Winders and rewinders

In the paper, tissue and nonwoven industries winders and rewinders are fundamental components in the last phase of the complex production process: the so-called end-of-line. Winding, unwinding, slitting and then rewinding a reel are in fact operations that require correct execution to obtain a final product which, once wound, maintains the characteristics and quality resulting from the production process.

The process of winding, unwinding, possible slitting and rewinding may appear relatively simple but, in reality, this is not the case if you want to obtain a finished reel of the highest quality, especially at high production speeds. Let's first see the difference between the different types of machinery:

• Winders: they have the purpose of creating the so-called Master Roll (or Jumbo Roll or Mother Roll), a reel of large size and diameter (variable depending on the type of material), starting from the continuous sheet coming off the production line.
• Unwinders: machines that take care of unwinding the incoming master roll to obtain, thanks to the downstream machinery, finished reels with a smaller diameter and, if necessary, a smaller width. While the unwinding of paper and nonwoven takes place by using a single unwinder, up to four unwinders are required for tissue paper, since the finished product is made up of several plies. The actual unwinding takes place instead through the use of motorized belts, in the case of tissue paper and nonwoven reels (peripheral unwinding), or, due to the higher tension of the sheet and the size of the reels to be processed, by means of a motor with axial coupling in the case of paper (axial unwinding). The unwinder is composed of a supporting structure suitable for receiving the reel equipped with the shaft and of a peripheral or axial unwinding device, according to the product to be processed.

• Slitter Rewinders: the function of these machines is to cut, in the width desired by the customer (converter) and through special cutting recipes, the sheet arriving from the unwinder and to wind the "strips" of material obtained to form a certain number of reels with a smaller diameter and width than that of the original master roll.

A.Celli, thanks to the E-WIND® product line, offers a wide range of solutions for the winding, unwinding, cutting and rewinding of nonwoven, paper and tissue.

Each of these materials has specific properties and characteristics that determine the correct winding and unwinding process. So, let's see the workflow required for the different types of products.

As for the characteristics of the nonwoven fabric, one of its peculiarities is certainly the elasticity, which leads to a progressive shrinkage of the starting width of the sheet (neck-in) from the winding phase to the final product. In addition to this, it is necessary to distinguish the specific characteristics of the two main nonwoven types: spunbond and spunlace.

The spunbond material, characterized by the random positioning of the fibers that compose it, is more resistant to traction, allowing the use of higher tension values ​​during the winding process. For this, spunbond is subject to a more marked shrinkage than Spunlace: for example, an initial sheet with width of 3600 mm leads to finished reels with a width of 3200 mm.

Spunlace, on the other hand, is characterized by an orientation of the fibers that compose it in the Machine Direction (MD), due to the use of cards in the forming process. This makes it resistant to traction in this direction, but much less in Cross Direction (CD), and also less prone to shrinkage.

Let's now analyze the process that leads to obtaining the finished nonwoven reels of the required size and width:

1. The winder, starting from the nonwoven sheet exiting the production line, creates the master roll, always keeping under control the three parameters with the so-called TNT (Tension - Nip - Torque) control, which we will discuss in the next paragraphs. The reel has to work continuously, without the possibility of stopping or reducing the production speed, not even during the reel change phase. Therefore, the engineering solutions applied for the design and construction of this machinery are aimed at creating reliable solutions able to work continuously without errors, in particular in the critical phase, that is the change of the jumbo roll.
2. The master roll is then loaded onto the unwinder of the rewinder by means of an overhead crane or with automatic loading systems. During the unwinding (usually peripheral with the use of belts) the main checks are made to ensure that everything happens correctly. The independent motorization of the unwinder, its axial displacement (+- 75 mm) and the use of a roll equipped with load cell allow precise control of the process parameters (tension and speed) to obtain the desired characteristics in the finished reel.
3. Subsequently, the rewinder (or slitter rewinder) cuts the nonwoven sheet into a series of strips as wide as the finished product requested by the customer (the cutting recipe) and winds each strip thus obtained around a cardboard core. The formation of the reel takes place between the two carrying drums and the rider roll (also called pressure roll), whose purpose is to apply pressure on the reels being formed in order to keep the linear load (Nip) under control. This is essential for sensitive products such as nonwoven and, as we will see in the next paragraph, tissue paper.

