CN1302146C - Dynamic control system for low-pressure carburating heat treament furnace - Google Patents

Abstract

A control system related to vacuum carburizing heat treatment technology, especially a dynamic control device and heat treatment method applied to a low-pressure carburizing heat treatment furnace. The invention includes the device of the system and the specific working steps of the heat treatment process method. The device is mainly composed of a computer and control software, a thermocouple, a vacuum gauge, and a quenching chamber. The vacuum gauge, the computer calculates and performs real-time dynamic control according to the input parameters, and controls the motor inverter to achieve the necessary suction volume of the vacuum pump system, and repeats it many times until the carburizing layer is deep. The advantages of the present invention are: it can save the amount of carburizing material; increase the loading capacity of the furnace; increase the uniformity of carburizing; reduce the carbon deposit in the vacuum system; can automatically generate complex process in a dynamic control mode; can complete computer automatic control, Eliminate possible human errors.

Description

Dynamic control device and heat treatment method applied to low-pressure carburizing heat treatment furnace

technical field

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

Vacuum carburizing is also called low-pressure carburizing; due to the design of no flame curtain, the influence of oil fume and high heat on the working environment is thoroughly solved. In addition, the technical difficulties have been gradually overcome in recent years. 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.

1. The technology of vacuum carburizing heat treatment has been studied in the 1960s. The most common carburizing materials such as methane CH ₄ or propane C ₃ H ₈ are directly introduced into the vacuum furnace in the heating state, and the surface carburizing is directly carried out. The purpose is to overcome the phenomenon of uneven carburizing of blind holes or deep holes during general gas carburizing. However, serious carbon deposits in the early stage and carburizing quality are still not ideal. Therefore, this technology is only in the laboratory stage and cannot enter mass production. .

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 the serious carbon deposits in the furnace still failed to achieve mass production.

3. In the 1980s, PLASMA equipment was used to accelerate the carburization of methane CH ₄ or propane C ₃ H ₈ gas, which could greatly reduce the amount of gas introduced and improve the carbon deposition phenomenon, but there were still maintenance problems and the equipment was too expensive.

4. In the 1990s, unsaturated carburizing materials such as acetylene C ₂ H ₂ , ethylene C ₂ H ₄ , hexane C ₆ H ₁₂ and various mixed gases were discovered one after another, which can be applied in the vacuum carburizing process. The amount of introduction is reduced to a very low level, and a good carburizing effect can be obtained. Because of the low amount of introduction, the situation of carbon deposition has been greatly improved to the stage where mass production can be carried out.

5. However, the current low-pressure carburizing heat treatment furnace adopts a staged fixed furnace pressure setting value, and the injection amount of carburizing material is controlled by a vacuum gauge at the outlet of the pipeline.

The current low-pressure carburizing heat treatment furnace is equipped with a set of vacuum pump system. In order to quickly discharge the air in the furnace for heat treatment and carburizing process, the vacuum pump system is equipped with a large capacity. When performing low-pressure carburizing, its design The fixed carburizing pressure is about 10 Torr or even lower. At this time, the pumping capacity of the large-capacity vacuum pump often leads to a large amount of carburizing hydrocarbons to be injected, and the actual pressure at the pump suction port is lower than the pressure at the far end, which easily leads to carburizing. Uneven, so the existing equipment is limited to the maximum area of loading, in order to be evenly carburized, and the pollution of the vacuum system is still unavoidable. In addition, the vacuum gauge is placed at the outlet of the pipeline. In addition to not accurately reflecting the real furnace pressure, it also cannot accurately reflect the various gases such as hydrogen and methane produced after the carburizing chemical reaction, so it often leads to process instability.

For example, the main reaction of using acetylene as the carburizing material in the low-pressure carburizing process is as follows:

At the carburizing temperature (900°C-1050°C), the workpiece to be infiltrated acts as a catalyst to crack C2H2 to produce 2 activated carbons and 2 hydrogens, and the 2 activated carbons directly penetrate into the surface of the workpiece, and the hydrogen gas In the furnace, as a reducing gas.

