A Complete Guide to Web Tension Control: Key to Improve Production Efficiency

What is Web Tension Control?

Web tension control is the process of controlling the force applied along the direction of the web in a continuous web material during its movement in a production line. This controlled force is very important in applications like printing, coating, textiles, converting and many others to ensure that the material is transported with a lot of precision. Web tension control is one of the most critical factors that determine the reliability and efficiency of web processing operations. It ensures that the material is gripped with the right amount of force required for its processing without causing any harm to it.

The Fundamentals of Web Tension Control

Web tension control is the control of the pulling force along the length of a continuous web of material. This force, usually expressed in force per unit width, is generated from several sources along the production line. Back tension is applied at the unwind stand, forward tension is applied by driven rollers and winding tension is applied at the rewind. This tension has to be measured in real-time using devices such as load cells to ensure accurate control. The measured tension is then passed through a tension controller that compares it with a desired value of tension. In case of deviation, the controller commands other components like brakes, clutches or motors to make the required corrections. This continuous feedback loop helps to maintain the web tension constant and steady throughout the entire process which is very important in web processing applications.

Why Precise Web Tension Control is Absolutely Essential

Web tension control is one of the most critical parameters that need to be maintained accurately in web processing industries. Lack of tension can cause problems like misregistration in printing, wrinkles in coatings, and slippage, which are costly since they lead to production of substandard products and wastage of material. On the other hand, high tension may lead to stretching, distortion or web breaks which results in more time wastage and loss of material. The effect on production efficiency is significant because fluctuating tension requires the reduction of the speed of the process to avoid producing faulty products. Furthermore, the higher probability of rejected products due to poor tension control impacts the profitability of the company. Apart from the above effects, fluctuating tension can also cause faster deterioration of the components of the machines, thus increasing the frequency of maintenance.

In other words, the ability to control the proper tension of the web is the key to successful web processing. It reduces the number of defects, avoids disruption of the production process, saves materials, and helps to preserve the tools. It is therefore important to note that tension control is not an expense that can be done away with but a strategic investment that any company that wants to achieve the best results in web-based manufacturing should consider.

Exploring Key Types of Web Tension Control Systems

Open-Loop Tension Control

Open-loop tension control is form of automated tension control that does not require the use of a tension sensor. It does not use any feedback control signals but rather uses preprogrammed control signals depending on the web speed and the roll diameter. For instance, as an unwind roll reduces in diameter, the braking force is regulated based on a pre-calculated profile. The advantages of open-loop systems include the fact that they are cheaper and easier to implement than closed-loop systems, and are ideal for use in applications where the material properties and processing conditions are constant and tension accuracy is not paramount. However, these systems do not provide real-time feedback and therefore cannot adapt to variations in material properties or other process perturbations, which can result in tension variations in more challenging applications. Open loop control is used in simple converting operations or where cost is a critical factor and the variation of tension is acceptable.

Closed-Loop Tension Control

Closed-loop tension control is more accurate and stable than open-loop tension control because it uses a feedback loop. In these systems, there is a tension sensor that measures the actual web tension and the signal is then taken to a tension controller. The controller then measures the tension and compares it to a set point and sends a signal to an actuator such as a brake, clutch or motor to bring the tension back to the set point. The main benefit of closed loop control is that it is capable of providing constant and precise tension despite fluctuations in the process conditions or the properties of the material being used. This results in improved product quality, less scrap, and higher throughput, especially in applications such as high-speed printing or thin-film deposition. Closed-loop systems are more complicated and costly because of the use of sensors and advanced controllers; however, their performance is usually better than that of the open-loop systems. They are widely used in printing presses, laminating machines, slitting machines and coating lines.

Manual Tension Control

The simplest method is the manual tension control where the operator adjusts the tensioning device such as a mechanical brake or clutch by feel or sight. The first type of control is manual control and it is the cheapest to implement since it does not require any equipment. This approach may be used for very low production volume or in cases where the tension accuracy is not critical. However, manual control is very much dependent on the ability and focus of the operator and therefore it is very prone to errors and variations at high speeds or during long operations. It is therefore not suitable for applications where high tension control is necessary or for automated web processing and is not commonly used in modern industrial web processing.

