What equipment?
Gas welding equipment for gas welding is a wide range of devices that allow you to carry out a number of works. This type of welding is considered simple, and the equipment itself is quite concise and easy to operate. Depending on the type of fuel, gas welding devices are propane-oxygen or acetylene-oxygen, gasoline or kerosene-oxygen. Most often, welding is carried out on the basis of propane-oxygen and acetylene-oxygen welding, since the flame of these gases has the highest temperature.
Gas welding equipment for gas welding is also a generator, which is supplemented with different types of gas. Also, when working, you will need an oxygen cylinder and reducers. The most common are acetylene generators for gas welding, which allow you to directly obtain acetylene by mixing calcium carbide and water. This type of generator is presented in five types, which allows you to choose the best option for a specific material.
Safety gates play an important role when working with welding, their task is to ensure safety during welding. With their help, the backfire of the flame that occurs during welding is prevented. In addition, check valves prevent gas backflow into rubber hoses during flame processing of metals and when working with compressed gases.
Technology features
When performing gas welding, it is important to obtain a high-quality joint, therefore, great attention is paid to careful preparation of the edges to be welded, the choice of the method of joining the metal, the installation of the torch in the desired position and the determination of the required parameters of the torch power. Gas welding technology assumes that the edges must be thoroughly cleaned of various contaminants. The bevel is performed using a manual or pneumatic chisel, and sometimes special machines are involved. Scale and slag can be removed with a wire brush. Tacking of edges prevents changes in their position during welding.
What gases are used?
Gas welding uses flammable gases. natural, acetylene, gasoline vapors, hydrogen. These gases are distinguished by good combustion in air, without developing a high temperature; an oxygen jet is sufficient for combustion. Gas welding is most often carried out on the basis of acetylene, which is created on the basis of water and calcium carbide. It burns at a temperature of 3200-3400 degrees.
What are the features?
The advantages of gas welding include the following:
- Simple technology.
- No need for a welding power source.
- The simplicity of the equipment on the basis of which gas welding is performed.
On the other hand, this process is not very productive. Welding is carried out only by hand, and the mechanical and operational properties of finished products are not always of high quality.
Features of welding various seams
To work with horizontal seams, the right method is used, which makes it easy to form a seam, and the metal of the bath itself does not drain. Welding of vertical and inclined seams is carried out in the left way, and if the metal thickness is more than 5 mm, a double bead is used. Welding ceiling seams involves heating the edges until they melt, then a filler wire is introduced into the bath. its end quickly melts. The process itself is conducted in the right way.
Welding methods
Gas welding can be carried out in several ways. The first is left-handed welding, which is the most common. It is used when working with thin and low-melting metals. The torch moves from right to left and the filler wire is guided in front of the flame towards the unwelded seam. Right-hand welding traces the torch from left to right and the filler wire trails behind the torch. With this method, the heat of the flame is dissipated to a lesser extent, therefore the seam opening angle is not 90 degrees, but less. 60-70.
It is advisable to use right-hand welding to join metal with a thickness of 3 mm and more, as well as metals with a high level of thermal conductivity. It is recommended to use a filler wire with a diameter equal to half the thickness of the metal to be welded.
Gas welding technology also involves a process that is carried out by a through bead. In this case, the sheets are installed vertically to the gap. it is equal in size to half the sheet thickness. The torch melts the edges to form a round hole. Then it is melted on all sides until the seam is welded. This method is good because the sheets to be welded have a tight seam without pores and slag inclusions.
Pot welding is good for welding joints and corners of metals that have a maximum thickness of 3 mm. As soon as a bath is formed on the seam, the end of the filler wire is introduced into it, which slightly melts, then the end of the wire is moved to another section of the seam. The peculiarity of this approach is in the seam of excellent quality, especially if thin sheets and pipes of steel (low-carbon and low-alloy) were welded.
Gas welding and cutting can be carried out on the basis of multi-layer welding. This method has a number of features:
- the heating zone is small;
- the underlying layers are simply annealed during the surfacing of the subsequent ones;
- each seam can be forged before applying the next.
This results in an improvement in the quality of the seam. On the other hand, this method is characterized by low productivity, requires a high gas consumption compared to single-layer welding, therefore it is used when it is necessary to create responsible and high-quality products.
