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Oxy-Fuel Primer — Introduction to an Essential Tool for the Aspiring Blacksmith

By John Henderson, Group Brand Manager, Victor Technologies

After hammers, anvils, tongs, vise and a forge, no other tool is more essential to the aspiring metalworker than an oxy-fuel combination torch. A combination torch features a torch handle and attachments for cutting metal, heating, welding and brazing. For an investment of a few hundred dollars, no other tool offers such process versatility.

Heating Scroll
A forge can only heat, a plasma cutter can only cut, and a welder can only weld — but with a combination torch, you can do it all, especially the pinpoint heating required for ornamental drawing, scrolls and twists.

What Is Oxy-Fuel Technology?

Oxy-fuel processes use a fuel gas — most commonly acetylene, but alternately propane, natural gas or propylene —in combination with pure oxygen to heat, cut and weld steel. Note that if you plan to weld, you must use acetylene. Oxy-acetylene combustion produces CO2 that shields the molten weld pool from contamination. Further, a neutral acetylene flame won’t introduce oxygen or carbon contaminants.

To control the oxygen and fuel gas, a combination torch handle has two valves, a barrel (handle body) through which the separated gases flow, and a threaded head for connecting attachments.

OxyAcetylene Welding
Gas welding works similarly to TIG welding in that the operator creates a molten weld puddle and manually adds filler.

A welding attachment mixes the gases and directs the homogenized flow through a single orifice that enables the user to gas weld. A welding tip also enables pinpoint heating, as well as brazing. A multiflame heating attachment, as its name implies, has multiple orifices to support a higher volume of gas flow to heat a larger mass more quickly.

A cutting attachment has three tubes: one for the fuel gas, one for pre-heat oxygen (the flow of which is controlled by the valve on the torch handle) and one for cutting oxygen, which is controlled by the valve and lever on the attachment.

Cutting Outfit
While some cutting attachments appear to have only two tubes, they actually feature a tube-in-tube design for the pre-heat oxygen and fuel gas, which adds strength and rigidity.

 

In oxy-fuel cutting, the cutting attachment mixes the pre-heat oxygen and fuel gas. Once ignited, the pre-heat flames bring the steel to its kindling temperature, or to the point where the steel becomes cherry red and will readily react with oxygen. As this point, the operator depresses the cutting oxygen lever to deliver a stream of pure oxygen through the cutting tip’s large central orifice. The resulting exothermic reaction is largely self-sustaining, and cutting proceeds quickly.

Cutting Oxygen
This photo clearly shots the cutting oxygen stream in the center of the flame.


Oxy-Fuel Compared to Plasma Cutting

As a point of clarity, oxy-fuel “cutting” of steel is actually high-efficiency, high-precision oxidation, or rusting. In short, the cutting oxygen does the real work. The process works because iron oxide melts at a lower temperature than iron. Oxides of other metals — notably aluminum — melt at a much higher temperature than base metal, which is why they are not candidates for oxy-fuel cutting.

Fortunately, the plasma cutting process cuts all electrically conductive metals. Novice operators learn to cut more precisely with plasma, and the process can be very precise when paired with an automated cutting table. Plasma also cuts thinner materials very quickly.

Plasma Cutting

The plasma process excels at cutting shapes, especially on thinner material.

Conversely, when cutting thicker material (say above 1-1/2” for hand-held applications), oxy-fuel cuts faster than plasma and cuts material 6” thick. As noted, an oxy-fuel combination torch also provides the ability to heat and weld. Because serious metal workers prefer to use the tool best suited for the task at hand, they usually end up complementing their torch with a plasma cutter as soon as funds allow. Table 1 compares the two processes.

 

 

 


Table 1 – Comparing Oxy-Fuel to Air Plasma Cutting

Oxy-Fuel

Air Plasma

Cutting Ferrous Metal

Yes

Yes

Cutting Non-Ferrous Metal

No

Yes

Cut Thickness Possible*

1/8 to 6”

Thin gauge to 1-1/2”

Precision Cuts

Yes, but requires more skill

Yes, and easier to learn

Dross and Clean-up

More slag to clean, slag can be harder to knock off

Less dross to clean, dross is usually easy to knock off

Heat Affected Zone

Larger

Smaller

Heating

Yes

No

Welding Steel

Yes – with acetylene

No

Brazing/Soldering

Yes

No

Portability

Easier – anywhere the operator can move tanks

More considerations for electricity and compressed air

Productivity

Slower – but not a primary issue in blacksmithing

Faster – a primary issue for higher volume fab shops

Purchase Price

Lower

Higher

Consumables Costs

Generally higher for gas and cylinder rental, lower for tips (tips tend to last if cared for)

Lower costs for electricity, shop air; higher tip and electrode consumption

Safety Issues

Flammable gases, flames, sparks, some UV rays. Safety gear required.

