Created on:2021-08-05 10:04

Hydraulic fault diagnosis and maintenance of rolling equipment_ Hydraulic failure of medium plate mill

轧钢设备液压故障诊断与维修_中板轧机液压故障
Hydraulic fault diagnosis and maintenance of rolling equipment_ Hydraulic failure of medium plate mill

    某公司中板轧机液压AGC系统由液压系统、控制系统(上位机与下位机)组成,其作用是对轧制的钢板的同板差、异板差进行精确自动控制,并保证钢板的良好板形,提高钢板的成材率。在钢板的轧制过程中液压系统的压力稳定性影响响应频率的快慢以及整个系统能否对钢板进行精确控制。液压AGC系统投入使用后出现了一些问题:在钢板投入自动轧制后阶段的最后2~3道出现失压。这样造成钢板的同板差异,板差较大并且不稳定,严重影响了产品的质量。
The hydraulic AGC system of medium plate mill in a company is composed of hydraulic system and control system (upper computer and lower computer). Its function is to accurately and automatically control the same plate difference and different plate difference of rolled steel plate, ensure the good shape of steel plate and improve the yield of steel plate. In the rolling process of steel plate, the pressure stability of hydraulic system affects the speed of response frequency and whether the whole system can accurately control the steel plate. There are some problems after the hydraulic AGC system is put into use: pressure loss occurs in the last 2-3 passes after the steel plate is put into automatic rolling. This results in the difference of the same plate, the plate difference is large and unstable, which seriously affects the quality of the product.

(1)失压原因分析
(1) Cause analysis of pressure loss

    在钢板的轧制过程中,其厚度是由上下工作辊的辊缝大小决定的。该液压AGC是由“电动APC+液压微调”进行控制,也就是由电动APC初摆辊缝。在轧制过程中,当钢板进入辊缝后,由AGC根据液压缸上安装的位移传感器所检测到的位移进行自动微调控制,以保证计算机所设定的钢板厚度。在电动APC定位准确,以及位移传感器检测数据准确的前提下,液压缸在高速轧制钢板的过程中,其控制辊缝大小的动作快慢就是最关键的因素。在这里电动APC的定位及位移传感器的检测可以通过选用质量较好的进口元件保证其精确性。
In the rolling process of steel plate, its thickness is determined by the gap size of upper and lower work rolls. The hydraulic AGC is controlled by "electric APC + hydraulic fine-tuning", that is, by the electric APC initial swing roll gap. In the rolling process, when the steel plate enters the roll gap, AGC will automatically fine tune and control according to the displacement detected by the displacement sensor installed on the hydraulic cylinder to ensure the steel plate thickness set by the computer. Under the premise of accurate positioning of the electric APC and accurate detection data of the displacement sensor, the speed of the hydraulic cylinder controlling the roll gap size is the most critical factor in the process of high-speed rolling steel plate. Here, the positioning of electric APC and the detection of displacement sensor can be ensured by selecting imported components with better quality.

(2)对策
(2) Countermeasures

    简化后的液压AGC的液压控制原理如图W所示,系统由、蓄能器、伺服阀、液压缸等元件组成。恒压变量泵能保持稳定的供油量;蓄能器分为两部分,一部分安装在油库,另一部分安装在伺服阀旁,其总容积为358L;伺服阀为三级的喷嘴挡板式伺服阀,其响应频率大于50Hz;液压缸活塞尺寸为1100mm,工作行程60mm。系统控制核心为伺
The hydraulic control principle of the simplified hydraulic AGC is shown in Fig. W. the system is composed of hydraulic system, accumulator, servo valve, hydraulic cylinder and other components. Constant pressure variable displacement pump can maintain stable oil supply; The accumulator is divided into two parts, one is installed in the oil depot, the other is installed beside the servo valve, and its total volume is 358l; The servo valve is a three-stage nozzle flapper servo valve, and its response frequency is more than 50 Hz; The piston size of the hydraulic cylinder is 1100mm and the working stroke is 60mm. The core of system control is server

服阀,整个电液控制系统采用位置反馈,其传递函数方块图见图X。
The whole electro-hydraulic control system adopts position feedback, and its transfer function block diagram is shown in Figure X.

