Metal cutting with propane, propane and oxygen consumption

24th December 2021

Basic information

The most common method for cutting metal today is autogenous, it is also called gas or oxygen. Its essence boils down to the fact that under the influence of a gas flame, the metal heats up and begins to melt, and under the influence of a stream of oxygen, it burns out, making a narrow groove.

Acetylene, propane-butane, natural, coke oven gas are used as a heater.

Metal cutting can be classified according to the desired end result:

superficial;
dividing;
spear cutting.

Surface flame cutting is used in cases where it is necessary to remove layers of metal to form splines, grooves and other structural elements.

The dividing view provides for a through cut to obtain the required number of metal elements and parts. Burning through metal to produce deep or through holes is called a sharp spear.

Conditions for cutting metal with gas

For high-quality operation of the installation, it is necessary to ensure a constant supply of gas, since oxygen needs a constant amount of heat, which is maintained mainly (by 70%) due to the combustion of the metal and only 30% provides the gas flame. If you stop it, the metal will cease to generate heat and oxygen will not be able to perform the functions assigned to it.

The maximum temperature of hand-held gas cutters reaches 1300 ° C, this is a sufficient value for processing most types of metal, however, there are those that begin to melt at particularly high temperatures, for example, aluminum oxide. 2050 ° C (this is almost three times higher than the temperature melting of pure aluminum), steel with m chromium. 2000 o C, nickel. 1985 o C.

If the metal is not sufficiently heated and the melting process has not begun, oxygen will not be able to displace the refractory oxides. The opposite of this situation, when the metal has a low melting point, under the influence of a burning gas, it can simply melt, so this method of cutting cannot be used for cast iron.

Technological process

The structure of the cutterbar is designed as follows:

gas-burner;
two cylinders;
mixer;
pressure regulator;
hoses.

A gas burner consists of a head with several nozzles, generally three are sufficient. Through two side ones, a combustible substance is supplied, through the third, which is located in the middle, oxygen is supplied. The cylinders are designed directly for gas and oxygen, depending on the volume of the proposed work, cylinders corresponding in capacity are selected.

To ensure one hour of continuous operation, an average of 0.7 m 3 of acetylene (1 m 3 of propane) and 10 m 3 of oxygen will be consumed. In general, the required amount of feedstock will depend on the density of the metal and the required temperature to heat it. It is possible to reduce the propane consumption by using special nozzles on the nozzles, which fix the gas supply in a certain direction, the closer the supply is to the oxygen stream, the higher the fuel consumption.

A pressure regulator is required to provide different modes and cutting speeds. By feeding less fuel, you can provide a low temperature, which is necessary for thin steel or metal of low strength, as well as reduce the consumption of raw materials.

Another important function of the reducer is to maintain an even pressure level. If the gas supply is interrupted during the cutting process, the metal will quickly cool down and further processing will become impossible.

Necessary equipment

The very first cutter was the P1-01 device, it was designed back in the USSR, then more modernized models appeared. P2 and P3. The devices differ in the size of the nozzles and the power of the reducer. modern manual settings:

Change;
Quicky;
Orbit;
Secator.

They differ in a set of additional functions and performance.

Quicky-E can carry out shaped cutting according to the given drawings, the speed of work reaches 1000 mm per minute, the maximum allowable metal thickness is up to 100 mm. The device has a set of removable nozzles for processing metal sheets or pipes of various thicknesses.

Autogenous cutting machine Messer

This apparatus can operate using various types of combustible gas, in contrast to the prototype P1-01, which only runs on acetylene.

Secator handheld cutter has improved performance compared to peers.

With its help, you can process metal up to 300 mm thick, this is provided by additional nozzles included in the kit, they are removable and can be purchased additionally, as they wear out. Secator can do the following types of cutting:

curly;
straight line;
annular;
under bevel.

The speed can be adjusted from 100 to 1200 mm per minute, and the built-in freewheel ensures smooth movement of the machine on the sheet of metal. Air-cooled gearbox for cleaner operation and reduced fuel consumption.

The above models are manual, that is, they are compact, controlled by the hands of a master. But for large volumes of processed metal, work with such

installations are inconvenient and ineffective. For industrial production, stationary cutting units are used. this is, in fact, the same technology.

They represent a machine with a table top in which the cutting mechanism is built. It is powered by an electric

a compressor that requires a mains supply with at least 380 V and three-phase sockets. The technology of operation of models of stationary cutting units is nothing, but different from manual ones. The only difference is in performance, maximum heating temperature, and the ability to process metal with a thickness of more than 300 mm.

