Introduction:

At CYKC Group, we are committed to providing high-quality, durable, and reliable rolls for the steel industry. Our composite rolls are known for their excellent wear resistance and performance under extreme conditions. However, like any equipment, they must be used and maintained under the right conditions to ensure optimal performance. In this article, we present a real case analysis of cracks in composite rolls used for φ12 rebar rolling, highlighting the importance of correct temperature control and roll design to maximize roll life and production efficiency.

Case Background:

A steel mill uses composite rolls for φ12 rebar rolling in the finishing mill (K1) and roughing mill (K2). The composite roll consists of four tungsten carbide (TC) rings, with a specification of φ380×φ260×110 and grade YGR60, containing 70% WC and 30% Co+Ni+Cr. The rings are fixed to the shaft using hydraulic locking nuts. The rolling speed is 15 meters per second.

Temperature measurements show:

• A-line billet temperature is 922°C, running smoothly.
• B-line billet temperature is 845°C, and cracks are visible on the surface of the composite rolls.

Crack Manifestation:

Cracks primarily appear on the surface or contact area of the composite roll rings, showing typical fatigue crack characteristics. These cracks not only affect the roll life but may also impact the surface quality of the rolled rebar.

Cause Analysis:

By comparing the operations of A-line and B-line, the following conclusions were drawn:

The main cause is insufficient billet temperature. The B-line billet temperature was lower than the optimal rolling temperature range (920±20°C). In lower temperature conditions, the steel’s deformation resistance increases, causing the roll rings to bear higher rolling forces, leading to fatigue cracks.

Additionally, improper roll pass design may cause increased stress concentration on the roll ring surfaces, accelerating crack propagation.

Solutions:

To resolve the above issues, the steel mill implemented the following measures:

• Optimized the roll ring pass design to improve metal deformation paths and reduce stress concentration.
• Adjusted the B-line billet heating process to ensure the temperature stays within the 920±20°C range before entering the mill.
• Enhanced temperature monitoring and process control, using more accurate temperature measurement devices to reduce errors.
• After these improvements, the crack issue in the composite rolls was effectively resolved. No similar problems were encountered in subsequent production.

Post-Processing and Maintenance:

For roll rings that have already developed cracks, the rolls are taken offline and ground to remove the cracks. However, repeated grinding reduces the remaining service life and rolling tonnage of the rolls. Therefore, prevention is better than repair in production processes.

Conclusion:

At CYKC Group, we understand that the quality of the rolls you use plays a critical role in your production’s success. Composite rolls, with their high hardness and wear resistance, are ideal for use in both finishing and roughing mill stands. However, to maximize their life and performance, attention to detail in temperature control, roll design, and maintenance is essential.

We are dedicated to providing not only top-quality rolls but also comprehensive technical support to ensure your operations run smoothly and efficiently. If you’re looking for reliable rolls and expert advice, contact CYKC Group today.

For inquiries regarding roll usage, maintenance, or procurement, feel free to contact us:
Email: cykc@cykcgroup.com.cn