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Oxygen cutting technology
Molten titanium and its oxides are able to dissolve any refractory. With this method of cutting, the speed of burning holes is three times higher than when cutting with ordinary oxygen spear.
Surface cutting. It is produced by a stream of cutting oxygen, inclined to the surface of the metal at an angle from 15 to 40 °. The sequence of operations during surface cutting is shown in the rice. 109, a, b. The depth of the groove increases with an increase in the angle of inclination of the mouthpiece, an increase in oxygen pressure and a decrease in the speed of moving the mouthpiece along the groove. The width of the groove is determined by the diameter of the channel for the cutting stream of oxygen. With a change in oxygen purity by 1 %, the cutting speed changes accordingly by about 15 %. The speed of surface cutting lies in the range of 1-6 m/min. One cutter can be removed up to 5 kg of metal per minute. Deep grooves are cut out in two to three passes. Surface cutting modes are as follows:
When using coking gas, according to E. X. Shamovsky, the rate of expiration of the combustible mixture of a heating flame should be 300 m/s, the composition of the mixture
In this case, multi.salt mouthpieces with the diameter of the channel of each nozzle from 1.8 to 3 mm are used, depending on the consumption of the mixture.
For laying sheets during machine cutting, special tables are used, which can be motionless or mobile, moving along the rails. The table frame is welded from the channel, on which cast.iron conical prisms are installed, which are supports for the cut sheet. Slags when cutting are collected in special containers located under the tables. Containers are unloaded using a crane.
The cut sheet is laid on prisms. Slag blended during cutting falls into a pallet. At the same time, the flow of hot gases at the level of the cut sheet is directed away from the workplace, which improves the working conditions of the cutter. To clean the content of containers from the rack, the grates with prizes lying on them are removed by the crane; Then the containers are taken out and the slag is poured into collections for production waste.
If you need to cut parts with exact dimensions, the sheet is corrected. Details carved from an wrong sheet can change their size during subsequent editing. The sheet, as well as the plane of the copy, should be strictly horizontally. It is necessary that the distance between the sheet and the pallet (or floor) is at least 0.5 S100 mm (where s is the thickness of the leaf), otherwise the flowing stream and toxins, reflected from the surface of the pallet, can ruin the cutting surface.
Curve accuracy and quality. The accuracy of the cut is characterized by the deviations of the cut line from the given, as well as the deviation of the cut plane from a given angle (in relation to the surface of the sheet). The quality of the cutting is determined by the purity (smoothness) of the cutting surface, the degree of melting (rounding) of the upper edge of the cut, the presence and degree of adhesion of slag (grata) with the lower edge, uniformity of the cut width along the entire metal thickness and the absence of local melting on the surface of the cutting surface (snaps).
The cutting fishing line for the cutting of the cut deviates from the cutting axis or deformation of the sheet specified as a result of the displacement of the axis. The greatest deviations are obtained with manual cutting.
The deviation of the cut plane from the given occurs when the angle of inclination of the cutter is changed to the surface of the sheet, as well as by expanding the cutting stream of oxygen
The smoothness of the cut surface is determined by the amount and depth of the grooves left by the cutting stream of oxygen. These grooves usually have a curvilinear outline due to some lag behind the mouthpiece of the cutting stream of oxygen, which is inevitable and caused by the delay of iron oxidation in the lower layers of the metal. The lower oxidation rate of the underlying layers is due to: the greater contamination of the cutting stream of oxygen in these layers due to an increase in the content of inert impurities in the thickness of the metal. Argon, nitrogen and combustion products; the impossibility of direct heating with the flame of the metal on the lower edge; decreasing speed and expansion of the cutting stream of oxygen. The size of the cutting stream of oxygen increases with an increase in the thickness of the metal and the speed of cutting or a decrease in the purity of the oxygen used.
If the lag is so large that it leads to the inconsistency of the outlines of the part on the upper and lower cuts of the cut, then it is reduced, reducing the speed of cutting. The use of step-cylindrical and expanding snot, which provides a cylindrical shape of the jet over a larger length, as well as cutting with oxygen of low pressure, when there is no severe expansion of the jet, significantly reduce the magnitude of the lag. With rectilinear cutting with normal speeds, step-cylindic shapes are: the lag is:
The depth of the grooves depends on the pressure of oxygen, the speed of moving the cutter and the type of fuel. When using natural gas, the cutting surface is obtained without melting and more even than when cutting acetylene.
