One of the most widely used cutting tools around is the oxy-fuel or oxy acetylene cutting torch, also commonly referred to as the blow torch. While using a cutting torch is easy in theory, many people find it difficult to properly use, let alone make a proper cut. Most of them have no idea about the proper settings, particularly involving the working pressure, that is why the cuts they made are of poor quality.
The proper use of an oxy acetylene cutting torch, especially with the right pressure settings, ensures that the quality of the cuts made would rival that of machine cuts. Not only that, but this will also guarantee a safe operation.
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How Do You Set Up an Oxy Acetylene Torch?
Unlike the portable blow torch, an oxy acetylene torch involves different components that must be correctly set up. Doing so not only ensures a proper operation that can result in quality cuts but also minimizes the risks of accidents, especially flashbacks and explosions.
Here are the important steps to follow when setting up an oxy acetylene torch:
- Ensure that the cylinders or tanks containing oxygen and acetylene are properly secured and in an upright position. Use a cylinder cart if available but if not, ensure that they are properly fastened or chained to a sturdy object, post, beam, or wall. They should never be knocked down during operation and even when not in use.
- Remove any coverings placed on the valve of the cylinder or tank. But if protective covers were not used, remove any dust or debris that has settled inside the valves, which can cause the torch to malfunction. To do so, stand away from the valve’s opening or outlet (preferably on its opposite side), turn the valve quickly about a quarter of the way, and immediately close it. This quick release of gas will immediately blow away the dust or debris.
- Connect the regulators to the valves but confirm first that they have the same threads. If not, use an adaptor to connect them. It is important that they have a completely tight and secure fit not just for safety but also for proper monitoring of the pressure settings. Manually screw them by hand as tight as you can, and use a wrench with a fixed opening to finish tightening them.
- Attach the proper hoses if they are not yet connected to the respective regulators. If you have already used them before, connect them to the same tanks as before. Note that the standard practice is to use green hoses for oxygen and red hoses for acetylene. Never apply any oil, grease, or any form of lubricant to the hoses, especially on its ends.
- Connect the torch handle to both of the hoses. Once they are securely attached, install the cutting torch to the handle and manually tighten the nut. Check the valves on both the cutting torch and its handle, as they must be closed before opening the valves of both cylinders.
- Turn the valve of the oxygen tank or cylinder until it is fully open. Locate the regulator’s adjusting screw and turn it clockwise until the gauge shows that the pressure being released is between 40 to 60 psi.
- For the acetylene cylinder, do a counterclockwise turn for the valve, but only a quarter of the way. Turn the adjusting screw on the regulator until it releases acetylene and the gauge shows 10 psi.
- Find the oxygen valve of the cutting torch and open it slightly to allow oxygen to flow. Do the same for the cutting torch’s acetylene valve but do not open it by more than 45 degrees or a 1/8 turn.
- To do a leak test, coat the valves and connections between the cylinder, hose, and regulators with a leak-test solution or a thin paste made by dissolving Ivory soap and use a clean brush for its application. A leak is present if you see any small bubbles on the coated surfaces after letting the solution sit for a few minutes.
- If leaks are present, you must retighten or reattach connections first and do another leak test before lighting the torch.
- Once there are no more leaks present, follow the manufacturer’s instructions to light up the torch.
Remember to watch the flame as you use the torch. If it goes out when using the torch, stop and simply relight the torch. This occurrence is known as a backfire and it happens when the torch itself and the metal being cut get into direct contact.
How to Light an Acetylene Torch
Lighting an acetylene torch is fairly easy, but you must follow the correct steps to do so, and this mainly involves tinkering with the oxygen and acetylene valves of the cutting torch to get the right kind of flame. Also, make sure that both oxygen and acetylene regulators show the right amounts of psi before lighting.
The following steps are the standard procedures but always check with the manufacturer for specific instructions:
- Open the acetylene valve with a half-turn first before using a friction or spark lighter, not a match, to create a flame coming from the torch. There should be a one-inch gap between the tip of the torch and the flame coming out of the lighter.
Using a match to light the torch is risky; you may accidentally burn yourself once the flame comes out. Some torches also come with their own ignition devices, so manually lighting them up with a lighter is unnecessary.
- Black smoke or soot may come out together with the flame. Wait until it disappears before slowly opening the oxygen valve. The oxygen being released will remove any yellow sections on the flame, which is essential for a neutral flame.
- Adjust both valves to achieve a neutral flame, which must have a small, whitish or bright blue center and is clearly shaped like a cone.
When lighting the torch, make sure that the tip faces away from people or any flammable object to avoid any accident.
Cutting Torch Tip Sizes
Choosing the right tip size for your cutting torch will mainly depend on the thickness of the metal to be cut and the application. While the different tips serve the same purpose, you must choose the correct cutting torch tip to make it easier to achieve a quality cut on the metal.
Each torch manufacturer has its own recommendations for tip or nozzle sizes that depend on the thickness of the plate or metal. They also have different means of classifying the different cutting torch tip sizes, but the standard practice is assigning a number. A low number indicates a small tip size, while a high number indicates a large tip size.
