A bar finish rolling and controlled cooling system and a controlled cooling method

Abstract

The application discloses a kind of bar finish rolling control cooling system and control cooling method, control cooling system includes the front cooling device, finish rolling entrance flying shear, finishing rolling unit, rear cooling device and finish rolling exit flying shear sequentially arranged on rolling line, the finishing rolling unit is made of multiple rolling mills in series, the front cooling device is connected with middle rolling unit rolling line before, the finish rolling exit flying shear is connected with cooling bed after, the front cooling device, rear cooling device are made of one or more cooling device;Control cooling method includes finish rolling front cooling, entrance flying shear cut head tail, finishing rolling unit rolling, finish rolling rear cooling, exit flying shear cut fixed size and cooling bed air cooling and so on process.The application can effectively reduce the cooling intensity of finish rolling exit rolling after rolling by reasonable equipment configuration and cooling process, so as to avoid the appearance of water cooling closed loop and martensite organization, and the resulting yin and yang surface and its bending phenomenon, can provide size precision high, surface quality good, temperature uniform, better microstructure and performance bar finished product.

Description

Technical Field

[0001] This invention belongs to the field of steel metallurgical rolling equipment technology, specifically relating to a bar precision rolling controlled cooling system and controlled cooling method. Background Technology

[0002] In bar finishing rolling, controlled cooling equipment is used to control the cooling rate of the rolled piece after rolling, ensuring rapid cooling to the phase transformation region and preventing rapid austenite grain growth. This results in a fine-grained structure, improved final strength, enhanced mechanical properties, and good surface quality of the finished product. Currently, rolling lines equipped with water-cooling devices typically use multiple water tanks arranged in series before the upper cooling bed after finishing rolling. This concentrated cooling section easily leads to uneven cooling of the steel, especially in the finishing rolling of larger diameter bars. This can cause abnormal structures such as quenching and tempering on the surface. Therefore, high-intensity post-rolling cooling is often accompanied by large temperature differences in the rolled piece and bending at the head and tail of the upper cooling bed. In severe cases, a water-cooling closed loop forms in the macroscopic metallographic structure, and tempered martensite appears in the microstructure of the finished base circle, failing to meet the requirements of the new national standard GB / T 1499.2-2018 for hot-rolled ribbed steel bars. These problems are particularly pronounced in older bar production lines.

[0003] In summary, how to solve the problems of large temperature difference in the rolled stock and bending at the head and tail of the upper cooling bed after bar rolling and cooling, as well as the formation of a water-cooled closed loop in the macroscopic metallographic structure and the appearance of tempered martensite in the microscopic structure, and how to provide stable and uniform mechanical properties for bar production, especially for older bar production lines built in earlier years, are urgent problems to be solved. At the same time, to implement the TMCP thermomechanical rolling process, finishing rolling is also required within a more suitable temperature range. Summary of the Invention

[0004] The purpose of this invention is to provide a bar finishing mill controlled cooling system and method with reasonable equipment configuration, front and rear cooling of the finishing mill, which can avoid water cooling closed loop and martensitic structure, as well as the resulting negative and positive surfaces and bending phenomena, improve the microstructure and properties of finished rolled products, reduce alloy costs, and improve product quality.

[0005] The first objective of this invention is achieved as follows: a bar milling controlled cooling system, comprising a front cooling device, a finishing mill inlet flying shear, a finishing mill unit, a finishing mill outlet flying shear, and a finishing mill outlet flying shear arranged sequentially on the rolling line. The finishing mill unit is composed of multiple rolling mills connected in series. The front cooling device is connected to the intermediate rolling mill unit before the front cooling device, and the finishing mill outlet flying shear is connected to the cooling bed after the front cooling device. The front cooling device and the rear cooling device are composed of one or more coolers.

[0006] The second objective of this invention is achieved by providing a controlled cooling method for a bar milling controlled cooling system, the method comprising the following steps:

[0007] 1) Pre-cooling before finishing: The target billet of the intermediate rolling mill enters the pre-cooling device for pre-cooling before finishing, and then is sent to the flying shear at the finishing mill inlet. The temperature before pre-cooling is 950-1070℃, and the temperature after pre-cooling is 800-930℃.

