Flame cutting is a common method for rough machining of steel plates. Flame cutting is gas cutting. Traditionally, acetylene gas is used for cutting. Later, propane is used for cutting. Now natural gas cutting appears. Because of its abundant natural gas reserves, low price, and pollution-free characteristics, it has become the first choice for flame cutting. Natural gas flame cutting generally adds natural gas additives to generate a new type of flame cutting gas. Flame cutting with this gas can make the cutting effect better, improve the cutting efficiency, and reduce the cutting cost.
Flame cutting is the oldest thermal cutting method. It is cutting metal thickness ranges from 1 mm to 1.2 meters. However, when the thickness of low carbon steel plates you need to cut is below 20 mm, other cutting methods should be used.
Flame cutting uses the high temperature generated during the combustion of iron oxide to cut carbon steel. The design of the flame cutting torch provides sufficient oxygen for burning iron oxide to ensure a good cutting effect.
The cost of flame cutting equipment is low and it is the only economical and effective means to cut thick metal plates, but it has its shortcomings in thin plate cutting. Compared with plasma, the heat-affected zone of flame cutting is much larger and the thermal deformation is larger. To cut accurately and effectively, the operator needs to have superb skills to avoid the thermal deformation of the metal plate in time during the cutting process.
Classification of flame cutting methods
Flame cutting methods include torch cutting and cutting machine cutting.
The cutting torch is also called the flame gun. The gas used is different, the structure is also different. Commonly used is an oxygen-acetylene flame gun. The acetylene pressure is 0.01 to 0.12 MPa, and the oxygen pressure is 0.50 to 1.0 MPa. The two gases are mixed and combusted in the flame gun through their respective passages. The size and nature of the flame sprayed can be adjusted by the hand-held flame gun for cutting. It is usually used for cutting large tube billets and slabs after rolling or for steel straightening. Removal of defects after supplementary cutting.
Cutting machine cutting
The general model structure of flame cutting machine mainly includes profiling cutting machine, portable CNC cutting machine, cantilever CNC cutting machine, gantry CNC cutting machine, desktop CNC cutting machine, and pipe CNC cutting machine specially used for cutting steel pipe intersecting lines. These structures can be cut by flame cutting. Flame cutting machines are mostly used as online cutting equipment for billets after continuous casting machines, cutting large-section billets, slabs, and large tube billets, and also used to cut finished steel plates with a thickness greater than 50mm.
Flame cutting gas
Commonly used flame cutting gases are acetylene, propane, liquefied gas, coke oven gas, natural gas, etc. From the comprehensive consideration of pollution, energy consumption, and cost ratio, natural gas is currently the most suitable gas for cutting. But natural gas also has its limitations, that is, the flame temperature is not high, which causes the cutting efficiency to be inferior to acetylene. To make up for this shortcoming, manufacturers who generally cut with natural gas choose to add synergists to natural gas to increase flame temperature and improve cutting efficiency.
Flame cutting tool
The cutting torch is the main tool for flame cutting. The cutting torch is divided into the manual cutting torch and machine cutting torch. Machine cutting torches are mainly used for various cutting machines. Whether it is a manual cutting torch or a machine cutting torch, there are two types of suction cutting torches and equal pressure cutting torches. The jet suction cutting torch does not require high gas pressure and can use low-pressure gas or medium pressure gas. The jet suction cutting torch is the most widely used general manual cutting torch. The gas and preheated oxygen of the equal-pressure cutting torch are mixed in the cutting nozzle through separate pipelines. Because the gas enters the cutting torch by its pressure, it is not suitable for low-pressure gas. Instead, medium-pressure gas must be used. The equal-pressure cutting torch has the advantages of gas adjustment, stable flame combustion, and difficult backfire. Its application is increasing more.
