A Brief Introduction To Slitter Rewinder Machines
What Are Slitter Rewinding Machines And How They Are Used
THE KEY ROLE OF SLITTER REWINDERS
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 civilized toilet in the world. In 1908, though, Frances Meisel of Boston, Massachusetts, patented an invention that would not only revolutionize toilet paper manufacturing, but would also have much, much broader soft material manufacturing implications: the slitter rewinder.
Slitter rewinders perform a few basic and essential functions that make modern soft material production, converting, packaging, and transportation possible. Their long history and keystone role in western industrialization earn them a spot of honor among quintessential commercial production machinery. Follow along with us below as we explore the history, advancements, functions, composition, and production of slitting rewinding machines.
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, which we’ll discuss further below. 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 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.
HOW THE SLITTING WORKS
There are three general functions that a slitter rewinder performs in fixed order. To begin the process, the already rolled paper (or other material) must be unwound to pass through the slitter rewinder in a single layer. As it passes through the machine, 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 the finished, market-ready dimensions, it is rewound into sellable rolls.
The actual cutting of the material can be done in a number of different ways, depending mostly on the material being cut. The oldest form of cutting, called score cutting, involved 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 this method 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 with 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 feed. 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 shearing cutting is that it uses two blades, usually rotating. The material is pulled between these two blades which cut the materials from above and below, similar to the way a pair of open scissors could be guided through paper.
ADVANCES IN SLITTER REWINDERS
In recent years, strides have been made in optimizing 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 digitalization, 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.
A LONG JOURNEY WITH TREMENDOUS RESULTS
Ultimately, the increasing automation and digitalization 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 specialized requirements, eliminating the need for a certain level of standardization 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.
Though the general concepts of pulping, slurries, and forming have endured for hundreds of years, modern paper production alone would not have been able to keep up with our modern demands for such a vast array of items without the benefits of continuous production and the ability to automatically reduce those bulk materials into smaller, individually consumable quantities. So, the next time you use a sheet of paper, a roll of tape, a roll of tin foil, a sheet of plastic, a roll of film or a roll or strip of any other non-woven, flexible material, keep in mind that there’s a very good chance the last machine that material saw before packaging was a slitter rewinder.