Safety engineering

It is better to entrust the implementation of metal cutting using a gas installation to an experienced specialist, since if carelessly handled, the consequences can be quite sad.

Safety precautions assume the following conditions are met:

Gas burner device

good ventilation in the room where the work will be carried out;
at a distance of 5 meters there should be no cylinders with gas and other flammable substances;
work must be carried out in a protective mask or special goggles, as well as in fireproof clothing;
it is necessary to direct the flame in the opposite direction from the gas source;
during the operation of the device, the hoses must not be bent, stepped on, pinched with feet;
if there is a break, then completely extinguish the flame at the burner and tighten the gas valves of the cylinders.

Observance of these simple conditions will ensure safe and efficient work on metal cutting with a gas installation.

Oxygen cutting of medium thick steel

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In oxygen separation cutting of steel, in accordance with the technological features, the cutting of metal of small thicknesses (up to 5 mm), medium thicknesses (5-300 mm) and large thicknesses (over 300 mm) is distinguished. This division is rather arbitrary, however, for each range of cut thicknesses, there are general patterns.

The most important technological parameters of oxygen cutting are cutting oxygen consumption, heating flame power, cutting speed.

For calculating the consumption of cutting oxygen, the following formula can be recommended, obtained on the basis of the results of processing data from VNIIavtogenmash and foreign firms,

where Vcr. consumption of “cutting” oxygen, m 3 / s; k2 is a coefficient that takes into account the state of the metal before cutting (k2 = 0.3. for rolled products; k2 = 0.6. for casting and forgings with a thickness of 0.3 to 0.6 m), kp, kp, km. see table 26.1.

The heating flame heats the surface layers of the metal to the ignition temperature at the beginning of cutting, and in the process of cutting. the front surface of the metal. The power of the heating flame will increase with an increase in the thickness of the cut metal, the distance between the end of the torch and the metal. When cutting contaminated metal, the flame power must be increased. The power of the flame is determined by the consumption of combustible gas, its type and the ratio of the consumption of combustible gas and heating oxygen. Oxy-fuel cutting uses gaseous and liquid hydrocarbons as fuel. When these fuels are burned in a mixture with oxygen, a high-temperature flame is formed.

Table 26.2 provides information on the basic properties of combustible gases.

The consumption of combustible gas and heating oxygen during cutting can be determined from the following dependencies:

where VR.r is the consumption of combustible gas, m 3 / s; Vc.p. heating oxygen consumption, m 3 / s; δ is the thickness of the metal being cut, m. The values of the coefficients included in the above equations for different cutting conditions are given in table. 26.1 and 26.2. The consumption of iron powder (qf, kg / s) when cutting high-alloy steels is determined by the formula:

At a given gas flow rate, the cutting speed decreases exponentially with an increase in the thickness of the cut metal, since the dynamic effect of the jet on the melt sharply decreases with distance from the nozzle exit. The cutting speed increases with an increase in the heating temperature of the metal due to an increase in the thickness of the liquid layer of the metal in the section, oxygen purity and oxygen pressure in front of the nozzle. An increase in the pressure of the “cutting” oxygen in front of the nozzle promotes an increase in its flow rate and its dynamic effect on the oxidized metal. The largest increase in the oxygen flow rate (up to 90%) is observed in the pressure range at the nozzle inlet from 98 to 2940 kPa, a further increase in the oxygen pressure in front of the nozzle from 2940 to 9800 kPa makes it possible to increase the oxygen flow rate by only 8%.

Based on the generalization of the experimental data, the following dependence was obtained to determine the cutting speed:

where v is the cutting speed, m / s; δ. thickness of the cut metal, m; kд. coefficient of cutting speed, depending on the pressure of the “cutting” oxygen,

where рk. pressure of “cutting” oxygen, kPa; kch. coefficient of cutting speed, depending on the purity of oxygen,

where ε. oxygen purity,%; kt, km, kp are selected in accordance with table 26.1.

Lower cutting speeds are selected for precise cutting of shaped parts, the highest for rectilinear separation oxygen cutting of metal into scrap (table, 26.3).

Volchenko V.N. “Welding and materials to be welded”.

Oxygen and propane consumption when cutting metal

When it becomes necessary to work with thick metal, a gas cutter is used. It cuts the sheet metal using a hot flame jet. It is formed due to the mixing of two gases. propane and oxygen.

It is impossible to cut high-carbon metals, copper and its alloys, aluminum with an oxygen-propane cutter. The range of influencing materials is limited to low-carbon steels of grade 08 to 20G in accordance with GOST (1050-60) and medium-carbon steels. from 30 to 50G2 (GOST 1050-60).

