What is Tension?

In the world of manufacturing and web tension control, tension is simply the level of force applied to a web that opposes the normal motion of the system. To help illustrate this, think of paper being wound into one large roll. If tension is too low, there would be too much slack for the paper to wind evenly on the roll. Too much tension would tear the paper as it winds onto the roll.  The required tension for each application is dependent on two factors: torque and radius. In the example of paper being wound onto a roll – as the roll diameter increases or decreases, torque must also be adjusted to maintain proper tension.

What is Web Tension Control?

Web tension control is the process of maintaining a predetermined amount of stress, or tension, on a given material. Proper tension control in the example above would allow the paper to be evenly wound onto the roll without errors. This can be accomplished using Placid Industries magnetic particle brakes, magnetic particle clutches, constant current power supplies, and accessories like follower arm potentiometers or ultrasonic sensors.

Why is Web Tension Control Important?

Web tension control allows for continuous, repeatable, and precise manufacturing. By controlling web tension, manufacturers prevent machine downtime, material damage, product quality issues, and inefficient raw material usage. Proper tension control is a key element that affects product quality, manufacturing efficiency, and profitability. Without proper tension control manufacturers face inflated product prices due to large scrap and waste costs. Simply put, improving your web tension control will directly impact the efficiency and profitability of manufacturing.

Application Examples of Web Tension Control with Magnetic Particle Brakes and Clutches

1. Unwinding Application Example with Magnetic Particle BrakesAn example of this application includes unwinding a large roll of paper to feed into a specialty converting machine that converts flat paper into envelopes. As paper is fed into the converter, appropriate tension is vital for controlling the manufacturing process and, in turn, the quality of the end product.Precise web tension control is accomplished by mounting a magnetic particle brake onto the roll. The magnetic particle brake creates tension by applying torque that the paper must overcome to be pulled into the converter. Without the brake, the paper would be pulled too freely into the converter, causing slack in the unwound paper, and ultimately, inconsistent end products.The level of torque the brake provides is related to the current applied by a constant current power supply. This allows for extremely precise web tension control, as torque can be controlled simply by adjusting the current being supplied to the brake. A Placid Industries constant current power supply can be paired with an accessory like a follower arm potentiometer or an ultrasonic sensor. These accessory devices provide feedback about the roll diameter to the power supply. The follower arm rides on the roll, measuring the roll’s diameter. As the roll size decreases, the arm moves downward, rotating the potentiometer shaft. This, in turn, sends a signal to the power supply to reduce its current, effectively reducing the torque applied by the magnetic particle brake and controlling the system’s web tension.
   
2. Re-winding Application Example with Magnetic Particle Clutches
   An example of this type of application is the rewinding cable from a large spool to smaller spools. This process of producing “sellable” cable sizes requires precise web tension control to prevent machine downtime and preserve quality standards.Magnetic particle clutches are attached to the smaller rolls in this application example, whereas a magnetic particle brake would be attached to the larger roll. The magnetic particle clutches provide a driving force used to rewind or take-up the unrolled cable. This is done by applying a current to the magnetic particle clutch. As the current increases the level of torque produced by the clutch increases, which rotates the smaller spools, allowing the cable to be rewound. When there is no current applied to the clutch, there is no engagement, and therefore, the small rolls will not rotate.In a similar fashion to magnetic particle brakes, magnetic particle clutches output torque is controlled by the current being supplied to the clutch. Using a Placid Industries constant current power supply with a follower-arm potentiometer or an ultrasonic sensor is the best way to ensure proper torque and tension control of a web. An ultrasonic sensor is used in a similar way to the follower-arm potentiometer. The sensor will analyze the diameter of the roll by sending an ultrasonic pulse of sound and then measuring the time for the return echo pulse. This information is then sent to the constant current power supply in the form of a 0 to 10 VDC signal. This signal will cause the power supply to adjust the current supplied to the clutch accordingly.

Why choose Placid Industries for your web tension control devices?

Placid Industries has more than 50 years of experience producing the highest quality products with unparalleled technical performance. Our business is built around continuous improvement of our performance, rapid delivery time, and responsiveness. Placid Industries offers a turnaround from order to shipment in as low as 24 hours. Placid Industries’ products are well known throughout the US and Europe for tension control applications where unwinding/rewinding is required or in applications where torque needs to be controlled independently of RPM. Placid also has the capability to package entire systems which may include a brake or clutch, power supply, and potentiometers or ultrasonic sensors for live feedback. Looking for assistance with your web tension control application? Give us a call today: 1-866-523-2423, and you will speak with a technical expert right away!