The uneven cutting surface may also be obtained as a result of the fluctuation of the cutter or the uneven speed of its movement.
The melting of the upper edges depends on the power of the heating flame and the speed of cutting. The greater the capacity of the flame and below the speed of cutting, the more significant the melting. Of great importance for obtaining a clean surface of the cut is the concentration (purity) of oxygen. A particularly smooth cut surface can be obtained using concentration oxygen at least 99%.
The main indicators of the quality of the cut surface are profile and cleanliness, depending on the thickness of the cut steel and the speed of cutting. The cut profile is evaluated by the degree of its perpendicularity to the surface of the sheet. The magnitude of the lag and the depth of the grooves depend on the perpendicularity of the profile and increase when it is deviated from the vertical plane. The main indicator of the purity of the cut surface is the depth of the grooves (roughness).
Setting the Correct Air Pressure and Amperage for your Plasma Cutter
The radius of rounding the upper edge can only be considered an auxiliary sign of the quality of the cut.
Based on these provisions and on the basis of studies of VNIIAVTOGENMASH, GOST 14792–69 “Oxygen and plasma-idle cutting was developed. Accuracy of parts and blanks and the quality of the cutting surface “. This GOST provides for three classes for the quality of the cutting surface:
What is oxygen cutting?
With oxygen cutting, the flame of oxygen fuel mixture pre-heats steel to the ignition temperature.
The oxygen stream is directed to the metal, creating a chemical reaction with the formation of iron oxide, also known as slag. A powerful stream of oxygen removes slag from a cut.
When using oxygen burners, the quality of the cutting, preliminary heating and the thickness of the metal depend on the type of fuel gas. In the process, one of four fuel gases in combination with oxygen are involved: acetylene, propane, propylene and natural gas.
Why is oxygen cutting?
Manual oxygen cutting is common in projects with small volumes, when the use of expensive units is not economically justified. For example, preparation of parts for subsequent forging and stamping, in foundry workshops, cutting pipes. Oxygen cutting is effective when working with thick steel and ferrous metals.
There are oxygen fuel burners that can be used for several processes, such as cutting, welding and soldering.
- An indisputable plus of this process is the low initial costs and portables of components compared to plasma cutting devices.
- The ability to quickly cut thicker steel, in addition, the universality of the system.
What is plasma cutting?
At the basic level, plasma cutting is a process in which the high.speed stream of ionized gas is supplied from the hole of the narrowing nozzle. High.speed ionized gas. plasma, conducts electricity from the burner of the plasma cutter to the workpiece. Plasma heats the workpiece, melting the material. Different gases are used for various types of metal: ferrous metals and alloys are cut using active gases. oxygen. Inactive, inert gases: nitrogen, argon, are used in cutting non.ferrous metals and alloys.
High.speed plasma stream created by a built.in or separately connected compressor, mechanically blows the molten metal, sharing the material.
What is plasma cutting for?
Plasma cutting is performed on any type of conductive metal, for example: non.ferrous metals, soft steel, aluminum and stainless steel. With the help of a plasma apparatus, soft steel is cut faster than alloys.
Plasma cutting is ideal for cutting blanks with a thickness of less than 25 mm. Plasma cutting copes with non.standard tasks, such as cutting metal foam: metal with a cellular structure, which is almost impossible to cut using oxygen cutting. Compared to mechanical agents, plasma cutting, as a rule, is much faster and easier to cut a non.linear cut.
- The pluses of plasma cutting include simplicity of use, the best quality of the edge and the high speed of movement.
- Plasma cutting does not depend on oxidation, so aluminum, stainless steel and any other conducting metal can cut.
- Working with any metals: black, non.ferrous, refractory.
- Productivity when cutting metal of small and medium thickness is 3 times higher than manual oxygen cutting.
- Point, local surface heating, without unnecessary deformation and overheating all parts.
- Safety because there are no fuel gas cylinders.
- The possibility of figure cutting of complex shapes.
It is needed for periodic repairs, maintenance or projects that require large amounts of cutting.
Characterization of work depending on the category
Depending on the category, the characteristic of the work is gradually becoming more complicated.
