Download
1 / 103
1.24k likes | 2.12k Vues
Oxyfuel Cutting and Welding. 8609-A Instructional Materials Service Texas A&M University. Introduction. 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
E N D
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
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.
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
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
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.
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 in2 (psi) • Supports combustion and is explosive if handled improperly • Cylinder sizes = 80 to 244 ft3
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 approximately 250 psi • May not be withdrawn at a rate higher than 15 psi
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 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.
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, dry 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 cylinders 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. • DoNot 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. • DONOT 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. • DONOT 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. • DONOT 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.
Check torch body for closed valves. • Check regulator for loose regulator adjusting screw. • Open acetylene cylinder valve ¼ to ½ turn (wheel-type valves one turn) maximum. • Turn acetylene regulator adjusting screw to desired working 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 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.