X.jpg

    图X中u1为输入指令信号电压,通过放大器变为电流i输到电一机械转换器(力矩电机)。与机械系统相比,电子系统频率响应相当快,放大器的传递函数可以认为是一个简单的放大环节,放大系数为Ka。在伺服阀先导级的电一机械转换器中通过电磁的作用,电流变成推动力使滑阀移动,这个变换速度也很快,也可以看成一个放大环节,放大系数为K2,即电一机械转换器的推力F=K2i。此推力使电一机械转换器的衔铁和滑阀一起移动。它的运动方程式为F=md2 Xv/dt2 +BdX/dt+C,对此式进行拉普拉斯变换可得:
U1 in figure x is the input command signal voltage, which is changed into current I through the amplifier and transmitted to the electro-mechanical converter (torque motor). Compared with the mechanical system, the frequency response of the electronic system is quite fast. The transfer function of the amplifier can be considered as a simple amplification link, and the amplification coefficient is Ka. In the electro-mechanical converter of the pilot stage of the servo valve, through the action of electromagnetism, the current turns into the driving force to make the slide valve move. This transformation speed is very fast, and it can also be regarded as an amplification link. The amplification factor is K2, that is, the thrust of the electro-mechanical converter is f = k2i. The thrust makes the armature of the electro-mechanical converter move together with the slide valve. The equation of motion is f = MD2 XV / DT2 + BDX / dt + C

                X(s)/F(s) =K3/(s2/ωv2+2sδv/ωv+1) (4-8)
X(s)/F(s) =K3/(s2/ ω v2+2s δ v/ ω v+1) (4-8)

如果令K1=K2K`,则从电流输人到滑阀位移的传递函数即为图中的第二个方块。其中叫ωv、δv分别为此环节的自然共振频率及阻尼比。由于采用的伺服阀为三级摩根阀,其动态响应速度很高,可以把此环节看成是放大环节,放大系数为K1。方块第三项为伺服阀的阀芯位移转化为通过伺服阀流量的变化,即流量增益系数。方块第四项为阀控缸的传递函数(液压缸位移与通过阀的流量之比)。传递函数的反馈采用位置反馈。由以上方块图可得整个系统的传递函数为:
If K1 = k2k ', the transfer function from current input to slide valve displacement is the second block in the figure. Which is called ω v、 δ V is the natural resonance frequency and damping ratio of the link. Because the servo valve is a three-stage Morgan valve, its dynamic response speed is very high, so this link can be regarded as an amplification link, and the amplification factor is K1. The third item is that the displacement of the spool of the servo valve is transformed into the change of the flow through the servo valve, that is, the flow gain coefficient. The fourth term is the transfer function of the valve controlled cylinder (the ratio of the displacement of the cylinder to the flow through the valve). The feedback of transfer function is position feedback. The transfer function of the whole system can be obtained from the above block diagram

               (4-9)
(4-9)

    式中,Kq为滑阀的流量增益;Ap为缸活塞面积。
Where KQ is the flow gain of the slide valve; AP is the cylinder piston area.