The welder of the second category should perform:
- seizing parts, products, as well as structures, regardless of the material in all existing types of spatial location of the welding joint or seam;
- manual arc and plasma welding of simple types in the lower and upper positions of the welded joint, as well as the fusion of simple parts;
- preparation of components individually, as well as the entire product for the performance of welding, as well as carry out work to clean up the joints after the completion of welding measures;
- measures to protect the back of the welded joint when working in protective gas;
- actions for the heating of individual parts and products as a whole before the implementation of welding measures;
- actions to read simple drawings.
With an increase in discharge, they increase by adding to the main characteristics and those characteristics that the welder should know. So, for the welder of the 6th category to the list of necessary work that he must perform, are added:
- performing manual arc and plasma welding in relation to complex devices, nodes, structures, pipelines, which are made from various steels, as well as non.ferrous metals and alloys;
- the implementation of manual arc and gas.electric welding in relation to complex construction and technological structures, the functioning of which is carried out under the loads of dynamic and vibrational types, as well as which are characterized by a complex design of configurations;
- the implementation of welding measures for the manufacture of experimental structures from metals, as well as from various alloys, which are characterized by limited welding, as well as structures from titanium and titanium alloys;
- performing welded joints on complex block design structures, regardless of the spatial arrangement of the weld.
Characteristics of the work. Manual oxygen cutting and cutting with gas.cutting and kerosene.cutting devices of steel lightweight and heavy scrap. Manual arc, plasma, gas, automatic and semi.automatic welding of simple parts, components and structures made of carbon steels. Oxygen and plasma straightforward and curved cutting in the lower and vertical position of the weld with metal, as well as simple and medium complexity of parts from carbon steels by manually marking, on portable stationary and plasma.cutting machines. Group of details, products, structures in all spatial positions. Preparation of products, components and joints for welding. Seaming after welding and cutting. Ensuring the protection of the back of the weld during welding in protective gases. Surfacing simple details. Elimination of shells and cracks in simple details, nodes, castings. Heating of structures and details when editing. Reading simple drawings. Preparation of gas cylinders for work. Maintenance of portable gas generators.
Must know: the device and the principle of operation of the serviced electric welding machines and apparatus for arc welding of alternating and direct current, gas welding and gas cutting equipment, gas generators, electric welding machines and semi.automatic machines, oxygen and acetylene cylinders, reducing instruments and welding burners; Rules for using used burners, gearboxes, cylinders; methods and basic techniques of the selection; Forms of seam cutting for welding; Rules for ensuring protection during welding in protective gas; types of welded joints and types of seams; rules for preparing the edges of products for welding; Types of sections and designation of welds on drawings; the main properties of the electrodes, welding metal and alloys, gas and liquids used in welding; allowed gas pressure in the cylinders; the purpose and brands of fluxes used in welding;purpose and conditions for the application of instrumentation; causes of defects during welding and methods of preventing them; characterization of gas flame; Lome dimensions according to the state standard.
- Transformers tanks. eyeliner under automatic welding.
- Lulence beams, bars of subressor and oversight all.metal wagons and wagons of electroseds. welding of amplifying squares, guides and centering rings.
- Rolling beams. brewing points, captivating lanes on marking.
- Shoes of leeric racks. cutting on the ship.
- Boyds and patterns of steam hammers. Frontier.
- Bolts are axle, column and centr. fueling places of production.
- Details of the frame of the on.board tent. Take and Object.
- Parts Metal containers. hot editing.
- Diaphragms of the frames of platforms and metal gondola cars. welding of the ribs.
- Foals. welding.
- Rivets. cutting heads.
- Frames and details of the brake platforms of freight cars and window frames of passenger cars. welding.
- Casings and fences, slightly loaded nodes of agricultural machines. welding.
- Casings of oil pumps and filters of cars. surfacing shells in castings.
- Brackets of the reapers, brake rollers. welding.
- The muffler mounting brackets to the car frame. Cracking.
- Brackets for fastening mining equipment. welding.
- Substers of subframes of car dampers. welding.
- Captacon lighting lids. welding.
- Corner and external sheathing sheets of tram. brewing cuts.
- Steel scrap for a shichta. cutting.
- Reference pads and linings. welding.
- Small delays. welding ears.
- Steel Steel Steel sizes. welding of ears.
- Steel and cast iron castings. eliminating shells in unsuccessful places by smelling.
- Pallets to machines. welding.
