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OxyFuel Equipment Section 7

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Presentation on theme: "OxyFuel Equipment Section 7"— Presentation transcript:

1 OxyFuel Equipment Section 7

2 Introduction Oxyfuel welding is a fusion welding process that uses oxygen and a fuel gas to provide the heat and shielding for welding. MAPP= (A mixture of stabilized methylacetylene and propadine.)

3 Requirements An oxyfuel system must: store the two gasses,
regulate the pressure, set the flow rate, mix the gasses, deliver the mixed gasses to the weld.

4 Fuel Gasses Propane (LPG) Natural Gas Acetylene MAPP Hydrogen
Different regulators recommenced Lower temperature flame Oxidizing flame at maximum flame temperature Natural Gas Different regulators and torches Delivered as a gas by domestic pipe system or in cylinders as LNG Lower temperature Good for brazing and soldering thin metal Acetylene Produces hottest flame Wide range of flammable limit Heavier than air Least stable of the fuel gasses MAPP Same equipment as acetylene Slightly larger tip size Is not sensitive to shock Lighter weigh cylinders Neutral flame has long inner cone Hydrogen Recommended for welding aluminum and lead. High cost of gas limits use. GMAW and GTAW process more popular. What are the advantages and disadvantages of each gas?

5 Uses How many people have used an oxyfuel system?
Is there anything else that it be used for? Why has the use of oxyfuel welding declined? Traditionally oxyfuel equipment was used for: Brazing Fusion welding Flame hardening Metalizing Soldering Stress relieving Cutting Bending

6 OxyFuel Safety Remember safety is based on a conscious decision and the management of hazards. What hazards are associated with an oxyfuel system? How do we manage these hazards? cylinders regulators flame hot metal harmful rays fumes fluxes Best management practices Job analysis sheet

7 OxyFuel system Before learning to use an oxyfuel system, it is important to know the name and function of each part. Oxygen safety disc Oxygen cylinder valve Oxygen cylinder pressure gauge Oxygen working pressure gauge Oxygen regulator Oxygen regulator adjusting screw G. Acetylene cylinder safety disc H. Acetylene cylinder valve I. Acetylene cylinder pressure gauge Function A. Oxygen cylinder pressure relief B. Open and close cylinder C. Indicates oxygen cylinder pressure D. Indicates oxygen working (hose) pressure E. Adjusts and regulates oxygen working pressure F. Used to adjust oxygen regulator G. Acetylene cylinder pressure relief H. Open and close acetylene cylinder I. Indicates acetylene cylinder pressure

8 OxyFuel System--cont. J. Acetylene working pressure gauge
K. Acetylene regulator L. Acetylene regulator adjusting screw M. Acetylene hose N. Oxygen hose O. Acetylene torch valve P. Oxygen torch valve Q. Torch R. Welding tip S. Acetylene cylinder T. Oxygen cylinder Function J. Indicates acetylene working pressure K. Sets and regulates acetylene working pressure L. Adjust acetylene regulator M. Transfers acetylene from regulator to torch N. Transfers oxygen from regulator to torch O. Sets flow rate for acetylene P. Sets flow rate for oxygen Q. Handle for manipulation, mounting four welding tip R. Mixes gases, different orifice sizes set welding heat S. Storage for acetylene T. Storage for oxygen

9 Oxyfuel System Components

10 Oxygen Cylinder What are the characteristics of an oxygen cylinder?
What are the primary hazards in the use of an oxygen cylinder? Seamless construction >2000 psi when full Valve with safety disc that releases at 3,000 psi Cap for cylinder when not in use Common sizes are 244, 150 & 80 cubic feet Do not use lubricant on any fittings. Always keep secure Always keep cap in place when regulator is not attached Do not drop

11 Oxygen Cylinder Valve What is different about an oxygen valve compared to a water faucet? How far should it be open when in use? Special double seat valve. Must be opened all of the way when in use.

12 Oxygen Valve—Parts Upper seat Lower seat Safety nut Safety disc
Cylinder connection Regulator connection Stem nut Valve stem Hand wheel

13 Oxygen Valve—cont. Closed Open

14 Acetylene Cylinder What are the characteristics of an acetylene cylinder? What are the primary hazards in the use of an acetylene cylinder? Acetylene cylinders are 90% full of a porous materials . 250 psi when filled. Protected by fuse plugs that melt at 212 oF. Common sizes are 300, 120 and 75 cubic feet. The cylinder should be opened only 1/2 to 3/4 of a turn when in use. The withdrawal rate in cubic feet per hour should never exceed 1/7 times the cylinder capacity. The cylinders must always be used, transported and stored upright. Cap must be on unless a regulator is attached. Should not be dropped.

15 Acetylene Valve What is different about an acetylene cylinder valve compared to an oxygen cylinder valve? single seat is used packing seals the valve stem. Fuel cylinders have left hand threads.

16 LPG Gas Cylinders How is an LPG cylinder different from an oxygen or acetylene cylinder? Simpler hollow steel containers. New regulations require float shut-off. Because LPG liquidizes with less pressure, cylinder contains both liquid and vapor. Equipped with spring loaded pressure relief valve. Newer style fitting being adopted. Common sizes are 30, 70, and 100 pound.

17 Regulators What is the function of an oxyfuel regulator?
Regulator parts: Pressure adjusting screw Bonnet Needle valve Hose connection Cylinder connection Needle valve seat Diaphragm Spring Nylon thread insert Reduce pressure from cylinder pressure to working pressure and maintain a constant working pressure. When the cylinder valve is turned on, pressure from the cylinder presses against the diaphragm and closes the needle valve. As the adjusting screw is turned in, the spring is compressed which applies force to the diaphragm from the opposite direction. If the spring force is greater than the force produced by the gas pressure, the needle valve opens and gas flows through the regulator into the hose. When the torch valve is opened, the pressure on the diaphragm is reduced and the spring opens the needle valve. When the torch valve is closed, the pressure equalizes and the diaphragm closes the needle valve. How does it work?