The configuration of the known technology is mainly to install the Pirani vacuum gauge at the outlet of the pipeline, then send the measured data to the vacuum controller, and then direct the control valve to control the injection amount of C2H2. Its main deficiencies are as follows:

1) The Pirani vacuum gauge cannot measure the actual furnace pressure during carburizing

When the Pirani vacuum gauge is used to cool the FILAMENT with gas, the Wheatstone circuit is unbalanced, and the amount of gas measured is the value of the vacuum degree. Because the weight and cooling rate of the gas are different, a known gas must be used to preset the parameters of the vacuum gauge to calculate the vacuum degree.

At the beginning of carburizing, it is all C2H2 gas, so the Pirani vacuum gauge can measure the real vacuum degree. As carburizing progresses, H2 gas is generated. At this time, the accuracy of the Pirani vacuum gauge decreases, so at this time The controlled C2H2 injection amount is not the correct amount.

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

The configuration of vacuum pump capacity in conventional technology, taking the heating chamber capacity of 7.8m ³ (effective working area 1.2m×0.76m×0.76m) as an example, the pumping capacity of the vacuum pump per hour is about 450m ³ . The main consideration is that a large pump can shorten the exhaust time before heating starts. However, the suction of the pump is too large, causing uneven pressure in the furnace when the carburizing material is applied. Generally, the pressure of low-pressure carburizing is set at 0.1TORR-10TORR. At this time, due to the large pumping capacity of the pump, the pressure difference between the position of the vacuum gauge at the pumping port and the farthest point in the furnace can reach 30%-50%.

In addition, due to the large pumping capacity of the pump, in order to maintain the pressure in the furnace, the flow rate of the carburizing material must be much higher than necessary.

6. European patent EP0818555A1 uses C ₂ H ₂ as carburizing material. During carburizing, C ₂ H ₂ is introduced and controlled in the pressure range of 1 to 7.5 Torr. In the diffusion stage, the furnace maintains a low vacuum state. This This method cannot accurately grasp the change of gas reaction in the carburizing process, and continuously introduces C ₂ H ₂ , consumes more C ₂ H ₂ , and causes pollution in the furnace and vacuum system.

7. The United States US6187111 is similar to the FIG1 device. When carburizing, C ₂ H4 is introduced and controlled within a certain pressure range. During the diffusion stage, the vacuum in the furnace is kept low. This method cannot accurately grasp the gas reaction in the carburizing process. Changes, and the continuous introduction of C ₂ H ₄ consumes more C ₂ H ₄ and causes pollution in the furnace and vacuum system.

8. JP2003-71756 uses C ₂ H ₂ as the carburizing pressure on a device similar to FIG1 to maintain the pressure at 1.5-3.5KPA and uses two-stage diffusion. The first-stage CO ₂ pressure is 0.3-15KPA, and the second-stage diffusion is The advantage is that the surface decarburization of CO ₂ can be carried out under controllable conditions, but the carburization of C ₂ H ₂ is still only carried out at a constant pressure. Not only is the surface difficult to control, but also the gas consumption is large, resulting in a vacuum The system is seriously polluted.

9. WO03/048405-A1, on a device similar to FIG3, C ₂ H ₄ +H ₂ is used as the carburizing pressure, and the C ₂ H ₄ and H ₂ detection device is used to detect the C ₂ H ₄ and H ₂ Partial pressure, and then calculate the carbon potential of carburizing and then use the material type and the setting value obtained from carburizing specifications to actually do control. The disadvantage of this device is that the detection and measurement equipment of C ₂ H ₄ and H ₂ is not only expensive but also practical The stability is not good during operation, and the method of using the bypass valve to control the furnace pressure is also relatively unstable.

10. US2003-020214-A1 uses C ₆ H ₁₂ as the carburizing material in this device. After C ₆ H ₁₂ is injected into the furnace, it immediately volatilizes into gas, and the exhaust vacuum pump is used to control the furnace pressure. Its disadvantages It is still poorly controlled and consumes a lot of carburizing material.

11. JP2003-119558 performs vacuum carburizing heat treatment on a device similar to FIG1, and its process is mainly divided into two-stage carburizing.

The first stage adopts C ₂ H ₂ , and the pressure is set at 11.3Torr～26.3Torr

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 disadvantages of this method are the same as before.

