A Brief Introduction To Slitter Rewinder Machines

How a Slitter Rewinder Machine Works

Slitter rewinders perform three essential functions that make modern soft-material production, converting, packaging, and shipping possible: they unwind, slit, and rewind continuous web materials. Below, we cover how each function works, the three primary cutting methods, the configurations Elite Cameron manufactures, and recent advances in the technology.

There are three general functions that a slitter rewinder performs in fixed order. To begin the process, the already-rolled parent material must be unwound to pass through the machine in a single layer. As it passes through, it is slit by one of a number of different cutting methods into strips of the desired thickness. Once the material has been slit to its finished, market-ready dimensions, it is rewound into sellable rolls.

The Three Cutting Methods

The actual cutting of the material can be done in a number of different ways, depending mostly on the material being cut. Each of the three primary slitting methods has its own advantages, ideal applications, and limitations.

The oldest form of cutting, called score cutting, involves slicing the material between a relatively dull blade and a hard surface. This method is beneficial for cutting adhesives (like various forms of tape), especially those with one sticky and one dry side. Although score cutting is quick and easy to set up, it is risky to use on many materials. It can potentially cause an excessive amount of dust when used with paper, stretching and warping when used with films, and cracking when used with hard plastics.

The second easiest cutting method to set up is razor blade cutting. It is also the most economical method. It uses a positioned blade often suspended over the area through which the sheet is fed. As the material is pulled across a drum or series of drums, it is drawn against the blade, which extends downward into either an empty space or a groove in one of the drums. This method cannot be used to cut heavy, abrasive, or rigid materials. Additionally, when used at high speeds, the friction between the blade and the material can heat the blade, which can cause beading along the edges of some materials like films.

Shear cutting is the most accurate slitting method, and it can be used against heavier, thicker, more rigid materials such as thicker films, foils, papers, and laminates. The defining characteristic of shear cutting is that it uses two blades, usually rotating. The material is pulled between these two blades which cut the material from above and below, similar to the way a pair of open scissors could be guided through paper.

Types of Slitter Rewinders

Slitter rewinders are categorised by how they wind the finished roll. The right configuration depends on slit width, finished roll diameter, material thickness, and production volume. Elite Cameron manufactures five primary configurations:

Center Winders

Center winders drive the rewind roll from its core using the rewind shaft. They are the most common slitter rewinder configuration and work well for slit widths of 25mm (1″) or greater and finished roll diameters up to 800mm (32″). Center winders are cost-effective, ergonomic, and suit general-purpose converting of paper, film, foil, and tape.

Center-Surface Winders

Center-surface winders combine center-driven winding with surface contact from a roller, providing superior web control for narrow slit widths, delicate materials, and large rewind diameters. They are the better choice for slit widths below 25mm or for stretch-sensitive films and battery separator materials.

Duplex Slitter Rewinders

Duplex slitter rewinders wind onto two parallel rewind shafts simultaneously, alternating finished rolls between the two sides. This configuration roughly doubles throughput on narrow-web converting applications such as labels, tapes, and flexible packaging.

Turret Slitter Rewinders

Turret slitter rewinders reduce changeover downtime by using a rotating turret with multiple rewind shaft positions. As one set of rolls finishes winding, the operator unloads finished rolls and reloads cores on the next shaft, ready for the next set. Turret machines are ideal for high-volume, multi-set production runs where downtime between sets directly impacts throughput.

Two-Drum Surface Winders

Two-drum surface winders drive the finished roll using surface contact from two driven drums, with the rewind roll sitting in the cradle between them. This configuration handles the largest rewind diameters and heaviest finished roll weights, making it the standard choice for paper mills and high-volume nonwoven converting.

Not sure which configuration fits your application? Read our guide on how to choose the right slitter rewinder, or contact Elite Cameron — we’ll spec a machine to your materials, slit widths, and production volumes.

Recent Advances in Slitter Rewinder Technology

In recent years, strides have been made in optimising the efficiency of slitting rewinding machines. One of these advancements has been the addition of inspection rewinding machines between the production line and the slitter rewinder. Although they add an additional step in the process, they drastically reduce the necessity for stopping the slitter rewinder due to quality concerns and misfeeds. Inspection rewinding machines guarantee the quality of the produced mother rolls by unwinding, inspecting, and rewinding them prior to loading them into slitter rewinders. According to a 1997 study by Farla, Blok, and Schipper, this process not only reduces machine downtime and material waste, but also increases finished product quality.