18 Regulators—cont. Do all regulators have a pressure adjusting screw?
No. Some are fixed pressure.

19 Regulators—cont. What hazards are associated with oxyfuel regulators?
Leaks Leaving adjusting screw turned in when opening the cylinder. Creeping regulator Gauge not returning to zero Lubricants on oxygen fittings

20 Regulator Creep What is regulator creep?
What can cause regulator creep? What hazards are associated with regulator creep? Regulator creep is a potentially dangerous condition that occurs when the regular does not maintain working pressure. When the system is on, and no gas is flowing, the working pressure slowly increases. If the cylinder is not shut off the working pressure will eventually equal the cylinder pressure. Causes Foreign material inside the regulator. Failure to release the regulator adjusting screw before opening the cylinder. Normal wear Potential outcomes: Rupture of regulator safety relief valve. Explosion of low pressure gauge. Rupture of gas hose.

21 Gauge Not Returning To Zero
Why would a gauge not return to zero? What can cause this condition? What are the possible outcomes of using a regulator that has a gauge that does not return to zero? The bourdon tube inside the regulator can be damaged, distorted. When this occurs, the gauge needle does not return to zero. _____ Opening cylinder with the regulator adjusting screw turned in. Hard impact. Unknown working pressure which could cause backfires and flashbacks.

22 Backfires and Flashbacks

23 Backfire What is a backfire when using an oxyfuel torch?
How do you know when a backfire has occurred? What is the primary cause of backfires? What are the hazards associated with a backfire? What should you do when one occurs? Backfire: The gasses rapidly combust inside the tip and cause a burst of high pressure Indicated when the torch goes out with a loud pop. May be accompanied sometimes with a loud shrieking sound. Note: flame may restart because of the heat of the weld. Caused by hot metal in the tip. High pressure burst will blow molten material into the surrounding area. When it occurs, stop and inspect the tip and clean if necessary. HIgh when fusion welding steel, will occur every time the tip is too close and the metal is overheated. What What is the risk of a backfire?

24 Flashback A. What is a flashback when using an oxyfuel torch?
B. How do you know when one has occurred? C. What causes flashbacks? D. What should you do if you suspect one has occurred? A. Flashback: occurs when the flame burns inside of the torch. B. Usually accompanied by a shrill hissing or squealing sound. Handle of torch will get very hot. May have puffs of black smoke coming out of the tip. C. Primary cause is a blocked tip and unequal working pressures. D. Shut off the acetylene gas and then the oxygen, clean the tip. Worse case--If left unchecked the flame will travel up the hose and ultimately reach the cylinder causing it to explode. The potential damage is so high, and the probability of occurrence is so high that all new systems must have check valves and flashback arrestors. Low if modern equipment is used or if check valve have been installed in the gas hoses. E. What is the potential hazard of a flashback? F. What is the risk of a flashback?

25 Check Valves and Flashback Arrestors
What is the purpose of a check valve? What does a flashback arrestor do? Check valves only allow the flow of gas in one direction. Flash back arrestor stops the propagation of a flame.

26 Working Pressure

27 Working Pressure Oxygen and fuel gas working pressure should be set according to manufactures recommendations for the job being performed. What factors influence the ideal working pressure? Can excessive working pressure cause problems when welding? Yes. What are they? Welding or cutting If welding, what welding process Joint Welding position Metal thickness If cutting, metal thickness Potential problems with excessive pressure. Harsh flame Damaged equipment Increased potential of flashback. Potential problems of insufficient pressure. Insufficient heat Unstable flame Increased plugging of welding or cutting tip Can insufficient working pressure cause problems when welding? Yes. What are they?

28 Oxyfuel Torch What is the purpose of the oxyfuel torch?
The oxyfuel torch is the handle for holding and controlling the system. It the controls the flow rate of the gasses and delivers them to the welding tip, or cutting attachment. The torch valves should only be hand secured, not tightened. The valve stem packing should be tightened if gasses leak past or when the torch valve becomes too easy to turn. Don’t attach a cold welding tip or cutting attachment to a hot torch. Tips and cutting attachments use o-rings for sealing, they do not need to be very tight. Important facts when using oxyfuel torch.

29 Hoses and Connections Are there any unique characteristics of oxyfuel hoses? Are there any unique characteristics of oxyfuel hose connections? Requires special nonporous hoses. Material must be resistant to degradation caused by oxygen and fuel gases. Hoses are color coded. Green: oxygen Red or Black: fuel gas Connections Oxygen: right hand Acetylene: left hand Hoses should be protected from hot metal and physical damage. How should hoses be treated?

30 PPE What are the three primary hazards associated with oxyfuel systems and how are they managed? Hazard Management Harmful light Shaded goggles or face shield Hot metal Pliers and gloves Flying molten droplets Welding apparel

31 Setting Up Oxyfuel System
Extinguish all open flames and stop processes that produce sparks. Steps (assuming new system) Secure cylinders Remove caps Crack cylinder valves Connect regulators Open cylinder valves Connect hoses to cylinders Connect hoses to torch body Connect welding tip to torch body Set working pressures Check system for leaks.

32 Shutting Down System Close cylinder valves Open torch valves
Leave open until regulator gauges read zero. Some sources recommend doing fuel first and oxygen last. Close torch valves Release tension on regulator adjusting screw. Roll up hoses and place torch in a safe position.

33 Questions?

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