4 Uses Traditionally oxyfuel equipment was used for: –Brazing –Fusion welding –Flame hardening –Metalizing –Soldering –Stress relieving –Cutting –Bending New technologies in the GMAW process has almost eliminated the need for oxyfuel welding. –Primary uses today are heating, brazing and cutting.
5 OxyFuel Safety The hazards of oxyfuel welding are primarily compressed gas cylinders, flammable gases and open flame. Common concerns are (pg 294) –PPE (shade 4 face shield/goggles, gloves). –Store and handle cylinders correctly. Keep caps on cylinders whenever regulators are not attached. Never use oil, grease, or any hydrocarbons on fittings. Store cylinders in a locked enclosure. –Check system for leaks –Follow correct procedures for turning on and off. –Remove combustible materials from area. Cutting slag can travel 35 feet on concrete –Insure adequate ventilation
6 OxyFuel system Before discussing how the system works, it is important to know the name of the parts. A.Oxygen safety disc B.Oxygen cylinder valve C.Oxygen cylinder pressure gauge D.Oxygen working pressure gauge E.Oxygen regulator F.Oxygen regulator adjusting screw G. Acetylene cylinder safety disc H. Acetylene cylinder valve I. Acetylene cylinder pressure gauge
7 OxyFuel System--cont. J. Acetylene working pressure gauge K. Acetylene regulator L. Acetylene regulator adjusting screw M. Acetylene hose N. Oxygen hose O. Oxygen torch valve P. Acetylene torch valve Q. Torch R. Welding tip S. Acetylene cylinder T. Oxygen cylinder
8 Oxygen Cylinder One piece, seamless construction. Each cylinder has unique serial number and number is recorded in national registry. Scheduled inspection required. 2,200+ psi when filled Safety disc, nut, releases at 3,000 psi. Must not be dropped. Should not be used as a roller. Never use any lubricates on threads or any part of the cylinder. Three common sizes are 244, 150 & 80 cubic feet. The valve should never be left exposed. It must always have the regulator attached or the cap on.
9 Oxygen Cylinder Valve Special double seat valve. Must be opened all of the way when in use. Right hand threads
10 Acetylene Cylinder Acetylene cylinders are filled entirely with a porous materials which must be able to stop the propagation of an acetylene decomposition within the cylinder initiated by a backfire or an external heating of the acetylene cylinder. 250 psi when filled. Protected by fuse plugs that melt at 212 o F. 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. Common sizes are 300, 120 and 75 cubic feet. The cylinders must always be used, transported and stored upright. Special cylinder because acetylene is unstable above 15 psi. Acetylene is shock sensitive.
11 Acetylene Valve Acetylene cylinders are low pressure cylinders, therefore the valve packing can contain the cylinder pressure and only a single seat is used. Fuel cylinders are left hand threads.
12 LPG Gas Cylinders Simpler hollow steel containers. New regulations require float shut-off. Because gas is under 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.
13 Pressure Regulators Gas systems must have a pressure regulator to reduce the pressure from the high pressure in the cylinder down to the working pressure. Many different designs are used. They range from simple fixed output, commonly used for gas grills and camping stoves, to double stage regulators used for oxyfuel welding.
14 Regulators Oxyfuel welding and cutting uses two types –Single stage –Two stage Correct use –Insure adjusting screw is back off when shut down. Check before starting. –Set correct working pressure. Two potential problems –Regulator creep –Gauge not returning to zero
15 Regulator Problems 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. Potential outcomes: –Rupture of regulator safety relief valve. –Explosion of low pressure gauge. –Rupture of gas hose. Causes –Foreign material inside the regulator. –Failure to release the regulator adjusting screw before opening the cylinder. –Normal wear
16 Regulator Problems Not Returning To Zero The bourdon tube inside the regulator can be damaged, distorted. When this occurs, the gauge needle does not return to zero. Causes –Opening cylinder with the regulator adjusting screw turned in. –Hard impact.
17 Working Pressure Oxygen and fuel gas working pressure should be set according to manufactures recommendations for the job being performed. 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.
18 Welding Tip Size Example welding tip selection and working pressure chart.
19 Backfire & Flashback Backfire: indicated when the torch goes out with a loud pop. –Caused by hot metal in the tip. –The gasses rapidly combust inside the tip and cause a burst of high pressure. –When it occurs, stop and inspect the tip and clean if necessary. Flashback: occurs when the flame burns inside of the torch. –Usually accompanied by a shrill hissing or squealing sound. –May have puffs of black smoke coming out of the tip. –A potentially serious condition. If not stopped the flame can travel up the hoses and into the regulator. –Primary cause is a blocked tip and unequal working pressures. The potential harm of both backfires and flashbacks is controlled through the use of check valves and flashback arrestors.
20 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.
21 Oxyfuel Torches Safety codes require torches to have check valves and flashback arresters. Note: this is a relative new code. Older torches will not have check valves or flashback arresters If not included, they should be added in line between the regulator and the torch. Check valves Flashback arrestor
22 Oxyfuel Welding Tips What is normally called a welding tip is actually a welding tip and a mixing chamber. Some manufacturers put the mixing chamber in the torch, Victor are in the welding tip. Tips for heating may have multiple orifices. Tips require periodic cleaning. –A dirty tip will have a forked outer envelope. Tip orifice should be cleaned with a tip cleaner. Tips have different sizes of orifices. –Size usually indicated by number. –Manufacturers use different number systems. –When fuel gas other that acetylene is used a larger size tip is required.
23 Using Tip Cleaner Start with the smallest size that will enter the orifice without excessive force and work up to orifice size. Be careful, a broken tip cleaner usually means a destroyed tip. Clean the face of the tip with the included file.
24 Airacetylene Torch Burns a mixture of acetylene or MAPP and air. As fuel gas flows through torch it draws in the correct amount of air. Lower temperature than oxyacetylene. Primary use is in soldering and brazing copper piping.
25 Hoses and Connections Requires special nonporous hoses. 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.
26 PPE Use protection for: –Eyes –Body Eyes –Correctly shaded lens--not sun glasses. –Shade 4 or 5 Body –Fire resistant gloves –Long sleeves –Button shirt
27 Setting Up Oxyfuel System Extinguish all open flames and stop processes that produce sparks. Steps (assuming new system) 1.Secure cylinders 2.Remove caps 3.Crack cylinder valves 4.Connect regulators 5.Open cylinder valves 6.Connect hoses to cylinders 7.Connect hoses to torch body 8.Connect welding tip to torch body 9.Set working pressures 10.Check system for leaks.
28 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.