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2026
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Sheet Machine Winding Tension Control: Say Goodbye to "Lily-Leaf Edges"—This One Article Is All You Need!
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In the sheet production workshop, one of the most troublesome issues for operators is the “lily-pad effect” that often occurs during the winding process—where the originally smooth edges of the sheets curl and undulate like those of a lotus leaf. This not only directly affects the product’s appearance but also dramatically increases cutting waste in subsequent stages and can prevent proper execution of further processing. In severe cases, an entire roll of product may even have to be scrapped altogether.
When many people encounter “ruffled edges,” they instinctively check their knives and adjust the temperature—but often they only address the symptoms rather than the root cause. In fact, the underlying reason for ruffled edges in sheet material winding usually lies in... Tension Control Up. Today, let’s dive deep into how we can tackle the “ruffled edge” problem at its source by precisely controlling the winding tension.
One, First, let’s figure out: Why do ruffles always seem to have trouble getting along with tension?
First, it’s important to clarify that the essence of “ruffled edges” lies in the uneven lateral stress distribution across the sheet material, which results in inconsistent shrinkage between the edges and the central portion. The winding tension is precisely the key factor determining the stress state of the sheet material. From a practical production perspective, there are three main categories of causes for “ruffled edges” related to tension:
01. Excessive or insufficient tension: When the tension is too high, the edges of the sheet material are overstretched, and after winding, the elastic recovery causes warping. When the tension is too low, the sheet material becomes loose and piles up, making the edges prone to wavy wrinkles. Particularly as the roll diameter gradually increases, if the tension is not adjusted in a timely manner, this imbalance will continue to be amplified.
02. Unstable Tension Fluctuations: Deviations in the matching between the feeding speed and the winding speed, mechanical intermittent movements, and velocity fluctuations—all these factors can cause tension to fluctuate wildly. Under the influence of unstable tension, the sheet material experiences uneven lateral stress distribution, with the edges becoming “hotspots” of stress concentration, ultimately leading to the formation of a ruffled edge.
03. Uneven Distribution of Lateral Tension: Even if the overall tension meets the standard, if the tension across the width of the sheet is inconsistent—for example, the tension on the two sides is greater than in the middle, or one side is tighter while the other is looser—the edges will warp due to differences in stress. This issue is often related to the synchronicity of the tension adjustment devices and the parallelism of the roller shafts.
In addition, factors such as fluctuations in raw material properties, contamination of roll surfaces, and static electricity can also indirectly trigger ruffled edges through changes in tension. However, the core issue always revolves around “tension control.” If the tension problem is properly addressed, 80% of ruffled-edge issues can be effectively resolved.
II. Core Solution: Precise Tension Control—Starting from These Three Dimensions
High-quality web tension control hinges on achieving “constant tension plus real-time dynamic adjustment.” By integrating current mainstream technological solutions, a comprehensive control system can be established across three key dimensions: mechanical structure, electrical control, and process integration.
1. Mechanical Structure: Building a “Foundation Line of Defense” for Tension Control
The prerequisite for tension adjustment is stable mechanical transmission, which forms the basis for preventing sudden changes in tension. The key components include:
01. Tension Frame and Floating Roller Mechanism: This is the most fundamental—and critical—mechanical structure, typically consisting of a frame, fixed guide rollers, and movable tension rollers. As the sheet material passes through the path formed by the guide rollers and tension rollers, the tension rollers will float up and down in response to changes in tension, thereby providing initial tension buffering via mechanical linkage. Advanced configurations may incorporate additional counterweight assemblies or cylinders; by adjusting the weight of the counterweights or the cylinder pressure, the base tension value can be preset, enhancing the stability of the buffering effect.
02. High-precision roller shaft and guiding structure: Ensures the parallelism and roundness accuracy of all drive rollers and guide rollers, thereby preventing uneven lateral stress on the sheet caused by skewed roller shafts. At the same time, vertical guide rods and sliders are installed on both sides of the frame to ensure smoother movement of the tension rollers and to avoid sudden changes in tension caused by jamming or sticking.
03. Select the winding method appropriately: Choose between center winding, surface winding, or a combined center-surface winding method based on the characteristics of the sheet material. For example, lightweight, thin, and easily stretchable sheets are best suited for surface winding, as this helps reduce stress concentration; thicker, stiffer sheets, on the other hand, are more appropriate for center winding, which enhances the compactness of the wound roll.
