1. Simple and Effective Work Roll Cooling Modification for Hot Mills
Mark Armstrong - Lake Erie Steel GP Inc.
Roland Van Rijn - Applied Fluids LLC.

2. Agenda Introduction The Cooling Mechanism Water Pressure
Water Distribution
Nozzle Selection
Spray Pattern and Strategy
System Balancing and Set-Up

3. The Cooling Mechanism
Discrepancies between the theoretical aspects and practical application
Roll area coverage
Changed angles and distances to the roll to cover more of the roll barrel – no improvement
Water temperature
The thermal gradient at the roll water interface
Noticeable improvements not expected with cooler water

5. Water Pressure
Yamaguchi et. al found no relationship between water pressure and cooling efficacy
Van Steden and Tellman found that the rate of energy transfer between roll and water increased for spray pressures up to 300 psi
Lake Erie Steel’s average roll temperatures decreased by 6°C to 10°C when the pressure was increased from 35 to 185 psi

6. Water Pressure Effects of pooling Removal of spent water
Ability to cut through the boundary layer

7. Water Distribution Entry to Delivery
Most opportunity for eat extraction on the delivery side as close to the roll bite as possible
Experiences at LES
Original configuration 40-45% entry, 55-60% delivery
Nozzles only modified to make the distribution 25% entry and 75% delivery yielded a 3°C to 5°C improvement in centerline roll temperatures
Addition of auxiliary headers on top and bottom on the delivery side closer to the roll bite
No noticeable change – notice the pooling

9. Water Distribution Optimization of header placement
Circumferential balancing of spray locations and volumes applied from the roll bite
Stand geometry and its affects
Roll sizes and their effect on spray coverage and overlaps
Uniformity of perpendicular distances

11. Water Distribution Top to Bottom
The amount of water applied to the top and the bottom work rolls should be roughly the same
Small modifications to header positioning or water volumes to account for top to bottom variations in strip surface temperature should be done carefully

12. Nozzle Selection KSAM – filtered nozzle with locating key
Thickening flat type
Straightening filter advantages
100% of rated flow even when 80% blocked
Improved impingement and more organized flow
More efficient use of available water

13. Nozzle Selection KSAM Nozzle with adapter base and attached filter
effective spray area
wasted water
KSAM Nozzle with adapter base and attached filter
Spray Pattern from a Typical Flat Fan Nozzle
effective spray area
wasted water
Spray Pattern from a Filtered KSAM

14. Spray Pattern and Strategy
Cross width flow density strategies (volume of water applied per unit width of roll barrel) – Blazevic’s findings
Uniform strategy was selected by LES for simplicity and rolling schedules
Importance of flow density analysis
Calculation of flow density variation

17. Spray Pattern and Strategy
Spray patterns should be designed to achieve a flow density variation that does not exceed 5%
Mill geometry and the range of roll diameters used must be examined to ensure that the flow density variation is acceptable for all operating conditions

18. System Balancing and Set-Up
Balancing the total flows, header flows and stand flows is critical to implementation
Accurate flow estimation is key
Flow estimation and balancing can be done with some work in excel
Using header pressures and flow curves for the selected nozzles will yield accurate results

21. Summary
Ensure that the cooling water pressure is adequate. Pressures for work roll cooling systems should be in the range of 7 bar to 15 bar (100 psi to 225 psi.).
Position headers for maximum heat extraction. Headers should be positioned as close as possible to the roll bite on the delivery side and out of the pool that is developed in the delivery guide apron if at all possible.
Headers should be positioned symmetrically about the top and bottom work rolls circumferentially from the roll bite. The volume of water and the positions it is applied in should also be symmetric about the top and bottom rolls circumferentially from the roll bite.
Select nozzles that provide a concentrated spray that matches well with the effective area used in spray overlap and flow density calculations.
Ensure system filtration of the cooling water is appropriate to prevent clogged nozzles or select a nozzle with attached filter to provide this filtration.
Design the spray overlaps to provide a flow density distribution with a variation of less than 5%.
Use header pressures to examine each branch of the work roll cooling system to ensure that the flows generated are balanced.