copyright © the mcgraw-hill companies, inc. permission required for reproduction or display....

1Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

PowerPoint to accompany

WeldingPrinciples and PracticesThird Edition

Sacks and Bohnart

PowerPoint to accompany

WeldingPrinciples and PracticesThird Edition

Sacks and Bohnart

Flame Cutting Principles

Chapter 6Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

6 - 2

1. Describe oxy-fuel cutting principles.

2. Identify oxy-fuel cutting equipment.

3. Explain the safety issues of oxy-fuel cutting.

4. Describe various support equipment for oxy-fuel cutting.

5. Identify various cutting techniques.

6. Describe the oxygen lance cutting process.

Objectives

6 - 3

Oxy-Fuel Gas Cutting Torch

• Become universal tool

• Used widely for straight-line shape cutting

• Used as means of scrapping obsolete metal structures

• Used to fabricate metal structures from heavy rolled steel

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

© EdDegginger

6 - 4

Oxyacetylene and Other Fuel Gas Cutting

• Oxyacetylene– Limited to cutting ferrous materials

• Ferrous materials have affinity for oxygen• Rusting process is slow form of oxygen cutting

– Chemical cutting process

• Arc or water jet process– Stainless steel, manganese steels and nonferrous

materials– Mechanical method of cutting

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Oxygen Cutting

• Requires that the part to be cut be raised to a temperature of 1,500-1,600ºF

• Stream of pure oxygen directed onto hot metal causing it to burn rapidly

• Burning steel gives off iron oxide as a product of combustion– Iron oxide solid at room temperature– Melting point below melting point of steel so iron

oxide runs off as molten slag, exposing more iron to jet

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Properties of CommonFuel Gases

Chemical formula C2H2 C8H8 C3H6 C3H4 CH4

Neutral flame Fº 5,6000 4,580 5,200 5,200 4,600

Primary flameheat emission Btu/ft3 507 255 433 517 11

Secondary flameBtu/ft3 963 2,243 1,938 1,889 989

Methylacetylene-propadiene (MPS)

NaturalGasPropylene

Propane

Acetylene

Look for the rest in Table 6.1 from text

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Oxy-fuel Gas Cutting Equipment

• Single-purpose cutting torch, or welding torch to which adaptable cutting head is attached

• Flint lighter• Oxygen regulator• Acetylene regulator• Oxygen welding hose with couplings

attached to each end• Acetylene welding hose with

couplings attached to each end• Flame arresters and check valves

6 - 8

Cutting Torch

The cutting torch mixes oxygen and acetylene or other fuel gases in the proportions necessary for cutting.

Hose Connection for Oxygen Acetylene

Handle

A high pressure oxygen valve operated by a lever controls the oxygen.

Connecting Tubes

Cutting Head

Adaptable Cutting HeadOxygen furnished to the preheating flameis regulated by a preheat valve on the side of handle.

A needle valve in the acetylene inletconnection controls the supply.


Thermadyne Industries, Inc

6 - 9

Internal Construction of a Standard Cutting Torch

Take a closer look at the cutting end of the torch!



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Now a closer look at the handle end of the torch!



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6 - 14

Standard Adaptable Cutting Attachment



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Cutting Tips

The cutting tip has a central hole through which the high pressure oxygen flows.

Around this center hole are a number of preheating flame holes.

Cutting tips may be obtained in various shapes and sizes. The thicker the metal that is to be cut, the larger the size of the center hole must be.



6 - 16

Standard Cutting Tips

The standard tip has a straight bore cutting oxygen port and is typically used with oxygen pressures in the 30 to 60 p.s.i. range.

Cutting tips are designated as standard or high speed.


American Welding Society, Welding Handbook,Vol. 2, 8th ed.,Fig. 14.5, p. 457

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High Speed Cutting Tips

The high speed tips have a diverging cutting oxygen port that flares out

toward the opening.

This flaring out allows much higher oxygen pressure (60–100 p.s.i.), while maintaining a uniform oxygen jet at supersonic velocities. These high speed tips are typically used only for machine cutting and will yield an increase in travel speed of 20 percent over standard tips.


American Welding Society, Welding Handbook,Vol. 2, 8th ed., Fig. 14.5 p.457

6 - 18

Orifice Size

• Cutting Oxygen orifice size not usually affected by type of fuel gas used

• Preheat orifices need to be of appropriate design for type of fuel gas being used.

• Various fuel gases require different volumes of oxygen and fuel

• Tips used for acetylene usually one piece, while other fuel cases may be one-or two-piece tips

6 - 19

Flame Tips


Acetylene tips areusually one pieceand flat on the flame end.

Tips may be obtained for flame machining, gouging, scarfing, and rivet cutting.

Tips for methylacetylene-propadiene (MPS) have a flat surface on the flame end.

Most propylene tips have a slight recess, and natural gas and propane tips usually have a deeper recess or cupped end.

Close quarters cutting attachment

1

Long cutting tip

2

Rivet-cutting tip3

Straight gouging tips4

Rivet-burning tips5

Bent gouging tip 6Sheet metal cutting tip

7 Thermadyne Industries, Inc

6 - 20

Lighters

• The cutting torch should be lighted with a friction lighter.

• The flints of friction lighters can be easily replaced at small cost when worn out.

• Matches should never be used because the thermal cutter’s hand has to be too close to the torch tip and may be burned when the gases ignite.

• There is also the danger that the supply of matches that the thermal cutter may be carrying in his or her pockets will ignite and cause severe burns.



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Goggles

The thermal cutter must wear protective goggles to prevent harm to his or her eyes from sparks, hot

particles of metal, and glare.



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Gloves

• Heat is very intense

• Shower of sparks and hot material

• Best gloves should be of non-burnable material

• Common practice to wear ordinary canvas glove with cuff which can be purchases at very small cost

Gloves should be kept free from grease and oil because of the danger involved in contact with oxygen.


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Magnetic Burning Square

The magnetic burning square makes it possible to cut straight lines with a high

degree of accuracy. It can be used for structural burning and layout work in general.

The tool is inscribed with a 90° protractor in 1° increments, allowing

a swing of 180° with the blade or tool.


Contour Sales Corp.

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The base of the tool is a perfect square, with two strong, cast-in magnets for

holding the tool in the overhead, vertical, angular,

and horizontal positions.


© Centour Sales Corp.

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The top part of the tool is

cast with an 18-inch blade

in 1/8-inch increments, and

it has a large knob for setting

and holding the blade in the

desired degree position. With

the exception of the magnets,

the tool is made of aluminum.


© Centour Sales Corp.

6 - 26

Oxy-Fuel Gas Cutting Machines

These machines have deviceto hold cutting torch and guide in along the work ata uniform rate of speed.

Small machines used with only one torch.

Work is of higher quality and faster than with the hand cutting

torch. They may be used for cutting straight lines, bevels, circles,

and other cuts of varied shape.


ESAB

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Multiple Cutting Torches


Large permanent installations can make use of several cutting torches to make a

number of similar shapes at the same time.

Automatic control

Multiple torches ESAB

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Automatic Control


ESAB

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Multiple Cutting Torches


A number of cutting torches are mounted on the machine so that a number of parts of the same shape can be cut

simultaneously. These machines can be used for

straight-line or circle cutting. They can be guided by hand

or a template.

Metal Fabricating Institute

6 - 30

Tracing Devices


Cutting machines may be guided by various types of tracing devices. One type follows a pattern line of tracer ink and electrically

controls the movement of the torch by means of a servomechanism.

Some units make use of a tracer roller, which is magnetized and kept in contact with a steel pattern. The tracer follows

the exact outer contour of the pattern and causes the cutting tools to produce a cut

in exactly the same shape. ESAB

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Stack Cutting

• Cuts made through several thicknesses at same time

• Plates in stack must be clean and flat with edges in alignment– Tight contact with minimum

of air space between

– Need to clamp them together


American Welding Society (AWS) Welding Handbook Committee, 2001,Welding Science and Technology, Volume 1 of Welding Handbook, 9 th ed.Miami: American Welding Society, Fig. 14.13, p. 468

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Stack Cutting


Stack cutting is particularly suitable for cutting thin sheets. A sheet 1/8 in. thick or less warps, and the edge is rough with slag if cut singly. If stack cut, the edgesare straight and smooth and freefrom slag.

Plates may be up to ½ in. thick.

American Welding Society (AWS) Welding Handbook Committee, 2001,Welding Science and Technology, Volume 1 of Welding Handbook, 9 th ed.Miami: American Welding Society, Fig. 14.13, p. 468

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Beam Cutter


The beam cutter is a portable structural fabricating tool. The operator can trim, bevel, and cope beams, channels and angles.

The beam rail is positioned across the flanges.

BUG-O

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Beam Cutter

• Two permanent magnets lock and square rail in position.

• Variable speed power units used on both horizontal and vertical drives

• Squaring gauge enables operator to adjust tip quickly from bevel to straight trim cuts

• Weighs only 60 pounds so one operator setup times is minimal

• Clean, accurate cuts done in minimum time

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Oxygen Lance Cutting

Oxygen lance cutting (OLC) is a method of cutting heavy sections of steel that would be very difficult by any other means.

The lance is length of black iron pipe.The pipe size may vary from 1/4 to 3/8 in.

Oxygen pressure used is 75 to 100 p.s.i.


American Welding Society, Welding Handbook, Vol. 2, 8 th ed., Fig. 14.25, p. 479

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In order to start the cut, it is necessary to preheat the cutting end of the pipe (lance) to a cherry red with an

oxy-fuel cutting or welding torch.



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Once it is cherry red the oxygen flow is started. The steel pipe burns in a self-sustaining, exothermic reaction, and the heating torch is removed. When the burning end of the lance is brought close to the workpiece, the work is melted by the heat of the flame.



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The lance is slowly consumed during the operation and must be replaced from time to time.

The oxygen lance is useful for piercing holes in heavy thicknesses of steel, cutting off large risers in the foundry, and opening holes in steelmaking equipment which have

become plugged with solidified metal.


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The lance is slowly consumed during the operation and must be replaced from time to time.

The oxygen lance is useful for piercing holes in heavy thicknesses of steel, cutting off large risers in the foundry, and opening holes in steelmaking equipment which have

become plugged with solidified metal.


copyright © the mcgraw-hill companies, inc. permission required for reproduction or display....

Documents

cutting end

standard cutting tips

cutting torch mixes

various cutting techniques

mcgrawhill companies

torch copyright

oxygen acetylene

chemical cutting process