Generally, the thicker the metal, the bigger the nozzle or tip size required. This means a thin plate requires a tip with a small nozzle to make a precision cut, while this kind of tip is insufficient for cutting through thick metal.
Cutting torch tips for general use have more sizes available. This variation allows them to cut through metals of varying thickness, from ¼ of an inch and up to 12 inches thick. On the other hand, specialized tips, such as angular ones, have more limited sizes.
Note that bigger cutting torch tips with larger nozzle sizes will require more oxygen and acetylene to create a neutral flame and a slower speed to cleanly cut through metal.
How to Use Acetylene Torch
To use an acetylene torch for cutting after properly setting up the equipment, conducting a leak test, and lighting up the torch, you must first pre-heat the metal in preparation for cutting. Do not press the torch lever when doing so, as the flame present is only hot enough for pre-heating, not cutting.
Do so at one of the edges or ends of the cut to be made, preferably at the most difficult section to cut. This will soften the metal to make it easier for cutting. Keep an eye on the metal being pre-heated; stop when the metal surface shows a bright cherry red color. This color indicates that the metal is ready for cutting.
Once the metal is soft enough, slowly press the torch lever to produce the flame suitable for cutting. Start at the pre-heated edge, check if a cut has been made, and slowly make your way to the other edge of the metal at an even speed and following the mark you made on the metal.
Keep in mind that the metals are still hot after cutting, so allow it to cool first before touching them even with gloved hands. Also, never lay down a lit-up torch on any surface.
What is the Ratio of Oxygen to Acetylene?
A neutral flame is produced when there is a 1:1 ratio of oxygen to acetylene. You need this kind of flame if you want a quality cut without affecting the metal’s properties. This is because the equal amounts of these gases will produce carbon dioxide that acts as a shielding gas. This shielding gas then prevents the oxidation of the metal and gives you a clean cut.
Oxy-Acetylene Torch Working Pressure Settings
While there should be equal amounts of acetylene and oxygen to produce a neutral flame, you must observe the right pressure settings when working with an oxy-acetylene cutting torch. Note that the ratio of oxygen to acetylene is different from the pressure required. This means that oxygen and acetylene should not have equal psi readings.
In general, oxygen must have a higher pressure setting than acetylene. The actual setting will depend on the cutting tip being used and manufacturer recommendations. But as a rule, more pressure for both oxygen and acetylene is needed for bigger-sized cutting tips.
In case the recommended working pressure settings are not indicated, safe numbers are 40 psi for oxygen and 10 psi for acetylene, regardless of cutting tip size. Simply adjust them until you get a neutral flame, but pay close attention to the acetylene pressure to prevent it from exceeding the limit.
What is the Maximum Working Pressure for Acetylene Gas?
The maximum working pressure for acetylene gas when using a cutting torch is 15 psi or 103.4 kPa. If the pressure goes beyond that, raw acetylene gets unstable and becomes dangerous to use. Acetylene is a flammable gas and when it becomes unstable, it is at risk of spontaneously combusting. Raw acetylene can cause an explosion even with a slight shock.
Fortunately, this risk is minimized because the acetylene stored inside cylinders or tanks is dissolved in acetone. Liquid acetone stabilizes this gas to prevent it from combusting. Also, the cylinders themselves are laced with acetone, which makes it possible to safely transport or move around the acetylene gas tank or cylinder.
If the acetylene pressure exceeds 15 psi, it will use up the acetone present in the cylinder to be stable. While it has a positive effect on acetylene, it negatively affects the components of your system. Acetone can cause damage or deterioration to any plastic or rubber parts, affecting cut quality. This will also eventually cause the regulator to fail, stopping the entire system. This failure is a sign that the acetone present is nearly depleted and what mostly remains in the cylinder is dangerous raw acetylene.
The worst-case scenario is that the rubber hose will deteriorate before the regulator fails because it has drawn up so much acetone. And when this happens, an explosion is likely to occur.
What Do You Turn Off First, Oxygen or Acetylene?
Turning off the cutting torch, particularly involving oxygen and acetylene, should follow the right order for safe operation. However, this is a point of contention for many; some believe that the acetylene valve must be switched off first, while others advocate cutting off oxygen supply first.
The consensus among manufacturers is that the oxygen should be switched off first followed by acetylene, not the other way around. This allows any soot that settled on the torch to be blown away by the acetylene. A buildup of soot can prevent the fuel valve from properly being sealed off, causing it to leak.
This method also allows you to see if any leaking is present before you completely switch off the cylinders. If there is an acetylene leak, a small flame will remain after you turn off oxygen then acetylene. Detecting a possible acetylene leak is crucial to avoid an explosion.
Interchanging them is possible, but hearing a loud bang is more likely if you switch off acetylene first before oxygen. This pop indicates a mini-flashback and when this happens, you must immediately turn off the oxygen. Even mini-flashbacks can be potentially dangerous.