2. 14
Chapter
Oxyfuel Gas Cutting

3. Describe the function of each component of an oxyfuel gas cutting outfit.
Correctly and safely assemble an oxyfuel gas cutting outfit.
Correctly and safely test the cutting outfit for leaks.
Describe the difference between a positive-pressure and injector-type cutting torch.
Properly turn on and shut down an oxyacetylene cutting outfit.
Correctly select the proper cutting tip and working pressures for cutting a particular thickness of steel.

4. Cut base metal using an oxyacetylene cutting torch.
Distinguish between a well cut surface and a poorly cut surface, and be able to adjust where necessary to perform a good cut.
Describe the gouging process and state when it is used.
Pass a test on safe practices and procedures while oxyfuel gas cutting or gouging.
List all the safety equipment that should be worn and used when oxyfuel gas cutting in various positions.

5. Oxyfuel Gas Cutting
An oxyfuel gas flame is used to heat the metal and an oxygen jet is used to perform the cutting
Oxyfuel gas cutting (OFC) is also called oxygen cutting
Many layers of metal can be cut at the same time (stack cutting)
OFC is useful when shape-cutting metal parts

6. The Heat of Combustion of Steel
Virtually all materials burn if they are heated to their ignition temperature in the presence of oxygen
During the process of burning, steel releases heat that is measured in British thermal units (Btu) or joules
This is called the heat of combustion

7. Oxyfuel Gas Cutting Process
A special torch and tip is used in the OFC process
Cutting tips have one or more preheating orifices
Cutting oxygen emits from the central orifice when the welder presses the cutting oxygen lever
(Victor, a division of Thermadyne Industries, Inc.)

8. Oxyfuel Gas Cutting Process
The preheating flames are used to heat a spot on the base metal to its ignition temperature
As the torch is moved along a line, the metal is cut, forming a kerf
The preheating flames are kept burning throughout the entire cutting process

9. Cutting Outfit
A cutting outfit includes all equipment required to make a cut
A cutting station includes the outfit, lighting, ventilation, a cutting table, and possibly a booth
The cutting torch, which provides an oxygen cutting jet, is quite different from a welding torch

10. Cutting Torch
The cutting torch is connected to oxygen and fuel gas cylinders
The welder controls the cutting operation using the cutting torch lever
(ESAB Welding and Cutting Products)

11. Cutting Torch
Before the torch is turned on, the desired cutting tip must be inserted into the torch
There are two types of OFC torches
Positive-pressure torches
Injector-type torches

12. Lighting a Positive-Pressure Oxyacetylene Cutting Torch
Check the condition of all equipment
Inspect the regulators
Open the oxygen valve very slowly
Turn the cylinder valve all the way open
Open the acetylene cylinder valve 1/4 to 1/2 turn

13. Lighting a Positive-Pressure Oxyacetylene Cutting Torch
Open the torch oxygen valve one full turn
Open the oxygen cutting valve
Adjust the oxygen regulator to give the desired pressure
Open the acetylene torch valve one turn
(Uniweld Products, Inc.)

14. Lighting a Positive-Pressure Oxyacetylene Cutting Torch
Turn in the acetylene regulator adjusting screw until the low-pressure gauge indicates the desired working pressure
Open the torch acetylene valve 1/16 to 1/8 turn before lighting the torch
Adjust the acetylene until most of the smoke clears from the flame
Open the torch oxygen valve and adjust it to obtain neutral preheat flames

15. Safety
The welder should stand to one side of the gauges when opening the oxygen valve
Leave the acetylene cylinder valve wrench in place so the valve can be turned off quickly
Never use acetylene at above 15 psig (103kPa)
Check the low-pressure gauge readings to make sure that the pressures are not rising
A rising pressure indicates that a valve is leaking
The outfit should be shut down immediately
Use a flint lighter to ignite the acetylene

16. Lighting an Injector-Type Oxyacetylene Cutting Torch
Several steps are required to turn on the outfit, purge the system, and light the torch
This illustration shows typical gas flow through an injector-type oxyacetylene cutting torch

17. Lighting an Injector-Type Oxyacetylene Cutting Torch
Check the condition of all equipment
Inspect the regulators
Open the oxygen cylinder valve until the regulator high-pressure gauge reaches its maximum reading
Turn the cylinder valve all the way open
Slowly open the acetylene cylinder valve 1/4 to 1/2 turn
Open the torch oxygen valve 1/4 turn
Open the torch oxygen cutting orifice lever wide open
Adjust the oxygen regulator screw for correct working pressure

18. Lighting an Injector-Type Oxyacetylene Cutting Torch
Open the torch oxygen valve 1/4 turn
Open the torch acetylene valve fully
Use a spark lighter to ignite the fuel gas
Press down the oxygen cutting lever and adjust the torch acetylene valve until the preheating flames are neutral
Close the torch oxygen valves
Open the torch acetylene valve fully
Adjust the acetylene working pressure
Close the torch acetylene valve
Check the low-pressure gauges