Servo-driven Tension Control

Servo driven tension control systems use servo motors to control the tension of the web. These motors can be directly coupled to rollers or can be incorporated with other tensioning systems. The control system is used to send signals to the servo motor to change its speed or torque to control the web tension with high accuracy and sensitivity. This makes servo driven systems suitable for applications where very high degree of tension control is required or where frequent tension variations are required. Also, they allow for fine-tuning of the speed and location of the web on the screen. The major disadvantage of servo-driven systems is that they are more expensive than other tension control methods, mainly due to the cost of the servo motors and the control electronics. They are commonly used in high-speed printing machines, sophisticated converting machinery, and where the material being converted is sensitive or expensive.

Pneumatic Tension Control

Pneumatic tension control systems utilize air pressure to apply force to a brake or clutch, thus regulating web tension. The air pressure is controlled by a pneumatic regulator, which can be adjusted manually or automatically in a closed-loop configuration. Pneumatic systems offer a balance of simplicity, reliability, and cost-effectiveness for many applications. They can provide smooth and consistent tension, particularly for lighter to medium loads, and are relatively easy to maintain. However, they may not achieve the same level of precision as servo-driven or some advanced electrical closed-loop systems and require a compressed air supply. Pneumatic tension control is widely used in various web processing applications, including certain printing presses, laminating machines, and unwind/rewind stands.

Hydraulic Tension Control

Hydraulic tension control systems use hydraulic pressure to produce the force needed for tensioning. These systems are normally applied in industries where high force and torque are required in the processing of thick or massive materials. Hydraulic systems can produce very high force and torque and are generally very strong and reliable. They are, however, more complicated and need more attention in terms of maintenance as compared to other tension control types. There is also a possibility of leakage of the hydraulic fluid. Hydraulic tension control is used in high load converting machines such as some paper mills or large scale laminating machines.

Sensor and Measurement-based Tension Control

This category broadly refers to closed-loop systems that rely on the direct measurement of web tension using various types of sensors, such as load cells, strain gauges, or ultrasonic sensors. The defining characteristic is the ability to use feedback from these sensors to control the tension in real time. Depending on the application and the material being processed, various sensors are selected. The first benefit of the sensor-based control is that it is accurate and responsive to the changes in the web and process conditions. However, these systems can be more complicated and the choice and location of the sensors should be made more carefully to get the best results. Tension control through sensors and measurements is important in web processing applications where tension is a critical parameter that affects both quality and productivity of the final product.

Brake Tension Control

Brake tension control systems employ a brake, which is usually a friction brake or a magnetic particle brake to apply back tension on the unwind roll to regulate the web tension. The degree of braking is used to control the tension of the string. Brake systems are quite simple and can be an economical solution for low-speed operations. Of all the types of brakes, magnetic particle brakes are particularly advantageous in that they provide smooth tension that can be easily controlled. However, friction brakes are known to wear out and may need to be adjusted from time to time and they also produce heat. Magnetic particle brakes may wear out over time and may not be ideal for high speed applications. Brake tension control is widely applied in unwind stands in different web processing industries, particularly in low to medium speed applications.

Magnetic Tension Control

Magnetic tension control systems involve the use of magnetic fields to produce a controlled braking force or torque. This is usually done with the help of a magnetic particle brake or a hysteresis brake. The strength of the magnetic field and therefore the tension can be controlled electrically. Magnetic tension control is smooth and non-contact with good controllability, which is suitable for applications where precise tension is needed, for instance, winding and unwinding of delicate materials. However, magnetic brakes can be affected by temperature and may have some drawbacks in terms of maximum torque and speed. Magnetic tension control is widely used in some particular fields such as textile industry for yarn winding, wire drawing and some printing and converting processes where the substrates are very sensitive.