Propane cutter cuts metal no more than 300 mm thick.

Cutting process

With the correct choice of the speed of movement of the torch, a stream of sparks and slag flies out of the cut straight down, while the edges are clean, there are no smudges and fusion.

If in the process of performing work your oxygen hose breaks, do not panic. Close the propane supply and then both cylinders. The flame that has disappeared during the adjustment process must be re-ignited, having previously closed the cutter valves.

To work, you must have

All parts of the gas equipment are standard and can be replaced in the event of a breakdown.

Technological process

The structure of the cutterbar is designed as follows:

gas-burner;
two cylinders;
mixer;
pressure regulator;
hoses.

Metal cutting technologies

Today, the industry uses three typical technologies for thermal separation of metal blanks:

Oxygen cutting.
Plasma cutting.
Laser cutting.

The first technology, oxyfuel cutting, is used to separate carbon and low alloy steel workpieces. In addition, the oxygen cutter can trim the edges of already cut workpieces, prepare the seam zone before welding and “clean up” the surface of the cast part. The flow rate of working gases, in this case, is determined by the consumption of both fuel (combustible gas) and oxidizer (oxygen).

The second technology. plasma cutting. is used for the separation of all types of steels (from structural to high-alloyed), non-ferrous metals and their alloys. There are no unavailable materials for a plasma cutter. it cuts even the most refractory metals.

The third technology. laser cutting. is used to separate thin-sheet workpieces. Accordingly, the volumes of consumed gases, in this case, will be significantly less than that of oxygen and plasma cutting, which are designed to work with large, thick-walled workpieces.

How metal is cut with gas

Basic information

Acetylene, propane-butane, natural, coke oven gas are used as a heater.

Metal cutting can be classified according to the desired end result:

superficial;
dividing;
spear cutting.

Surface flame cutting is used in cases where it is necessary to remove layers of metal to form splines, grooves and other structural elements.

The dividing view provides for a through cut to obtain the required number of metal elements and parts. Burning through metal to produce deep or through holes is called a sharp spear.

How to cut

Before starting work, first of all, it is necessary to purge the hoses with oxygen in order to remove the debris or dirt that has got there.

Second, check for leaks in the cutter passages. To do this, you need on it:

connect the oxygen hose to the oxygen connection (the heating gas connection must remain free);
set the oxygen supply pressure to 5 atmospheres and open the gas and oxygen valves on the torch;
check the free fitting with your finger to make sure: is there an air leak? If not, clean the injector and blow out the torch passages.

After that, they are connected to the device:

the oxygen hose is attached to the right-hand threaded fitting with a nipple and a nut;
propane hose. to the left-hand threaded fitting in the same way.
check the detachable connections for leaks. Eliminate the detected leaks by tightening the nuts or changing the seals;
check the tightness of the fastening of the gas reducers and the serviceability of the pressure gauges.

Gas cutting of metal should be started by mechanically removing rust and other contaminants from its surface. The necessity of this operation is due to the following. When carbon burns, CO oxide is formed. It, when interacting with iron, increases the carbon on its surface (especially at the cut). This leads to the formation of hardened structures in the metal, which will heat up unevenly. This, in turn, will lead to the appearance of mechanical stress at the edges of these structures and, as a consequence, to their some shortening. As a result: deformations and cracks are formed. Mechanical cleaning of the surface to be cut avoids such defects.

Further, the workpiece, sheet or other workpiece should be set in such a position that the ball is provided with the freedom of passage of the cutting gas jet through it.

We set the working pressure on the gas cylinder reducers. Typically, the ratio of preheating gas pressure to oxygen is 1:10. Therefore, we expose, atm:

on propane. 0.5;
on oxygen. 5.

Further actions have the following sequence:

on the cutter, open the propane a little (a quarter turn of the valve flywheel or a little more) and ignite the gas;
we rest the mouthpiece of the cutter nozzle against any metal (preferably at an angle) and slowly open the regulating (heating) oxygen.

Be very careful. Do not confuse the heating oxygen valve with the cutting gas valve.

alternately adjusting both valves (opening and closing them), achieve the flame strength we need. The length of the flame (it is also its strength) is selected based on the thickness of the metal: the thicker the sheet or other part to be cut, the stronger the flame should be. Accordingly, the consumption of oxygen with propane also increases. When the flame is adjusted, it turns blue and crown.

