How to Optimize Shear Slitting for Flexible Metal Foils

In foil and flexible material converting, achieving clean slit edges and stable winding is not a matter of luck. It depends on how precisely the slitting station is set up. Every detail counts: from blade geometry and overlap to side pressure and web tension. Even small deviations can cause burrs, dusting, or faster wear of the blades.

Tangent or Wrap Slitting?

​Choosing the right slitting method is the first decision that needs to be made. Tangent slitting is often preferred for cutting thin and flexible foils. To achieve the best results, use a fine tip grind angle of about 25–30 degrees, an overlap of approximately 0.7 mm, and a cutting face that is at least 2 mm wide.

For general-purpose materials, both tangent slitting and wrap slitting are effective when using a tip grind angle of 35–45 degrees. In wrap slitting, the web partially wraps around the bottom knife, which provides more stability and control. This method is suitable for slightly thicker or multilayer materials.

Blade Geometry and Overlap Settings

The geometry of the circular machine knife edge determines how efficiently it cuts through the material. Bevel profiles such as 30, 45, or 60 degrees, or compound grinds like 45 + 15 degrees, can be selected depending on the type and thickness of the material.

The overlap depth, where the upper dished and bottom blades intersect, should usually be between 0.5 and 0.75 mm, or adjusted according to foil thickness. Too much overlap shifts the cut point forward, causing the web to be slit before it is fully supported by the lower knife. This results in burrs, dusting, or fine edge cracks. Too little overlap, on the other hand, leads to incomplete cuts or tearing.

The cut point should occur inside the wrap area, where the web is in contact with the bottom knife. This provides a stable and accurate cutting position and reduces foil lifting or tearing.

Cant Angle and Side Force

The cant angle, sometimes called the shear angle, ensures that the two blades maintain a closed nip, like the blades of scissors. The right cant angle depends on the web’s elongation and stiffness. A practical rule is: low-elongation materials = small cant angle, and high-elongation materials = larger cant angle. For most converters, a range of 0.5 to 1 degree works well.

The side force, the lateral pressure between the top and bottom blades, drives the upper blade’s rotation and determines contact pressure at the nip. Too little pressure causes slippage and incomplete shearing; too much increases heat, friction, and blade wear. In general, aim for the lightest pressure that still allows the bottom knife to drive the top knife and maintain a closed nip.

Precision and Stability

Mechanical precision is just as important as blade setup. Minimizing both axial and radial runout reduces blade wobble and helps to maintain consistent slit width. Regular inspection and maintenance of knife holders and slitting stations ensure longer blade life and predictable performance over time.

Controlling Tension, Heat, and Aluminum Powder

Proper tension control prevents stretching or tearing during slitting. If the tension is too high, the foil can deform or curl; if it is too low, wrinkles and poor edges can occur.

At high line speeds, friction between the knives generates heat and fine aluminum powder. This powder should be collected efficiently to prevent it from settling on the web surface. Otherwise, it can cause pitting during the next winding stage. Excessive heat can also make the powder stick to the blade edge, which quickly dulls it. Use blades with mirror-polished or low-friction coatings to reduce adhesion and keep temperatures stable. For these demanding applications, tungsten carbide or coated polished blades from Sollex offer excellent wear resistance and precision.

Order Slitting and Converting Knives for Foils

Optimizing shear slitting is all about precision rather than force. Correct tip angles, controlled overlap, light side pressure, and stable web tension result in cleaner cuts and longer intervals between blade changes. For battery and electrode foils, where dry slitting without lubrication is mandatory, see our article Dry Slitting of Battery Foils: Clean Cutting of Copper and Aluminum Without Lubrication. It covers how to achieve burr-free edges under strict cleanliness constraints. Read it here: *Dry Slitting of Battery Foils.*

Sollex supplies high-quality shear slitting blades made for foil and flexible material converting. Our blades are designed for consistent performance, long life, and clean cuts even in demanding production environments.

Sollex is a Swedish supplier of industrial knives and machine blades for plastic film, packaging, paper and cardboard industries! With the right knives and blades, you can get simplified maintenance, time savings, and an improved end product. You are welcome to contact us with your questions:

Customer service and orders: order@sollex.se

Telephone: +4635–15 75 00 Address: Box 5161, 200 71, Malmö, Sweden