Features of pipe welding
Welding of gas pipes is carried out in several stages. First, the metal is prepared, that is, the marking is carried out, the pipes are cut and assembled. Due to the circular cross-section of the pipes, cutting is performed with a thermal cutter. Most of the work on welding is the assembly of parts for it, when you need to take into account many parts. from a series of products to their diameter and other factors. Assembly is carried out with welding tacks to prevent possible displacement of the pipe sections, which affects the appearance of cracks during cooling.
The arc is ignited. This is done in a variety of ways. Then the melting of metals begins. the base and electrode. For a high-quality weld, it is important to pay attention to the angle of inclination of the electrode.
Gas welding and metal cutting. Gas welding technology. Gas welding equipment
Gas welding is a type of welding work where parts need to be heated to a molten state by means of a high-temperature flame. This method is widely used in the creation of structures based on thin carbon steel, in the repair of cast iron products, as well as when it is necessary to weld defects in various products obtained by casting from non-ferrous or ferrous metals.
Acetylene production by pyrolysis method
Pyrolysis acetylene is produced by burning methane mixed with oxygen in reactors at a temperature of 1300-1500 ° C. The result is a mixture that contains:
- acetylene. up to 8%;
- hydrogen. 54%;
- carbon monoxide. 25%;
- impurities. up to 13%.
With the help of a solvent (dimethylformamide), acetylene with a concentration of 99.0-99.2% is extracted from it. The rest of the pyrolysis gases are used for the production of ammonia and other products.
Also, acetylene is obtained by the decomposition of liquid fuels (oil, kerosene) by the action of an electric arc discharge, which is called electrolysis.
Pyrolysis and electropyrolysis acetylene in its properties is identical to acetylene obtained from calcium carbide, but cheaper by 30-40%.
Acetone
When passing a mixture of acetylene and water vapor in a ratio of about 1:10 at a temperature of 430-450 ° C over a zinc-vanadium catalyst, acetone is formed according to the equation:
The specified process has found application on an industrial scale.
Effect of impurities in acetylene on the quality of the weld
Let’s dwell on some more features of the use of acetylene in gas welding. the effect of impurities on the quality of the weld. The following impurities have a harmful effect:
- hydrogen sulfide
- phosphorous hydrogen
The above impurities must be removed from acetylene, not only because of the effect on the quality of the weld, but also because of the detrimental effect on the respiratory and vision organs of the welder (see the article Explosion hazard, toxicity and spontaneous ignition of acetylene).
During combustion, hydrogen sulfide forms sulfuric acid, which, when transferred to the weld metal, causes red brittleness. It was found that the presence of hydrogen sulfide up to 0.007% does not have a harmful effect on the strength of the welded seam.
It is quite easy to determine the presence of hydrogen sulfide in acetylene; it is necessary to bring filter paper soaked in a solution of mercury chloride under a stream of acetylene. In the presence of hydrogen sulfide. the paper will turn white.
The process of purification from hydrogen sulfide is also quite simple. it is necessary to pass the acetylene through water, as a result of which the hydrogen sulfide will dissolve in the water.
During combustion, hydrogen phosphide forms phosphoric acid, which, when transferred to the weld metal, causes cold brittleness. It was found that the presence of phosphorous hydrogen up to 0.027% does not have a harmful effect on the strength of the weld.
To determine the presence of phosphorous hydrogen, it is necessary to bring a piece of filter paper soaked in a ten percent solution of silver nitrate under a stream of acetylene. With a content of 0.01% hydrogen phosphide, the paper takes on a distinct light yellow color, with a content of more than 0.02%. the paper darkens.
Chemical purification of acetylene from phosphorous hydrogen is carried out by passing it through a special cleansing mass. heratol. Heratol is a yellow mass, which, as a result of interaction with phosphorous hydrogen, turns green.
Production and use of acetylene
Before we start explaining where acetylene is used, let’s take a look at how to get it.
Vinyl Chloride
When acetylene interacts with hydrogen chloride at 200 ° C over a catalyst, which is mercury chloride deposited on activated carbon, vinyl chloride is formed according to the equation:
Use of acetylene
Acetylene is used in all processes of flame processing of metals (gas welding and gas cutting), due to the high flame temperature, which cannot be reached when using other fuels.