Now you can start processing the metal (we remind you that processing begins with heating and then separation):

we bring the nozzle of the cutter to the edge of the metal and hold it at a distance of 5 mm from the part to be cut at an angle of 90 °. In the event that a sheet or other product must be cut not from the edge, then the metal should be heated up from the point from which the cut will go. We heat the upper edge of the part to a temperature, ° C: T = 1000 1300 (the value of the parameter depends on the brand of the metal being cut and the temperature of its ignition). Visually, it looks as if the surface has begun to “get wet” a little. In terms of time, the warm-up will last only a few seconds (up to 10);
when the metal ignites, open the cutting oxygen valve. A powerful, narrowly directed jet of cutting oxygen is supplied to the part to be cut. Open the torch valve very slowly. In this case, oxygen will ignite from the heated metal on its own, and this will avoid a back blow of the flame, accompanied by a pop. When cutting has begun, turn off the heating gas (propane).

Important! From this point onwards, it is very important to ensure a continuous supply of cutting oxygen. Otherwise, the flame may go out, the burning of the metal will stop and you will have to start all over again (ignition, setting the flame, heating the surface to be cut, etc.).

Choosing a combustible gas

When using a conventional flame cutter for cutting metal, both propane and acetylene are used as preheating. However, in most cases propane is used for cutting. The reasons for this choice are the following:

the cost of propane is much lower than acetylene;
less explosive propane. There is a possibility of quick detection of leaks, since mercury-containing additives are added to the propane cylinders. The specific smell of these additives makes it easy to locate a gas leak (depressurization). In addition, acetylene requires much more careful observance of safety rules, which is not always easy to do in the locksmith’s area;
when carrying out propane cutting, a narrower cutting edge is created than when working with acetylene; the pungent smell of acetylene creates discomfort and is not always acceptable. This is especially true if the cutting is carried out in a regular workshop in which other workers are also working. Considering the above, propane is preferred.

Oxygen consumption during welding

The most common metal operation is cutting. And indeed:

in the course of this operation, the part is “born” in the blank section of the metalworking production;
the same operation terminates its practical use after disposal;
shaping, repair, etc. cannot do without it.

In industry and everyday life, many methods of cutting metal are used. Gas cutting is not the last among them. The most economically profitable, and therefore widespread. oxygen-propane metal cutting (hereinafter. KPRM), we will discuss in this article.

Oxygen and propane consumption when cutting metal

Oxygen consumption for metal cutting is calculated by the formula:

Рdet. volume of oxygen required for cutting, cubic meters;
H. consumption standards during the working process, cubic meters / m;
L is the total length of the cut of the part to be cut out, m;
Kh is a coefficient that takes into account many features of the work process that require gas consumption for:

initial stage:

purge;
adjustment;

heating the metal;

the process of starting cutting

1.1. for one-off production;
1.05. in industrial (serial) production.

The oxygen consumption rate “H” for metal cutting depends on the power of the equipment and the cutting mode. It is calculated using the following formula:

Н. oxygen consumption rate, cub.m / m;
Р. permissible gas consumption, cubic meters / hour. It is indicated in the technical characteristics of the equipment used;
V is the speed of cutting metal, m / h.

The most commonly used gas flow rates (measured in cubic meters / hour) for various cutting speed ranges for some types of equipment are shown in the following table.

Equipment types	Optimal range of cut thicknesses, mm	Cutting speed range, m / h	Oxygen	Acetylene	Propane
Manual oxygen cutter	40. 60	30. 6	5.0. 10.0	0.12. 0.45	0.21. 0.75
Machine Oxygen Cutter	5. 300	40. 5	2.5. 25.0	0.2. 1.2	0.32. 2.04

Considering that the cutting speed and the thickness of the metal being processed directly depend on the permissible gas consumption, these values can be easily and simply determined by interpolation. Therefore, it is possible to enlarge (estimate) the calculation of the consumption of various gases, regardless of the type of thermal cutting of metals. For this you only need:

length of the cut;
metal thickness;
equipment power.

The value of the permissible flow rate (oxygen and propane) is taken from the equipment passport. Cutting speed is found in reference books that contain special tables or diagrams that link all the original data.

Metal cutting with oxygen and propane

First, let’s figure out how the separation of metal by oxygen is carried out in general. Cutting with this gas is based on the property of a metal to burn under the action of a jet of this gas, or rather, on the temperature of its combustion. Further, under the action of its pressure, the resulting combustion products are removed from the cut.

