How to cut thick metal with a cutter

4 Igniting the torch and heating the metal

Before igniting the torch, you need:

  • make sure that all connections are tight (valves, pressure gauges, hoses, other fittings) – any gas leak can instantly cause a fire;
  • check again the place of work for the absence of flammable materials, strangers (especially children), animals;
  • make sure you are ready to work;
  • wear safety glasses and gloves.

The acetylene valve is then opened on the torch, allowing the oxygen that is in the mixing chamber to escape. A few seconds are enough for this. Then the valve is turned on until it becomes audible that the acetylene is barely coming out. A special lighter is placed in front of the cutter, as shown in the video, so that its inside touches the mouthpiece. Then press on the lighter lever. When the sparks produced ignite the acetylene, a small yellow flame should form in front of the mouthpiece..

By turning the gas supply valve, the flame length is increased to about 25 cm. The torch should start at the very mouth of the torch. The flame will burst from it or jump when too much acetylene is supplied.

Open the front oxygen valve slowly. In this case, the flame should change color from yellow to blue – at this moment, the supply of such an amount of oxygen will be provided, which is sufficient for the complete combustion of acetylene. The oxygen supply should be increased until the inner blue flame tongue diminishes and contracts towards the mouthpiece.

The oxygen valve is opened even further – the size of the torch is increased until the length of the inner flame becomes slightly greater than the thickness of the steel being cut (for cold-rolled sheet thickness of 9.5 mm, an excess of the flame length by 1.3 mm is sufficient). When you hear “puffing” or the blue flame seems to be feathery and unstable, it means too much oxygen is being supplied. It is reduced until the entire flame is stabilized, and the inner flame takes the shape of a clear cone..

The inner flame is brought with its very tip to the surface of the steel being processed. It is heated until a puddle of molten glowing metal forms at the point of contact. The tip of the flame must be held still at a distance of about 10 mm from the surface of the steel as shown in the video so that all the heat is concentrated in one area..

How to Cut Thick Metal – Kevin Caron

3 Preparing and setting up gas cutting equipment

To work safely with a gas torch, it is important not only to correctly select the appropriate set of equipment, but also to connect and configure it correctly. First, the appropriate tubes are connected to the oxygen and acetylene cylinders. Oxygen hoses and containers are usually green, acetylene ones are red.

At both ends of the hoses, install safety seals (a device that retards back blows of the flame).

The next step is to check that the acetylene supply is working properly. First, close the flow control valve – turn the T-handle back several times. On the cylinder, in its upper part, open the valve – turn it 1 turn of the hand. They do this for security purposes. The acetylene pressure in the cylinder must not be allowed to exceed 1 atm – in the case of high pressure, this gas becomes unstable and may even spontaneously explode or ignite. To check that the acetylene pressure is adjusted correctly, proceed as follows:

  • The main valve of the vessel is unlocked, then the control valve is opened by turning the knob clockwise. This should be done very slowly, observing the readings of the pressure gauge installed at the low pressure outlet. The control valve is opened until the pressure is 0.34-0.54 atm.
  • Then air is blown from the hose – the acetylene valve of the torch is opened until the sound of escaping gas appears. After that, they look at the readings of the low pressure gauge. During purging, the pressure value must be stable (if not, then make sure that the regulator is installed correctly).
  • The valve on the torch is closed.

They check and adjust the oxygen supply – turn off the regulator of its supply (twist it down), and then adjust the pressure. To reduce the oxygen supply, twist the pressure gauge knob a few turns back. Then follow the sequence of the following steps:

  • On the oxygen cylinder, the main valve is fully unlocked. It is double-seated and in the case of its partial opening due to high pressure in the cylinder (150 atm) oxygen escapes around the sealing ring of the valve stem connection.
  • Slowly open the flow regulator, following the readings of the pressure gauge installed at the low pressure outlet, until the oxygen pressure is set within 1.7-2.7 atm.
  • The atmosphere is blown out of the hose – the oxygen valve is opened on the torch. The cutter has 2 valves for oxygen: one closer to the hose, controls the supply to the chamber, where oxygen is mixed with acetylene to heat the steel (combustion of the mixture), as well as to supply it to the oxygen nozzle for cutting; the other is located further away and supplies oxygen to a separate cutting nozzle (until this valve is open or the special cutting lever is released, oxygen should not come out of the cutting nozzle). First, the first valve is opened and turned several times to ensure sufficient oxygen supply for both functions. After that, the second (front) valve is slightly opened – for a while until the hose is cleaned (3-5 s for a 7.5 m tube).
  • The front valve is closed.

