In the construction process, it is impossible to use the shaped material, that is, it is not necessary to directly process the material, especially in the installation profession. Because various materials such as pipes, sections and plates need to be cut and processed into certain shapes and sizes, various cutting techniques are widely used in engineering construction and installation projects. The most common application is Oxyacetylene cutting method. Other cutting methods such as mechanical cutting, plasma cutting, pulsed CNC cutting and other technologies tend to increase and improve, but they all have some limitations, such as higher requirements on the site, more complex equipment and expensive equipment. Affected by the space, it is certain that the cutting quality of these cutting methods is very high, which can significantly reduce the labor intensity of workers and improve work efficiency in large-scale factory flow operations. Therefore, in large pressure vessel prefabrication plants, It is widely used in shipyards and military enterprises. Compared with these cutting methods, the oxyacetylene cutting method has obvious advantages: the equipment and tools are simple and practical, and cut into! Conclusion The above numbering method is summarized in the practice process. Its advantage is to ensure the uniqueness of the welding joint number. At the same time, according to the welding port number, the specific position of each welding joint, the construction direction and the sequence of adjacent welding joint construction can be seen. The sequence has good practicability and traceability in the construction of mountain pipelines.
The low position; the spatial position of the cutting is not limited, the operation is convenient and flexible; the workpiece is suitable for cutting any complicated shape, and the material is saved. Since oxyacetylene cutting has these advantages, it is widely used in various industrial sectors.
In the installation process, it is often necessary to encounter the case of cast iron machining. According to the current status of cast iron cutting technology, the cutting of cast iron is generally performed by mechanical cutting or plasma cutting machine. Ordinary oxyacetylene cutting cast iron is considered to be infeasible. To this end, we have studied the manual cutting of oxyacetylene in cast iron to make it better for production.
1Oxyacetylene cutting technology 1.1 Basic conditions for oxyacetylene cutting 1) The burning point of the metal material should be lower than the melting point. If the ignition point is higher than the melting point, the metal will be melted into a liquid state before combustion. Under the injection of oxygen, the liquid metal flows around, so that the obtained cuts are uneven and cannot meet the requirements of use. In severe cases, the cutting process may not be normal. get on.
1974-), male, Shandong Dongying, engineer, Master of Engineering, School of Naval Architecture and Ocean Engineering, Shanghai Jiaotong University, is currently engaged in technical management of oilfield ground and offshore engineering.
2) The melting point of the oxide should be lower than the melting point of the corresponding metal, and the flowability of the oxide in the molten state is large. If the melting point of the generated oxide is higher than the melting point of the metal, the oxide will solidify first than the liquid metal itself to form a solid film on the surface of the liquid metal, so that the underlying metal is isolated from oxygen, which is not conducive to the slag blowing, but also to continuous cutting. In addition, the oxide in the molten state has a large viscosity and poor fluidity, which makes it difficult to blow the slag and also covers the underlying metal, hindering the cutting process.
8) The thermal conductivity of the metal is relatively poor. During the cutting process, the sum of the heat generated by the oxidative combustion of the metal and the heat supplied by the preheated flame is higher than the heat conducted by the metal, so that the temperature at the slit can be maintained, so that the cutting process proceeds normally, otherwise, when a large amount of heat is lost When the cut point temperature is lower than the metal ignition point, the cutting cannot be performed normally.
Metal combustion is an exothermic reaction and the heat of formation of oxides is high. The metal releases a large amount of heat during the oxidative combustion process, preheating the underlying metal together with the preheating flame, and the proportion of heat generated by oxidative combustion exceeds 60%, which plays a very large role. The greater the heat generated during combustion, the faster the cutting speed and the smoother the cutting process.
The metal contains less components and impurities that hinder cutting and improve hardenability. The higher the content of C, Si, Mn, etc. in the metal, the more oxygen is consumed. At the same time, the solid oxides of some trace elements contained in the metal have relatively poor fluidity and high melting point, which is also unfavorable for oxyacetylene. Normal cutting.
1.2 Oxyacetylene cutting process Oxyacetylene cutting has 8 processes of preheating, burning and blowing.
When the oxyacetylene is cut, the preheated flame is used to preheat the metal at the cutting point to the burning temperature.
The metal is jetted to the metal that is heated to the ignition point to cut the oxygen, causing the metal to burn intensely in pure oxygen.
8) After the metal is oxidized and burned, the slag is formed and a large amount of heat is released. The slag is blown off by the cutting oxygen, and the generated heat and the heat of the preheating flame heat the lower layer metal to the ignition point, and the metal is gradually cut through. The torch moves and cuts out the desired shape and size. 1.3 Cutting performance of cast iron The burning point of cast iron is 1850.) higher than the melting point of 1200.). When cutting, the cast iron is not fully burned, and the cast iron at the cutting place has been melted, so that when the slag is blown, the slit is too wide and uneven. In the case of Qi, the requirements for use cannot be met.