For brazing, cutting, surfacing, flame hardening, metallization, gas-pressure welding, welding of non-ferrous metals and alloys, acetylene substitute gases are successfully used:
- propane-butane mixtures
- city gas
- natural gases
- hydrogen
- gasoline vapors
- kerosene vapor
- IAF
- and etc.
In terms of chemical composition, all of them, with the exception of hydrogen, are either compounds or mixtures of various hydrocarbons.
The correct choice and use of substitute gases allows to achieve high quality welding and cutting, and when gas cutting of metals of small thickness gives a higher cut purity.
Gas welding is possible provided that the flame temperature is twice the melting temperature of the metal being welded. Therefore, substitute gases whose flame temperature is lower than that of acetylene are used for welding metals with a melting point lower than that of steels.
For gas cutting, the choice of combustible gas is based on its calorific value, but it must be borne in mind that the gas, when burned in a mixture with oxygen, must form a flame with a temperature of at least 2000 ° C.
Acetylene is produced in two main ways:
- from calcium carbide by hydrolysis reaction
- from hydrocarbon products contained in natural gases, oil, gases from the processing of coal and peat shale.
At the moment, the method of producing acetylene from calcium carbide is rarely used, since it is rather bulky, expensive and requires a lot of electricity.
Therefore, it was replaced by a method of producing acetylene from natural gas (methane) by thermooxidative pyrolysis of methane with oxygen (the so-called pyrolysis acetylene).
Manual gas welding and metal cutting.
Gas welding is carried out due to the heat released during the combustion of the acetylene-oxygen mixture. At a flame temperature of up to 3150 ° C, the edges of the pipes to be joined and the filler material. welding wire of the Sv-08 or Sv-08A brands are melted. Acetylene for welding is supplied in cylinders or obtained locally in portable gas generators. In the first case, steel cylinders with a capacity of 40 or 50 liters with an initial pressure of 15-18 kgf / cm2 are used. To avoid an explosion of acetylene during transportation, the cylinder is filled with a porous mass of activated carbon, and the acetylene is dissolved in acetone. In the case of using gas generating units, acetylene is obtained by decomposition of calcium carbide (CaC2) in water. The reaction proceeds according to the equation CaC2.j-2H20 = C2Ht.f- Ca (OH) 2. For 1 kg of calcium carbide, 5-10 liters of water are spent, while 230-280 liters of acetylene are formed.
Oxygen is delivered to the work site in steel cylinders with a capacity of up to 40 liters under a pressure of 150 kgf / cm 2. It should be remembered that in order to avoid an explosion, oxygen cylinders should not have contact with oil, oily gloves or rags.
To reduce the pressure of acetylene to 0.1-1.5 kgf / cm 2, reducers of the ABO-5, ABD-5, ASO-10 and ARD-30 types are used, and the oxygen pressure is reduced by reducers of the types
one. points with acetylene (in the gas cylinder version); 2. acetylene reducer; s. gas generator (with gas generator version); four. oxygen cylinder; five. oxygen reducer; 6. rubber-fabric sleeves; 7. torch or cutter; eight. wire.
KBO-60, KBD-60, KBD-25 and KSO-Yu. The above designations are deciphered as follows: K. oxygen, A. acetylene, B. balloon, R. ramp, C. network, O. one-stage, D. two-stage. The numbers after the designation show the throughput of the reducer, cubic meters per hour.
The production of an acetylene-oxygen mixture and its combustion are carried out in hand-held welding torches of the GS-2 and GS-3 types with replaceable tips. Gas and oxygen are supplied to the burner through rubber-fabric hoses 6 (fig. VII.3) with internal diameters 6, 9, 12 and 16 mm.
Installations for gas welding are simple, transportable, versatile, but gas welding is accompanied by the burnout of carbon, manganese and silicon from the pipe metal, which reduces the mechanical properties. Therefore, gas welding is permissible only for gas pipelines with a diameter of up to 150 mm with a wall thickness of no more than 5 mm at a gas pressure in the gas pipeline of up to 3 kgf / cm 2. Generally, gas welding is used when installing indoor gas pipelines with small diameters.
