02 Geary Chap01

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C H A P T E R

9

1Oxyacetylene Weldin

Performance ObjectivesAfter reading this chapter you should be able to:

n Identify oxygen tanks by their color.n Understand how acetylene is produced.n Understand the process used to purify oxygen.n Know how to store acetylene and oxygen tanks properly.n Know how to safely handle acetylene and oxygen tanks.n Know how acetone is used with acetylene.n Know how to keep gas cylinders properly positioned.n Know at what temperature an acetylene tank’s safety plug

melts.

W elding is a method used to join two or more pieces of metal insuch a way as to make the finished piece as strong as the original

metal. The oldest type of welding, oxyacetylene welding, was devel-oped about 100 years ago. There have been many developments inmetal joining processes since then.

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O X YA C E T Y L E N E W E L D I N G F U E L S 11

Heating with the oxyacetylene process is often used for formingmetals into various shapes and heat treating metals in operations suchas annealing, flame hardening, tempering, case hardening, and stressrelieving (Fig. 1.2).

One last important use of oxyacetylene is to cut metals. In thisapplication, a stream of pure oxygen is directed against an area ofheated metal. This action causes the metal to oxidize, or burn, andthus be cut (Fig. 1.3).

It is obvious from the name “oxyacetylene” that this type of weld-ing uses a combination of oxygen and acetylene. To understand these basic components, it may be helpful to discuss these two substancesand explain their significance to the welding process.

F I G U R E 1 . 1

Welding is a metalworking process. The joint metal is heated to the melting point andthe pieces are fused together.

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OxygenOxygen is present in small amounts in the air we breathe. About one-fifth of our atmosphere is oxygen. Oxygen used in the welding processis about as pure as possible—over 99 percent pure. The method usedto produce pure oxygen for welding and medical purposes is calledthe liquid-air process.

Liquid-Air Process

The following is a simplified but adequate description of the liquid-air process. Atmospheric air, as mentioned earlier, consists ofabout 20 percent pure oxygen, 78 percent nitrogen, and 2 per-cent other gases (by volume). Oxygen and nitrogen have different

boi ling temperatures. In the liquid-air process, the two gases are

F I G U R E 1 . 2

Welding is often used to heat and shape metals, as is being done to this automobilefender.

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separated by heating atmospheric air to a certain temperatureand holding it at this temperature until the nitrogen, which hasa boiling point of 295°F, boils off. After the nitrogen has beenremoved from atmospheric air, oxygen and a small amount ofother gases remain. These include carbon dioxide, argon, hydro-gen, neon, and helium. Oxygen has the highest boiling point ofall these gases; thus to separate it completely, the remaining mix-ture is further heated until only pure oxygen remains. The pureoxygen is then stored as either a gas or liquid, depending on itseventual use. The liquid-air process is probably the most widely

used method of producing pure oxygen.

CylindersOxygen is commonly sold in cylinders in three sizes: 244 cubicfeet, 122 cubic feet, and 80 cubic feet (Fig. 1.4). There are very strict

F I G U R E 1 . 3

Metal cutting can be accomplished using welding equipment.

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requirements for oxygen cylinders. Theymust be able to withstand over 1 ton ofpressure per square inch. The InterstateCommerce Commission (ICC) has set upguidelines for oxygen cylinders. No partof the cylinder may be less than 1/4 inchthick. Each cylinder must be made orforged from a single piece of steel. Thesteel itself must be armor plate, high-carbon steel (Fig. 1.5).

Since the ICC requires periodic inspec-tion of oxygen cylinders, which are ship-ping containers, very few oxygen cylinders

are actually owned by private individuals.Oxygen supply houses, which own andlease oxygen cylinders, are responsible forcomplying with ICC regulations and inspec-tions. This makes using the gases easier onthe consumer.

The widely accepted color for oxygencylinders, lines, and control knobs is green.However, there is no federal regulationthat requires oxygen cylinders to be green;

thus, many companies paint their oxygencylinders a special identifying color. It will

be to your advantage to become familiarwith the color used by your dealer. Oftentwo oxygen supply houses in the same citywill have two different colors for their oxy-gen tanks.

Safety PracticesOxygen cylinders are not dangerous whenused and stored according to generallyaccepted safety precautions. It is best touse only cylinders carrying ICC markings,however. You can be certain that cylinders

F I G U R E 1 . 4

The three most popular sizes of portable oxygencylinders, left to right, are 244 cubic feet, 122 cubicfeet, and 80 cubic feet.

