FIELD OF INVENTION

The present invention relates to an edger roll lubrication system for hot strip mill. More particularly, the present invention relates to reducing of high wearing of the rolls and increases the service life of the edger rolls.

BACKGROUND ART

All the hot strip mills in steel plants have two groups of mill stands - a group of roughing stands and a group of finishing stands. At the roughing stands, slabs are rolled into transfer bars, which are further rolled at the finishing stands to get hot rolled (HR) coils. Besides reducing thickness of a slab, the roughing stands are also used to give width reductions to the slab and thus desired width of the HR coils is prepared in roughing group of the stands. For this purpose, each roughing stand is coupled with a vertical stand, namely edger stand, for rolling of slab at its edges in width direction (Fig.1). The edger stand takes care of spread of material during normal rolling at roughing stand and helps in achieving desired width of the HR strips. It is also important for rationalising slab sizes for different widths of HR coils. Each edger stand is equipped with two vertical rolls, which impart reduction to the slab either in reversing passes or in continuous pass. Edger rolls are exposed to arduous roll bite conditions due to presence of heat, pressure, mass flow, moisture and scale. Under such conditions they get worn out through adhesive, abrasive and/or fatigue wear-modes. Detrimental effect of scale on roll-wear might be more due to inefficient decaling at slab edges. High temperature rolling may also cause generation of fire cracks on rolls, which may further increase the wear rate.

If high wear rate of edger rolls is not taken care of, there may be formation of grooves on barrel of the rolls. Under such condition it is difficult to control width and edge quality of the HR strips. High wearing of the rolls is also prone to generate edge sliver in the HR strips. To avoid these problems, edger rolls are required to be changed at shorter campaign sizes. Every roll change reduces availability of the mill significantly. Beside this, service life of the edger rolls is also reduced due to wear as well as due to very high grinding off take in each roll dressing. Ultimately, the average specific roll consumption increases to very high level and the cost of rolling is affected adversely.

Use of lubrication is an established tool for reducing wear of any machine component. It was however not common for rolls of hot strip mills till sometimes back as suitable lubricant and a well engineered lubricant application system were not available. This necessity gave rise to the present innovation wherein an integrated automatic edger roll lubrication system was developed and implemented at all the 4 edger stands of a hot strip mill (HSM) of an integrated steel plant. Operation of the developed system was satisfactorily coupled with operation of the existing mill and its benefits were demonstrated through long term industrial trials. The roll lubrication works on the principle of creating a thin molecular boundary layer of lubricant between the mating surfaces of workpiece and edger rolls. The lubricating oil is applied in the form of oil-in-water dispersion. The lubricant film reduces the contact area of interaction and thus decreases the levels of friction and wear rate at the interface. The benefit is further converted to improvements in production of mill, life of rolls and quality of the rolled products.

OBJECTS OF INVENTION

The present innovation suggests design of an Edger Roll Lubrication System for preparation and application of hot rolling oil dispersion on edger rolls of a group of roughing stands of HSM along with automated control and monitoring of the lubrication process by integrating it with the existing mill system. The system is used to meet the following functions:
(a) Introduce lubrication at roll-slab interface to reduce friction and wear of rolls at continuous and/or reversing edger stand,
(b) Integrate the lubrication system with the existing mill installation,
(c) Automatically control operation of the lubrication system, and
(d) Log process parameters and generate diagnostics reports.
SUMMARY & TECHNICAL DISCLOSURE
Identification of Basic Features and their Relevance
Design features of the edger roll lubrication system to be patented are summarised below:
(a) The edger roll lubrication system has been developed for preparation and application of hot rolling oil-in-water dispersion directly over edger rolls of a group of edger stands of HSM. In this system, dispersion of oil-in-water is prepared by mixing oil and water at high pressure in a mixer close to the mill stand and is sprayed over the edger rolls. While the water pumping system is centralised for all the stands, there is dedicated oil pumping system for each stand.
(b) The system has been designed to provide variable lubrication conditions suiting to requirements of edger rolls at drive side and work side of different mills stands. Oil flow rate can be varied from minimum 0 to maximum 350 ml/min at each roll. Oil spray is switched on only when material is being rolled in the mill and its spray-timing can be varied as per length of the bar. Water flow rate and pressure can also be varied. However, it may be kept spraying even when no material is being rolled in the mill.
(c) Precise control of the oil flow rate is achieved using diaphragm type duplex metering pump with variable frequency drive. Separate cylinder is used for supplying lubricant to two edger rolls, which is useful in maintaining differential flow rate, if required. A multi-stage inline vertical centrifugal pump with suitable water distribution network is used to supply water at all the rolls. An automatic self cleaning filter is used to clean water pumped to the oil-water mixer.
(d) A tube type static mixer is used to mix the oil with water near the individual rolls. Dispersion so formed is sprayed over each roll using header with nozzles. A combination of mechanical wiper and air wiper is used to wipe out roll cooling water from the roll surface before spray of lubrication. It helps in formation of stable oil film on the roll surface.
(e) The edger roll lubrication system is designed with a centralised programmable logic controller (PLC) based automation system to automatically control the following operating conditions of the system:
i. Filling and controlling level of water and oil in their respective tanks,
ii. Level of oil flow rate to be pumped to each mill stand,
iii. On and off timing of oil pump to spray lubricating oil only when material is in the mill, which is identified through signal from hot metal detector placed before the mill stand,
iv. Generating alarm during violation of any protocol, and
v. Switching off the system in case of overshooting of any limiting conditions.
(f) It is designed with a centralised Human-Machine-Interface (HMI) based operating station for direct access of mill operators for operation and monitoring of the lubrication parameters. This station logs all the strategic parameters of the system including various alarms and is useful in diagnosis of any problems with the system. Emergency switch provided with the HMI station is useful in shutting off the system in case of any cobble or misbehaviour of the mill.
(g) The system is operated using PLC and HMI software which have been developed and customised for integrated operation with the HSM. It involves suitable logic for feeding lubrication set points and recording of actual lubrication parameters.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