12. JP2002-173759 uses the furnace pressure measured by the pressure gauge and the hydrogen partial pressure measured by the hydrogen detector during the vacuum carburizing heat treatment, and then calculates the carbon potential to control the amount of carbonitride. This technology uses the hydrogen detector The main structure is to use a ceramic tube, vacuum weld a thin film (proton proton) at the end as a hydrogen detector, that is, read the data through the thin film, the standard hydrogen is passed through the middle of the ceramic tube, and the outside is exposed to the furnace gas, using hydrogen on both sides Different anvils for partial pressure produce a potential difference, and the hydrogen content is converted by the size of the potential difference. This structure and principle are very similar to the oxygen probe made of zirconium oxide. However, in the actual carburizing heat treatment, the carburizing material is easy to form a layer of soot on the probe, which seriously affects the detection accuracy. The carbon furnace gas burns the accumulated soot. However, during vacuum carburizing, there is not enough furnace gas to burn off the soot, so the design of this structure is not suitable for mass production.

13. JP2002-2167658 uses C ₂ H ₂ or a mixture of C ₂ H ₂ and H ₂ as the carburizing material during vacuum carburizing heat treatment, and sets 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 to save the consumption of carburizing materials. However, the carburizing reaction in the furnace cannot be realistically set by setting the furnace pressure, so it is easy to cause uniform infiltration.

14. JP2001-262313 conducts vacuum carburizing heat treatment on a device similar to FIG1, using a mixture of C ₂ H ₄ and H ₂ as the carburizing material, the mixing ratio of hydrogen is 15% to 50%, and the pressure in the furnace is set At 40-65Torr, the disadvantages of this method are the same as others.

15. JP2001-240954 FIG8, the vacuum carburizing heat treatment on the device uses the mixed gas of C ₂ H ₄ and H ₂ as the carburizing material, and uses the C ₂ H ₄ detector to detect the content of C ₂ H ₄ in order to control the vacuum pumping For the valves of the gas system, the C ₂ H ₄ detection equipment used in this technology is expensive and has poor reliability. In addition, the valves are used to control the vacuum pumping system, and its accuracy is not good.

16. JP2001-81543 FIG9 device performs vacuum carburizing heat treatment, uses laser light to detect the injection amount of hydrocarbons, and then controls its required amount. This technology uses laser light to detect reliability. When there is carbon deposit in the furnace, the reliability decreases .

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 ₂ consume more C ₂ H ₂ and cause pollution in the furnace and vacuum system.

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 vacuum pump makes the gas consumption very large.

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.

20. US PAT 6.187.111 adopts a smaller capacity original to reduce gas consumption, but it will affect the initial vacuum suction time.

The above is prior art.

Contents of the invention

In order to overcome the above disadvantages, the main purpose of the present invention is to provide a control based on multi-parameter input computer, using more than two kinds of vacuum gauges, to truly react the chemical changes of carburizing gas in the furnace, and control the motor The frequency converter is used to achieve the necessary suction volume of the vacuum pump system, which is applied to the dynamic control device and heat treatment method of the low-pressure carburizing heat treatment furnace.

The technical problems to be solved in the present invention are: to solve the control problem of multi-parameter input computer; how to use more than two kinds of vacuum gauges; .

The technical solution adopted by the present invention to solve its technical problems is: the device mainly consists of computer and control software, programmable controller, thermocouple, vacuum gauge, power supply, workpiece and quenching chamber, etc., its programmable controller, computer and The control software modules are connected to each other, one end of the silicon controlled rectifier is connected with the input end of the programmable controller, the other end of the silicon controlled rectifier is connected with one end of the power supply, and the other end of the power supply is connected with the input end of the heating chamber, The programmable controller and the heating chamber are connected to each other by the main control furnace temperature thermocouple and the over-temperature control thermocouple. One output end of the programmable controller is connected to the input end of the heating chamber through a digital signal output line. One output end of the controller is connected to the output end of the heating chamber through a digital signal input line, one end of the PIRANI vacuum gauge display is connected to the heating chamber through a vacuum gauge, and its output end is connected to the input end of the programmable controller. One end of the type vacuum gauge display is directly connected to the heating chamber, and its output end is connected to the input end of the programmable controller. The heat treatment workpiece is placed in the heating chamber, and the heating chamber and the quenching chamber are connected as a whole, and there is a door isolation in the middle. Among them:

The outside of the heating chamber is connected in series with the vacuum valve, the vacuum pump, the vacuum pump motor and the frequency conversion controller of the vacuum pump motor. The PIRANI vacuum gauge is connected to the heating element, and the thin-film vacuum gauge is connected to the heating element.

