The proper control of web tension is especially important for maintaining consistent and high quality in coating and laminating processes.
For example, in coating, variation in web tension can lead directly to variations in coat weight and may cause spreading problems leading to carry over onto rollers. Even variations across the web width can cause quality problems with Meyer bar, air knife, or reverse roller coating systems. A display of right, left, or total tension can be invaluable in counteracting this.
In the case of laminating lines it is not only the absolute tensions that are important, but also the relative tensions of one laminated material to another. These must be correctly related to the stress/strain characteristics of the material if subsequent distortion due to differential contraction is to be avoided. Curl is often a particularly acute problem with sheets as the end product. Montalvo tension control systems are available which can automatically maintain the correct tension ratio between the materials in spite of all of the variables such as reel diameter, acceleration/deceleration and non-linearity in the system.
Coating and laminating lines also present more difficulties in respect to the use of isolating wraps and nips than many other converting processes.
When this is combined with the effects of drying ovens, especially flotation types, where the tension must be maintained at a constant low value, proper control can be problematic.
The Montalvo X-3400HD analog/digital tension controller and the S4 digital tension controller have been designed for maximum control-ability irrespective of the materials and machine variables. These controllers are generally used in conjunction with Montalvo load cells and/or indicators/amplifier modules for a complete web tension sensing and control solution.
The X-3400HD is the most advanced closed-loop controller from Montalvo, offering the widest variety of functions and features for coating and laminating. The unit can utilize load cell or dancer input signals and a ‘Progressive PID’ regulator. It can be configured for use in unwind, rewind, and even intermediate control positions as well.
The S4 provides accurate and repeatable control on all web applications employing a torque device. It is ideal for unwind and rewind tension applications. Employing a ‘diamatic’ control algorithm the S4 ensures uniform response, regardless of roll diameter. This model is both fast and precise and includes a non-volatile memory for the storing of control parameters.
Features on both controllers include semi-automatic calibration and control tuning, user adjustable soft-start and anti-coast; sample/hold/ratio splice functions and bump-less transfer between auto and manual, as well as rewind taper.
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