A water-cooled annealing system and process for ductile iron pipes

Abstract

The present invention discloses a water-cooled annealing system and process for centrifugal ductile iron pipes, belonging to the field of centrifugal ductile iron pipe production. On the basis of the original annealing furnace and annealing process, a compressed air cooling device is added. This device can automatically identify the specifications of the pipes coming out of the annealing furnace and accurately measure the temperature of each pipe coming out of the furnace. According to the measured specifications and temperatures of the pipes, through algorithm control, it automatically adjusts the flow rate of the compressed air sent out, so that each specification of pipe is cooled at a predetermined cooling rate. At the same time, the measured temperature value of the pipe coming out of the furnace is fed back to the temperature control system to adjust the air volume of the fast-cooling section and slow-cooling section of the annealing furnace in real time, so that the temperature of the pipe coming out of the furnace meets the target requirement value. By precisely controlling the temperature of the pipe coming out of the furnace and the cooling rate after coming out of the furnace, the present invention enables about 15%-25% of the austenite in the pipe material structure to transform into pearlite, while increasing the tensile strength of the pipe material and slightly reducing the elongation after fracture of the pipe material.

Description

Technical Field

[0001] The present invention relates to the field of production and manufacturing of centrifugal ductile iron pipes, in particular to a water-cooled centrifugal ductile iron pipe annealing system and its process. Background Art

[0002] In the production of traditional water-cooled centrifugal ductile iron pipes, in order to eliminate free cementite and pearlite in the as-cast state, two-stage annealing is required. At about 950°C in the high-temperature stage, free cementite decomposes into graphite and austenite. In the furnace cooling stage, austenite decomposes into graphite and ferrite. Usually, the outlet temperature of small-sized ductile iron pipes with DN80 - DN300 is 600°C - 630°C, and the outlet temperature of medium and large-sized ductile iron pipes with DN350 - DN1000 is 650°C - 710°C. After being discharged from the furnace, they are all air-cooled. Although the cooling rate of small-sized ductile iron pipes can reach 80°C / min, the outlet temperature is relatively low, and austenite has basically decomposed, and almost no austenite transforms into pearlite. For medium and large-sized ductile iron pipes, although the outlet temperature is relatively high and there is still a part of austenite that has not decomposed completely when discharged from the furnace, its cooling rate is 20°C - 40°C / min, and the remaining austenite cannot transform into pearlite and finally decomposes into graphite and ferrite. In production, in order to prevent the existence of pearlite from affecting the performance of the pipe material (when the pearlite content exceeds 45%, the elongation after fracture is significantly reduced), the common practice is to retain 5% - 10% of pearlite in the matrix structure after annealing. Although the elongation level is relatively high (basically maintained at about 15% - 20%), the minimum tensile strength can only be stabilized at 430MPa - 450MPa, and the yield strength is around 270MPa. This is not conducive to fully exploiting the potential of material utilization rate.

[0003] In view of this, it is necessary to develop a water-cooled centrifugal ductile iron pipe annealing system and its process to solve the above problems. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a water-cooled centrifugal ductile iron pipe annealing system and its process, so that 15% - 25% of pearlite is retained in the structure of the annealed pipe, effectively improving the minimum tensile strength of the pipe, increasing the minimum value of the yield strength, and slightly reducing the elongation after fracture of the pipe while increasing the tensile strength of the pipe.

[0005] To solve the above technical problems, the technical solution adopted by the present invention is:

[0006] A water-cooled centrifugal ductile iron pipe annealing system, comprising an annealing furnace and a temperature control system; a heating section, a heat preservation section, a rapid cooling section and a slow cooling section are arranged in the annealing furnace; the temperature control system includes a plurality of thermocouple temperature measuring devices arranged in the annealing furnace, capable of controlling the temperature of each section in the annealing furnace; it further includes a compressed air cooling device arranged on the pipe outlet side of the annealing furnace, an infrared thermometer fixedly arranged on the side of the pipe away from the outlet on the annealing furnace, a pipe diameter identification system arranged beside the infrared thermometer, a lifting support wheel mechanism arranged directly below the compressed air cooling device, and a compressed air flow control system connected to the compressed air cooling device; the infrared thermometer and the pipe diameter identification system are both connected to the temperature control system and the compressed air flow control system; the lifting support wheel mechanism can lift the pipe from the furnace chain and drive the pipe to rotate around its axis; an electromagnetic flow regulating valve capable of adjusting the magnitude of the compressed air flow is arranged between the compressed air cooling device and the compressed air flow control system.