Fig. 1 illustrates the schematic arrangement of Edger Rolling as prior art;

Fig. 2 illustrates the layout of Hot Strip Mill showing location of Edger Stands as prior art;

Fig. 3 illustrates the schematic arrangements of edger roll lubrication system in accordance with the present invention;

Fig. 4 illustrates the flow diagram for operation & control of lubrication system in accordance with the present invention;

Fig. 5 illustrates the typical HMI screens for automatic control of edger lubrication in accordance with the present invention;

Fig. 6 illustrates the effect of lubrication on roll force at edger stands in accordance with the present invention;

DETAILED DESCRIPTION

HSM, BSL, is equipped with 4 edger stands in roughing mills for controlling width of HR coils. The first stand is of reversing type and is designed for heavy width reductions (over 100 mm) to the slabs. Other three edger stands are of continuous type and are used primarily to contain spread of material and for finer width control through automatic system. As the edger rolls were subjected to high mechanical and thermal loads, they were getting worn out at faster rate. It required frequent roll change, however, at the cost of loss in production. Longer campaigns were causing groove formation in rolls which were leading to difficulty in rolling, width control problems, high grinding off-take, and high specific roll consumption.

In order to reduce wear rate of rolls, an Edger Roll Lubrication (ERL) system was developed and introduced for pass lubrication in all the 4 edger stands. The system consisted of oil flow circuit, water flow circuit, oil-water dispersion mechanism, PLC based control station and HMI based operating station. For developing the ERL system, the following activities were carried out:
(a) Study of operating conditions and wear of edger rolls at HSM, BSL
(b) Design of the lubrication system with various control features
(c) Fabrication, installation and commissioning the lubrication system
(d) Stabilization of the system and optimizing oil flow rate and spray timing
(e) Performance evaluation of the system during extended trials

Identification of Optional Features and their Relevance

The edger roll lubrication system has been designed with its PLC having direct connectivity with the PLC of the mill for smooth exchange of data and signals between the two systems. This helps in proper integration of the lubrication system with the mill system. The lubrication system has been provided a programming station which can be used as an additional HMI for feeding important input data and monitoring the output information during stabilisation and maintenance of the system. It can be used for making suitable changes in the logic and program of the PLC and HMI.

ILLUSTRATION OF THE BEST WORKABLE EMBODIMENT OF THE INVENTION

An edger roll lubrication system was designed with the said features and got fabricated, installed and commissioned for providing lubrication to edger rolls of all the 4 edger stands of an industrial HSM of an integrated steel plant. Layout of the mill where the innovated system was tested is given in Fig. 2 and its brief details are given in Table 1.

This mill was not having any edger roll lubrication system installed in them. Rolling of slabs was carried out without use of any hot rolling oil. Only water was sprayed over rolls to cool them. Under such condition rolls of the mill were subjected to high friction and wear at roll-slab interface. The higher friction values were responsible in increasing roll force and power consumption making higher width reduction difficult. With higher wear, groove was formed on the roll barrel making width control of HR coils very difficult. The rolls were therefore changed frequently at shorter campaign sizes. This obviously was at the cost of loss in production due to increased delay on account of roll changes. Beside this it was also causing very high roll consumption.

