Flame Cut – What Is Flame Cutting

Flame cutting is the oldest thermal cutting method. The cutting metal thickness ranges from 1 mm to 1.2 meters. However, when the thickness of most low carbon steel plates you need to cut is below 20 mm, other cutting methods should be used.

Flame cutting is to use 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 relatively large. In order 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.

Flame cutting methods include torch cutting and cutting machine cutting.

Flame Cutting is a common method for rough machining of steel plates. Flame cutting is gas cutting. Traditionally, acetylene gas is used for cutting, and then propane is used. Now natural gas cutting has appeared, and it has become the first choice for flame cutting due to its abundant natural gas reserves, low price, and pollution-free characteristics. 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.

Classification of flame cutting

Torch cutting

The cutting torch is also called the flame gun. The gas used is different, and 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 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

It is composed of a cutting torch with a working principle similar to a flame gun, a fixed-length mechanism and a slit cleaning device. The sizing mechanism has mechanical, pulse and photoelectric type, which can realize automatic sizing. The kerf cleaning device specially cleans the residues adhering to the kerf, so as not to affect the surface quality of the steel during rolling.

The cleaning method is to use a scraper to scrape off the sticky slag, and also use a set of high-speed rotating sharp-angled hammers to remove the sticky slag and burrs. Flame cutting machines are mostly used as on-line 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 of more than 50mm.

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, cost ratio and other aspects, 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. In order to make up for this shortcoming, the manufacturers who generally cut with natural gas choose to add synergist to natural gas to increase flame temperature and improve cutting efficiency. For example, Baotou Steel and China Railway Shanqiao Group use synergistic natural gas added with Shenqi booster. The medium and heavy plates produced by Baotou Steel won the bid for the Wenchang Satellite Center project because of its high flatness. China Tieshan Bridge uses synergistic natural gas for Preparing for the construction of the Zhuhai-Hong Kong-Macao Bridge, as a result, the effect of increasing the efficiency of natural gas is very significant.

Tool

The cutting torch is the main tool for flame cutting. The cutting torch is divided into 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, it can be divided into a jet suction cutting torch and an equal pressure cutting torch. 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 own 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 difficulty in tempering. Its application is increasing. more.

Development Trend

Since the establishment of the China Welding Society and China Welding Association, the two sessions have made outstanding contributions to the development of the cutting industry, cutting technology, and promotion and application. Especially in recent years, the two associations have organized various forms of domestic and foreign academic exchange activities, and on-site exchange meetings for new products and new technologies in the welding and cutting industry. The organization has formulated a series of new national standards and product grading standards for welding and cutting equipment products. Through these work, we have a certain understanding of the development support of the cutting industry at home and abroad, and it also provides a good opportunity for technical exchanges and information exchanges between companies in the industry, thus effectively promoting the technology of the entire cutting industry. Progress and development.

In today’s industrial field, welded structural parts have been widely used in all walks of life. Sheet cutting is the first step in the process of welding finished products, and it is also an important process to ensure the quality of welding. The use of advanced modern cutting technology can not only ensure the welding quality of the product, improve labor productivity, but also greatly reduce the manufacturing cost of the company’s products. , Shorten the product production cycle. With the widespread use of new products, new processes and new technologies, intelligent precision cutting will also become the future development trend of the cutting industry.

Process

• 1. Check whether the work site 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 up the workpiece and leave a certain gap under the workpiece to facilitate the blowing of iron oxide slag. When cutting, in order to prevent the operator from being burned by the splashed iron oxide slag, a baffle can be added to cover if necessary.
• 3. Check the wind line, the method is to ignite the flame and adjust 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 and 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 torch has 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 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 cutting torch has suction ability and can be used; otherwise, it means that the torch is not working properly. , Cannot be used, should be checked and repaired.

Influencing factors

Flame cutting is affected by many factors, but the main factors that affect the 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 influence 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 inevitably affect the cutting quality.
• (2) The influence of impurities and defects in gold chips The impurities in the metal have a great influence on flame cutting, and some impurities even make the metal unable to perform flame cutting.
• (3) The influence of gas purity on cutting quality The purity of gas has little influence on cutting quality and cutting process, but the impurities in the gas will have a certain influence.
• (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 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 slagged, the slit will become wider, and the quality of the cutting surface will be very unsatisfactory. .