[0007] A further improvement of the technical solution of the present invention lies in that: the compressed air cooling device and the lifting support wheel mechanism are arranged at a position 0.6 m - 1.5 m behind the annealing furnace.

[0008] A water-cooled centrifugal ductile iron pipe annealing process, comprising the following steps:

[0009] Step 1, heat the pipe in the annealing furnace to 920 - 960 °C and keep it warm for 10 - 15 min, quickly cool it to about 830 °C by blowing air in the furnace, and then slowly cool it with the furnace to 720 °C ± 30 °C for discharging, and the specific pipe discharging temperature is determined by the pipe specification size;

[0010] The temperature control system controls the temperature of each section of the heating section, heat preservation section, rapid cooling section and slow cooling section in the annealing furnace to ensure that the measured value of the pipe discharging temperature is controlled within the target set value range;

[0011] The infrared thermometer measures the temperature of the pipe after discharging, and immediately feeds back the initial temperature value of the measured pipe after discharging to the temperature control system, and feeds back the real-time value of the measured temperature to the compressed air flow control system; the pipe diameter identification system synchronously feeds back the pipe specification information to the temperature control system and the compressed air flow control system; the temperature control system adjusts the air volume of the rapid cooling section and the slow cooling section according to the difference between the initial temperature value of the pipe after discharging and the target value, so as to ensure that the measured value of the pipe discharging temperature is controlled within the target set value range;

[0012] Step 2: The lifting idler wheel mechanism lifts the pipe from the furnace chain and can drive the pipe to rotate around its axis, so that the pipe is within the cooling range of the compressed air cooling device and can be evenly air-cooled. The compressed air flow control system receives the pipe specification signal transmitted by the pipe diameter identification system and the real-time temperature signal of the pipe transmitted by the infrared thermometer, and sends the signal of the corresponding compressed air flow rate to be blown for the pipe specification to the electromagnetic flow regulating valve that can adjust the size of the compressed air flow, so as to adjust the flow rate of the compressed air blown according to the different pipe specifications and quickly cool the pipe to below 630°C. When receiving the temperature value signal transmitted by the infrared thermometer equal to 630°C, the electromagnetic flow regulating valve is controlled to close.

[0013] The compressed air flow control system receives the pipe temperature signal in real time, calculates the cooling rate of the pipe in real time, then compares it with the target cooling rate value, and controls the electromagnetic flow regulating valve to increase or decrease the change of the compressed air flow rate in real time, so that the cooling rate accurately meets the target setting value.

[0014] Step 3: The pipe cooled to below 630°C is re-placed on the furnace chain by the lifting idler wheel mechanism and then enters the subsequent fog cooling process with the furnace chain and enters the normal production process.

[0015] A further improvement of the technical solution of the present invention is that in Step 1, usually, the outgoing furnace temperature of medium and large-sized pipes is higher than that of small-sized pipes; the annealing furnace has a function of judging the position distribution of pipes of each specification in the furnace, and the temperature change of the pipes in the annealing furnace is always monitored by the temperature control system. The temperature value of the pipe measured by the infrared thermometer after leaving the furnace is fed back to the temperature control system for rechecking and verifying the outgoing furnace temperature of the pipe; if the outgoing furnace temperature deviates from the target setting value, the temperature control system adjusts the air volume of the fast cooling section and the slow cooling section to adjust the outgoing furnace temperature of the pipe to the target setting value.

