Abstract: As a new type of cooling control technology, the Quenching-Cooling cooling technology has many unique advantages and broad application prospects compared to the traditional cooling technology. It is especially suitable for the quenching of large-scale workpieces. This article begins with the diagnosis and treatment of the quenching and cooling technology in the helium-environmental control system, analyzes and discusses the diagnostics-theory, content and characteristics of the technology, and conducts actual process formulation, required production equipment, and control methods in its specific implementation process. A brief analysis and introduction.
The main heat treatment form of large-size alloy steel parts is overall conditioning. For alloy steel parts with large cross-section dimensions, complex shapes, and mechanical properties, if simple oil quenching is used, mechanical properties are often not achieved, and water quenching can cause cracking. At present, quenching of this kind of workpieces is usually performed by water quenching, oil cooling, or quenching with a water-soluble medium (PAG). However, the effect of these two kinds of quenching cooling methods is often not ideal. Not only the mechanical properties are low, but also the use cost of the medium is high. At the same time, there are also environmental pollution and safety hazards.
The Cyclical Timed Quenching and Processing (CTQP) technology introduced by Shanghai Jiao Tong University has achieved very good results in solving the problem of low quenching performance and water quench cracking of alloy steel parts. This paper has been applied in this paper, starting from the diagnosis and treatment of the quenching and cooling technology in the helium-environmental control, analyzed and discussed the diagnostics-theory, content and characteristics of this quenching and cooling control technology, and the actual process formulation and the The required production equipment and control methods were briefly analyzed and introduced.
A, 裓 - Environmental Control Quenching and Cooling Technology (CTQP) Diagnosis - Management
The ideal cooling curve in the quenching process can be divided into 3 stages.
(1) Slow cooling phase from austenitizing temperature to A1 temperature: The purpose of this phase is to reduce the thermal stress caused by rapid cooling and at the same time reduce the overall heat capacity of the quenched workpiece.
(2) Rapid cooling phase in the pearlite transformation temperature region of the TTT curve: The purpose of this phase is to avoid pearlite or upper bainite transformation of supercooled austenite as much as possible.
(3) Cooling at a slower rate in the martensite transformation temperature region (near the Ms point): The purpose of slow cooling in this stage is to reduce the stress due to a large amount of martensite structure.
The cooling curves for water, water-soluble media, oil, and air are quite different from this ideal cooling curve, but if a suitable dual medium is used, the curve that approximates the ideal cooling curve can be obtained by controlling the media conversion time. This is裓-Cyclic cooling control technology (CTQP) basic control ideas.
Fig. 1 is the cooling curve during quench cooling of the surface layer, subsurface layer, and core of the workpiece when using water-air helium-loop control. It can be seen from the figure that the first stage of cooling is pre-cooling, that is, in the temperature range between the austenitizing temperature and the A1 temperature, air cooling is used for slow cooling.
1 - surface cooling curve; 2 - subsurface curve; 3 - heart cooling curve; Ta - austenitizing temperature;
A1—folding temperature; T—tempering temperature; Bs—starting temperature of bainite transformation; Ms—starting temperature of martensite transformation.
Fig. 1 quenching cooling process during cycle control
The effect is to reduce the overall heat capacity of the workpiece and provide conditions for increasing the cooling rate in the next stage (rapid cooling stage); at the same time, slow cooling in this region has little effect on the pearlite transformation incubation period of the subsurface layer and the core. For some workpieces with no special surface texture and hardness, it is also possible to obtain a certain amount of pearlite in the surface layer through this stage of pre-cooling. This process can increase the depth of the hardened layer of the workpiece.
The second stage of quenching cooling is performed using a fast cooling (water cooling) and a slow cooling (air cooling) helium-ring alternation. In rapid cooling (water cooling), when the surface layer of the workpiece is cooled to a temperature near or below the Ms point, rapid cooling is stopped and slow cooling is performed; in the case of slow cooling (air cooling), the heat of the subsurface layer is transmitted to the surface layer. As the temperature rises, the martensite, which has just undergone surface transformation, is self-tempered, and the plasticity and stress state of the surface layer are adjusted to avoid cracking. The alternating process of rapid cooling and slow cooling is repeated continuously (time ratio needs to be adjusted according to actual conditions) until the temperature of a part of the workpiece reaches the temperature required by the cooling process.
Second, the characteristics of quenching cooling technology
Since CTQP technology can be completed by multiple immersion (or liquid) and air-cooled helium-ring cooling steps, this technology is particularly suitable for quenching applications for large-size alloy steel workpieces. Has the following characteristics:
(1) Using water as the main quenching medium, instead of water-soluble medium (PAG), oil and other media. Wide range of applications (theoretically, the cooling capacity can reach any value between water and air by adjusting the time ratio of water and air treatment). Strong cooling ability, by adding a simple injection process, can significantly increase the heat transfer capacity in water cooling; and its safe processing, low cost, no environmental pollution.
(2) The main objects of treatment are alloy steel workpieces and workpieces with complex shapes. Since the CTQP technology consists of multiple helium-ring cooling steps, it can be applied to the quench cooling of complex-shaped workpieces, and the quench cooling requirements of the corresponding parts of the workpiece can be achieved in different quenching and cooling steps.
