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Increasing productivity and reducing down- time with the right web cleaning solution Meech offers both contact and non-contact
onverters know that a clean web is a productive web. By removing the contamination that is an inevitable by-
product of high-speed webs, web cleaning systems increase productivity, reducing maintenance downtime and minimising the waste caused by sub-quality product. Converting lines process different materials at
different speeds and tensions. The types and levels of contamination differ, as do the reasons why web cleaning is necessary. Is it principally a customer requirement? Or a maintenance issue? Given that any web cleaning solution will almost certainly have to fit into an existing production line, how does this influence the choice of system? All these factors, and more besides, will contribute to the final equipment selection. To decide which factors are most important, it is fundamental to understand the basics of web contamination and how to tackle it. There are two main reasons why a web
attracts a variety of contamination; firstly, the boundary layer of any moving web and secondly, the generation of static charges. A web cleaning solution must be capable of tackling both.
two approaches - vacuum technology, such as the Meech VacClean, or adhesive rollers, as used in the Meech TakClean. Contact vacuum systems incorporate brushes
to free debris before vacuuming. Whilst this approach is effective when large particles need to be removed from heavily contaminated surfaces, it can be a harsh cleaning method for use on sensitive materials (although some systems feature retractable brushes to avoid damaging abrasion). In addition, the necessity of removing contaminants from the brushes raises the possibility of cross-contamination. Brush systems also require a significant capital investment. Contact systems using adhesive rollers
incorporate twin elastomer rollers, which are in contact with the full width of the web, breaking down the boundary layer and lifting contamination from the web’s surface. This is then transferred to a second roller with a high adhesive mass, which removes debris from the first roller, preventing recontamination. Adhesive roller systems perform well on small particles (down to as low as 0.5 micron), but are not designed for more demanding applications where higher levels of contamination are involved, as the adhesive rolls can quickly become tainted. For this reason, adhesive roller systems also require more monitoring by the operator. Another limitation of adhesive roller systems is the machine speed, normally limited to less than 250mpm, which can prove problematic for certain applications. The choice of non-contact technologies is
Above, the CyClean system. Below, the TakClean.
between ‘blow-and-vacuum’ such as the Meech CyClean and boundary layer solutions as used in the Meech ShearClean. 'