Managing Water Contamination in Hot Rolling Mills to Improve Productivity Toby Hlade Products Technical Advisor ExxonMobil Timothy Hurley Engineering Manager Primetals Technologies
What we ll discuss today Water contamination and its impact Circulating oils for flat and long rolling systems o Continuous system monitoring o Water removal strategies Greases for continuous casters and hot rolling mills
Water contamination: an unavoidable challenge On average, steel plants use 6,854 gallons of water per ton of steel produced.* Source: World Steel Association, 2015
Effects of water contamination Accelerated wear Lubricant film is interrupted, creating metal-to-metal contact Corrosion Due to water settling on bearing and gear surfaces during downtime Lubricant degradation Water accelerates oxidation, damaging base oils and stripping additives Filterability Water affects oil s ability to pass through filter without clogging or plugging
Three types of water contamination 1. Dissolved water Water absorbed at molecular level Least harmful form of water contamination 2. Emulsified water Fine droplets tightly dispersed in oil Can disrupt lubricating films 3. Free water Causes immediate collapse of lubrication films, resulting in metalto-metal contact
Water content vs. equipment life expectancy
Protecting equipment from water contamination Proper lubrication is essential it s the first line of defense. Operators must understand the different lubrication requirements of flat and long rolling systems. Continuous monitoring is a key tool. Water removal is a last line of defense.
Circulating Oils for Flat and Long Rolling Mill Equipment
Key oil characteristics: demulsibility Defined by an oil s ability to readily separate from water. Need oils with super demulsibility (SD) properties. Oils must pass the UEC Dynamic Demulsibility Endurance test.
Key oil characteristics: corrosion protection Corrosion performance measured using the EMCOR rig test. Distilled water Oil A (left) passes, while Oil B (right) fails. 0.5% NaCl water Both oils fail, but Oil A (left) scores better.
Key oil characteristics: wet filterability Defined by an oil s ability to filter small particles when wet. Measured using the ISO 13357 Filterability Test. Performance is formulation dependent.
Lubrication requirements vary by application In hot strip mill systems, circulating oils lubricate back-up roll bearings: Bearing Operate under hydrodynamic lubrication. Require higher viscosity oils (ISO 460-680). Journal Acceptable water level threshold of 2%. Antiwear and EP additives not needed. Oil Hydrodynamic Wedge
Lubrication requirements vary by application In long rolling systems, oils lubricate gear and roller bearings: Bearing Operate under elastohydrodynamic (EHL) lubrication. Require lower viscosity oils (ISO 460 or less). Lower water level threshold of 0.2%. Require anti-wear components. Outer race Lubricant
Suitable circulating oil types Rust and oxidation (R&O) inhibited oils Best suited for continuous flat mill backup bearing systems. EP gear oils Used in segregated gear boxes or central gear lube systems in flat rolling mills, continuous casters and hot mills. Specialized oils Designed for high speed rod mills combine wear protection of EP oil with water tolerance of R&O oil.
Monitoring for contamination and water removal
Common monitoring options Inline sensors Measure relative humidity. Good for systems that are usually dry, such as gear drives in flat mills. Not ideal for monitoring applications that are constantly exposed to significant water. On-site kits Better monitoring option for applications constantly exposed to water. Low-cost kits can measure all forms of water. Results are reasonably accurate, making them good for daily testing. Source: Parker Kittiwake
Common monitoring options Used oil analysis Most accurate form of monitoring. Typically conducted by an oil supplier or third party lab. Testing also provides insight into key lubricant performance parameters. Results can take some time to process. Manual checks Important to check low point drains manually on a regular basis
The last line of defense water removal options Vacuum dehydrators Centrifuge Two-tank system Use vacuum and heat to evaporate water from oil. Doesn t rely on an oil s demulsibility performance. Can remove dissolved water. Typically a good long-term investment. Increase gravity to accelerate demulsification. Does rely on good demulsibility of the oil and cannot remove dissolved water. Not ideal for rod mill applications. Sometimes used for flat mill backup bearing systems. Relies on using oils with excellent demulsibility. Good for keeping oils below 1-2% water contamination.
Greases for continuous casters and hot rolling mills
Important grease characteristics To properly lubricate bearings across integrated hot rolling mill systems, greases require: High base oil viscosity High load carrying ability High temperature performance Excellent water resistance Strong corrosion protection
Calcium sulfonate greases the best technology Calcium sulfonate greases are excellent for very wet applications: Can absorb substantial amounts of water while maintaining performance. Have ability to resist oil bleed in temperatures above 400 F. Offer high EP properties and do not need sulfur-phosphorous agents. Can help reduce feed rates.
Calcium sulfonate greases the best technology This bearing was exposed to severe water contamination. The grease s consistency remains excellent. And, there is no free water, corrosion or wear.
Other thickener technologies Lithium grease Poor water resistance. Softens when emulsified with water. High replenishment rates. Aluminum complex grease Resists wash-off and spray-off best, but does not absorb any water. Leads to free water in the bearings. Lithium complex grease With the right balance, lithium complex greases can work well. Some do not deliver the required performance.
Bethlehem Steel Grease Stability Combo Test Excellent measure of grease wet performance. Worked Penetration Water Spray-Off 400 350 300 250 200 150 100 50 0 NLGI 1 Calcium Sulfonate A Calcium Sulfonate B Worked penetration, mm/10 50 45 40 35 30 25 20 15 10 5 0 Calcium Sulfonate A Calcium Sulfonate B Emulsified penetration, mm/10 Initial Water Sprayoff, % Emulsified penetration Part B, mm/10 Emulsified Water Sprayoff, %
Switching greases improves caster performance A steel manufacturer operated continuous casters at its Indiana plant lubricated with a lithium complex mill grease. Continuous caster foot rolls experienced high temperature bleed and water washout, resulting in frequent locked rolls and production delays. Converted to a high performance calcium sulfonate grease.
Switching greases improves caster performance Results Immediate decrease in foot roll lock-ups. In an extreme case, the grease performed for up to 10 hours without resupply. Reduced feed rates by 62%. Improved maintenance intervals, increasing employee safety and lowering overall operating costs.
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Toby Hlade Products Technical Advisor ExxonMobil Industrial Lubricants mobil.com/steel Timothy Hurley Engineering Manager Primetals Technologies primetals.com AISTech Booth #1935 AISTech Booth #