1、大学毕业设计 外文翻译 1 Appication of hydraulic AGC and width control to a hot strip mill D.Alan Davies,Project Sale Manager,Engineering and Construction Div. Davy Mckee (Sheffie id)Lid, Sheffieid, U. K. THE Pohang Iron & Steel Co.(POSCO) No.2 hot strip mill at Pohang, South Korea,is a modern, three-quarter c
2、ontinuous mill built by Mitsubishi in 1980.The mill is 2050mm wide,has four roughing stands and seven finishing srands.The seven finishing srands have a combined power of 56,000kw with a maximum strip speed of 21 metres/s.Coil weight is up to 35.3 tonnes. Annual mil capacity is 3.56 million tonnes.
3、To improve width and gage tolerances,POSCO decided to install hydraulic automatic width contol (HAWC) on the last edger (E4) and hydraulic automatic gage control (HAGC) on finishing stands F4 to F7. Davy McKees contract was for the total ackage associat-ed with modernization of the mechanical and hy
4、draulic systems,the computer-bassd AWC/AGC controls, new widthmeter, mechanical installation, commissioning and training. The new equipment was put into service during a 14-day shutdown in 1987. Outline of new facilities A priority requirement was that the new equipment should be integrated with the
5、 existing facility in such a way as to permit reversion to conventional operation in a few seconds. Accordingly, hydraulic AGC and AWC cylinders were designed to withstand normal rolling conditions when in a collapsed state. All of the control systems had to be in parallel with the existing systems
6、(which were retained ) and existing operators desk contromechanical system, depending on which system was selected. The AWC system comprises short-stroke, single-acting cylinders (four in total )engineered between the ends of the horizontal screwa and the vertical roll chocks . These cylinders are s
7、ervo-controlled, with a stroke speed of 100 mm/s (4 ips) to provide in -bar width control. (With the bar being typically 50 mm thick at this stage, only a limited 大学毕业设计 外文翻译 2 amount of correction was expected.) A new widthmeter after roughing stand R3 is used to give feed forward control signals t
8、o the edger E4 AWC with the existing widthmeter after rougher R4 providing bar to bar updating . The AGC system on the last four finishing stands has short-stroke, single-acting cylinders located between the top chocks and the acrewdown thrust bearing/load cell units.These cylinders have excetionall
9、y high dynamic performance (28 Hz ,10 mm/s velocity ). Becayse of the physlcal distance between the edger E4 and the finishing stands F4 to F7 ,separate pump sets serve each atra ,The hydraulic pressure is 275 bars, mineral oil,with a filtration level of 3 microns . The new computer configuration co
10、mpries a network of seven PDP 11/73 microprocessors linked by an Ethernet highway . An unusual feature of the system was the need to tap into the existing 64-way parallel communications link between the existing supervisory control computer (SCC) and the melplac plcs which perform the screwdown AGC,
11、 The tap had to be transparent to existing communication and of a high integrity . (Hence a warm spare stand by computer was included in the system .) The required data for the AGC/AWC was extracted , serialized and communicated to the new system along the Ethernet , highway , This had the advantage
12、 of opening up the computer system to easier communications in the future , as new systems could be attached easily to the Ethernet .(A few months later , a further contract for ENCO heat retention panels and interstand water curtains was retention panels and interstand water curtains was received w
13、hich required a further 11/73 miceoprocessor .) Mechanical/hydraulic design features AGC cylinders -Various components of the AGC cylinders and their assembly are illustrated in Fig . 4,5 and 6. The cylinder design incorporates a single , low -friction seal that constests of a Teflon band mounted on
14、 the piston below a bronze , side trust ring . The base of the piston is chamfered to give a rocking surface when the cylinder is used in a collapsed state .It gives the necessary degree of freedom to absorb the normal deflections in the mill . 大学毕业设计 外文翻译 3 A hydraulic manifold is mounted to the fr
15、ont of each cylinder that includes the servo-valves.One of the position transducers is slightly discernible behind the small accumulator .Another position transducer is fitted diametrically opposite . The two signals from the transducers are averaged to provide a mean stroke signal . The transducer
16、package is shown in .The Sonymagnescale transducers with 1 micron resolution are hermetically sealed insode the brass bodies . Three-stage servo-valves are employed (Moog 79 series ) .The third stage has its own built-in closed-loop position control . Each valve is nominally rated at 230 litres /min
17、 . Two valves are fitted to each cylinder and operate electrically in cascade , ie , as the drive signal to the first valve reaches saturation , it spills over to the second valve . They have a frequency response of 200 Hz . Cylinder parameters and performance data are summarized in Table I . Dynami
18、c performance was checked on a similar cylinder (890 mm dia compared to 960 mm on the POSCO mill ) with identical transducers , servo-valves , etc , installed on a mill housing equipped as a test rig . Steel blocks accurately represent the masses of the chocks and rolls , giving a truerepresentation
19、 of the mass-spring conditions in a real mill . The frequency resonse as a function of the rolling load is illustrated in , Loop gain is automatically adjusted by the software to optimize the dynamics . One of the inberent features of a single-acting cylinder design is that the flow rate through the
20、 servo-valves and , thus , the cylinder speeds , is a function of the actual pressure in the cylinder . To prevent unnecessarily high speeds at the higher and lower sections of the range , simple software rules limit the electrical drive signals to the servo-valves ,effectively creating a stable and
21、 symmetrical velocity performance in both the extending and retacting directions , over the working range of the cylinder . AWC cylinders -The AWC cylinders have a thrust bearing with spherical seating , embedded into the piston . Each cylinder is served by its own 3-stage servo-valve located nearby
22、 . The servo-valves and position transducers are interchangeable with the AGC counterparts . Performance details are also summarized in Table 1 . Collapse force is provided by pull-back cylinders acting on the roll chocks . These cylinders are controlled to maintain a constant , low , pull-back force during the body of the bar , but increasing to a higher value to assist in achieving the tail end antinecking feature .