[0016] A further improvement of the technical solution of the present invention is that the outgoing furnace temperature of DN1000 specification pipes should reach 750°C; the outgoing furnace temperature of DN100 specification pipes should reach 690°C.

[0017] A further improvement of the technical solution of the present invention lies in: in step 2, the cooling rate of small-sized pipes is relatively fast. Therefore, by adjusting the appropriate blowing flow rate of compressed air, the cooling rate above 630 °C reaches 200 °C / min, and all the austenite that has not been decomposed when leaving the furnace can be transformed into pearlite. While the cooling rate of large-sized ductile iron pipes is relatively slow. By adjusting the appropriate flow rate of compressed air, the cooling rate above 630 °C reaches 100 °C / min. Part of the austenite that has not been decomposed when leaving the furnace is transformed into pearlite, and the other part is decomposed into ferrite and graphite. Finally, a structure containing 15%-25% pearlite + ferrite in the ductile iron matrix is obtained, and there are no carbides and phosphide eutectics.

[0018] A further improvement of the technical solution of the present invention lies in: the target tapping temperature and target cooling rate corresponding to each specification of the water-cooled centrifugal ductile iron pipe are shown in the following table:

[0019]

[0020] Due to the adoption of the above technical solution, the technical progress achieved by the present invention is:

[0021] 1. The compressed air cooling device and its auxiliary devices set in the present invention enable the minimum tensile strength of the annealed pipe material to be increased to more than 500 MPa because 15%-25% of pearlite is retained in the structure of the pipe material. Compared with the traditional minimum tensile strength of 430 MPa, it is increased by 70 MPa; the minimum yield strength is increased to 330 Mpa, compared with the traditional yield strength of 270 MPa, it is increased by 60 MPa, providing a basic condition for the lightweight design of the product.

[0022] 2. Compared with the traditional annealing process, the tapping temperature of the present invention is increased (about 50 °C). Therefore, under the same furnace cooling conditions, the residence time of the centrifugal ductile iron pipe in the slow cooling section is significantly shortened. Further, the length of the slow cooling section of the annealing furnace can be shortened, which not only reduces the investment cost of the annealing furnace (including the furnace body and furnace chain, etc.), but also saves the production site space and effectively improves the production efficiency. Description of the Drawings

[0023] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings;

[0024] Figure 1 It is a schematic layout diagram of the annealing system for water-cooled centrifugal ductile iron pipes provided by the present invention;

[0025] Figure 2 The annealing process curve graph of the ductile iron pipe of the water-cooled centrifuge provided by the present invention;

[0026] Wherein, 1. Annealing furnace; 1-1. Heating section; 1-2. Heat preservation section; 1-3. Quick cooling section; 1-4. Slow cooling section; 2. Temperature control system; 3. Compressed air cooling device; 4. Compressed air electromagnetic flow regulating valve; 5. Infrared thermometer; 6. Pipe diameter identification system; 7. Lifting support wheel mechanism; 8. Compressed air flow control system; 9. Pipe. Specific embodiments

[0027] It should be noted that the terms "including" and "having" and any variations thereof in the description and claims of the present invention and the above drawings are intended to cover non-exclusive inclusion. For example, a process, method, system, product or device that includes a series of steps or units does not necessarily have to be limited to those steps or units clearly listed, but may include other steps or units not clearly listed or inherent to these processes, methods, products or devices.

[0028] The present invention will be further described in detail below with reference to the drawings and embodiments:

