.Readily available in most areasDue to cost,propane cutting is heavily used in the metal recycling industry.,Propylene(C3H6),Has been used for approximately 30 yearsStable in both liquid and gas statesEconomicalProduces little slagHas a high heat valueDoes not have the withdrawal pr
5、essure limitations that are necessary with acetyleneApproximately 5%propylene,87%propane&traces of other gases,Acetylene(C2H2),Most widely used fuel gas for welding and cutting applicationsProduces a clean weld and a controllable flameLess stable and more expensive than other fuel gasesPerforms most
6、 functions well and is widely available,Compressed Natural Gas(CH4),Adaptable for cutting,soldering,brazing,and preheatingA water seal or blowback valve to prevent backfiring into the gas supply line must protect the natural gas source.,Facts About Oxygen(O2),Odorless,colorless,tasteless&heavier tha
7、n airMakes up about 20%of the atmosphereWill not burn by itselfProduced commercially by causing air to liquefyCompressed into steel cylinders at 1,800 to 2,400 pounds per in2(psi)Supports combustion and is explosive if handled improperlyCylinder sizes=80 to 244 ft3,Facts About Acetylene(C2H2),Colorl
8、ess,but has a very distinct odorHighly combustibleCylinder sizes=60 to 300 ft3Cylinder contains a porous substance saturated with liquid acetoneAcetylene is pumped into the cylinder,displacing some of the acetoneNot under extremely high pressureFull cylinder is pressurized to approximately 250 psiMa
9、y not be withdrawn at a rate higher than 15 psi,Functions of Oxyfuel Heat,Oxyfuel cutting of mild carbon steel heats the metal to rekindling temperature(1,400oF to 1,800oF),then oxidizes and blows the slag from the cut with a stream of pure oxygen.Oxyfuel welding fuses two pieces of metal by heating
10、 them to the melting point with a combustible mixture of oxygen and fuel gas.Can be done with or without the use of a welding rodBrazing:the joining of metals by adding bronze fillerSoft and hard solders(lead&silver alloys)are the filler materials used in soldering.The oxyfuel flame is also used to
11、bend,shape,preheat,stress relieve,post-heat&temper metal.,Assembly of the Oxyfuel Rig,Secure the oxygen and fuel gas cylinders to a wall,a special cylinder cart,or a special rack if transported to job sites in a truck.Remove the valve protection caps and wipe off any dirt accumulation with a clean,d
12、ry cloth(free from oil or grease).Slightly open(crack)both cylinders to make sure they do not stick and to blow out any dirt or dust lodged in the valve.Close the valves.,Check all valves,connections,and soft plugs for leaks with mild soapy water and a clean brush.Attach the regulators to the cylind
13、ers pointing toward the sky to prevent someone from getting in front of the regulator.The regulators,safety check valves,and hoses should be tightened securely with a wrench.Do Not use a wrench to attach the welding tip or cutting attachment to the torch.,Oxyfuel Equipment,Designed with several buil
14、t-in safety precautions:Oxygen hoses are usually green.Fuel gas hoses are red.All oxygen connections and cylinders have right-hand threads.All fuel gas connections and cylinders have left-hand threads.Fuel gas fittings have a“V”notch cut around the the outside of the connectors.Oxygen fittings and c
15、onnectors are smooth.,Cylinders:TwoRegulators:Two setsTwo stage regulators are the safest to use.Hoses:Color-coded&specifically designed based on useType R:designed specifically for acetylene useType T:approved for all fuel gases,Safety Check Valves:Two sets recommendedAttach between regulators and
16、hoses and between hoses and torch to prevent reverse flow of the gases and flame that could cause hose fires,regulator ruptures,and cylinder firesTorch Handle:Regulated by two valvesOften equipped with internal reverse flow check valvesCutting Attachment:Regulated by preheat oxygen control valveOper
17、ated by depressing the cutting oxygen lever,Torch Butt,Cutting Attachment,Cutting Tips:3 to 8 preheat orifices and 1 oxygen-cutting orificeDrill size determines tip sizePropane tip is a 2-piece tip with at least 6 preheat orificesWelding Tip:1 orifice for gas mixtureSize is determined by drill size
18、of orifice,Safety Precautions,Keep oil and grease away from all parts of the oxyfuel apparatus.Secure the cylinders in an upright position so they cannot be overturned.Face the regulator gauges toward the sky making it impossible to stand in front of them.Store and use oxyfuel units in well ventilat
19、ed areas adequately separated from other activities.Acetylene pressure in the lines should NEVER exceed 15 psi.,Open the acetylene cylinder valve to turns;if it is the wheel type,open all the way.Use an approved spark lighter to light the torch;never use matches or cigarette lighters.NEVER use oxyge
