氧乙炔-切割和焊接-Oxyfuel-Cutting-and-Welding课件.ppt

1、Oxyfuel Cutting and Welding Oxyfuel:the process of combining pure oxygen with a combustible fuel gas to produce a flame Can be used for welding,brazing,cutting,and heating metals Oxygen&fuel gases are stored under pressure in cylinders and are released as individual gases through valves,regulators,a

2、nd hoses.Mixed as they flow through torch assemblies Burn as they are discharged through special tips Fuel gases:Propane,natural gas,propylene&acetylene Vary in their chemical composition React with the metal in different ways Factors to consider in selecting a gas:Availability&cost Welding process

3、or operation to be performed Thickness of metal&type of welded joint to be produced Physical properties of metals Chemical properties of metalsPropane(C3H)Supplied in a liquid form under positive pressure,which varies with temperature Most oxyfuel cutting torches can use LP gas,but special hoses and

4、 cutting tips are required.Readily available in most areas Due to cost,propane cutting is heavily used in the metal recycling industry.Propylene(C3H6)Has been used for approximately 30 years Stable in both liquid and gas states Economical Produces little slag Has a high heat value Does not have the

5、withdrawal pressure limitations that are necessary with acetylene Approximately 5%propylene,87%propane&traces of other gasesAcetylene(C2H2)Most widely used fuel gas for welding and cutting applications Produces a clean weld and a controllable flame Less stable and more expensive than other fuel gase

6、s Performs most functions well and is widely availableCompressed Natural Gas(CH4)Adaptable for cutting,soldering,brazing,and preheating A 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

7、&heavier than air Makes up about 20%of the atmosphere Will not burn by itself Produced commercially by causing air to liquefy Compressed into steel cylinders at 1,800 to 2,400 pounds per in2(psi)Supports combustion and is explosive if handled improperly Cylinder sizes=80 to 244 ft3Facts About Acetyl

8、ene(C2H2)Colorless,but has a very distinct odor Highly combustible Cylinder sizes=60 to 300 ft3 Cylinder contains a porous substance saturated with liquid acetone Acetylene is pumped into the cylinder,displacing some of the acetone Not under extremely high pressure Full cylinder is pressurized to ap

9、proximately 250 psi May not be withdrawn at a rate higher than 15 psiFunctions 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 piece

10、s of metal by heating 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 rod Brazing:the joining of metals by adding bronze filler Soft and hard solders(lead&silver alloys)are the filler materials used in soldering.The oxyfuel

11、 flame is also used to bend,shape,preheat,stress relieve,post-heat&temper metal.Assembly of the Oxyfuel RigA.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.B.Remove the valve protection caps and wipe off any dirt ac

12、cumulation with a clean,dry cloth(free from oil or grease).C.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.D.Check all valves,connections,and soft plugs for leaks with mild soapy water and a clean brush.E.Attac

13、h the regulators to the cylinders pointing toward the sky to prevent someone from getting in front of the regulator.F.The regulators,safety check valves,and hoses should be tightened securely with a wrench.G.Do Not use a wrench to attach the welding tip or cutting attachment to the torch.Oxyfuel Equ

14、ipment Designed with several built-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

15、 connectors.Oxygen fittings and connectors are smooth.Cylinders:Two Regulators:Two sets Two stage regulators are the safest to use.Hoses:Color-coded&specifically designed based on use Type R:designed specifically for acetylene use Type T:approved for all fuel gases Safety Check Valves:Two sets recom

16、mended Attach between regulators and hoses and between hoses and torch to prevent reverse flow of the gases and flame that could cause hose fires,regulator ruptures,and cylinder fires Torch Handle:Regulated by two valves Often equipped with internal reverse flow check valves Cutting Attachment:Regul

17、ated by preheat oxygen control valve Operated by depressing the cutting oxygen leverTorch ButtCutting Attachment Cutting Tips:3 to 8 preheat orifices and 1 oxygen-cutting orifice Drill size determines tip size Propane tip is a 2-piece tip with at least 6 preheat orifices Welding Tip:1 orifice for ga

18、s mixture Size is determined by drill size of orificeSafety 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.St

19、ore and use oxyfuel units in well ventilated 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 matc

20、hes or cigarette lighters.NEVER use oxygen 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 ope

21、n the oxygen cylinder valve to prevent a 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 torch Repair hoses with proper hose splices,not friction tap

22、e.NEVER use a leaking hose.Test for leaks 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 cylin

23、ders and hoses.DO NOT strike an arc on a 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 f

24、ull or empty)MUST be stored separately in accordance with safety and fire codes.Set-Up Procedure for Oxyfuel Torch Nozzle1.Check torch body for closed valves.2.Check regulator for loose regulator adjusting screw.3.Open acetylene cylinder valve to turn(wheel-type valves one turn)maximum.4.Turn acetyl

