We've been told many times as a kid not to play with fire, but growing up, we find that there are so many applications for it: from minor activities such as cooking to industrial work such as metal fabrication. A cutting torch is a great tool that uses the combined pressure of oxygen and fuel gas— this process is called “oxy-fuel cutting.” However, this piece of equipment comes with precautions as in any other power tool. You must regulate and monitor both elements to avoid serious accidents such as fire, burns, or explosions. This article will teach you all about oxy-fuel cutting, plus a step-by-step guide on how to use a cutting torch safely.
What is oxy-fuel cutting?
According to The Welding Institute (TWI), oxy-fuel cutting is a thermal cutting process that uses the combined power of oxygen and fuel gas (such as acetylene, hydrogen, propylene, propane, and natural gas) to slice through metals.
The oxy-fuel cutting torch kit is inexpensive, making it ideal for those just starting to learn how to cut metal or work on small-to-medium projects. You can use it manually or mechanized. This industrial thermal cutting process can work on metals with thicknesses of 0.5 mm to 250 mm.
How exactly does this metal cutting torch work? On steel, the torch needs to be preheated to its "ignition" temperature, which is 700°C - 900°C. It should be just below its melting point because the steel would melt and flow away before you can even cut it. The fuel gas used here preheats the metal.
From there, a jet of pure oxygen is aimed into the preheated area to form a slag. The oxygen jet wipes out the slag so the jet can pierce through the steel and continue to cut through it.
The most frequently used fuel gas for this application is acetylene—which produces the highest flame temperature among other fuel gases. Here’s a table to illustrate and compare:
|Fuel Gas||Maximum Flame Temperature °C|
This article will focus on an oxy-acetylene cutting torch.
What is inside a cutting torch kit?
Before we discuss how to use a cutting torch, below are the components you need to assemble an oxy-acetylene torch:
- oxy-acetylene cutting torch
- hoses for acetylene (red) and oxygen (blue)
- oxygen and acetylene bottles/tanks
- gas regulators for each tank
- flame traps (or flashback arrestors)
- hose couplings
- flint lighter or flint striker
Safety Tips Before Cutting Metal
It is crucial to create a safe work environment before you light that torch up. Remember that a cutting torch is fire hazard equipment.
Personal Protective Equipment (PPE)
As recommended by the Canadian Centre for Occupational Health and Safety (CCOHS):
- Make sure your clothes are flame or fire-resistant and well-fitted.
- Only wear clothes made from 100% cotton or wool.
- Avoid loose-fitting clothes made of flammable synthetic materials like nylon.
- Don't wear clothing with torn edges or frayed since it may catch fire.
- The clothes must be long sleeves and pant legs without cuffs.
- Invest in sturdy, leather-soled boots.
- Don't slip into rubber-soled shoes or pull-on boots because slags may enter into it.
- Put on leather gloves and safety goggles or a welding helmet.
- Don't use greasy or oily gloves.
- Don't wear rings or any jewelry.
Maintain a work area free of flammable materials by doing the following:
- Work on a concrete slab or bare earth.
- Keep cardboard, sawdust, paper, grass, or dried plant foliage at least 15 feet away from your workspace, or throw these materials in a bin.
- Set up the project on a steel table, not wooden.
- Don't work on a table that has had flammable residue on it.
- Before and after you work, make it a habit to check for leaks and tighten hose connections.
- Don't keep fuel, paints, and solvents near the work area.
- Put an "ABC" fire extinguisher nearby in case of emergency.
- It would be better to have a work buddy that can alert you of any fire-related mishaps.
How to Use a Cutting Torch
Before you set up the metal cutting torch, mark your cut with soapstone. Ensure it's a straight line using a speed square and a measuring tape. Now, let's set up your cutting torch kit. We have divided it into four parts, as follows:
Part 1: Set the regulators
- Connect the regulators to their respective tanks or bottles using a wrench and tighten them securely.
- Ensure the acetylene regulator is switched off.
- Open the gas valve located above the acetylene bottle with one single turn.
- You can now open the acetylene regulator until it reads between 5-8 psi.
- Release the atmosphere from the acetylene hose by opening the gas valve on the torch handle.
- Ensure the oxygen regulator is turned off.
- Turn the handle of the oxygen tank to open it all the way.
- Turn on the oxygen regulator slowly until it reads between 25-40 psi.
- Allow a small flow of oxygen to escape by opening and closing the valves.
Part 2: Light the torch
- Open the acetylene valve slowly.
- Ignite the torch using a flint striker. A yellow flame should appear when you do this.
- Carefully adjust the acetylene valve until the yellow flame is about 10-12 inches long.
- Open the oxygen valve all the way. This can be found at the bottom of the handle.
- Next, slowly open the second oxygen valve until the flame turns blue.
- Keep adding oxygen until the inner blue flame constricts down towards the tip. It should look like a crown-shaped cone.
Note: The inner flame's length should be over the steel's thickness. For instance, a ½ inch inner flame is suitable for a 3/8 inch metal.
Part 3: Cutting with the torch
- Bring the tip near the surface of the metal.
- Heat the metal with the flame until the surface is near the melting point and turns bright red.
- Release the oxygen jet by slowly pushing the cutting valve down to ignite the molten metal.
- Slowly drag the cutting torch tip along the mark that you drew.
Note: While doing this, you will notice molten slag and sparks blown at the bottom of your cut. Watch out for these and ensure you don't get heated metal underfoot.
- Continue the slow, steady cutting process until it is complete.
Part 4: Shut down the cutting torch and cool down the finished workpiece
- Switch off the torch valve and then the oxygen.
- Turn the oxygen tanks' cylinder valves off.
- Pull back the regulator pressure screw.
- Repeat nos. 1 to 3 for the acetylene bottle.
Note: Please read the manufacturer's instruction manual carefully because some models may require you to switch off the acetylene tank first before the oxygen bottle.
- Let the finished workpiece cool naturally, especially if the metal is a temper or quench-type.
Note: You may cool it by pouring a bucket of cold water if you're in a hurry. But take note that this action produces a cloud of scorching steam.
We hope this tutorial on how to use a cutting torch may help you with your future projects. Keep in mind that you have to be self-aware when using a fire hazard tool. Follow the safety protocols and step-by-step guide above to ensure your safety as you work.