A New Electrohydraulic Hybrid Energy-Saving System Used on the Reversible Rolling Mills

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Introduction
In the face of the global energy crisis, environmental pollution, increasing stringent emission standards, and the "double carbon" (carbon peak and carbon neutral) vision, the promotion of energy-efcient technologies is one of the initiatives to promote energy saving and emission reduction continuously and to reach carbon peak and carbon neutrality.Regarding energy consumption and carbon emissions, China is currently the world's largest carbon emitter and consumer.Among the 31 sectors of the manufacturing industry, the steel industry accounts for around 15% of the country's carbon emissions, making it the second largest emitter of carbon dioxide after the power industry.To achieve carbon neutrality in the steel industry, energy-saving and energy-reducing designs are adopted in the manufacturing process [1].
Approximately 90% of China's steel is rolled into the material.Steel rolling mills are the equipment to complete the whole rolling process [2].Some small-and mediumsized mills with constant loads and some large openers and slab mills are equipped with fywheels, which are designed to reduce the main motor spike load when rolling milling, increase the main motor load at no load, and uniformly distribute the load in order to improve the transmission's stability and overload capacity.
However, for pure rolling times with a long gap time, no spike load mill and reversible rolling mills should be installed on the fywheel because, in this case, the fywheel storage and energy release role is not signifcant, and the fywheel itself consumes a certain amount of energy as a load.New mills rarely use fywheels.It is also possible to feedback excess power from the mill's main drive motor to the grid through power generation devices.In this method, additional generators and rectifers are required, as well as inverters and other corresponding supporting equipment.
Generally, reversible rolling mills are driven directly by motor rolls to achieve reversible drive [2].Te frequent starting and braking of the drive motor dissipate kinetic braking energy in the form of heat, which contributes to energy loss and a reduction in component service life.When the reversible rolling mills are equipped with an additional energy recovery system, the reversible rolling mills' roll braking energy and surplus power from the original primary drive motor are collected and used to start or accelerate the roll in the next pass until the entire rolling process is completed.Te main drive motor of the mill can be reduced in installed power as well as the heat generated during motor braking is reduced and the motor's service life is extended.A dual-drive model combining the main and auxiliary drives is also created.An energy recovery system can also be ofset by energy savings or increased steel production.
Storage of energy requires having a high energy density (can provide an endless supply of energy), a high power density (can absorb and release high power quickly), a high number of charge and discharge cycles, a high energy conversion efciency, and several other characteristics.In Table 1, diferent energy storage components are compared based on their performance parameters [3][4][5][6][7][8][9].Electric drives ofer zero emissions, low noise, high efciency, strong overload capacity, large starting torques, fast torque responses, ample charging and discharging currents, high-speed regulation efciency, etc.However, they also sufer from a low power density and a low braking energy recovery efciency.Te hydraulic drive is particularly suitable for instantaneous high power demand conditions because of its high power density and low cost [10].In order to reduce emissions and energy consumption, energyregenerative electrohydraulic hybrid drive technologies based on reversible rolling mills are the best options.
Te reversible rolling mills, however, generally roll at a maximum speed of 2 to 7 m/s [2], according to relevant literature.Roll braking produces a small amount of kinetic energy, and the energy recovery device contributes a small amount of this energy back to the central drive system, which presents a challenge in designing the electrohydraulic hybrid drive system confguration for reversible rolling mills.It has neither reported how electrohydraulic hybrid drive systems are used in reversible rolling mills nor the relevant aspect been applied.In this article, we propose a confguration that reduces both peak and valley power of the main drive motor of the reversible rolling mill, as well as recovering kinetic energy from the braking of the rolls.As a result of the incorporated energy recovery system, the reversible rolling mill's braking cycle can be shortened, thereby increasing production yield and reducing rolling cycle time.Presented in this article is the frst proposal for an electrohydraulic hybrid drive for reversible rolling mills.By using a motor control strategy, a hydraulic pump displacement control, and other techniques, the auxiliary power source can be improved for better drive efciency [11].
Tis article is organized as follows: frst, the mechanical system and operating conditions of a reversible rolling mill are illustrated in Section 2. Te proposed system is described in Section 3. Te system parameter matching is developed in Section 4. Simulation modeling, analysis, and calculation are carried out in Section 5. Conclusions are drawn in Section 6.