The Benefits of Automated Web Tension Control

คุณสมบัติ	Manual Tension Control	Automated Tension Control
ประสิทธิภาพการผลิต	Lower, prone to interruptions due to web breaks or adjustments	Higher, continuous operation with minimal manual intervention
ค่าใช้จ่าย	Lower initial cost	Higher initial cost, but lower long-term operational costs
Accuracy	Highly dependent on operator skill, inconsistent	Precise and consistent tension maintained automatically
ความสม่ำเสมอ	Variable, prone to fluctuations	Stable tension throughout the production run
Waste Reduction	Higher due to web breaks, misregistration, and wrinkles	Lower due to consistent tension preventing defects and breaks
Labor Requirements	Requires continuous operator attention and adjustment	Reduces the need for manual adjustments and monitoring
Suitability	Low-volume, non-critical applications	High-volume, high-precision applications

From the table, it is clear that automated web tension control has the following benefits:

• Higher Production Rates: Automation means that the production process can be done at a faster rate and with less interuptions such as web breaks or manual intervention. This translates directly into increased throughput and reduced production time.
• Lower Operating Expenses: Although the initial capital outlay is high, the operating expenses are much lower since the system does not require frequent operator attention. This saves time for other tasks and reduces the general expenses on labor.
• Better Quality: The tension is well controlled and consistent in automated systems hence reducing on defects like misregistration, wrinkles, stretching and uneven coating. This results in improved quality of the products and low scrap levels.
• Less Web Breaks and Defects: Automated tension control helps to reduce web breaks and defects, which in turn reduces material wastage and thus saves a lot of money particularly when working with expensive materials.
• Better ความสม่ำเสมอ และ Repeatability: Automation also helps to maintain the tension within a narrow range throughout the production process and hence the quality of the product is not compromised from the first piece to the last piece. This is important in ensuring that quality standards are met since the process can be repeated several times.
• Safer Operation: Automation helps to minimize the human interference in the dangerous zones of the production line, which in turn makes the working environment safer for the operators.
• Data Logging and Analysis: Most of the contemporary tension control systems are automated and are capable of logging tension data over a period of time and analyzing it to help the manufacturer improve the efficiency of the process.

In other words, the advantages of automated web tension control are a more efficient, cost-effective, and reliable manufacturing process that can produce better quality products with less waste. Such systems are a good investment that pays off in the long run as it helps to improve the company’s performance.

Choose KETE: Ensuring Stable Tension Control for Superior Printing and Slitting

At KETE, we know that success in flexible printing and slitting depends on the stability of web tension control. That is why we incorporate state of the art automated tension control systems into our wide portfolio of machinery. In our KTGP series rotogravure and KTFP series flexographic printing presses, these are important automatic control systems for web tension control during printing. In addition, in our KTSM series slitting machines, tension control is important factor that helps to provide clean cuts and perfectly wound finished rolls. KETE machinery also has a highly developed system of tension control that does not require frequent manual intervention, thus reducing the possibility of human error and maintaining stable production throughout the long run. KETE has been in the flexible printing and packaging industry for more than 15 years and has always adhered to the business philosophy of “Quality First, Customer Foremost” to offer you the best solutions for your success.

Contact us:

• Address: 20th Floor, Xinchao Building, Anyang Street, Ruian City, Wenzhou City, Zhejiang Province, China 325200
• Phone: +86-577-66873227 / 66689036 / 66689037
• WhatsApp / WeChat: +86-18806770163
• E-mail: ติดต่อฝ่ายขาย@ketegroup.com

Troubleshooting Common Web Tension Control Challenges

Addressing Issues with Inconsistent Tension

There are several forms of inconsistent tension, including varying tension readings, uneven winding, and product defects. The first thing that needs to be done in order to solve the problem is to determine where the discrepancy is coming from. This may involve:

• Examining the tension sensor: The tension sensor should be calibrated, clean and not damaged in any way. Ensure that the wiring connections are properly made and that the sensor is giving a stable and accurate signal.
• Check the actuator: Look for signs of wear, damage or malfunction of the brake, clutch or motor. Check that it is responding appropriately to the control signal from the tension controller.
• Web path inspection: Ensure that there are no barriers, skewed rollers, or high friction in the web path that may be causing tension fluctuations.
• Checking the control system settings: Ensure that the tension set point is properly set and that the control parameters such as the PID control parameters are optimized for the material and process.
• Roll dynamics: Fluctuations in tension can be attributed to out of round rolls or variation in roll density.