[0029] As Figure 1 shown, a water-cooled centrifugal ductile iron pipe annealing system includes an annealing furnace 1 and a temperature control system 2; the annealing furnace 1 is divided into a heating section 1-1, a heat preservation section 1-2, a quick cooling section 1-3 and a slow cooling section 1-4; the temperature control system 2 includes a plurality of thermocouple temperature measuring devices arranged in the annealing furnace 1, which can control the temperature of each section in the annealing furnace 1; it also includes a compressed air cooling device 3 arranged on the pipe outlet side of the annealing furnace 1, an infrared thermometer 5 fixedly arranged on the side of the pipe 9 away from the furnace outlet on the annealing furnace 1, a pipe diameter identification system 6 arranged beside the infrared thermometer 5, a lifting support wheel mechanism 7 arranged directly below the compressed air cooling device 3, and a compressed air flow control system 8 connected to the compressed air cooling device 3; the infrared thermometer 5 and the pipe diameter identification system 6 are both connected to the temperature control system 2 and the compressed air flow control system 8; the lifting support wheel mechanism 7 can lift the pipe 9 from the furnace chain and drive the pipe 9 to rotate around its axis; an electromagnetic flow regulating valve 4 capable of adjusting the size of the compressed air flow is arranged between the compressed air cooling device 3 and the compressed air flow control system 8.

[0030] Specifically, the infrared thermometer 5 is installed on the annealing furnace 1, at approximately the same height as the outgoing pipe 9, but at a certain distance from the pipe 9 to prevent it from being damaged by high temperature. The distance from the pipe 9 is 1.5 m - 2.5 m. The thermocouple temperature measuring device installed in the annealing furnace 1 belongs to a contact thermometer and is distributed in each section (heating section 1-1, heat preservation section 1-2, rapid cooling section 1-3, and slow cooling section 1-4) of the annealing furnace 1 for measuring the furnace temperature. The temperature measurement method of the thermocouple temperature measuring device is different from that of the non-contact infrared thermometer 5.

[0031] Furthermore, the compressed air cooling device 3 and the lifting support wheel mechanism 7 are installed at a position 0.6 m - 1.5 m behind the annealing furnace 1.

[0032] A water-cooled centrifugal ductile iron pipe annealing process includes the following steps:

[0033] As Figure 1-2 shown, the molten iron for preparing the water-cooled centrifugal ductile iron pipe (hereinafter referred to as pipe 9) can be prepared by the method of tempering with an induction furnace or melting pig iron with a cupola. The key requirements for the molten iron composition are as follows: the Si content is 1.8% - 2.1%, the Mn content ≤ 0.3%, the P content ≤ 0.06%, the S content ≤ 0.02%, the Cr content ≤ 0.06%, the Cu content ≤ 0.1%, the total content of Mo and V ≤ 0.01%, and the Ti content ≤ 0.08%.

[0034] Step 1, the annealing furnace 1 heats the pipe 9 to 920 - 960 °C and holds it for 10 - 15 min, which is basically the same as the traditional annealing process. The furnace is blown with air for rapid cooling to about 830 °C, and then slowly cooled in the furnace to 720 °C ± 30 °C for discharging. The temperatures at the end of the rapid cooling section and the slow cooling section are higher than those of the traditional annealing process (traditional annealing process: usually, the outgoing temperature of small-sized ductile iron pipes with DN80 - DN300 is 600 °C - 630 °C, and the outgoing temperature of medium and large-sized ductile iron pipes with DN350 - DN1000 is 650 °C - 710 °C). The purpose is to retain a higher volume fraction of austenite when discharging. The temperature recheck and measurement after the pipe 9 is discharged are completed by the newly added fixed infrared thermometer 5. The initial temperature value of the pipe 9 after discharging is measured and immediately fed back to the temperature control system 2. The real-time temperature value is fed back to the compressed air flow control system 8 behind the furnace. The pipe diameter identification system 6 installed beside the infrared thermometer 5 synchronously feeds back the pipe 9 specification information to the above-mentioned temperature control system 2 and compressed air flow control system 8.