2 Preparing the site and conditions for safe and comfortable work

To ensure safe work using a gas torch, the following rules and recommendations must be followed:

  • To do the work, choose only a place in an ideally ventilated room or in the open air.
  • Can be cut away from flammable substances and materials.
  • The floor in the room must be concrete or earthen.
  • The surface of the earth or concrete must be free of any foreign objects and materials within a radius of at least 5 m, since sparks from the cut metal fly up several meters and can set fire to dry rags, shavings, paper, dried plants or leaves.
  • Place the metal to be cut on a suitable support to use the torch at a comfortable working height. For these purposes, it is best to use a steel table..
  • Do not allow the flame to touch concrete (especially if it is fresh) – this will cause its expansion and subsequent intense cracking with small fragments of concrete flying out of it.
  • It is strictly forbidden to use flammable surfaces as workers, or on which flammable, explosive materials are spilled.
  • The place of the metal cut is marked as shown in the video.

1 Gas torch basics

The process of cutting with a gas torch occurs due to the combustion of metal in a stream of oxygen supplied under pressure. The alloy must be preheated to the required operating temperature using a burning mixture of acetylene and oxygen. The only metals that can be cut in this way are various grades of carbon steel and unalloyed steel. Stainless steel, non-ferrous metals and alloys cannot be cut with an oxygen-acetylene cutter..

To perform this type of work, in addition to the corresponding set of gas equipment, you will need the following:

  • Fire extinguisher.
  • Protective equipment: special glasses; thick leather gloves; sturdy work shoes with leather soles.
  • Appropriate clothing – It is recommended to wear fire resistant clothing, but if not available, a well-fitting cotton will do. Do not wear things made of synthetic and flammable fabrics, loose fit, with torn or worn edges.
  • Measuring and marking tools: ruler, square and soapstone pencil.
  • Torch lighter – designed to properly ignite the torch flame. It is very dangerous to use ordinary matches, lighters.
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How to use a gas torch – the basics of safe and quality work

Cutting metal with an oxyacetylene torch requires certain precautions and the correct sequence of actions. This gas equipment is classified as flammable and explosive.

5 Cutting steel with a gas torch

The handle of the gas cutting valve is slowly released downward – a stream of oxygen is supplied, igniting the molten metal. If a violent reaction immediately begins to occur, then the steel caught fire and you can continue to gradually increase the oxygen pressure until its jet cuts through the material. When the reaction does not take place, the metal is not heated enough to ignite in a stream of oxygen. It is necessary to add oxygen to the heating flame and allow it to heat up the steel.

When the oxygen jet begins to cut, the cutter head is slowly moved along the cut line. At the same time, almost all processing products (molten slag, sparks) are blown away by a jet to the rear side of the cutting zone, as shown in the video. If this flow comes back or slows down, then reduce the speed of the torch or stop it and warm up the material even more (it is better to work very slowly than trying to cut too fast). Cutting continues until the intended cutting or separation of the metal is completed..

Preparation for work

Before starting gas cutting, it is necessary to inspect the device to make sure that the propane torch is in working order. Next, you need to perform the following operations:

  • Preparing the cutting machine begins with connecting the hoses to it. Even before attaching the sleeve, it is purged with gas – this will remove debris and dirt from it.
  • The oxygen hose must be connected to a right-hand threaded nipple and a nut. As for the hose through which the propane will flow, it is attached to the left-hand threaded fitting. Before connecting the gas hose, it is imperative to find out if there is a suction in the cutter channels. This problem can be solved by connecting the oxygen hose to the oxygen fitting, while making sure that the gas fitting remains free..
  • Next, you need to set the oxygen supply level to 5 atmospheres, after which you need to open the valves that regulate the flow of gas and oxygen. Touch the free fitting with your finger – this way you will know if there is an air leak. If it is absent, you will have to clean the injector and blow out the cutter channels..
  • After that, you need to make sure that the detachable connections are sealed. If it is possible to identify a leak, fix it by tightening the nuts or replacing the seals. You should also make sure that the mountings of the gas reducers are sufficiently tight, whether the pressure gauges are in working order..

