Enhancing Weld Integrity and Tooling Design Through Mill Evaluation

Over the years, Roll-Kraft has conducted thousands of mill evaluations on a variety of equipment. We are now sharing these stories in our Tube & Pipe Field Service Report Article Series. We hope you find the information contained in this series helpful. If you have any questions regarding your mill, use our contact form to request more information about our on-site mill evaluation.

Problem: 
The evaluation revealed multiple design and mechanical concerns across both mills. Entry guides used only two rolls, allowing the strip to pivot and misfeed into the first breakdown pass. The impeder system was also located several inches upstream from the weld point, forcing excessive power usage and contributing to weld instability.

On Mill 1, tooling inspection showed weak edgeform designs with shallow contours that failed to support consistent presentation into the fin passes. Certain tooling sets, including the 9.625” and 10.750”, had overly large flats in their transition areas, misproportioned drive points, and excessive reductions in the fin section—nearly double normal practice. Some fin passes were designed with floating blades and excessive rim clearances, contributing to torque fluctuations and uneven reduction.

Mechanical inspections revealed severely worn bearing blocks on the first stand, likely caused by speed mismatches in the drive system. The strip was observed to consistently run to the back side, leaving grooves in the final cage rolls. Misalignment corrections helped reduce this on the second day, but the behavior indicated deeper centerline issues. Tooling charts also prescribed variable girths based on gauge, leading to inconsistent weld presentations. Excessive burn-off (squeeze-out) of .156” at the welder was identified, higher than typical design targets.

On Mill 2, the drive shaft configuration was unconventional, driving only selective stands and leaving others undriven, creating unbalanced loads. Pass 6 side rolls appeared misformed compared to others, suggesting possible elevation or design errors. The tooling also included a double “W” formation design, which was unnecessary for the product mix being produced.

Solution: 
Roll-Kraft delivered a comprehensive plan for both mechanical and tooling improvements. Entry guide assemblies were recommended for upgrade to four-roll systems to stabilize strip entry. Impeders were to be repositioned within 1/8” beyond the weld roll centerline, significantly reducing weld power requirements and improving bead quality. Tooling designs were advised for revision—flattened contours to be removed, girths standardized regardless of gauge, and fin pass reductions decreased to industry norms. Burn-off targets were adjusted down to .100” for better weld flow and reduced scrap.

Bearing blocks and first-stand components were recommended for replacement, and shaft loading distribution reviewed to eliminate speed mismatch wear. Drive configurations on Mill 2 were to be redesigned to ensure balanced torque transmission across all passes. Side roll corrections and elevation checks were planned to resolve misformed patterns at pass 6. Roll-Kraft also suggested phasing out unnecessary double “W” formations and reviewing all top-to-bottom radii for proper ratio and contour fit.

Together, these changes were designed to reduce weld defects, extend component life, and standardize tooling performance across sizes, ensuring consistent tube quality and improved operational efficiency.

Contact Roll-Kraft for a Tube & Pipe Mill Evaluation
Do you have issues you would like a second opinion on regarding your mill? Roll-Kraft on-site evaluations really make an impression with your staff, confirming you are serious about producing quality tube, pipe, and roll form products. Our technicians will tell you exactly where you are currently doing a great job, in addition to pointing out any areas that could be improved. We have been doing training and evaluations for over 30 years and understand the sensitive nature of bringing someone in to talk about improvements. Your staff will be in good hands with Roll-Kraft. Click here to learn more about our tube & pipe evaluation service.