1. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. PowerPoint to accompany Welding Principles and Practices Third Edition Sacks and Bohnart 1 Gas Welding Chapter 5

2. 5 - 2 Oxyacetylene Welding Definition: –Join metal by heating surfaces to be joined to melting point with gas flame –Fusing metal into homogeneous mass –Letting it solidify into a single unit Flame in cone reaches temperatures as high as 5800º to 6300ºF Filler rod may or may not be used to intermix with molten pool

3. 5 - 3 Oxyacetylene Process During first part of this century used as major welding process both for fabrication and construction, maintenance and repair Today use limited for industrial production purposes Still used for brazing, soldering, welding metals with low melting points; general maintenance and repair work

4. 5 - 4 Gases Oxyacetylene welding process uses two principal gases –Oxygen and acetylene Other gases can be used for cutting and heating –Propane –Natural gas –Mapp® gas\

5. 5 - 5 Various Fuel Gas Efficiencies Normal BtusUsable heatFlame Oxygen velocity Fuel Gas (ft 3 ) (s/ft 2 )temp.per ft 3 of fuel (ft/s) Acetylene143312,7005,420ºF 1.0417.7 Mapp ®2 2381 5,5405,301ºF 2.4 7.9 Propane2309 5,5005,190ºF 4.0011.9 Natural gas 3 918 5,6005,000ºF 1.5015.2 Hydrogen 275 7,5004,600ºF 0.2536

6. 5 - 6 Various Gas Cylinders Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Thermadyne Industries, Inc.

7. 5 - 7 Oxygen Gaseous Chemical element in air –Necessary for life No color, odor, or taste Does not burn, but supports combustion –Substances that do not burn in air will in oxygen

8. 5 - 8 Oxygen Production Two commercial processes used in production of oxygen –Separation of water into oxygen and hydrogen by electrolysis of water –Separation of air into oxygen and nitrogen by liquefying air

9. 5 - 9 Oxygen Distribution Distributed in steel or aluminum cylinders Aluminum cylinders Used for medical gases (smaller size) Made of high strength 6061-T6 alloy Steel cylinders Made from single plate of high-grade steel Heat treated to develop maximum strength and hardness Seamless, drawn-steel vessels with iron neck ring shrunk on at top and cylinder value screwed into neck High pressure – undergo rigid testing Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

10. 5 - 10 Valve Mechanisms Must be opened to release oxygen Double-seated valve perfectly tight when completely open or closed –Valve protected from damage by iron cap that screws on neck ring Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

11. 5 - 11 Gas Cylinders Charged with oxygen at pressure of about 2,200 p.s.I. at 70ºF Gas temperature –Increase: gas expands and increases pressure –Decrease: gas contracts and reduces pressure Safety device on cylinder valve to blow off oxygen when excess pressure –Occurs, oxygen lost –DO NOT store where cylinder can be overheated

12. 5 - 12 Safety Precautions Take special care to keep oil and grease away from oxygen When using, do not place cylinders where oil might drop of them from overhead bearings Never use oxygen in pneumatic tools or to start internal combustion engines Never use oxygen to blow out pipe or hose lines, dust clothes or create head pressure in tank of any kind

13. 5 - 13 Acetylene Most widely used of all fuel gages –Both welding and cutting Generated as result of chemical reaction that takes place when calcium carbide comes in contact with water Tests show oxyacetylene flame temperatures up to approximately 6,300ºF –Very rapid rate of preheating –Burns with smoky flame, gives off carbon, has peculiar odor

14. 5 - 14 Characteristics of an Effective Welding Fuel Gas High flame temperature High rate of flame propagation Adequate heat content Minimum chemical reaction of flame with base and filler metal Acetylene most closely matches all these requirements and used for welding purposes.

15. 5 - 15 Acetylene Production and Distribution Commercial acetylene made from calcium carbide – referred to as carbide –Gray, stonelike substance –Product of smelting coke and lime in electric furnace –Several sizes available Distributed in standard steel drums –100 pounds for use in acetylene generators

16. 5 - 16 Acetylene Cylinders Constructed differently from oxygen cylinders –Free acetylene should not be stored at pressure above 15 p.s.i. Safety solved by packing cylinders with porous material saturated with acetone –Acetone – liquid chemical having property of dissolving or absorbing many times the volume of acetylene Strong steel container (packed completely full) Handle with care

17. 5 - 17 Safety Precautions Do not store oxygen cylinders near acetylene generator, carbide, acetylene, or other fuel-gas cylinders Do not use cylinder as roller or lift it by cap Keep cylinders away from welding operation and close cylinder valve when work completed Keep cylinders away from any electrical contact

18. 5 - 18 Valve Mechanisms Acetylene drawn off through valve –Some cylinders valve located in recessed top –Others valve located on convex top Simpler in construction than oxygen valve –Does not have to stand high pressure Max open only about 1 ½ turns –Can be turned off quickly in case of fire Safety fuse plugs also provided

19. 5 - 19 Capacity of Cylinder Full cylinder of acetylene has pressure of about 225 p.s.i. Two sizes used for welding and cutting –Large size contains 300 cubic feet of acetylene and weighs about 232 pounds when full –Small size contains 100 cubic feet and weighs 91 pounds when full Two special sizes (10 cubic ft. and 40 cubic ft.) Not all acetylene in cylinder can be used

20. 5 - 20 Safety Precautions Do not leave acetylene cylinders on their sides –Store valve end up Store cylinders in well-protected, ventilated, dry location –Away from highly combustible material or sources of heat –Keep valve cap on when not in use Remember acetylene will burn. It will form explosive mixture with air.

21. 5 - 21 Safety Precautions Use warm (not boiling) water on the valve if it becomes clogged with ice (Never a flame!) –Fusible safety plugs melt at boiling point of water Handle acetylene cylinders carefully –Damages could cause leakage Advise supplier immediately if acetylene leaks around valve spindle when valve opened –Close spindle and move cylinder to outside area Never tamper with fuse plugs

22. 5 - 22 Protective Equipment Functions may be combined in one device or provided by separate devices –Located in main supply line, head of each branch line in manifold system or at each location where fuel gas withdrawn Backflow protection should be provided to prevent fuel gases from flowing into oxygen system Flashback protection should be provided to prevent flame from passing into fuel-gas system

23. 5 - 23 Flash Arrestors Generally make of sintered metal alloy Prevents flame from moving upstream of arrestor Does not protect torch or tip –Neither does check valve Best way to assure that accidents don’t happen is to follow all safety operating procedures.

24. 5 - 24 Internal View of a Check Valve Prevents the Reverse Flow of Gases Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Thermadyne Industries, Inc./Victor Equipment Company

25. 5 - 25 Internal View of a Flashback Arrestor Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Thermadyne Industries, Inc./Victor Equipment Company