19. Safety Leave the wrench in place on the acetylene cylinder valve
Check the low-pressure gauges for any gradual increase in pressures
If the pressures are increasing, the regulator seat may be leaking
If the pressure on either of the low-pressure gauges is increasing, shut down immediately
Use a spark lighter to ignite the fuel gas

20. Using a Cutting Torch
To cut, bring the tip of the inner cone of the preheating flames to the edge of the metal to be cut
The jet of oxygen coming from the oxygen jet causes the heated metal to burn away, forming the kerf

21. Using a Cutting Torch
Drag is a measurement made in the direction of travel between the entry and exit points of the cutting jet
The slag stream can lag excessively behind the torch tip travel
Possible causes include
The flame adjustment may be incorrect
The cutting oxygen pressure adjustment may be too low
The tip travel is too fast and the metal is not being preheated enough

22. Cutting Attachments
The cutting attachment is connected to the welding torch body to change the torch from a welding torch to a cutting torch
For portable kits, the attachment saves space
The operation of the torch with the cutting attachment is the same as the operation of a regular cutting torch

23. Cutting Attachments
This illustration shows a cutting attachment installed on a torch
The welding torch body has an oxygen valve and a torch acetylene valve
The cutting attachment has a torch oxygen valve and a cutting oxygen lever
(CONCOA)

24. Safety
The torch valves on the welding torch body must be turned off before the cutting attachment is disconnected

25. Cutting Tips Cutting tips normally have at least two orifices
One orifice is for the cutting oxygen
One or more small orifices are for preheating the metal to be cut
One-piece tips are used for oxyacetylene cutting only
Two-piece tips are used for all other gas cutting

26. Cutting Steel with the Oxyfuel Gas Cutting Torch
Metals that can be cut with the oxyfuel gas cutting torch are divided into two classes
Metals whose oxides have a lower melting temperature than the metal itself
Metals whose oxides have a higher melting temperature than the metal itself
Practically all steel falls under the first classification

27. Cutting Steel with the Oxyfuel Gas Cutting Torch
The second class includes cast iron, some alloy steels, stainless steel, and nonferrous metals
It is very important that refractory oxides be reduced by chemical action or be prevented from forming
If too much oxygen is fed to the steel being cut, this leaves a bell-mouthed kerf on the side of the metal away from the torch

28. Cutting Steel with the Oxyfuel Gas Cutting Torch
The metal at the bottom of the cut is not burned away if the torch is moved too rapidly
The large drag leaves a kerf that is very rough and irregular in shape

29. Cutting Steel with the Oxyfuel Gas Cutting Torch
Metal that is very dirty and rusty should be cleaned before starting the cutting operation
In some cases the thickness of the metal requires an oscillating motion in order to obtain the necessary width of a cut
The welder should stand in a comfortable position that permits looking into the cut as it is being formed

30. Safety Welders should wear
Safety boots with high tops
Trousers without cuffs
Leggings to protect against flying molten slag
Welding leggings are pieces of leather that cover the shin and top of the shoe
If trousers have cuffs, they must be covered to keep them from catching slag

31. Cutting Thin Steel
Cutting steel that is 1/8″ or less in thickness requires the use of the smallest cutting tip
A tip with only a few preheat holes is often used
The tip is usually pointed in the direction the torch is traveling
Be careful to keep the end of the preheating inner cone just above the metal

32. Cutting Thick Steel
Steel over 1/2″ thick should be cut by holding the torch so the tip is perpendicular to the surface of the base metal being cut
A cut is normally started at the edge of the stock

33. Cutting Thick Steel
The thicker the steel, the greater the time required to raise the temperature of the steel high enough to make clean cuts
To start a cut faster, a welder begins at the corner of the metal by slanting the torch in the direction opposite the direction of travel
One method used to start cuts is to nick the edge of the metal with a cold chisel

34. Cutting Thick Steel
Another method used to start cuts is to place an iron filler rod under the preheating flames at the edge of a thick plate
Shaping cutting can be done by
Free-hand cutting
Using special attachments or guides
Setting up an automated cutting torch

35. Safety
Be sure to read and carefully follow all manufacturer’s tables and safety charts prior to attempting a cutting operation for very thick metal

36. Cutting Chamfers (Bevels)
Thicker pieces of steel must be prepared with a chamfered edge so the weld penetrates the metal
Bevel angles can be cut at the same time the metal is being cut to size and shape

37. Cutting Chamfers (Bevels)
A chamfer can also be cut as a separate operation
The technique used to cut a bevel is similar to that used to cut thick metal
The torch is held at an acute angle to the base metal
The cut is generally made at an existing edge of the metal

38. Cutting Pipe or Tubing
When cutting small-diameter pipe, it is best to keep the tip almost tangent to the inner circumference of the pipe
For larger pipes, it is possible to keep the torch tip perpendicular to the pipe surface while cutting
(Thermadyne Industries, Inc.)