[0008] 2) The entry flying shear removes the irregular head and tail of the rolled piece, and then immediately sends it into the finishing mill.

[0009] 3) Finishing mill rolling: The finishing mill performs six passes of finishing rolling on six stands until the finished bar is rolled into the target size.

[0010] 4) Cooling after finishing rolling: After the finished bar exits the finishing mill, it enters the cooling device for post-rolling cooling. The temperature after cooling after finishing rolling is 720-900℃.

[0011] 5) After the finished bars are cut to length by the exit flying shear and then air-cooled on the cooling bed, the finished bars are air-cooled on the cooling bed after being cut to length by the exit flying shear of the finish rolling mill. The inlet temperature of the cooling bed is 700-960℃.

[0012] The present invention has the following technical effects: by adopting the pre-entry controlled cooling process before finishing milling, the cooling intensity after finishing milling can be effectively reduced, thereby avoiding the occurrence of water cooling closed loop and martensitic structure, as well as the resulting negative and positive surfaces and bending phenomena. Through reasonable equipment configuration and pre- and post-finish mill cooling processes, the output efficiency of the entire unit is further improved, and bar products with high dimensional accuracy, good surface quality, uniform temperature, better microstructure and performance can be provided.

[0013] 1. This invention, through reasonable equipment configuration and pre- and post-cooling processes of the finishing mill, can realize temperature-controlled rolling processes of low-temperature finishing rolling and segmented water cooling, thereby achieving the production of alloy-reduced hot-rolled steel bars.

[0014] 2. This invention, through reasonable equipment configuration and pre- and post-cooling processes at the finishing mill, controls the cooling rate of the rolled piece after rolling in bar rolling production, enabling it to cool rapidly to the phase transformation region and preventing rapid austenite grain growth. This results in the finished product having a fine grain structure, improving the final strength and toughness of the steel, enhancing the overall mechanical properties of the final product, and ensuring good surface quality of the rolled piece exiting the finishing mill.

[0015] 3. Through reasonable equipment configuration and cooling processes before and after the finishing mill, this invention can further reduce the intensity of post-rolling cooling at the exit of the finishing mill, thereby avoiding the formation of a water-cooling closed loop, avoiding serious macroscopic metallographic problems such as tempered martensite microstructure in the finished base circle, and avoiding the large temperature difference of the rolled piece and the bending problems at the head and tail of the upper cooling bed and the phenomenon of uneven surfaces that are accompanied by high-intensity post-rolling cooling, thus better meeting the requirements of the national standard GB / T 1499.2-2018 for hot-rolled ribbed steel bars;

[0016] 4. Furthermore, through reasonable equipment configuration and cooling processes before and after the finishing mill, the present invention can implement the TMCP thermomechanical rolling process for bar rolling, thereby reducing the cost of steel alloy consumption.

[0017] 5. This invention is particularly suitable for modifying the cooling devices and processes before and after the finishing mill in older bar production lines built in earlier years, with particularly significant results. It is applicable to the production of hot-rolled ribbed steel bars with diameters of Ф12~Ф22 mm, and can be extended to the production of hot-rolled ribbed steel bars with diameters of Ф23~Ф50 mm. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the cooling system structure of the present invention;

[0019] Figure 2 This is a process flow diagram of the controlled cooling method of the present invention;

[0020] In the diagram: 1-Bar stock, 2-Front cooling device, 3-Finishing mill inlet flying shear, 4-Finishing mill unit, 5-Post-cooling device, 6-Finishing mill outlet flying shear, 7-Cooling bed. Detailed Implementation

[0021] The present invention will be further described below with reference to the accompanying drawings, but this is not intended to limit the present invention in any way. Any modifications or substitutions made based on the teachings of the present invention shall fall within the protection scope of the present invention.