- Profit and summer tints on steel castings up to 300 mm thick. cutting.
- Frames of transformer tanks. welding.
- Frames of mattresses of beds, and rhombic grids. welding.
- Reception pipes. salary of safety nets.
- Car wings amplifiers. welding.
- Hydraulic mechanisms of car dashboard. welding.
- The foundations are non.real, small nodes made of low.carbon and low.alloy steels. semi.automatic welding on the rack.
Characteristics of the work. Manual arc, plasma, gas welding, automatic and semi.automatic welding of simple parts, components and structures from structural steels, non.ferrous metals and alloys and medium complexity of parts, nodes, structures and pipelines made of carbon steels in all positions of the seam, except for the ceiling. Oxygen plasma straight and curved cutting in various positions of metals, simple and medium complexity of parts from carbon and alloy steels, non.ferrous metals and alloying by manually marking on portable, stationary and plasma.cutting machines in all positions of the weld. Manual oxygen cutting and cutting with gas.cutting and kerosene.cutting devices to the specified dimensions with the release of non.ferrous metals and with the preservation or cutout of the units and parts of the machine. Manual arc air harvesting of simple and medium complexity of parts from various steels, cast iron, non.ferrous metals and alloys in various positions. Surfacing shells and cracks in details, nodes and castings of medium complexity. Preliminary and related heating when welding parts in compliance with a given mode. Reading drawings of various complexity of details, components and structures.
Must know: the device of the served electric welding and plasma.cutting machines, gas welding equipment, machine guns, semi.automatic machines and plasmoron; requirements for the weld and surfaces after air harming; methods for selecting grades of electrodes depending on steel grades; properties and value of coating electrodes; The structure of the weld; methods of testing and types of control; rules for preparing parts and assemblies for welding and tea leaves; the rules for selecting the metal heating mode depending on the brand of the metal and its thickness; the causes of internal stresses and deformations in the welded products and measures of their prevention; The main technological techniques for welding and surfaces of parts from various steels, cast iron, non.ferrous metals and alloys; GAZ cutting and consumption regime for oxygen and gas.electric cutting.
Oxygen-dug and air-antigod
Oxygen-duging cutting is used for cutting carbon steels and is distinguished from arc in that the metal is served by a stream of technically pure oxygen, which intensively oxidizes the metal and removes from the cut, the resulting oxides. When the metal is combined in a stream of oxygen, additional heat is formed, which accelerates the process of cutting metals. As electrodes, steel tubes are used with an outer diameter of 8 mm, 340-400 mm long. For sustainable combustion of arcs, a special coating is applied. The electrode when the source voltage is turned on is directed to the cutting point of the cut at an angle of 80-85 ° to the processed surface. During cutting, the cutter moves the cutter along the cut line.
In practice, both dividing and superficial airborne cutting is used. The essence of this method of cutting is to melt the metal along the cutting line of the coal arc burning between the end of the coal electrode and the metal, and the forced removal of the molten liquid metal with a stream of compressed air. Airborne cutting is used mainly when cutting carbon steels, non-ferrous metals and cast iron are amenable to air-anthews worse than steel. Airborne cutting is used when pruning profits from casting, removing defective places of welds. The disadvantage of this method of cutting is to scooter the surface layer of metal.
With manual dividing cutting, the electrode is recessed into the cut metal, the angle between the electrode and the surface of the cut metal is 60-90 °, and with surface cutting it does not exceed 30 °. The departure of the electrode should not exceed 100 mm. When working, the electrode is burned and periodically put forward to the recommended value. It is not recommended to press the electrode, since when heated it becomes fragile and can break. The width of the groove is 1-3 mm larger than the diameter of the electrode used. Air-bottom cutting modes are given in the table.
Features of the design of the gas machine
Equipment for cutting metal of this type is equipped with a special head, from which a stream of oxygen mixed with combustible gases breaks out under pressure. Tables in portal machines of this type have a special design that allows them to withstand high temperatures and the load from very heavy blanks. As in plasma, in such machines there is a cutter, devices for its movement and a control system. Gas is supplied from connected cylinders when working. Cutting safety is provided by special fire.fighting valves.
