Claims:CLAIMS:

1. A system for automatic control the rolling of accurate thickness of plates manufactured in a plate mill comprising of:

at least one set of Rolling Finishing stand comprising of one set of work rolls top

/ bottom, one set of back up rolls top / bottom, one set of left and right screw downs with hydraulic capsules; to set the gap between rolls to produce desired thickness plates;

at least two linear encoders each mounted on said left and right screw downs to generate signals representative of the linear motion of screw down and a joy stick;

at least two encoders each mounted on said left and right hydraulic capsules along with two servo valves;

at least two load cells each mounted bottom of the said bottom work roll to generate signals representative of the load on stand;

at least one set of record, reproduction switch & gauge control on off switch at control pulpit;

a logic controller connected to said encoders, load cell, switches, servos and comprising digital input, digital output, encoders interface & analogue output cards to receive the signals generated by encoders, load cell & switches and to control servos to provide constant thickness (gauge) by varying gap during rolling by means of logic developed in the PLC and

at least one HMi terminal displaying load, gaps, produced thickness, recorded gap values & HAGC capsules stroke.

2. A system for automatic control the rolling of accurate thickness of plates manufactured in a plate mill as claimed in claim 1, wherein the work rolls top / bottom, back up rolls top / bottom, left and right screw downs with hydraulic capsules are configured for setting the gap between rolls to produce desired thickness plates.

3. A system for automatic control the rolling of accurate thickness of plates manufactured in a plate mill as claimed in claim 1, wherein the joy stick is configured to operate screw down.

4. A system for automatic control the rolling of accurate thickness of plates manufactured in a plate mill as claimed in claim 1, wherein at least two encoders each mounted on said left and right hydraulic capsules are configured to generate signals representative of the motion of hydraulic capsules.

5. A system for automatic control the rolling of accurate thickness of plates manufactured in a plate mill as claimed in claim 1, wherein the servo valves are configured to control left and right hydraulic capsule motion.

6. A system for automatic control the rolling of accurate thickness of plates manufactured in a plate mill as claimed in claim 1, wherein the said two switches are mounted at control pulpit , one record / reproduction switch & another gauge control on / off switch .

7. A system for automatic control the rolling of accurate thickness of plates manufactured in a plate mill as claimed in claim 1, wherein the roll gap is expressed by formula :
ROLL GAP (16) = SCREW DOWN ENCODER (7) READING – HYDRAULIC CAPSULE ENCODER (6) READING

8. A system for automatic control the rolling of accurate thickness of plates manufactured in a plate mill as claimed in claim 1, wherein the thickness of plate is expressed by formula:
GAUGE (THICKNESS OF PLATE) = ROLLGAP (16) + MILL STRETCH AS PER LOAD (8) STRETCH CURVE (store in PLC (12))

9. A system for automatic control the rolling of accurate thickness of plates manufactured in a plate mill as claimed in claim 1, wherein the roll gap for passes is maintained by signals generated at reproduction block of PLC by controlling

screw down and the gauge of the plate during rolling is control by Gauge block of

PLC by varying the hydraulic capsule stroke, with the help of servos.

10. A system for automatic control the rolling of accurate thickness of plates manufactured in a plate mill as claimed in claim 1, wherein the servo valve reference signal is modulated to eliminate vibrations in stand during GMC operation and also take care of metal temperatures.

Dated: this 07th day of March, 2016.

(N. K. Gupta) Patent Agent, Of NICHE,
For SAIL.

To,
The Controller of Patents, The Patent Office, Mumbai.
, Description:SYSTEM FOR AUTOMATIC CONTROL THE ROLLING OF ACCURATE THICKNESS OF PLATES MANUFACTURED IN A PLATE MILL

FIELD OF INVENTION

This invention relates to a system for controlling a continuous hot rolling mill for maintaining the target gauges. More particularly the present invention relates to system for controlling of a continuous hot rolling mill wherein the roll gap and the roll peripheral speed of each mill stand is controlled according to a predetermined pattern in order to maintain the gauge of the finished plates at a constant value throughout the profile of plates manufactured in a plate mill.

BACKGROUND OF THE INVENTION

In the manufacture of plates the steel manufactured is brought from the continuous casting to re-heating furnaces in a Plate Mill. Here, the slabs are first re-heated to pre-determined temperature and rolled into the stands in the mill. In a typical plate mill there are three stands namely vertical stand, roughing stand & finishing stands. The rolling is such that it only reduces the thickness of the stock in the rolling direction while the width is kept constant.