20、n to operate pneumatic tools,blow out lines,inflate tires,or dust off clothing.NEVER hang clothing on cylinders,running the risk of saturating them with oxygen and acetylene.DO NOT convert an acetylene regulator to an oxygen regulator or vice versa.,Slowly open the oxygen cylinder valve to prevent a
21、 sudden surge of pressure.Release or loosen the regulator adjusting screw before opening a cylinder valve.DO NOT walk with a lighted torch or lay down a lighted torch.Purge hoses before attaching the torchRepair hoses with proper hose splices,not friction tape.NEVER use a leaking hose.Test for leaks
22、 with soap and water,not matches.,If valves on cylinders are faulty or too tight,notify the supplier;undue force would be dangerous.Keep a fire extinguisher handy at all times.Dress properly and wear eye protection.Prevent heat and sparks from getting to cylinders and hoses.DO NOT strike an arc on a
23、 cylinder or hit a cylinder with a metal object.NEVER use a cylinder as a ground in an electrical circuit.,NEVER guess;get the correct information from a qualified person.Mark,isolate,or otherwise designate empty cylinders.Oxygen and fuel gas cylinders(either full or empty)MUST be stored separately
24、in accordance with safety and fire codes.,Set-Up Procedure for Oxyfuel Torch Nozzle,Check torch body for closed valves.Check regulator for loose regulator adjusting screw.Open acetylene cylinder valve to turn(wheel-type valves one turn)maximum.Turn acetylene regulator adjusting screw to desired work
25、ing pressure.Open oxygen cylinder valve completely.Turn oxygen regulator adjusting screw to desired working pressure.,Crack acetylene torch valve and light the torch,open acetylene torch valve until soot disappears.Open oxygen torch valve to adjust to neutral flame;no acetylene feather and sharp inn
26、er coneWhen welding,the ratio of oxygen to acetylene is approximately 1:1.Oxygen and acetylene settings will vary depending on the attachment tip and thickness of metal to cut or weld.,Types of Oxyfuel Flames,Shutdown Procedure for Torch Nozzle,Turn off acetylene valve on torch butt.NEVER turn off o
27、xygen first.Turn off oxygen valve on torch butt.Close acetylene cylinder valve.Bleed acetylene hose by opening acetylene torch valve;close valve.Back acetylene regulator adjusting screw until loose.Close oxygen cylinder valve.,Bleed oxygen hose by opening oxygen torch valve;close valve.Back oxygen r
28、egulator adjusting screw until loose.Recheck valves for closure,roll up hoses.If rig is not to be used for some time,remove the regulators and put the safety caps back on the cylinders.NEVER leave equipment under pressure 24 hours a day.,Cutting Metals,Metal to be cut should be clean,marked with a p
29、unch or soapstone,and placed in a suitable position for cutting.DO NOT cut over a concrete floor.Use a container or special cutting table device to catch the molten metal.Oxyfuel cutting is limited to ferrous metals.Steels with a high tungsten or chromium content or stainless steel cannot be cut wit
30、h oxyfuel.Cast iron is more difficult to cut than steel.An excess fuel flame is usedMore oxygen pressure is needed,Steps to Follow in Making a Cut,Hold blowpipe perpendicular to surface of metal unless bevels are to be cutHold the flame inner cone about 1/16 to 1/8 inch above the plate.Proper distan
31、ce away from plate will prevent metal from sticking to the tipHold tip so that two preheat holes are in line with the cutHold torch at edge of metal until metal begins to meltTop of torch may be slanted toward the cut&changed to a vertical position as cut progresses,Press down slowly on the cutting
32、oxygen lever until cutting valve is completely openWhen the cut is through the metal,move torch along markTilt torch tip toward direction of cut on thin metalIt should be held in a vertical position on thick metal,Move torch slowly along surface or oxygen stream will not pass completely through thic
33、k metalTo restart the cut,release cutting lever and reheat metal again before pressing cutting levelLosing the cut may cause irregular edges.When beveling plate edges or cutting at an angle,lean the tip at the desired angle and hold the torch parallel to the work.,Correct CutNotice that the top edge
34、 is square and that the drag lines show a slight curve.Oxygen Pressure Too LowProduces a cut with rough surface,makes it difficult to hold cut and results in slow speed with too much lag.,Speed Too FastProduces a rough cut with pronounced drag line very similar to too low oxygen pressure.Oxygen Pres