The profitability of the use of machines for heat cutting is determined by two factors: cutting volume and accuracy requirements. When in production processes you have to cut a small volume of blanks, for example, parts for the release of 10-20 barbecue per month, and the main time is spent on assembly and packaging, then the operation of automatic cutting is not justified. But the situation changes when the production of barbecue is on a global scale of 300-1000 units per month and there is a large network for product sales. In such cases, everyday cutting processes, charm and other operations performed in automatic mode will significantly speed up the release of goods and reduce the number of people involved for this.
The second factor is the requirements for the accuracy of the cut. If expensive metals (sheets or stainless steel pipe, aluminum, etc. are used in the production. D.), then a high.precision cut with a narrow cut and a minimum of waste will help reduce the costs of materials. The use of machines for automatic cutting of metals and in the case of high accuracy requires the details, which will then be used in structures that do not allow errors in sizes (flanges of pipes and high.pressure tanks, collectors of chemical installations, complex water filters, etc. D.). Manual cutting will not give such accuracy and take more time, so it is profitable to buy an automatic installation and optimize the production process.
Types of machines by cutting method
For cutting in machines, three main processes are used: air-plasma, gas-flaming (air-fuel) and laser. But the third is too expensive and specific, so we will consider only the first two. Each has its own characteristics and pluses.
A current source that forms an electric arc works here. The compressor shakes the air passing through the nozzle. From the heating of the arc, the air flow goes into a plasma state that can cut solid materials. The more powerful the device, the more thick the machine will sober up. The current range of such machines from 40 to 300 A, which allows you to cut the steel section from 6 to 60 mm. Such a cut is very narrow and with a smooth edge that does not require further machining.
Together with compressed air (AIR), technological oxygen (O2) can be supplied. This provides an even high.speed cut of ferrous metals. After cutting the surface is immediately ready for welding. The use of only ordinary air (AIR) as plasma.forming and protective gas gives a more subtle slot and saves material. This combination is suitable for low.carbon steel and non.ferrous metals.
Here are some of the most popular machines that supports this method of cutting:
- Siberia ARM to 1.5/3.0. a model with CNC and a three.coordinate movement of the cutting head. Supports automatic search for metal and the height of the cutter above it. Plasma is formed from an inverter type current of Siberia 105 pr. The dimensions of the working area are 1500×3000 mm, and the maximum cut thickness reaches 100 mm.
- Svarog Valiant 3.0. a novelty from a welding brand with high control accuracy 0.1 mm. Supports air-plasma and gas-plasma cutting. Equipped with a manual inclination of plasmoron to remove chamfers, there is protection against electromagnetic interference. CNP with memory of 4 GB for storing parts of parts. Management programs interact with the automated design system, which gives minimal waste of material.
Gas-flame cutting (air-fuel cutting)
In equipment with such a process, three channels are suitable in the burner:
- combustible gas (methane, acetylene or propane);
- technological oxygen to maintain combustion;
- cutting oxygen to dissect the already warmed metal.
This is a rude method of machine cutting, which allows you to cut metals with a thickness of 200-300 mm, but with less evenness of the edge. Immediately put the blanks for welding will not work and you will have to process the edges of the corner grinder. But the cut process is very fast.
A great version of the car with this cut is Messer Quicky-E. It belongs to portable machines working on combustible gas and oxygen. Supports moving forward and backward with the speed set by the operator, as well as the circular clipping of flanges. It is designed to work in the field and is convenient for frequent transportation. Maximum cut thickness 100 mm.
Some machines are universal and support work with burners of both types (air-plasma and air-fuel), which expands the possibilities for their operation.
Oxygen cutting is based on the combustion of metal in the jet of technically pure oxygen.
|Rice. 1 scheme of the process of gas acid cutting: 1. cutting mouthpiece; 2- cutting oxygen; 3- cut metal; four. heating mouthpiece; 5. heating flame; 6. slag|
The metal during cutting is heated by a flame, which is formed during the combustion of any combustible gas in oxygen. Oxygen burning heated metal is called cutting. In the process of cutting a stream of cutting oxygen, it is fed to the site of the cut separately from the oxygen, which goes to the formation of a combustible mixture for heating the metal. The combustion process of the cut metal extends to the entire thickness, the formed oxides are blown out of the place of cutting with a stream of cutting oxygen.
Metal, exposed to oxygen, must satisfy the following requirements:
one. The combustion temperature of the metal should be lower than the temperature of its melting, t.e. Metal should burn in a solid state. Otherwise, the molten metal is difficult to remove from the cutting cavity. 2. The melting point of melting during the cutting of oxides should be lower than the melting point of the metal itself. In this case, oxides are easily blown out of the cutting cavity. 3. The thermal effect of oxides should be high.