Electricity, cutting arc, sparks, UV rays/arc flash. Safety gear required.

Key take away

Essential for heating in ornamental work, offers process versatility

Essential for higher productivity, cutting thin gauge metal, precision cuts

* For the medium- to heavy-duty torches appropriate for ornamental work and hand-held air plasma cutting systems.

What to Look for when Purchasing an Oxy-Fuel System

For those making a first purchase, consider an oxy-fuel system that contains all of the essential items (except gloves and leathers). A typical oxy-fuel “outfit” comes with:

  • Oxygen and fuel gas regulators. Note: acetylene and alternate fuelsrequire different regulators. Purchase an outfit with the regulator that matches your fuel gas choice.
  • Hoses
  • Torch handle
  • Attachments for cutting, heating and welding
  • Cutting tip (Note: all cutting tips are gas specific)
  • Spark lighter
  • Tinted safety goggles or glasses
  • Gas flow rate “tip” charts for easy set-up
  • Operator’s manual

Note that some torch systems are fuel-specific, while others feature a “universal” design, or one whose gas mixer works equally well with acetylene and alternate fuels. With a universal gas mixer, you’ll never have to worry about not having the right attachment if your preferred fuel gas isn’t available.

One Torch All Flames
With a universal torch, you only need to select the correct cutting tip to switch between acetylene and alternate fuels.

Torch handles also vary widely in their design. For example, newer torch handles feature improved ergonomics and color-coded and labeled valves for greater clarity. Premium handles feature built-in check valves and/or flashback arrestors, which, respectively, help prevent reverse gas flow and extinguish a flashback before it can reach the gas cylinders.

Premium Torch Handle
If a torch does not feature check valves or flashback arrestors, install them as an aftermarket item for added safety.

Regulators also come in a wide variety of designs and duty levels. Some of them are color-coded to indicate gas type (e.g., green for oxygen, red for acetylene and orange for alternate fuels) and even feature “crumple zones” that can keep the regulator intact in case the cylinder tips over. The key points for the beginner are to select a regulator from a reputable manufacturer, to select one that matches your fuel gas and to be sure the threads match the gas cylinders you plan to use.

On all of the above items, consulting with a knowledgeable welding supply distributor during the purchase process can save a lot of headaches down the road.

What “Size” System Do you Need?

When considering a torch system from one of the leading manufacturers, you’ll see that they offer “light,” “medium” or “heavy-duty” systems. Duty does not refer to durability. These manufacturers engineer and build all their torches to take decades of hard use. Instead, it refers to physical size and — most critically — the ability to support the gas flow rates associated with a particular attachment or tip size.

With plasma cutting, you increase current to cut thicker metal. With oxy-fuel processes, you increase gas flow and select a tip or attachment specifically engineered to support that flow. A “tip chart” inside the outfit or in the owners’ manual provides the needed guidance, but either a medium or heavy-duty system would be appropriate for ornamental work. Light-duty torches work well for artistic welding and brazing applications, but you might not get the cutting and heating capacity desired for thicker metal.

Heavy Duty
A heavy-duty acetylene outfit might include a #1 cutting tip for metal up to 3/4”, #1, #3 and #5 welding tips for metal up to 1/2” and a #8 multiflame attachment.

If the system you select doesn’t have the correct tip or attachment size, don’t worry. You can find the right size at your local welding supply store, which is another advantage of purchasing a system from one of the leading brands: consumables and parts are widely available.

Fuel Gas Choices

If you plan to weld, choose acetylene. Most experts also prefer this fuel gas because it also cuts, pierces and heats most effectively, and that includes consuming the lowest amount of oxygen (see Table 2 below). However, an acetylene cylinder must stay upright (see cylinder section below). For those who need to move cylinders and/or need to store a cylinder on its side, consider an alternate fuel.

Table 2 – A comparison of fuel gases.

Acetylene

Propane

Propylene

Oxygen to Fuel Gas Ratio

1.2:1

4.3:1

3.7:1

Withdraw Limits

1/7th of cylinder contents per hour

N/A

N/A

Neutral Flame Temp in oF

5720

4600

5240

Burning Velocity in Oxygen ft/sec.