Table 1 Brief description of the HSM where the innovation was introduced

Rated capacity ~ 4.5 MT/year
Configuration 2000 mm continuous mill
Roughing stands 1 No. reversing 2-Hi stand & 3 No. non-reversing 4-hi stands
Edger stands 1 No. reversing (E1) & 3 No. non-reversing stands (E2-E4) coupled with roughing stands
Edger rolls E1: 1450-1350 mm diameter; 600 mm barrel; Hi-Cr forged steel; Max speed 3.85 m/s; Max roll force 7 MN
E2-4: 900-810 mm diameter; 420 mm barrel; Forged steel; Max speed 1.86-2.95 m/s; Max roll force 1.5 MN
Finishing stands 7 No. tandem 4-hi stands
Materials being rolled All types of carbon and alloy steels
Input size Slabs of 200-250 mm thickness
Finished gauge 1.8-16.5 mm
Width range 750-1850 mm
Maximum rolling speed 20 m/s

An edger roll lubrication system was therefore developed for application of hot rolling oil over the rolls of all the 4 edger stands of the mill. The system was designed on following basis:
(a) Making buffer storage of oil and water separately in two tanks
(b) Drawing constant quantity of water from the water tank and pumping it to the mill stand through an oil-water mixer and spray header
(c) Drawing metered quantity of oil from the oil tank and pumping it to mix with water in the above said mixer for making dispersion to be sprayed over the edger rolls
(d) Oil pump to be automatically switched on when metal gets rolled in the mill stand and to be switched off when metal leaves the mill stand.
(e) Timing of spray of lubrication to be controlled using signal of hot metal detector (HMD) at the entry of the edger stand (with some time delay) using PLC
(f) Flow rate of the oil to be controlled using Variable Frequency Drive (VFD) for the metering pump
(g) A combination of mechanical wiping and air wiping to be used for wiping out roll cooling water from the roll surface before application of lubrication
(h) Proper instrumentation to be used to monitor pressures of oil, water and dispersion, level of fluid in oil and water tanks, etc.

Schematic arrangement of the developed system is given in Fig. 3.

The system was comprised of:
(a) Oil pumping station having individual duplex metering pump with variable frequency drive for each stand,
(b) Centralised water pumping station with inline vertical centrifugal pumps and automatic self-cleaning filter,
(c) Dispersion devices including static oil-water mixer, spray header with nozzles, mechanical wiper and air wiper for individual edger roll,
(d) PLC based monitoring, control and data logging system,
(e) HMI workstation for direct control by operators

It consisted of various mechanical, electrical, automation and instrumentation components or subsystems for achieving specific functions. List of these components is given in Table 2 and functions of major components are given in Table 3. Quantities of these components shown in Table 2 are for all the 4 Edger Stands of the HSM.

Table 2 Components of Roll Lubrication System

(i) Water pumping station
(a) Water storage tank with fittings : 1 set
(b) Level switch for water tank : 1 No.
(c) Water pump with motor and suitable coupling : 2 sets
(d) Water filter : 1 set
(e) Water pipelines with strainers, valves and fittings : 1 lot

(ii) Oil pumping station
(a) Oil storage tank with fittings : 4 sets
(b) Oil pump with motor and suitable coupling : 4 sets
(c) Calibration cylinder : 4 No.
(d) Oil pipelines with strainers, valves, fittings : 4 lots

(iii) Dispersion station (Oil-water mixing and spray station)
(a) Static mixer : 8 No.
(b) Dispersion spray header with nozzles : 8 sets
(c) Air blow-off headers with nozzles : 8 sets
(d) Spring loaded mechanical wiper : 8 sets
(e) Pneumatic pipelines : 1 lot
(f) Valves, hoses and fittings : 1 lot

(iv) Control station
(a) Variable Frequency Drive (VFD) : 4 No.
(b) Programmable Logic Controller (PLC) : 1 set
(c) Operating station with HMI : 1 No.
(d) Programming station : 1 set
(e) Electrical & relay panel : 1 set
(f) Software : 1 lot
(g) Power supply & accessories : 1 lot
(h) Power, control and communication cables : 1 lot
(i) Pressure transmitter & gauge : 1 lot