[0035] The specific tapping temperature depends on the size of the pipe 9. Generally, the tapping temperature of medium and large-sized pipes 9 is relatively high (for example, the tapping temperature of a DN1000 pipe 9 should reach 750°C), while that of small-sized pipes 9 is relatively low (for example, the tapping temperature of a DN100 pipe 9 should reach 690°C). Therefore, there is a relatively high content of austenite in the matrix structure of medium and large-sized pipes 9 with higher temperatures that has not decomposed. The annealing furnace 1 has a function to judge the position distribution of pipes 9 of various specifications in the furnace. The temperature control system 2 only collects the maximum value of the temperature measurement of the tapped pipes. If the tapped temperature deviates from the target set value, the temperature control system adjusts the air volume of the rapid cooling section 1-3 and the slow cooling section 1-4 to adjust the tapped temperature of the pipe 9 to the target value;

[0036] It should be noted that: the temperature of the tapped pipe is regulated by the temperature control system 2 of the annealing furnace 1. The temperature control system 2 includes temperature measuring devices in the furnace, and the temperature measurement after tapping is for temperature review and confirmation.

[0037] Step 2, the lifting support roller mechanism 7 lifts the pipe 9 from the furnace chain and drives the pipe 9 to rotate around its axis, lifting it into the covered cooling range of the compressed air cooling device 3 to ensure that the pipe 9 can be evenly air-cooled, providing conditions for the uniform air-cooling of the pipe 9. The compressed air flow control system 8 on the compressed air cooling device 3 can receive the pipe 9 specification signal transmitted by the pipe diameter identification system 6 and the real-time temperature signal of the pipe 9 transmitted by the infrared thermometer 5, and send the corresponding blown compressed air flow rate signal to the actuator - the electromagnetic flow regulating valve 4 that can adjust the compressed air flow rate, so as to adjust the blown compressed air flow rate according to the different pipe 9 specifications and quickly cool the pipe 9 to below 630°C. When receiving the temperature value signal transmitted by the infrared thermometer 5 equal to 630°C, the electromagnetic flow regulating valve 4 is controlled to close. In addition, the compressed air flow control system 8 receives the temperature signal of the pipe 9 in real time, calculates the cooling rate of the pipe 9 in real time, then compares it with the target cooling rate value, and controls the electromagnetic flow regulating valve 4 to increase or decrease the compressed air flow rate change in real time, so that the cooling rate accurately meets the target setting value. The cooling speed of small-sized ductile iron pipes (pipe 9) is relatively fast. Therefore, by adjusting the appropriate blown compressed air flow rate, the cooling rate above 630°C can reach 200°C / min, and almost all the austenite that has not been decomposed when leaving the furnace can be transformed into pearlite. While the cooling speed of large-sized ductile iron pipes (pipe 9) is relatively slow. By adjusting the appropriate compressed air flow rate, the cooling rate above 630°C can reach 100°C / min. Part of the austenite that has not been decomposed when leaving the furnace is transformed into pearlite, and the other part is decomposed into ferrite and graphite. Finally, a structure containing 15%-25% pearlite + ferrite in the ductile iron matrix is obtained, and there are no carbides and phosphide eutectics. By increasing a certain proportion of pearlite structure, the tensile strength and yield strength of the pipe material are improved. The target tapping temperature and target cooling rate corresponding to each specification of the water-cooled centrifugal ductile iron pipe are shown in Table 1.

[0038] Table 1 Recommended values of target tapping temperature and cooling rate corresponding to each specification of water-cooled centrifugal ductile iron pipe

[0039]

[0040] Step 3, the pipe 9 cooled to below 630°C is re-placed on the furnace chain by the lifting support roller mechanism 7 and then enters the subsequent fog cooling process with the furnace chain to enter the normal production process.

[0041] Example 1

[0042] DN100mm and DN300mm water-cooled centrifugal ductile iron pipe mixed annealing process flow:

[0043] Step 1: The annealing furnace 1 heats the pipe 9 to 920 - 940 °C and holds for 10 minutes, then enters the rapid cooling section 1 - 3. It is rapidly cooled to about 810 °C in the rapid cooling section 1 - 3, and then enters the slow cooling section 1 - 4. The furnace outlet temperature of the pipe 9 is controlled to ensure that the inner wall temperature at the position within half a meter of the socket end is 690 °C and 700 °C respectively after the DN100mm and DN300mm pipes leave the furnace, measured by the infrared thermometer 5, with an upper and lower deviation not exceeding 5 °C. The measured temperature is fed back to the temperature control system 2. If the temperature is too close to the upper limit, the temperature control system 2 increases the air volume in the rapid cooling section 1 - 3 and the slow cooling section 1 - 4 according to the magnitude of the exceeded value, and vice versa, to ensure that the measured furnace outlet temperature is controlled within the target range.

