Presentation on theme: "Simple and Effective Work Roll Cooling Modification for Hot Mills"— Presentation transcript:
1Simple and Effective Work Roll Cooling Modification for Hot Mills Mark Armstrong - Lake Erie Steel GP Inc.Roland Van Rijn - Applied Fluids LLC.
2Agenda Introduction The Cooling Mechanism Water Pressure Water DistributionNozzle SelectionSpray Pattern and StrategySystem Balancing and Set-Up
3The Cooling MechanismDiscrepancies between the theoretical aspects and practical applicationRoll area coverageChanged angles and distances to the roll to cover more of the roll barrel – no improvementWater temperatureThe thermal gradient at the roll water interfaceNoticeable improvements not expected with cooler water
5Water PressureYamaguchi et. al found no relationship between water pressure and cooling efficacyVan Steden and Tellman found that the rate of energy transfer between roll and water increased for spray pressures up to 300 psiLake Erie Steel’s average roll temperatures decreased by 6°C to 10°C when the pressure was increased from 35 to 185 psi
6Water Pressure Effects of pooling Removal of spent water Ability to cut through the boundary layer
7Water Distribution Entry to Delivery Most opportunity for eat extraction on the delivery side as close to the roll bite as possibleExperiences at LESOriginal configuration 40-45% entry, 55-60% deliveryNozzles only modified to make the distribution 25% entry and 75% delivery yielded a 3°C to 5°C improvement in centerline roll temperaturesAddition of auxiliary headers on top and bottom on the delivery side closer to the roll biteNo noticeable change – notice the pooling
9Water Distribution Optimization of header placement Circumferential balancing of spray locations and volumes applied from the roll biteStand geometry and its affectsRoll sizes and their effect on spray coverage and overlapsUniformity of perpendicular distances
11Water Distribution Top to Bottom The amount of water applied to the top and the bottom work rolls should be roughly the sameSmall modifications to header positioning or water volumes to account for top to bottom variations in strip surface temperature should be done carefully
12Nozzle Selection KSAM – filtered nozzle with locating key Thickening flat typeStraightening filter advantages100% of rated flow even when 80% blockedImproved impingement and more organized flowMore efficient use of available water
13Nozzle Selection KSAM Nozzle with adapter base and attached filter effective spray areawasted waterKSAM Nozzle with adapter base and attached filterSpray Pattern from a Typical Flat Fan Nozzleeffective spray areawasted waterSpray Pattern from a Filtered KSAM
14Spray Pattern and Strategy Cross width flow density strategies (volume of water applied per unit width of roll barrel) – Blazevic’s findingsUniform strategy was selected by LES for simplicity and rolling schedulesImportance of flow density analysisCalculation of flow density variation
17Spray 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
18System Balancing and Set-Up Balancing the total flows, header flows and stand flows is critical to implementationAccurate flow estimation is keyFlow estimation and balancing can be done with some work in excelUsing header pressures and flow curves for the selected nozzles will yield accurate results
21SummaryEnsure 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.