CLIAMS:1. An integrated automatic roll lubrication system comprising
lubricating agent generating unit for preparing the lubricating agent in form of dispersion;
applicator means operatively connected to the said lubricating agent generating unit for controlled application of the said lubricating agent over backup rolls in the form dispersion to form a thin molecular boundary layer of the lubricant agent between mating surfaces of workpiece or feedstock and the work rolls for achieving controlled lubrication at the roll bite of finishing stands of a hot strip rolling mill.

2. An integrated automatic roll lubrication system as claimed in claim 1, wherein said lubricating agent generating unit comprises
an oil tank for storing the oil;
a water tank for storing water;
an oil pumping system for drawing requisite amount of oil form the oil tank;
a water pumping system for drawing requisite amount of water form the water tank;
mixing device for receiving the oil and the water and thereby mixing the oil with the water to form the lubricating agent in form of oil-in-water dispersion.

3. An integrated automatic roll lubrication system as claimed in anyone of claim 1 or 2, wherein the applicator means for applying the lubricating agent includes
segmented headers having spraying device with nozzles for spraying the oil-in-water dispersion over backup rolls of the finishing stands at specified flow rate and pressure which creates the thin molecular boundary layer of the lubricating agent between the mating surfaces of the workpiece or feedstock and the work rolls in the finishing stand.

4. An integrated automatic roll lubrication system as claimed in anyone of claims 2 to 3, wherein said water pumping system comprises
multi-stage inline vertical centrifugal water pump with a central water distribution network for supplying water at a specified flow rate and pressure (20-50 m3/hr, 8-10 bar) into the mixing device;
an automatic self cleaning filter for cleaning the water before pumping it into the mixing device.

5. An integrated automatic roll lubrication system as claimed in anyone of claims 2 to 4, wherein said oil pumping system comprises
dedicated diaphragm type duplex metering pumps with variable frequency drive with specified pumping rate (500-1000 ml/min) for each of the finishing stands;
Oil filter preferably Y strainer with 50-100 micron rating for cleaning the oil before pumping it into the mixing device.

6. An integrated automatic roll lubrication system as claimed in anyone of claims 2 to 5, wherein said mixing device comprises dedicated tube type static mixer preferably with 10-50 mm diameter for each of the finishing stand, each of said mixer of a finishing stand is disposed in operative communication with the oil pump dedicated for that finishing stand and the central water distribution network for receiving the oil and the water and thereby mixing the oil with the water.

7. An integrated automatic roll lubrication system as claimed in claim 6, wherein the mixers are disposed near the backup rolls of the finishing stands for facilitating the spraying of the oil-in-water dispersion after its formation by using the segmented headers.

8. An integrated automatic roll lubrication system as claimed in anyone of claims 3 to 7, wherein the segmented header comprises
a central segment for spraying the oil-in-water dispersion on narrow coils and
two end segments for spraying the oil-in-water dispersion for wider coils,
selection of the end segments is controlled by involving solenoid valves and width signal.

9. An integrated automatic roll lubrication system as claimed in anyone of claims 2 to 8, wherein said oil pumping system is operatively connected with the finishing stands to facilitate automatic activation of said oil pumping system with entry of feedstock in the finishing stands and automatic deactivation of the oil pumping system before exit of tail of the feedstock from the finishing stands.

10. An integrated automatic roll lubrication system as claimed in anyone of claims 1 to 9, optionally comprising
electronic level sensors disposed with the oil and the water tanks for measuring and displaying level of the oil and the water in their respective tanks and thereby facilitate automatic or manual refilling of the tanks from their respective feed tanks;
pressure gauge to monitor pressure of the oil and the water in the water and the oil pumping system.

11. An integrated automatic roll lubrication system as claimed in anyone of claims 1 to 10, comprises a centralised programmable logic controller based automation system to automatically control anyone or more operating conditions of the roll lubrication system, said operating conditions includes filling and controlling level of the water and the oil in their respective tanks, level of the oil flow rate to be pumped to the each finishing stand, on and off timing of the oil pumps for feeding coils in each finishing stand under un-lubricated condition for avoiding skidding during threading operation, selecting proper header segments configuration as per width of coils being roller, selecting suitable lubrication regime as per gauge of the coils being rolled, switching off the system during major mill delay like roll change, generating alarm during violation of any protocol, and switching off the system in case of overshooting of any limiting conditions.

