Definition
The adhesion slatter, also known as a hundred-grid knife or scribber, is a hand tool used to assess the bonding strength between a coating and the substrate. It applies standard pressure to etch specific grid patterns at specific intervals on the coating surface, then combines tape peeling or visual inspection to determine the degree of coating peeling. Simply put, you rely on a knife and tape to see if the patent leather is easy to peel off.
Principle
The core principle is based on the stress concentration generated when the coating deforms under force. The blade of the swipe knife cuts into the coating layer into the substrate layer, forming a cross mesh, and the exposed mesh edge area becomes a weak point. When peeling forces are applied, if the adhesion between the coating and the substrate is insufficient to resist external forces, the coating will detach at the grid intersection or edge. Based on the proportion or shape of the detachment area, the adhesion grade is inferred. It's a bit like breaking a cookie—it's easier to break along the notch, except here the focus is on "tearing open" rather than "breaking."
Measurement method
The operation isn't too complicated, but the details are crucial. First, ensure the coating surface is clean and dry, then use a spatula to cut vertically into the coating at least up to the substrate with stable pressure and angle, drawing two mutually perpendicular parallel lines, with spacing adjusted according to coating thickness and substrate type (usually 1mm or 2mm). After scraping, use a soft brush to gently sweep the debris, then stick the special tape onto the mesh and press it firmly. After a few seconds, quickly peel it off at an angle close to 60°. Evaluate the spalling by comparing standard images or descriptions—for example, no detachment at all is rated at level 0, and if the shedding area exceeds 65%, the worst is level 5. The whole process depends a bit on feel—too much force can damage the substrate, too light and it won't cut through.
Case study
For example: During a test of the aluminum surface spray coating, the operator noticed scattered small pieces falling off the mesh edges after scratching. Initially, it was thought that the substrate pretreatment was substandard, but after retesting with different tool spacings, the results were consistent. Later, when I examined the scratches with a magnifying glass, I found slight wear on the tip—the depth of the incisions was uneven, resulting in a localized pseudo-low adhesion. After replacing the blade head, the problem disappeared. This case serves as a reminder: instrument condition and analysis direction are equally important; you can't immediately blame the coating for problems.
Application:
This is especially common in industries such as coatings, automotive, furniture, and electronic product casings. For example, on the coating production line, workers regularly sample and mark the grid to prevent the spraying process from getting out of control; During home renovation inspections, you can also use a scratcher to quickly determine whether the wall paint is up to standard. In ship anti-rust coating testing, it is often used alongside salt spray testing. However, note that it is not suitable for coatings that are too soft or too thick, such as rubber-based ones, because scratches tend to heal on their own, making it hard to measure accurately.
Selection
When choosing a swipe cutter, the first consideration is the blade hardness—it should be one or two orders of magnitude harder than the coating; otherwise, it will dull quickly—for stainless steel substrates, at least the carbide blade head should be used. Next, look at the blade angle and notch spacing specifications. Common 6-flute and 11-edge tools on the market correspond to 1mm and 2mm pitches respectively, compatible with ISO and ASTM standards. Another niche point: the grip's slip resistance is also not to be overlooked; if your fingers slip, it's hard to maintain consistent force. Next, check if the blade is replaceable, since the blade head is a consumable. The price range is quite large, but don't be tempted by the low price. If the blade tip accuracy is insufficient, the entire test data is worthless and all the effort is wasted.