Cast iron has a high silicon content and generates Si2 during combustion. Its melting point is 1710.) It is higher than the melting point of cast iron. 1 The molten Si2 has a large viscosity and poor fluidity, which hinders the transfer of heat, consumes oxygen, and its viscosity is also The slag cannot be properly carried out, so that the operating parameters are not easy to control, and the quality of the cut is poor.
When a large amount of CO and C2 are generated during combustion, a large amount of oxygen is consumed, and the purity of oxygen is lowered, so that the combustion is less sufficient, and finally the quality of the cut is lowered.
2 Cast iron oxyacetylene cutting technology and process parameters were selected after many tests, and according to the actual application on site, we determined the process parameters of cast iron oxyacetylene cutting technology.
2.1 Cutting tool The oxyacetylene cutting tool for cast iron includes a set of injection suction cutters with corresponding cutting nozzles, one oxygen cylinder and acetylene bottle with decompression gauges, one set, one set of leather tubes and round steel.
2.2 Preheating Because the carbon content of cast iron is high and it is one of the factors affecting normal cutting, the preheating flame adopts a neutral flame. At this time, the acetylene burns completely and does not increase the carbon at the cutting port during the cutting process. This leads to a greater brittleness and avoids cracking when cooling after cutting.
The preheating time depends on the thickness of the cutting piece. The burning point of the cast iron is 1850. According to the field practice, cutting! The 219 mmx10mm cast iron pipe generally needs about preheating for about 7s.
2.3 The pressure of cutting oxygen cutting oxygen should be within the appropriate range. If the pressure is too high, the cutting mouth is too wide, the surface of the cutting mouth is rough, and the oxygen is wasted. If the pressure of oxygen is too small, the slag is difficult to be slag, and the slag is bonded. It is difficult to remove or even cut through.
The pressure of oxygen has a certain relationship with the thickness of the cutting member. When the thickness is increased, the oxygen consumption is increased, the cutting nozzle should be increased, and the pressure of cutting oxygen is increased accordingly.
The purity of oxygen has a large effect on gas consumption, cut quality and cutting speed. When the oxygen purity is low, the metal oxidation process becomes slow, the cutting speed is lowered, the cut quality is deteriorated, and the oxygen consumption is increased.
In summary, during cutting, the pressure of oxygen is generally increased, which is about 15% larger than that when cutting ordinary carbon steel, in order to provide a large amount of oxygen consumed in the combustion process, and to increase the strength of blowing slag; The plum-shaped cutting nozzle with less amount and more burning can be larger than the ordinary carbon steel with the same thickness; the purity of oxygen is greater than 99.5 2.4 Cutting speed The cutting speed is related to the thickness of the cutting piece, and the thicker the cutting part The slower the cutting speed. During the cutting process, pay attention to the condition of the molten pool, and adjust the cutting speed in time. If it is too slow, the burning process at the slit will be lengthened, the edge of the slit will melt, become dull, the slit becomes wider and uneven, and the requirements for use cannot be met. If it is too fast, it will produce a great amount of back drag, the slag is not completely slag, the slag solidifies quickly, and it adheres to the surface of the slit, resulting in the cut through the wall.
In the actual operation process, the cutting speed depends on the diameter and wall thickness of the cut piece, and the cutting speed is generally maintained at 60% 70mm/min (cutting speed of 219mmx10mm cast iron pipe); if the cutting is thin and the pipe diameter is small Cast iron pipe, the speed can be accelerated.
2.5 Combustion round steel According to the cutting performance and cutting principle of cast iron, the combustion-supporting round steel is generally used, which is made of round steel of 0235 series as the combustion-supporting flux, which is close to the slit width of 6~8mm and easy to operate.
The addition of combustion-supporting round steel actually improves the metallurgical process at the cutting point of the molten state. In this process, the incorporation of low-carbon molten steel reduces the ignition point at the cutting point and reduces the relative oxidation of oxides SiO, CO, CO, The content enhances the fluidity of the slag, making the slag easier; and the purity of oxygen during combustion is increased, the consumption is reduced, and the heat is also fully utilized.
After many tests, for the cutting of pipelines, we have determined the expression of the amount of combustion-supporting round steel: k cutting coefficient, generally 0.5% 1.2, increasing with the increase of pipe diameter; D* pipe nominal diameter.
2.6 The angle between the cutting nozzle and the cutting piece, the combustion-supporting round steel, the relative cutting nozzle between the operator and the cut-point section should be kept in a vertical state, and inclined at most to the operator's station direction, so that the slag can be blown To the leading edge of the slit, in order to make full use of the heat generated by the flame energy and the metal oxidation combustion, the gas cutting speed is increased, and the rear drag amount during the gas cutting is reduced, as shown.
The combustion-supporting round steel should always be at the upper part of the cutting point, about 2% 3mm from the upper part of the cutting point. At the front end of the flame flame, be careful to keep it in the red hot molten state, and lift it slightly when the droplet falls. Then return to the original position and continue cutting. The angle between the cutting tip and the combustion-supporting round steel is preferably maintained at 45.±5.