Let’s take a closer look at the process. It is divided into two main stages:

at the first stage, the alloy is heated to the required operating temperature (at this temperature, the metal ignites in the oxygen stream). For this, the flame of a burning mixture of a heating gas (acetylene, propane, etc.) with oxygen is used;
on the second, cutting oxygen is supplied in the form of a narrow jet under high pressure. It leads to the continuous formation of metal oxides throughout its entire thickness (the metal is “burned” through and through). The torch moves and burns the metal with a jet of oxygen, removing combustion products along the way. As a result, a cutting line is formed. The heating gas is used only until the working area on the surface of the workpiece is heated up to the metal combustion temperature. At the second stage, it is not needed (it is blocked). the required temperature regime is maintained by oxygen.

Oxygen cutting, as follows from its definition, can be applied far from all metals and alloys. It can be carried out only by those of them, which, under the influence of oxygen, have the following properties:

their combustion temperature must be lower than this indicator when they melt;
metal oxides formed during the cutting process must have a melting point below this indicator of the metal itself;
the amount of heat released during the processing should be sufficient to maintain the continuous oxyfuel cutting process;
the slags formed during the processing of parts must be fluid. This will ensure their easy removal from the working area;
cut alloys and metals should not have high thermal conductivity. These include:

low carbon steels. For example, brands from 08 to 20G;
medium carbon steels. For example, brands from 30 to 50G2;
malleable iron.

ATTENTION! On the other hand, it is impossible to cut high-carbon steels with oxygen cutting (they have the letter “U” in their designation). This is due to the fact that their melting point is close to the flame temperature. As a result, the dross will not be ejected from the back of the sheet (in the form of pillars of sparks), but will mix with the molten metal along the edges of the cut. This will prevent oxygen from penetrating deep into the metal and burning it through. The shape of the grains and the graphite between them will interfere with cutting the cast iron (the exception is ductile iron). Do not give in to oxygen cutting, also aluminum, copper and their alloys.

Advantages and disadvantages

The advantage of KPRM is the low cost of the heating gas. propane, and the disadvantage. they can only handle low and medium carbon steels, as well as ductile iron. KPRM is beneficial to use for large volumes of work (cutting steel for scrap metal, etc.). Conventional oxygen cutting of pipes made of chromium and chromium-nickel steels, as well as cast iron, copper and its alloys KPRM is practically impossible. To process these parts made of these metals, the following are used:

oxygen-acetylene cutting. The use of acetylene for heating makes it possible to increase the heating temperature and, accordingly, the thickness of the workpieces being processed. But at the same time, the cost of work rises sharply;
oxygen-flux cutting. This method consists in the fact that a powdery flux is supplied to the jet of cutting oxygen. This material is designed so that, burning in oxygen, it releases additional heat at the cutting site. It should facilitate the melting of refractory oxides. The molten oxides, in turn, form liquid slags that run off and do not interfere with the cutting process. The main component of these fluxes is iron powder of the PZh5M, VM, VS brands and various additives (for example, aluminum powder);
oxygen-arc (also called gas-electric) cutting. This is a cutting method in which the metal melted by an electric arc is continuously removed by a gas jet. The following can be used as gas:

compressed air;
oxygen;
nitrogen, etc.

The most widely used technology is compressed air. This is due to its lowest cost. Air arc cutting is used for:

smelting of defective welds, cavities and cracks;
V-shaped preparation of edges for welding;
separation cutting of carbon and alloy steels, cast iron and non-ferrous metals.

It is most widely used for dividing cutting of stainless steel up to 20 25 mm thick. The advantage of these types of cutting is the possibility of expanding the range of processed metals, and the disadvantage is the complication of technology and increased cost.

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PROPERTIES AND REGULATION OF WELDING FLAME

The appearance, temperature and effect of the welding flame on the molten metal depend on the composition of the combustible mixture, i.e., the ratio of oxygen and acetylene in it.

When acetylene burns in air without the addition of oxygen, a yellowish flame is formed, which has the shape of a long torch without a light core. Such a flame has a low temperature and smokes, giving off a lot of soot (unburned carbon), therefore it is not suitable for welding.

If oxygen is added to the flame, it abruptly changes its color and shape, and its temperature rises significantly. By changing the ratio of oxygen and acetylene, you can get three main types of welding flame (Fig. 84, a, b, c): normal, also called reducing; oxidative (with an excess of oxygen) and carburizing (with an excess of acetylene).

For most metals, a normal (reducing) flame is used. In theory, it is formed when one volume of oxygen is supplied to the burner for one volume of acetylene. Acetylene is then burned by the oxygen of the mixture by the reaction

Subsequent combustion occurs due to the oxygen of the ambient air according to the reaction

Carbon monoxide and hydrogen formed in the flame during phase I of combustion deoxidize the metal, reducing the oxides present in the weld pool. In this case, the weld metal is obtained without pores, gas bubbles and oxide inclusions.

