What are the wear mechanisms and failure modes of roller tables for strip mills under high-temperature and heavy-load conditions?
Publish Time: 2025-09-24
In modern steel production processes, roller tables for strip mills, as a critical conveying system connecting the heating furnace, roughing mill, finishing mill, and cooling zone, operate continuously under extremely harsh conditions. High temperatures, heavy loads, frequent starts and stops, and direct contact with hot steel slabs make them one of the most severely worn components in the entire rolling mill. Understanding their wear mechanisms and failure modes under these high-temperature, heavy-load conditions is fundamental to developing effective maintenance strategies, extending equipment lifespan, and ensuring continuous production.
The wear of roller tables for strip mills is not the result of a single factor, but a complex phenomenon involving multiple physical and chemical processes. Firstly, thermal effects are a dominant factor. When red-hot steel slabs emerge from the heating furnace, their surface temperature is extremely high, causing the roller surface to heat up instantly upon contact. This periodic thermal shock repeatedly subjects the surface material to severe expansion and contraction, eventually leading to thermal fatigue cracks. These microcracks gradually propagate and interconnect, ultimately causing surface material spalling, resulting in typical thermal fatigue wear. Simultaneously, high temperatures reduce the hardness and strength of the roller material, making it more susceptible to plastic deformation and wear under mechanical loads.
Regarding mechanical loads, the rollers not only bear the immense weight of the steel slabs but also experience sliding, rolling, and impact forces during transport and during start-up and shutdown. This continuous pressure and friction leads to abrasive and adhesive wear. Abrasive wear occurs when oxide scale from the steel slab surface detaches and embeds into the roller surface, acting like sandpaper during relative motion. Adhesive wear occurs when the metal surfaces soften at high temperatures, causing temporary localized fusion between the steel slab and the roller surface, which then separates during movement, transferring material from the roller, resulting in adhesive transfer.
Furthermore, rollers are often cooled with water or spray cooling to control temperature and remove scale. However, this cooling medium vaporizes instantly on the hot roller surface, generating intense thermal stress, further exacerbating thermal fatigue. Simultaneously, impurities or chemical components in the cooling water can cause slight corrosion, which, combined with mechanical wear, leads to corrosive wear, accelerating material loss.
During long-term operation, these wear mechanisms accumulate, ultimately resulting in various failure modes. The most common is roll surface spalling, where the surface material flakes off due to thermal fatigue and stress concentration, forming pits or spots. This not only affects the smooth transport of the steel billet but can also leave indentations on the rolled product, impacting product quality. Another issue is reduced roll diameter; continuous abrasive wear gradually decreases the roll diameter, leading to inconsistent line speed, affecting rolling speed and tension control. In severe cases, the overall strength of the roll body decreases, potentially causing bending or fracture, resulting in unplanned downtime.
Another failure mode is premature failure of the hardened surface layer. Many rolls use surface hardening or cladding processes to improve wear resistance, but under high temperatures and impact loads, delamination or cracking may occur between the hardened layer and the substrate, leading to loss of protection and rapid wear of the substrate material.
It's important to note that roll failure often isn't an isolated event, but rather the result of systemic degradation. Abnormal wear on one roll can cause uneven stress on adjacent rolls, triggering a chain reaction. Simultaneously, damage to auxiliary components such as roll bearings and the drive system can exacerbate roll wear, creating a vicious cycle.
Therefore, maintenance of roller tables for strip mills should not be limited to surface replacement or repair, but should encompass material selection, cooling methods, operational control, and regular inspection. By using materials with superior thermal fatigue resistance, optimizing cooling strategies, and implementing advanced technologies such as periodic laser surface hardening, the wear process can be effectively slowed, improving the reliability and service life of the rolls under extreme operating conditions. This not only affects the equipment's lifespan but directly impacts the efficiency and cost control of steel production.