In a plate-rolling mill, a heated plate passes between a pair of rotating work rolls forming an unloaded opening smaller than the entry gauge of the plate. The passage of the plate between the rolls results both in a reduction in plate thickness and a bending of the rolls. The rolls, being confined at their ends, separate more at their middles when bent by the roll separating forces. Consequently, the gauge or thickness along the centreline of the delivered plate is normally somewhat greater than at the edges. The difference between the gauge along the centreline and the gauge at the edges of a plate is referred to as the crown on the plate. Where the centre gauge is thicker than the edge gauge, the crown is termed positive. Where the centre gauge is thinner, the crown is termed negative. The magnitude of crown formed on a plate is determined by the amount of bending of the rolls and by the shape of the rolls themselves. The bending of the rolls is partly a junction of roll-separating force which, in turn, varies with the magnitude of the draft (reduction in gauge) taken during a pass.

The shape or effective crown of the rolls is determined by their initial shape as altered due to thermal expansion and wear. New rolls are normally ground with a positive crown to partially offset the effects of roll-bending, thereby preventing the formation of excessive crowns on plates. The ground crown increases once rolling begins due to a thermally induced roll crown which results from unequal thermal expansion along the surface or face of the roll. As the rolls wear from continued use, the total or effective crown diminishes due to the unequal wear pattern across the face of the roll.

Under the currently practised process the thickness of the plate is achieved by changing roll gap between work rolls & monitoring the load (by load cell) at stand during rolling in different passes at Finishing Stand i.e. by pass schedules. The roll gap is set with the help of screw downs & further roll gap during rolling is varied with the help of HAGC Capsules ( hydraulic capsules ) to maintain uniform
&accurate thickness throughout the profile of plates.

Conventionally the rolling of plates as per order thickness depends on the Operator skill & experiences. The operator records the Pass schedule for the first plate & reproduce it for next plate, this pass schedule is for roll gaps in different passes.Now as per Load shown by Load cell & thickness by PLC the operator takes correction for gap during rolling by varying HAGC capsules stroke, to achieve desired gauge of Plate.

The conventional system for rolling of desired gauge plate has many draw backs

.Firstly it solely depends on operator experience. Secondly the correction during rolling is not continuous in nature due to manual procedure, thus thickness of plate obtained is not uniform throughout the length. The load at stand also depends at metal temperatures as well as grades& makes the process morecomplex. Thus error in thickness of plates rolled by operator affects the rolling of plates with stringent tolerances thereby the diversion due to thickness variations increases.

The other known methods / devices for plate thickness control include plan view rolling methods,Level – 2 mathematical model method – it requires data entry at different level starting from slab charging , slab discharging, furnace mapping , metal chemistry & temperature , metal tracking, which are in vogue in modern

steel plants. But such advancedsystem requires very high development &

installation cost.

Thus there is a need for a plate thickness auto control system while rolling which provide very accurate results & is in – house.

OBJECTS OF THE INVENTION

The object of the invention is to provide a system for auto control the rolling of accurate thickness of plates manufactured in a plate mill with excellent consistency.

Another object of the present invention is to provide for a system for the rolling of desired thickness of plates manufactured in a plate mill which is cost effective &in
– house.

Another object of the present invention is to provide for a system for the rolling of desired thickness of plates manufactured in a plate mill with excellent consistency throughout the profile of plate.

Another object of the present invention is to provide for a system for the rolling of desired thickness of plates manufactured in a plate mill with operator monitored & operator override provision.

SUMMARY OF THE INVENTION

Thus according to the present invention there is provided a system for auto control the rolling of accurate thickness of plates manufactured in a plate mill with excellent consistency, with operator monitoring & operator override provision comprising of:

At least one set of Rolling Finishing stand comprising of one set of work rolls top / bottom, one set of back up rolls top / bottom, one set of left and right screw downs with hydraulic capsules to set the gap between rolls to produce desired thickness plates

At least two linear encoders each mounted on said left and right screw downs to generate signals representative of the linear motion of screw down& a joy stick to operate screw down.

At least two encoders each mounted on said left and right hydraulic capsules to generate signals representative of the motion of hydraulic capsules along with two servos to control left and right hydraulic capsule motion

At least two load cell each mounted bottom of the said bottom work roll to generate signals representative of the load on stand.

At least one set of record, reproduction switch & gauge control on off switch at control pulpit.

A logic controller connected to said encoders , load cell , switches ,servos and comprising digital input , digital output , encoders interface & analogue output cards to receive the signals generated by encoders , load cell &switches and to control servos to provide constant thickness (gauge) by varying gap during rolling by means of logic developed in the PLC.