In practice, a little more oxygen is supplied to the mixture than is needed to obtain a reducing flame according to the above combustion scheme. A normal reducing flame is obtained with an excess of oxygen in the mixture up to 30% against theoretical, i.e., with a ratio of acetylene and oxygen from 1: 1 to 1: 1.3.

A diagram of the formation of a normal reducing acetylene-oxygen flame is shown in Fig. 85, a. A normal flame has a core, a recovery zone, and a torch. The core has a well-defined shape, close to the shape of a cylinder with a rounded end, and a brightly luminous shell of incandescent carbon particles, the combustion of which occurs in the outer layer of the shell. The dimensions of the core depend on the consumption of the combustible mixture and the rate of its outflow. If the oxygen pressure in the burner is increased, then the rate of the mixture outflow will increase and the core will lengthen. With a decrease in the flow rate of the mixture, the core shortens. In fig. 85, and below are the lengths and diameters (mm) of the nuclei of the acetylene-oxygen flame obtained in the mouthpieces of different numbers.

The recovery zone is dark in color, distinguishing it from the core and the rest of the flame. The length of this zone reaches 20 mm from the end of the core, depending on the number of the mouthpiece. It contains carbon monoxide and hydrogen. The recovery zone has the highest temperature at a point 2–6 mm from the end of the nucleus. This part of the flame heats and melts the metal during the welding process.

The rest of the flame beyond the reduction zone is called the torch. The torch contains carbon dioxide, water vapor and nitrogen, which are formed during the combustion of carbon monoxide and hydrogen in the reduction zone due to the oxygen of the ambient air, which includes nitrogen. The flame temperature is significantly lower than the temperature of the reduction zone.

If you increase the oxygen supply or decrease the acetylene supply to the burner, an oxidizing flame is produced. It is formed when the mixture contains more than 1.3 volumes of oxygen per volume of acetylene. Oxidizing flame is characterized by a shortened, sharpened core with less sharp outlines. The temperature of an oxidizing flame is higher than the temperature of a normal reducing flame, but such a flame can oxidize the metal being welded.

By decreasing the oxygen supply or increasing the acetylene supply, a carburizing flame is produced, which is sometimes called acetylene. It is formed when 0.95 or less volume of oxygen is supplied to the burner per volume of acetylene. In an acetylene flame, the size of the combustion zone increases, the core loses its sharp outlines, becomes blurry, and a green corolla appears at the end of the core, which is used to judge the excess of acetylene. The recovery zone is lighter, almost merges with the core, and the flame takes on a yellowish color. With a large excess of acetylene, the flame smokes due to the lack of oxygen necessary for the complete combustion of acetylene.

Excess acetylene in an acetylene flame decomposes into hydrogen and carbon, transforms into molten metal. The temperature of such a flame is lower than the temperature of the reduction flame. By reducing the supply of acetylene to the burner (until the green corolla at the end of the core completely disappears), the acetylene flame is converted to normal.

When regulating the flame, attention should be paid to the correct setting of the oxygen pressure and the size of the flame core. With an increase in oxygen pressure, the rate of flow of the mixture from the mouthpiece increases and the flame becomes “hard”, that is, inflates the metal of the weld pool and thus complicates welding. If the mixture flow rate is too high, the flame can be torn off the mouthpiece. If the oxygen pressure is too low, the flame becomes shorter and as the end of the mouthpiece approaches the metal, the burner begins to pop.

The welding flame must have sufficient heat output, i.e., provide the amount of heat required to melt the welded and filler metal and cover heat losses to the environment. The thermal power of the flame is determined by the acetylene consumption (dm3 / h) in the burner.

When welding, the thermal power of the flame is selected depending on the thickness, welded metal and its physical properties. A metal that is thick and conducts heat well requires a more powerful welding flame than a thin, less thermally conductive and less melting metal. By changing the thermal power of the flame, it is possible to regulate the heating and melting rate of the metal over a wide range, which is one of the positive qualities of the gas welding process. The diagram and temperature distribution for methane-oxygen and propane-butane-oxygen flame are shown in Fig. 85, b.

METALLURGICAL PROCESSES IN GAS WELDING

Metallurgical processes in gas welding are characterized by: a small volume ^ of a bath of molten metal; high temperature and heat concentration at the welding site; high rate of metal melting and cooling; intensive mixing of the bath metal with a gas flow of a flame and a filler wire; chemical interaction of molten metal with flame gases.

