How to properly cut metal with propane and oxygen

Principle design of a gas cutter

Injector or twin-tube torch

It’s the most popular model by design. The name “two-pipe” comes from the separation of process oxygen into two streams. This is done to functionally separate the work of oxygen.

A second flow of oxygen goes directly to the injector. The procedure in the injector chamber is as follows: oxygen enters the chamber at high pressure and high velocity, as a result of which a rarefied pressure zone is formed in this space. In this case the oxygen is injected.

Through special side openings in the walls of the chamber a combustible gas is drawn into the chamber. in this case it is injected. The gases mix, the velocities are equalized and finally at the chamber outlet a gas mixture with a lower velocity than that of injected oxygen, but a higher one than that of combustible ejectible gas is formed.

At the next stage, the formed gas mixture enters the tip. first into its head and then exits through the nozzle between the mouthpieces and forms the very flame in the form of a torch, which heats the metal to its burning temperature. All gas flows are controlled by dedicated valves on the outside of the body. for oxygen supply and separately for fuel gas supply to the injector.

The non-injected or three-pipe gas torch

In this case the construction of the gas cutter is more complicated. Oxygen enters it through two tubes, the third tube is rightfully occupied by combustible gas. In this welding torch, the gases are mixed inside the head, there is no chamber. This system is safer than the dual-chamber model.

This model has a significantly higher cost. In addition to this drawback, the three-tube torch has another nuance: it requires a very high pressure of flammable gas. higher than with the injector device.

How to cut metal with a gas cutter: equipment

On a professional level, an angle grinder and engraver are not always sufficient. For larger amounts of ferrous metal, metal cutting with a gas cutter is already necessary. And about its advantages and how to use it. read this article.

The principle of operation and types of torches

Regardless of the size of the autogenous torch and the variety of heated gas mixture, cutting can be performed by the process of metal combustion in a stream of pure mixture oxygen, injected through a special nozzle in the head of the working area.

The main and principal feature of gas cutting is the combustion temperature, which should be not less than the melting point. Otherwise, the metal, not having time to ignite, will melt all the time and flow down. Low-carbon steels must meet these conditions, but base metals and cast iron do not.

A large number of alloyed steels will also not be amenable to the process of gas cutting. there are significant restrictions on the maximum rate and the allowable doses of alloying components, carbon, impurities, above which the burning process inside oxygen will be the most unstable or even cease to flow.

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The cutting itself should be divided into two stages:

  • Heating one part of the part to a temperature where the metal starts to burn. In order to get a flare of heating flame, some of the technical oxygen in a certain ratio is mixed together with the gas.
  • Combustion process (oxidation) of heated metal in the oxygen stream and the overall removal of the combustion product from the cutting zone.

If we begin to consider the classification of only hand torches, this value will have the following features:

Type of fuel, power and method of obtaining a mixture of gases for the heating flame.

  • Classification according to the type of combustible gas: propane-butane, methane, universal MAF, as well as acetylene.
  • Power feature: small (cutting metal of thickness from 3 to 100 mm). marking P1, medium (up to 2-0 mm). marking P2, higher (about 300 mm). marking P3. There are special models with a cutting thickness of about 500 millimeters.
  • And if the first feature will only affect the overall temperature of the heating flame, as well as the power. the maximum thickness of the metal, then another feature will be determined by the design feature of the torch.

How to choose a better torch?

How a gas torch works. Here is a block of useful information that will help you get oriented better in specifications and technical characteristics of torches in advance:

  • The nipples come in brass and aluminum. Brass versions are more durable.
  • If possible, choose models with aluminum handles rather than plastic ones. No matter how heat resistant plastic is, it will “float” faster than aluminum.
  • The handle must be massive enough: at least 40 mm in diameter.
  • Valves must work well. That means it can turn without much effort.
  • Lever operated machines are more convenient and economical to use, they save gas.
  • The valve spindles must be made of stainless steel, not brass, which is too short-lived. There are “combined” versions, they occupy the middle position in terms of durability.
  • The best material for the torch body is metal: brass, copper, stainless steel.
  • We remember that acetylene torches are more expensive. Take care of the material of the parts that are in direct contact with flammable gas before mixing in the chamber. Warning! They should not be made of copper or copper alloys, which have at least 65% copper.
  • If it is collapsible, it is better: it is easier to clean and repair.
  • Copper only! Only copper outside nozzle!
  • The correct inner mouthpiece on an acetylene type gas torch should also be copper. But the oxygen metal torch is made of brass. Here are some more details.
  • Be sure to check with your salesperson about spare parts and consumables.
metal, propane, oxygen

Metal cutting torch: a type

Gas torches for metal are divided according to different criteria. For example, there is a classification according to the gas used, size, type of cutting, design, method of mixing consumables.

Acetylene

It is a metal cutter, which is used for cutting metal parts of great thickness. Acetylene equipment is equipped with additional valves, which allows you to set a high gas flow rate. There are industrial and portable models of torches. Acetylene provides maximum flame temperature. It results in great depth of cut of metal.

