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3.0 OXY-ACETYLENE WELDING

Prepared by:

.Fabrication and Joining Section

ni r it K l L m r

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Outline

. . n ro uc on

3.2. Principle of operation

. .

3.3.1 Oxygen & acetylene cylinders

3.3.2 Regulator

3.3.3 Regulator Hoses

3.3.4 Torch, Tip & Welding Rod

3.4. Fuel Gases

3.5 Flames

. vantages an imitations

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3.1: Introduction

the torch movement and filler rod application.

y n ers con a n oxygen s an ace y ene gas ps aextremely high pressure.

OFW or OAW has many important uses: Welding, Cutting, hardening,tempering, bending, forming, preheating, postheating, brazing etc.

Its major industrial applications are in the field of maintenance andrepair, the welding of small- diameter pipe, and for lightmanufacturing.

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3.2 Princi le of o eration

and acetylene(C2H2 ) gas to provide a high temperature flame(6300F or 3482 C).

C2H2 + O2 = 2CO + H +heat

Filler metal is added and solidify to produce the weld joint

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3.2 Princi le of o eration cont

,

selected and used.

e er me a mus ma c e compos on o e ase me a o ewelded and normally contains deoxidizers to aid in producing sound

welds.

The oxyacetylene welding process is normally used for weldingthinner materials up to in. (6.4 mm) thick.

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3.3 E ui ments

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3.3 E ui ments cont

(1) welding torch and tips,

(2) oxygen and acetylene hose,

(3) oxygen and acetylene regulators,

4 ox en c linder

(5) acetylene cylinder.

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3.3 E ui ments cont

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3.3.1 Ox en c linders

ranging from 2000- 2640 PSI. (Pounds Per square inch) .

xygen cy n ers are orge rom so armor p a e s ee . o par othe cylinder may be less than 1/4 thick.

Cylinders are then tested to over 3,300 PSI using a (NDE) hydrostaticpressure test.

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3.3.1 Ox en c linders cont

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3.3.1 Acet lene c linders cont

help prevent large pockets of pure acetylene form forming.

y n ers ave sa e y use p ugs n e op an o om es gne omelt at 212 F (100 C).

Safety valves and plug in oxygen and acetylene cylinder is purpose toprevent the cylinder burst from overpressure.

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3.3.2 Re ulator

1. Single-stage regulator2. Two-stage regulator.

The single-stage regulator reduces the cylinder pressure of the gas to a

working pressure in one step.

Single-stage regulators must be re-adjusted from time to time tomaintain the required working pressure. The gas pressure in the

cylinder decreases gradually as gas is withdrawn. Single-stageregulators are less expensive than two-stage regulators and are morepopular

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Sin le-sta e re ulator

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3.3.2 Re ulator cont

- .

The first step reduces the cylinder pressure to an intermediatepressure. e secon s ep re uces s n erme a e pressure o edesired working pressure.

The two-stage regulator provides more accurate regulation andeliminates the need to re-adjust the regulator as the pressure in thesupply tank is reduced.

Regulators have two pressure gauges: one shows the pressure of thegas inside the cylinder; the other shows the working pressure that ise ng supp e to t e torc .

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TWO

-STAGE REGULATOR

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The different between Acetylene and Oxygen fitting

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Re ulator Pressure Settin s

e max mum sa e wor ng pressure or ace y ene

is 15 PSI !

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Check Valves & Flashback Arrestors

Check valves allow gas flow

in one direction only

Flashback arrestors are

designed to eliminate the

possibility of an explosion at.

Combination Check/

Flashback Valves can be

placed at the torch orregulator.

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3.3.3 Re ulator Hose

Oxygen hoses are green in color andave r g an rea .

Acetylene hoses are red in color withleft hand thread.

Left hand threads can be identified b

a grove in the body of the nut and itmay have ACET stamped on it

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3.3.4 Torch

,

1. medium- pressure torch(most popular)

. -type.

-pressure torch, both oxygen andacetylene are supplied ata roximatel the same

pressure, which may vary from 1to 10 psi depending on the sizeof the tip being used. The twogases are m xe oge er n emixing chamber in the torchhandle

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3.3.4 Ti

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3.3.4 Weldin Rod The American Welding Society provides a specification covering

welding rods or filler metal used for the oxyacetylene or oxyfuel

gas welding process.

The specification number has the prefix letter R. This is followed

b two or three di its, 45, 60, 65, or 100, which desi nate theapproximate tensile strength in ksi (1000 psi).

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3.4 Fuel Gases

Why acetylene?

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3.5 Flame

- ,

1. Neutral

2. Carburizing (or excess acetylene)

3. Oxidizing (or excess oxygen )

The type of flame produced depends upon the ratio of oxygen toacetylene in the gas mixture which leaves the torch tip.

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3.5 Flame cont

,

in the mixture leaving the torch, is almost exactly one-to-one. Itstermed neutral because it will usually have no chemical effect on themetal bein welded. It will not oxidize the weld metal

The excess acetylene flame is created when the proportion ofneutral flame. Used on steel, it will cause an increase in the carboncontent of the weld metal.

The oxidizing flame results from burning a mixture which containsmore oxygen than required for a neutral flame. It will oxidize or

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3.5 Flame cont

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3.5 Flame cont

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3.6 Advanta es

.

It is relatively inexpensive

it can be used in all welding positions

the pool is visible to the welder.

e equ pmen s versa e. can e use or we ng, raz ng,soldering, and with proper equipment, for flame cutting.

It can also be used as a source of heat for bending, forming,

straightening, hardening, and so on.

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3.6 Limitations

.

It is one of the slowest processes due to the heat transfer andempera ure nvo ve .

For this reason oxy acetylene welding has been largely supplanted formost manufacturing operations.

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