(3) The standard for the formulation of the quenching and cooling process is based on a comprehensive consideration of the components of the workpiece and the state of stress and strain. Therefore, it is not possible to simply plan the processing of the workpiece through tests and inspections. A numerical simulation method must be used to acquire the process through simulation calculations combined with test data. Process formulation is the core and difficult point in quench-cooling technology during the helium-loop control.
(4) Ancillary equipment that satisfies the processing requirements must be used to achieve the quenching and cooling process through computer control. The realization of the quenching and cooling process during the helium-loop control requires precise, sensitive conversion of the air-to-air cooling mode and the adjustment of the air-to-air cooling time ratio, which cannot be provided by conventional quenching and cooling equipment, and must therefore be completed using redesigned supporting equipment. At the same time, the process of the CTQP process is often relatively complicated and the control requirements are strict. Therefore, professional computer control software and hardware must be used to guarantee the process.
III. Formulation of Quenching and Cooling Processes during the Environmental Control
裓 - The quenching and cooling process during the environmental control shall comprehensively consider the shape, size, material and quenching requirements of the organization, mechanical properties, stress and strain states. Therefore, it must be based on numerical simulation techniques and combined with experimental verification. Taking the f220mm long axis (42CrMo material) as an example, Fig. 2 shows the change of temperature from the shaft surface to the subsurface to the center after a series of helium-ring cooling processes. Figure 3 shows the corresponding final organization score.
Figure 2 shows the simulated temperature change process
Figure 3 shows the final organization of the simulation
Through the method of numerical simulation, it is possible to predict and analyze the preset process. Under the premise that the results of simulated data can meet the expectation of quenching treatment, further verification by a small amount of tests and correcting the process parameters can obtain relatively effective and practical actual processing content.
The table below lists the mechanical properties of the long axis at 1/2 radius after quenching and quenching of the above series (after quenching and tempering).
Mechanical properties at the 1/2 radius of the long axis (after conditioning)
Fourth, the design and implementation of helium-ring control quench cooling equipment
The traditional quenching equipment cannot meet the need of quenching and cooling process during the helium-loop control. Especially for large and complex workpieces, if traditional quenching and cooling with a water tank and a crane are used, it is not able to adapt to the rapid and frequent water quenching and cooling conversion of workpieces, and precise control of the cooling time cannot be achieved. Therefore, special equipment needs to be designed to satisfy the process. The requirements for the equipment.
For example, quenching of large crankshafts, large die steels, etc., Shanghai Jiaotong University has developed quenching tank equipment with corresponding functions to meet the process requirements (as shown in Fig. 4).
Fig. 4 Illustration of CTQP quenching and cooling equipment
In the figure, part A is the quenching and cooling zone of the workpiece and B is the reservoir zone. The workpiece is hung in position A in the figure. During the water quenching process, the spray array located on both sides of the workpiece position rapidly injects the medium into the A position to achieve immersion quenching of the quenched part. When it is converted to air-cooled, the valve below the A position is opened, the water in the quenching cooling zone rapidly flows into the B zone, and the quenched part in the A zone is air-cooled.
The most important feature of this design is that the quick water injection is used instead of the traditional workpiece lifting immersion method to achieve liquid quenching, which is particularly suitable for the processing of large-size workpieces. At the same time, the reliability and stability of the equipment are also higher than that of the bench-top quenching equipment. To improve. Since the water injection system uses a multi-point injection array design, the water injection system can also provide a variety of cooling means such as water spraying, spraying, and the like, which allows the quench tank to also perform a variety of composite processing on the workpiece.
Fifth, helium-ring control quench cooling control
To realize the helium-ring control quenching and cooling process, in addition to designing the above-mentioned function quenching tank, a corresponding control system is also required to be realized.
This control mode needs to include three levels from the structure, as shown in Figure 5. From the bottom up, they are the electrical drive layer, PLC control layer and software management layer.
Figure 5 CTQP control structure
(1) The electric drive layer This layer mainly includes: Motor drive module for driving various types of motors, fans, pumps; Trigger module, used to assist the drive other non-strong electric institutions, such as solenoid valves and other devices; sensors The module, which connects various sensor elements on the device, collects various data parameters throughout the process.
(2) PLC control layer The core of this level is the PLC (programmable controller). It controls downwards and controls all the operations of the public-tuned electrical drive layer, returns various data information upwards, and accepts the management information sent by the software management team for implementation. PLC (Programmable Logic Controller) is widely used at present, and the control period can reach milliseconds. The control capability and precision of the PLC are far beyond the traditional control instruments. Therefore, it can provide more reliable and precise control capability for the quenching process. .
(3) Software Management This level mainly provides human-machine interface and advanced management functions. As we discussed previously, the process of quenching and quenching controlled by helium-ring control needs to be completed through complicated numerical simulation and experimental verification. In the actual operation, a large number of pre-simulation calculations and tests are needed to establish the necessary process. The database, in order to provide a reliable data basis for the actual process generation of the workpiece, the process database system is the core content of the software management layer.
6. Conclusion
The above analysis of the helium-ring controlled quench-quench cooling diagnosis-treatment and the corresponding quenching equipment, the diagnostics and equipment and the equipment has been flawed-has been successfully applied in the enterprise. It is hoped that through the promotion of this technology, companies can solve more difficult problems that cannot be solved with traditional methods.
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