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Acetylene torch for metal

Propane torch

Propane-fueled equipment is used for cutting alloys, non-ferrous and ferrous metals. Maximum cutting thickness of 300 mm. Propane torches are more reliable, which leads to their durability during active use. Masters pay attention to the safety of such devices. They are often used for do-it-yourself work in private workshops.

Portable gas torch

You can buy a device for stand-alone operation. Mini torches fit in the palm of your hand. Are a metal cylinder with gas, on which a nozzle with a system of combustible substance supply is screwed on. You can compare a handheld unit to a turbo lighter. With matches, lighter or installed ignition system, the gas is ignited, passes through special nozzles, nozzle, which form a thin jet of high temperature flame. It does not blow out in strong winds, making it easy to use the handheld torch outdoors. To fill a small cylinder, you can use a special nipple for refilling or buy a new full container.

Principle of operation and classification of gas torches

Can the metal be deformed??

Cutting with gas involves a thermal impact on the material, as a result of this deformation changes can not always be avoided. Deformation includes lengthening, shortening, or bending. The cut part can be turned inward or outward.

There are factors that contribute to the deformation of metal:

It is necessary to exclude the action of these factors, otherwise you will have to correct the received defect. There are a few simple methods that allow you to return the workpiece to its correct shape: use roasting or tempering, steel straightening on the rolls.

Deformation can be avoided by pre-fixing and preheating the workpiece, observing the gas mixture feed rate, and adhering to the correct cutting technique. It is important to carry out all stages consistently, and choose a cutting mode based on the thickness and type of material. Do not start cutting at high cutting speeds.

If you do not have much experience, you should start with small billets, and not with cutting products from solid sheets.

Safety Requirements

Gas equipment used in metal cutting, namely, an oxyacetylene torch, is classified as explosive and flammable. So before you use a gas cutter, you should follow all the mandatory safety recommendations.

For this purpose, the workplace should be equipped with:

  • a fire extinguisher. The use of a gas torch is accompanied by an open flame and high temperatures, so the fire extinguishing equipment must be present at the post;
  • Protective overalls consisting of:
  • A cotton suit, if possible, impregnated with a flame retardant;
  • gloves or mittens made of tarpaulin or thick enough leather;
  • boots with leather soles;
  • safety glasses with integrated light filters.
metal, propane, oxygen

No articles of clothing made of synthetic or other readily flammable fabrics shall be worn when working with the torch, nor shall they fit snugly against the body or have badly worn edges. All of these things can lead to fire, and consequently, to danger to health and life.

Only different grades and types of unalloyed carbon steel can be cut with gas. Stainless steel, nonferrous metals, and various alloys cannot be cut with a propane torch.

Standards and dimensions

Welding with a welding torch and gas.

All standard measurements regarding gas torches are specified in GOST 5191-79. Naturally, the weight and size of the units are directly related to their power. Weight, for example, there are only two values: torches models P1 and P2 weigh 1.0 kg, and a high-power model P3 weighs 1.3 kg and not a gram more or less.

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By the way, type of combustible gas is also related to power and size. If high-powered P3 torches can work only with a mixture of oxygen and propane, the smaller P1 and P2 torches can work with any gas type.

How to properly use an oxygen acetylene torch for cutting

Plug-in gas torches:

Besides classic models with different power there is a separate category. the so called plug gas torches with a special marking PW. According to GOST they are called very strange: the tips to a gas torch for metal cutting. In general, they differ from traditional torches: mixing of combustible mixture and oxygen is carried out in the tip itself.

The weight of these devices is much lighter than torches. The PB1 weighs 0.6 kg, but the PB2 and PB3 weigh only 0.7 kg each. But do not let this apparent elegance mislead you. Let’s not forget that these are tips to the torch, complete with which they will weigh no less than conventional torches. What is the advantage then?

They can be added to your existing torch and thus you can save some money. And the compactness of the whole set, packed in a special case. And one more important detail, which concerns the nature of the combustible gas. The fact that acetylene is much more expensive than propane.

But for welding metal much more preferably just acetylene: torch with it gives the flame with the temperature higher by 400 ° C than the same with a mixture of oxygen and propane.

Portable models: to a small ship. a small voyage

The structure of the torch.

The market now offers many portable versions of autogenerators. this is how they are positioned. They are sold as an attachment to a compact collet gas bottle. But in their essence and principle of operation, these are torches. Most of them have a torch temperature of less than 1300°C.

There are, of course, and portable models “professional” range. collet torches that give a temperature above. up to 2000. 2500 ° C, which is generally close in performance to the classical oxypropane torch. But physics is physics: even these models don’t have the main component that cuts the metal. oxygen jet, which oxidizes this very metal.

Where a portable gas torch is good? When cutting easily fusible metals or alloys like tin, brass, bronze, copper. But even these “kids” versions don’t cut, they melt. So the compact torch tips are used more for soldering or welding small non-ferrous workpieces. It can be parts of household appliances like refrigerators or air conditioners. Welding, not cutting, in a word.

In any case be careful when choosing such models not always their suggested “portability” in the end is justified.

Advantages and disadvantages of the technology

if the technician has little experience, he should not take on precise operations, since skills and knowledge are required to perform them;

  • The method is not safe, because the gas/air mixture might explode
  • a large area is exposed to heat;
  • low cutting accuracy.