Removablemetal cap

Bronze valve

Safety device

Pressed steelneck ring

Oxygen capacity of cylinder 244 cu. ft. at

2,200 lb. per sq. in.pressure at 70°F.

Airco 244 cubicfoot oxygen cylinder

9 O.D51

8½I.D.

F I G U R E 1 . 5

A typical oxygen cylinder.

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of this type comply with the stringent reg-ulations of the ICC.

Store cylinders only in a safe location,and fasten them in place. This will ensurethat the cylinders cannot be knocked over.Keep tanks in an area away from stoves, radi-ators, furnaces, or other overly warm equip-ment or pipes. Oxygen cylinders should also

be kept away from all combustible materialsor liquids. If cylinders are stored in the open,they should be protected from water, heat,cold, and the sun’s direct rays.

Never use oxygen cylinders for any

purpose other than holding oxygen. Youshould never use oxygen cylinders as roll-ers to help move large or heavy objects, forexample. Nor should you use oxygen cyl-inders as supports.

Oxygen cylinders should be storedand used in an upright position. In mostcases, a hand truck specifically designedto hold two cylinders (both oxygen andacetylene) is the best means for storing

and using oxygen. The cylinders should be securely chained or strapped to thecart to prevent them from falling over,allowing the tanks to be transportedsafely (Fig. 1.6).

Never use the valve on top of the cyl-inder to lift the cylinder from a horizontalto a vertical position. The best way to lift acylinder is to make sure that the valve pro-tection cap is secured tightly. Then raisethe cylinder by grasping the cap firmly andlifting (Fig.1.7).

Never allow oxygen cylinders to comein contact with live electrical wires or other electrical equipment.

You can rent oxygen (aswell as acetylene) cylinders for a fixedperiod of time. When you require moreoxygen, you simply return the empty cyl-inder to the dealer, who replaces it with afull one. All you pay for is the oxygen. Theoxygen itself is what you use. In most partsof the country a 20-year lease is availableand quite reasonable. In our case, the costof a cylinder for oxygen and a cylinder foracetylene costs about $10 a year. You canbuy oxygen and acetylene to fill the tanksas you need them. In different parts of thecountry the price may vary.

F I G U R E 1 . 6

Both oxygen and acetylene tanks should be chainedto prevent their accidental falling.

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Keep cylinders away from welding andcutting work. Make certain that the hosescontaining oxygen and acetylene do not lieunder the work.

Open cylinder valves all the waywhen working, and always close cylindervalves when you have completed working.Never leave the cylinder valve open whenyou are not in the immediate vicinity.Cylinder valves should always be tightlyclosed when not in use—whether they areempty or full. If you stop working for lunch,for example, turn off the valves and bleed

the lines. This procedure is explained later(see Fig.1.8).Never use oxygen around oil or grease

as these substances burn violently in thepresence of pure oxygen under pressure.Do not use any oil or grease on the regula-tor fitting.

Never use oxygen for anything otherthan welding and cutting. Pure oxygen isnot in itself flammable, but is an accelerant

that can cause intense heat when added toa flame of even very small nature. There isa very real danger if it is used to “dust off”work or clothing. Similarly, oxygen shouldnever be used for ventilation, pressuretests of any kind, or for any other similarpurpose.

AcetyleneAcetylene is produced by combining cal-

cium carbide and water. When calcium carbide, commonly calledcarbide in the trade, is dropped into water, a reaction occurs thatcauses gas bubbles to rise. The gas is acetylene. It has a peculiar

F I G U R E 1 . 7

Whenever you pick up a cylinder of oxygen or acetylene,always lift it by the protective cap.

F I G U R E 1 . 8

Always turn off the flow of both oxygen and acetyleneat the tank when you stop work for more than 10minutes.

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odor, and, if lighted, it burns with a black, smoky flame. After the action ofthe carbide has ceased, a whitish residueremains in the water. This end productis hydrated, or slaked, lime (calciumhydroxide ), and it has many uses in thefertilizer industry.

It is interesting, as a side note, to men-tion that old-time miners’ headlamps arecalled carbide lamps, and they work sim-ply by adding water to carbide pellets. Agas is formed in a special container and isforced out of a jet. This gas is ignited in

front of a reflector plate, which throws a bright beam of light (Fig. 1.9).

