Understanding the Art and Science of Log Slitting

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When we use tape products, we typically use them in rolls. Tapes can also be supplied as die cut or kiss cut parts in a specific shape but the overwhelming majority of the time, it’s in a roll.Rolls are a really great way to deliver tapes. The roll format helps protect the adhesive until you’re ready to apply and rolls are easy to package, store, and transport. Two of the most common slitting techniques for tapes are rewind slitting and log slitting. Rewind slitting actually forms the roll from the core out until you have the correct length on the roll. That type of slitting will be covered in a separate blog post.

What is Log Slitting?

Log slitting starts with a large, wide roll of tape that is supplied by the tape manufacturer. This large roll is called a “log roll’ since it resembles a tree trunk. The log roll is loaded onto a machine called a log slitter. It can also be referred to as a single knife slitter, a “Lever Slitter”, a “lathe” slitter, or a “baloney slicer” (since it can somewhat resemble cutting bologna on a deli slicer).

The log slitter can be thought of as a cross between a lathe and a circular table saw. The log roll is loaded onto a mandrel through the core that supports the roll horizontally. One end of the log roll is secured onto a chuck that secures the tape being cut onto the drive mechanism of the machine.

The carriage that contains the blade and the sharpening stones moves parallel to the log roll. The slitting process begins on the end of the roll opposite the chuck with a ”trim cut”.  This trim cut produces a smooth edge from which to start and helps create a datum so that the machine indexes automatically along the roll to make precise cuts.

Roll Quality

The blade then indexes to the next position to cut the next roll. The blade is brought into the material at a specified speed. The blade and material rotation speeds and directions are also specified depending on the material to be cut. These speed selections are important. If you try to move the blade through the tape too fast, the material will compress and produce a poor cut in terms of edge quality and evenness. If it is too slow, it results in increased friction and heat build-up which can damage temperature sensitive materials.

Another critical variable is the blade itself. There are different types of blades that have different bevel profiles. Slitting foam tape requires one type of bevel profile while harder self-wound tapes such as surface protection films and strapping tapes will require a different profile. There are also saw blades with specific teeth counts that work to cut hard films such as polyester.

The sharpness of the blade is crucial to a quality slit roll. The sharpening frequency is programmed into the machine. If the material is dense, the blade may need to be sharpened after each cut. If the material is a lower density and not abrasive, the blade may be able to make several cuts before a sharpening sequence is required.

In any case, if the blade is dull, it compresses the material excessively and the edge will be uneven. If the blade is too sharp, it can result in “whiskers’ or “angel hair” along the edge of the roll.

Working in tandem with blade sharpening is lubrication. 99% of the materials processed on a log slitter require lubrication of the blade as it rotates. It may be as simple as a plain water spray or water plus another lubricant such as a glycol or silicone. The amount of lubrication is usually kept to the minimum level possible to reduce friction and heat build up. This function is programmed into the machine so it is performed automatically based on the material being cut.

The log slitters at Tom Brown, Inc. can handle log rolls up to 23” in diameter. We can slit foams with adhesive on one or two sides, single coated and double coated film tapes and just about anything else you can imagine. Contact us today to learn more or to have us cut a sample roll for your evaluation.

Rick Alexander

About the Author

Rick Alexander is the National Sales Manager for Tom Brown, Inc. His early experience was in R&D, product management, and sales management for both Main Tape and Adhesives Research, Inc. Rick brings over 40 years of pressure-sensitive tape experience and Tom Brown’s world class converting capabilities to help solve customer bonding, assembly, and sealing challenges.