Advantages of Shear, Razor and Crush Web Slitting Techniques

Published: April 17, 2025

By Ralph Beier, Business Development Director, EyeC GmbH

When choosing a slitting method, many factors must be considered, including interaction with inspection systems. Whether slitting occurs on the press or a finishing machine, the positioning of the inspection system should be carefully evaluated.

Slitting is most commonly performed on a rewinder, which often includes 100 percent inspection to ensure complete compliance with every final roll being sent to the end user. Since inspection slitting/rewinding machines are designed to stop on defective labels or repeats for replacement or correction, the stop position should generally be selected before the slitting system.

Required stopping accumulation idlers must be installed ahead of the slitting system, and the rewinder must not be reversed over it. A web guide should always be positioned directly before the slitting system to ensure accurate slitting, even if there is already an inspection web guide at the unwind.

There are three major types of slitting systems commonly used in the label and flexible packaging industry — shear, razor and crush knife — each with distinct advantages and challenges. Regardless of which system is selected, it is crucial to control the tension of the web at the position of the knives. Often, an outfeed nip roller is added after the slitting section to maintain tension independently of the rewind tension.

Shear Knife Slitting

One of the most popular slitting methods is shear knife slitting, because it can handle a variety of materials and thicknesses, generates low levels of dust, and provides a smooth cut due to the scissoring action of the blades. Two rotary knives are used: the bottom knife turns in the direction of the web, while the top knife rotates counter to it. Light spring pressure holds the blades together.

The main challenge of shear slitting is the difficulty of setup, as both knives must be positioned with great precision. To reduce setup time, many manufacturers now offer automated knife positioning systems. Another drawback of shear slitting is the tendency to fold narrow trim instead of cutting it, but this issue is often resolved by adding razor knives to both edges of the web specifically for trim slitting.

Razor Knife Slitting

Razor knife slitting is also popular, particularly for thin films and foil materials. It is generally easy to set up, and the blades are inexpensive and simple to replace. However, razor slitting has challenges, including heat buildup and a short blade lifespan, as the cutting position is usually in the same position on the blade. Oscillating blade systems, which continuously vary the cutting position along the blade edge, can help mitigate these issues.

Crush Knife Slitting

The third common slitting method is crush knife slitting. This system uses a rotary knife and a hardened anvil, similar to a rotary die cutter. Crush knife systems are easy to set up and can handle various materials, particularly thicker or harder substrates like paperboard. Many manufacturers offer fully automated setup options for these systems. The main drawbacks are the need for regular knife replacement or re-sharpening and the tendency to produce dust when used with fiber substrates.

A Fourth Option: Die Cut Slitting

An additional slitting method gaining popularity as the industry aims to reduce waste and improve sustainability is die cut slitting. This method is necessary when items on the web are printed in an interleaved pattern without a consistent linear gap between lanes, maximizing the number of labels on a roll and minimizing waste.

Die cut slitting requires the cutting to follow a contour instead of a straight line, so conventional methods cannot be used. This is achieved using a rotary die cutter, which makes a full cut rather than the typical kiss-cut, enabling the separation of lanes and rewinding of the label or film roll.

Slitting on the Press

When slitting directly on the press is deemed the most efficient workflow, it is usually because the press includes a fully automatic rewind system, allowing single-lane, customer-ready rolls to be produced without an additional finishing step.

In such setups, inspection is typically used for passive quality management, and defect data does not cause the press or rewind system to stop automatically. Inspection on the press is generally positioned just after the die-cut matrix stripping system and before the slitter to verify proper matrix removal.

Inspection in Laminate Tube Production

In laminate tube production, the inspection can be conducted on the press before the automatic slitting and rewinding system, benefiting from a full Quality Link/Manager system. Here, the inspection system must generate a defect report for each lane and track these rolls through the system until they reach the tube seamer.

This requires automatically placing a unique identifying label or barcode on each lane before slitting. The automatic rewinder must interact with the inspection system and label applicator to ensure the lane identifier label is applied just before the flying splice. These unique identifier labels are then used at the seamer to load specific defect data and eject defective tubes after seaming and singulation.

Choosing the Best Slitting System

Selecting the most effective slitting system requires considering the material type, number of job changes, run lengths, and whether the slitting is performed on the press or a finishing machine.

If in-line inspection is required, it is advisable to consult the inspection system supplier to ensure proper system positioning within the machine.

About the Author

As business development director at EyeC GmbH, Ralph Beier focuses on expanding special projects, products and markets, as well as identifying strategic business opportunities in the print inspection market. With over 40 years of experience in sales and marketing, Ralph holds a technical degree in avionics technology. Through his previous role as sales director at EyeC, and senior roles at Rotoflex and Roto-control, he has gained extensive knowledge of the printing industry including print finishing and inspection/quality control technology.