When replacing a gas torch with a torch, for example “Flame-62”, the installation can be used for cutting metal. In the cutters, instead of acetylene, propane-butane, mains natural gas, kerosene, gasoline can be used.
Gas cutting is widely used in the installation of fittings for gas pipelines, for cutting out defective joints and for tie-in bends.
Automatic submerged arc welding. The peculiarity of submerged arc welding is that the welding arc formed between the workpiece to be welded and the end of the filler wire burns under a layer of free-flowing flux based on manganese, silicon or magnesium silicates. Due to the heat of the arc, the edges of the welded product, the end of the filler wire and part of the flux melt. The lightweight molten flux forms a gas and liquid layer over the bath of molten metal, protecting it from exposure to air. In addition, the layers of flux create thermal insulation of the weld pool, providing a slower cooling down.
Automatic welding of gas pipelines is performed on the first (root) layer welded by manual welding. In this case, the section of the pipes to be welded rotates uniformly on the stand with an end rotator, and the welding machine (welding head), stationary above the joint to be welded, evenly feeds the filler wire and flux into the welding zone.
Due to the welding current increased to 900 A and reliable flux thermal insulation, a large amount of heat is concentrated in the welding zone, providing deep penetration of the metal and slow cooling of the seam. This allows to reduce the number of welding layers (excluding the root layer) to two, and with small pipe wall thicknesses. to one layer, which significantly increases the productivity of welding.
Acetylene or Propane. Which Fuel Gas is best for you?
Installation of automatic submerged arc welding consists of source of direct or alternating current, a welding machine, a stand for assembling and welding pipes (first layer) in a section and a welding stand with an end rotator of the sections.
Gas-electric welding. At present, during the construction of gas pipelines, electric arc welding in carbon dioxide environment has become widespread, characterized by a powerful and stable arc discharge. Due to the heat of the arc discharge, the edges of the pipes to be welded and the end of the electrode wire supplied to the welding zone melt. The resulting pool of molten metal is protected from the air by a cloud of carbon dioxide, continuously flowing through the nozzle of the electric holder (Fig. VII.4).
At the stands, automatic gas-electric welding is used, similar to automatic welding under a layer of flux. In route conditions, semi-automatic gas-electric welding of rotary and non-rotary joints is more convenient, the technique of which is not much different from the technique of manual electric arc welding, since the electric holder is moved manually over the workpiece to be welded (Fig. VII.5).
DC generators or AC converters with a power of 5-10 kW are used as current sources for semi-automatic gas-electric welding. For automatic feeding of the electrode wire and the supply of carbon dioxide to the electric holder, hose semiautomatic devices A-547, A-607 and others are used with their remote shutdown by a button on the welder’s protective shield. The mode of semi-automatic welding of rotary joints is as follows: welding current 180-200 A, arc voltage 24-26 V, carbon dioxide pressure on the reducer 1.5-2.0 kgf / cm2, wire feed speed 5-15 m / min.
one. products to be welded; in. electrode wire; in. gas nozzle; four. current supply shoe; 6. protective gas layer; 6. deposited metal.
Welding in a carbon dioxide environment is simple, ensures good quality of seams, does not require the use of fluxes that form a slag crust that must be removed, is carried out in any spatial positions, has a lower cost compared to welding under a layer of flux.
Calcium carbide and acetylene. friends do not spill water!
Calcium carbide has a pungent garlic odor and is highly water-absorbing. Its density increases with an increase in the amount of impurities and varies in the range of 2.22-2.8 g / cm 3. Molecular weight. 64.102. Technical calcium carbide is produced in accordance with GOST 1460.
Flammable gases
Combustible gases mixed with oxygen are intended for flame treatment of metals. Most often, acetylene is used for gas welding. For gas cutting of steels, when the temperature of the heating flame does not have a decisive effect on the course of the process, but only increases the duration of the initial heating of the metal before cutting, it is recommended to use acetylene substitute gases with a flame temperature of at least 1800-2000 ° C.