With an excess of oxygen in the flame, oxidation reactions of iron, manganese, silicon and carbon occur according to the equations:

The resulting iron oxide (FeO) can oxidize manganese, silicon and carbon by reactions:

Since the oxides MnO and SiO2 pass into the slag, the amount of deoxidizers (manganese and silicon) in the weld metal decreases. This leads to the appearance of an excess of oxygen in the deposited metal and deterioration of its mechanical properties.

As carbon monoxide escapes from the weld pool, metal boils and splashes.

If the flame is of a reducing nature, the reverse reactions of the above will occur in the weld pool, namely:

Reduction of iron with carbon monoxide:

Hydrogen is highly soluble in liquid iron. When the weld pool cools quickly, it can remain in the seam in the form of small gas bubbles. However, gas welding provides a slower cooling of the metal compared to arc welding. Therefore, during gas welding of carbon steel, all hydrogen has time to evolve from the weld metal and the latter turns out to be dense.

Hydrogen poses a great danger for welding copper and brass, as it can cause “hydrogen disease” (cracking) of copper and porosity of the seam when welding brass.

The reduction of iron from its oxide FeO is carried out by manganese and silicon according to the above equations 2 and 3.

If there is an excess of carbon in the flame, then it can pass into the metal and carburize it according to the reactions:

Free carbon is formed in a flame during the decomposition of acetylene according to the reaction C2H2 = 2C H2.

During gas welding, structural changes occur in the weld metal. Due to the slower (compared to arc welding) heating, the zone of influence in gas welding is larger than in arc welding.

In gas welding of carbon steels of small thicknesses, the zone of thermal influence of the base metal extends by 8-15 mm, and of medium thicknesses. by 20-25 mm to either side of the seam. The nature of the change in the structure of the metal in the heat affected zone is determined by the composition of the metal (alloy) and its state before welding. To improve the structure and properties of the weld metal and the heat-affected zone, hot forging of the weld, general or local heat treatment is often used. Local heat treatment is also carried out by heating the weld metal and the heat-affected zone with the flame of a welding torch.

Administration General Published: 2011.05.31 Updated: 2020.03.04

Section I. Welding of pipelines from alloy steels. 2

Chapter 1. Manual arc welding with covered electrodes. 3

§ 1. Connections C8 of horizontal pipe joints with a bevel of one edge. 3

§ 2. Connections C18 of vertical pipe joints with beveled edges on a removable lining. four

§ 3. Connections C5 of vertical pipe joints without beveling the edges on the remaining cylindrical lining. five

Propane & Oxygen Torch Cutting Instructional Video

§ 4. Connections C10 of horizontal pipeline joints with a bevel of one edge on the remaining cylindrical lining. five

§ 5. Connections C19 of vertical pipe joints with beveled edges on the remaining cylindrical lining. 6

§ 6. Connections C52 of vertical joints of pipelines with curved bevel edges with a bore on the remaining cylindrical lining. 7

§ 7. Connections C53 of vertical pipe joints with curved bevel edges with a bore on the remaining cylindrical lining. eight

§ 8. Connections U7 corner flanges with a pipe with a bevel of one edge are double-sided. eight

§ 9. Angle joints U8 flanges with a pipe with a symmetrical bevel of one edge are double-sided. nine

§ 10. Angle joints U18 without beveling edges (welding of branch pipes) 10

Chapter 2. Manual argon-arc welding. eleven

§ 11. Connections C2 of vertical joints of pipelines without beveling the edges. eleven

§ 12. Connections C17 vertical joints of pipelines with bevel edges. eleven

§ 13. C18 joints of vertical pipeline joints with beveled edges on a removable lining. 12

§ 14. C5 joints of vertical pipe joints without beveling the edges on the remaining cylindrical lining. 12

§ 15. C19 joints of vertical pipeline joints with bevel edges on the remaining cylindrical lining. 13

§ 16. Angle joints U19 with a bevel of one edge (welding of branch pipes) 13

§ 17. Angle joints U16 without beveling edges (welding of branch pipes) 14

§ 18. Connections C17 of vertical pipe joints with bevel edges. fifteen

§ 19. Connections C18 of vertical pipe joints with beveled edges on a removable lining. sixteen

§ 20. C19 joints of vertical pipe joints with bevel edges on the remaining cylindrical lining. 17

§ 21. Connections C52 of vertical joints of pipelines with curved bevel edges with a bore on the remaining cylindrical lining. eighteen