Flame cutting process
1. Check whether the worksite meets the safety requirements, whether the cutting torch, oxygen cylinder, acetylene cylinder (or acetylene generator and tempering preventer) rubber tube, pressure gauge, etc. are normal, and connect the gas cutting equipment according to the operating procedures.
2. Before cutting, first level the workpiece, leaving a certain gap under the workpiece to facilitate the blowing of iron oxide slag. When cutting, to prevent the operator from being burned by the splashing iron oxide slag, a baffle can be added to cover if necessary.
3. Check the wind line by lighting the flame and adjusting the preheating flame appropriately. Then open the cutting oxygen valve and observe the shape of the cutting oxygen flow (ie the wind wire). The wind wire should be a straight, clear cylinder and have an appropriate length. Only in this way can the cut surface of the workpiece be smooth and clean, with the same width. If the wind line is irregular, all valves should be closed, and the inner surface of the cutting nozzle should be trimmed with a needle or other tools to make it smooth.
4. Adjust the oxygen to the required pressure. For jet suction cutting torches, check whether the cutting torch has the jet suction capability. The method of inspection is to first unplug the acetylene intake hose and bend it, then open the acetylene valve and preheating the oxygen valve. At this time, put your finger on the acetylene gas pipe joint of the cutting torch. If the finger feels pulling force and can be adsorbed on the acetylene gas pipe joint, it means that the torch has the suction capability and can be used; otherwise, it means the torch is abnormal, Cannot be used, should be checked and repaired.
Influencing factors of flame cutting
Flame cutting is affected by many factors, but the main factors affecting cutting quality and cutting process are as follows:
(1) The influence of oxygen purity
In the gas cutting process, oxygen purity has a relatively large impact on cutting speed, oxygen consumption, and cutting quality. The purity of oxygen decreases, the cutting speed becomes slower, and the burning effect of metal in oxygen becomes worse, which will affect the cutting quality.
(2) The influence of impurities and defects in gold chips
Impurities in metal have a great influence on flame cutting, and some impurities even make the metal unable to perform the flame cutting.
(3) The influence of gas purity on cutting quality
The purity of the gas has little effect on the cutting quality and the cutting process, but the impurities in the gas will have a certain impact.
(4) The influence of cutting speed on cutting quality
The flame cutting speed should be appropriate, not too fast or too slow. If the cutting speed is too fast, it will cause back drag and impenetrable cutting, and even burn out the cutting and interrupt the cutting; if the cutting speed is too slow, the upper edge will burn down, the bottom edge will be severely slagging, the slit will become wider, and the quality of the cutting surface will be very unsatisfactory.
What are the hazards of flame cutting?
Fire and explosion hazard
If the flame cutting is not done properly, it may cause fire and explosion hazards. This is mainly caused by the failure of the gas supply system or the high temperature of the cutting flame. The specific reasons may be as follows.
Flammable gas or oxygen leaks cause fires and explosions. These gases can leak from the joints of the gas supply system, the connection point of the gas hose, or the gaps in the fittings.
Excessive pressure in the air supply system caused an explosion.
There is flammable material on the surface of the workpiece. If there is flammable material on the surface of the workpiece during the cutting process, it will cause a fire. In addition, if flammable gas is generated during the cutting process, it will also cause a fire.
These disadvantages are few in CNC flame cutting. Because the human body is not in direct contact with flame cutting. In addition, in the cutting process of the CNC cutting machine, the gas is completely controlled by the system, and the total price of the electrical appliances and the safety system is much higher. There has been no safety accident caused by the CNC flame cutting machine.
Harm to the human body
The hazards of flame cutting to the human body are mainly due to the radiation, toxic gas, and toxic smoke generated during the cutting process. The infrared radiation emitted by the molten metal can cause thermal cataracts, resulting in blurred vision. The arc eye caused by the ultraviolet radiation emitted during the cutting process causes eye pain and tears. Skin exposed to radiation for a long time will be irritated and reddened. Toxic gases and toxic fumes can affect internal organs.