How many types of slitting are there?

Shearing operation

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"Slitting" redirects here. For slitting of iron bars into rods, see slitting mill

Slitter rewinder

Roll slitting is a shearing operation that cuts a large roll of material into narrower rolls. There are two types of slitting: log slitting and rewind slitting. In log slitting the roll of material is treated as a whole (the 'log') and one or more slices are taken from it without an unrolling/re-reeling process. In rewind slitting the web is unwound and run through the machine, passing through knives or lasers, before being rewound on one or more shafts to form narrower rolls. The multiple narrower strips of material may be known as mults (short for multiple) or pancakes if their diameter is much more than their width.[1] For rewind slitting the machine used is called a slitter rewinder, a slitter or a slitting machine these names are used interchangeably for the same machines. For particularly narrow and thin products, the pancakes become unstable, and then the rewind may be onto a bobbin-wound reel: the rewind bobbins are much wider than the slit width and the web oscillates across the reel as it is rewound. Apart from the stability benefit it is also then possible to put very long lengths, (frequently many tens of kilometres), onto one bobbin.

Process

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Soft materials

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Several methods are available for soft materials like plastic films, textiles, adhesive tapes, and paper. Razor blades, straight, or circular blades are being used. Some blades cut through the material while others crush the material against a hard roll. Those are similar to knives. The cutting blades can be set to a desired width. Some machines have many blades and can produce a number of output rolls at once. The slit material is rewound on paper, plastic or metal cores on the exit side of the machine.

The process is used because of its low cost and high precision for mass production. Some machines have a program that monitors the blades and sharpens the blades often to maintain the quality and precision of the cut. Depending on the industry and the product that is being slit these machine can run between 10m/min (special metal webs) and m/min (paper making process). The machines can also incorporate extensive automation to precisely control material tension, automatically position the slitting knives, automatically align the cores onto which the material is wound and to reduce manual handling of the rolls.

Examples of materials that can be cut this way are: adhesive tape, foam, rubber, paper products, foil, plastics (such as tarps and cling wrap), glass cloth, fabrics, release liner and film.

Hard materials

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For harder materials, such as sheet metal, blades cannot be used. Instead, a modified form of shearing is used. Two cylindrical rolls with matching ribs and grooves are used to cut a large roll into multiple narrower rolls. This continuous production process is economical yet precise; usually more precise than most other cutting processes. However, the occurrence of rough edges known as burrs is commonplace on slit edges. Also, the geometry of these rolls is determined by specific tolerances in addition to the type of material and workpiece thickness.[2]

Machinery

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For metal coils, the slitter consists of three main parts: an uncoiler, slitter, and recoiler.[3] The material is fed from the uncoiler, through the nip between the two circular cutting wheels (one on top and another underneath), and then re-wound in slit pieces on the recoiler.

When the term "slitter rewinder" or "slitting machine" is used to describe the machine, the three parts are referred to as the unwind, the slitting section and the rewind. Slitter rewinders are normally used to slit plastic films, paper and metal foils. The unwind stage holds the roll stably and allows it to spin; it is either braked or driven to maintain accurate tension in the material. Some machines have a driven unwind which reduces the effect of inertia when starting to unwind heavy rolls or when the material is very tension-sensitive.

The slitting section has four main options:

• Razor slitting, which is ideal for thin plastic films the system is very simple and quick to set. Although the razor blades are of low cost, they need to be frequently changed to ensure a good quality slit edge.
• Rotary shear slitting. Male and female circular knives engage to give a scissor cutting effect. This system is used widely on paper, films and foils. Although the knives take longer to position, they stay sharp longer than razor blades. The setting time can be reduced by using an automatic knife-positioning system.
• Crush cut slitting. A male knife runs against an anvil. The system works well with certain materials including non-wovens and foams.
• Hot knife slitting. A heated round blade (similar to a score or crush cut blade) or sharpened piece of metal also runs against an anvil in order to cut through the material. The heat of the blade seals the edges without burning in order to prevent the material from fraying.

The rewind section also has options. The main type is centre winding using differential rewind shafts. These shafts are becoming universal on most slitting machines. The differential shafts ensure an even tension across the full width of the material. Closed-loop control of the winding tension using feedback from load cells provides the total tension-control system required for running tension-sensitive materials. Precise and accurate tension control is the key to good roll slitting. Modern machines use AC vector drives with closed-loop feedback from AC motors. When used with the correct control algorithms, they produce excellent results with the minimum of maintenance.

Industry usage

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Roll slitting is a technique heavily used by Converters (industry). The converter industry normally refers to companies who print, coat and laminate materials. A typical converter is a company that produces flexible packaging material for packaging food. This may involve purchasing large rolls of plastic film such as biaxially orientated polypropylene (BOPP) which is then printed to the customer's design and coated with cold seal adhesive for use on high speed packaging machines. This material is printed and coated in wide, large diameter rolls for maximum efficiency. The rolls are then slit, using a slitting machine, into smaller rolls of the size to be used on the packaging machine.[4]

See also

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References

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November 5

Slitting Techniques: A Basic Guide

Slitter rewinder machines use three types of slitting methods to cut material: razor blade, shear cut, and score cut. The most appropriate slitting technique to use depends on a variety of factors, such as the type and thickness of the materials being processed. With well over a century of combined manufacturing expertise in Dusenbery converting systems, we've gained valuable insight into the use of slitter rewinders. This article is based on our hands-on experience and explains, on a very basic level, which slitting methods are suitable for various applications.

Razor blade : Used primarily with light and non-abrasive materials, this method employs a simple razor blade slit in the air or in a grooved roll.

Pros: This is the most economical method, along with having a fast and easy setup.

Cons: This method is not capable of easily cutting through heavy, rigid, or abrasive materials. At high speeds, the razor blade method can also burnish film. If enough heat is generated, it will melt the film, creating a bead that is detrimental to achieving good winding.

Shear cut : This slitting method uses two rotary knives to produce the same cutting effect as obtained by pushing a pair of opened scissors through a sheet of paper. It is used for slitting heavier gauge material such as thicker film/sheet, paper, foil, and most laminates.

Pros: The benefits of this method include accurate slit widths and close tolerances.

Cons: The setup for this method needs to be extremely precise, and requires achieving an ideal angle at the junction of the blades.

Score cut : Also referred to as crush cut, the score cut method is the oldest form of cutting and the first employed in slitter rewinder machinery. It involves crushing the material to sever one part from the other by using a dull knife making contact with a hard surface. This method is ideal for slitting pressure-sensitive adhesives, since it creates a dry, non-sticky edge.

Pros: Quick setup is a major advantage of this method.

Cons: When the score cut method is used to slit paper material, it creates dust that can accumulate and cause equipment malfunction. Also, if a defect appears when slitting plastic film and sheet, this can create film stretching and deformities (leading to rejects). When used on hard plastic, it may cause cracking.

While this information will help you determine which methods may be best for your application, its important to keep in mind that every project has different goals and uses varying machinery, materials, and processes. Please contact the Dusenbery sales and engineering team at to discuss the specifics of your slitting and rewinding project.

To receive our complimentary Dusenbery® Slitting Techniques Guide, please fill out the form below.

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