Composition of the Reversible Rolling Mills and Their Operating Conditions
2.1.Components of the Reversible Rolling Mill.Generally, steel rolling machines consist of three components: the main drive motor, a primary transmission device, and a working machine [2].
In order to roll metal, the motor's output torque is transmitted to the work roll, which rotates at a certain speed.As shown in Figure 1, most steel rolling machinery uses a reducer, gear seat, connecting shaft, and coupling as its main drive device.To compensate for the motor's frequent starting, acceleration, and braking, a lowspeed, high-torque motor must directly drive the work roll in the reversible rolling mill for medium-thickness plates, as shown in Figure 2. Due to the absence of a gear seat and reducer, frictional losses can be reduced and mill productivity can be increased.At the same time, motor fywheel torque decreases signifcantly due to this solution.

Te Operation Mode of Reversible Rolling Mills.
Rollers are rotated by the motor of reversible rolling mills.A low speed is used to bite into the bar and then a higher speed is used to increase its speed.Tis process is repeated until the end of the rolling process, where the speed of the motor is reduced, the roll is thrown out at low speed, then its direction of rotation is changed, and then the reverse rolling is carried out.Tere are two types of velocity diagrams for reversible rolling mills: the triangular velocity diagram and the trapezoidal velocity diagram.Triangular velocity diagrams do not have a constant speed rolling phase such as trapezoidal velocity diagrams.Reversible rolling mills have six stages of speed and torque relationship, which can be seen in the trapezoidal speed diagram in Figure 3: 0, idling constant speed period; 1, idling acceleration period; 2, accelerated rolling period; 3, constant speed rolling period; 4, slow rolling period; 5, idle deceleration period.Rolling speed and torque for the reversible rolling mills are shown in Figure 3, and the speed and torque from t 0 to t 5 stage in Figure 3 are described in Table 2.

Confguration of Energy Recovery System Based on the
Reversible Rolling Mills.Due to the low speed of the reversible mill and the efect of the speed of the recovery pump/motor on recovery efciency, a recovery scheme is proposed with high-speed gearing at roll speed and reduced motor at roll speed.Table 3 shows the confguration of the proposed schemes.Series construction has the advantage that there is no mechanical connection between the motor and the load and that the motor will not be afected by fuctuating loads, but there are more energy conversion links and more changes to the original primary drive.With a parallel structure, the hydraulic pump/motor and motor can be driven together or separately to move the load.In comparison to a non-coaxial parallel structure, the control of the coaxial parallel structure is more complex and requires more changes to the original central drive system.

