Generally speaking, steel with a thickness of more than 300 mm is called large thickness cutting. According to the principle of gas cutting, large thickness steel can be cut through as long as the oxygen supply is sufficient and can reach the bottom of the cut.



Major difficulties



1. The upper and lower parts of steel are not uniformly heated, the upper part is hot and the lower part is cold, and the operation is improper. When cutting, it often fails to cut along the thickness direction smoothly, resulting in cutting failure.


2. Because of the thickness of steel, it takes considerable time for combustion reaction to propagate along the thickness direction. At the same time, the lower the purity of cutting oxygen flow to the lower part of the incision, the lower the kinetic energy, and the larger the drag, the better the cutting speed must be controlled.


3. With more slag, the ability of slag discharging by cutting oxygen flow is weakened, which can easily lead to slag blockage at the bottom of the incision and destroy the normal gas cutting process.


The most important condition for large thickness cutting is to supply enough oxygen flow to the cutting area.


In order to ensure adequate oxygen supply, attention must be paid to:


1. The size of the whole oxygen supply system, including pressure reducer, aerosol pipe, various joints and valves, cutting torch intake pipe and cutting nozzle aperture, should meet the corresponding oxygen supply capacity to avoid throttling phenomenon.


2. According to the thickness of steel and cutting length, sufficient air supply should be prepared to avoid cutting interruption due to exhaustion of oxygen. Generally, it is extremely difficult to re-cut large thickness steel.


Another important factor is cutting oxygen pressure, which should be low rather than high. When using common cutting nozzle, the oxygen pressure at the entrance of cutting torch should be between 152 kPa and 386 kpa. 0.49-0.69 Mpa cutting nozzle should be used when using diffusion cutting nozzle. If the cutting oxygen pressure is too high, the temperature of oxygen flow will decrease. On the contrary, it will play a cooling role in the gas cutting area. In some cases, it may even break the gas cutting process.