The following are used as acetylene substitute gases:
- natural gas
- coke oven gas
- propane
- butane
- propane-butane mixture
- gasoline vapors
- kerosene vapor
- city gas
- IAF
Acetylene generator
Acetylene generators used for welding and cutting metals in accordance with GOST 5190-78 are classified according to the following criteria:
Explosion hazard, toxicity and self-ignition of acetylene
When working with acetylene (C2H2), special safety measures must be taken as it is a poisonous gas and is prone to spontaneous combustion and explosion. According to GOST 12.1.007, acetylene hazard class. 4. For those who are too lazy to deal with the normative document, let us explain that harmful substances are divided into four classes according to the degree of impact on the body and acetylene belongs to low-hazard substances. But this does not mean that this gas is completely safe, so below we will consider in detail why it is still dangerous.
Production and use of acetylene
Before we start explaining where acetylene is used, let’s take a look at how to get it.
Acetylene chemical purifiers
Obtained in acetylene generators, as a result of the reaction of calcium carbide and water, acetylene contains solid particles of lime, water vapor and various chemical compounds of ammonia, hydrogen sulfide, phosphorous and siliceous hydrogen. The solids are removed by washing the acetylene with water. Dryers and moisture separators are used to clean the gas from moisture, and to clean it from phosphorous hydrogen and hydrogen sulfide. chemical cleaners.
The influence of harmful impurities on the quality of welds is described in the article on the production of acetylene.
Welding, cutting and brazing of metals
In the repair of agricultural machinery, gas welding and cutting are widely used.
The accumulated production experience has shown that propane and butane are good substitutes for acetylene and kerosene for flame treatment of metal. Liquefied gas is cheaper than acetylene, and the quality of cutting with propane-butane-oxygen flame is higher than that with acetylene-oxygen flame. When working in winter conditions, obtaining gas from a cylinder with a propane-butane mixture usually does not cause difficulties. Working with liquefied gases is significantly safer than using calcium carbide and acetylene.
Gas welding is performed with a welding flame formed during the combustion of a mixture of oxygen with a combustible gas, which can be a liquefied gas (propane or propane-butane mixture). The welding flame, depending on the ratio of oxygen and propane-butane, is normal, oxidizing and carburizing.
For most metals, a normal flame with a slight excess of oxygen is used. Welding of mild steel with a propane-butane-oxygen mixture is carried out with a gas to oxygen ratio of 1: 3.
By reducing the content of propane-butane or increasing the amount of oxygen, an oxidizing flame is obtained, and with an increase in the amount of propane-butane, a carburizing flame.
Oxy-fuel welding and cutting of metal can be carried out both in workshops and in the field, for which single cylinders are usually used.
Due to the small amount of bled gas, the mobile station can be powered from the cylinder without an evaporator at an air temperature of up to minus 25-30 ° C. When powering several posts from the gas network, i.e. with a significant white gas consumption, a group balloon installation can be used.
Gases are delivered to the workplace either through a pipeline from stationary containers, or in steel cylinders.
To reduce the pressure of liquefied gas, conventional reducers such as RDK, RDG-6 and others can be used.
When using an acetylene reducer, it is necessary to replace the clamping clamp with a transition union with a union nut.
The housing of the hydrogen, oxygen or acetylene reducer used to reduce the pressure of LPG and the housing of the pressure gauge are colored red. On the dial of the pressure gauge the inscriptions “Hydrogen”, “Oxygen”, “Acetylene” are replaced by the inscription “Propane”.
The handling of pressure regulators for liquefied gas is the same as for oxygen pressure regulators. The use of oxygen and hydrogen reducers for oxygen, after using them for liquefied gas, is strictly prohibited in order to avoid an explosion.
It is prohibited to take gas from a cylinder without a reducer.
When testing a gas cutting station from a gas network with a gas pressure of 1 to 5 kg / cm 2, the installation of a reducer is also absolutely mandatory.
When working with propane-butane mixtures, it is necessary to carefully monitor the rubber membranes, since when gas leaves the gas cylinder in liquid form and penetrates into the reducer, the rubber membrane gradually erodes and becomes unusable.
Liquefied gas transmission capacity for RDK-00 is 1.3; for RD-1-0.25. 5 m 3 / h.
To connect the torch (cutter) to the reducer installed on the cylinder, use rubber-fabric hoses in accordance with GOST 8318-57, designed for a working pressure of 10 kg / cm 2.