12. An integrated automatic roll lubrication system as claimed in anyone of claims 1 to 11, which is operatively connected to a centralised Human-Machine-Interface based operating station for direct access of mill operators for operation and monitoring of lubrication parameters, said Human-Machine-Interface includes emergency switching means for shutting off the roll lubrication system in case of any cobble or misbehavior of the hot strip rolling mill.

13. An integrated automatic roll lubrication system as claimed in anyone of claims 11 to 12, wherein said programmable logic controller of the roll lubrication system is adapted to establish direct connectivity with PLC of the hot strip rolling mill for smooth exchange of data and signals and facilitating proper integration of the roll lubrication system with the hot strip rolling mill.

Dated this the 12th February, 2015.

Anjan Sen
Anjan Sen & Associates
(Applicants Agent)
IN/PA-199
,TagSPECI:FIELD OF THE INVENTION:
The present invention relates lubricating work rolls of finishing stands of a hot strip rolling mill. In particular the present invention is directed to develop an automatic and integrated roll lubrication system for preparation and application of lubricating agent in the work rolls of the finishing stands of hot strip rolling mills. The present system advantageously achieves an optimum lubrication condition and controlled operation in the finishing stands of hot strip rolling mills avoiding side effects of lubrication, particularly skidding and cobble generation in the hot strip rolling mills mill.

BACKGROUND ART:
Hot strip mill is a vital installation in any steel plant which converts thick cast or rolled slabs into thin strips by rolling them in hot condition at series of mill stands. Each stand of the hot strip mill uses two or more rotating rolls to impart the desired plastic deformation to the feedstock. These stands are divided in two groups, namely the roughing stands and the finishing stands. A typical hot strip mill comprises 3-5 roughing stands and 6-7 finishing stands. The roughing stands are used to impart bulk reduction in thickness, say from 200-250 mm to 30-40 mm, the finishing stands are used to achieve remaining reductions in thickness, say up to 2-20 mm. However, with fine control of dimensions, shape, surface quality and above all their mechanical and metallurgical properties, rolling process at finishing stands is highly critical and sensitive as it directly affects attributes of the rolled strips.
Rolls of the mills are subjected to arduous conditions as they face high cyclic mechanical and thermal loads, frictional shear stress, roll bending stresses, abrasive scales, etc. These conditions lead to high wear rate of rolls as well as requirement of more force and power for achieving the desired plastic deformation of steel. Rolls are therefore changed frequently at a pre-determined campaign size to avoid any defect in the rolled material. Every roll change however causes loss in production and reduced life of rolls.
Use of lubrication is an established technique for reducing wear of any machine component. It was however not common for rolls of hot strip rolling mills till sometimes back as it not only required availability of a suitable lubricant but also a well engineered lubricant application system. This is why all the old hot strip mills were not provided with any roll lubrication system. Subsequently, some of the oil companies started developing suitable hot rolling oils and some arrangement for applying them over the rolls.
The crude systems were however considered as an external aid for the mill and necessitated further requirement of having an integrated system suitable to logistics of the mill operation. Such integrated system needed to have sophisticated automation for achieving optimum lubrication and controlled operation to avoid side effects of lubrication, particularly skidding and cobble generation in the hot strip rolling mills mill.

OBJECT OF THE INVENTION:
It is thus the basic object of the present invention is to develop an automatic roll lubrication system which would be adapted for implementing at all the finishing stands of a hot strip mill of integrated steel plant and creating a thin molecular boundary layer of lubricant between the mating surfaces of workpiece or feedstock and work rolls.
Another object of the present invention is to develop an automatic roll lubrication system which would be adapted to apply lubricating agent between the mating surfaces of workpiece or feedstock and work rolls in the form of oil-in-water dispersion for achieving optimum lubrication and controlled operation to avoid side effects of lubrication, particularly skidding and cobble generation in the mill.
Yet another object of the present invention is to develop an automatic roll lubrication system which would be adapted to introduce lubrication at roll bite to reduce friction and wear of rolls at tandem hot mills.
A still further object of the present invention is to develop an automatic roll lubrication system which would be adapted to integrate with any existing steel rolling mill installation, and automatically control the lubrication operation and simultaneously generate diagnostics reports.

SUMMARY OF THE INVENTION:
Thus according to basic aspect of the present invention there is provided an integrated automatic roll lubrication system comprising
lubricating agent generating unit for preparing the lubricating agent in form of dispersion;
applicator means operatively connected to said lubricating agent generating unit for controlled application of said lubricating agent over work rolls in the form of a thin molecular boundary layer of the lubricant agent as said dispersion between mating surfaces of workpiece or feedstock and the work rolls for achieving controlled lubrication in the work rolls of finishing stands of a hot strip rolling mill.

According to another aspect in the present integrated automatic roll lubrication system, the lubricating agent generating unit comprises
an oil tank for storing the oil;
a water tank for storing water;
an oil pumping system for drawing requisite amount of oil form the oil tank;
a water pumping system for drawing requisite amount of water form the water tank;
mixing device for receiving the oil and the water and thereby mixing the oil with the water to form the lubricating agent in form of oil-in-water dispersion.

According to a further aspect in the present integrated automatic roll lubrication system, the applicator means for applying the lubricating agent includes segmented headers having spraying device with nozzles for spraying the oil-in-water dispersion over backup rolls of the finishing stands at specified flow rate and pressure which creates the thin molecular boundary layer of the oil-in-water dispersion between the mating surfaces of the workpiece or feedstock and the work rolls in the finishing stand.

According to yet another aspect in the present integrated automatic roll lubrication system, the water pumping system comprises
multi-stage inline vertical centrifugal water pump with a central water distribution network for supplying water at a specified flow rate and pressure (say 20-50 m3/hr, 8-10 bar) into the mixing device;
an automatic self cleaning filter for cleaning the water before pumping it into the mixing device.

According to a further aspect in the present integrated automatic roll lubrication system, the oil pumping system comprises
dedicated diaphragm type duplex metering pumps with variable frequency drive with specified pumping rate (say 500-1000 ml/min) for each of the finishing stands;
Oil filter preferably Y strainer with 50-100 micron rating for cleaning the oil before pumping it into the mixing device.

According to another aspect in the present integrated automatic roll lubrication system, the mixing device comprises dedicated tube type static mixer preferably with 10-50 mm diameter for each of the finishing stand, each of said mixer of a finishing stand is disposed in operative communication with the oil pump dedicated for that finishing stand and the central water distribution network for receiving the oil and the water and thereby mixing the oil with the water.

According to another aspect in the present integrated automatic roll lubrication system, the mixers are disposed near the backup rolls of the finishing stands for facilitating the spraying of the oil-in-water dispersion after its formation by using the segmented headers.

According to yet another aspect in the present integrated automatic roll lubrication system, the segmented header comprises
a central segment for spraying the oil-in-water dispersion on narrow coils and
two end segments for spraying the oil-in-water dispersion on wider coils,
selection of the end segments is controlled by involving solenoid valves and width signal.

According to a further aspect in the present integrated automatic roll lubrication system, the oil pumping system is operatively connected with the finishing stands to facilitate automatic activation of said oil pumping system with entry of feedstock in the finishing stands and automatic deactivation of the oil pumping system with exit of tail of the feedstock from the finishing stands.

According to another aspect, the present integrated automatic roll lubrication system optionally comprises
electronic level sensors disposed with the oil and the water tanks for measuring and displaying level of the oil and the water in their respective tanks and thereby facilitate automatic or manual refilling of the tanks from their respective feed tanks;
pressure gauge to monitor pressure of the oil and the water in the water and the oil pumping system.

In accordance with another aspect, the present integrated automatic roll lubrication system comprises a centralised programmable logic controller based automation system to automatically control anyone or more operating conditions of the roll lubrication system, said operating conditions includes filling and controlling level of the water and the oil in their respective tanks, level of the oil flow rate to be pumped to the each finishing stand, on and off timing of the oil pumps in the each finishing stand to feed material under un-lubricated condition for avoiding skidding during threading operation, selecting proper header segments configuration as per width of coils being roller, selecting suitable lubrication regime as per gauge of the coils being rolled, switching off the system during major mill delay like roll change, generating alarm during violation of any protocol, and switching off the system in case of overshooting of any limiting conditions.

In accordance with another aspect, the present integrated automatic roll lubrication system is adapted to be operatively connected with a centralised Human-Machine-Interface based operating station for direct access of mill operators for operation and monitoring of lubrication parameters, said Human-Machine-Interface includes emergency switching means for shutting off the roll lubrication system in case of any cobble or misbehavior of the hot strip rolling mill.

According to another aspect in the integrated automatic roll lubrication system, the programmable logic controller of the roll lubrication system is adapted to establish direct connectivity with PLC of the hot strip rolling mill for smooth exchange of data and signals and facilitating proper integration of the roll lubrication system with the hot strip rolling mill.

BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURES:
Figure 1 shows a schematic layout of hot strip mill.
Figure 2 is the schematic arrangements of roll lubrication system in accordance with the present invention.
Figure 3 shows various controls by PLC system in accordance with the present invention.
Figure 4 shows a typical screen shot of HMI in accordance with the present invention.
Figure 5 shows the effect of roll bite lubrication (RBL) on (a) roll force and (b) power for steel strip.

DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE ACCOMPANYING FIGURES:
Thus present invention discloses a roll lubrication system for preparation and application of lubricating agent over backup rolls of a group of finishing stands of hot strip mill. The present system basically includes means for preparing the lubricating agent in form of oil-in-water dispersion by mixing hot rolling oil (hence forth called oil) and water at high pressure and means for applying said lubricating agent over the backup rolls which create a thin molecular boundary layer of the lubricant agent in the form of oil-in-water dispersion between the mating surfaces of workpiece or feedstock and work rolls in the finishing stand. The system of the present invention is particularly designed to provide variable lubrication conditions suiting to requirements of top and bottom rolls of different mills stands.
Reference is first invited from the accompanying figure 1, which illustrates a preferred embodiment of the hot strip mill as used in a steel plant. As shown in the referred figure 1, the typical hot strip mill includes a Reheating furnace (1), a Descaling station (2), five Roughing stands (3), a Delay table (4), Crop shear (5), Finishing descaling station (6), seven Finishing stands (7), a Run out table (8), a Cooling spray (9) and a Downcoiler (10).
The detail of the components of the said hot strip mill is provided in the table 1
Table 1
Rated capacity ~ 4 MT/year
Configuration 2000 mm continuous mill
Roughing stands 5 No. non reversing 4-hi stands
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
Finishing mill work roll 810-750 mm diameter; material: Hi-Cr iron (first 3 stands) / ICDP cast iron (remaining stands)
Backup rolls 1610-1460 mm diameter of alloy forged steel (3% Cr)

This conventional hot strip mill does not include any roll lubrication system installed in them. Rolling of the strip was carried out without use of any hot rolling oil. Only water was sprayed over work and backup rolls to cool them. Under such condition work rolls of the mill were subjected to high friction and wear at roll bite. The higher friction values were responsible in increasing roll force and power consumption making rolling difficult specially for high strength steels and coils in critical sizes. With higher wear, the contour of roll gap was becoming uneven besides increasing friction values further. These conditions were unfavourable for obtaining desired shape and surface quality of the HR coils. The work rolls were therefore changed frequently at shorter campaign sizes say below 100 km. This obviously was at the cost of loss in production due to increased delay on account of roll changes. Introduction of lubrication at roll bite was an established approach for reducing friction and roll wear.
The roll lubrication system of the present system is installed near the Finishing stands (7) of the Hot strip mill. A preferred embodiment of the present roll lubrication system is illustrated in the accompanying figure 2.
As shown in the accompanying figure 2, the present roll lubrication system basically comprises lubricating agent generating unit for preparing lubricating agent and applicator means for applying said lubricating agent. The lubricating agent generating unit preferably includes an oil tank (12) having a capacity between 1000-3000 litre for storing hot rolling oil, a water tank (13) having a capacity between 4000-6000 litre for storing water, an oil pumping system (11), a water pumping system (19) for drawing requisite amount of oil and water form the oil tank (12) and the water tank (13) respectively and mixing device (14) for mixing the oil with water to form the lubricating agent i.e. the oil-in-water dispersion near the individual rolls of the finishing stands. The applicator means is operatively connected to said lubricating agent generating unit for controlled application of the lubricating agent. The applicator means includes segmented headers (15) for spraying the lubricating agent i.e. the oil-in-water over each roll of the finishing stands when the dispersion is formed.
As illustrated in the figure 2, in the present system, the water pumping system (19) is centralised for all the finishing stands while dedicated oil pump is used for each finishing stand. The oil pumping system (12) is operatively connected with the finishing stands to facilitate the automatic activation of said oil pumping system (12) with entry of the strip in the finishing stands and automatic deactivation of the oil pumping system (12) prior to exit of tail of the strip from the finishing stands.
In a preferred embodiment of the present invention, the water pumping system includes multi-stage inline vertical centrifugal water pump with suitable water distribution network for supplying water at a specified flow rate and pressure (20-50 m3/hr, 8-10 bar) centrally for all the stands and distributing it into the mixing device for top and bottom rolls of the individual finishing stand. An automatic self cleaning filter is used to clean the water before pumping it into the oil-water mixing device.
The oil pumping system preferably includes diaphragm type duplex metering pump with variable frequency drive (e.g. Diaphragm proportionate dosing pump with pumping rate, 500-1000 ml/min) for precisely drawing exact amount of the oil from the oil tank. In the present system, separate cylinder is used for supplying the lubricant to top and bottom rolls, which is useful in maintaining differential flow rate of oil at the top and bottom rolls, if so required. An Oil filter preferably Y strainer with 50-100 micron rating can be used to clean the oil before pumping it into the mixing device.
The mixing device (14) of the present system includes dedicated tube type static mixer preferably with 10-50 mm diameter for each finishing stand. Each mixer of a finishing stand is connected with the oil pump dedicated for that finishing stand and the central water distribution network for receiving the oil and the water for mixing the oil with the water. The mixers are disposed near the backup rolls of the finishing stands so that when the dispersion is formed it can be sprayed over each backup roll by using the segmented headers (15). The headers (15) includes spraying device with nozzles for spraying the dispersion over backup rolls at specified flow rate and pressure which later on create the thin molecular boundary layer of the lubricant agent between the mating surfaces of workpiece or feedstock and work rolls in the finishing stand. The segmented header comprises a central segment for spraying the oil-in-water dispersion on narrow coils and two end segments for spraying the oil-in-water dispersion when wider coils are being rolled. Selection of the end segments is controlled using solenoid valves and width signal. This is helpful in reducing wastage of oil during rolling of different sized coils.
In a preferred embodiment of the present system, electronic level sensors are disposed with the oil and the water tanks to measure and display of level of the oil and the water in their respective tanks and thereby facilitate automatic or manual refilling of the tanks from their respective feed tanks. A pressure gauge can be used in the water and the oil pumping system to monitor pressure of the oil and the water.
The present roll lubrication system is designed with a centralised programmable logic controller (PLC) (17) 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 feed the coil in each mill stand under un-lubricated condition for avoiding skidding during threading operation,