    伺服系统的频宽是衡量其动态性能的指标,反映伺服系统响应速度的快慢。这里只对它进行定性分析,找出影响系统反应快慢的因素。在传递函数中系统的频宽反映系统动态响应的快速性,截止频率的大小反映频宽的大小。系统放大倍数的增加会使得频宽变宽,相应地动态响应变快,但放大系数太大会影响系统的稳定性。因此波德图中在保证系统稳定余量的情况下尽可能增加放大倍数。从以上整个系统的传递函数看,放大系数为K=KaK1Kq/Ap。从影响系数K的因素看:Ka是力矩电机的放大系数,伺服阀一旦选定Ka基本不变;K1=K2K3,其中K2为电流变成推动力环节的放大系数,伺服阀一旦选定也基本不变;K3为推力使电一机械转换器的衔铁和滑阀一起移动的拉普拉斯传递函数的放大系数,各相同型号的伺服阀该系数虽不一样,但变化不太大,对K1大小的影响有限;Kq为伺服阀的流量增益,也叫流量放大系数,表示伺服阀芯位移Xv有微小增量时所引起流量增量,其可变数较大;Ap为液压缸活塞面积,一旦选定数据已定。因此从影响K的几个数据看Kq是一个可变数较大的因子。
The bandwidth of servo system is an index to measure its dynamic performance, which reflects the response speed of servo system. Here only qualitative analysis is carried out to find out the factors that affect the reaction speed of the system. In the transfer function, the bandwidth of the system reflects the rapidity of the dynamic response, and the cut-off frequency reflects the bandwidth. With the increase of system magnification, the bandwidth becomes wider and the dynamic response becomes faster, but the stability of the system will be affected if the amplification factor is too large. Therefore, in order to ensure the stability margin of the system, we should increase the magnification as much as possible. From the above transfer function of the whole system, the amplification factor is k = kak1kq / AP. From the factors that affect the coefficient K, Ka is the amplification factor of torque motor, once the servo valve is selected, Ka is basically unchanged; K1 = k2k3, where K2 is the amplification factor of the current into the driving force, and the servo valve is basically unchanged once it is selected; K3 is the amplification factor of the Laplace transfer function that the armature and slide valve of the electro-mechanical converter move together with the thrust. Although the coefficient of each servo valve of the same type is different, it does not change much and has limited influence on K1; KQ is the flow gain of the servo valve, also known as the flow amplification factor, which indicates the flow increment caused by the small increment of the displacement XV of the servo valve core, and its variable is large; AP is the piston area of hydraulic cylinder, once the selected data has been determined. Therefore, from several data affecting K, KQ is a variable factor.

我们从有关阀的流量增益公式看:
We can see from the flow gain formula of the valve concerned:

                       Kq=Q1/Xv=CdW(ps-p1)/ ρ (4-10)
Kq=Q1/Xv=CdW(ps-p1)/ ρ ( 4-10)

式中,Cd为流量系数,随阀口形状结构及流态而变(0.6~1.0之间);W为阀的开口度;ps为系统压力;p1为负载压力;ρ为油密度。
Where, CD is the flow coefficient, which varies with the shape and structure of the valve port and the flow pattern (between 0.6 and 1.0); W is the opening degree of the valve; PS is the system pressure; P1 is the load pressure; ρ Is the oil density.

也就是伺服阀定下来后,在其执行微调过程中(初始W=0),其Kq主要由(ps –p1)决定。因此要想提高Kq值可有以下三个方案。
That is to say, after the servo valve is set, its KQ is mainly determined by (PS – P1) in the process of fine-tuning (initial w = 0). Therefore, in order to improve the KQ value, there are the following three schemes.

①提高系统压力ps 提高系统压力ps对Kq值的影响较明显,但每个系统的允许压力由其所选的元件决定。若系统压力大于元件的压力范围,则元件会急速损坏,不能正常工作。
① The effect of increasing system pressure PS on KQ value is obvious, but the allowable pressure of each system is determined by its selected components. If the system pressure is greater than the pressure range of the component, the component will be rapidly damaged and cannot work normally.

②降低负载p1 降低负载就意味着降低轧制力,降低轧制力就得减少压下量,这就需要每块钢都要增加轧制道次,即增加每块钢的轧制时间,这会减少机时产量,影响生产。
② Reduce the load P1, reduce the load means to reduce the rolling force, reduce the rolling force will have to reduce the reduction, which requires each steel to increase the rolling pass, that is, increase the rolling time of each steel, which will reduce the machine hour output and affect the production.