§ 22. Angle joints U18 without bevel edges (welding of branch pipes) 19

§ 23. Angle joints U19 with a bevel of one edge (welding of branch pipes) 20

SECTION II. Automatic submerged arc welding of sheet metal structures. 21

§ 24. Butt joints C4 without bevel edges are one-sided. 21

§ 25. Butt joints C5 without bevel edges are one-sided. 22

§ 26. Butt joints C47 without bevel edges are one-sided. 22

§ 27. Butt joints C7 without bevel edges are double-sided. 23

§ 28. Butt joints C29 without bevel edges, double-sided on a flux cushion. 23

§ 29. Butt joints C9 with a bevel of one edge, one-sided 23

§ 30. Butt joints C10 with a bevel of one edge, one-sided on the remaining lining. 24

§ 31. Butt joints C12 with a bevel of one edge, double-sided 24

§ 32. Butt joints C31 with a curved bevel of one edge are one-sided. 24

§ 33. Butt joints C32 with a broken bevel of one edge are one-sided. 25

§ 34. Butt joints C15 with two symmetrical bevels of one edge are double-sided. 25

§ 35. Butt joints C18 with bevel edges are one-sided. 26

§ 36. Butt joints C19 with bevel edges are one-sided on the remaining lining. 26

§ 37. Butt joints C21 with bevel edges are double-sided with preliminary welding of the root of the seam. 27

§ 38. Butt joints C33 with bevel edges are double-sided on a flux cushion. 27

§ 39. Butt joints C34 with curvilinear bevel of the edges are one-sided on the remaining lining. 27

§ 40. Butt joints C36 with broken bevel of edges, one-sided on a flux cushion. 28

§ 41. Butt joints C25 with two symmetrical bevels of the edges are double-sided. 28

§ 42. Butt joints C38 with two symmetrical bevels of the edges are double-sided on a flux pad. 29

§ 43. Butt joints C26 with two symmetrical curved bevels of the edges are double-sided. thirty

Chapter 5. Welding of corner T-joints. thirty

§ 44. Angle joints U5 without bevel edges, double-sided with preliminary overlapping of a weld seam. thirty

§ 45. Angle joints U7 with a bevel of one edge are double-sided with preliminary overlapping of a weld seam. 31

§ 46. T-joints TK without bevel edges are double-sided. 31

§ 47. T-joints T7 with a bevel of one edge, double-sided with a preliminary overlay of a weld seam (position “in a boat”) 31

§ 48. T-joints T8 with two symmetrical bevels of one edge, double-sided (position “in the boat”) 32

§ 49. Overlap joints H1 without bevel edges are one-sided. 32

Section iii. Welding of reinforcement joints and embedded parts of reinforced concrete structures. 33

Chapter 6. Welding cross-shaped connections of reinforcement bars. 34

§ 50. Spot welding with tacks (horizontal and vertical position of the rods) 34

§ 51. Welding with forced formation of a seam (vertical position of seams) 34

Chapter 7. Welding of butt joints of reinforcement bars. 35

§ 53. Welding on a steel backing bracket. 38

§ 54. Welding on a steel strap-lining. 39

§ 55. Manual arc welding with multilayer seams without forming elements (vertical position of the rods) 39

§ 56. Welding with long overlapping seams. 40

Chapter 8. Welding of T-joints of embedded parts. 42

§ 57. Single-electrode bath welding in inventory forms (horizontal position of the rods) 42

§ 58. Mechanized welding in carbon dioxide. 43

§ 59. Manual arc welding by roller seams. 44

§ 61. Cutting of rolled equal-flange angle steel. 45

§ 68. Cutting holes for branch pipes or trimming the ends of branch pipes. 49

The ratio of oxygen to propane when cutting metal

Oxygen cutting is based on the combustion of metal in a jet of commercially pure oxygen. From the description above, you know that propane mixed with oxygen is only needed to heat the metal being processed. The amount of heating gas depends on many factors:

steel grade;
material thickness;
cutting length, etc.

Additional factors affecting consumption are:

gas consumption at the initial stage of cutting:

purge;
equipment adjustment;

ignition and torch adjustment.

Recommended ratios are indicated in the accompanying documentation for specific equipment. The calculated ratio of gas volumes is determined by reference books that contain special tables and diagrams that link all the data. These parameters are indicated in the accompanying technological documentation. In the process of work, they can be adjusted in one direction or another.

If you do not have the specified documentation, then the pressure should be set in accordance with the above ratio. Typically, the ratio of preheating gas pressure to oxygen is 1:10. Therefore, we expose, atm:

on propane. 0.5;
on oxygen. 5.

In addition, propane consumption will depend on the amount and duration of warm-ups.

Sources:

http://crast.ru/instrumenty/rashod-kisloroda-i-propana-pri-rezke-metalla
http://grebnoykanaldon.ru/rashod-kisloroda-pri-svarke/

Articles cutting, metal, oxygen, propane