iv. Selection of proper header configuration as per width of coils being roller (wider/narrower),

v. Selecting suitable lubrication regime as per gauge of the coils being rolled (to switch off the system during thicker gauge rolling),

vi. Switching off the system during major mill delay like roll change,

vii. Generating alarm during violation of any protocol, and

viii. Switching off the system in case of overshooting of any limiting conditions.

The present system is disposed in operative communication with a centralised Human-Machine-Interface (HMI) (16) 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 misbehavior of the mill.

The 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 of the present invention has been provided a panel view touch screen with its electrical panel so that it can be used as an additional HMI for feeding important input data and monitoring the output information during stabilisation and maintenance of the system. The system has also been designed with an engineering station (20) for making suitable changes in the logic and program of the PLC and HMI.

Test Results:
The above lubrication system was fabricated, installed and commissioned at an industrial hot strip rolling mill. It was integrated with the existing rolling mill system both mechanically and electrically. Various signals from the operating mill were fed to the PLC of the lubrication system for controlling its functioning as shown schematically in the accompanying figure 3. Operating logic for the system was developed and loaded in the operating station placed in operator’s cabin. Typical screen of the operating station is shown in the accompanying figure 4.
After commissioning and integration of the lubrication system in the hot strip rolling mill it was required to stabilise its operation such that an optimum oil flow rate was achieved where there was significant improvement in rolling performance without any skidding or adverse effect of lubrication. 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 and cobble formation of coils. 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 for the mill.
It was observed that use of lubrication applied through the innovated system led to significant improvement in surface quality of the used work rolls due to reduction in wear rate. On experimental basis campaign size was increased even over 120 km without peeling of work rolls at all the stands. On an average, campaign size of rolling was increased by 16.4% from average 95 km during base period to average 111 km after stabilisation of the lubrication.
Grinding off-take of work rolls could be reduced with lubrication by 10-20% at different stands at the existing campaign size. With increase in campaign size of rolling and reduced mill wear the specific roll consumption decreased by around 20%. Lubrication was also helpful in reducing roll force and power by 5-10% leading to ease in processing of value added steels as shown in the accompanying figure 5 for steel rolling. Surface quality of the hot rolling coils improved with the lubrication as evidenced by reduction in ridge formation. All these benefits could be achieved at a very low specific oil consumption of 20-25 ml/t compared to its envisaged value of 65 ml/t. The above results finally validated the superiority of the present roll lubrication system.