22.7

15.2

15.0

Primary Flame in BTU/ft3

507

55

403

Secondary Flame in BTU/ft3

963

955

1969

Total Heat in BTU/ft3

1470

1050

2372

Cylinders Size and Safety Considerations

Can you afford to run out of gas in the middle of a project? Can you quickly and conveniently obtain new cylinders, or does the welding supply route truck only stop in your area every other week? Do you need to move the cylinders? And lastly, with acetylene, can the cylinder size support your withdraw rate requirements?

Acetylene Cutaway
An acetylene cylinder contains a porous mass saturated with liquid acetone.

The basic structure of an acetylene cylinder is very different from other cylinders, which are only shells. An acetylene cylinder contains a porous mass saturated with liquid acetone.The acetylene gas is then pumped into the cylinder and absorbed into the acetone. As you use the gas, it is released from the acetone. Because of its nature, there are several important safety considerations specific to acetylene.

First, always use and store the acetylene cylinder in an upright position. If you must put a cylinder on its side, restore it to an upright position as soon as possible. Without going in to regulatory requirements, simply play it safe and leave the upright cylinder sit for 24 hours before using it. Second, never use acetylene above 15 pounds pressure. Acetylene has a tendency to disassociate above 15 psi, and it can cause a chemical reaction. Third, you can only withdraw 1/7th of the cylinder volume per hour; any more and you risk withdrawing liquid acetone.

Take, for example, a 75 cubic foot . acetylene cylinder, often called “WQ” size in industry lingo. Dividing 75 by 7 gives you 10.7 usable cubic feet per hour of gas. By cross referencing a chart for multiflame attachments (MFA), you can see that a #6 MFA has a minimum gas flow rate of 14 ft3/hour — which means you absolutely cannot use this size tip with this size cylinder. Either step down to a #4 MFA (6 ft3/hour minimum), step up to a 125-cubic foot “WS” acetylene cylinder (17.9 ft3/hour maximum withdraw rate) or use one of the alternate fuels, as they have no withdraw limitations.

On a related note, you may be tempted to save a buck and purchase a light-duty “tote” system. They’re popular with maintenance and HVAC/R professionals because of their portability. However, the small “MC” acetylene tank size cannot support the flow required for heating, so they are not suitable for ornamental work.

If you’re not sure about the right cylinder size, start out renting — some distributors will even count your rental fee toward the purchase price.

Blacksmith Fundamentals

To help beginning blacksmiths get the most out of their oxy-fuel torch, we turned to Neil Mansfield, lead instructor at Assabet Valley Regional Technical High School in Marlboro, Mass. Mansfield uses blacksmithing as a hook to attract students to the school’s 4-year metalworking program. The chance to express themselves with hot metal not only appeals to their creativity, it forms a strong foundation for the other cutting and welding processes used in a skilled trade career.

“The oxy-acetylene torch is in the DNA of a welder. It’s seeped into our bone marrow,” says Mansfield, a former Navy Seabee and third generation Ironworker from New York City.

When the Navy sent him to welding school, he saw rows of oxy-acetylene welding torches and questioned why they were teaching an archaic process.

“Then I realized that the oxy-acetylene weld puddle slows everything down,” says Mansfield. “It gave me a chance to learn how to manipulate the weld puddle. All concepts of puddle manipulation, whether from gas or an arc welder, stem from the skills I learned while gas welding.” Carrying this realization forward, students at Assabet learn to gas weld before they arc weld.

Mansfield himself took up blacksmithing 14 years ago, and today he creates and sells ornamental work much of it the gates, railings, fences and decorative home items associated with a master craftsman.

“Bar stock as it comes from the steel mill has no life in it. The hammer, anvil and torch’s heat bring life to a dead piece of metal,” he says. “We bring life by twisting, scrolling and making it decorative. You need a railing for safety, but a railing is kind of like a Christmas tree – you make it decorative to add eye appeal.”

Mansfield believes that blacksmiths feel a connection between their eyes and the hammer, the metal and their brain. They use the connection to add “radius lines” to the metal, keeping the lines smooth and undulating — and never flat. To add lines to metal, blacksmiths use three fundamental techniques: drawing, scrolling and twisting.

[Note: In the following sections, the short tips are basically the photo captions in and of themselves, so there are no separate captions for these images.]

Basic Ornamental Techniques

Mansfield and two of his post-graduate students, Cameron Hulme and K.C. Waldbillig, kindly shared their time to demonstrate these techniques and share related tips.


