Above: Valmet’s optical detection system locates faults by using both a high-angle geometry and a low-angle geometry so that no flaw remains undiscovered.

Camera system classifies coating defects, improves safety, reduces quality claims

January 2016 - Steelscape, which processes and distributes metallic-coated and prepainted steel, has been able to justify the purchase of an integrated coating defect inspection system designed so line operators could avoid contact with the moving strip. Another key objective was to quickly detect, classify and locate defects so operators could avoid them by proactive remedial action, thereby reducing customer quality claims.

The selected high-definition camera system, designed and manufactured by Valmet, uses two optical reflection geometries to detect defects on the coated surface. The system reports defect types and their location in the coil immediately, via the user interface, and catalogues them in a database. Using the Valmet system, Steelscape’s operators can spot a defect, stop the section for a physical inspection, confirm the origin of the defect and make the proper adjustments, and then resume the motion of the line.

The detection system also helps with claims investigations. Steelscape has been able to inform its customers if the defect will diminish or if it continues for a defined number of feet. This capability potentially reduces the cost of the claim. On other occasions, it has led Steelscape to hold defective material in-house, preventing it from shipping to the customer. Within the first year after commissioning, customer claims for surface defects were reduced by 69 percent on a tonnage basis and by 79 percent as measured in dollars.

Safe inspection

Steelscape’s products are used in a wide range of construction-related applications, from metal buildings to architectural roofing to decking and framing. The main feature of its Rancho Cucamonga, California, plant is a continuous paint line that has a maximum line speed of 350 fpm and has the capacity to coat 10,000 tons per month. The range of substrates includes hot-dipped galvanized, Galvalume, cold-rolled carbon steel strip, aluminum and stainless steel. 

When choosing a new inspection system, Steelscape wanted to detect and correct flaws in the coating, and simultaneously protect workers who are there to respond and take action to stop defects from extending through lengths of a coil. One way to protect workers is to prevent them from touching the coil while it’s moving.

Valmet (formerly Metso) supplied a camera system to detect coating defects at Steelscape.

Optical challenges

Typical coating defects include paint blisters and dirt or debris streaks from the coating applicator roll. The defects could be the size of pinpoints or up to the size of a coin. They can appear in clusters, at repetitive intervals or sporadically. The detection of these defects is challenging for an optical system because the products under inspection possess different colors, and textures from matte to gloss.

To evaluate potential suppliers of this equipment for their defect detection capability, Steelscape asked for online machine trials and offline tests of defects in its suppliers’ testing facilities. Online machine trials involved introducing water, oils, streaks and other defects onto the moving strip. The offline tests were conducted on samples featuring a variety of gloss finishes and colors from white to black. Using these tests, Steelscape determined the optimum optical geometry required to detect flaws in all these various finishes.

Steelscape selected Valmet (formerly Metso) for this project. Valmet configured a dual geometry system to detect faults regardless of the surface finish. One beam of high-intensity pulsed LED lights illuminates the strip and the details of the reflection from the strip is captured by a beam containing four high-definition matrix cameras. These cameras see the reflected light at 17 degrees elevation from the plane of the strip. Another beam of LED lights illuminates the strip at 75 degrees elevation from the strip and the images are detected by a beam containing four cameras at 90 degrees from the plane of the strip surface. 

For the best defect resolution, Valmet found that the light intensity should change according to the surface texture.

Ease of access

The system was installed at the first inspection point after the curing ovens. It was mounted directly above a set of bridle rolls that need to be removed for service and resurfacing twice a year. Steelscape wanted a system that could be easily disconnected and removed to access these rolls and just as easily reconnected and reinstated without any performance problems. Valmet designed mounting brackets for the camera and LED beams that would allow the removal of the system without jeopardizing the precise geometry needed for the cameras and light beams to accurately see defects. Quick disconnect cables were used on the camera and LED beams for easy removal of the inspection package.

Steelscape performed most of the installation with Valmet’s supervision. Steelscape used its own electrical engineers, electrical and mechanical technicians on the project. Most of the installation was done offline with little or no affect on the production line. Certain portions of the job required roughly eight hours of downtime. The work was completed in about two weeks.

The measurement commissioning with Valmet engineers on site required two weeks. Fine tuning was performed during the first few months in operation. Operators began using the inspection system immediately. Steelscape and Valmet continue to make small changes to achieve the greatest accuracy possible.

Steelscape products are used in a wide variety of construction-related applications, including metal buildings, architectural roofing, decking and framing.

Diagnostic tools

The types of defects are classified according to the system’s library of fault types and displayed on a user interface screen. The coil location coordinates of faults are shown graphically in the defect map on the right and the operator-selected defect image and numerical coordinates in the coil are shown in the upper left corner of the user interface screen. Defects from previously made coils stored in the system’s database can be accessed in the lower left corner. The repetition rate of defects is also calculated by the system.

In practice, the camera system alerts operators about a defect via the monitor. If the defect looks to be problematic, operators will then stop the line to physically inspect the targeted section and confirm the defect. From there, operators make the proper adjustments to address the defect. 

Steelscape found the inspection system has also been a great help in claims investigations. It creates a coil production history that can tell operators whether a particular defect traveled throughout the coil or only for a few hundred feet. Steelscape shares that information with its customers. On other occasions, the system allowed Steelscape to hold defective material back and give the customer a defect-free coil instead. 

Value proposition

The inspection system provides defect inspection in addition to operator-initiated checks. The system identifies defects that are on the moving strip and has helped prevent defective material from shipping to Steelscape customers. Operators are able to get a jump start on problems which allows them to eliminate issues more quickly, another cost-saving advantage.

It has also proven valuable for claims investigations. The ability to go back to any particular coil and be able to see if there were any defects is worthwhile. The defect detection capability is still a work in progress as not all defects are visible. Steelscape continues to work with Valmet to address these issues along with others that would help to make the system simpler and more user friendly in the area of classifying defects. 

With the great emphasis that Steelscape places on safety—in its culture and throughout its network of operations—doing everything possible to keep all employees protected from harm is a priority. Whether it is through processes or equipment or engineering, keeping people whole and healthy on the job is the primary objective. This project is proof of that commitment.

Hector Quezada is paint line process engineer for Steelscape and John Gallinger manages SAL business sales for Valmet.