The cutting nozzle, the combustion-supporting round steel, the relative position of the cut-point section and the thickness of the cutting piece are determined. When cutting the thin piece, the cutting speed is faster, the flame is lengthened, and the cutting nozzle is farther away from the cutting point; When the cutting speed is slower, the flame is shortened, and the distance between the cutting point and the cutting point is closer; in the actual operation, the distance of the cutting nozzle from the cutting point is about 10% 15mm, that is, the surface distance of the flame core cutting piece is kept. In the range of 2% 4mm, this temperature range is the best, the heat of the flame can be fully utilized, and the possibility of carbon addition at the slit is also minimized.
2.7 The state of the pipe to be cut When cutting the pipe, the pipe should be kept stable. Do not rotate the pipe and keep it at rest. This can make full use of the heat of the melt flowing down the upper cut, so after cutting 30. 45. When the cast iron pipe is used, it can be cut without the help of the combustion-resistant round steel. Under the constant oxygen pressure, it can be cut like ordinary carbon steel, as shown.
The actual cutting position in the middle shows the actual application. In the installation process of the boiler of Henan Sanli Brewery Co., Ltd., the bottom plate material of the furnace wall support seat is cast iron and the thickness is 20mm), but the drill is used in the field, but the electric drill is used because of the high hardness of the cast iron. Drilling is extremely difficult, so we solved this difficulty by using cast iron oxyacetylene cutting technology.
During the water supply and drainage construction process of the heating adjustment project of Zhongyuan Oilfield Base, since the underground water supply and drainage pipe network of about 2km is connected by cast iron pipes, it is necessary to cut various specifications of cast iron pipes.
Previously used mechanical cutting and electric welding, each cut! <200" cast iron nozzle, it takes nearly 1h. It is cut by electric welding, not only the quality of the cut is poor, but also needs to use about 20 pieces of welding electrode 3.2mm) and a part of the electricity, the cost is high. In addition, the electric welding cutting is easy to cause air. Pollution, solid waste is also the distance from the cutting point to the point of stability according to the length of the preheated flame 1 | Liu Xiaojian, Zheng Qijun (China Petroleum Group Engineering and Technology Research Institute, Tianjin 300451) heat can effectively improve permafrost The stability and bearing capacity of the foundation prevent frost heaving and deformation of the foundation. The article briefly describes the principle of thermal technology and introduces the application of thermal technology in the construction of highways and railways in the United States, Canada, Russia and China. Point out the limitations of the application of this technology.
0 Introduction Frozen soils, especially the mechanical properties of permafrost and general soils, are significantly different, mainly due to the mechanical properties and volume changes of soil during the freezing and melting process.
The cementation and frost heaving force generated by the water in the soil during the freezing process makes the water and the soil glue together; while the water becomes ice, its volume expands, causing the soil to shift; when there is external constraint, the volume of the frozen soil The expansion forms a frost heave force. When the ice in the frozen soil melts, the volume of the soil decreases, the strength decreases, and the frozen soil is likely to cause freezing damage such as hot melt subsidence and melted mud flow. When the engineering facilities in the permafrost zone encounter freezing damage, it will cause great economic losses if not handled properly. As a more effective technology to prevent freezing damage, heat has been widely used in the construction of basic projects in cold areas, such as pipeline engineering, bridges and culverts, tunnels, airport runways, roadbeds, transmission line towers, water conservancy projects and port projects. To cool the foundation, prevent frost heaving and deformation of the foundation, and improve the stability of the permafrost foundation.
The introduction of crude oil and natural gas from Russia is a major strategy to solve the energy shortage in China. The Sino-Kazakhstan oil pipeline under construction, the proposed Sino-Russian and domestic Manzhouli to Daqing oil and gas pipelines will pass through more; mechanical cutting is easy to cause noise pollution; using plasma cutting machine for cutting, subject to site and power restrictions, equipment is larger Cutting can not be done anytime and anywhere, and the plasma arc generated during cutting and the nitrogen oxides generated by ionized air are also harmful to the human body. Therefore, on the basis of full consideration of the site conditions, we use the oxyacetylene cutting technology to cut the cast iron pipe, which solves the problems of short construction period, wide site construction, narrow working surface of the pipe trench, and lack of equipment. Under the environment of environmental protection, the construction task of the water supply and drainage cast iron pipe network was completed with high quality and efficiency.
4 Conclusion According to the cutting principle and the cutting performance of cast iron, we have studied and optimized some proposed methods, combined with the actual production, tested the oxyacetylene cutting technology of cast iron, obtained the relevant process parameters, and mastered certain methods and Experience has led to the quantification of the process of cutting cast iron with ordinary oxyacetylene. The cast iron is cut according to the determined process parameters and operation methods, and the quality of the cut is almost the same as that of the ordinary low-carbon steel. It has achieved good results in practical applications in the field, and regardless of equipment and human resources. In terms of investment considerations, from the perspective of energy consumption, health, safety and environmental protection, ordinary oxyacetylene cutting cast iron technology has great superiority and practical value.
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