Oxygen cutting

We must immediately note that this cut yielded only those metals which meet the following main requirements.
The melting point of the metal should be higher ignition temperature of its oxygen. Otherwise, the metal will just melt, but it will not burn. For example, mild steel has a flash point in oxygen 1300-1350 ° C, and the melting temperature - about 1500 ° C.
However, increasing the amount of carbon in the steel will be accompanied by an increase in the ignition temperature in oxygen and decrease the melting point. Therefore, cutting steel with high carbon content and impurities becomes problematic.
The melting point of the metal should be higher than the melting point of the oxides. This requirement is to ensure that the image of the cutting oxygen oxides easily blown out and did not prevent further oxidation and cutting. For example, when cutting aluminum oxides are formed with a melting point of about 2050 ° C, and the cutting of chromium steels - oxides with a melting point of about 2000 ° C. It is obvious that these oxides cover the surface of the metal and thus stop further cutting process.
Thermal conductivity of the metal should be as small as possible, because at high heat imparted to the metal heat quickly away from the cutting area and a metal heat up to the ignition temperature will be difficult.
Amount of heat of combustion heat of the metal must be large enough, because this heat warms the border zone with cutting metal parts, thus ensuring the continuity of the cutting process. For example, when cutting mild steel 65-70% of the total amount of heat released by the combustion of the metal in a stream of oxygen, the remaining 30-35% of the heat from the flame torch HEATING.
Encountered when cutting slag must be sufficiently fluid and easily blown out of the cut. Viscous slag and refractory will seriously hamper the cutting process.
Before cutting to thoroughly clean the surface of the cut metal from rust, dirt and paint. To remove them, slowly carry the torch flame on the surface of the metal along the intended line of the cut. At the same scale behind metal, paint and oil burned. After this, the metal surface should be cleaned with a brush. It should be noted that different metals are in varying degrees of oxygen cutting. Low-carbon steel with a carbon content of 0.3% cut is very good, while the medium carbon steel (with the amount of carbon is not more than 0.7%) cut a bit worse. High carbon steel cut with great difficulty, and with a carbon content of more than 1% cut is not feasible without the addition of special fluxes. Oxyfuel welding of high-alloy steels can not be, for cutting to use plasma-arc and oxy-flux cutting, which can be cut more copper, brass, bronze. For cutting aluminum and aluminum alloys applied plasma-arc cutting. Thus, after the performance should be considered separable technology features cutting different metals depending on their thickness, the type of cut profile, chemical composition and strain as a result of high temperature exposure.
If the thickness of the metal is less than 300 mm, it is sufficient to a normal flame. When the thickness of the metal over 400 mm length of the torch flame HEATING be increased by the excess flow of acetylene. This will warm up the deep metal. Cutting speed plays a large role in the effectiveness of the work. Travel speed cutter to match the speed of burning metal. The easiest way to determine the speed will be the nature of the discharge of sparks and slag (Fig. 128).


Определение скорости резки по выбросу искр


Fig. 128. Determination of the cutting speed on emission of sparks: a - slow cutting speed, b - normal cutting speed and in - fast cutting speed.

If the speed of the cutter is correct, then the flow of sparks and slag comes out of the cut straight down, and you get a clean edge, no sag and podplavleny. At low speeds the flow of sparks ahead cutter and cutting edge fused and covered with drips. At a high rate sparks behind the cutter, and the metal in the lower edge does not have time to burn, so the through cutting of stops.
Cutting performance depends on the correct positioning of the cutter. Cutting steel up to 50 mm is as follows. Early on the cutting edge of the cut metal-heating is necessary to direct the flame to heat the edge to reflow temperatures. Then you need to install mouthpiece torch perpendicular to the surface of the metal to be cut so that the jet of flame HEATING and then cutting oxygen is along the vertical side of the metal. After warming up to the ignition temperature of the metal should be let jet cutting oxygen. Cutter to move only after the metal has to be cut through the entire thickness of it at the beginning of the cutting line.
To keep pace with cutting in the lower layers of the metal, at the end of the process to make the angle cutter at 20-30 ° in the opposite direction to its motion, and the speed of the tool to reduce.
When working with metal thicker (100-200 mm), the angle should be reduced to 10-15 °. Pre-heating to 300-400 ° C would allow cutting at high speed. The torch in the process shown in Figure 129. The width of the cut and purity depend on how cutting and metal thickness. Cutting machine gives a smaller width of the cut edge and cleaner than manual cutting. The thicker the metal to be cut, the greater the width of the cut.