Structural Scheme and Principle of Energy Recovery System
Based on the Reversible Rolling Mills.Te previous analysis indicates that large amounts of recoverable energy generated 2 Advances in Materials Science and Engineering during frequent braking of the reversible rolling mills, which is converted into thermal energy in the original system by the heat generated by motor resistance, results in energy waste and reduced motor life.As shown in Table 3, the noncoaxial parallel structure does not require signifcant changes to be made in the primary drive system, and the load can be driven by both the motor and the hydraulic pump/motor separately, so we focus on this confguration in this article, while the other confguration options are only discussed as options.A hydraulic energy recovery system consisting of a hydraulic recovery pump/motor, motor, and hydraulic accumulator is introduced based on the rotary hydraulic energy recovery system of construction machinery.Hydraulic recovery pump/ motor added accumulators are adopted as energy recovery modes and electrohydraulic hybrid drives are adopted as energy utilization modes (mainly electric drive, supplemented by hydraulic drive) [12].Figure 4 illustrates the electrohydraulic hybrid drive rotary energy recovery system based on large reversible rolling mills.As a principle of energy recovery and utilization, the auxiliary system starts the hydraulic motor M2, flling the low-pressure accumulators with oil.Te pressure sensor 25 measures the low-pressure accumulator's flling pressure and changes in pressure.Once the low-pressure accumulator flling pressure reaches the set value, the oil pump motor unit 18 stops and the flling is complete.
Te electromagnetic clutch 2 is combined and the main drive motor 1 drives the rolls clockwise when the variable displacement pump/motor 6 rotates clockwise.Once the speed has been reached, the electromagnetic clutch 2 is disengaged, allowing the rolls to spin under inertia, and the variable pump/motor 6 brakes the rolls with the electromagnetic clutch 5 combined.
Terefore, solenoid ball valves 8.3 and 8.4 operate in the lower position when the roller decelerates or brakes counterclockwise.Te hydraulic pump/motor 6 continues to rotate due to the large inertia of the rolls.Tere are two ports on the hydraulic pump/motor 6: one on the high-pressure side and one on the low-pressure side.Currently, the hydraulic pump/motor 6 is in pump mode, with the lowpressure port on the A port.Trough the upper position of the reversing valve 10, the B port of the hydraulic motor draws oil from the low-pressure accumulator 23.1 and 23.2.Te A port of the hydraulic motor produces high-pressure oil, which enters the high-pressure accumulator 13.1 and 13.2 through the solenoid ball valve 8.3 at the lower position     Advances in Materials Science and Engineering so that the roller braking process energy can be recovered, as shown in Figure 5. RED arrows are in the direction of highpressure oil, and BLUE arrows are in the demand of lowpressure oil.
Te main drive motor becomes the primary power source when the roll rotation is started by electromagnetic clutches 2 and 5. Te high-pressure accumulator is used as an auxiliary power source.
When the roll accelerates counterclockwise or starts, the solenoid ball valve 8.4 gets the signal and opens, while the solenoid ball valve 8.3 closes.High-pressure oil is connected to port B and low-pressure oil is connected to port A of the hydraulic motor.Te hydraulic reversing valve ten is in the on position after setting it to the lower position.With the upper position of the solenoid ball valve 8.4, the highpressure accumulators 13.1 and 13.2 drive the rolls of the hydraulic motor.In contrast, the low-pressure oil from the A port is stored in the low-pressure accumulators 23.1 and 23.2 through the lower position of the reversing valve 10. Figure 6 illustrates how the system reuses energy in this way.RED arrows are in the direction of high-pressure oil, and BLUE arrows are in the demand of low-pressure oil.

Simulation Parameter Calculation of Energy
Recovery System of Reversible Rolling Mills  4. Te work roll material is ductile iron, and its density is 7.3 g/cm 3 .Tis study ignores the masses of the shaft and head due to their small sizes.
Equation (1) shows the moment of inertia of one work roll of the four-roller reversible rolling mill: where m is the mass of the roll, r is the roll diameter, h is the roll length, and ρ is the density of the corresponding material of the roll.Diferent materials' rolls or hollow rolls can be calculated according to the actual situation.If the quality of the roll neck and the shaft head cannot be ignored, then this part of the mass should also be added.Tis is usually calculated using equation ( 2) when it comes to electric drive: where J m is the moment of inertia corresponding to the noload torque of the motor, GD 2 is the fywheel moment, which is obtained from the product catalog, and g is the gravitational acceleration taken as 10 m/s 2 .
In the following equation, the roll line speed is calculated as where the maximum rolling speed is v max , the diameter of the roll is D, and the maximum speed of the roll is n rmax .We get the selected motor fywheel moment GD 2 for 156 kg•m 2 and bring in the data from (1) to (3) to get J r for 1.091 (kg•m 2 ), J m for 3.9 (kg m 2 ), and n rmax for 695 (r/min).
Te maximum speed of the ladder speed diagram can be selected within the maximum speed allowed by the motor.For determining the biting and throwing speed, the goal is to obtain a shorter rolling rhythm time, ensure smooth biting of the rolled piece, facilitate the operation, and adjust to the reasonable speed range of the main motor.We get the shortest rolling rhythm when the current pass's throwing speed equals the next pass's biting speed.Tere is no requirement for the shortest rolling rhythm in this article.When the roll speed is set to n p , the kinetic energy of the roll can be recovered.Te roll can be rotated from static to n y when the kinetic energy is recovered.Te rolled piece is assumed to bite in at 3.7 m/s during the idling acceleration period and throw out at 4.375 m/s during the idling deceleration period.Take a bite from the mill and throw out the mill speed based on the actual operating conditions of the selected rolling mill.Bringing in the data, ny is 321.4 r/min, np is 380 r/min, ωy is 33.64 rad/s, and ωp is 39.77 rad/s.