The vacuum gauge applied to the dynamic control device of the low-pressure carburizing heat treatment furnace has at least two or more components.

A heat treatment method applied to the dynamic control system of a low-pressure carburizing heat treatment furnace. The method uses multi-parameter input to the computer as the control basis, uses more than two vacuum gauges to react the chemical changes of the carburizing gas in the furnace, and controls the motor frequency converter. To achieve the necessary suction volume to command the vacuum pump system, pull the ground to complete the computer and control software simulation work, of which:

The parameters input into the computer include two ways: the parameters measured in real time during the carburizing process and the parameters input before operation, including: a), the material of the workpiece; b), the total surface area of the workpiece; c), the carburized layer Depth requirement; d), surface carbon content requirement; e), maximum operating temperature limit; f), type of carburizing material; g), frequency of power supply, it is characterized in that: the specific working steps of this method are:

Step 1. The workpiece is sent into the heating chamber

After the workpiece is ready, the front door of the quenching chamber and the front door of the heating chamber are opened, and it is directly sent into the heating chamber;

Step 2. Vacuum

The vacuum valve of the vacuum system and the vacuum system of the quenching chamber are opened to start vacuuming, and the frequency converter of the vacuum pump motor is set at the normal power supply frequency;

Step 3. Heat Run

When the vacuum reaches 1torr or less than 1torr, start heating, and the vacuum pump continues to run;

Step 4. Continue soaking

After the temperature reaches the carburizing temperature, continue to run the soaking program until the workpiece temperature is uniform;

Step 5. Inverter working

After entering the carburizing process, according to the process, the frequency converter will reduce the frequency to 60%-5% of the normal frequency, and the vacuum pump will maintain a small suction volume;

Step 6. Inject carburizing material

The carburizing agent control valve is opened and a certain amount of carburizing material is injected;

Step 7. Set the value

When the pressure in the furnace reaches the set value, use the frequency converter to control the suction volume of the vacuum pump and maintain the furnace pressure at the set value;

Step 8. Vacuum Gauge Display Working

When the gas in the furnace undergoes carburizing reaction, PIRANI vacuum gauge display V1 and film vacuum gauge display V2 begin to show different readings. When the ratio of PIRANI vacuum gauge display V1/film vacuum gauge display V2 is constant, the frequency converter will Adjust to normal power supply frequency, vacuumize;

Step 9. Repeat execution

After staying for a period of time for diffusion, repeat the process of steps 5, 6, 7, and 8;

Step 10. Automatic Control

The number of repetitions of step 9 and the time of each residence and diffusion are automatically controlled by the computer according to the carburizing requirements;

Step 11. Cool down

When the carburizing and diffusion stages are completed, the cooling begins;

Step 12. Workpiece loading

When the temperature drops to the quenching temperature, the front door of the heating chamber is opened, and the workpiece is moved into the quenching chamber;

Step 13. Specified pressure

Send the workpiece to the quenching lifting table, close the front door of the heating chamber, and inject nitrogen _N2 into the heating chamber through the stamping pipeline until the specified pressure;

Step 14. Quenching Stroke

The quenching lifting platform is immersed in the oil tank to perform the quenching stroke.

The multi-parameter input computer is used as the control basis, and more than two vacuum gauges are used to truly react the chemical changes of the carburizing gas in the furnace. During the process, the computer calculates and calculates immediately based on the input parameters, including the total surface area of the workpiece, layer depth requirements, material type, maximum set temperature and other parameters, and accepts the real-time input temperature value and two or more vacuum degree values. For real-time dynamic control, the control mechanism, in addition to controlling the necessary suction volume of the vacuum pump system by controlling the motor frequency converter, controls the injection volume, injection time and stroke of the carburizing material by the above-mentioned various parameters, and repeats Multiple times until the carburized layer is deep.

The computer and control software of the heat treatment process method applied to the dynamic control system of the low-pressure carburizing heat treatment furnace use the input parameters to perform dynamic full-range control, and the computer uses the input parameters to determine the following control conditions:

a), carburizing pressure;

b), carburization and diffusion time.

In the early stage of carburizing, a high amount of carbon is immediately established on the surface, and the carbon content below the surface is very low, and the carbon diffuses rapidly. The diffusion time after the first time gradually elongates. As for the time to complete each small section of carburizing, (2 seconds-100 seconds) The difference between the PIRANI vacuum gauge display (V1) and the film vacuum gauge display (V2) determines that the carburizing material has completed carburization.

