As the Covid-19 pandemic has spread, face masks have become increasingly “in your face” – and on your face – around the world. And as demand for these protective items has surged, I and my team of nonwovens specialists have seen a clear rise in requests for help from nonwoven manufacturers working to expand their production capacity.
So it’s exactly the right time to turn the spotlight on the growing nonwovens industry, and the key role belting plays in it.
High tech, customizable, for numerous applications
Over the last 50 years, nonwovens have gone from being low-price substitutes for traditional textiles to today’s innovative, high-tech, engineered fabrics made of natural and man-made fibers, with customizable physical and mechanical properties. Used in a vast range of consumer and industrial products, alone or with other materials, nonwoven fabrics range from thin, lightweight and single-use to strong and durable.
Non-wovens in daily life
Aside from their rapidly expanding use in medical settings, nonwovens are found in absorbent hygiene products, automobiles and transport, clothing and footwear, geosynthetics and civil engineering, construction, household and commercial items, industry and the military – in fact almost everywhere. They are even used in some conveyor belt types, like the heavy conveyor belts installed in airports and distribution centers, where non-woven materials ensure low noise, no delamination, and no fraying – all the while ensuring excellent tracking and powerturn suitability.
Challenges for nonwoven producers
Clearly, demand is growing for nonwovens, but as for all manufacturers, raw material availability and price volatility are ongoing challenges. Beyond this, key requirements are to ensure strong products that not only have a long service life, but also a long shelf life. Minimized running costs, along with low wastage and high and reliable throughput are essential to profitability.
A complex production process
From fiber bale opening, weighing and blending; through web formation using drylaid, wetlaid, airlaid, spunlaid, meltblown or submicron spinning processes; to thermal, mechanical or chemical bonding; and finally to the various finishing treatments, nonwovens manufacture depends heavily on conveyor belting at every stage.
I want to focus now on one particularly important application: the crosslapper.
Challenges in the crosslapper process
The basic function of a crosslapper is to accept lightweight fiber web from the carding machine and produce a heavier web by placing the incoming web in layers on a conveyor belt positioned at a lower level. During this process, the material flow changes direction by 90 degrees. From three to 20 or more layers are possible, although the more layers there are, the slower the material exits the crosslapper. (Inlet speeds of up to 150 meters a minute are common.) Most crosslappers have exit widths of 3 to 7 meters, although papermaker felt crosslappers can be much wider.
The fiber web is driven by two (sometimes even three) processing belts. On this kind of application, it’s essential that the feeder belts offer high transversal rigidity and high longitudinal flexibility, particularly when used for high-speed, latest-generation crosslappers. This is important because it makes the belts lay flat, ensuring that the card/web is homogenous and the belt can run across smaller pulleys (as small as 50 mm). This permits rollers that are lighter, resulting in less inertia and allowing high belt acceleration and deceleration for prompt start/stop movements and a continuous infeed and outfeed speed.
Belt challenges and how to crack them
The most common issues that arise with processing belts for crosslappers are fibers sticking to the belts, and cupping of the belts at the sides. Why does this happen?
Fibers can stick to the belts for many reasons. These include:
- The type of material or fibers used for manufacture
- Electrical conductivity through the fibers
- General aging of the belts and loss of release properties, particularly at joints
- Limited chemical resistance against aggressive spin finisher oils that migrate into the belt. When the belt is fully soaked, oil remains on the conveying surface and fibers can stick to it
- Belt materials, such as nylon or polyamide. While these have very good chemical resistance, over time the material shows signs of fatigue, which leads to micro cracks on the surface where fibers can stick
Belts can cup at the sides because of:
- Mistracking (touching the sides)
- Environmental factors like ambient temperature and humidity
- Poor machine/roller alignment
- Incorrect tension following initial elongation
These challenges are all solvable. For example, Habasit belts are anti-statically equipped to effectively prevent static build-up from the running belt. To deal with joints, and ensure that the fingers are perfectly joined together during fabrication, Habasit has a strict procedure for every belt type to ensure the highest quality. The problem of oil is solved by belts with specially impregnated PUR top surfaces – as described below.
Dedicated belts for crosslappers
For high-end, high-speed crosslapper applications, Habasit has a range of premium solutions offering key features that include high transversal rigidity, light and high longitudinal flexibility, plus high wear- and scratch resistance, conductive properties, and excellent release.
For very demanding applications that use specialty oils and chemicals to assist with fiber bonding, Habasit has also developed a new chemically resistant crosslapper belt featuring a PUR-impregnated non-adhesive top surface, good chemical-, wear and scratch resistance, high lateral stability, longitudinal flexibility, and low belt weight.
Expert technical support
Contact me at any time for help or advice on your production challenges, visit our website to find out more on our solutions for nonwovens, or listen to my interview with Noemi Bangel.