Welding Lecture 2

7/31/2019 Welding Lecture 2

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MP-IICode-151901

Metal Joining Process


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Welding Classification

Welding

GasWelding

ArcWelding

ResistanceWelding

RadiantEnergy

Solid StateWelding

ThermoChemical


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Welding Class. Cont.

Gas Welding

Oxy Acetylene

Air Acetylene

Oxy Hydrogen

Pressure Gas


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Arc WeldingCarbon Arc

Shilded Metal Arc

Submerged Arc

TIG

Flux Cored Arc

MIGPlasma Arc

Electro Slug

Stud Arc


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Solid State Welding

Cold

Diffusion

Forge

Friction

Explosive

Hot PressureRoll

Ultrasonic


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Thermo Chemical Welding

Thermit

Atomic Hydrogen


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Oxyacetylene Welding (OAW)

OAW is a manual process in which the welder mustpersonally control the the torch movement and

filler rod application

Cylinders contain oxygen and acetylene gas atextremely high pressure.


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Typical Oxyacetylene Welding(OAW) Station


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Cylinder Transportation

Never transport cylinders without the safety caps inplace

Never transport with the regulators in place

Never allow bottles to stand freely. Always chainthem to a secure cart or some other object thatcannot be toppled easily.


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Pressure Regulators for Cylinders

Reduce high storage cylinder pressure tolower working pressure.

Most regulators have a gauge for cylinderpressure and working pressure.


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Pressure Regulators for Cylinders

Regulators are shut offwhen the adjusting screw

is turn out completely. Regulators maintain a

constant torch pressurealthough cylinder pressuremay vary

Regulator diaphragms aremade of stainless steel


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Pressure Regulators GaugesUsing a Bourdon movement

Gas entering the gauge fills aBourdon tube

As pressure in the semicircularend increases it causes the freeend of the tube to moveoutward.

This movement is transmitted

through to a curved rack whichengages a pinion gear on the

pointer shaft ultimately showingpressure.


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Regulator Hoses

Hoses are fabricated fromrubber

Oxygen hoses are green in

color and have right handthread.

Acetylene hoses are red incolor with left hand thread.

Left hand threads can beidentified by a grove in the

body of the nut and it may haveACET stamped on it


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Check Valves &Flashback Arrestors

Check valves allow gas flow in one direction only

Flashback arrestors are designed to eliminate the possibilityof an explosion at the cylinder.

Combination Check/ Flashback Valves can be placed at the

torch or regulator.


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Acetylene Gas

Virtually all the acetylene distributed for welding and cutting useis created by allowing calcium carbide (a man made product) toreact with water.

The nice thing about the calcium carbide method of producingacetylene is that it can be done on almost any scale desired.Placed in tightly-sealed cans, calcium carbide keeps indefinitely.For years, miners lamps produced acetylene by adding water, adrop at a time, to lumps of carbide.

Before acetylene in cylinders became available in almost everycommunity of appreciable size produced their own gas fromcalcium carbide.


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Acetylene Cylinders

Acetylene is stored in cylinders specially designedfor this purpose only.

Acetylene is extremely unstable in its pure form atpressure above 15 PSI (Pounds per Square Inch)

Acetone is also present within the cylinder tostabilize the acetylene.

Acetylene cylinders should always be stored in theupright position to prevent the acetone formescaping thus causing the acetylene to becomeunstable.


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Acetylene Cylinders

Cylinders are filled with a very porous substancemonolithic filler to help prevent large pockets of pureacetylene form forming

Cylinders have safety (Fuse) plugs in the top and bottomdesigned to melt at 212 F (100 C)


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Acetylene Valves

Acetylene cylindershut off valves should

only be opened 1/4 to1/2 turn

This will allow the

cylinder to be closedquickly in case of fire. Cylinder valve

wrenches should be

left in place on


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Oxygen and Acetylene RegulatorPressure Settings

Regulator pressure may vary with different torch styles andtip sizes.

PSI (pounds per square inch) is sometimes shown as PSIG

(pounds per square inch -gauge) Common gauge settings for cutting

1/4 material Oxy 30-35psi Acet 3-9 psi

1/2 material Oxy 55-85psi Acet 6-12 psi

1 material Oxy 110-160psi Acet 7-15 psi Check the torch manufactures data for optimum pressure

settings


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Regulator Pressure Settings

The maximum safe working pressure foracetylene is 15 PSI !


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Typical startup procedures

Verify that equipment visually appears safe. Clean torch orifices with a tip cleaners (a small wire

gauge file set used to clean slag and dirt form the torchtip)

Open cylinder valves slightly allowing pressure to enterthe regulators slowly

Opening the cylinder valve quickly will Slam theregulator and will cause failure.


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Typical startup procedures

Never stand directly in the path of a regulator whenopening the cylinder

Check for leaks using by listening for Hissing orby using a soapy Bubble solution

Adjust the regulators to the correct operatingpressure

Slightly open and close the Oxygen and Acetylenevalves at the torch head to purge any atmospherefrom the system.


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Flame Settings

There are three distinct types of oxy-acetyleneflames, usually termed:

Neutral Reducing Carburizing (or excess acetylene) Oxidizing (or excess oxygen )

The type of flame produced depends upon the ratio

of oxygen to acetylene in the gas mixture whichleaves the torch tip.


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Neutral Flame

The neutral flame (Fig. 4-1) isproduced when the ratio ofoxygen to acetylene, in themixture leaving the torch, isalmost exactly one-to-one. Itstermed neutral because it willusually have no chemical effecton the metal being welded. Itwill not oxidize the weld metal;

it will not cause an increase inthe carbon content of the weldmetal.

Inner Cone

Outer Cone


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Neutral Flame

O2 = C2H2

Inner cone must be remain 1.5-3 mm above the weld puddle

Equation of flame No chemical reaction take place

3260* C temp. can be archived

Suitable for

- Mild Steel,

- Cast Iron

- Stainless Steel

- Copper

- Aluminium

Inner Cone

Outer Cone


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Reducing Flame(Carburizing)

The excess acetylene flame (Fig.Beside), as its name implies, iscreated when the proportion ofacetylene in the mixture ishigher than that required to

produce the neutral flame.

Increased the Carbon Contain tothe Weld

Outer cone is Longer than

Neutral flame Low Temp. 3038o C (5500o F)

http://ronreil.abana.org/design1.shtml

Reducing Flame

Inner Cone

Outer Cone Acetelyne Feature
http://ronreil.abana.org/design1.shtmlhttp://ronreil.abana.org/design1.shtml


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Reducing Flame(Carburizing)

It produced very hard and brittlesubstances Iron Carbide

This chemical change makes

metal unfit for application Its used forLead & Carburizing

purpose.

Suitable for

- Low Alloy Steel.

- Non Ferrous. ( They dontabsorbed carbon )

- High Carbon Steel

http://ronreil.abana.org/design1.shtml

Reducing Flame

Inner Cone

Outer Cone
http://ronreil.abana.org/design1.shtmlhttp://ronreil.abana.org/design1.shtml


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Oxidizing Flame

Excess Oxygen ratio 1.5:1

Hotter than Neutral

3480o C

Excess O2 causes the weld beddurty

Suitable for

- Cooper Based

- Zinc

- Ferrus ( Manganese )


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Welding Techniques

Welding Techniques

RightwardLeftward


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Welding Lecture 2

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