The design of the gas welding torch is simple and can be manufactured in any workshop.
For welding low-carbon steels with a thickness of 0.5 to 5 mm and other types of flame treatment of metals (brazing, heating, etc.) using propane or propane-butane as a combustible gas, you can use the Ufa welding torch, the diagram of which is shown in Fig. 40.
The Ufa burner tip differs from the existing oxygen-acetylene tips by the presence of chambers for preliminary and final heating of the combustible gas in front of the injector.
When taking gas from gas networks with a pressure of 70 mm of water. Art. up to 10 thousand mm of water. Art. (1 kg / cm 2) the reducer may not be installed, but a safety water seal is installed.
At gas pressure in gas networks from 70 to 200 mm of water. Art. on the descent to the working post, a water seal ZGG-3 designed by VNIIavtogen is installed. At a pressure of 200 to 1000 mm of water. Art. installed water locks of open type VZND-3 with a maximum throughput of 3 m 3 / h. At gas pressure from 1000 to 7000 mm of water. ap. water gates of a closed type (medium pressure ZSD-Z-07 and high VES-10) are installed at 1.5 kg / cm 2 and with a throughput of 3 and 10 m 3 / h. The memorial capacity of the water seal should correspond to the greatest possible gas extraction.
how to cut with a torch. oxygen acetylene welding cutting torch
The assembled burner is inserted into the barrel socket and secured with a nut, and an asbestos cord should be wound between the mixer rim and the sealing washer.
After performing this operation, you can open the valves on the oxygen and liquefied gas cylinders, then open the liquefied gas and oxygen valves on the barrel, ignite the mixture at the tip. After 2-3 minutes of burner combustion, the required flame is regulated by oxygen and gas valves on the barrel. Flame selection is made within a few seconds.
Oxygen and propane-butane, passing through the barrel, valves, enters the mixing chamber. Part of the mixture enters the burner to heat the chamber, and the bulk of the mixture goes to the heating chamber filled with catalyst (0.2 mm thick nickel strip rolled in the form of a spring), where it is heated to 270 ° C. After that, the mixture enters the cone and to mouthpiece. Combustion produces a flame with a temperature of up to 3100 ° C, sufficient for welding mild steel.
Welding, depending on the thickness of the material to be welded, is carried out at an oxygen pressure of 3.5-5 kg / cm 2 and a gas pressure of 0.8-1.3 kg / cm 2. When the hoses are lengthened, the pressure increases slightly.
The length of the burner flame must be between 12-23 mm. Its color should be pale blue.
The welder needs to monitor the process in the weld pool and conduct more intensive mixing of the molten metal. The flame should be kept at an angle of 60-80 ° relative to the metal surface, welding from left to right, blowing out possible slag from the bath (uncleaned ends). With cleaned ends, slag deposits are insignificant.
If it is necessary to replace a larger mouthpiece number with a smaller size, an adapter must be included in the torch kit.
Depending on the number of the mouthpiece, the tip is also replaced. With a larger mouthpiece number, a larger tip number is used, and vice versa. The oxygen injector changes accordingly.
It should be mentioned that when a welder masters welding steel with a propane-butane-oxygen mixture at first, difficulties and disadvantages in welding are possible, but when the welder masters the flame adjustment, depending on the thickness of the metal being welded, the welding proceeds normally and the seams are good.
It is known from the practice of welding with a propane-butane-oxygen mixture that for more intense vaporization it is advisable to place the cylinder in a heated room.
According to VNIIavtogen, good results in welding low-carbon steel can be obtained by using filler wire of the SV-08GS and SV-082GS grades.
It can also be noted that with an increase in the propane content in the propane-butane-oxygen mixture, the welding quality improves.
In practice, propane-butane-oxygen mixture in rural areas can be used for welding water and gas pipes with a diameter of up to 4 “, sheet mild steel up to 5-6 mm thick, welding tanks and cans for milk, parts of agricultural machines, fenders and hoods of cars and for soldering. non-ferrous metals.
The low melting point of aluminum makes it possible to use propane-butane mixtures for their welding in agricultural workshops.
