The large vertical medium frequency induction heating supporting roller compound quenching machine tool is a new type of machine tool designed under a new concept to replace the gas, oil, and supporting roller differential temperature furnace. It’s hoisting, heating, operation, and injection quenching mode are different from the traditional supporting roller differential temperature furnace. The design concept of the new type of machine tool is aimed at the shortcomings of gas-fired differential temperature furnaces in the production process (heating time is long, energy consumption is high, lifting is inconvenient, etc.) and the design. Therefore, the new machine tool in the production efficiency, heating mode, injection quenching mode, production cost, work safety, labor intensity, workpiece adaptability, workpiece quality, and process Settings have shown a strong advantage.
It is well known that to improve the quality, precision, service life, and shorten the processing cycle of supporting roll is an important research topic in the field of steel rolling. The utilization rate of materials can be improved effectively by studying the new technology of producing supporting rollers.The service life of the supporting roller is closely related to the surface hardness and the depth of the hardening layer and the wear resistance of the roller. At the same time, improving the original manufacturing method and selecting better supporting roller material are the primary measures to improve the performance of supporting roller.
The scope of the machine treatment workpieces: the total length of the supporting roller is 6000mm, the diameter of 800~ 1680mm, the length of the roller is 780~ 2500mm, quality ≤ 60T, the depth of the hardening layer is 30~118mm.
1. Design concept of supporting roller induction heating
Induction heating technology has been widely used in mechanical processing, but the application of low-frequency and high-power power supply in heat treatment is rarely used. This application of low-frequency and high-power heating as supporting roll induction heating is a major breakthrough in induction heat treatment technology, which provides a new technical platform for induction heat treatment.
Using Visual Basic software package ANSYS, combined with the change of parameters of the support roller induction heating temperature field was simulated and analyzed. The temperature field of inductive heating of supporting roller material is numerically simulated, and the relevant data of the heating process of supporting roller, including sensor design, heating process formulation, magnetic field strength, and magnetic field distribution, are obtained.
2. Design and manufacturing characteristics of machine tools
This method of inductive heat treatment and spray quenching of supporting roller is a new concept.
(1) The vertical supporting roller induction differential temperature quenching machine tool can be completed in a station feeding, heating, spray quenching work.
(2) The large hanging workpiece to do up and down operation and smooth rotation.
(3) Low frequency and high power integral induction heating and temperature control.
(4) Spray quenching station water spray, spray, air injection according to the process can be automatically converted.
Backup roll induction heating quenching machine tool whole, is I have the latest research and development of the most advanced supporting roller heat treatment equipment, it has low carbon, environmental protection, energy saving, low use cost, product quality, and the advantages of ultra-deep hardening layer, over 30% of energy than traditional backup roll heat treatment equipment, and greatly reduce the labor intensity of operators, is the ideal equipment of backup roll heat treatment.
(1) Machine tools
The design and manufacture of machine tools are based on the principle of heating and quenching the whole vertical workpiece. Machine tools are required to have load-bearing capacity, stability, seismic resistance, stability, and safety reliability. The main body of the machine tool (see Figure 1) is a gantry structure with a concave design on the top. The movable beam on the machine tool lifts the supporting roller through a special clamp. The upper moving beam can run up and down through the lead screw. The running position includes feeding, heating, and spraying, and quenching positions. The descending speed of the upper moving beam is adjustable by frequency conversion; The lower beam is adjusted up and down by the light bar, which ACTS as the neutralization and locking function of the workpiece. The machine tool is equipped with a hydraulic counterweight device, which can balance the force of the machine tool, increase its stability, and prolong its service life.
During operation, the upper moving beam hangs the workpiece and runs down to the center of the lower beam center, and locks the lower beam, so that the upper and lower beam and the workpiece are connected into a load body. The workpiece is rotated in the induction furnace for heating. After heating, the load body descends to the position of spray quenching for spray quenching. Return to a neutral position after spray quenching, unlock and lift to feed position. Therefore, it is called to complete the feeding, heating, and quenching work in the same station. The design of each structure is through the expert’s precise calculation and demonstration.The machine has strict structure, short distance, a wide range of application,s and stable operation.
(a) Photographs of supporting roller induction vertical machine tools
(b) Schematic diagram of supporting roller vertical machine tool
(2) Power supply
Using SCR frequency conversion power supply, high efficiency, small volume, light weight, easy to operate, flexible to start. The power supply frequency is 36 ~ 60Hz. According to the empirical formula, the penetration depth of steel current at 900℃ is:
Delta =500/ F1 /2 (f is the power frequency)
As can be seen from the above equation, the lower the frequency is, the deeper the current penetration depth is, and the diathermy depth, diathermy temperature, and holding time determine the austenitizing depth. Under the condition of certain diathermy depth, the length of holding time determines the austenitizing depth after the diathermy depth. Because austenitizing depth is controllable, heating speeds are increased, saving time and energy.