For oxygen cutting, combustible gases and pairs of combustible liquids are suitable, giving the temperature of the flame when combustion in a mixture with oxygen at least 1800 ° C. The purity of oxygen has a particularly important role in cutting. For cutting, it is necessary to use oxygen with a purity of 98.5. 99.5 %. With a decrease in the purity of oxygen, the productivity of the cutting is very reduced and the oxygen consumption increases. So with a decrease in cleanliness from 99.5 to 97.5 % (t.e. on 2 %). productivity decreases by 31 %, and oxygen consumption increases by 68.1 %.
Cutting can be carried out manually or machine.made in semi.automatic machines and machine guns. The process of the process of dividing gas acid cutting is shown in the rice. 1 A mixture of oxygen with combustible gas emerges from the heating mouthpiece of the cutter and burns, forming a heating flame. With this flame, the metal heats up to the temperature of its combustion. After that, a stream of cutting oxygen is supplied along the axial channel of the cutting mouthpiece. Oxygen enters heated metal and lights it. During its combustion, a significant amount of heat is released, which, together with the heat released by the heating flame, is transmitted by the underlying layers of metal, which also burn. Slags formed in this case (iron oxides and t.D.) are blown by a stream of cutting oxygen from the gap between the cuts of the cut.
When cutting steel, the main amount of heat (70. 95 %) is formed during the oxidation of the metal. These conditions are satisfied with low.carbon and low.alloy steels, titanium alloys. Cast iron is not cut by oxygen due to a low melting point and high burning temperature; copper. due to the high melting temperature and low heat of combustion; aluminum. Due to the high tightness of the resulting oxides. Highly legged steels (chromium, chromium.nickel, etc.D.) are not cut due to the formation of tight, viscous slags.
The surface of the cut metal should be cleared of rust and other contaminants. The metal is installed in the position, best in the lower, but so that there is a free exit of the cutting stream from the back. Cutting operation begins with preliminary heating at the site of cutting at a metal burning temperature (1200. 1350 ° C). The installed power of the heating flame depends on the type of combustible gas, thickness and composition of the cut metal. They usually start cutting with the edge of the metal. At thickness up to 80. 100 mm can cut the hole anywhere in the sheet. The core of the heating flame is at a distance of 2. 3 mm from the surface of the metal. Когда температура подогреваемого металла достигнет необходимой величины, пускают струю режущего кислорода. The higher the purity of cutting oxygen, the higher the quality and performance of the cutting. As the cutting stream deepens into the thickness of the cut, the speed and power of the jet of cutting oxygen decreases. Therefore, its curvature is observed, to reduce which the slope of the cutting stream is given. When cutting thick metal, the cut width increases to the lower edge due to the expansion of the stream of cutting oxygen. A certain amount of slag remains on the edges on their lower side.
If subsequent welding is carried out to prevent increased carbon in the joint of the seam (the formation of hardened structures), it is necessary to mechanical processing or cleaning the cutting surface. During the cut process, heat treatment of the metal edges corresponding to hardening occurs. The width of the zone of thermal influence (up to 6 mm) depends on the chemical composition and increases with an increase in the thickness of the cut metal.
Low.carbon steel of hardening is practically not amenable. Only the enlargement of the grain and the appearance in the structure along with the perlite areas of sorbitis occur. When cutting steels with increased carbon or alloying impurities in the structure of the metal may appear trocketing and even martensitis. Uneven heating of the edges creates stresses in the metal and deforms it. The cut edges are somewhat shortened, and in the adjacent layer there are stretching stresses, which can lead to the formation of cracks.
A peculiar way is to cut an oxygen spear (burning holes). For this, long thick.walled tubes with a diameter of 8 are used. 10 mm from low.carbon steel. Prior to cutting, the working end of the tube is heated by a welding flame or a coal electric arc to the temperature of the metal of the metal in oxygen. When the cutting oxygen is turned on, the end of the tube is ignited. Then the working end of the tube is slightly pressed to the metal and deepened into it, burning the hole. The resulting slag is blown out of the hole outward with excess oxygen and the formed gases. With a significant depth of the burned hole, the product must be put in a position that facilitates the flow of toxins.