The Chelyabinsk Intersectoral Research and Design Institute of Automation and Mechanization of Mechanical Engineering carried out a series of experiments on welding and cutting with propane at the Stepnoy state farm in the Chelyabinsk region. These experiments showed that the use of propane instead of acetylene gives positive results.
For cutting, acetylene cutters PP-53 with alteration were used (the holes in the injector and the mixing chamber increased, respectively, to 1 and 3 mm, the annular gap between the inner and outer mouthpiece increased). Similar changes were made to the injector and mixing chamber for the GS-53 acetylene burner (for the tip). After these alterations and using propane, it was possible to weld non-ferrous metals and cast iron.
A propane-oxygen flame was used to weld aluminum flanges of the intake manifold of the Belorus tractor, to repair aluminum tanks, pipelines and milk cans at the creamery. Productivity when welding aluminum sheets 3-4 mm thick with a propane-oxygen flame is higher than with an acetylene-oxygen flame: 46 running hours are welded in 6 hours of operation. m seam.
Intro to Oxy-Acetylene Welding. Part 1
The main difficulty in welding aluminum, as is known, lies in the formation of a film of refractory aluminum oxides on the metal surface, which prevents fusion. These oxides are not reduced by propane-oxygen flame; they are heavier than aluminum and sink in it. To achieve high quality, the edges of the parts are cleaned with a steel brush before welding; the burner flame should be normal. AF-4a flux is applied to the filler rod of AD or AK grade.
When welding aluminum with a thickness of up to 3 mm, the torch is given only a translational movement, and the bar makes oscillatory movements, which removes the film and slag and makes it easier for gas bubbles to float to the surface. The flame of the burner is directed to the filler rod at an angle of 40-60 ° and at the same time covers the edges to be welded.
When welding, the core of the flame should be at a distance of no more than 3 mm from the surface of the bath. When these requirements are met, the welding quality is high, there is no porosity, and no crystallization cracks are formed. The strength of aluminum welds obtained by welding with propane and acetylene is practically the same. Although the thermal conductivity of aluminum is almost 5 times, and the heat capacity is 2 times that of steel, a propane-oxygen torch can weld aluminum tires up to 10-12 mm thick without using preheating.
Lead welding. Lead is welded with a neutral flame with the smallest possible angle of inclination of the flame to the surface of the part. With a metal thickness of more than 2 mm, the seam is applied in several layers (individual sections overlap).
Practice has shown that welding of lead with a propane-oxygen flame can be successfully performed with a burner, combustible and lubricating materials without its alteration. The welded seams are of a fairly high quality. This method has been successfully applied for welding lead terminals of acid storage batteries.
Copper welding. Due to the high thermal conductivity of copper, a large heat input is required during its welding, therefore, the torch flame should be held perpendicular to the surface of the weld pool; the torch is chosen two numbers larger than for welding steel of the same thickness, and in some cases welding is performed with two torches.
Welding is carried out with a neutral flame, if possible without interruption. The edges and wire must be melted at the same time. You should not bring the bath to a very mobile state. Borax or a mixture of borax and boric acid is used as a flux. As a filler rod, copper wire deoxidized with phosphorus (phosphorus 0.03-0.08%) and silicon (silicon 0.5-1.0%) gives good results. For the best quality of the seam with a product thickness up to 5 mm, forging is performed. Forging is carried out in a cold state, and at large thicknesses. at a temperature of 400-500 ° C. To reduce the brittleness, after cooling the welded part to 500 ° C, the product is quickly cooled by immersion in water. The speed of welding with a propane-oxygen flame of copper sheets with a thickness of 4-5 mm is the same as the speed of welding with acetylene.
Brass welding. Bronze and brass are also easily welded with a propane-oxygen flame. The main difficulty in welding brass with a gas-oxygen flame consists in the evaporation of zinc (up to 20%), as a result of which the seam turns out to be porous. Zinc burnout at a propane-oxygen flame is less than 1%, due to which the seam is tight. The filler wire is taken of the same composition as the base metal. Fused borax is recommended as a flux. When using LK-02-05 filler wire with a known skill, welding in any spatial positions is possible.
In one state farm, worn bronze bearing shells and various brass parts were fused with bronze in this way. The quality of welding and surfacing was good in all cases.
