Bearing Technical Solutions for Different Rolling Processes

 

Steel and non-ferrous metal rolling production encompasses multiple process types including hot rolling, cold rolling and continuous casting, each imposing significantly different technical requirements on bearings. NMT provides differentiated bearing product configurations and technical solutions according to the operating characteristics of each process.

 

Hot Rolling Bearing Solutions

 

Hot rolling production lines are characterized by the coexistence of high temperature, heavy loads and impact loads. In hot roughing and finishing mill stands, bearings must maintain stable rotational accuracy and dimensional stability under the combined effects of thermal radiation from red-hot steel (bearing housing surface temperatures reaching 150-250°C) and alternating cooling water spray.

 

NMT's bearing solutions for hot rolling equipment primarily consist of four-row tapered roller bearings and four-row cylindrical roller bearings. Four-row tapered roller bearings are used for hot rolling work rolls, simultaneously withstanding radial rolling forces and axial forces; four-row cylindrical roller bearings are used for backup rolls, primarily承担 radial loads. Both bearing types utilize thermally stabilized high-temperature bearing steel materials, maintaining dimensional stability and hardness retention under high-temperature conditions. Ring wall thickness is specially calculated to resist deformation under thousands of tons of rolling force while maintaining geometric accuracy.

 

In terms of roller crowning for hot rolling bearings, NMT employs logarithmic curve crowning design to ensure uniform load distribution along the full roller length, avoiding edge stress concentration. This design is particularly important for hot rolling conditions——the impact during billet biting and rolling force fluctuations subject bearings to frequent instantaneous overloads, and uniform load distribution helps extend bearing fatigue life under impact conditions.

 

The sealing systems for hot rolling bearings must simultaneously address the combined effects of high temperature and water spray. NMT configures combinations of labyrinth seals, contact rubber seals and metal shields according to specific operating conditions. Labyrinth seals use multi-stage annular gaps and centrifugal force to fling water and scale particles outward; contact rubber seals (FKM/HNBR materials) serve as the second line of defense, maintaining slight positive pressure inside the bearing; metal shields provide auxiliary protection. Seal lips are optimized through finite element stress analysis, balancing sealing effectiveness with friction resistance.

 

For lubrication, hot rolling bearings are pre-filled with grease formulated with high-viscosity base oils and extreme-pressure anti-wear, rust-preventive and water-resistant additives, maintaining stable lubricating films under high-temperature and water spray conditions. Internal grease channels are optimized to ensure continuous lubricant supply to rolling contact areas during low-speed heavy-load operation.

 

Cold Rolling Bearing Solutions

 

Cold rolling production lines are characterized by high precision, high speed and significant rolling forces. Strip steel passes through mills at relatively high speeds during cold rolling, with final thickness tolerances controlled to micron levels, imposing high requirements on bearing rotational accuracy and rigidity.

 

NMT's bearing solutions for cold rolling equipment primarily consist of high-precision four-row tapered roller bearings and four-row cylindrical roller bearings. Work roll bearings must simultaneously withstand radial and axial loads, typically using four-row tapered roller bearings; backup roll bearings primarily承受 radial loads, using four-row cylindrical roller bearings. Both bearing types are controlled to P5 or higher precision grades, with raceway roundness and rolling element grading precision subject to precision inspection and matching.

 

Cold rolling bearing radial clearance is precisely set to enhance overall roll system rigidity, minimizing elastic deflection of rolls under rolling forces. Axial clearance is precisely calculated based on operating speed and temperature rise conditions to ensure reasonable internal clearance at thermal equilibrium during high-speed operation. For cold rolling backup roll bearings using oil-mist lubrication, NMT provides four-row cylindrical roller bearings with condensation nozzles, allowing oil mist to condense into larger droplets before entering the bearing, enhancing lubrication effectiveness.

 

Cold rolling bearing sealing systems focus on preventing emulsion and fine particle ingress. Contact rubber seals provide reliable active blocking under cold rolling conditions, keeping external contaminants outside the bearing. Seal materials use specialty rubber formulations resistant to emulsion corrosion, maintaining elasticity and sealing performance in prolonged contact with coolant environments.

 

Continuous Caster Bearing Solutions

 

Continuous caster segment bearings operate under conditions of low speed, heavy loads and continuous water spray. Bearings承受 significant radial loads at very low speeds, while continuous caster cooling water spray poses ongoing challenges to sealing systems.