Table 3 Function of major components of Edger Roll Lubrication System

Sl. Components Feature Function
1 Oil tank 500-1000 litre capacity Storage of hot rolling oil for supply to oil pump
2 Water tank 3000-5000 litre capacity Storage of water for supply to water pump
3 Level sensors Electronic type Measurement and display of level of oil and water in their respective tanks and automatically/manually refilling the tanks from their feed lines
4 Water pump Multi-stage centrifugal water pump, 10-20 m3/hr, 8-16 bar Supplying water at specified flow rate and pressure centrally for all the stands and distributing it to mixers for two rolls of individual stand
5 Water filter Automatic self cleaning type, 10-20 m3/hr, 100-200 micron Cleaning of water and preventing nozzle blockage/chocking
6 Oil pump Diaphragm proportionate dosing pump, 500-1000 ml/min Supplying oil at specified flow rate and pressure separately to mixers for two edger rolls of an individual stand
7 Drive for oil pump Variable frequency drive Automatically control supply of oil flow rate suiting to varying requirements of each stand for varying rolling conditions
8 Oil filter Y strainer, 50-100 micron rating Cleaning of oil
9 Flow meter Calibration cylinder, 500-1000 ml Measurement of flow rate of oil pumped by each oil pump
10 Pressure gauge Pressure transmitters, 0-20 bar Measurement of supply pressure of oil, water and dispersion in each flow line
11 Oil-water mixer Static tube type, 10-50 mm diameter Mixing of oil and water to form dispersion at specified flow rate and pressure
12 Spray header with nozzles 2-4 nozzles per header, 10-20 litre/minute per header Spraying of dispersion over edger rolls at specified flow rate and pressure
13 Valves and pipelines Ball and solenoid types Manual control of oil and water flow using ball valves and automatic control of fluid flow using solenoid valves
14 Controller PLC with HMI Automatically controlling different functions of the lubrication system
16 Electrical panel Front open type Housing power system, PLC, HMI, VFD, relays, switches, circuit breaker, level monitor, etc.

The above lubrication system was fabricated, installed and commissioned at the industrial mill. It was integrated with the existing mill system both mechanically and electrically. HMD signals from all the edger stands of the operating mill were fed to the PLC of the lubrication system for controlling its operation as shown in Fig. 4.

Operating logic for the system was developed and loaded in the operating station placed in operator’s cabin. Typical screens of the operating station are shown in Fig. 5

After commissioning and integration of the lubrication system in the mill it was required to stabilise its operation such that an optimum oil flow rate was achieved where there was significant reduction in roll wear without any adverse effect on rolling operation. For this, use of lubrication at each stand was started with a very low oil flow rate and it was increased in steps judiciously to avoid skidding of bars. Finally, the oil flow was increased to a maximum level at which working of the system was found satisfactory and all the control functions were performed as per design. Subsequently performance of the system was evaluated in terms of effect of lubrication on various process and economic parameters important to the mill.
It was observed that use of lubrication applied through the innovated system led to the following benefits:
(a) There was appreciable reduction in friction and roll wear.
(b) Roll force with lubrication was lower by around 5-10% due to reduction in friction as shown in Fig. 6.
(c) Significant improvement in surface quality of the used edger rolls due to reduction in wear rate.
(d) The campaign size of edger rolls was increased by minimum 30% to maximum 75% at different stands. Average increase in combined campaign size was over 40%.
(e) Average off-takes or reductions in diameter of rolls with and without lubrication were of comparable level despite increase in campaign size.
(f) Productions per unit roll off-take increased by over 40% (from over 33000 t/mm to over 48000 t/mm).
(g) It finally led to reduction in average specific edger roll consumption by over 25%.
(h) The specific oil consumption varied from 10 ml/t initially to maximum 20 ml/t after final round of stabilisation of the system for all the four edger stands. The average specific oil consumption for the entire trial period was around 15 ml/t.
(i) The edger roll lubrication was recommended for regular use at all the four edger stands.

The above industrial results finally validated the design of the innovated edger roll lubrication system.

HIGHLIGHT OF INVENTIVE STEP
Rolls of edger stands are getting worn out at faster rate due to high mechanical and thermal loads and presence of abrasive scale. It is causing high roll consumption and lower campaign size of rolling. Control of width and edge quality also becomes difficult with worn out edger rolls. For controlling roll-wear, an edger roll lubrication system was developed, fabricated, installed, commissioned and stabilised at all the four stands of a Hot Strip Mill of an Integrated Steel Plant. The system consisted of a centralised water station; an individual oil station for each stand; a dispersion station for each edger roll; a centralised PLC based control station; and an operating station. A semi-synthetic hot rolling was procured and used with the edger roll lubrication. Operation of the lubrication system was stabilised by regulating oil flow rate and fine tuning of the system. Finally, performance of the lubrication was evaluated in a yearlong trial where over 30 lakh ton of steels were processed through it and effects of lubrication on roll force, campaign size, roll off-take and roll consumption were studied.