Speed and Time Required for Each Stage of One Pass for the
Roll.We assume that the acceleration a j of the main motor in the acceleration period is 160 r/s 2 and the deceleration b z in the deceleration period is 240 r/s 2 .According to the actual rolling time of the selected mill and rolls, the acceleration and deceleration are calculated.Table 5 shows the duration of each of the abovementioned six stages.

Torque Calculation of the Reversible Rolling Mills and
Parameter Matching of Recovery System.As shown in the following equation, the main motor drive torque of the mill is calculated as where M D is the torque of the main motor, rolling torque is measured by M Z , and M f is the additional friction torque occurring on the roller bearing and transmission mechanism during rolling.Te idling torque, M kon , is the friction torque during idling.Whenever the roller moves at nonuniform speeds, M don is required to overcome inertial forces.Te frst three moments of the transmission rolls for the static moment M j , is calculated by the following equation: In the abovementioned formula, torque is measured when the roller rotates at a constant speed.Tese three items are indispensable for any rolling mill.Generally, rolling torque is the largest.Te rolling torque can be determined in two ways: one by measuring the force of metal on the roller and the other by measuring energy consumption.Equation 6Advances in Materials Science and Engineering where P is the vertical pressure applied to the roller by the metal, i.e., the rolling force, and a is the length of the force arm.In order to eliminate the infuence of geometric factors on the force arm, the force arm coefcient is often determined by Ψ, and the force arm value is determined by following equation.Cold-rolled strip, rolling force arm coefcient Ψ number for 0.33∼0.42,here, take Ψ � 0.42.
where φ 1 is the closing pressure action angle, the contact angle is α j , and l j is the contact arc length, which is calculated by where R is the roll radius and ∆h is the thickness diference before and after rolling.
It is the rolling torque on a single roll that is calculated here.With the help of the following equation, we calculate the displacement of the recovery pump/motor based on the maximum rolling torque of a specifc model 650 four-roller reversible rolling mill: where T is the torque.Te hydraulic pump/motor's maximum displacement is V g , Δp stands for diferential pressure, which is 31.5 MPa, and η mh stands for mechanical efciency, which is taken as 1.Te displacement of the recovery pump/ motor is calculated as 3488.9ml/r according to equation (10).However, it can be seen from the abovementioned calculation that the rolling torque is ample and the recovered energy is limited in the onload rolling stage.If this part of the energy is recovered, it must match the recovery pump/motor with a large displacement, and the cost is high.Moreover, the rolling torque required during onload startup is large, and the torque provided by the recovered braking energy is small, which is not enough to overcome the rolling torque and drive the roll movement.Terefore, this article only gives the confguration of the recovery scheme.
It is possible to use multiple recovery pumps/motors in parallel to reduce the input torque of the recovery pump/ motor.Motors with high speeds can be used in conjunction with pumps and motors to avoid the problems associated with low-speed motors, such as energy efciency or failure to recover braking energy.However, the abovementioned calculation indicates that the rolling torque is ample and the recovered energy is limited during the onload rolling stage.For this part of the energy to be recovered, the pump or motor must have a large displacement, and the cost is high.In addition, during onload startup, the rolling torque required is large, and the torque provided by the recovered braking energy is small, so the roll movement cannot be driven.Te article only describes the confguration of this recovery scheme.
In the no-load period, the static moment is not a rolling moment, and the dynamic moment is calculated by where G is the gravity of the rotating part, the rotating part's inertia diameter is D, and ω stands for the angular velocity of the rotating part, calculated by equation (10).
Te formula for estimating no-load torque is complex, and it is usually estimated by using the following formula: where T m represents the motor's rated torque, P m represents its rated power, and n m represents its rated speed.In this case, M kon is 286.47 N•m, idling acceleration torque M D1 is 295.777N•m, and idling deceleration torque M D5 is 272.509N•m; M D1 matches the hydraulic pump/motor maximum displacement V g , which is 58.97 ml/r.Tis article chooses a two-way variable pump/motor with a maximum displacement of 80 ml/r Figure 7 shows the working speed diagram for the reversible rolling mill roll.