[0022] As attached Figures 1-2 The present invention discloses a bar finishing rolling controlled cooling system, which includes a front cooling device 2, a finishing mill inlet flying shear 3, a finishing mill unit 4, a rear cooling device 5, and a finishing mill outlet flying shear 6 arranged sequentially on the rolling line. The finishing mill unit 4 is composed of multiple rolling mills connected in series. The front cooling device 2 is connected to the intermediate rolling mill unit before the rolling line, and the finishing mill outlet flying shear 6 is connected to the cooling bed 7 after the rolling line. The front cooling device 2 and the rear cooling device 5 are composed of one or more coolers.

[0023] The finishing mill 4 is a six-stand finishing mill.

[0024] The post-cooling device 5 consists of three sections of coolers, each section equipped with two sets of water tanks. Each section is ≥5000mm long, and the total length is ≥20000mm. Only a distance of ≥20000mm is required between the finishing mill 4 and the finishing mill exit flying shear 6 to accommodate the three-section post-cooling device 5. In the three-section post-cooling device 5, each section is ≥5000mm long and consists of two sets of water tanks. Preferably, the cooler and conduit length of each set of water tanks is ≥600mm. Preferably, the total length of the three-section post-cooling device 5 is ≥20 meters, including the inlet guide groove and conduit, and the outlet converging conduit length.

[0025] The post-cooling device 5 includes a forward cooling device and a reverse cooling device. The forward cooler of the forward cooling device is a swirl-type cooler, and the reverse cooler of the reverse cooling device is a shell-and-tube cooler. The nozzle gap between the forward cooler and the reverse cooler is adjustable and can be preset. The post-cooling device 5 consists of a water tank, a support beam, a forward cooling device (including a forward cooler and a base), a reverse cooling device (including a reverse cooler and a base), and a water tank cover. The forward cooler and the reverse cooler can be installed offline onto the base, and then the cooler, along with the base, is hoisted onto the support beam of the rolling line and fixed with bolts. The forward cooler, the reverse cooler, and the base, as well as the base and the support beam, are fitted with appropriate machining precision and tolerances to ensure installation accuracy. Preferably, the alignment accuracy of each line of the bar stock 1 is ≤ ±0.3 mm, ensuring that the forward cooler and the reverse cooler in each of the two positions are interchangeable and that the bar stock 1 is well aligned.

[0026] The forward cooler and reverse cooler of the post-cooling device 5 can be selected and adjusted according to different diameter specifications, uniform heat exchange, and the sealing water requirements of each inlet and outlet section, so as to obtain the required cooling effect on the bar stock 1. When changing specifications for rolling, the forward cooler, reverse cooler, transition pipe, and empty pipe can be pre-installed offline on the base, and then the base can be hoisted and replaced on the support beam of the rolling line. After tightening the fixing bolts, the cover can be closed.

[0027] The swirl-type positive cooler features a columnar water jet with a cone angle of 35–55° and a spiral angle of 10–25°, cooling the bar stock 1. The swirl-type cooler shell contains a water flow channel structure formed by a bevel helical gear and a funnel-shaped sleeve, as well as a spiral nozzle structure with gradually narrowing channels. The bevel helical gear has a cone angle of 35–55° and a spiral angle of 10–25°. The sleeve-type reverse cooler connects to a sleeve after the direct-injection annular nozzle. Cooling water flows from the annular nozzle and cools the bar stock 1 within the sleeve. The cone angle between the annular nozzle slit and the bar stock axis is 35–55°. The size of the water flow channel formed by the bevel helical gear and the funnel-shaped sleeve within the swirl-type cooler shell can be pre-adjusted by selecting different bevel helical gear tooth thicknesses, further pre-adjusting the size of the columnar water jet from the swirl-type positive cooler. The size of the annular cooling water flow in the sleeve-type reverse cooler can also be pre-adjusted by pre-setting the structural spacing of the annular nozzle slits.

