Dynamic control system for low-pressure carburating heat treament furnace

Abstract

The invention is a control system relating to a vacuum carburizing heat-treatment technique, especially a dynamic control system used in low-pressure carburizing heat-treatment furnace, including a corresponding device and the concrete working steps, where the device is mainly composed of computer and control software, PLC, thermocouple, vacuum meter, power supply, workpiece, quenching room, etc, adopting a multi-parameter input computer as control basis, and using above two kinds of vacuum meters, the computer calculates and makes real-time dynamic control according to various inputted parameters, and controls a motor inverter to command the necessary suction of a vacuum pump system, repeating this many time until the depth of carburized layer. Its advantages: it can save carburizing materials; increase loading capacity of the furnace; improves carburizing uniformity; reduce carbon accumulation of the vacuum system; automatically generate complex making course in dynamic control mode; and complete automatic control by computer, eliminating the possible errors caused by artificial operation.

Description

technical field [0001] The invention relates to a control system of vacuum carburizing heat treatment technology, especially a dynamic control system applied to a low-pressure carburizing heat treatment furnace. Background technique [0002] Vacuum carburizing is also called low-pressure carburizing; due to the design of no flame curtain, it completely solves the influence of oil fume and high heat on the working environment, and in addition to gradually overcoming technical difficulties in recent years, the quality and reproducibility of carburizing are obviously better than Traditional gas carburizing heat treatment, so this technology has been valued by the automobile industry, precision component industry and aerospace industry, and gradually used to replace the traditional gas carburizing heat treatment process, and even integrated with the machining process in the same factory area. [0003] 1. The technology of vacuum carburizing heat treatment has been studied in the...

AI Technical Summary

Problems solved by technology

[0003] 1. The technology of vacuum carburizing heat treatment has been studied in the 1960s, using the most common carburizing materials such as methane CH 4 or propane C 3 h 8 It is directly introduced into the vacuum furnace in the heating state, and the surface carburizing is carried out directly. Its original intention is to overcome the phenomenon of uneven carburizing of blind holes or deep holes during general gas carburizing. The ideal cannot be achieved, so this technology is only in the laboratory stage and cannot enter mass production

[0004] 2. In the 1970s, more experiments were carried out using other parameters, such as increasing the gas flow rate, which could indeed improve the carburizing depth, but serious carbon deposits occurred in the furnace, and mass production was still not possible.

[0005] 3. In the 1980s, the PLASMA device was used to accelerate methane CH 4 or propane C 3 h 8 The carburizing effect of the gas can greatly reduce the amount of gas introduced and improve the carbon deposition phenomenon, but there are still troubles in maintenance, and the equipment is too expensive

[0015] At the beginning of carburizing, all C 2 h 2 gas, so the Pirani vacuum gauge can measure the true vacuum degree, and as the carburizing progresses, H 2 At this time, the accuracy of the Pirani vacuum gauge decreases, so the C of the control at this time 2 h 2 The injected amount is not the correct amount

[0016] 2) The large displacement vacuum pump system causes uneven pressure in the furnace

[0019] 6. FIG1 European patent EP0818555A1, using C 2 h 2 As a carburizing material, when carburizing, C 2 h 2 Introduce and control the pressure in the range of 1~7.5Torr. During the diffusion stage, the furnace will maintain a low vacuum. This method cannot accurately grasp the changes in the gas reaction during the carburizing process, and continuously introduces C 2 h 2 , consume more C 2 h 2 , and cause pollution in the furnace and vacuum system

[0020] 7. In US6187111, on a device similar to FIG1, when carburizing, C 2 h 4 It is introduced and controlled within a certain pressure range. During the diffusion stage, the furnace will maintain a low vacuum. This method cannot accurately grasp the changes in the gas reaction during the carburizing process, and continuously introduces C 2 h 4 , consume more C 2 h 4 , and cause pollution in the furnace and vacuum system