Modeling of System Simulations.
Based on the working principle of the energy recovery system of the reversible rolling mill and the parameters of the components calculated in the previous article, a model of the energy recovery system of the reversible rolling mill is established by AMEsim.Te model consists of a primary motor drive module, a speed control module, an energy recovery module, and an oil replenishment system module.For each stage of the reversible rolling mill, the speed of the main drive motor is fxed for a given thickness of a particular rolled part, so PI speed control is used.Te torque input for rolling diferent mill parts is given by a signal, which controls whether the energy recovery system is connected to the original system by the clutch on/of.Figure 8 illustrates the energy recovery model for reversible rolling mills, and Table 6 shows the system's basic parameters.

Simulation Results and Analysis.
Te following two central studies were carried out through this energy recovery system.
(1) For example, the energy recovery device is started in the frst pass when the roll is thrown out to recover the energy of one working roll of the reversible rolling mill.In other words, during the rolling deceleration period at speed n p , the electromagnetic clutch between the recovery pump/motor and the roll is engaged, driving the roll from 0 to n y using the recovered energy.In this period, the electromagnetic clutch between the main drive motor and the roll is disconnected, the motor is idle with low-speed n 0 , and the main drive motor starts driving the roll rotation when the roll speed reaches n y , and the energy recovery device stops working.Figure 9 shows the roll speed and high-pressure accumulator 13.1 pressure and volume changes.Recovery pump/motor braking, starting torque, and power changes are shown in Figure 10.(2) In the case of a reversible rolling mill, for example, the energy recovery device is activated during the frst bite and it throws of the rolled part.Furthermore, it absorbs the motor's surplus power in addition to recovering the kinetic energy of the braking rolls.To recover the energy from the two parts independently, two high-pressure accumulators are used.As shown in Figure 11, the clutch on/ of signal is displayed.Te ideal speed profle of the roll, the actual speed profle, and the speed profle of the recovery pump/motor are shown in Figures 12  and 13, which also illustrates the change in fuid pressure and volume during the bite-in and throwout periods in the high-pressure accumulator.Te change in torque and power of the energy recovery system is shown in Figure 14.Te simulation results are shown in Tables 7-12, and due to space limitations, only some of the essential results are listed in this article.
(3) Te energy recovery system brakes the roll at 380 r/ min, with a braking time of 1.366 s, when the highpressure accumulator 13.1 is infated to 18.126 MPa.Gap time for each pass is 3.634 s, which can be adjusted according to the actual situation.5 s into the energy utilization phase, the recovery pump/motor drives the roll, with a maximum speed of 321.4 r/min.As can be seen in Figure 10, the pump/motor provides the required braking and starting torque for the rolls during the energy recovery and utilization phase, with a maximum value of 142.423 Nm and 142.344 Nm, respectively.In the energy recovery phase, the pump/motor has the maximum power at 0.089 s with a value of 5.354 kW.In the energy utilization phase, the pump/motor has a maximum power of 4.525 kW, and this power is obtained at 6.267 s. (4) Figure 11 shows the on/of signals for clutches 2 and 5, which indicate the diferent phases of energy recovery.Rolls are driven by the primary drive system between 0 and 3.696 s and 4.696 and 9.344 s.A transition occurs between 3.696 and 4.696 seconds, Advances in Materials Science and Engineering when the energy recovery system intervenes, which marks the beginning of the bite into the rolled part.During 9.344 seconds, the energy recovery system works; when the rolls are rolled and the energy recovery system brakes them, the braking time is slightly reduced compared to the original system (see Figure 12), which shortens the rolling cycle PI control of the motor speed which is used by the original mill drive system, as shown in Figure 12, and the actual speed is lower than the ideal speed and the pump motor speed fuctuates a little at 4.696 seconds.Tis is because the simulation sampling interval afects the antireverse valve's operating time in the energy recovery system.As the hydraulic system is already disconnected from the original mill drive system at this point, this fuctuation does not afect the regular operation of the system.As can be seen from Figure 13, the energy recovery system starts to fll rapidly with liquid from 3.696 to 3.905 s.Te fuid pressure in the high-pressure accumulator 13.1 increases rapidly from 0 to 18.0 MPa and then stabilizes.Te maximum charge pressure was obtained at 4.719 s with a value of 18.188 MPa.Te volume change in accumulator 13.1 was 40-39.706L. At 9.344-9.548s, the liquid pressure in high-pressure accumulator 13.2 increased rapidly from 0 to 18.0 MPa and then stabilized.Te maximum charge pressure was obtained at 10.846 s with a value of 18.328 MPa.Te volume of accumulator 13.2 varied from 40 to 39.792 L. As seen in Figure 14, the change in pump/motor torque for energy recovery stage 1 was a rapid increase from 0 to 141.328 Nm, followed by a maximum value of 143.140 Nm in 0.781 s.Te pump/motor torque for energy recovery stage 2 rapidly increased from 0 to 141.328 Nm, followed by a maximum value of 143.140 Nm in 0.781 s.In energy recovery phase 2, the pump/motor torque reaches its maximum at 10.802 s with a value of 142.469 Nm.Energy recovery phase 1 reaches its maximum power at 4.686 s with a value of 7.002 kW, and energy      12 Advances in Materials Science and Engineering recovery phase 2 reaches its maximum power at 9.548 s with a value of 5.284 kW.