[0044] Step 2: The compressed air flow control system 8 receives the pipe diameter identification signal of the furnace outlet pipe provided by the pipe diameter identification system 6. If DN300mm is in the front, the compressed air flow control system 8 determines that the average cooling rate requirement for this specification is 175 °C / min. At this time, the pipe 9 has entered the compressed air cooling station, and the roller mechanism 7 drives the pipe 9 to rotate around the axis of the pipe 9 at a rotation speed not lower than 10 r / min in this station, ensuring that the entire circumferential surface of the pipe 9 is evenly cooled by the compressed air during the cooling process. At the same time, the compressed air flow control system 8 can also receive the temperature value of the inner wall of the socket end of the pipe 9 provided by the infrared thermometer 5 in real time. The compressed air flow control system 8 opens the electromagnetic flow regulating valve 4 on the compressed air pipeline, and the pipe 9 starts to cool down. The control system also calculates the actual cooling rate of the pipe 9 in real time and compares it with the target cooling rate, and adjusts the compressed air flow in a timely manner to make the final cooling rate of the pipe 9 match the target cooling rate. When the infrared thermometer 5 measures that the temperature of the pipe 9 drops to 630 °C, the compressed air flow control system 8 receives the signal and sends a signal to close the compressed air to the electromagnetic flow regulating valve 4 to terminate the compressed air cooling.

[0045] Step 3: The DN300mm pipe stops rotating and leaves the lifting roller mechanism 7, and is re - placed on the furnace chain and enters the subsequent fog cooling process along with the furnace chain.

[0046] Similarly, the DN100mm pipe has the same process, except that the parameters given by the compressed air flow control system 8 are different, ensuring that the cooling rate of the DN100mm pipe above 630 °C reaches 200 °C / min.

[0047] Example 2

[0048] The mixed annealing process flow of DN400mm and DN1000mm water - cooled centrifugal ductile iron pipes:

[0049] Step 1: The annealing furnace 1 heats the pipe 9 to 940 - 960 °C and holds for 10 min, then enters the rapid cooling section 1 - 3. It is rapidly cooled to about 830 °C in the rapid cooling section 1 - 3, and then enters the slow cooling section 1 - 4. The furnace outlet temperature of the pipe 9 is controlled to ensure that the inner wall temperature at the position within half a meter of the socket end is 705 °C and 750 °C respectively after the DN400mm and DN1000mm pipes leave the furnace, measured by the infrared thermometer 5, with an upper and lower deviation not exceeding 5 °C. The measured temperature is fed back to the temperature control system 2. If the temperature is too close to the upper limit, the temperature control system 2 increases the air volume in the rapid cooling section and the slow cooling section according to the magnitude of the excess value, and vice versa, to ensure that the measured furnace outlet temperature is controlled within the target range.

[0050] Step 2: The compressed air flow control system 8 receives the pipe diameter identification signal of the furnace outlet pipe provided by the pipe diameter identification system 6. If DN1000mm is in the front, the compressed air flow control system 8 determines that the average cooling rate requirement for this specification is 100 °C / min. At this time, the pipe 9 has entered the compressed air cooling station, and the supporting roller mechanism 7 drives the pipe 9 to rotate around the axis of the pipe 9 at a rotation speed not lower than 10 r / min at this station, ensuring that the entire circumferential surface of the pipe 9 is evenly cooled by compressed air during the cooling process. At the same time, the compressed air flow control system 8 can also receive the temperature value of the inner wall of the socket end of the pipe 9 provided by the infrared thermometer 5 in real time. The compressed air flow control system 8 opens the electromagnetic flow regulating valve 4 on the compressed air pipeline, and the pipe 9 starts to cool down. The control system also calculates the actual cooling rate of the pipe 9 in real time and compares it with the target cooling rate, and adjusts the compressed air flow in a timely manner to make the final cooling rate of the pipe 9 match the target cooling rate. When the infrared thermometer 5 measures that the temperature of the pipe 9 drops to 630 °C, the compressed air flow control system 8 receives the signal and sends a signal to close the compressed air to the electromagnetic flow regulating valve 4 to terminate the compressed air cooling.

