Slitter Burrs, Waviness and Delamination

Burrs and wavy edges on cell electrodes can have serious consequences up to and including an internal short-circuit and thermal runaway. Hence it is important to understand the slitting process and under what conditions burrs and waviness occurs.

Slitter Cutting Control Parameters

There are basically three slitter cutting control parameters for the shear cut method, which uses the same principle as scissors.

These notes are based on years of experience of cutting paper, foils and battery electrodes by the Maysun Corporation.

Tendencies for Burrs and Waviness

1. Upper Knife Tip Angle
   • Generally, larger angles result in delamination, while smaller angles tend to produce burrs. The threshold is approximately 60 degrees.
2. Relationship between the Upper and Lower Knives
   • Contact or Gap
     In coated areas, a small gap results in burrs, while a large gap results in delamination: approximately 5 μm.
     In foil areas, a gap of almost zero to a strong contact results in burrs, while a large gap results in poor cutting or tearing without cutting.
     With a digital slitter, you can freely digitally set optimal quality from both gaps and contact in both coated and foil areas, from quality and durability to the point of contact.
3. Toe-in
   If the toe-in is too strong, burrs will occur; if it is too weak, delamination or waviness will occur.
   For digital slitters, the toe-in is approximately 0-0.5 N.

Equipment Specifications to Avoid

1. The material enters and exits the upper and lower knives in a straight line. Changing or fluctuating the speed and tension can cause the material to become unstable
   at the cutting point, resulting in poor cutting.
2. Independent upper knife drive (in the case of independent holders)
   Slight discrepancies in the relationship between the rotation speed of the upper and lower knives and the material speed can cause burrs or waviness (single-axis systems require both knives to be driven at the same speed).

Specifications to be Aware of During Operation

1. Integrated calender and slitting
   • Production can be halted due to poor calender quality,
   • Integrated operation results in significant material and time losses due to the need to adjust the conditions for each machine.
2. Wider width
   The calender roll’s pressing tendency can cause differences in the material’s condition between the centre and both ends, affecting slitting quality (especially with single-axis systems).
3. Wider width and more stripes
   Achieving consistent quality at all knife positions is extremely difficult due to subtle material differences at each cutting position and individual differences between knives. Furthermore, cutting multiple stripes is even more difficult.
4. Knife elasticity
   With the Goebel type, knife elasticity is essential to prevent damage between the knives without a contact pressure indicator. However, this can lead to unstable contact pressure during operation, resulting in poor cutting. This is not a concern with the gang type, which uses fixed knives.
5. Trim Specifications and Processing Methods
   Whether trim is reel-mounted or air-fed, tension must be removed from the knife cutting point. Failure to do so will result in poor cutting on the side of the trim that should become the final product.

With a Digital Slitter

• The contact pressure between the upper and lower knives is digitally monitored in 0.1N increments using direct sensors.
• Knives over 2mm thick are highly rigid and non-elastic, ensuring stable cutting quality even during operation.
• Cutting conditions are set before operation and the cutting status during operation are digitally monitored. Any poor cutting can be traced back to the cause and prevented from recurring, enabling digital quality assurance for the entire product.
• *) Even unavoidable and difficult-to-predict changes in operating conditions can be detected and digitally grasped through advance confirmation tests, allowing for quick digital response without cutting material during mass production.
  

Maysun Corporation was established based on a Paper-making company in 1967. So we see from perspective of Paper-making manufacturers and have developed technology which they require truly.
We are pioneers in the introduction of numerical control to Paper-making machine, and rated highly by our customers.

And other than paper-making, orders of NC Slitters and Non-contact thickness gauges for optical films for Flat Panel Display and electrode materials of lithium-ion battery are increasing in number. Our products rated highly by trendsetter material manufacturers.

Contact Hiroshi Yamada (h.yamada@maytech-corp.jp) for more information (LinkedIn)