The beneficial effects of the present invention are: it can save the amount of carburizing material; increase the loading capacity of the furnace; increase the uniformity of carburizing; reduce the carbon deposition in the vacuum system; Control to avoid possible errors of human operation.

Description of drawings

The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

Accompanying drawing 1 is a schematic diagram of the system architecture of the present invention;

Accompanying drawing 2 is the schematic diagram of the implementation of the device of the present invention and the vacuum pump, the frequency conversion controller of the vacuum pump motor, etc. connected in series;

Accompanying drawing 3 is the first test schematic diagram of the embodiment of the present invention;

Accompanying drawing 4 is the second test schematic diagram of the embodiment of the present invention;

Explanation of the numbers in the accompanying drawings:

1-Computer and control software 17-Variable frequency controller of vacuum pump motor;

2-programmable controller; 18-heating element;

3-PIRANI vacuum gauge display (V1); 19-Infiltration agent control valve;

4-film vacuum gauge display (V2); 20-pressure regulating valve;

5-silicon controlled rectifier; 21-infiltration agent storage cylinder;

6-Power supply; 22-PIRANI vacuum gauge;

7-workpiece; 23-thin-film vacuum gauge;

8-The main control furnace temperature thermocouple; 24-The front door of the heating room;

9-over-temperature control thermocouple; 25-stamping pipeline;

10-input (D1); 26-quenching chamber vacuum system;

11-Output (D2); 27-Quenching chamber;

13-heating room; 28-quenching room front door;

14-vacuum valve; 29-quenching lifting platform;

15-vacuum pump; 30-oil tank stirring;

16 - Vacuum pump motor;

Detailed ways

Please refer to shown in accompanying drawing 1, the device of the system of the present invention is mainly made up of computer and control software 1, programmable controller 2, thermocouple, vacuum gauge, power supply 6, workpiece 7 and quenching chamber 27 etc., and its programmable controller 2. The computer and control software 1 modules are connected to each other, one end of the silicon controlled rectifier 5 is connected to the input end of the programmable controller 2, and the main control furnace temperature thermocouple 8 is connected between the programmable controller 2 and the heating chamber 13 and the over-temperature control thermocouple 9 are connected to each other, an output end of the programmable controller 2 is connected with the input end of the heating chamber 13 through a digital signal output (D2) 11 line, and the output end of the heating chamber 13 is input through a digital signal (D1 ) 10 lines are connected with the input end of the programmable controller 2, one end of the PIRANI vacuum gauge display 3 is connected with the heating chamber 13, and its output end is connected with the input end of the programmable controller 2, and the thin-film vacuum gauge display 4 One end of the heating chamber is connected to the heating chamber 13, and its output end is connected to the input end of the programmable controller 2. The heat treatment workpiece 7 is placed in the heating chamber 13, and the heating chamber 13 and the quenching chamber 27 are connected as a whole, but there is a door in the middle to isolate them. .

The vacuum gauge used in the dynamic control system of the low-pressure carburizing heat treatment furnace has at least two or more components.

Please refer to accompanying drawing 2,3, shown in 4, the outside of described heating chamber 13 of the dynamic control system that is applied to low-pressure carburizing heat treatment furnace is successively connected with vacuum gauge, vacuum valve 14, vacuum pump 15, vacuum pump motor 16 and vacuum pump motor The frequency conversion controllers 17 are connected in series; the osmotic agent storage cylinder 21 is connected in series with the pressure regulating valve 20, the osmotic agent control valve 19 and the heating element 18 in sequence, the PIRANI vacuum gauge 22 is connected to the heating element 18, and the thin film vacuum gauge 23 It is connected with the heating element 18, the stamping pipeline (N2) 25 is connected with the quenching chamber 27, and the vacuum system of the quenching chamber is connected with the quenching chamber 27. On one side of the quenching chamber 27 is the front door 28 of the quenching chamber, and on the side of the inner wall of the quenching chamber 27 An oil tank stirring 30 is provided, and a quenching lifting platform 29 is arranged in the middle.