[0051] Step 3: The DN1000mm pipe stops rotating and leaves the supporting roller mechanism 7, and is re - placed on the furnace chain and enters the subsequent mist cooling process with the furnace chain.

[0052] Similarly, the DN400mm pipe also has the same process, except that the parameters given by the compressed air flow control system 8 are different, ensuring that the cooling rate of the DN400mm pipe above 630 °C reaches 160 °C / min.

[0053] After testing the DN100mm and DN300mm water - cooled centrifugal ductile iron pipes prepared in Example 1 and the DN400mm and DN1000mm water - cooled centrifugal ductile iron pipes prepared in Example 2, 15% - 25% of pearlite is retained in the pipe microstructure, and the minimum tensile strength of the pipes all reaches above 500 MPa; the minimum yield strength is increased to 330 Mpa.

[0054] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A water-cooled centrifugal ductile iron pipe annealing system, comprising an annealing furnace (1) and a temperature control system (2); a heating section (1-1), a heat preservation section (1-2), a rapid cooling section (1-3) and a slow cooling section (1-4) are arranged in the annealing furnace (1); the temperature control system (2) includes a plurality of thermocouple temperature measuring devices arranged in the annealing furnace (1), capable of controlling the temperature of each section in the annealing furnace (1), and is characterized in that: It further includes a compressed air cooling device (3) arranged on the tube outlet side of the annealing furnace (1), an infrared thermometer (5) fixedly arranged on the side of the annealing furnace (1) away from the outlet tube (9), a pipe diameter identification system (6) arranged beside the infrared thermometer (5), a lifting support wheel mechanism (7) arranged directly below the compressed air cooling device (3), and a compressed air flow control system (8) connected to the compressed air cooling device (3); both the infrared thermometer (5) and the pipe diameter identification system (6) are connected to the temperature control system (2) and the compressed air flow control system (8); the lifting support wheel mechanism (7) can lift the tube (9) from the furnace chain and drive the tube (9) to rotate around its axis; an electromagnetic flow regulating valve (4) capable of adjusting the magnitude of the compressed air flow is arranged between the compressed air cooling device (3) and the compressed air flow control system (8).

2. The water-cooled centrifugal ductile iron pipe annealing system according to claim 1, characterized in that: The compressed air cooling device (3) and the lifting support wheel mechanism (7) are arranged at a position 0.6 m - 1.5 m behind the annealing furnace (1).