1. Clean and organize your work area. Place tools within easy reach, as you’ll only have about 30 seconds to work the metal before it cools. Clamp the barrel of the torch handle in a vice to free your hands. Pinpoint Heating
2. With a torch or forge, heat the steel to what Mansfield calls “forging yellow,” a temperature of about 2,000 – 2,500oF. Heating Scroll
3. Work on the edge of the anvil, not the center, so the metal has a place to go. When the hammer blow compresses the metal, it squeezes forward. Drawing out is the technical term for this process. Working on the Edge
4. Make hammer blows at 90 degrees to each other to start, and develop a consistent rhythm. Hammer 1-2-3-4, turn the metal 90 degrees and hammer 1-2-3-4, turn back to your starting point and repeat. Once the metal gets drawn to a spear point, hit the corners to turn a square into an octagon; hit the corners of the octagon to create 16 sides, working until you have a round point that flows back into the square bar stock.
5. Using the torch to direct heat to specific areas of metal “protects” the unheated area of the metal from being worked. Note that a larger welding tip such as this can also heat a large area if needed. Pinpoint Heat
6. Use a multiflame attachment to heat a part more quickly or to heat a larger work area. Multiflame attachment
7. To turn a point into scroll, heat the point and hammer it over the edge of the anvil. Then, turn the point upright and, working from the far side, hammer it toward you. Starting Scroll
8. After starting the scroll, use scrolling tongs to bend the metal. Move the tongs about 1/4” at a time to prevent flat spots. Isolate the bends by directing pinpoint heat with a torch, as well as by holding the bar stock with a pair of wolf jaw pliers (these tongs have indentations to firmly grip square stock on the diamond, not the flat). Tongs and Pliers
9. Decorative twists are another essential element, and you’ll need stock with square edges to obtain the desired eye appeal. To provide even twisting power and obtain better leverage, Mansfield cut out a “twisting wrench” on an automatic plasma cutting machine. The wrench slots match common bar stock sizes. Twisting Wrench
10. Use a vice to straighten out imperfections. Sometimes blacksmiths straighten stock with a rawhide mallet to avoid damaging the edges of a twist. Straigthen

 

You’ll make lots of mistakes while learning, but don’t worry. Just straighten out an ugly scroll…or put on the cutting attachment, remove the offending piece and start over.

 

Tips to Get the Most Out of Your Torch

1. Carefully follow the safety and operating instructions included with your new oxy-fuel system. In addition, Victor Technologies offers dozens of gas equipment videos and support material on its training website, http://training.victortechnologies.com. No registration is required and access is free.

2. Set gas flow rates according to the tip chart or owner’s manual included with the torch (or on the manufacturer’s website). Pressures of 3-5 psi are common for welding tips and cutting tips size 0 and smaller.Acetylene

3.   When using a cutting attachment, open the pre-heat oxygen valve on the handle all the way so as not to restrict flow of the cutting oxygen. Adjust the oxygen-to-fuel ratio using the valve on the cutting handle.

4. To light the torch, open the acetylene valve 1/8 turn and ignite the gas with a spark lighter. The resulting flame gives off smoke and soot. Slowly open the acetylene valve until the smoke disappears. Now slowly open the oxygen valve until you establish a bright neutral flame and the “acetylene feather” extending beyond the inner cone disappears. If using a cutting attachment, depress the cutting oxygen lever; you may need to rebalance gas flow afterward.

5. Learn to recognize a neutral flame, or one with the proper oxygen-to-fuel ratio. With acetylene, look for a well defined, bright blue inner cone. An “acetylene feather” protruding beyond the inner cone indicates a carburizing flame (too much acetylene), as does a light yellow flame. An oxidizing flame (too much oxygen) shrinks the size of the inner cone and turns it white, burns with a loud hissing sound and throws excessive sparks while welding.

6. Change tip sizes to increase or decrease heating or cutting capacity. Always keep gas pressures within recommended limits.

7. Alternate fuels are much heavier or lighter than air, so they tend to “float” when lit. As a result, you need to learn different lighting techniques. Turn the fuel valve 1/4 to 1/2 turn and light. Place the tip on the workpiece at about a 45-degree angle, open the oxygen preheat valve 1/4 to 1/2 turn until the flame “snaps” into place, then walk up the flame as normal. Use this technique on a windy day, if the shop fan is blowing on the work area or if the flame goes out when using technique 1.Snapping Flame

8. To extinguish the flame, shut down the oxygen pre-heat valve first, fuel last. If, after you have shut off both valves and a small flame remains, it can indicate a leaking fuel valve. If you hear a popping sound, one of two things happened. You either reversed the shut off order, or you have a leaking oxygen control valve. If you suspect a leak, have your equipment inspected and repaired by a qualified technician.