2. Electrical Control: Achieving “Precise Closed-Loop Tension Regulation”
If mechanical structures represent “coarse adjustment,” then electrical control is the “fine adjustment.” Especially in the winding process, where the roll diameter is constantly changing, dynamic compensation must rely on the electrical system. Currently, there are two mainstream control approaches:
01. Variable Frequency Drive (VFD) Speed Control + Torque Control: The winding motor is controlled by a vector-type VFD, with the core logic being “real-time adjustment of the motor torque based on changes in the roll diameter.” Since the winding tension F is related to the motor torque T and the roll diameter D by the equation T = F × D/2, once the target tension is set, the system uses an encoder to detect changes in the roll diameter, automatically calculates the required torque, and outputs the corresponding control signal via the VFD to ensure constant tension. This solution offers moderate costs and high stability, making it suitable for most general-purpose sheet production applications—for example, in plastic sheet extruders, three VFDs are commonly used to synchronously control the speeds of three rollers while maintaining constant tension.
02. Automatic Roll Diameter Calculation and Speed Limiting: The system uses an encoder to detect the reel’s rotational speed and calculates the current roll diameter in real time, thereby avoiding insufficient tension compensation caused by errors in roll diameter estimation. At the same time, a maximum speed limit is set to prevent sudden tension changes resulting from motor “runaway,” especially during stop-and-restart operations, where it is crucial to ensure zero-speed tension output to avoid slackening of the rolled material.
3, Process Matching: Parameters “Tailor-made” Based on Material Characteristics
Sheets made of different materials—such as plastics, paper, and metal foils—vary greatly in their sensitivity to tension. Even for the same material, different thicknesses and widths will require different tension levels. At the heart of process matching lies “precisely setting tension parameters”:
01. Basic Tension Setting: For lightweight, easily stretchable materials (such as PET film or thin paper), the tension should be set relatively low to prevent stretching and deformation. For thick, rigid, and high-strength materials (such as thick PP sheets or metal foils), the tension can be appropriately increased to ensure tight winding.
02. Segmental Tension Adjustment: For long-roll winding, a “segmental tension” strategy can be employed—during the initial stage of winding (small roll diameter), the tension should be slightly higher to ensure that the initial layer of material is tightly wound; in the middle stage, the tension should remain constant; and in the later stage (large roll diameter), the tension should be appropriately reduced to prevent edge warping.
03. Eliminate interfering factors: Quantitative fluctuations in raw materials and differences in moisture content can lead to changes in tension requirements. Therefore, it is necessary to pre-test the characteristics of raw materials and adjust parameters accordingly. Additionally, install an electrostatic eliminator to prevent static electricity from causing the sheets to adhere or shift, which could indirectly affect the distribution of tension.
Three, Practical Tips to Avoid Pitfalls: 3 Key Details Often Overlooked
Many times, even when the tension system is properly configured, ruffles still appear. The problem lies in the details:
01. Equipment Calibration and Maintenance: Regularly check the accuracy of tension sensors and the detection precision of encoders to prevent control deviations caused by sensor drift. Promptly replace worn roller bearing components to avoid sudden changes in tension resulting from bearing seizure or jamming.
02. Operator Training: Avoid the arbitrariness of manual adjustments—for example, frequently changing inverter parameters or touching the tension rollers. Instead, establish standardized operating procedures: only make fine adjustments according to prescribed steps when the system indicates a tension deviation.
03. Linking Control of Upstream and Downstream Processes: The winding tension is not an isolated parameter; it must be synchronized with the speeds of upstream processes such as traction and extrusion. For example, by using a virtual shaft control system, the speeds of the traction roller and the winding roller can be linked to prevent tension fluctuations caused by speed differences.
Summary: The core of tension control is “stability + precision + matching.”
In summary, the root cause of the “ruffled edge” phenomenon in sheet machine winding lies in unstable and mismatched tension. The core solution involves establishing a three-in-one control system comprising “mechanical buffering + precise electrical adjustment + process matching.”
Most companies don’t need to blindly pursue high-end configurations; optimizing mechanical precision, perfecting the tension control system, and upgrading to vector frequency converters can already solve most problems. For high-precision sheet production, simply adding tension sensors and nonlinear PID control will suffice.
If your workshop is still plagued by “ruffled edges,” you can systematically troubleshoot using the three key dimensions—mechanical, electrical, and process—as mentioned above. By addressing the root causes, you can achieve stable tension and completely eliminate the issue of “ruffled edge” defects.
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