25、ene regulator adjusting screw to desired working pressure.5.Open oxygen cylinder valve completely.6.Turn oxygen regulator adjusting screw to desired working pressure.7.Crack acetylene torch valve and light the torch,open acetylene torch valve until soot disappears.8.Open oxygen torch valve to adjust

26、 to neutral flame;no acetylene feather and sharp inner 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 FlamesShutdown Procedure for Torch Nozzle1.Turn

27、 off acetylene valve on torch butt.NEVER turn off oxygen first.2.Turn off oxygen valve on torch butt.3.Close acetylene cylinder valve.4.Bleed acetylene hose by opening acetylene torch valve;close valve.5.Back acetylene regulator adjusting screw until loose.6.Close oxygen cylinder valve.7.Bleed oxyge

28、n hose by opening oxygen torch valve;close valve.8.Back oxygen regulator adjusting screw until loose.9.Recheck valves for closure,roll up hoses.10.If rig is not to be used for some time,remove the regulators and put the safety caps back on the cylinders.11.NEVER leave equipment under pressure 24 hou

29、rs a day.Cutting Metals Metal to be cut should be clean,marked with a punch 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

30、 high tungsten or chromium content or stainless steel cannot be cut with oxyfuel.Cast iron is more difficult to cut than steel.An excess fuel flame is used More oxygen pressure is neededSteps to Follow in Making a Cut1.Hold blowpipe perpendicular to surface of metal unless bevels are to be cutHold t

31、he flame inner cone about 1/16 to 1/8 inch above the plate.Proper distance away from plate will prevent metal from sticking to the tipHold tip so that two preheat holes are in line with the cut2.Hold torch at edge of metal until metal begins to meltTop of torch may be slanted toward the cut&changed

32、to a vertical position as cut progresses3.Press down slowly on the cutting oxygen lever until cutting valve is completely openWhen the cut is through the metal,move torch along mark4.Tilt torch tip toward direction of cut on thin metalIt should be held in a vertical position on thick metal5.Move tor

33、ch slowly along surface or oxygen stream will not pass completely through thick metalTo restart the cut,release cutting lever and reheat metal again before pressing cutting levelLosing the cut may cause irregular edges.6.When beveling plate edges or cutting at an angle,lean the tip at the desired an

34、gle and hold the torch parallel to the work.Correct CutNotice that the top edge 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

35、 with pronounced drag line very similar to too low oxygen pressure.Oxygen Pressure 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 th

36、e factors of tip size,pressures and speed are correctresults in square top edge 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

37、 in gouges at bottom edge of cut.Oversize TipProduces a kerf which is too wide,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 Fo

38、llow When Piercing Holes1.Hold blowpipe tip perpendicular to the surface until a spot on the surface begins to melt2.Raise torch until tip is about 1/2”from the surface and slowly press the lever as torch is raised3.Move tip to one side of the heated area so that the slag can be blown out4.Move inne

39、r cone within about 1/8”from the surface and make the cut on the inside edge of the hole5.To 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

40、that may cause inferior work.To clean tips:Rub emery cloth,steel wool,or the file 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

41、particles.Care should be taken not to damage the threads and seats of the tips.Preparing 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.Al

42、ign the plates to be welded and tack weld them to prevent warping.Proper Welding 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

43、 the metal.Preheating the metal is very important in making a successful weld;therefore,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 p

44、uddle of metal along the line or seam of parts to be joined.Forming&running the bead:Flame held at starting point until a bright round pool(1/4”to 3/8”in diameter)is formed Welding speed should be adapted to maintain a uniform puddle width.Inner cone held 1/16”to 1/8”above surface Slow speed:flame b

45、urns a hole through the metal Fast speed:bead will be irregular and narrow Most common movement pattern for fusion welding is the circular motion Zigzag motion is best when using a filler rod Torch should be held at about 45o to the surface Welding rod should be held at 45o,but slanted away from the

46、 torch tip Rod diameter should be equal to the thickness of the metal Torch may be held 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 joints Butt welding:Two pieces of metal are butted

47、together and welded,with or without beveling Fillet welding:Metal pieces are joined together forming an angleWelding Cast Iron Usually done with a bronze rod,unless the color of the base metal must be matched Cast iron rods require higher preheating than bronze rods.Practice procedure for welding ca

48、st iron:Select the correct flux.Clean and bevel the edges of the stock.Use a 3/16”rod 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 s

49、teel.Dip the hot tip of the rod in flux from time to time.If bubbles appear,add more flux.Practice Procedure for Braze Welding:Does not require extremely high welding temperature Clean surface to be welded Bevel and align edges of the metal Use neutral flame and heat the end of the rod and dip into

50、the flux Heat the area to be welded to a dull red and tack ends Apply flux from rod on heated 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