[0028] The positive cooler and reverse cooler can be partially replaced with transition pipes and empty pipes to achieve intermittent cooling. Each water tank group can be arbitrarily configured with any two of the following four components: positive cooler, reverse cooler, transition pipe, and empty pipe. Two positions within each water tank group allow for the arbitrary installation and interchange of these four components. This satisfies the cooling, uniform heat exchange, and water sealing requirements for bar stock 1 of different diameters, achieving the desired ideal cooling effect and meeting the mechanical properties and metallographic structure requirements of national standards.

[0029] The pre-cooling device 2 is a Venturi tube cooler.

[0030] The Venturi cooler has a length ≥3000mm, a water supply flow rate ≥700m³ / h, and a water pressure of 1.0~3.0Mpa. The Venturi (turbulent flow) cooler, with a length ≥3000mm, is supplied with water by a single pump, with a water supply flow rate ≥700m³ / h and a water pressure of 1.0~3.0Mpa. Preferably, the pre-cooling device 2 is a single section, but it can also be configured as two sections if necessary.

[0031] The cooling sections and retracting sections of the aftercooling device 5 are each equipped with a protective cover to reduce the impact of fumes generated during cooling on the on-site environment and ensure personnel safety. Preferably, the protective covers are made of stainless steel with a thickness of not less than 4mm, and two covers are arranged as a set.

[0032] The main pipe and branch pipes of the pre-cooling device 2 and the post-cooling device 5 are all connected by rigid pipes made of stainless steel with a wall thickness of ≥4mm. The branch pipes and the bottom beam are connected by stainless steel flexible metal hoses with a pressure of 3MPa.

[0033] Both the pre-cooling device 2 and the post-cooling device 5 are equipped with independent flow monitoring and valve control systems, which can reasonably and timely adjust the water inlet and pressure of the cooler.

[0034] In the aforementioned front cooling device 2 and rear cooling device 5, the base, support beam, and components fixed to the base and support beam are made of stainless steel. Preferably, the cooler bracket is made of stainless steel with improved wear resistance and corrosion resistance. Preferably, the positive cooler, reverse cooler, transition conduit, and empty conduit nozzle are made of alloy material with higher wear resistance and corrosion resistance.

[0035] The main control system of the first section of the post-cooling device 5 is a centralized remote control system. Through regulating valves and pressure and flow detection elements, it remotely regulates the overall water flow and pressure of the first section. The main and branch pipe control systems of the second and subsequent sections of the post-cooling device 5 all possess dual control functions: centralized remote control and local manual adjustment control. Stainless steel pneumatic regulating valves and pressure and flow detection elements are installed to achieve single-point adjustment control of each single-line bar stock 1 during the slitting rolling process. All stainless steel pneumatic regulating valves can be centrally controlled in the finishing mill operating room, with valve position, flow, and pressure signals and feedback provided.

[0036] In the pre-cooling device 2 and post-cooling device 5, the pressure and flow measurement elements, including the control input and feedback signals required by the pneumatic regulating valve, are connected to the control box of the programmable controller via cables. This allows for the creation of a monitoring screen, system programming, debugging, and integration. The programmable controller centrally collects signals and connects the flow and pressure signals to the monitoring operating system via Ethernet or fiber optic communication. The monitoring computer is located in the finishing mill main control room and has the functions of real-time monitoring of pressure and flow data required by the HMI screen and remote control of the regulating valve position. It also establishes a pressure and flow tracking database for monitoring and retrieval, as well as other necessary monitoring, operation, and trend analysis functions. Simultaneously, the existing high-temperature signals from the rolling mill's initial rolling, finishing mill, and upper cooling bed pyrometers, as well as real-time data such as furnace number, steel grade, and rolling speed, are connected to the tracking database of the signal monitoring system for monitoring and retrieval.

[0037] Before the rolled piece enters the pre-cooling device of the finishing mill, the heat detection signal of the sixth stand of the finishing mill 4 is collected, and the first flow regulating valve of the post-cooling device 5 is controlled to realize the automatic control of the pneumatic regulating valve, so as to reasonably adjust the flow rate and appropriately adjust the cooling intensity of the head and tail of the bar rolled piece 1 to ensure the uniformity of cooling of the head, middle and tail of the bar rolled piece 1.