39. Cutting Pipe or Tubing
If the pipe is being chamfered, most welders start the cut at the extreme edge of the pipe and cut back to the marked chamfer ring
It is not the diameter of the pipe that determines the size of the cutting torch tip
The thickness of the pipe wall is the controlling factor

40. Piercing and Cutting Holes
The term pierce means to produce a relatively small hole through a steel plate
A greater amount of heat is required to preheat the surface for piercing than when starting on a edge
For this reason, a larger tip may be needed
It is good practice to outline the hole first, using special chalk

41. Safety
Until the steel plate is melted through the bottom surface, molten metal is blown upward by the pressure of the cutting oxygen

42. Cutting and Removing Rivet Heads
Cutting torches are frequently used in salvage operations
Torches are used to remove the two types of rivet heads
Round-head
Countersunk-head
If possible, the welder should do the cutting without damaging the steel plate

43. Cutting and Removing Rivet Heads
For cutting the round-head rivet, preheat the head of the rivet to a bright cherry red
The steel plate is usually adequately protected from the flame by a coating of scale (oxide)
Countersunk rivet heads can be removed by carefully cutting around the countersunk angle

44. Gouging with the Cutting Torch
Gouging is a process that removes metal from the surface of a part to a desired depth
For gouging, a lower oxygen cutting pressure and a larger diameter cutting tip orifice are used

45. Gouging with the Cutting Torch
In a gouging tip, there are five or six preheat orifices to provide even distribution of the preheat flames
The speed of torch movement is important
Moving the torch too rapidly creates a groove that is too narrow and shallow
Moving the torch too slowly creates a gouge that is too deep and wide

46. Cutting Alloy Steels
Of the alloy steels, stainless steel is the most widely used
Many alloy metals have melting temperatures below that of mild steel
The metal to be cut should be placed so that the cutting tip and flame are in a horizontal position whenever possible

47. Cutting Alloy Steels
A slight, quick up-and-down motion of the torch facilitates the removal of slag
Like carbon steel, alloy steels must be preheated before the cutting operation is started

48. Cutting Alloy Steels
Stainless steel must be preheated to a white heat before the cutting oxygen is turned on
When the cutting is often interrupted by unmeltable slag, a welder may hold a mild steel welding rod in the kerf of the metal
Adding welding rod is also useful when cutting poor grade steels, cast irons, and old, oxidized steel castings

49. Cutting Cast Iron It is more difficult to cut cast iron than steel
This is because iron oxides of cast iron melt at a higher temperature than the cast iron itself
It is important to preheat the whole casting before starting the cut
Use a carburizing flame to prevent oxides from forming on the surface before cutting starts
The casting should be cooled very slowly if gray cast iron is desired
Rapid cooling creates a white cast iron grain structure

50. Automatic Cutting
Automatic cutting equipment requires a controller or a computer to control the operation
Feedback controls monitor the automatic cutting process and make needed corrections
In semiautomatic cutting, some changes to the process may be required while cutting is taking place

51. Automatic Cutting
There are many automatic and semiautomatic mechanisms available to perform cutting operations
(ESAB Welding and Cutting Products)

52. Automatic Cutting
Practically all automatic cutting machines and their torches are moved by servomotors
Special cutting torches are mounted on a light, rigid rail called a gantry
A vernier gear mechanism permits fine adjustments to raise and/or lower the torch
A magnetic tracer with a steel pattern can be used as a cutting torch guiding device

53. Safety
Dangers can be greatly reduced through the correct handling of oxygen and fuel gas equipment
Many potential hazards exist when cutting
Every welder must follow approved procedures to eliminate these dangers

54. Safety in Oxyfuel Gas Cutting
Floors on which cutting is done should be concrete or other fireproof material
Shop furniture should be made of metal or fire-resistant material
Flammable materials should not be in the room where cutting is done

55. Safety in Oxyfuel Gas Cutting
Leather or slow-burning fabrics should be worn
Welders’ trousers should not have cuffs
Welders’ pockets should not contain flammable items
Tanks and containers should be welded only by experienced welders

56. Safety
It is generally required to pass an inert gas or steam through the tank as it is being cut
The steam or inert gas is intended to displace any combustible gases in the tank
The tank may also be filled with water except in the area of work
In all cases the tank must be vented to prevent the entrapment of potentially explosive gases

57. Safety in Oxyfuel Gas Cutting
Certain metals, such as magnesium, can burn with an explosive force if flame-cut
The face and hands must be protected from metal splatter
A fire extinguisher should be at hand and a fire watch posted during cutting operations
Follow correct procedures for using cylinders, regulators, hoses, and torches

58. Safety in Oxyfuel Gas Cutting
Review metal fume hazards
Know what metal is being worked on before performing any cutting operation
Check that ventilation systems are working
As the oxygen content in an enclosed space is increased above a certain percentage, there is an increasing danger of a spark or flame causing a fire or explosion

59. Safety Be certain of what metal is being cut
Never use acetylene at a pressure greater than 15 psig (103kPa)
Acetylene becomes unstable above that pressure and may explode