Calculation of Energy Recovery and Utilization Efciency.
Te kinetic energy of the roller at the rotational speed n y is calculated by equation (12), and the kinetic energy of the roller at the rotational speed n p is calculated by equation ( 13).Te value of E y is calculated to be 2.824 kJ and the value of E p is 3.947 kJ: Te formula for Boyle's law is as follows: where p 0 is the gas precharge pressure of the accumulator, the charging volume of the accumulator is V 0 , p 1 is the lowest working pressure of the accumulator, V 1 is the volume of the accumulator at the lowest working pressure, p 2 is the highest working pressure of the accumulator, the volume of V 2 corresponds to the accumulator's highest working pressure, p a is the pressure under the free state of the accumulator, and the volume of the accumulator under free state pressure is V a .
Te energy equation of the accumulator is calculated by Bringing p 0 : 18 MPa, V 0 : 40 L, P a : 18.126 MPa, and V a : 39.802 L into equation (15), the energy recovery efciency calculated by equations ( 16) and ( 17) represents the calculation of the energy utilization rate.Te value of E acc is calculated to be 3.594 kJ, the value of E er is 91.056%, and the value of E eu is 78.575%.Te overall energy efciency rate is around 71.547%.
Based on the abovementioned calculation, the reversible rolling mill has a recoverable energy of 3.947 kJ, an actual energy recovery of 3.594 kJ, and an energy recovery efciency of 91.056% during the no-load deceleration period.In the reversible rolling mill's no-load acceleration period, the useable energy is 3.594 kJ, the utilized energy is 2.824 kJ, and the energy utilization rate is 78.575%.Te coefcient of    16), the value of E acc1 is calculated to be 5.358 kJ and the value of E acc2 is 3.781 kJ.
A single roll absorbs 5.358 kJ of extra motor power and recovers 3.781 kJ of roll braking kinetic energy so that the two rolls can recover 18.278 kJ of energy in one rolling pass.An energy recovery of 255.892 kJ can be achieved by rolling 14 passes.Te part of the energy can be used for roll no-load start, at the sudden change in load as an auxiliary power source to provide instantaneous high power, for the mill and other auxiliary equipment to provide power, such as winders.