The specific working steps of a heat treatment process method applied to a dynamic control system of a low-pressure carburizing heat treatment furnace are:

Step 1. The workpiece 7 is sent into the heating chamber 13

After the workpiece 7 is ready, the front door 28 of the quenching chamber and the front door 24 of the heating chamber are opened, and are directly sent into the heating chamber 13;

Step 2. Vacuum

The vacuum valve 14 of the vacuum system and the vacuum system 26 of the quenching chamber are opened to start vacuuming, and the frequency converter 17 of the vacuum pump motor is set at the normal power supply frequency, for example: 50HZ in China and 60HZ in the United States;

Step 3. Heat Run

When the vacuum reaches 1torr or less than 1torr, start heating, and the vacuum pump 15 continues to run;

Step 4. Continue soaking

After the temperature reaches the carburizing temperature, continue to run the soaking program until the workpiece temperature is uniform;

Step 5. Inverter working

After entering the carburizing process, according to the process, the frequency converter will reduce the frequency to 60%-5% of the normal frequency, and the vacuum pump 15 will maintain a small suction volume;

Step 6. Inject carburizing material

Carburizing agent control valve 19 is opened, begins to inject a certain amount of carburizing material;

Step 7. Set the value

When the pressure in the furnace reaches the set value, use the frequency converter to control the suction volume of the vacuum pump 15, and maintain the furnace pressure at the set value;

Step 8. Vacuum Gauge Display Working

When the gas in the furnace is carburized, the PIRANI vacuum gauge display (V1) 3 and the thin-film vacuum gauge display (V2) 4 begin to show different readings. When the PIRANI vacuum gauge display (V1) 3/thin-film vacuum gauge display ( When the V2)4 ratio is constant, the inverter will adjust the frequency to the normal power supply frequency, and pump the vacuum to the highest in the fastest time;

Step 9. Repeat execution

After staying for a period of time for diffusion, repeat the process of steps 5, 6, 7, and 8;

Step 10. Automatic Control

The number of repetitions of step 9 and the time of each residence and diffusion are automatically controlled by the computer according to the carburizing requirements;

Step 11. Cool down

When the carburizing and diffusion stages are completed, the cooling begins;

Step 12. Workpiece loading

When the temperature dropped to the quenching temperature, the front door of the heating chamber 13 was opened, and the workpiece 7 was moved into the quenching block 27;

Step 13. Specified pressure

The workpiece 7 is sent to the quenching lifting platform 29, the front door 24 of the heating chamber is closed, and the stamping pipeline (N2) 25 is injected until the specified pressure;

Step 14. Quenching Stroke

The quenching lift table 29 is immersed in the oil tank to carry out the quenching stroke.

The computer and control software of the heat treatment process method applied to the dynamic control system of the low-pressure carburizing heat treatment furnace use the input parameters to perform dynamic full-range control. Before operation, the following parameters are pre-input:

a), the material of the workpiece;

b), the total surface area of the workpiece;

c) Requirements for the depth of the carburized layer;

d), surface carbon content requirements;

e), the maximum working temperature limit;

f), the type of carburizing material;

g), the frequency of the power supply;

The multi-parameter input computer is used as the control basis, and more than two vacuum gauges are used to truly react the chemical changes of the carburizing gas in the furnace. During the manufacturing process, the computer calculates and calculates immediately based on the input parameters, including the total surface area of the workpiece, layer depth requirements, material type, maximum set temperature and other parameters, and accepts the input temperature value and more than two vacuum degree values. Dynamic control during operation, the control mechanism, in addition to controlling the motor inverter to achieve the necessary suction volume of the vacuum pump 15 system, and the above-mentioned various parameters to control the injection volume, injection time and stroke of the carburizing material, Repeat many times until the carburized layer is deep.

The computer and control software of the heat treatment process method applied to the dynamic control system of the low-pressure carburizing heat treatment furnace use the input parameters to perform dynamic full-range control, and the computer uses the input parameters to determine the following control conditions:

a), carburizing pressure;

b), carburization and diffusion time.

