The rolling mill deviation analysis and improvement in Hydraulic pressure Kaishi Tuan1 a Longlong Chen2 b1Shaanxi Longmen Iron & Steel Co. , Ltd, Xian, Shaanxi，China2Xian Poitechnic University，Xian，Shaanxi，ChinaaEmail： qilianbiyu163.com bEmail：chen40802040213163.comKey words: Hydraulic pressure fault analysis improvementAbstract: This paper introduces the working principle and the failure phenomenon of the steel hydraulic station of Xian steel rolling mill, Shaanxi Longmen Iron & Steel Co.,We made a synthesis of the reasons of the failure phenomenon,on this basis, we put forward the improvement measures about the steel hydraulic system,the work showed that this improved method can effectively solve the failure phenomenon of the Steel hydraulic station，thereby achieves good results and a certain economic and social benefit.Shaanxi Longmen Iron & Steel Co.,Ltd(short for Xian rolling mill ),builts a production line In 1998 October,It mainly produces semi - continuous bar，and the output growth from the initial plant 200000 tons per year to 800000 tons per year now.after several upgrades.This production line consists of 12 rolling mill rolling,all of them are closed-type rolling mill.The advantages of closed-type rolling mill are solid and durable machine construction,good rigidity, the great rolling force,because of these advantages closed-type rolling mill have been widely used in steel rolling system.But it is very troublesome to change the roll, we must change the roll from the side,so almost all the closed-type rolling mill should be equipped with roll change buggy.When roll changing,separates roll changing buggy and rolling mill firstly and then approximation hydraulic cylinder push forward the roll changing buggy from shift. And the working principle is similar to most domestic and foreign manufacturers,roll changing buggies are driven by hydraulic cylinder.（Figure 1） Figure 1 Driven by Hydraulic cylinderIn the steel rolling system of new generation, Groove of each rolling mill stand in a straight line in the rolling process, so each mill can move laterally enough.When the rolling mill begins move, roll changing buggy should be chained with the mill, so we can move the mill parallel by hydraulic cylinder.Moreover, in order to avoid the scrap accident, in order to prevent mill remove during machine operation, so we use the clamping cylinder to intensify the mill during the rolling process. （Figure 2）Figure 2 intensify the mill Rteel mill nameplates一、The working principle of the mill of the hydraulic system Mill of the hydraulic system are composed of two hydraulic pump （One of them is spare）as the power component, hydraulic pump make use of medium and high pressure vane pumps (Model t67-017-1R00), Its characteristic is uniform flow, smooth running, low noise, small volume, light weight. Control components are composed of inserting check valve and a pressure regulating valve, One is working and another work as a backup. Accessory is composed of differential pressure type filter, pressure gauges, liquid level meter, but also for the sender, heaters, pressure controller and a circulating pump, They serve to protect the system, control the temperature and the role of the oil filter. The actuator part consists of 12 translational hydraulic cylinder (one mill equipped with one)and 30 clamping cylinder（6 medium mill every equipped with one,6 high mill every equipped with one）.The system uses 46# antiwear hydraulic oil, which can work within the range of 10C-60C.Its rated working pressure is from 12Mpa to 14MPa, maximum operating pressure is 18 Mpa. There is no need to consider the issue of high oil temperature, or to design hydraulic system of cooling, due to the introduction of an intermittent working system.The hydraulic pump is running, while the solenoid Y1 and Y2 are lack of electrocity, the system pressure rises, in working condition, otherwise, when electromagnet Y1 or Y2 powered, the hydraulic pump will be in the unloaded state, and the system will lost pressure.When the system is working, the electromagnetY3 may not, clamping cylinder is in clamping state. when the need to move the mill, the electromagnet Y3 electricity, clamping cylinder is in release state. At this time, the electromagnet Y4 electricity, it can transfer mill.When replacing the roller mill, the mill will be unmoved, we only need to move the roll changing buggy.Then, we can put the roll changing buggy away from the mill chain. Once clamp cylinder clamping mill, Y3 and Y4 electromagnet electricity, you can push out the roll changing buggy (Table 1)Figure 3 Mill of the hydraulic system二、Remove the hydraulic system fault and improvement1. leakage analysis and improvement measures of Clamping cylinder(1) clamping cylinder leakageThe hydraulic system runs well at the early time in Xian rolling mill. But at the beginning of 1999, the clamping cylinder began to leak oil. It is still difficult to avoid oil leaka