Getting Started

First, it is necessary to move the oxygen reducer to the position corresponding to 5 atmospheres, the gas reducer – 0.5. You also need to make sure that each valve is in the closed position..

After that, you need to take a propane cutter and slightly open the propane, and then ignite it. The torch nozzle must be positioned so that it rests against the metal, after which the regulating oxygen must be slowly opened. Next, these valves should be adjusted one after the other, thereby providing the required flame power. During such a setting, it is necessary to sequentially open gas, oxygen, gas, oxygen.

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When choosing the strength of the flame, it is necessary to focus on the thickness of the metal. With an increase in the thickness of the sheet, it will be necessary to increase the strength of the flame, which will lead to an increase in oxygen and propane consumption. After adjusting the flame strength, you can start cutting the metal. The nozzle must be held in relation to the edge of the metal in such a way that it is 5 mm away from the object being cut, and it itself must be at an angle of 90 degrees. In some cases, it may be necessary to cut through the sheet or product in the center. In this case, the place from which the cut will go is chosen as the starting point..

The essence of the procedure is reduced to heating the upper edge to a temperature of 1000-1300 degrees Celsius. The exact temperature is determined by taking into account the metal. In practice, such work will look like the surface is “wet”. It will take no more than 10 seconds to warm up itself. After waiting for the metal to ignite, you need to open the cutting oxygen valve, after which a powerful narrowly directed jet will begin to flow.

Preparation for work

Insert cutter diagram.

Before starting work, it is imperative to inspect the device to make sure that the torch is fully functional. Then follow these steps:

  • The first step is to connect the hoses to the cutting machine. Before attaching the hose, you need to purge it with gas to remove any debris or dirt that has got there. The oxygen hose is attached to the right-hand thread with a nipple and nut, the second (for propane) hose to the left-hand thread. Remember to check the torch passages for leaks before attaching the gas hose. To do this, connect the oxygen hose to the oxygen connection, and the gas connection must remain free. Set the oxygen supply to 5 atmospheres and open the gas and oxygen valves. Feel the free fitting with your finger to see if air is leaking. If not, clean the injector and blow out the torch passages..
  • Next, check the detachable connections for tightness. If you find a leak, tighten the nuts or change the seals.
  • Do not forget to check how tight the mountings of the gas reducers are and whether the pressure gauges are in good working order..

Nuances of metal cutting

Flow diagram of the separation oxy-fuel cutting process.

You need to cut the metal at the right speed. The optimal speed can be determined visually by how the sparks fly away. A stream of sparks at the correct speed flies out at an angle of approximately 88-90 ° to the cut surface. If the sparks are flying in the opposite direction of the torch, the cutting speed is too slow. If the angle of flow of sparks is less than 85 °, this signals an overspeed.

When working, it is always necessary to focus on how thick the metal is. If over 60 mm, it is better to place the sheets at an angle to ensure the drainage of slags, and do the job as accurately as possible..

Cutting thick metal has its own characteristics. You cannot move the torch before the metal has been cut to full thickness. By the end of the cutting process, it is necessary to smoothly reduce the advance speed and make the cutter tilt angle 10-15 ° more. It is not recommended to stop during the cutting process. If work is interrupted for any reason, do not continue cutting from the point at which you stopped. It is necessary to start cutting again and only in a new place.

After finishing cutting, first shut off the cutting oxygen, then turn off the regulating oxygen, last turn off the propane.

Despite the fact that, against the background of gas welding, gas cutting has its positive aspects, this work should be approached with the same responsibility. In addition to preparing the necessary equipment, you should familiarize yourself with the main nuances of performing this work. And although this operation seems simple enough, nevertheless, if mistakes are made during gas cutting, this can lead to serious problems associated with the subsequent use of the product..

How to properly cut metal with an Oxy-propane cutter?

Compared to gas welding, gas cutting requires much less skill from a person. Therefore, mastering a gas torch is not that difficult. It is enough to understand how to do it correctly. The most widespread in our time are propane cutters. They use propane and oxygen together, since their mixture gives the highest combustion temperature.