In the initial stage of carburizing, a high amount of carbon is immediately established on the surface, and the carbon content below the surface is very low, and the carbon diffuses rapidly. The diffusion time after the first time gradually elongates. As for the time to complete each small carburizing (2 seconds to 100 seconds ), completely according to the difference between the PIRANI vacuum gauge display (V1) 3 and the thin-film vacuum gauge display (V2) 4, that is, the carburizing material has completed carburizing, which has very obvious advantages as follows:

(1) All areas of the workpiece in the furnace receive the same carbon potential all the time, so the carburizing speed is exactly the same, especially for deep holes;

(2) The fresh carburizing material is discharged immediately after the reaction in the furnace is completed, so it will not form carbon deposits in the furnace;

(3) Carburizing can be precisely controlled by computer, and the carburizing layer can be long, accurate and uniform;

(4), the loading capacity can be greatly increased;

(5) Fully automatic control without human error.

Equipment specification of the present invention:

(1), two-chamber oil quenching carburizing heat treatment furnace;

(2) The effective size of the heating chamber: 1200MM×760MM×800MM;

(3), heating chamber volume: 8.0 cubic meters;

(4), vacuum system: mechanical vacuum pump 300M3/HR, Lushi vacuum pump 2000M3/HR

The workpiece size of the present invention:

1. S15C steel plate: 52MM×52MM×3MM 80 pieces

2. SCM 420 steel rod: diameter 40MM×65MM 10 pieces

The first test result of the present invention: the effective carburized layer is 0.6~0.68mm, the condition in the furnace is good, and there is no carbon deposit.

The second test result of the present invention: the effective carburized layer is 0.9-0.95mm, the condition in the furnace is good, and there is no carbon deposit.

The working principle of the vacuum gauge of the present invention is explained:

(1) PIRANI GAUGE

When the Pirani vacuum gauge is used to cool the FILAMENT with gas, the Wheatstone circuit is unbalanced, and the amount of gas measured is the value of the vacuum degree. Because the weight and cooling rate of the gas are different, a known gas must be used to preset the parameters of the vacuum gauge to calculate the vacuum degree.

(2) Thin film vacuum gauge

The thin-film vacuum gauge uses the collision motion of gas molecules to generate pressure, and its behavior is close to the ideal gas state. The pressure is related to the number of moles of gas, and has nothing to do with the type of gas.

PV=NRT

P: gas pressure

V: Furnace volume

N: number of moles of gas

R: constant

T: temperature

The feature description of the vacuum gauge of the present invention:

(1), the uniformity of the atmosphere

When the carburizing starts, the pumping capacity of the vacuum pump 15 is reduced to a very small level, so the carburizing material can quickly establish a uniform carburizing atmosphere. Because the pumping capacity is very small, the furnace will not revolve around due to strong suction. Uniform, and because of the intermittent quantitative injection, the carburizing material can be greatly reduced. In addition, the timing of pumping air is completely based on the gas reaction conditions in the furnace, so vacuum carburizing is carried out under a controllable state.

So its advantages are very obvious:

1) The atmosphere in the furnace is more uniform, and the carburizing uniformity can be greatly improved;

2), can increase the workpiece loading capacity;

3) In a controllable state, the depth of the seepage layer can be fully grasped;

4), greatly reduce the consumption of carburizing materials, and greatly reduce the carbon deposition and pollution in the furnace and vacuum system;

(2), the computer generates the manufacturing process, and the dynamic whole process control

Before operation, the engineer has pre-entered the following parameters

1), the material of the workpiece;

2), the total area of the workpiece;

3) Requirements for carburizing layer depth;

4), surface carbon requirements;

5), the maximum working temperature limit;

6), the type of carburizing material;

7), the frequency of the power supply;

According to the above parameters, the computer automatically generates a suitable process. In the actual process, the computer corrects or compensates the process according to the data input from time to time, so the production can be fully automated and the production quality can reach the best.

Claims (4)