 

NMT's bearing solutions for continuous caster segments primarily consist of four-row cylindrical roller bearings, mainly承担 radial loads. Bearing rolling elements and raceway materials use corrosion-resistant bearing steel, maintaining surface integrity in prolonged water spray environments. Ring and rolling element hardness and toughness are specially balanced to achieve both wear resistance and crack resistance under low-speed heavy-load conditions.

 

Sealing systems for continuous caster bearings are critical to bearing life. NMT employs combinations of labyrinth seals and contact rubber seals——the outer labyrinth seal blocks most water and scale particles, while the inner contact seal provides final blocking protection. Seal materials use water-resistant, steam-resistant specialty rubber (FKM or HNBR), maintaining sealing performance in high-temperature moisture environments.

 

Continuous caster bearing greases use formulations with excellent water resistance, resisting emulsification and washout under cooling water spray. Internal grease channels are specially designed to ensure grease reaches rolling contact areas even at very low speeds.

 

Bearing Material Adaptation to Operating Conditions

 

NMT selects different grades of bearing steel according to mill type and operating conditions. For conventional hot and cold rolling conditions, GCr15 high-purity bearing steel is used, processed through vacuum degassing and electroslag remelting double refining to significantly reduce non-metallic inclusion content and size. For high-temperature conditions (operating temperatures above 200°C), M50 high-temperature bearing steel is used, with special thermal stabilization treatment to maintain dimensional stability and hardness retention at elevated temperatures. For corrosive media environments, specially passivated corrosion-resistant bearing steel or corrosion-resistant coating solutions are used to resist chemical attack.

 

In terms of heat treatment, NMT employs controlled-atmosphere heat treatment and surface carburizing/induction hardening processes. Raceway surfaces achieve a high-hardness hardened layer of HRC60-64 while the core maintains toughness. This structure enables bearings to resist indentation and spalling on the surface while the core absorbs impact energy under impact loads, extending bearing service life under heavy-load and impact conditions.

 

Systematic Configuration of Seals and Lubrication

 

Rolling mill bearing sealing systems must be configured according to specific operating conditions. NMT provides labyrinth seals, contact rubber seals, metal shields and air curtain-assisted seals, used in combination according to mill type, water pressure, speed and temperature conditions. Seal materials are selected from FKM (fluororubber, temperature resistance 150-250°C) or HNBR (hydrogenated nitrile rubber, water-resistant and wear-resistant), maintaining sealing performance under high-temperature and water spray conditions.

 

For lubrication, NMT selects greases with different viscosity grades and additive formulations according to bearing type, load, speed and temperature conditions. Base oil viscosity ranges from ISO VG 150 to ISO VG 1000, with proportions of extreme-pressure anti-wear additives, rust inhibitors and water-resistant additives adjusted according to operating conditions. Bearings are pre-filled with grease at 30%-50% of internal free space, ensuring continuous lubrication while avoiding churning heat generation.

 

Application References and Technical Support

 

NMT rolling mill bearing products have been applied in hot rolling, cold rolling and continuous casting lines at multiple domestic steel mills. In hot roughing mill stands, four-row tapered roller bearings maintain stable operation under thousands of tons of rolling force and high-temperature water spray environments; in cold rolling mills, high-precision four-row cylindrical roller bearings meet micron-level strip thickness tolerance control requirements; in continuous caster segments, four-row cylindrical roller bearings achieve long-term maintenance-free operation under low-speed heavy-load and water spray environments.

 

NMT provides full-process technical support from bearing selection, installation guidance to operational monitoring and failure analysis. Based on users' specific mill parameters (mill type, rolling force, speed, temperature, coolant conditions, etc.), NMT provides precise bearing selection recommendations and installation parameter settings. During installation, NMT can provide on-site guidance to ensure clearance setting, preload control and seal installation meet specifications. During operation, NMT provides condition monitoring recommendations and periodic follow-up services to assist users in optimizing maintenance strategies.

 

NMT also provides bearing remanufacturing services, removing fatigue layers from raceway surfaces through precision grinding, restoring geometric accuracy, and replacing rolling elements and cages to restore bearing performance to near-new levels. Remanufacturing services help extend the overall service life of bearings and reduce users' lifecycle bearing costs.