Experimental Verifcation.
To verify the efciency of the reversible rolling mills braking energy recovery, the fywheel is used as the load to simulate the roll braking.Te following equivalent test scheme is designed based on the principle that the energy before roll braking equals the energy before fywheel braking.First, the electromagnetic clutch YC1 is engaged, and the motor drives the fywheel to rotate to the set speed.Next, the electromagnetic clutch YC1 is disconnected and the electromagnetic clutch YC2 is combined to brake the fywheel via the hydraulic pump/motor.When the hydraulic motor is in oil pump mode, oil is sucked from the low-pressure accumulator and supplied to the high-pressure accumulator, converting the rotational kinetic energy of the fywheel into hydraulic energy to be stored in the highpressure accumulator until the fywheel stops spinning.Te Advances in Materials Science and Engineering brake energy recovery test rig is shown in Figure 15.Te fywheel runs through the motor at a speed of 380 r/min.Terefore, the braking efciency is calculated to be 56.92%.

Conclusion
Tis article proposes a new type of noncoaxial parallel electrohydraulic hybrid drive system confguration and applies it to the reversible rolling mill.It is proposed to collect the braking energy of the previous pass of the reversible rolling mill roll and the surplus power of the original primary drive motor.Ten, we start or accelerate the process for the next roll pass.As an auxiliary power source, this portion of energy can be used for no-load roll start, in load mutation to provide instantaneous high power and to power other auxiliary equipment in the rolling mill.During the noload deceleration period of the reversible rolling mill, the energy recovery efciency is 91.056%, while the energy utilization rate is 78.575% during the no-load acceleration period.Te overall energy efciency rate is around 71.547%.
Experimental results indicate that the overall energy efciency rate of the reversible rolling mill is 56.92%.Te correctness of the simulation results and the efectiveness of the proposed scheme are well verifed.Reversible rolling mills with energy recovery systems and innovative energy innovation drive schemes can reduce energy consumption, which lays the foundation for energy recovery systems in reversible steel rolling machinery.Tere are still some limitations to this article; however, as roll braking produces a small amount of kinetic energy, the energy recovery device contributes little to the original drive system after recovering this energy, so designing the electrohydraulic hybrid drive system for a reversible rolling mill presents a new challenge.In the future, our eforts will focus on developing an energy management strategy for reversible rolling mills.Advances in Materials Science and Engineering

Figure 3 :
Figure 3: Rolling speed diagram and load diagram of the reversible rolling mill.

4. 1 .
Te Rotational Inertia of Work Roll and a Maximum Speed of Roll.We take a model 650 four-roll reversible rolling mill as an example.Its work roll is the drive roll, and its main parameters are shown in Table

Figure 5 :
Figure 5: Deceleration or braking of the roll.

Figure 6 :
Figure 6: Acceleration or starting of the roll.

Figure 7 :
Figure 7: Working speed diagram of the reversible rolling mill roll.

Figure 8 :
Figure 8: Energy recovery model based on the reversible rolling mill.

Figure 9 :
Figure 9: High-pressure accumulator change in pressure and volume and roll speed change.

Figure 12 :
Figure 12: Speeds of the recovery pump/motor, the ideal speed, and the actual speed for the roll.
high-pressure accumulator 13.2 [L] Pressure of high-pressure accumulator 13.2 [bar] Gas volume of high-pressure accumulator 13.1 [L] Pressure of high-pressure accumulator 13.1 [bar]

Figure 13 :Figure 14 :
Figure 13: Pressure and volume changes in high-pressure accumulators during bite-in and dump-out.

Table 2 :
Description of speed and torque of one pass of the reversible rolling mills.
j − M don 5 (t 4 -t 5 ) Idling deceleration period n p ⟶ 0 Te rotation speed is reduced from n p to 0 M D5 M kon − M don 4 Advances in Materials Science and Engineering

Table 4 :
Main parameters of the 650 four-roller reversible rolling mill.

Table 5 :
[2]e of each stage of one pass of the reversible rolling mills[2].

Table 6 :
Basic parameters of the energy recovery model of reversible rolling mill.

Table 8 :
Variations in starting torque, pump/motor braking, and power.

Table 7 :
High-pressure accumulator change in pressure and volume and roll speed change.

Table 9 :
Signal for clutch on/of.

Table 11 :
Pressure and volume changes in high-pressure accumulators during bite-in and dump-out.

Table 10 :
Speeds of the recovery pump/motor, the ideal speed, and the actual speed for the roll.

Table 12 :
Variations in torque and power in energy recovery systems.