As in all the previous phases of the process, the three parameters Tension, Nip and Torque will be kept under control also during the rewinding.

Once the value of linear meters or diameter required in the finished reel has been reached, the product is cut transversely and the reels are transferred to the unloading table, to then continue with the subsequent phases of the process. Complementary systems are available for the semi-automatic or automatic handling of the winding shaft and the positioning of the knives.

These two materials have very different characteristics from nonwoven fabric, which translate into different needs during the winding and rewinding process. 

Tissue paper, for example, must preserve the creping obtained in the production process to maintain the softness and bulkiness, and this leads to precisely controlling the elongation in order to maintain as much as possible the creping obtained during the formation of the sheet. 

Also for this reason, Tissue paper requires the use of a Nip value lower than normal paper, to avoid excessive compression of the reel. Now let's see the winding and rewinding process of these types of products:

1. Once the jumbo roll has been obtained, it is loaded onto the unwinder by means of an overhead crane (mainly tissue paper), and is centered with respect to the axis of the machine thanks to a transversal movement system of the sides of the unwinder. In paper or nonwoven rewinders, the unwinder can be in line with the winder to avoid transfers with the overhead crane.
2. Tissue paper reels are unwound thanks to the use of motorized belts, which slide tangentially to the circumference of the reel. To reduce the markings on the product, the pressure of the belts is carefully adjusted, while the sheet tension is controlled by a speed differential or by load cells. As for paper, on the other hand, given the greater inertia and dimensions of the reel, the unwinding takes place through axial unwinding, in which a motor brakes the master roll in order to control the sheet tension and compensate for the inertial components during the transient. Also in this case, the tension of the unwinding sheet is controlled by load cells. Once the jumbo roll has been unwound, the empty shaft is returned by means of an overhead crane to the winder of the paper machine for the loading of a new reel and the drawing-in of a new sheet.
3. The unwound sheet is then cut into smaller sizes thanks to a scissor cutting system, operated by slitting units consisting of knives and counter-knives. These units can be positioned manually or automatically whenever it is necessary to change the slitting width. To ensure a precise cut, the rotating blade of the counter-knife is motorized, while the knife is equipped with a wear recovery system.
4. The strips of the sheet are finally rewound around a cardboard core (using double-sided tape, glue or other for the start), held in an axial position by two tailstocks, which are free to move vertically along special low-friction guides. The formation of the reel takes place, as in the case of nonwoven, between the two carrying drums and the rider roll. The function of the latter is also fundamental in this case, since it is necessary to maintain a constant linear load in the initial phase since the reel is still "light". As we mentioned in the previous paragraph, tissue and nonwoven materials need a lower nip value to avoid excessive compression. The tissue reel being formed is then lightened by gradually reducing the pressure of the rider roll and increasing the lifting pressure of the tailstocks. For this reason the winding, in these machines, is carried out on cardboard cores keyed on particular expandable winding shafts.
5. Once the desired length or diameter of the finished reel has been reached, the machine is stopped, the sheet is cut and the reel is freed from the tailstocks and pushed onto an unloading table, thus completing the production cycle.  The insertion of a new shaft or new cores and the gluing of the sheet tails can be automatic or semi-automatic.

As mentioned above, three fundamental parameters are kept under control during winding and rewinding, namely Tension, Nip and Torque:

• Tension: is the tension of the material, generally defined as force per unit of length (N/m) or expressed as unit of force (N) in the Machine Direction (MD). Correct and constant tensioning of the web, measured by means of appropriate load cells throughout the entire process and different depending on the material processed, is necessary to ensure a compact reel that, at the same time, maintains the characteristics of the product.
• Nip: indicates the average linear load, measured in force per unit of web width meter (N/m), between a reel being formed and a roll placed in contact (e.g. the drive roll in the winding phase or the rider roll in the rewinding phase ), which acts along the line passing through their centers. This load has the task of avoiding the entrapment of air between the coils which, especially for non-porous materials, generates telescoped reels. Furthermore, the nip cannot be too high in order to avoid damaging both the processed material (for example causing a loss of bulk in the crepe papers, or the marking of coated papers) and the carrying drum.
• Torque: this is the torque difference between two motorized rolls, and is the last parameter that affects the correct compactness of the final reels. The control of this parameter is carried out by acting on the torque of the motors of the carrying drums, in order to distribute the load in a controlled way, or by introducing a difference in speed between the two rolls.

