During the web handling process, having the appropriate web tension control in place can help your facility profit from a substantial time savings, reduction in loss of material, and reduction in overall production expenses. Web handling involves moving flexible, thin materials such as film, paper, nonwoven material, foil, etc. from batch to continuous processing. This is different from sheet processing due to the continuous length of a web.
Webs often start and end on a roll; this is referred to as a roll-to-roll or R2R process. Before the web handling phase begins, it’s usually proceeded by the process of web creation, including extrusion, paper-making and other creation processes. Die-cut pieces or sheets may be the end result depending on the application.
Understanding the web handling process as well as how web tension control works can help you increase your bottom line by eliminating unnecessary waste. Waste usually results from breakage, deformation, wrinkling, misalignment or abrasion of the web material. Waste may also occur during the slitting, winding or laminating processes.
Why does web tension matter?
During the web handling process, the material is generally fed into a finishing machine directly from a reel. It is then treated and rewound onto a second roll. Seems to be a fairly simple process…correct? Unfortunately, the material may develop defects or the quality of material may be lowered due to incorrect web tension during the process. When the material is being unwound from a roll, having too little web tension can cause the material to become slack before it reaches the transport drive. When the web tension is too high, however, this can cause creases lengthwise, thus, causing deformation in the web material.
Web tension should be accurate between clamping points as well to maintain the desired quality. When web material approaches the rewinder that winds it back onto a roll, then inadequate web tension can cause reel telescoping (e.g. Coil defects occur when the coil wraps thrust forward from the side of the coil). If the tension is too high, then the force will destroy the inner windings.
Web Tension Control Loop
A web tension control loop involves several key products to ensure the tension is never too high or too low. The loop may consist of tension load cells, a load cell amplifier, a web tension controller and an actuator. The web tension controller is installed to compare the actual web tension of a load with the desired tension (target value). It sends corrective signals to the actuator, which can then be communicated to the main equipment or motor to develop an accurate speed for the tension measurement.