Oxygen. Flus cutting (CFR)
The CFR is used in the cutting of highly alloyed steels, cast iron, alloys and aluminum alloys, slagged metal, as well as refractory and reinforced concrete. The CFR process is based on the introduction of a powder flux reaction in the reaction zone, which releases an additional amount of heat in the crust due to combustion in the oxygen stream of metal powders.
The flux from the hopper is supplied to the site of the cut or directly cutting a stream of oxygen or oxygen stream of low pressure, and then in the head of the cutter this jet comes the injector and is carried away by oxygen of higher pressure.
Arc or electric harsh is the methods of paying the material along a given path using heat released by electrical sources of energy. At the same time, heating with an electric arc (coal, graphite or metal electrode), contact resistance induction (cutting with stretching by a non.gas method or using oxygen or air) can be used.
The essence of the method is to melt the metal object processed with a compressed plasma arc and intense removal of a melt with a stream of plasma. The plasma stream is obtained in plasmotrons. To arouse the plasmogenesing arc is the electrode located in the arc camera. The column of the arc is oriented along the axis of the forming channel and fills almost all its sections. Working gas (plasma.forming environment) is served in the arc camera). Gas, entering the column of arc, filling the forming channel, turns into plasma. The flow of plasma stabilizes the arc discharge that arises from the nozzle. The gas and walls of the forming channel limit the section of the pillar (compress it), which leads to an increase in plasma temperature to 20,000. 30000 ° C. Two plasma formation schemes using a direct arc and an indirect arc are used, when the processing object is not included in the electrical circuit.
As workers of plasma-forming environments with plasma-arc cutting, nitrogen is used, its mixtures with hydrogen, oxygen and its mixture with nitrogen, especially. compressed air, sometimes helium, carbon dioxide, ammonia and water are used.
For cutting steel, the use of oxygen.containing gases, especially compressed air, is most advisable. As a result of the absorption of oxygen with metal on the surface of the cut into steel, oxygen is dissolved, which reduces the temperature of its melting, and exothermic reactions of iron oxidation develop, ensuring an additional flow of heat.
Along with this, the molten metal on the cut edges is noticeably saturated with other gases contained in plasma.forming and, partly, in the environment. At the same time, burning out of alloying elements, a noticeable decrease in their content in the edges and a decrease in the strength, anti.corrosion and other properties of the metal may occur. Cutting in hydrogen.containing media is often accompanied by saturation of metal in the edges of hydrogen. With air-plasma cutting, the metal of the cast section on the edges of the cut steel is significantly saturated with nitrogen. These facts lead to the fact that with subsequent welding of such edges in the welds, porosity may occur.
Cutting with an oxygen spear, underwater and electric acid
Cutting with an oxygen spear consists in burning (drilling) in the metal of the holes with a stream of oxygen supplied along the steel tube, the end of which, adjacent to the cut metal, will be heated to the ignition temperature in oxygen. Another end the tube joins the handle with a valve for oxygen.
Before cutting, the end of the tube is heated to the ignition temperature. This is carried out by a welding burner, an electric arc with a coal electrode or passing the current from the welding installation through the tube and the coal plate laid on the product to be drilled. The heated charcoal plate is ignited when oxygen is supplied to the tube of 1-2 kgf/cm 2 and provides heating the end of the tube until it is ignited. Then oxygen pressure is increased to 5-6 kgf/cm 2 and the end of the tube is pressed to the burned product. Further, the combustion of the tube and processed metal is carried out without any additional heat source; As the tube and burning the hole burn out, the tube is supplied forward. The burned tube is replaced by a new.
The greatest difficulties in drilling with an oxygen spear are the removal of slag from the hole. The most easily slag is removed when cutting from the bottom up, when the slag flows under the influence of gravity in the lumen (gap) between the tube and the walls of the hole, which has a larger diameter than the tube. The slag flows worse with an inclined arrangement of the burned hole (from the bottom up), however, this location during cutting with a spear is more convenient. It is possible to carry out cutting with a horizontal arrangement of the burned hole
To obtain round-shaped holes, the spear during cutting is rotated alternately by half a turn in both directions.
Spear material are low.carbon steel tubes, better thick.walled, for example 17/8, 19/6. To reduce the flow of tubes and obtain the proper passing section for oxygen, continuous wires with a diameter of about 5 mm are laid inside the tubes.
