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Oxyfuel Cutting and Welding 8609-A Instructional Materials Service Texas A&M University
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, and 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 or operation to be performed –Thickness of metal & type of welded joint to be produced –Physical properties of metals –Chemical properties of metals
Propane (C 3 H)
Supplied in a liquid form under positive pressure, which varies with temperature Most oxyfuel cutting torches can use LP gas, but special hoses and cutting tips are required. Readily available in most areas Due to cost, propane cutting is heavily used in the metal recycling industry.
Propylene (C 3 H 6 )
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 withdrawal pressure limitations that are necessary with acetylene Approximately 5% propylene, 87% propane & traces of other gases
Acetylene (C 2 H 2 )
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 gases Performs most functions well and is widely available
Compressed Natural Gas (CH 4 )
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 (O 2 )
Odorless, colorless, tasteless & 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 in 2 (psi) Supports combustion and is explosive if handled improperly Cylinder sizes = 80 to 244 ft 3
Facts About Acetylene (C 2 H 2 )
Colorless, but has a very distinct odor Highly combustible Cylinder sizes = 60 to 300 ft 3 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 approximately 250 psi May 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 (1,400 o F to 1,800 o F), then oxidizes and blows the slag from the cut with a stream of pure oxygen. Oxyfuel welding fuses two pieces 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 flame is also used to bend, shape, preheat, stress relieve, post-heat & temper metal.
Assembly of the Oxyfuel Rig
A.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 accumulation 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.Attach 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.
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 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 recommended –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: –Regulated by preheat oxygen control valve –Operated by depressing the cutting oxygen lever
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 gas mixture –Size is determined by drill size of orifice
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 ventilated areas adequately separated from other activities. Acetylene pressure in the lines should NEVER exceed 15 psi.
Open the acetylene cylinder valve ¼ to ½ 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 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 open 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 tape. 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 cylinders 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 full or empty) MUST be stored separately in accordance with safety and fire codes.
Set-Up Procedure for Oxyfuel Torch Nozzle
1.Check torch body for closed valves. 2.Check regulator for loose regulator adjusting screw. 3.Open acetylene cylinder valve ¼ to ½ turn (wheel-type valves one turn) maximum. 4.Turn acetylene 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 to neutral flame; no acetylene feather and sharp inner cone When 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
1.Turn 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 oxygen 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 hours a day.
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 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 needed
Steps to Follow in Making a Cut 1.Hold blowpipe perpendicular to surface of metal unless bevels are to be cut –Hold the 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 tip –Hold tip so that two preheat holes are in line with the cut 2.Hold torch at edge of metal until metal begins to melt –Top of torch may be slanted toward the cut & changed to a vertical position as cut progresses
3.Press down slowly on the cutting oxygen lever until cutting valve is completely open –When the cut is through the metal, move torch along mark 4.Tilt torch tip toward direction of cut on thin metal –It should be held in a vertical position on thick metal
5.Move torch slowly along surface or oxygen stream will not pass completely through thick metal –To restart the cut, release cutting lever and reheat metal again before pressing cutting level –Losing the cut may cause irregular edges. 6.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 Cut Notice that the top edge is square and that the drag lines show a slight curve. Oxygen Pressure Too Low Produces a cut with rough surface, makes it difficult to hold cut and results in slow speed with too much lag.
Speed Too Fast Produces a rough cut with pronounced drag line very similar to too low oxygen pressure. Oxygen Pressure Too High Produces a rough surface, melts down top edge and wastes oxygen.
Too Much Acetylene in Preheats Reduces cutting speed approximately 25%. Forms carbon deposits on cut surface and wastes acetylene. Correct Cut Here the factors of tip size, pressures and speed are correct…results in square top edge and uniform narrow kerf.
Preheats Too Heavy Top edge is melted down, kerf irregular and excess gas is consumed by the preheat flame. Preheats Too Small Wastes time as maximum speed cannot be obtained. Low cutting speed results in gouges at bottom edge of cut.