[0038] A controlled cooling method for a bar finishing rolling system, the method comprising pre-finishing cooling, inlet fly shearing of the head and tail, finishing mill rolling, post-finishing cooling, outlet fly shearing for length setting, and air cooling on a cooling bed, specifically including the following steps:

[0039] 1) Pre-cooling before finishing: The target billet of the intermediate rolling mill enters the pre-cooling device for pre-cooling before finishing, and then is sent to the flying shear at the finishing mill inlet. The temperature before pre-cooling is 950-1070℃, and the temperature after pre-cooling is 800-930℃.

[0040] 2) The entry flying shear removes the irregular head and tail of the rolled piece, and then immediately sends it into the finishing mill.

[0041] 3) Finishing mill rolling: The finishing mill performs six passes of finishing rolling on six stands until the finished bar is rolled into the target size.

[0042] 4) Cooling after finishing rolling: After the finished bar exits the finishing mill, it enters the cooling device for post-rolling cooling. The temperature after cooling after finishing rolling is 720-900℃.

[0043] 5) After the finished bars are cut to length by the exit flying shear and then air-cooled on the cooling bed, the finished bars are air-cooled on the cooling bed after being cut to length by the exit flying shear of the finish rolling mill. The inlet temperature of the cooling bed is 700-960℃.

[0044] In step 4), for finishing mills with pre-finishing and finishing division, two finishing and cooling sections are added at the pre-finishing exit. The temperature after cooling at the pre-finishing exit is 780-930℃, and the temperature after cooling at the finishing exit is 720-900℃.

[0045] The steps also include pre-setting before rolling. Before the bar finishing rolling, the opening of the regulating valve is remotely controlled from 0 to 100% to reasonably and timely adjust the flow rate and pressure of the cooler inlet of the pre-rolling cooling device 2 and the post-rolling cooling device 5 to meet the cooling temperature process parameter requirements of bars with different diameters. The gap of the nozzle of the positive cooler of the post-cooling device 5 can be pre-adjusted. By pre-selecting different tooth thicknesses of the conical helical gears, the size of the water flow channel formed by the conical helical gear and the funnel-shaped sleeve in the shell of the vortex cooler is pre-adjusted, and the size of the columnar water flow sprayed by the vortex positive cooler is pre-adjusted to meet the cooling temperature process parameter requirements of bars with different diameters. The gap of the nozzle of the reverse cooler of the post-cooling device 5 can be pre-adjusted. By pre-adjusting the spacing of the structural plates, the gap of the annular nozzle is pre-adjusted, and the size of the annular cooling water flow of the reverse cooler of the sleeve-type cooler is pre-adjusted to meet the cooling temperature process parameter requirements of bars with different diameters.

[0046] In step 4), the post-rolling cooling consists of three or more sections, including an inlet guide groove and guide pipe, six sets of water tanks in three sections, and an outlet converging guide pipe. Each section consists of two sets of water tanks. Each set of water tanks can be arbitrarily selected and assembled with any two of the following four components: a positive cooler, a reverse cooler, a transition guide pipe, and an empty pass-through guide pipe. Two positions in each set of water tanks allow for the arbitrary installation and interchange of the four components: the positive cooler, the reverse cooler, the transition guide pipe, and the empty pass-through guide pipe. Preferably, the positive cooler and the reverse cooler can be replaced with the transition guide pipe and the empty pass-through guide pipe to achieve intermittent cooling. This satisfies the cooling, uniform heat exchange, and water sealing requirements for bars of different diameters, achieving the desired ideal cooling effect and meeting the mechanical properties and metallographic structure requirements of national standards.

[0047] In step 4), during the post-rolling cooling process, the base and support beam, positive cooler, reverse cooler, transition conduit, and empty passage conduit in each section and each group of water tanks are fitted with appropriate machining precision and tolerances to ensure that the alignment accuracy of each group of water tanks, between each wire rod rolled piece during the split rolling process, and between each section of the entire length, is ≤±0.3 mm, so as to ensure good alignment of the wire rod rolled pieces when passing through the steel.