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The propane cutter is designed for manual separation oxyfuel cutting of carbon and low-alloy steels using propane.

Pros and cons

Gas cutting and metal welding has many advantages, but we are only interested in cutting, which has the following advantages:

  • It is in demand when a thick metal is cut or a stencil cut is needed, and an angle grinder cannot cope with curved sections.
  • The gas analogue is much more convenient for work, has a low weight, acts twice as fast as equipment with a gasoline engine.
  • Propane is cheaper than acetylene and gasoline, so its use is more cost-effective.
  • The cut edge is much narrower and the structure is cleaner than from an angle grinder or gasoline equipment.

Disadvantages – a narrow range of metals subject to similar processing.

Disadvantages of processing

Low carbon steel is most suitable for flame cutting, but medium and high carbon steel is not a very suitable material for cutting. The high carbon content raises the flash point and lowers the melting point. And this condition complicates the cutting process..

Cutting metal with a gas mixture is difficult if it has low thermal conductivity. Therefore, these types of material are not suitable for processing.

Flame cutting of metal should only be performed by a qualified and experienced technician. It is important to respect all the key factors for proper treatment: oxygen pressure and procedure speed. Consider product thickness and torch nozzle diameter. If the speed of oxidation and cutting of metal does not correspond to each other, then poor-quality processing will result..

Oxygen cutting involves the use of explosive substances. If safety rules are not followed, there is a high probability of an explosion of the gas-air mixture; it is necessary to monitor the condition of the gas equipment. To protect against burns, you need to use personal protective equipment..

A significant disadvantage is the possibility of metal deformation and low cutting accuracy..

Application features

To understand how to properly cut metal with a cutter, you need to study the design and know that such equipment is not used for cutting steels with high carbon, since there is no way to create a temperature that can ensure stable melting. When cutting cast iron workpieces or structures, there is a concentration of graphite between the metal grains, which complicates the work.

Preparatory work

How to set up a torch for cutting metal – first of all, you need to make sure that the product is in good condition, ready for work, then the following procedure is performed:

  • The hoses from the cylinders are connected to the cutter by pre-blowing the product to remove foreign inclusions from the inside.
  • Oxygen is connected to the right hand thread and propane to the left hand thread.
  • Set the propane supply level to 0.5, and oxygen supply to 5.0 atmospheres.
  • We check connections for leaks, as well as the operation of reducers and pressure gauges.

If gas leaks are found, then the nuts are tightened or the gaskets are changed..

The diagram shows the correct connection of the cylinders to the cutter.

Terms of use

They are similar to safety precautions for welding, but have specific additions:

  • It is not recommended to neglect protective equipment, since this leads to injuries in the form of skin burns or damage to the cornea of ​​the eyes by flying sparks, therefore glasses and gloves with long sockets to the elbow are required.
  • The performer’s clothes and footwear are made of non-combustible material..
  • Gas cylinders are located at least five meters from the cutting site.
  • The torch flame is directed only in the opposite direction from the hoses.
  • Cutting is carried out in rooms equipped with strong ventilation or in open areas.

If the equipment is idle for a long time, it is necessary to carry out preventive work before using the torch for its intended purpose..

Advantages and disadvantages

Cutting metal with propane has a number of advantages, among which the following can be distinguished:

  • Gas cutting is in demand in a situation where there is a need to cut metal of considerable thickness or create products according to templates that provide for the manufacture of a curved cut that cannot be performed using an angle grinder. Also, you can not do without a gas cutter, and then, as there is the task of cutting out a disk from thick metal or making a blind hole by 20-50 mm.
  • The torch is a very easy-to-use tool and is lightweight. All DIYers who have had experience with gasoline models are aware of the inconvenience associated with heavy weight, size and noise. In addition to the significant inconvenience caused by vibration, the operator is forced to provide serious pressure during operation. Gas models, on the other hand, seem to be a more attractive alternative due to the lack of all the above-mentioned disadvantages..
  • The use of cutting metal with gas allows you to speed up the work 2 times, which cannot be done using a device equipped with a gasoline engine.
  • Among most gases, including gasoline, propane stands out at a lower price. For this reason, it is better suited for a significant amount of work, for example, if there is a task to cut steel for scrap..
  • With propane cutting it is possible to create a narrower cut edge than with acetylene cutters. At the same time, the considered method allows you to create a cleaner cut than that which can be done using gasoline burners or an angle grinder..

