Precision Tension Control in Non-Woven Converting

New kinds of non-woven and composite textile structures have experienced phenomenal growth in technology and in commercial product importance.

Originally, most non-wovens were produced by using a wet laid process where short length fibres of less than 2.5mm were added to modified paper machines in place of, or in addition to beaten pulps and were held together with resin binders. Among the commercial products that most people will be familiar with are products as diverse as diapers and car engine oil filters.

Non-woven and composite materials are employed in many unusual and exotic applications, and are produced in many different ways. In fibre extrusion technology where melted polymer is forced under pressure to make non-wovens directly (spinnerette), two techniques have been developed, one of which is termed ‘spun wound’ and the second is ‘melt blown.’

The webs produced by the melt blown technique can be controlled to provide a high-density capillary structure suitable for meeting two seemingly entirely different requirements. In the manufacturing process the structure can be made so dense that it resists moisture and is used for waterproof liners, etc. Conversely the structure can be made so that it provides excellent water pick up making it ideal for kitchen surface wipes.

Some of the most recent areas in which non-wovens and composites are becoming widely used are in the production of geo-synthetics, geo-textiles, geo-membranes, geo-grids and geo-nets. This group of products is used in a variety of civil engineering applications. Non-woven geo-textiles for example are highly desirable for sub-surface drainage and erosion control purposes.

To be a leading player in non-wovens the producer of web fed rolled goods must not only master new production techniques, which include a greater emphasis on satisfying customer quality requirements, there is also a need to master the inconsistencies and irregularities that crop up in the day to day production process. One of the most effective ways is by improving web control through better tension control.

The production of non-woven materials can present unique tension control problems, for instance, the production of kitchen towels, wipes and toilet tissue, some of which may be embossed and/or printed require very low tensions. Low extensibility and tight tolerances has meant that many producers and OEM’s require precision tension control systems that integrate seamlessly with the parent machine control logic, i.e. PLC/PC systems; systems and system components that are highly responsive to changing conditions in the web, and that are able to provide repeatability of results.

Montalvo’s latest control modules, a critical component of closed loop tension control systems are provided with the latest communication and diagnostic protocols such as DeviceNet, Profibus, and CANopen, at the same time each of the control modules, that is the X-3400 tension controller , the D-3400 dancer controller and DTI-3400 dancer controller with tension indication incorporate features such as web break detection, inertia compensation, range expanding functions (brakes), sample, hold and ratio splice function and transferable memory card.

In certain circumstances, particularly when running delicate non-wovens or ultra-thin films contact with the web must be avoided. In these situations Montalvo can provide converters with an alternative control module, the U4 open loop/diameter based controller. . The US4 ultrasonic sensor together with the U4 tension controller provides for a wide range of configuration possibilities – from simple unwind/rewind through to more complex multiple unwind systems.

Fundamental to many processes is the need first to obtain a measurement and then instigate some form of control procedure so that process variables and inconsistencies can be regulated. Montalvo control modules provide the means whereby torque generating devices such as drives and brakes regulate the web so that inconsistencies are equalized or smoothed out; Montalvo tension-sensing load cells (transducers) provide the measurement element within the tension control equation.

Montalvo load cells (transducers) are compact, ruggedly constructed yet highly sensitive devices that continuously measure ‘actual’ tension; the signal summed enable the control module, whether the X-3400 tension controller or one of the other controller options, to compare this measurement against operator ‘set point’ and make the necessary adjustment.

Closed loop load cell-based control eliminates human subjectivity, reduces waste, ensures maximum machine throughput while maintaining quality at the highest level – free from wrinkles, creases, baggy edges, dished rolls and, when printing is involved, free from registration irregularities. A further benefit is that because the process is precisely controlled downtime is minimized, production output is at the highest and the risk of missing customer on-demand delivery requirements is lessened.

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