3. A water-cooled centrifugal ductile iron pipe annealing process, using the annealing system according to any one of claims 1-2, characterized in that: It includes the following steps: Step 1, heat the tube (9) to 920 - 960 °C in the annealing furnace (1) and keep it warm for 10 - 15 min, quickly cool it to 830 °C by blowing air in the furnace, and then slowly cool it to 720 °C ± 30 °C with the furnace and take it out of the furnace. The specific tube outlet temperature is determined by the size of the tube (9). The temperature control system (2) controls the temperature of each section of the heating section (1-1), heat preservation section (1-2), quick cooling section (1-3), and slow cooling section (1-4) in the annealing furnace (1) to ensure that the measured value of the tube (9) outlet temperature is controlled within the target set value range. The infrared thermometer (5) measures the temperature of the tube (9) after it comes out of the furnace, immediately feeds back the initial temperature value of the measured tube (9) after it comes out of the furnace to the temperature control system (2), and feeds back the real-time value of the measured temperature to the compressed air flow control system (8); the pipe diameter identification system (6) synchronously feeds back the specification information of the tube (9) to the temperature control system (2) and the compressed air flow control system (8); the temperature control system (2) adjusts the air volume of the quick cooling section (1-3) and the slow cooling section (1-4) according to the difference between the initial temperature value of the tube (9) after it comes out of the furnace and the target value to ensure that the measured value of the tube (9) outlet temperature is controlled within the target set value range. Step 2, the lifting idler mechanism (7) lifts the pipe (9) from the furnace chain and can drive the pipe (9) to rotate around its axis, so that the pipe (9) is within the cooling range of the compressed air cooling device (3) and can be evenly air-cooled; the compressed air flow control system (8) receives the pipe (9) specification signal transmitted by the pipe diameter identification system (6) and the real-time temperature signal of the pipe (9) transmitted by the infrared thermometer (5), and sends the signal of the corresponding compressed air flow rate to be blown for the pipe (9) specification to the electromagnetic flow regulating valve (4) capable of adjusting the compressed air flow rate, so as to adjust the blown compressed air flow rate according to the different pipe (9) specifications and quickly cool the pipe (9) to below 630°C. When receiving the temperature value signal transmitted by the infrared thermometer (5) equal to 630°C, the electromagnetic flow regulating valve (4) is controlled to close; The compressed air flow control system (8) receives the pipe (9) temperature signal in real time, calculates the cooling rate of the pipe (9) in real time, then compares it with the target cooling rate value, and controls the electromagnetic flow regulating valve (4) to increase or decrease the compressed air flow rate change in real time, so that the cooling rate accurately meets the target setting value; Step 3, the pipe (9) cooled to below 630°C is re-placed on the furnace chain by the lifting idler mechanism (7) and then enters the subsequent fog cooling process with the furnace chain to enter the normal production process.

4. The water-cooled centrifugal ductile iron pipe annealing process according to claim 3, characterized in that: In Step 1, the outgoing furnace temperature of the medium and large-sized pipes (9) is higher than that of the small-sized pipes (9); the annealing furnace (1) has the function of judging the position distribution of each specification of pipes (9) in the furnace. The temperature change of the pipes (9) in the annealing furnace (1) is always monitored by the temperature control system (2). The temperature value of the pipe (9) measured by the infrared thermometer (5) after leaving the furnace is fed back to the temperature control system (2) for rechecking and verifying the outgoing furnace temperature of the pipe (9); if the outgoing furnace temperature deviates from the target setting value, the temperature control system (2) adjusts the air volume of the fast cooling section (1-3) and the slow cooling section (1-4) to adjust the outgoing furnace temperature of the pipe (9) to the target setting value.

5. The water-cooled centrifugal ductile iron pipe annealing process according to claim 3, characterized in that: The outgoing furnace temperature of the DN1000 specification pipe (9) should reach 750°C; the outgoing furnace temperature of the DN100 specification pipe (9) should reach 690°C.

6. The water-cooled centrifugal ductile iron pipe annealing process according to claim 3, characterized in that: In Step 2, the cooling rate of the small-sized pipes (9) is relatively fast. Therefore, by adjusting the appropriate blown compressed air flow rate, the cooling rate above 630°C reaches 200°C / min, and the austenite that is not decomposed when leaving the furnace can all be transformed into pearlite. The cooling rate of the large-sized ductile iron pipes is relatively slow. By adjusting the appropriate compressed air flow rate, the cooling rate above 630°C reaches 100°C / min. Part of the austenite that is not decomposed when leaving the furnace is transformed into pearlite, and the other part is decomposed into ferrite and graphite. Finally, a structure containing 15%-25% pearlite + ferrite in the ductile iron matrix is obtained, and no carbides and phosphide eutectics are contained.

7. The water-cooled centrifugal ductile iron pipe annealing process according to claim 3, characterized in that: The target outgoing furnace temperature and target cooling rate corresponding to each specification of the water-cooled centrifugal ductile iron pipes are shown in the following table:

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