Among the disadvantages that propane cutters have, only one should be highlighted: they can be used only for a limited range of types of metals. They are suitable for cutting extremely low to medium carbon steels and also ductile iron.

How to cut thick metal with a cutter

For oxygen cutters of a conventional device, the thickness of the cut steel up to 200-300 mm can be considered normal, as they do not cause special difficulties and do not require special special cutting techniques. Thicknesses exceeding the indicated ones are considered large and require special equipment and special cutting techniques, which meet significant difficulties.

Difficulties in cutting large thicknesses are mainly as follows. Special heavy-duty torches with an increased preheat flame and an increased diameter of the cutting oxygen nozzle are required. According to the existing theory, the pressure of the cutting oxygen should increase with increasing times
cut thickness. There are empirical formulas for determining the cutting oxygen pressure depending on the thickness being cut. In conventional cutters with a cylindrical or stepped-cylindrical nozzle, the cutting oxygen pressure at the inlet to the cutter varies from 3-4 atm for small thicknesses to 8-9 atm for a thickness of 100 mm, 11-12 atm for 200 mm, 12-14 atm for 300 mm, 20-25 ati for 400-500 mm. Cutting large thicknesses becomes practically impossible partly due to the difficulty of using high-pressure oxygen (the need for particularly strong armored hoses, etc.), mainly due to the rapid expansion of the oxygen jet at the exit from the nozzle and the significant cooling of oxygen due to the throttling effect. The expansion of the jet is explained by the imperfection of the cylindrical nozzle; therefore, the oxygen at the exit from the nozzle has a pressure that is significantly higher than atmospheric pressure and continues to expand in the jet outside the nozzle, which causes an increase in the jet cross section. The drop in oxygen pressure from the inlet to atmospheric pressure causes its significant cooling; the higher the inlet pressure, the stronger the cooling. The expansion of the jet and the cooling of oxygen, which slows down the cutting process, affects more and more as the inlet pressure of the cutting oxygen increases, i.e., the thickness of the metal increases..

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The continuously growing demand for cutting more and more thicknesses of metal, in line with the general growth of industry power, makes us take a closer look at the study of the oxygen cutting process. Since the end of 1948, eng. MM Bort and the author of this book, who came to the following main conclusions. The oxygen pressure entering the torch is primarily determined by the torch design and is not a factor in the cutting process. The main quantities are the speed, length and cross-section of the oxygen jet. The speed must be supersonic. The length of the jet depends on its initial section, the design of the nozzle and the speed at the exit..

thick, metal, cutter

The structure of the jet and the distribution of velocities in it are schematically shown in Fig. 234. The jet of cutting oxygen A has a conical shape and gradually fades away. The oxygen jet carries with it the surrounding air, forming a gradually expanding outer zone B, filled with a mixture of oxygen and air. The gases of the outer shell B move in the axial direction, but at a much lower speed, rapidly decreasing in the radial direction. The approximate distribution of velocities in the jet sections 1-1, 2-2, and 3-3 is shown in Fig. 234.

As the distance from the mouthpiece edge decreases, the cross section of the oxygen stream and the velocity of oxygen movement in it decrease, and, finally, the stream becomes practically unsuitable for cutting. A decrease in the cross section and speed of the jet is the main reason for the so-called cutting lag, which was mentioned above..

thick, metal, cutter

The active length of the jet L, suitable for cutting, is determined by several factors, the most important of which are the initial velocity and section of the jet, the correctness of its shape, and the presence of, if possible, a laminar movement of oxygen in it. The rapid decrease in the cross-section and speed of the jet and the lack of its active length especially affect when cutting large thicknesses. Conventional means of increasing the active jet length: increasing the oxygen pressure at the inlet to the torch and increasing the jet cross section are insufficient.

FIG. 234. A jet of cutting oxygen.

A closer examination of the oxyfuel cutting process leads to the following conclusions.