Induction furnace heating is started with load, so the medium frequency power supply and furnace body can resist high-power shock and low-frequency vibration, the power starts success rate is 100%. Because the workpiece rotates during heating, the phenomenon of uneven heating caused by the eccentricity of the workpiece can be overcome.
Induction furnace temperature measurement system USES infrared measuring temperature closed-loop control, the closed-loop process is the workpiece temperature – infrared measuring temperature – PLC computer control output signal to medium frequency power supply and control induction furnace output power, the temperature of the workpiece, thus ensure the workpiece set temperature within plus or minus 10 ℃ when heating operation, also has realized the roll surface evenly austenitizing.
(3) Spray quenching
After heating, the workpiece goes down to the spray quenching position for spray quenching. The spray quenching mechanism is composed of a multi-channel mixed spray quenching body, and several quenching belts are formed on the surface of the workpiece during spray quenching. Since the workpiece is rotated during spray quenching, the multi-channel spray quenching belts can cover all the surfaces of the supporting roller within 3s. The working mode of spray quenching mechanism has water state, fog state, gas 3 kinds, in each way the size proportion of the amount of spray can be adjusted, so as to form a more complete quenching process chain, the size, way and time of spray quenching is controlled by computer, can adapt to a variety of specifications of the supporting roll quenching process.
The injection and quenching part of the overall structure adopts mechanical movement, according to the size of the outer diameter of the supporting roller at any time to adjust the injection and quenching distance, so that the surface pressure and density of the various specifications of the roller are the same, to ensure the unity of the workpiece quality.
(4) Electric control
The electronic control of the vertical supporting roller induction heating quenching machine is composed of machine operation, intermediate frequency heating, equipment cooling, spray quenching cooling, closed-loop temperature control, PLC, and computer system. The operation of the equipment can not only be on-line automatic operation by the main control computer but also can be controlled step by step independently.
In online operation, process parameters are transmitted from the computer to THE PLC, the PLC sends instructions to control the start and stop and operation of each part, and each parameter, state, and temperature in the operation are displayed from the computer display, and the operation data will be saved in the computer for a long time. The control part has a complete information detection and recording system and is equipped with an interface controller system for networking management with a second-level computer, logic control, and the state detection system of the electrical system and instruments in the system.
3. Practical application effect
(1) Differential temperature thermal treatment process
The supporting roller should be preheated to 350~500 ℃ in the box furnace before rapid induction differential heating (preheating can make the temperature inside and outside the roller uniform). After preheating, through rapid induction heating, a heating layer of 810~940℃ is formed on the surface of the roller to the depth of the 190mm layer, which causes the difference in temperature between inside and outside the workpiece and thus reduces the thermal stress caused by heating.
After preheating, the supporting roller is transferred into the induction differential temperature furnace, passing through three stages:
(1) Quickly heat the preheating temperature to the process set temperature, from the surface of the roll to a depth of 70mm and is simultaneously heated by electromagnetic induction, to form a surface high temperature energy storage layer, to provide thermal power for the temperature to the inner conduction.
After the surface heating layer passes the Curie point, the power is increased and the heat preservation begins. At this time, the energy storage area is further expanded to 90mm. Meanwhile, the heat of the high temperature energy storage layer is conducted inward, and the heat preservation time determines the depth of the austenitized layer required.
(3) after the workpiece heat preservation, drop to the spray quenching position for strong water-jet quenching; When the temperature of the surface layer of the workpiece drops to the first transition point of the process, the strong water spraying mode is transformed into the strong spray mode. When the second transition point of the process is reached, the strong spray mode is changed to the weak spray mode. Can make the workpiece to get the best quenching effect.
Note: The length of heat preservation time is determined according to the diameter of the roll, the requirements of the depth of the hardening layer, and the actual temperature rising speed. Too long heat preservation time will cause the temperature of the roll core to be too high, and the process controls the temperature of the roll core <600℃.
Austenitized layer is at least 2 times as deep as the required hardened layer so that the hardened layer obtained after quenching has enough gentle transition layer distribution space, the hardened layer and the transition layer in the compressive stress zone, and the tensile stress peak to the interior, so that the surface layer has and greatly improve the anti-fatigue performance.
The induction differential temperature vertical machine tool has obvious energy saving and high product quality. At the same time, conventional differential temperature furnace oil or natural gas more or less will cause environmental pollution, while induction heating vertical machine tool environmental pollution, low carbon environmental protection. Moreover, it can be intuitively seen from Figure 5 that the adoption of induction differential temperature vertical machine tool can greatly shorten the heating time of supporting roller, reduce the labor intensity of workers, and improve the production efficiency.
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