In the zone: how load cells keep the web under tension

We’ve all seen images of newspapers rolling through the presses, a continuous stream of paper that starts blank at one end and covered with Brexit news at the other!

Many manufacturing processes rely on a similar technique of unrolling material at one end, passing it through various processes, and then rolling it up again. The material is usually known as a web. The web is simply a term for any material that is continuously pulled from a roll through a manufacturing process of some sort.

Load cells: maintaining tension in each zone

The web runs through three main stages; the unwind, intermediate and rewind zones. Inconsistent or incorrect tension in any zone may result in reduced efficiency, fluctuations in quality and, at worse, possible damage to the material involved. This might include:

• wrinkling
• uneven pressure on layered materials causing them to ‘star’
• printed images becoming smeared or blurry
• over stretching of the material

The tension of the web may also need to change from zone to zone as well, which would be hard to judge by feel alone, the traditional method.

Instead, load cells mounted in the rollers, pulleys or sheaves in the web setup can constantly monitor the tension, and trigger automated adjustments to the brakes, gear ratios, motors or dancers if the tension falls out of the preset PLI. (Tension is measured in pounds per lineal inch, PLI). The combination of load cells and controller ensure that tensions are kept at their optimum, resulting in a smooth, unbroken web and minimal wastage.

 

Changes in fabric technology

This technology and methodology may not be new, but the complexity of the processes involved, from specialist printing to coating, have developed enormously. This is particularly true in the manufacture of technical textiles, from carbon fabrics to digital printing substates, to materials which incorporate sensors. All require highly controlled and precise coating and finishing, and a manufacturer might need to swap for one type of fabric to another several times during a 24 hour period.

 

Load cells and multi-functioning coating heads

Enter multi-functioning coating heads, which can be used for a range of fabric coating including screen printing, magnetic roller coating and knife coating. These heads are them mounted in a complete finishing line, or as a complete system such as the Monfort Allround system. This system allows modular coating heads to be quickly swapped out, with load cells at the heart of its functionality, as the manufacturer states:

“The Montex Allround consists of a load cell, a spreading unit and a pulling device along with the selected coating head. It allows for tension-free coating of the substrate along a greatly-reduced web path and a very short period of “open” coating prior to the substrate entering the dryer to ensure a significantly reduced chance of contamination.”

Load cells also ensure that woven fabrics on a loom are consistent in tension, especially at the start and finish of weaving. As the Textile Schools website explains:

“A position sensor or a load cell signals at any moment the tension operating on the back rest roller and permits to adjust the let-off speed so that the tension remains absolutely constant from the start to the end of the weaving cycle. Furthermore, the positions of the take-up and let-off motions during the critical starting phases can be adjusted to the running behavior of the material in progress, in order to avoid stripes on the fabric.”

 

Load cells for fabric testing

Load cells come into play again in materials testing machines and jigs. Once a fabric is woven or created, it needs to be tested to internationally recognised standards, such as the ASTM test standards. These test standards:

“Provide the specifications and test methods for the physical, mechanical, and chemical properties of textiles, fabrics, and cloths, as well as the natural and artificial fibers that constitute them. The textiles covered by these standards are commonly formed by weaving, knitting, or spinning together fibers such as glass fiber strands, wool and other animal fibers, cotton and other plant-derived fibers, yarn, sewing threads, and mohair, to name a few. These textile standards help fabric and cloth designers and manufacturers in testing textiles to ensure acceptable characteristics towards proper end-use.”

 

Load cells for all types of materials testing

Need a load cell for a particular test, or for a new range of testing machines? We can help! Our load cells are already hard at work in a wide variety of testing machines across diverse industries. They can also be found in bespoke, one of a kind testing apparatus in research labs.

Call us to discuss your particular requirements, or drop us an email. We design, manufacture and deliver load cells right here in the UK, so and we also stock ‘off the shelf’ load cells too, which you can buy online, right now, by clicking the Shop button above.