[0026] The second stage uses 13A urban gas, the pressure is set at 3.76Torr~60Torr, and the diffusion is still carried out in a vacuum state. The disadvantage of this method is that the control is poor, the change of the gas reaction during the carburizing process cannot be accurately grasped, and a large amount of carburizing is consumed. Material

However, during the actual carburizing heat treatment, the carburizing material is easy to accumulate on the probe, forming a layer of soot, which seriously affects the accuracy of detection. Gas carburizing furnace gas and additional air will burn off the accumulated soot, but in vacuum carburizing, these conditions do not exist, that is, there is not enough furnace gas to burn off the soot, so this structure The design is not suitable for mass production in vacuum carburizing heat treatment

[0028] 13.FIG7, JP2002-2167658 adopts C during vacuum carburizing heat treatment 2 h 2 or C 2 h 2 with H 2 As the carburizing material, set a carburizing upper limit and lower limit, turn on the vacuum pump at the upper limit of the furnace pressure, and turn off the vacuum pump at the lower limit, so as to save the consumption of carburizing materials. The pressure setting cannot be carried out in real reaction furnace carburizing reaction, so it is easy to produce uneven carburizing

[0029] 14. JP2001-262313 performs vacuum carburizing heat treatment on a device similar to FIG1, using C 2 h 4 and H 2 The mixed gas is used as the carburizing material, the mixing ratio of hydrogen is 15%~50%, and the pressure in the furnace is set at 40~65Torr. The disadvantage of this method is that the control is poor, and the change of the gas reaction during the carburizing process cannot be accurately grasped. And consume a lot of carburizing material

[0030] 15. JP2001-240954 FIG8, the vacuum carburizing heat treatment on the device adopts C 2 h 4 and H 2 The mixed gas is used as carburizing material, using C 2 h 4 Detector detects C 2 h 4 In order to control the valve of the vacuum pumping system, this technology adopts C 2 h 4 The detection equipment is expensive and has poor reliability. In addition, the valve is used to control the vacuum pumping system, and its accuracy is not good.

[0031] 16. Vacuum carburizing heat treatment is carried out on the JP2001-81543 FIG9 device, and the injection amount of hydrocarbons is detected by laser, and then the required amount is controlled. The reliability of laser detection in this technology decreases when there is carbon deposit in the furnace. However, the generation of coal ash is hard to avoid in the mass production process of vacuum carburizing heat treatment, so the design of this structure is not suitable for mass production of vacuum carburizing heat treatment

[0032] 17. US6187111 performs vacuum carburizing heat treatment on a device similar to FIG1. ​​Using ethylene as the carburizing raw material, the carburizing furnace pressure is 1-10KPA. In the diffusion stage, the vacuum in the furnace is kept low. This method cannot accurately grasp the carburizing process. The change of gas reaction, and the continuous introduction of C 2 h 4 , consume more C 2 h 4 , and cause pollution in the furnace and the vacuum system. The disadvantage of this method is that the control is poor, the change of the gas reaction in the carburizing process cannot be accurately grasped, and a large amount of carburizing materials is consumed

[0033] 18.US PAT NO.5.702.540 uses ethylene as the raw material for carburizing, and reduces the furnace pressure to below 1KPA, but the price of ethylene is very expensive, and it is not easy to store and handle in large quantities. Since the pressure is set at 1KPA, a large capacity is used The disadvantage of this method is that the control is poor, the change of the gas reaction in the carburizing process cannot be accurately grasped, and a large amount of carburizing materials is consumed

[0034] 19. US PAT NO.5.205.873 uses ethylene and hydrogen as carburizing raw materials, and controls the furnace pressure at 1~10KPA, but hydrogen is explosive, and safety must be considered. The disadvantage of this method is that the control is poor and it cannot be accurately grasped. Changes in the gas reaction during carburizing and consume a large amount of carburizing material

[0035] 20.US PAT 6.187.111 adopts a smaller capacity original, intending to reduce the gas consumption, but it will affect the initial vacuum suction time, the disadvantage of this method is that the control is poor, and the change of the gas reaction in the carburizing process cannot be accurately grasped

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