[0048] In step 4), each section of the cooling section and the gathering section of the entire length of the finishing rolling cooling assembly is equipped with a protective cover to reduce the impact of the flue gas generated during cooling on the on-site environment and to ensure the safety of personnel.

[0049] In step 4), the cooling after finishing rolling has a swirl-type cooler for the positive cooler and a shell-and-tube cooler for the reverse cooler; the gap between the nozzles of the positive cooler and the reverse cooler can be pre-adjusted.

[0050] In step 4), the water jet in the swirl-type positive cooler for post-finishing cooling is a columnar water jet with a density of 35-55. ° Cone angle and 10-25 ° The spiral angle of the jet water cools the bar stock; preferably, the size of the water flow channel formed by the bevel helical gear and the funnel-shaped sleeve in the shell of the swirl cooler can be pre-adjusted by pre-selecting different tooth thicknesses of the bevel helical gears, and the size of the columnar water jet sprayed by the swirl positive cooler can be further pre-adjusted.

[0051] In step 4), the water jet in the sleeve-type cooler after finishing rolling is a shaped water jet. Preferably, the cone angle between the annular nozzle slit and the axis of the bar stock is 35-55°. The size of the annular cooling water jet in the sleeve-type cooler can be pre-adjusted by adjusting the structural spacing.

[0052] In steps 1) and 4), the first section of the main pipe of the pre-cooling device and post-cooling device of the finishing mill is centrally remotely controlled; the second section and subsequent main pipes and branch pipes are all equipped with centralized remote control and local manual adjustment control functions.

[0053] In steps 1) and 4), the post-rolling cooling device collects the heat detection signal from the outlet of the finishing mill (sixth stand), controls the flow regulating valve of the first stage of the post-rolling cooling device, makes reasonable flow adjustments, and appropriately adjusts the cooling intensity of the head and tail of the bar to ensure the uniformity of cooling of the head, middle and tail of the bar.

[0054] In steps 1) and 4), the pre-cooling device and post-cooling device for finishing milling are controlled by a programmable logic controller (PLC). The monitoring computer HMI screen has real-time monitoring functions for pressure and flow data, as well as remote control functions for regulating valve positions. It can also build a pressure and flow tracking database for monitoring and retrieval, and perform other necessary monitoring, operation, and trend analysis functions. Simultaneously, existing real-time data such as temperature signals from the initial rolling mill, the finishing mill, and the upper cooling bed pyrometer, as well as furnace number, steel grade, and rolling speed, are integrated into the tracking database of the signal monitoring system for monitoring and retrieval.

[0055] The present invention will be further described in detail below through embodiments:

[0056] Example 1

[0057] like Figure 1 As shown, the φ12mm four-slit rolling process is followed by cooling before finishing. Cooling after finishing is shown in the table below. The upper cooling bed temperature is controlled at 910–920℃, with no uneven surfaces, straight beginnings and ends, a ReL of 445MPa, and normal metallographic properties. Hot-loaded billets have a ReL of 440–450MPa, while cold-loaded billets have a ReL of 410–415MPa.

[0058]

[0059] Example 2

[0060] like Figure 1 As shown, the φ14mm diameter was four-slit rolled, and cooled briefly before finishing. Cooling after finishing is shown in the table below. The temperature on the upper cooling bed was controlled at 870–890℃. There were no uneven surfaces, the tail was straight, the metallographic structure was normal, and the ReL was 430–455 MPa.

[0061]

[0062] Example 3

[0063] like Figure 1As shown, the pre-cooling of φ16mm and φ18mm bars in the finishing mill is carried out without cooling, with a total pipe pressure of 1.8±0.1MPa and valve opening of 50-90%. The post-cooling after finishing milling is shown in the table below. The upper cooling bed temperature is controlled at 860-880℃, with straight front and rear ends, a ReL of 445MPa, and normal metallographic properties. Hot billet ReL is 440-450MPa, and cold billet ReL is 410-415MPa.

