Application of Medium Frequency Heating Induction Technology in Heat Treatment Process of Steel Tubes

The process and equipment for heat treatment of steel tubes are carried out by using the principle of induction heating of medium frequency current. It is pointed out that the process technology has low investment, no environmental pollution, meets environmental protection requirements, and the process control is labor-saving and labor-saving, especially convenient for tissue production, compared with gas heating and anti-corrosion. Steel pipes Heat treatment has certain technical advantages and should belong to new technologies and new processes that the government encourages development and enterprises can give priority to.
The use of the principle of electromagnetic induction heating of medium frequency current for quenching, tempering and normalizing of oil well pipes has become a mature process technology in the developed countries such as the United States, and has been widely used in the manufacture of petroleum special pipes. American LONGSTAR, unrestricted pipe companies, Volga steel mills and other pipe manufacturers have their own medium frequency induction heat treatment production line. Induction heating uses electricity as an energy source. It is completely different from the use of natural gas, gas, or liquefied petroleum gas. In the heating process of steel pipes, soot is generated and air pollution is formed. Because electric energy belongs to green energy, it will not cause damage to the environment and meet the requirements of human society for environmental protection. Therefore, it is also an environmentally-friendly technology development project encouraged by domestic and foreign governments. At the same time, the induction heating technology is used to quench, temper or normalize the steel pipe, the heating speed is fast, the efficiency is high, the production organization is flexible and convenient, and the time and energy consumption required for heating and cooling of the furnace when the gas heating steel pipe is avoided are avoided and saved.
 
Induction heating technology was first applied in the military, automobile, machinery and other industries in China, and gradually expanded to the metallurgical industry. In the early 1980s, Shougang Special Steel Co., Ltd. first began to use intermediate frequency heating technology in China, for 45MoMnB, 35CrMo, 40Cr, 40Mn2Mo. And 45# steel pipe for quenching and tempering; softening heat treatment in the middle of cold processing of GCr15 steel pipe; solid solution heat treatment of 5Cr21Mn9Ni4N steel pipe; annealing heat treatment of T10A, 20Mn2, 20# steel bar, all achieved good results.
 
Oil wells induction heat treatment steel grades include carbon manganese steel series and alloy steel series.
 
Practice has proved that the medium heat frequency induction heating technology for heat treatment of steel pipes not only has low environmental pollution, high production efficiency, but also the cost can reach the level equivalent to gas heating; if used in the low peak period of electricity consumption, the cost will be lower. At the same time, if the process parameters are selected reasonably and the process is well controlled, the straightening process can be omitted.
 
The process of induction heat treatment of steel pipes is the same as that of conventional gas-fired step furnaces, but the working principle and processing engineering are completely different. In the gas-fired stepping furnace, the steel pipe is integrally heated; in the induction furnace, the steel pipe is continuously heated in stages and successively; the quenching process and the tempering process are also carried out. Therefore, when the steel pipe is heated, quenched, and tempered, it is basically moving in the longitudinal direction and spiraling forward, and the rest is to make the lateral movement. The specific processing process is as follows: according to the API 5 CT standard for the quenching and tempering requirements of the oil well pipe, the oil well pipe blank is lifted from the crane to the loading gantry, and the artificial appearance inspection is arranged in a neat arrangement.
 
When the work positions of the production line enter the normal working state, the inductor is energized and ready for feeding, the variable frequency feeder starts to rotate, the stepper feeder is manually operated, and the first oil well pipe is smoothly lifted from the outlet end of the loading gantry. It is sent to the roller table of the aligning device. The variable frequency feeder feeds forward at the set speed. The variable frequency feeder is single-roller transmission, and the speed and height are adjustable. The roller type is a roller feeder specially designed for tilting 15°. The horizontal feeding correction centering and the workpiece self-rotating function, wherein the feeding roller between the induction heating coil and the feeding roller of the inlet and outlet are made of heat-resistant steel, and is equipped with a rotary sealing internal water cooling device, cooling the feeding roller and making the outer surface of the feeding roller Dry, easy to heat the tubing, the rest of the feed roller is made of wear-resistant steel. The oil pipe enters the intermediate frequency quenching heating zone through the roller conveyor. The heating zone consists of a set of 3000kW intermediate frequency power supply and a set of 1200kW intermediate frequency power supply with multiple sets of heating induction coils to form a quenching induction heating zone to ensure uniform temperature of the workpiece. The heating temperature is 850 °C ~ 1000 °C. An imported two-color colorimetric infrared thermometer is installed at the outlet of the heating coil to monitor the heating temperature of the tubing, and the signal is fed back to the control system of the intermediate frequency power supply, and the output power of the intermediate frequency power supply is automatically adjusted to form a closed loop control system, thereby adjusting The heating temperature of the steel pipe is controlled within the allowable error range.
 