Propane-butane mixtures are also full-fledged substitutes for acetylene and when brazing with PMTs-54 and L-02.
Cast iron welding. Gray cast iron is widely used in tractor and agricultural machinery parts. All complex parts: cylinder blocks, block heads, crankcases, gearboxes and clutches, exhaust and intake pipes, pulleys, chain sprockets and a number of other parts, are cast from cast iron.
As you know, in the case of repairing cast iron parts of complex geometrical shape, for example, block heads, preheating of the part is required. However, many parts of agricultural machinery. brackets, levers, valuable sprockets. can be repaired without preheating.
When welding cast iron, there is a large burnout of carbon and silicon. Therefore, the welding rods must have heightened of these elements. Good results were obtained when using worn cast-iron piston rings of engines as a filler material.
When welding defects of complex cast iron parts, it is advisable to solder cast iron with brass. The graphite is removed from the surface by burning out, with a welding torch with an oxidizing flame, and the part is heated to a temperature of 750-900 ° C. Then, the place to be repaired is sprinkled with flux and covered with a layer of brass. After soldering, the part is covered with a sheet of asbestos and slowly cooled. In this case, large stresses do not arise in the part and the seam is well processed.
As practice has shown, propane can be successfully used to repair cast iron parts, mainly for welding cracks.
Metal cutting. For separation cutting with liquefied gas of metals, cutters of the RZR-01-55, URZ and RZP types, as well as gasoline and kerosene cutters are used.
In the absence of these cutters, you can use an ordinary UR cutter, increasing the diameter of the injector hole to 0.3-0.9 mm.
External mouthpiece. having a diameter of 5.5 mm, should be used instead of the mouthpiece. and a mouthpiece with a 0.5 mm hole. instead of a mouthpiece For cutting thick sheets, the diameter of the injector nozzle is increased to 0.95 mm, and the diameter of the hole in the outer mouthpiece is increased to 7 mm. The diameter of the mixing chamber channel can be increased up to 3 mm when cutting thicker thicknesses.
Caring for propane / butane torches is the same as for Oxyacetylene torches.
Prepare the workplace for work, reducers, hoses, torch and torch, purge cylinders, install a reducer, fill the water seal with water, attach the torch and torch hoses, check the presence of feed in the torch, ignite and extinguish the torch and torch in the same sequence as and in oxy-acetylene cutting and welding.
When a propane-butane mixture burns in a stream of oxygen, a properly adjusted flame has a brightly defined core, burns calmly and steadily. The flame length of the propane-butane mixture is greater than the flame length of the acetylene-oxygen mixture.
The preheating flame is adjusted in the torch to the maximum temperature (with a slight excess of oxygen) according to the flame at the mouthpiece.
The use of a propane-butane mixture is quite possible for cutting carbon and structural (low-alloy) steels, as well as cast iron, chromium-nickel steels and non-ferrous metals.
The value of oxygen pressure is set depending on the thickness of the cut metal in the range from 2 to 15 kg / cm 2. The pressure of the propane-butane mixture can be in the range from 0.007 to 0.5 kg / cm 2. with long hoses and in stationary networks. up to 1 kg / cm 2.
Cutting usually begins with an edge that has been previously cleaned of dirt and scale. If you need to start cutting from the middle (with a large metal thickness), then you need to drill or burn a hole with a diameter of 5-10 mm.
To increase the heating rate of the metal in the initial period (with round metal sections), it is necessary to make notches with a chisel or substitute a metal bar at the beginning of the cut. With a heating flame, the metal is first heated in the place where cutting begins to the temperature of its ignition (for steel 100-1200 ° C, light red heat), then a cutting oxygen jet is launched and the cutter is moved along the cut mowing line. The distance between the cutter and the line of the cut should be as even as possible. To fulfill this condition, it is necessary to use devices (guide ruler, etc.). At very high speed of movement of the cutter, cutting may stop, and at low speed, the upper edges of the cut metal are melted.
When cutting pipes to a chamfer, the cutter lead angle should be 5-10 °, and when cutting pipes without a chamfer. 10-15 °.
Otherwise, the technology for cutting steel with a propane-butane mixture does not differ from the technology for cutting with an acetylene-oxygen flame.
When welding and cutting metal, safety precautions must be followed.
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