Once the potential cause has been identified, corrective actions can be taken, for example, recalibration of the sensor, replacement of a worn out actuator component, cleaning or realignment of rollers, adjustment of the control system parameters or problems with the incoming roll quality.

Preventing Web Breaks and Material Damage

Web breaks and material damage are usually the direct result of tension. To prevent these issues:

• Check the tension setpoint: The tension setpoint should be set according to the material being used and should not be more than the tensile strength of the material. Review material specifications and process procedures.
• Gradual tension changes: It is important not to change the tension suddenly because this will exert a lot of pressure on the web. The control system should be designed in such a way that it gradually increases and decreases tension.
• Check for web flaws: It is also important to inspect the web for any existing flaws such as tears, cuts, or thin areas that could make it more susceptible to breaking under tension.
• Proper roller surfaces: If the roller surfaces are damaged or dirty, then there will be increased friction and localized stress on the web. Maintain rollers in good condition.
• Monitor tension peaks: It is possible that certain processes may have short-term tension fluctuations. The control system should be able to identify such peaks and avoid web breaks.

Resolving Problems with Web Wrinkling and Stretching

Web wrinkling and stretching are usually related to tension variations in the web width or to tension that is too high or too low for the material. To address these problems:

• Check tension profile across the web: In wide-web applications, it is necessary to check the tension profile across the width of the material. This is because uneven tension can cause wrinkling and tracking problems. It may be necessary to use specialized sensors or techniques to measure the tension profile.
• Tune tension: Try raising or lowering the tension a little to get the right setting for the material. It is important to understand that different materials require different levels of tension.
• Check the rollers: improper positioning of rollers may lead to improper tracking of the web and may result in wrinkling or stretching of the web. Ensure that all rollers are parallel to each other and perpendicular to the direction of web travel.
• Examine spreader rollers: Spreader rollers are used to reduce the wrinkles by stretching the web slightly in the cross direction. Make sure that these rollers are working fine and are placed at the right location.
• Take into account the characteristics of the material: Some materials are more likely to wrinkle or stretch than others. In some cases, it may be necessary to change the process parameters or even select a different material.

Adjusting the tension levels, checking the rollers, and using the right web handling techniques are some of the ways of addressing the problem of web wrinkling and stretching.

Dealing with Tension Spikes and Oscillations

Vibration and fluctuation of tension can be attributed to instability in the control system or mechanical problems. To address these problems:

• Check tension control system tuning: The tension controller may require tuning of the PID parameters to achieve the best response of the system and avoid oscillations.
• Check for mechanical backlash: Mechanical backlash in gears, couplings or other mechanical parts can cause oscillations in the tension. Check and fix any mechanical problems that may be present.
• Assess sensor response: A slow or noisy tension sensor can cause tension to rise and fluctuate. Make sure that the sensor is working properly and giving a clean signal to the circuit.
• Identify tension changes: Some processes may naturally cause tension variations. This knowledge can be useful in developing a better control strategy for the system.
• Consider using damping mechanisms: In some cases, it is possible to use damping mechanisms, for example, inertia compensation or filtering in the control system to reduce tension fluctuations and oscillations.

Properly calibrating the control system, addressing any mechanical issues, and understanding the process dynamics are essential for resolving problems with tension spikes and oscillations.

บทสรุป

In conclusion, web tension control is an important factor that needs to be addressed in order to increase efficiency and quality of the industries that deal with continuous web materials. Optimal tension is one that is precise and consistent in order to reduce the number of defects, minimize waste, and increase the rate of throughput. The choice of the tension control system, whether it is manual or automated, open-loop or closed-loop, depends on the particular manufacturing process that is to be controlled. It is crucial to comprehend the differences between various tension control technologies and their application to optimize the production process, increase the quality of the final product, and ultimately succeed in the web processing industry.