The decisive factor for the success of cutting is the speed of movement of oxygen in the cutting jet, sufficient to successfully blow off molten oxides from the metal surface in the cut cavity. When cutting large / thick thicknesses, the initial oxygen velocity should be especially high to ensure a sufficient jet length..

The oxygen pressure at the inlet to the torch to provide the required initial oxygen velocity is primarily determined by the torch design. The design imperfection of existing standard cutters makes it necessary to use significant oxygen pressures at the inlet to the torch, as well as quickly increase the pressure with increasing thickness of the cut metal.

The main design flaws of existing standard cutters are as follows: poor shape of the cutting oxygen nozzle, the presence of sharp deviations in the oxygen path in the cutter, especially when moving from the barrel to the mouthpiece, the presence of sharp changes in the cross section on the oxygen path, for example, in the valve. The usual cylindrical or step-cylindrical shape of the nozzle unsatisfactorily converts the potential energy of the compressed gas into the kinetic energy of the jet at supersonic speeds. At the same time, a significant amount of energy is lost in the form of sound vibrations, turns into heat, etc., which necessitates the use of increased inlet pressures. Sharp deviations of the oxygen line in the torch and changes in the section increase losses and cause vortices and turbulent movements that disrupt the correct shape of the jet and reduce its stability and working length..

Considering the above, M.M.Bort and the author of the book designed and built at the Kiev Polytechnic Institute a powerful R-100 oxygen cutter for cutting steel up to 2 m thick. In the R-100 cutter, schematically shown in Fig. 235, the above requirements have been met. Based on the results of extensive experimentation, the nozzle is shaped as shown in FIG. 236 and called the double conoid. The generatrix of the nozzle is plotted point by point based on experimental data. The oxygen line of the torch, which supplies oxygen to the nozzle, is a straight tube of considerable length and diameter. The cutting oxygen valve has been replaced by a valve that does not narrow the section of the oxygen line. For the preheat flame mixture, there is a series of nozzles arranged concentrically around the cutting oxygen nozzle. The torch mouthpiece is cooled by running water to eliminate the possibility of blowback from the heating flame, especially when cutting hot metal, for example in metallurgical plants. The design of the cutter has fully justified itself both in laboratory and production conditions. The cutter delivers the correct long throw. Oxygen leaves the nozzle at a pressure close to ambient, and its further expansion in the jet practically does not occur. The jet is stable due to the correct laminar gas flow in it and the absence of eddies. The main technical data of the R-100 cutter are given in table. 33.

Gas cutting seems to be a simpler process than gas welding, and therefore even a person without special skills can cope with it. For this reason, almost any of us can learn to work with a gas torch. The main thing here is to learn the essence of gas cutting technology. In modern conditions, propane cutters are increasingly used. Working with them requires the use of propane and oxygen at the same time, since the combination of such substances provides the maximum combustion temperature.

Propane to oxygen ratio

To properly cut metals with an oxy-propane cutter, you need to adjust the flow of gases to the nozzle. Such adjustment is carried out according to the recommendations of reference books, where tables and diagrams are available; in the absence of the necessary literature, one must check the technology specified in the product documents. In the absence of regulatory documents, the ratio of one part of propane to ten parts of oxygen is used..

Preparation for work

Before starting gas cutting, it is necessary to inspect the device to make sure that the propane torch is in working order. Next, you need to perform the following operations:

  • Preparing the cutting machine begins with connecting the hoses to it. Even before attaching the sleeve, it is purged with gas – this will remove debris and dirt from it.
  • The oxygen hose must be connected to a right-hand threaded nipple and a nut. As for the hose through which the propane will flow, it is attached to the left-hand threaded fitting. Before connecting the gas hose, it is imperative to find out if there is a suction in the cutter channels. This problem can be solved by connecting the oxygen hose to the oxygen fitting, while making sure that the gas fitting remains free..
  • Next, you need to set the oxygen supply level to 5 atmospheres, after which you need to open the valves that regulate the flow of gas and oxygen. Touch the free fitting with your finger – this way you will know if there is an air leak. If it is absent, you will have to clean the injector and blow out the cutter channels..
  • After that, you need to make sure that the detachable connections are sealed. If it is possible to identify a leak, fix it by tightening the nuts or replacing the seals. You should also make sure that the mountings of the gas reducers are sufficiently tight, whether the pressure gauges are in working order..