[0064]

[0065] Example 4

[0066] like Figure 1 As shown, the φ20mm bar underwent pre-rolling cooling without cooling. Post-rolling cooling is shown in the table below. The upper cooling bed temperature was controlled at 860–890℃, the head and tail were still straight, and the macroscopic metallographic structure showed a water-cooled closed loop with a ReL of 460 MPa.

[0067]

[0068] Example 5

[0069] like Figure 1 As shown, the cooling section before the finishing mill of φ20mm bar is opened, with a total pipe pressure of 1.8±0.1Mpa and a valve opening of 50~90%. The cooling after finishing mill is shown in the table below. The temperature of the upper cooling bed is controlled at 910~920℃, with no uneven surfaces, straight beginnings and ends, normal metallographic structure, and ReL440Mpa.

[0070]

[0071] Example 6

[0072] like Figure 1 As shown, the pre-cooling of the φ25mm bar finishing mill is in two stages, with a total pipe pressure of 2.1±0.1Mpa, valve opening of 70~90%, pre-cooling temperature of 1000~1020℃, and post-cooling temperature of 980~1000℃; post-cooling is shown in the table below, with a post-cooling temperature of 860~880℃; the upper cooling bed temperature is controlled at 850~870℃, with no eccentric surfaces, straight heads and tails, normal metallographic structure, and ReL445~450Mpa.

[0073]

[0074] Example 7

[0075] like Figure 1As shown, the pre-cooling of the φ28mm bar finishing mill has two stages, with a main pipe pressure of 2.1±0.1 MPa, valve opening of 80-100%, and a pre-cooling temperature of 990-1015℃ and a post-cooling temperature of 970-1005℃. Post-cooling is shown in the table below, with a post-cooling temperature of 880-900℃. The upper cooling bed temperature is controlled at 860-890℃, with no uneven surfaces, straight beginnings and ends, normal metallographic structure, and a ReL of 430-45 MPa.

[0076]

[0077] Example 8

[0078] like Figure 1 As shown, the pre-cooling of the φ32mm bar finishing mill has two stages, with a total pipe pressure of 2.1±0.1 MPa, valve opening of 80-100%, and a pre-cooling temperature of 980-1005℃ and a post-cooling temperature of 970-995℃. Post-cooling is shown in the table below, with a post-cooling temperature of 880-900℃. The upper cooling bed temperature is controlled at 860-895℃, with no uneven surfaces, straight beginnings and ends, normal metallographic structure, and a ReL of 430-455 MPa.

[0079]

[0080] Example 9

[0081] like Figure 1 As shown, the pre-cooling of the φ32mm bar finishing mill has two stages, with a total pipe pressure of 2.1±0.1 MPa, valve opening of 80-100%, and a pre-cooling temperature of 955-995℃ and a post-cooling temperature of 910-970℃. Post-cooling is shown in the table below, with a post-cooling temperature of 830-880℃. The upper cooling bed temperature is controlled at 825-865℃, with no uneven surfaces, straight beginnings and ends, normal metallographic structure, and a ReL of 435-465 MPa.

[0082]

[0083] When the bar diameter is small, whether or not the bar pre-cooling is turned on has little impact on the quality of the bar finishing mill (Examples 1 and 2). However, when the bar diameter is large, macroscopic metallographic problems such as uneven surface and closed-loop water cooling are likely to occur without pre-cooling of the finishing mill (Examples 3 and 4). These problems can be avoided by turning on the bar pre-cooling of the finishing mill (Examples 5 to 9).

