Cross-cutting quo vadis? – Step by step out of user dependency – CrossScan 295

What does the CrossScan do?

• Provide numerical values of the percentage coating loss where until now only vague estimates were usual.
• Correct assignment of the cross-cut characteristic value according to ISO 2409.
• Creation of a measurement report with data and images, for documentation, communication and reproducibility of the measurement at any time.
• Helping to lower users' blood pressure through confidence-building measurement rather than estimation.

How do you perform a measurement?

After placing the dome on the cross-section to be evaluated, first the available cross-section size (related to the common standardised cross-sections) is selected, whereby the pattern is marked widely delimited by a coloured frame. Then, by activating the "preprocessing" mode, a binary, i.e. in fact a black/white display is called up at the push of a button, which shows the contrast ratio of the relevant "area of interest" (not influenced by colour shading) available for calculating the percentage coating loss. By pressing another button, a grid is digitally applied to determine the width of the cut channel. After manual adjustment of the width of the cut channel and the user's confirmation of his or her impression in comparison with the original image (the representation must be logical and coherent; it is possible to jump back and forth between all representations for quick and direct comparison), the measurement is completed and can be stored as a measurement report or communicated further.

Measuring principle and realities from the daily practice of cross hatch cutting users

Example of a measurement report

The visibility of detached areas depends entirely on the contrast between the coating and the exposed substrate. To achieve optimal contrast, which can also be effectively detected by software, additional measures can be taken. For instance, a lateral ring light can be activated alongside horizontal lighting to enhance contrast. This ring light accentuates the height differences between the coating and the exposed substrate, further improving contrast. By adjusting the lighting setup through a "trial and error" approach, it is possible to fine-tune the contrast ratio for the best possible visibility, if necessary. Additionally, the threshold value can be manually shifted as needed to appropriately strengthen or soften markings. The progress or status of this initial basic adjustment can be directly observed in live mode.

The exclusion of the areas covering the cut channels from the detection must be considered. During the standard 30°-angled cut as per ISO 2409, the depth of the cut directly affects the width of the cut channel. To correctly apply a grid pattern, it is essential to cut through the coating down to the substrate and fully expose the substrate along the entire length of the cut. It is normal and unavoidable in most applications to cut superficially into the substrate, which is fine in terms of the testing process. However, the real-world application presents a different situation: particularly with "soft" substrates such as zinc, aluminum, plastics, and similar materials, cuts often go deeper than necessary. Since re-cutting is generally not intended and undesirable, the user may instinctively apply too much force on the first attempt rather than too little. A grid pattern that is not fully cut through to the substrate is worthless for testing and could generate misleading but better-than-true values. The 30°-angled cut widens the resulting cut channel as the depth of the cut increases, which reduces the size of the square areas evaluated in the grid pattern. As only these areas can be used to assess material loss, the cut channel must be fully excluded. This is achieved through a software-generated grid with adjustable line widths simulating the "cut width", which visually covers the grid pattern as completely as possible. Overlaps or underlaps can be compensated by adjusting the line width until the display appears logical to the user, who can switch between images for optimal clarity. Overall, the user’s impression is crucial for the accurate determination of numerical values.

Where are the limits, what no longer works?

• Curved surfaces, one- or multi-dimensional, with small radii.
• Multi-layer systems with simultaneous adhesion loss occurring on multiple levels within the grid pattern.
• Coating structures without contrast to the substrate or intermediate layer (primer, undercoat, filler, etc.).
• Matching colors of substrate and coating, or possibly primer and top coat.
• Clear coats or translucent/transparent coatings.
• Often, the user can coax usable contrasts by adjusting settings as deemed appropriate, but this must be individually assessed for suitability.

Summary

The capabilities offered by the CrossScan are long-awaited by countless grid-cutting users, marking a significant step towards increased testing security in grid-cutting, for which there was little cause for optimism just recently. Despite all the ongoing customer demonstrations, there is no reason for euphoria as if misunderstanding the quality: "scanning with a measurable value at the push of a button." With all the positive facts, a sober view of the possibilities and limits remains essential to avoid disappointment, as the CrossScan does not replace the user as an independent worker but serves as a new, potentially helpful tool for unmistakable improvement in the globally similar, uncertainty-ridden evaluation situation for grid cuts. In short, the user is still indispensable, but under suitable conditions and with proper use, they feel significantly more comfortable with a large number of typical measurement requirements because they are more objectively reliable – not only the user but also all parties involved in the subsequent documentation and communication chain. Removing dependence on "faith certainty" with a verifiable improvement in safety ("you see, what you get") is a good example of a "win-win" situation for both sides.

Author

Günter Kalinna,
Product Manager Surface Technology,
Erichsen GmbH & Co. KG