The studies revealed that with the use of lubrication at the edger stands there was appreciable reduction in friction and wear. Roll force with the lubrication reduced by 5-10% and there was increase in average campaign size of rolling for all the four stands by over 40%. Average off-takes of rolls with and without lubrication were of comparable level even at higher campaign size. It led to reduction in average specific edger roll consumption by over 25%. Specific oil consumption during the trial period varied from 10-20 ml/t for all the edger stands. Regular use of the edger roll lubrication was recommended for all the coils at the Hot Strip Mill.

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 by way of examples and description and is not intended to be exhaustive or to limit the invention to the particular embodiments and applications disclosed. 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.

WE CLAIM:

1. An edger roll lubrication system for application of hot rolling oil over the edger rolls of the mill comprising of:
an oil pumping station having individual duplex metering pump with variable frequency drive for each stand;
a centralised water pumping station with inline vertical centrifugal pumps and automatic self-cleaning filter;
a plurality of dispersion devices including static oil-water mixer, spray header with nozzles, mechanical wiper and air wiper for individual edger roll; and
a PLC based monitoring, control and data logging system along with a HMI workstation for direct control.

2. The edger roll lubrication system as claimed in claim 1, wherein dispersion of oil-in-water prepared by mixing oil and water at high pressure in a mixer is directly sprayed over the said edger rolls of a group of edger stands.

3. The edger roll lubrication system as claimed in claim 1, wherein said spraying is configured for variable lubrication conditions suiting to requirements of edger rolls at drive side and work side of different mills stands.

4. The edger roll lubrication system as claimed in claim 2, wherein said oil flow rate during the mixing operation is varied from minimum 0 to maximum 350 ml/min at each roll and the spray is switched on only when material is being rolled in the mill and its spray-timing can be varied as per length of the bar.

5. The edger roll lubrication system as claimed in claim 1, wherein the said control of the oil flow rate is achieved using diaphragm type duplex metering pump with variable frequency drive and separate cylinder is used for supplying lubricant to two edger rolls, which is useful in maintaining differential flow rate.

6. The edger roll lubrication system as claimed in claim 1, wherein multi-stage inline vertical centrifugal pump with suitable water distribution network is used to supply water at all the rolls along with an automatic self cleaning filter is used to clean water pumped to the oil-water mixer.

7. The edger roll lubrication system as claimed in claim 1, wherein a tube type static mixer is used to mix the oil with water near the individual rolls. Dispersion so formed is sprayed over each roll using header with nozzles.

8. The edger roll lubrication system as claimed in claim 1, wherein combination of mechanical wiper and air wiper are used to wipe out roll cooling water from the roll surface before spray of lubrication which helps in formation of stable oil film on the roll surface.

9. An edger roll lubrication method for application of hot rolling oil over the edger rolls comprising of:
making buffer storage of oil and water separately in two tanks;
drawing constant quantity of water from the water tank and pumping it to the mill stand through an oil-water mixer and spray header;
drawing metered quantity of oil from the oil tank and pumping it to mix with water in the above said mixer for making dispersion to be sprayed over the edger rolls;
switching of Oil pump automatically on when metal gets rolled in the mill stand and to be switched off when metal leaves the mill stand.
controlling the timing of spray of lubrication using signal of hot metal detector (HMD) at the entry of the edger stand (with some time delay) using PLC;
controlling the flow rate of the oil using Variable Frequency Drive (VFD) for the metering pump;
wiping out roll cooling water from the roll surface before application of lubrication; and
monitoring the pressures of oil, water and dispersion, level of fluid in oil and water tanks, etc.

10. The edger roll lubrication method as claimed in claim 9; further comprising the steps of :
i. Filling and controlling level of water and oil in their respective tanks;
ii. Maintaining Level of oil flow rate to be pumped to each mill stand;
iii. Controlling the on / off timing of oil pump to spray lubricating oil only when material is in the mill, which is identified through signal from hot metal detector placed before the mill stand;
iv. Generating alarm during violation of any protocol; and
v. Switching off the system in case of overshooting of any limiting conditions.