Pinch rolls serve an important role in hot strip steel mill applications. Mill practices such as material selection, change-out criteria, campaign length, engagement practice, alignment, and maintenance procedures are all determined by optimizing quality and productivity in the mill. When it comes to pinch rolls, variables such as roll size, mechanical design, size and number of coilers, roll consumption rate, and product are all factors in determining the best pinch roll selection, along with price and operational cost.
In steel mill coiler applications, there are two sets of pinch rolls installed at the entrance to the coiler, one at the top and one at the bottom. The pinch rollers receive the head end of the hot strip and direct it into the coiler, while providing back tension for the strip during the coiling process.
Typically the top pinch roll is only in contact with the head end and tail end of the strip. In some mill applications, the top roll remains in continuous contact with the strip in order to create slight tension as it is coiling, creating a tighter coil. In both cases, the bottom roll maintains contact with the strip throughout the coiling process. Since they are the last set of rolls in the mill with which the hot rolled product comes in contact, the quality demands on pinch rollers are extremely high.
When it comes to achieving the highest degree of quality in the hot strip steel mill product, more mills are realizing the benefits of Xtek Bemcalloy™ Pinch Rolls. The inherent lubrication characterics of the graphitic in Bemcalloy, combined with its natural resistance to adhesion of dissimilar metals, results in the material’s superior pickup resistance. This pickup resistance has been demonstrated to eliminate the rejection of coils due to poor surface quality that is attributable to adhered debris on the pinch roll working surface.
The metallurgical attributes of Bemcalloy promote resistance to both adhesive and abrasive wear. This wear resistance promotes extended campaign lengths, as well as uniform and consistent wear throughout each campaign. Xtek Bemcalloy pinch rolls also require less stock removal during regrinding, maximizing the stock available throughout the entire life cycle of the pinch roll.
Engineered for optimal performance and value, top pinch rolls are an assembly consisting of a forged alloy steel through-shaft, two forged alloy steel hubs, the Bemcalloy sleeve, and associated hardware. Bottom pinch roll assemblies include a forged alloy steel through-shaft, the Bemcalloy sleeve, and related hardware. In both types of pinch rolls, the sleeve is a horizontally, centrifugally cast, thick-walled piece with a specific Bemcalloy chemistry that has been tailored to meet the specific needs of the application. The Bemcalloy C-141 material is the most established of Xtek’s pinch roll material technology.
Bemcalloy C-141 material is a hypoeutectic alloy gray iron enriched with minimal amounts of Chromium, Molybdenum, and Nickel. The addition of these alloys enhances the material’s wear and pick-up resistance. Niobium is also added to promote the formation of extremely hard niobium carbides that further enhance wear resistance. This specially balanced combination aids in the integrity and stability of the pinch rolls while they are in service with thermal stability, high thermal conductivity, resistance to thermal fatigue and a moderate resistance to thermal shock.