Roll slitting is also called log slitting or rewind slitting. It is a shearing operation that slices a large roll of material into narrower rolls. The log slitting terminology refers to the olden days of sawmills when they cut logs into smaller sections. These sawmills also cut iron rods into smaller sections. Today, slitting is a process in which a material coil is cut down into many smaller coils of narrower measure. The potential workpieces are selectively thin (0.001 to 0.215 in.) and can be machined in sheet or roll form.
Slitting is seen as a practical alternative to other cutting methods due to its high productivity and the variety of materials it can manage. Rewind slitting entails rewinding the material through several knives to form narrower rolls of materials.
A slitting machine has three main parts: the unwind, the slitting section, and the rewind. The unwind usually is braked to maintain proper tension in the material. Some machines have a driven unwind, which decreases the effect of inertia when starting to unwind heavy rolls or when the substance is very tension sensitive. The slitting section has three primary options: rotary shear slitting, score slitting, and razor slitting, which is ideal for thin plastic film.
The rewind section also had different options. The main type is center winding using differential rewind shafts. These shafts are becoming universal on slitting machines. The differential shafts guarantee an even tension across the entire material width. Closed-loop control of the winding tension gives the total tension-control system needed for running tension-sensitive materials. Precise and accurate tension control is a must for roll slitting. Machines now use AC vector drives with closed-loop feedback from AC motors. The correct control algorithms ensure they produce excellent results with minimum maintenance.
Roll slitting is a procedure mainly used by the converters industry. The converter industry refers to companies that print, coat, and laminate materials. Converter companies specialize in modifying or combining raw materials such as polyesters, silicone, adhesive tapes, adhesives, foams, plastics, felts, rubbers, liners, and metals to create new products. A standard converter is a company that manufactures flexible packaging material. Their packaging process may involve large rolls of plastic film such as biaxially orientated polypropylene which is then printed according 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 with a slitting machine, into smaller rolls of the size to be used on the packaging machine.
Blades cannot be used for harder materials such as sheet metal. Instead, a different form of shearing is used. Two cylindrical rolls with matching ribs and grooves cut a large roll into multiple narrower rolls. This continuous production process is economical yet precise and is usually more accurate than most other cutting processes. However, rough edges known as burrs are commonplace on slit edges. The geometry of these rolls is also determined by specific tolerances and the type of material and workpiece thickness.
There are three types of slitting: razor slitting, shear slitting, and score slitting. Each type is distinguishable by the kind of blade, knife, or device used to cut. Therefore, deciding which system is best depends mainly on the type of material being cut.
Shear slitting involves a two-part knife with a male and female end through which the substrate passes and is cut. This process is ideal for fast converting and is perfect for transforming various thin materials with precision.
Razor slitting uses a razor blade or a series of razor blades mounted onto a machine that slices the material into the desired widths as it passes through. Depending on the placement of the razors, slitters using this method can convert either slowly (top) or quickly (bottom). Of the three types, razor slitting is the least expensive and is best for converting very thin substrates like films.
Score involves a moving substrate passing between a solid rotating anvil and a circular rotating knife or series of blades. This method is the most popular of the three and is ideal for converting various substrates of varying thicknesses and rigidities.