Oversize Tip Produces a kerf which is too wide, causing not only a waste of plate but also a waste of both gases. Undersize Tip Inefficient 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 1.Hold blowpipe tip perpendicular to the surface until a spot on the surface begins to melt 2.Raise torch until tip is about 1/2” from the surface and slowly press the lever as torch is raised 3.Move tip to one side of the heated area so that the slag can be blown out
4.Move inner cone within about 1/8” from the surface and make the cut on the inside edge of the hole 5.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 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 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. Align 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 45 o 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; 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 puddle 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 burns 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 45 o to the surface –Welding rod should be held at 45 o, but slanted away from the 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 together and welded, with or without beveling Fillet welding: –Metal pieces are joined together forming an angle
Welding 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 cast 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 steel. 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 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.
Application of an all alloy material to another metal for the purpose of reducing wear Procedure: –Thoroughly clean the metal before applying alloy. –Place the material to be hardsurfaced in a flat position. –Heat a small section of the area with an excess acetylene flame until the metal begins to sweat.
–Touch the tip of the alloy rod to the surface and melt enough of the rod to form an alloy cover 1/16” thick and a desirable width without heating the base metal to a melting point. –Maintain the hardsurfacing temperature in front of the path on the hard metal. Add just enough rod to the metal to maintain a uniform thickness and width. –Hardsurfaced metal should be allowed to cool slowly. Dry lime serves as a good cover for cooling metal. –Be sure to follow recommendations of the manufacturer of the hardsurfacing rods.
American Welding Society Certification
The American Welding Society (AWS) is the professional organization responsible for setting standards for the certification of weldors. 1 st step in becoming a highly skilled craftsman is to certify as an Entry Level Weldor
Certification process for Entry Level Weldor consists of: –A Practical Knowledge Test: Welding/cutting theory Welding/cutting inspection & testing Skill-related vocabulary Metal identification Welding variables Electrical fundamentals Welding symbol interpretation Fabrication principles & practices Safety Requires a minimum passing grade of 75%, with a minimum score of 90% on safety-related questions
–A Performance Test: Reading welding symbols Following written procedures Cutting parts to proper specifications Fitting parts correctly Performing specific welding techniques Prepare test coupon by oxyfuel (OFC) and plasma-arc cutting (PAC) –Includes both cutting straight lines and piercing holes
Checking for Cylinder Leaks
Standard acetylene cylinder contains from 90 to 154 ft 3, stored in a porous filler saturated with acetone Cylinders are filled under pressure and may develop leaks around the valve stem or in the “soft plugs” An acetylene cylinder leaking for an entire weekend into a closed facility can become a tragedy of significant proportions. –Sparks from electrical switches or pilot lights on forced-air heaters can provide the necessary ignition source.
To guard against fire damage, a good practice is to check acetylene cylinders for leaks when delivered. Materials: –Small paintbrush –One-quart container –One pint liquid soap, or a soap and water solution Procedure: 1.Lay acetylene cylinder on its side and “paint” the soft plugs with the soap solution. A leak here will cause bubbles to form.
2.Stand the cylinder upright and paint the soft plugs on the shoulders of the bottle. DO NOT try to stop leaks in or around soft plugs—call the dealer and have the cylinder replaced!! 3.Paint the regulator receptacle or main opening before attaching the regulator. If the bottle shows a leak now, this means that the main valve seat is damaged and leaking, regardless of how tightly the cylinder valve is closed. 4.Paint the main valve stem around the ring nut at the top of the valve. If a leak is present here, stop the leak by tightening the ring nut with an adjustable wrench.
5.Attach the regulator to the cylinder and open the cylinder valve; paint the regulator ring nut and repaint the cylinder valve stem. 6.Ask the distributor that any leaking bottles be replaced at their cost. Oxygen cylinders can be checked in the same manner EXCEPT: –A commercial leak detector liquid such as “Snoop TM ” should be used (BEST IDEA). OR –A non-petroleum based liquid detergent must be used (such as Ivory TM liquid). –Remember, oxygen cylinders are pressurized to about 2,200 lbs. psi.
Acknowledgements Kirk Edney, Curriculum Specialist, Instructional Materials Service, edited and reviewed this PowerPoint presentation. Kristie Weller, Undergraduate Technician, Instructional Materials Service, organized and developed the information used in this PowerPoint presentation.
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