The heated steel pipe enters the spray quenching zone. Since the workpiece is made of carbon-manganese steel with a carbon content of about 0.3% or medium-low alloyed chromium-molybdenum steel and chromium-manganese-molybdenum steel, pure water is suitable as the quenching medium. We use a ring-shaped cooling device to continuously spray high-pressure water onto the surface of the heated steel pipe, and spray it for about 5 to 15 seconds to achieve the microstructure transformation of the quenched martensite. To this end, we have selected two sets of high-flow high-pressure water pumps (pressure is 1000m3/h for a lift of 125m per minute), and the total power is above 500kW, so as to achieve the effect of rapid and uniform cooling required for complete quenching of the pipe wall. It is ensured that the vapor film generated on the surface of the steel pipe is broken, and the steel pipe quickly reaches the martensite transformation temperature, and all of them are transformed into quenched martensite, and no quenched troostite is produced, thereby ensuring tempering sorbite. Since the scale and the dust on the surface of the steel pipe will fall into the quenching medium during the spraying, the quenching medium must be subjected to multi-stage treatment such as coarse filtration, magnetic suction filtration and mesh filtration in the sedimentation tank to make the turbid water clean and can not be blocked. The nozzle can be recycled.
 
The spray zone is provided with an isolation baffle to prevent water splashing, which is beneficial to water recycling and reducing the loss of turbid water. A protective cover is also provided to prevent steam from being sprayed out to ensure the drying of the workshop.
After the spray quenching, the steel pipe is conveyed by the roller conveyor to the water removal section of the pipe, and the pipe is lifted on the inclined table by the pneumatic turning machine, and after being drained for more than 5 minutes, it is lifted by the pneumatic turning machine to the tempering roller table. In the transmission of the roller conveyor, it enters the intermediate frequency tempering induction heating zone, and the tempering heating temperature range is generally 600 ° C to 750 ° C. The IF induction heating power supply is a tempering induction heating zone consisting of a set of 1900 kW and a set of 900 kW consisting of multiple sets of induction coils. An imported two-color colorimetric infrared thermometer is installed at the exit of the last induction coil to monitor the temperature of the oil pipe, and is responsible for feeding back the signal to the intermediate frequency power supply, and automatically adjusting the output power of the intermediate frequency power supply to form a closed-loop control system. After the tempered steel pipe passes through the high-pressure water descaling device on the roller table, the steel pipe reaches the descaling effect under the scouring of the high-pressure jet water. After the descaling steel pipe passes through the sensor in the tempering zone, the pneumatic transmission is stepped over. The material machine lifts the steel pipe smoothly, put it on the cold bed and slowly rotates it, and gradually cools it. The steel pipes are then collected into the basket at the exit of the cold bed and manually bundled and packaged for transport to the next section.
 
3, the basic composition of the equipment
 
3.1. Feeding part: It consists of the following equipment: feeding rack---- turning mechanism-- longitudinally rotating feeding roller road ---- inclined roller road
 
3.2, quenching heating part: divided into two zones, heating zone and heat preservation zone; wherein: heating zone has 12 induction coils, design power 2500kW, design frequency 300HZ, insulation zone has 8 induction coils, design power 2500kW, design frequency 1000HZ .
 
3.3. Quenching device: Two closed spray quenching devices, equipped with hundreds of nozzles, and forming different angles, spraying high-pressure water flow to the steel pipe, and ensuring quenching at every section in the process of steel pipe running. The water volume is equal, the cooling rate is the same, and the heat is deformed evenly. For induction heating quenching, the biggest difference from gas heating quenching is that the quenching method is different.
 

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