Carbide-to-Water GeneratorsAcetylene is produced commercially by basically the same pro-cess as used in a miner’s headlamp, only on a much largerscale. Companies that use great amounts of acetylene will usu-ally have their own generator that supplies them with all of theacetylene they can use. These generators are called carbide-to-water generators, and they are almost totally automated. In these typesof generators, small amounts of calcium carbide are fed into a largesealed container of water. The heat given off as the reaction occurs isabsorbed by the water. The acetylene gas is captured when it rises tothe top of the tank. This gas is then either used directly or stored forfuture use (Fig. 1.10).

ContainersFor the beginner welder, the only practical way to obtain acetylene isin a special tank, which is similar to but much smaller than a standard

oxygen cylinder. The three common sizes of acetylene cylinders are300 cubic feet, 100 cubic feet, and 60 cubic feet. A full tank of acety-lene will register approximately 225 psi (pounds per square inch) on apressure gauge (Fig. 1.11).

F I G U R E 1 . 9

A miner’s carbide lamp works on the same basicprinciple as does an acetylene generator.

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cylinder is filled to about 225 psi with acety-lene, the acetone dissolves the acetylene andmakes it safe because the acetylene is not free(Fig. 1.12).

Acetylene cylinders have a valve ontop to which the regulator is attached.This valve is similar to the valve onoxygen cylinders except that it hasleft-handed threads. You must turnthe valve counterclockwise to open itand clockwise to close it. This turn-ing action is the opposite of a standardcontrol valve.

All acetylene tanks have safety plugson the top or bottom of the cylinder. Theseplugs are designed to melt, in the event ofa fire, at around 212°F. Needless to say, thecylinders should be stored and used awayfrom any heat source. Once these safetyplugs melt, all of the acetylene and ace-tone in the cylinder is allowed to escape(Fig. 1.14).

PrecautionsAs with oxygen cylinders, there are a fewgeneral safety precautions that shouldalways be followed. These include the fol-lowing guidelines for safe operation andstorage of acetylene.

Always call acetylene by its propername: “acetylene.” It should never becalled “gas” as it is very different from thetype of gas used in a kitchen, furnace, orautomobile.

Acetylene should be stored away fromall heat sources and other fuels. An idealstorage location is a cool, dry area awayfrom all combustible materials.

F I G U R E 1 . 11

The three most popular sizes of portable acetylenecylinders, left to right, are 300 cubic feet, 100 cubicfeet, and 60 cubic feet. Cylinders of other shapes arealso available.

Filler

F I G U R E 1 . 1 2

A cutaway view of a typical acetylene cylinder showingthe filler material.

Note that all acetyleneconnections on the cylinder, hoses, and torchhandle are left-handed. Each brass fittinghas a groove cut around its circumference forquick identification (Fig. 1.13).

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Handle acetylene cylinders with special care. The safety plugs meltat about the same temperature as boiling water, and they can “blowout” as a result of rough handling. As with oxygen, cylinders of acety-lene should be secured while being used to eliminate the possibility ofthe cylinder falling over. A specially designed hand truck is the bestway of moving and storing acetylene and oxygen.

Do not open the valve on an acetylenecylinder more than 1 1 ⁄ 2 turns as this maycause some of the acetone in the tank toescape with the acetylene. Acetone willdamage all rubber and plastic parts in thesystem, including the hose and regula-tor. Therefore, it should not be allowed to

escape.Always use an acetylene cylinder inan upright position. Never use it whenthe cylinder is in any position other thanvertical.

Review Questions

1. What is the oldest type of welding?

2. How hot is the oxyacetylene flame? 3. Who was the French chemist who

discovered acetylene welding?

4. What type of welding was used inWorld War I?

5. Oxyacetylene is also used to __________ metals.

6. How pure is the oxygen used in welding?

7. What is the name of the process used to purify oxygen?

8. Pure oxygen can be stored as a gas or __________. 9. What are the three sizes of oxygen cylinders?

10. Which government agency regulates oxygen cylinders?

Nut

F I G U R E 1 . 1 3

A fitting for an acetylene regulator. Notice that thenut has grooves around the middle. All left-handed-threaded fittings have these grooves.

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11. Oxygen cylinders should always bekept away from __________ __________ or__________.

12. Both oxygen and acetylene t anksshould be __________ to keep them fromaccidentally falling.

13. Acetylene is produced by using waterand __________.

14. What are the three sizes of acetylenecylinders?

15. Which type of welding tank has aregulator with left-handed threads?

16. At what temperature does the acetylenecylinder plug melt?

Safety plug

F I G U R E 1 . 1 4

The safety plug on an acetylene cylinder is speciallydesigned to melt at temperatures in excess of 212°F.

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02 Geary Chap01

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