Положение резака при работе с листовой сталью


Fig. 129. The torch when working with sheet metal: a - start cutting, b - the cutting process.



If there is a cut blank round, then in the early cutting angle of the cutter needs to be done, and then gradually reduce it in operation until the torch perpendicular (Fig. 130). It should be noted that when cutting out the curved parts the torch to the surface of the metal must be perpendicular. When cutting multiple sheets of metal to fix in the package to make the process productive. The edges of the sheets in place to start cutting folded up, as illustrated in Figure 131.


Положение резака при работе с круглыми заготовками


Fig. 130. The torch when working with circular blanks.



Пакетирование листов металла



Fig. 131. Packaging the sheet metal.



Burn holes has a number of features. When the thickness of the metal to 20 mm must first perform heating to the desired temperature, then the flame-heating must be switched off and the cutting oxygen valve to let a smooth opening to the torch. From hot metal oxygen ignites. This course of action to prevent flashback.
With a thickness of 20-50 mm metal sheet or piece to be installed in a vertical or inclined position to drain slag formation is immediate. In this case, the initial hole is drilled at a shallow depth. Further progress is the same as in the previous case.
Mouthpiece at work should be kept from the surface at a certain distance. You can use a trolley or other devices, which are attached to the head of the torch.
When cutting metal up to 100 mm distance between the metal surface and the end of the mouthpiece should be 2-3 mm larger than the core of the flame.
When cutting metal thickness greater than 100 mm and cutting performed on the gas-acetylene substitutes, the distance should be increased by 30-40% in order to prevent overheating of the mouthpiece.
Non mouthpieces (internal and external) must be chosen depending on the thickness of the metal.
Thus, hand-cutting can only be successful when working in compliance with the recommended angle cutter to pinpoint the beginning of cutting, carefully selected number of mouthpieces, and combustible gas.
Pipe cutting can be performed using acetylene and its substitutes. In the implementation of cutting the pipe can rotate the rollers, as shown in Figure 132.



Разрезание труб



Fig. 132. Cutting the pipe: a - speed cutting, b - cutting roller.



This illustration shows the correct position and the cutter, in which area vzaimodeysviya metal with oxygen increases dramatically, and the formed slag in the process heats the border zone of a pipe. This, in turn, greatly improves conditions for metal cutting. However, this situation prolongs torch preheat the metal to the ignition temperature of 60-70 s.
To reduce the heating time must immediately be cut in the area of ​​steel bars or iron powder. Then the speed of cutting pipes with wall thickness up to 12 mm and a diameter of 300-1020 mm reach 1.5-2 m / min.
In cutting of castings and forgings 300-800 mm thick, you can use a manual cutter type RZR-2, which in the beginning to make cutting perpendicular to the surface of the cut position (or at an angle of 5 ° in the direction opposite to the movement). Followed through to cut metal of the early cut line after preheating. Next you need to start moving the tool at the same angle, and by the end of the cut to make the angle tool to 10-15 ° in the direction opposite to the movement, and reduce speed. It is necessary for the final cutting of the final segment.
The deformation of the cutting and the fight against it. Uneven heating and cooling of the parts or pieces in the cutting process leads to residual stresses and strains in the metal. To avoid this, you need to perform when using best practices listed below:
- Before starting work a holiday;
- Cutting always start with the highest along the edges, and finish on the short edge;
- First cut small parts, and then large;
- Cutting speed should be as high as to the edge of the metal not much warming up;
- Cutting holes should be done before the other works;
- During the cooling of the metal water;
- First need to perform zigzag incisions, and then straight;
- Before handling metal sheets in firmly secured to prevent their displacement under the influence of residual stresses;
- If they eliminate the jumper after the completion of the cut.
Hand cutting thick metals (300-700 mm) is cutter type RZR-2, which gives a carburizing flame required value. Cutting tool at the beginning should have a slope-side movement in 2-3 ° relative to the plane of the end, and at the end of the process - 2-3 ° in the opposite direction of motion (Fig. 133).


Положение инструмента при резке металла большой толщины


Fig. 133. Position of the tool when cutting thick metal: a - before cutting, b - before the end of cutting.
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