At least one HMi terminal displaying load, gaps, produced thickness, recorded gap values & HAGC capsules stroke.

According to a preferred embodiment two switches are mounted at control pulpit, one record / reproduction switch & another gauge control on / off switch.

For the first plate of section the operator select the record position. Now operator starts rolling as per pass schedule, for all the passes the PLC collects information of load, from load cell output , roll gap from output of screw down & hydraulic capsules encoders & process in a record block of the PLC .After finishing rolling of plates the operator selects reproduction & switches on gauge control .Now for the next plate the roll gap for passes is maintain by signals generated at reproduction block of PLC by controlling screw down & the gauge of the plate during rolling is control by Gauge block of PLC by varying the hydraulic capsule stroke, with the help of servos.

The system of invention carries rolling of accurate thickness of plates manufactured in a plate mill with excellent consistency. It tries to maintain same gauge (thickness) by varying Capsule Stroke. The response time set is 10 m sec

it works within +/- .06 mm. of set thickness. In the system the SERVO VALVES Reference signals modulated to eliminate vibrations in stand during GMC operation, & also take care of metal temperatures. The system not dependent on metal chemistry. During rolling in reproduction mode if operator gives correction to screw down the corresponding new screw down gap & Plate thickness is also recorded & this correction will be reproduced in next Plate.

The accuracy of the thickness produced depends on stand gap calibration & stand load vs. stretch curve. Gap calibration here is the determination of stand roll gap zero position, this is to perform at each roll changing activity. Whereas stand load vs. stretch curve is to be stored & up dated in PLC whenever there is major changes in stand components

BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS

The invention will now be described with reference to non-limiting embodiments illustrated by figures.

Figure 1 shows the assembly consisting of finishing stand, screw down, hydraulic cylinders, work roll ,backup roll & load cell in accordance with the present invention;

Figure 2 shows the arrangement of components for auto control the rolling of accurate thickness of plates manufactured in a plate mill in accordance with the present invention.

DETAILED DESCRIPTION

As shown in Figure 1, a plate mill comprises Finishing stand ( 1), The hot steel plate (4) rolling process is in progress by the means of feeding roll tables (5), backup rolls (2) & work rolls (3).Before feeding of plate to stand the roll gap is set by screw down (9) as per the reading of screw down encoders (7) . While rolling the gauge (thickness) of plate is maintain by moving hydraulic capsules (10) as per the hydraulic capsule encoders (6) with the help of servos (11) depending on the load cell (8) output. Referring now to Figure. 1, the system of reducing a short, thick metal slab to a much longer and much thinner finished metal plate is

normally carried out in two successive phases. During the first or roughing phase, the heated slab may be reduced to a desired gage and a desired length by passing it back and forth through a roughing mill consisting of a pair of reversibly driven work rolls. The distance between adjacent faces of the work rolls is reduced between succeeding passes by a screw down mechanism including a screw down control which controls the angular position of a screw threaded through an anchored nut in the housing for the roughing mill. The roll separating forces produced by the passage of a slab between the work rolls are monitored by a load cell interposed between the lower end of the screw and the end support for the work roll.

The objective of the roughing phase is to produce a slab of predetermined length and rectangular configuration or pattern when viewed from above. In the roughing mill, the slab pattern is monitored by an element referred to as a pattern monitor. In practice, the function of monitoring the pattern of a slab is generally performed by a mill operator.

Upon completion of the roughing phase the slab may be turned before delivery to a finishing mill located along a mill table. During a finishing phase, the plate passes back and forth between a pair of reversibly driven work rolls in the finishing mill. The finishing mill may be a four-high mill in which the work rolls are backed by larger backup rolls, respectively. As in the roughing mill, the relative positions of the work rolls are controlled by a screw down mechanism including a screw down control which controls the angular position of a screw threaded through an anchored nut in the housing for the finishing mill.

It is possible to use the same mill for roughing and finishing purposes. For this reason, the rolling operations are described generally in terms of roughing and finishing phases. These phases may be carried out in a single roughing and finishing mill or a separate roughing mill and a separate finishing mill. The present invention is equally applicable to either arrangement.