1. A dynamic control device applied to a low-pressure carburizing heat treatment furnace. The device has a computer and control software (1), a programmable controller (2), a thermocouple, a vacuum gauge, a power supply (6), and a workpiece (7) And quenching chamber (27), it is characterized in that: programmable controller (2), computer and control software (1) module are interconnected, one end of silicon controlled rectifier (5) and the input end of programmable controller (2) The other end of the silicon controlled rectifier (5) is connected with one end of the power supply (6), the other end of the power supply (6) is connected with the input end of the heating chamber (13), and the programmable controller (2) and The heating chamber (13) is connected to each other by the main control furnace temperature thermocouple (8) and the over-temperature control thermocouple (9), and an output terminal of the programmable controller (2) is connected with the digital signal output (11) line The input end of heating chamber (13) is connected, and an output end of programmable controller (2) is connected with the output end of heating chamber (13) by digital signal input (10) line, the PIRANI vacuum gauge display (3) One end is connected to the heating chamber (13) through a vacuum gauge, its output end is connected to the input end of the programmable controller (2), and one end of the thin-film vacuum gauge display (4) is connected to the heating chamber (13) through a vacuum gauge. connection, its output end is connected with the input end of the programmable controller (2), the heat treatment workpiece (7) is placed in the heating chamber (13), the heating chamber (13) is connected with the quenching chamber (27) as a whole, and there is door isolation, where: The outside of the heating chamber is connected in series with the vacuum valve (14), the vacuum pump (15), the vacuum pump motor (16) and the frequency conversion controller (17) of the vacuum pump motor, and the PIRANI vacuum gauge (22) is connected to the heating element (18) , the thin-film vacuum gauge (23) is connected to the heating element (18). 2. The dynamic control device applied to a low-pressure carburizing heat treatment furnace according to claim 1, characterized in that the vacuum gauge has at least two or more components. 3. A heat treatment method applied to the dynamic control system of a low-pressure carburizing heat treatment furnace. The method uses multi-parameter input to the computer as the control basis, uses more than two vacuum gauges to react the chemical changes of the carburizing gas in the furnace, and controls the motor The frequency converter is used to achieve the necessary suction volume to command the vacuum pump system, and to complete the fast work of the computer and control software, among which: The parameters input into the computer include two ways: the parameters measured in real time during the carburizing process and the parameters input before operation, including: a), the material of the workpiece; b), the total surface area of the workpiece; c), the carburized layer Depth requirement; d), surface carbon content requirement; e), maximum operating temperature limit; f), type of carburizing material; g), frequency of power supply, it is characterized in that: the specific working steps of this method are: Step 1. The workpiece is sent into the heating chamber After the workpiece is ready, the front door of the quenching chamber and the front door of the heating chamber are opened, and it is directly sent into the heating chamber; Step 2. Vacuum The vacuum valve of the vacuum system and the vacuum system of the quenching chamber are opened to start vacuuming, and the frequency converter of the vacuum pump motor is set at the normal power supply frequency; Step 3. Heat Run When the vacuum reaches 1torr or less than 1torr, start heating, and the vacuum pump continues to run; Step 4. Continue soaking After the temperature reaches the carburizing temperature, continue to run the soaking program until the workpiece temperature is uniform; Step 5. Inverter working After entering the carburizing process, according to the process, the frequency converter will reduce the frequency to 60%-5% of the normal frequency, and the vacuum pump will maintain a small suction volume; Step 6. Inject carburizing material The carburizing agent control valve is opened and a certain amount of carburizing material is injected; Step 7. Set the value When the pressure in the furnace reaches the set value, use the frequency converter to control the suction volume of the vacuum pump and maintain the furnace pressure at the set value; Step 8. Vacuum Gauge Display Working When the gas in the furnace undergoes carburizing reaction, PIRANI vacuum gauge display V1 and film vacuum gauge display V2 begin to show different readings. When the ratio of PIRANI vacuum gauge display V1/film vacuum gauge display V2 is constant, the frequency converter will Adjust to normal power supply frequency, vacuumize; Step 9. Repeat execution After staying for a period of time for diffusion, repeat the process of steps 5, 6, 7, and 8; Step 10. Automatic Control The number of repetitions of step 9 and the time of each residence and diffusion are automatically controlled by the computer according to the carburizing requirements; Step 11. Cool down When the carburizing and diffusion stages are completed, the cooling begins; Step 12. Workpiece loading When the temperature drops to the quenching temperature, the front door of the heating chamber is opened, and the workpiece is moved into the quenching chamber; Step 13. Specified pressure Send the workpiece to the quenching lifting table, close the front door of the heating chamber, and inject nitrogen N2 into the heating chamber through the stamping pipeline until the specified pressure; Step 14. Quenching Stroke The quenching lifting platform is immersed in the oil tank to perform the quenching stroke. 4. The heat treatment process method applied to the dynamic control system of a low-pressure carburizing heat treatment furnace according to claim 3, characterized in that: the computer and control software use the input parameters to perform dynamic full-range control, and the computer uses the input parameters The parameters determine the following control conditions: a), carburizing pressure; b), carburization and diffusion time.

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