Estimated modes of cutting with an oxygen spear according to MVTU data to them. Bauman are given in the table. 26.
Fly acid cutting with a spear is possible. In this case, powder flux is supplied inside the steel tube along with oxygen. When cutting, the tube with the diameter of the V3-V2 “does not based on the burned metal, but is maintained at a certain distance (50-100 mm) from the product.
When cutting hardened steels to prevent the formation of cracks, the total preliminary heating of the workpiece is recommended to 300 ° C. When cutting carbon steels with M with less than 0.4%, heating is not needed.
The cutting with a spear is used for cutting goats in metallurgical production, removing profits of steel casting, forming axial holes in romes, deep holes during subversive work, holes in the workpieces of large thickness for subsequent dividing oxygen cutting and in other cases in other cases. Finds the use and cutting with a spear of reinforced concrete products.
Underwater oxygen cutting
When performing ship repair, shipping, emergency rescue, restoration and construction work in some cases, underwater oxygen cutting is used.
Heating of the metal during cutting under water is ensured by creating a gas bubble, pushing water from both the flame and from the heated section of the metal. As gases to create such a bubble, gases that are non.watering in water can be used: nitrogen, oxygen, air, carbon monoxide and carbon dioxide.
The gas bubble is formed under a special cap mounted at the working end of the cutter, as a result of the creation of gases that exceeds the value of hydrostatic pressure at this depth. The need to use high pressure (for example, at a depth of 15 m more than 1.5 kgf/cm 2) limits the use of acetylene, therefore, in this case, hydrogen or gasoline is used as combustible.
The use of hydrogen-acid heating flame provides the best quality of cutting under water. However, due to the fact that the water determines a very intense heat-air, the power of the heating flame under water should be 5-10 times more than when cutting in the air, with a corresponding increase in fuel consumption. Therefore, the use of gasoline as fuel is more convenient.
Gasoline-acid combustible mixtures for cutting under water are created without the use of evaporators who did not justify themselves under these conditions. The use of gasoline sprayers (oxygen. on the principle of motor fuel), giving a stable flame. In Fig. 127 The design of the gas tanker for cutting under water is presented.
To ignite the flame under water, special electric fuses are used, with the help of which the cutter by closing the fuse to the tip causes sparks and ignition of the mixture. For underwater cutting, the installation of BUPR is used. Oxygen cylinder ramp, gasoline tank, nitrogen cylinders and installation control panels are located above the water. Technical characteristics of BUPR are given in the table. 27.
Excess gas, popping up to the surface of the water, can ignite, therefore, gas polling cutting is not applicable in small reservoirs and closed spaces.
Oxygen cutting with a heating flame can be used under water to separate continuous metal and bags. With a total metal thickness of up to 30 mm, it is possible to use an electric driving cutting with a melting electrode, although the quality of the cut is much worse. Packages can also be cut out by the method of underwater electric acid cutting, which has received significant development and use recently.
Electric acid cutting
The principle of electrical acid cutting is the use of the heating effect of an electric arc burning between the hollow rod electrode and the cut product, and the burning of a heated metal with oxygen, which comes under the necessary pressure along the axial channel of the electrode. The holder, which is used in this case, provides electrical contact with the electrode and supply oxygen.
|Limitation||Laser cutting||Plasma cutting|
|The minimum diameter of the hole||(0.3.0.4) s||(0.9.one.4) s|
|Cut material||Metals, plastics, wood||metals|
|Maximum effective cutting thickness, mm||Up to 40||Up to 150|
|Cutting internal corners||With a radius|
The accuracy, the quality of the cut, the perpendicularity of the edges depends on the established gap between the nozzle and the processed sheet of the metal. (the so.called torch clearance). The gap also affects the power of the plasma arc, density and it to resist. The gap from 1.5 mm to 10 mm is considered optimal. The larger the gap, the higher the corruption of the plasma arc, the greater the angle of inclination of the cut edge.
CNC automation on machines for plasma cutting metal automatically supports a given constant height of the torch clearance. This allows you to get high.quality cut with the lack of defects on the edges of the parts. It must be borne in mind that a small gap leads to burnout of plasmotron, large. to loss of quality. On modern machines for plasma cutting, automation itself controls the parameters of the clearance and ensures its constancy in the process of cutting the metal.