Adjustments to winding tension, to roll hardness, and to material ironing have improved avoidance of improper winding issues like buckling, air pockets, telescoping, starring, and tin-canning. This is especially important in rewinding more rigid materials like film. All non-woven sheet materials, however, are currently benefiting from the increasing digitalisation, networking, and automation of production machines. These advancements allow for more precise adjustment throughout the entire process and have decreased the need for a great deal of manual interaction.

Another relatively recent development in slitter rewinders is the use of independent winding mechanisms. According to 2012 patent USB210462B2, this allows the remainder of winding elements to continue working even if one is removed or shut down. This also allows for a variety of rewinding configurations to achieve desired tensions and winding angles.

Ultimately, the increasing automation and digitalisation of slitter rewinders enables manufacturers of papers, tapes, films, thin plastics, and foils to adjust the dimensions of their products to virtually any width with a uniformity and accuracy unattainable through basic manual operation. Dynamic blade spacing can be adjusted to satisfy even the most specialised requirements, eliminating the need for a certain level of standardisation in design. Meanwhile, various blade styles ensure that each material is slit in the cleanest, most economic, and most efficient way, drastically reducing production costs and times. Learn more about the industries we serve and how our equipment supports each one.

A Brief History of Slitter Rewinders

The Francis Meisel Patent

Aside from sparking the infamous “over-under” and “empty roll” controversies that continue to rage today, Seth Wheeler’s inventions of the toilet paper roll and dispenser in 1891 quickly made their way to the side of every civilised toilet in the world. In 1908, though, Francis Meisel of Boston, Massachusetts, patented an invention that would not only revolutionise toilet paper manufacturing, but would also have much, much broader soft-material manufacturing implications: the slitter rewinder.

Continuous Paper Production as an Example

Although thousands of years passed from the creation of paper’s earliest ancestors to paper production as we know it today, the industrial cutting and rolling of paper has really only been necessary since the advent of mass production. The continuous paper creation process is first credited to the inventors of the Fourdrinier machine just after 1800. Early paper slurry was poured onto a mesh conveyor belt and carried to a forming area. Through the early 1800s, sections and mechanisms were added to the Fourdrinier production lines at the few existing paper mills until the first cylinder-type paper mill began operation in 1817 in Delaware.

Slitter rewinders are used to roll thin, flexible, non-woven materials, of which paper is a popular, versatile, and prototypical representative, which is why we use it as an example here. However, these slitting rewinding machines can be and are used for a multitude of non-paper materials as well. For the time being, we’ll continue the paper example to more clearly illustrate the process and place of slitter rewinders in production.

The ingredients used to make a particular type of paper are combined, mixed, and pulped into a thick, sludgy liquid called a slurry. The composition and weight of the paper being created — whether it is notebook paper, construction paper, tissue paper, paper towels, etc. — depends on the amounts and types of ingredients used in creating the slurry. This slurry is poured onto a mesh conveyor belt, sometimes called a wire, and generally carried through a four-section process.

Sections of the Mother Roll Production Process

The first is the forming section, which has the main purpose of draining excess water from the slurry while arranging the mixture’s solid materials into a continuous layer. This can be accomplished through the use of gravity, shaking, vacuum, and tension. Once the majority of the loose water has been drained from the slurry, the sheet is carried into the press section, where a series of revolving cylinders (called “drums”) use pressure and felt to squeeze out the remaining moisture and to remove it through absorption.

Once the sheet has undergone forming and pressing, and the liquid has been removed, the damp remaining material is carried through a series of steam-heated machines in the dryer section to completely dry the sheet. After drying, the paper material is essentially created, but requires a number of finishing processes in order to attain the desired appearance, feel, and performance. It first undergoes a process called sizing that determines the paper’s water resistance and reduces the potential for fuzz through the addition of different glues and resins. Following that, the large paper sheet passes through a process called calendaring, where it is again pressed, but this time with the goal of finally increasing smoothness, gloss, and uniformity. At this point, the continuous sheet of finished paper is wound onto large metal spools, and finished rolls of paper have been created.

It may not have escaped your notice that a slitting rewinding machine was not mentioned at any point in the above process. That’s because the slitter rewinder is normally employed after all of the above has been accomplished. Once the manufactured paper has been created and is already standing in rolls on the exit end of the finishing process, it can then be unwound, fed into the slitter rewinder, cut into narrow strips of any desired width, and rewound back onto multiple smaller spools on the other side.