35、sure Too HighProduces a rough surface,melts down top edge and wastes oxygen.,Too Much Acetylene in PreheatsReduces cutting speed approximately 25%.Forms carbon deposits on cut surface and wastes acetylene.Correct CutHere the factors of tip size,pressures and speed are correctresults in square top ed
36、ge and uniform narrow kerf.,Preheats Too HeavyTop edge is melted down,kerf irregular and excess gas is consumed by the preheat flame.Preheats Too SmallWastes time as maximum speed cannot be obtained.Low cutting speed results in gouges at bottom edge of cut.,Oversize TipProduces a kerf which is too w
37、ide,causing not only a waste of plate but also a waste of both gases.Undersize TipInefficient cut because piece will not drop when end is reached as slag has not cleared the kerf and cutting time will be excessive.,Steps to Follow When Piercing Holes,Hold blowpipe tip perpendicular to the surface un
38、til a spot on the surface begins to meltRaise torch until tip is about 1/2”from the surface and slowly press the lever as torch is raisedMove tip to one side of the heated area so that the slag can be blown out,Move inner cone within about 1/8”from the surface and make the cut on the inside edge of
39、the holeTo facilitate the cutting of a hole in thick metal,drill a hole 1/4”in diameter or larger and start the piercing in this hole.,Care of Oxyfuel Tips,Tips frequently become spattered with metal or other materials that may cause inferior work.To clean tips:Rub emery cloth,steel wool,or the file
40、 on a tip cleaner to clean and square the tip point.Insert the correct size cleaner into each orifice.Push in and pull out;do not twist or bend the cleaner.Open oxygen slightly during this procedure to blow out foreign particles.Care should be taken not to damage the threads and seats of the tips.,P
41、reparing Metal for Welding,Free the metal from oil,paint,grease,dirt,rust,and other foreign material.Heat the metal with the torch,and then clean with a wire brush.Thick metal should be beveled with a grinder or torch.Align the plates to be welded and tack weld them to prevent warping.,Proper Weldin
42、g Tip Positions,The blowpipe can be held like a hammer when standing or like a pencil when sitting.The tip and welding rod should be held at a 45o angle to the work surface.The inner cone flame should be 1/16”to 1/8”above the metal.Preheating the metal is very important in making a successful weld;t
43、herefore,the flame should be moved in the direction of the weld,and the cone should stay inside the puddle.,Oxyfuel Welding Procedures,One of the most important steps in learning to weld with oxyfuel is to carry a molten puddle of metal along the line or seam of parts to be joined.Forming&running th
44、e bead:Flame held at starting point until a bright round pool(1/4”to 3/8”in diameter)is formedWelding speed should be adapted to maintain a uniform puddle width.Inner cone held 1/16”to 1/8”above surfaceSlow speed:flame burns a hole through the metalFast speed:bead will be irregular and narrow,Most c
45、ommon movement pattern for fusion welding is the circular motionZigzag motion is best when using a filler rodTorch should be held at about 45o to the surfaceWelding rod should be held at 45o,but slanted away from the torch tipRod diameter should be equal to the thickness of the metalTorch may be hel
46、d so tip is pointed in direction of weld(forehand welding)or tip pointed toward weld(backhand welding),Types of Welded Joints,Most are either butt joints or fillet jointsButt welding:Two pieces of metal are butted together and welded,with or without bevelingFillet welding:Metal pieces are joined tog
47、ether forming an angle,Welding Cast Iron,Usually done with a bronze rod,unless the color of the base metal must be matchedCast iron rods require higher preheating than bronze rods.,Practice procedure for welding cast iron:Select the correct flux.Clean and bevel the edges of the stock.Use a 3/16”rod
48、with a neutral flame and tack the ends together.Heat the rod tip to a red-colored heat and dip it in the flux,then dip the tip into the molten puddle of cast iron.Weld in the same manner as fusion welding on mild steel.Dip the hot tip of the rod in flux from time to time.If bubbles appear,add more f
49、lux.,Practice Procedure for Braze Welding:Does not require extremely high welding temperatureClean surface to be weldedBevel and align edges of the metalUse neutral flame and heat the end of the rod and dip into the fluxHeat the area to be welded to a dull red and tack endsApply flux from rod on hea
50、ted area,then pass rod into flame and deposit a small amount of bronze at the intervals until the weld is complete.Add flux from time to time.,Hardsurfacing,Application of an all alloy material to another metal for the purpose of reducing wearProcedure:Thoroughly clean the metal before applying allo