Claims

1. A controlled cooling system for bar milling, characterized in that, It is applicable to the production of hot-rolled ribbed steel bars with diameters of Ф12~22mm, and can be extended to the production of hot-rolled ribbed steel bars with diameters of Ф23~50mm; the controlled cooling system includes a front cooling device (2), a finishing mill inlet flying shear (3), a finishing mill unit (4), a rear cooling device (5), and a finishing mill outlet flying shear (6) arranged sequentially on the rolling line. The finishing mill unit (4) is composed of multiple rolling mills connected in series; the front cooling device (2) is connected to the intermediate rolling mill unit in front, and the finishing mill outlet flying shear (6) is connected to the cooling bed (7) behind; the front cooling device (2) consists of one or two coolers, and the rear cooling device (5) consists of one or two coolers. The device consists of three sections of coolers, each section is equipped with two sets of water tanks, each section is ≥5000mm long and the total length is ≥20000mm; the post-cooling device (5) includes a forward cooling device and a reverse cooling device. The forward cooler of the forward cooling device is a swirl cooler and the reverse cooler of the reverse cooling device is a shell-and-tube cooler; the forward cooler and the reverse cooler can be partially replaced with transition pipes and empty pipes to achieve intermittent cooling; the forward cooling device (2) is a Venturi cooler with a length ≥3000mm, a water supply flow rate ≥700m³ / h, and a water pressure of 1.0~3.0Mpa.

2. The bar milling controlled cooling system according to claim 1, characterized in that, The nozzle gap between the positive cooler and the negative cooler is an adjustable gap, which can be pre-adjusted. Specifically, the nozzle gap of the positive cooler is pre-adjusted by pre-selecting different tooth thicknesses of the bevel gears, and the nozzle gap of the negative cooler is pre-adjusted by pre-adjusting the spacing of the structural plates.

3. The bar finishing rolling controlled cooling system according to claim 1, characterized in that, In the swirl cooler, the jet water is columnar and has a cone angle of 35°~55° and a spiral angle of 10°~25° to cool the bar rolled piece (1). Inside the shell of the swirl cooler, there is a water flow channel structure formed by the cooperation of a bevel helical gear and a funnel-shaped sleeve, as well as a spiral nozzle structure with the channel gradually narrowing. The cone angle of the bevel helical gear is 35°~55° and the spiral angle is 10°~25°. The sleeve-type cooler is connected to the sleeve after the direct-injection annular nozzle. The cooling water flows out from the annular nozzle and cools the bar rolled piece (1) in the sleeve. The cone angle between the gap of the annular nozzle and the axis of the bar rolled piece is 35°~55°.

4. The bar milling controlled cooling system according to claim 1, characterized in that, Both the pre-cooling device (2) and the post-cooling device (5) are equipped with independent flow monitoring and valve control systems, which can reasonably and timely adjust the water inlet and pressure of the cooler.

5. The bar finishing rolling controlled cooling system according to claim 4, characterized in that, The main control system of the first section of the aftercooling device (5) is a centralized remote control system. Through the regulating valve and pressure and flow detection elements, the overall water flow and pressure of the first section are remotely controlled. The main and branch pipe control systems of the second section and subsequent sections of the aftercooling device (5) have dual control functions of centralized remote control and local manual adjustment control.

6. A cooling method based on the bar finishing rolling cooling system according to any one of claims 1 to 5, characterized in that, The method includes pre-finishing cooling, inlet fly shearing of the head and tail, finishing mill rolling, post-finishing cooling, outlet fly shearing for length, and air cooling on a cooling bed, specifically including the following steps: 1) Pre-cooling before finishing: The target billet of the intermediate rolling enters the pre-cooling device (2) for pre-cooling before finishing and then sends it to the flying shear at the finishing mill inlet (3). The temperature before pre-cooling before finishing is 950~1070℃ and the temperature after pre-cooling before finishing is 800~930℃. 2) The entry flying shear cuts off the head and tail of the workpiece. After the irregular head and tail of the workpiece are cut off by the entry flying shear (3), it is immediately sent into the finishing mill (4). 3) Finishing mill rolling: The finishing mill (4) performs six passes of finishing rolling on six stands until the finished bar of the target size is rolled. 4) Cooling after finishing rolling: After the finished bar exits the finishing mill, it enters the cooling device (5) for cooling after rolling. The temperature after cooling after finishing rolling is 720~900℃. 5) The finished bar after finishing milling is cut to length by the exit flying shear (6) and then air-cooled on the cooling bed (7). The inlet temperature of the cooling bed (7) is 700~960℃.

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