③适当提高ps及降低p1 也就是把系统压力调定在系统元件允许的较高的范围内;同时根据每块钢的道次的温度不同,适当分配压下量,使其达到产量与AGC微调功能的平衡。
③ Increasing PS and decreasing P1 appropriately means that the system pressure is set in a higher range allowed by the system components; At the same time, according to the different pass temperature of each steel, the amount of reduction should be properly distributed to achieve the balance between output and AGC fine-tuning function.

因此影响整个液压AGC系统反应快慢的因素主要有两个:系统压力ps及轧制压力p1。
Therefore, there are two main factors affecting the response speed of the whole hydraulic AGC system: system pressure PS and rolling pressure P1.

依据以上原理,在整个液压AGC使用过程中要控制好系统压力ps及轧制压力p1。但实际上系统压力ps是按一定规律变化的动态量,在整个油路系统中,它与蓄能器的容量及压力密切相关。依据气体状态方程有:
According to the above principle, the system pressure PS and rolling pressure P1 should be well controlled in the whole process of using hydraulic AGC. But in fact, the system pressure PS is a dynamic variable according to a certain rule. In the whole oil system, it is closely related to the capacity and pressure of the accumulator. According to the equation of state of gas, there are: 1

                         p1V1 =p2V2 (4-11)
p1V1 =p2V2 (4-11)

式中,p1、V1为充油前(或微调前)的系统压力及蓄能器气体容积;p2、V2为充油后(或微调后)的系统压力及蓄能器气体容积。在这里充油时间短,发生在瞬间,可忽视的补充流量。
Where P1 and V1 are the system pressure and accumulator gas volume before oil filling (or fine adjustment); P2 and V2 are the system pressure and accumulator gas volume after oil filling (or fine adjustment). Here the oil filling time is short and occurs in an instant, which can be ignored by the replenishment flow.

将式(4-11)整理后,有:
After formula (4-11) is sorted out, there are:

p2 =p1V1/V2
p2 =p1V1/V2

在这里p2也就是动态变化的系统压力ps。要使得p2有较高压力,必须有较高的p1、V1值。因此的容量越大及压力越高,在整个AGC实施调整过程中系统压力p1越稳定,整个液压AGC系统反应越快。
Here P2 is the dynamic system pressure PS. In order to make P2 have higher pressure, we must have higher values of P1 and v1. Therefore, the larger the capacity and the higher the pressure, the more stable the system pressure P1 is and the faster the response of the whole hydraulic AGC system is.

(3)实施效果
(3) Implementation effect

曾有过一段时间部分蓄能器漏油,不得不取消部分蓄能器,结果在轧钢过程中系统压力波动较大,有时p2值(也就ps值)跌得很厉害,引起整个液压AGC系统反应变慢,所要控制的钢板尺寸达不到要求。一旦修复蓄能器,使用恢复正常,达到预期的控制效果。
There was a period of time when part of the accumulator leaked oil and had to cancel part of the accumulator. As a result, the system pressure fluctuated greatly in the process of steel rolling, and sometimes the P2 value (PS value) fell sharply, causing the response of the whole hydraulic AGC system to slow down and the steel plate size to be controlled could not meet the requirements. Once the accumulator is repaired, it will return to normal and achieve the expected control effect.

为了能使液压系统正常使用,将使用压力调定在20MPa左右,不仅在设备许可的压力范围内,而且使用效果也很好。
In order to make the hydraulic system work normally, the operating pressure is set at about 20MPa, which is not only within the allowable pressure range of the equipment, but also has a good effect.

针对轧制压力p1,工艺技术人员通过合理调整不同钢种每道的压下量来达到AGC系统反应频率,也取得了一定效果。
According to the rolling pressure P1, the process technicians can achieve the AGC system response frequency by reasonably adjusting the reduction of each pass of different steel grades, and some results have been achieved.
According to the rolling pressure P1, the process technicians can achieve the AGC system response frequency by reasonably adjusting the reduction of each pass of different steel grades, and some results have been achieved.

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