Effect of Preheating on Cladding Cracks of Calender Rolls

Literature Overview

This 2006 study by Wang Lihua and Hui Yuanbo, published in Hot Working Technology, investigates the influence of preheating on crack formation during weld overlay of calender rolls. Calender rolls are critical components in rubber and polymer processing industries, where their surface integrity directly determines product quality. The authors conducted systematic experiments varying preheat temperatures to evaluate how thermal management strategies affect the crack susceptibility of the overlay layer. This research is particularly relevant for engineers who must balance productivity with surface durability in roll remanufacturing operations.

Core Technical Analysis

Crack Mechanisms in Calender Roll Cladding

Calender rolls typically consist of a carbon steel or low-alloy steel substrate overlaid with high-hardness, wear-resistant alloy layers. The cladding process introduces several crack-promoting factors: high carbon and alloy content in the overlay material, rapid cooling rates due to the thermal mass of the roll, residual stresses from differential thermal contraction, and hydrogen-induced cracking susceptibility. The authors identified that without adequate preheating, the thermal gradient between the substrate and overlay layer creates tensile stresses that exceed the yield strength of the weld metal at elevated temperatures, leading to hot cracks. Upon cooling, the brittle microstructure of the overlay material combined with residual stresses produces cold cracks, particularly at the fusion line.

Preheating Temperature Windows

The study established practical preheating temperature ranges based on the specific overlay material composition and substrate geometry. The following table summarizes the key findings:

The optimal preheat temperature was found to be in the 300–400°C range for most common overlay compositions, providing a favorable balance between crack resistance and post-weld hardness retention. Preheating above 550°C was found to excessively reduce the hardness of the overlay layer, compromising the wear resistance that is the primary purpose of cladding.

Engineering Implications

The study recommends a multi-pass approach where the first pass receives the highest preheat treatment to minimize thermal shock, followed by subsequent passes at slightly lower temperatures to control overall heat input. Interpass temperature monitoring is essential, as exceeding 450°C between passes can cause grain coarsening and loss of mechanical properties in the overlay.

Integration with Engineering Practice

In calender roll remanufacturing, the preheating strategy must account for the cylindrical geometry, which creates non-uniform heat distribution. Practical experience shows that circumferential preheating using induction heating or flame heating should be performed in segments of no more than 300 mm arc length, with overlapping zones to ensure uniform temperature distribution. The study's findings align with industry practice where preheating is routinely applied at 250–400°C for high-alloy overlay materials on carbon steel substrates.

A critical observation from this research is that the crack prevention benefit of preheating is most significant during the first overlay pass, where the thermal gradient is most severe. Subsequent passes benefit from the thermal mass already deposited, reducing the need for equivalent preheat levels. This insight has practical value in optimizing production schedules, as it allows for reduced preheating time on subsequent passes without compromising quality.

Key Questions and Reflections

The study raises an important question about the relationship between preheat temperature and hydrogen diffusion. While higher preheat temperatures promote hydrogen escape, they also increase the risk of tempering the overlay microstructure. The authors suggest that post-weld heat treatment, specifically a controlled tempering cycle at 200–300°C for 2 hours, can effectively remove residual hydrogen without significantly degrading the overlay hardness. This approach represents a more nuanced strategy than relying solely on preheating for crack prevention.

Another reflection concerns the economic trade-off. Preheating large-diameter calender rolls to 300–400°C requires significant energy input and extended cycle times. In high-volume manufacturing environments, the cost of preheating must be weighed against the cost of rework due to cracking. The study's data suggests that the defect reduction achieved through proper preheating far outweighs the additional energy costs, particularly when considering the downtime associated with cracked rolls in production lines.

Study Insights and Implications

This research provides a clear, data-driven framework for preheating decisions in calender roll cladding operations. The most valuable contribution is the quantification of crack frequency versus preheat temperature, which allows engineers to make informed decisions rather than relying on empirical rules of thumb. The findings also highlight the importance of considering the entire thermal cycle—preheat, interpass temperature, and post-weld treatment—as an integrated strategy rather than isolated process steps. For engineers working in roll remanufacturing, this study reinforces the principle that adequate thermal management is not optional but essential for achieving reliable, crack-free overlay surfaces that deliver the required service life in demanding calendering applications.