The centre and edge gauge of a finished plate produced by a series of passes is determined by thickness gauge. The gauge may have separate gaging mechanisms located above the centreline and the edges of the finished plate or a single traversing gage which scans across the plate transversely to the direction

of travel. A mechanical device, designated a flatness monitor, may determine whether the finished plate is perfectly flat, has wavy edges, or has a buckled centre area. Figure 2 shows the arrangement of components for auto control the rolling of accurate thickness of plates manufactured in a plate mill. The control switches(14) in control pulpit (15) are connected to PLC .PLC takes input from encoders(7) & (6) to calculate roll gap (16) & further depending of load cell input (
8) give signal to servo valves (11) to operate hydraulic capsules (10) ,the data are displayed at HMI (13). As a practical matter, however, an operator normally observes plate flatness and submits encoded observations indicating which of the three flatness conditions exists. The encoded observations are supplied to a PLC which also accepts signals from the load cells, the pattern monitor, and the thickness gauge. Other inputs to the PLC are from a plate-tracking system which determines the position of a plate within the mill by means of hot metal detectors or similar sensors and an auxiliary input through which data is supplied as to initial and final dimensions, the composition, and the temperature of the plate at the beginning of the roughing phase. Data on roll diameters and on the crowns of newly installed rolls may also be supplied through auxiliary input.

While the PLC receives several input signals representing the end results of shape control in both the roughing mill and the finishing mil, it provides only two output signals for affecting that shape control. The first of these output signals is applied to the screw down control to adjust the angular position of the screw and thus the relative position of the work rolls in the roughing mill. The second of the signals is applied to the screw down control which adjusts the relative position of the work rolls in the finishing mill.

Methodology (Figure 2)

Thee gauge of the plate depends on the mill modulus. The Mill stretch Vs. Load readings were taken & stored in HIPAC PLC. The following expressions are used as a base for logical calculations along with work rolls (3) rotation direction.

ROLL GAP (16) = SCREW DOWN ENCODER (7) READING – HYDRAULIC CAPSULE ENCODER (6) READING ------------------------------------------ (a)

GAUGE (THICKNESS OF PLATE) = ROLLGAP (16) + MILL STRETCH AS PER LOAD ( 8) STRETCH CURVE ( store in PLC (12) ) –---------------- (b)

** MILL STRETCH CURVE IS THE CURVE STORED IN PLC, THIS CURVE GIVES THE VALUE OF MILL STRETCH AS PER LOAD

RECORDING MODE

When operator selects the recording mode switch (17) at pulpit ( 14 ) first operator sets the roll gap (16 ) for different passes by operating screw down(9) joy stick (20) before metal enters the stand(1) .now during rolling in stand( 1 ). The average gauge of plate for different passes along with corresponding roll gap (16) are recorded in the PLC (12) record block.

REPRODUCTION MODE

When operator selects the reproduction mode switch (18) with gauge control switch (19) on at pulpit (14) the gauge for the passes is achieved automatically with the PLC logic blocks. The first screw down (9) is operated by PLC (12) reproduction block to obtain recorded roll gap (16) before metal enters the stand(1) & then gauge control blocks in the PLC ( 12 ) gives position correction signal during rolling to hydraulic capsules (10 ) as per load ( 8)/ stretch curve (Store in PLC (12)).

OPERATOR CORRECTION

• If the operator gives correction signal by operating screw down (9) by joy stick (20) during reproduction mode in any passes the gauge control stops & now from this pass onwards to the last pass of recorded rolling schedule the gauge of plates for these passes with roll gap (16) are updated and recorded in record block at reproduction mode itself & this updated schedule is reproduced in next plate rolling.

HIGH LIGHTS

• The error in gauge is <+/-.02mm

• The Thickness of plate is maintained constant throughout the length

• Irrespective of temperature and steel grade variations for the same section of plate the Thickness is maintained as the recorded values.

• By maintaining uniform thickness constant length is also achieved in all plates, thus direct reduction in thickness diversion & indirect reduction in length diversion (sls) is achieved.
• Quality of Plate improved giving uniform profile.

• The system is In- House & does not require Level -2 models for HAGC (hydraulic automatic gauge control )

Although the foregoing description of the present invention has been shown and described with reference to particular embodiments and applications thereof, it has been presented for purposes of illustration and description and is not intended to be exhaustive or to limit the invention to the particular embodiments and applications disclosed. It will be apparent to those having ordinary skill in the art that a number of changes, modifications, variations, or alterations to the invention as described herein may be made, none of which depart from the spirit or scope of the present invention. The particular embodiments and applications were chosen and described to provide the best illustration of the principles of the invention and its practical application to thereby enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such changes, modifications, variations, and alterations should therefore be seen as being within the scope of the present invention as determined by the appended claims when interpreted in accordance with the breadth to which they are fairly, legally, and equitably entitled.