To carry out a correct winding process it is necessary to follow a series of fundamental principles:

• Make sure that the part of the reel closest to the core is sufficiently compact, as the first turns will serve as the basis for subsequent;
• Conversely, the reel at the final diameter must be less compact, to avoid damage to the underlying material;
• The transition of compactness from the core to the maximum diameter must take place gradually.

During the winding and rewinding processes there are many issues that can arise and that risk affecting the final result. Let's see the most common.

Settings of TNT parameters

In general, errors in setting the aforementioned parameters can compromise the quality of the final reels, or even prevent the winding operation. Among the main defects we can find:

• Telescoping or non-cylindrical shape, symptom of insufficient compactness due to excessive trapping of air between the reels;
• Collapse of the core or gluing of the single coils, due to excessive compactness;
• Starring, due to an uneven increase in tension as the diameter of the reel increases;
• Taper effect, that is the phenomenon whereby as the diameter of the reel increases, the innermost layers are crushed by the external ones due to excessive tension;
• Stretching of the sheet and a consequent excessive reduction of the width of the final reels, for materials with elastic properties;
• Loss of volume and bulk, in case of excessive compactness in the reels of creped products

Machine Cycle Time

Problems of poor speed and productivity can be caused by the lack of optimization of the machine cycle times, such as the master roll change operations, knife positioning, finished reel change, defect management and in general all the operations that take place when the machine is stopped.

Slitting

As for nonwoven and elastic materials, the setting of the slitting width must consider the phenomenon of the neck-in, that is the elongation of the material when the cut strip is subjected to traction in the Machine Direction by means of the carrying drums and wound around the cardboard core. In addition to this, attention must be paid to possible problems of radial or axial eccentricity, vibrations, cutting angle, lateral load and wear of the blades.

Presence of slitting dust and other contaminant agents

For hygienic products, it is essential that the dust created during the various rewinding phases is sucked up by means of special systems to prevent possible contamination. Other contaminants to watch out for during the winding and rewinding process can be dust, grease or oil.

We can deduce, from these issues, how many variables are that must be kept under control to produce a high quality paper, tissue or nonwoven reel. For this reason A.Celli has created E-WIND®, a range of products dedicated to winding, unwinding and rewinding capable of guaranteeing extraordinary performance, flawless finished reels, high automation capabilities and ease of control and use.

Given the problems of winding, unwinding and rewinding, there is only one way to ensure that these processes take place in an optimal manner: rely on machinery of absolute reliability and quality. So let's see the salient features of the A.Celli E-WIND® range:

• High quality of the finished reels of both standard and specific products, which require special controls in order to maintain the intrinsic characteristics of the material (less bulk loss, for example);
• Productivity increase linked to the optimization of machine cycle times (master roll change, knife positioning, finished reel change cycle, defect management and, in general, all operations that take place when the machine is stopped);
• Total digital integration of the end-of-line with upstream and downstream machines, for perfect product traceability;
• Easy to use 3D HMI, combined with intuitive diagnostic tools;
• Reliability, with longer maintenance intervals than the competition;
• Various levels of automation available to meet any need;
• Operational flexibility;
• Security: protections, crossings, gates and locks designed and manufactured following customized risk analysis.

Finally, thanks to A.Celli you will have the opportunity to upgrade and revamp existing rewinders (both of our production and of other manufacturers) to increase productivity, efficiency and safety.

Do you want to discover the best solutions of the E-WIND® range? Download our free eBook “A.Celli E-WIND®: the best winders and rewinders on the market for nonwovens, tissue and paper”!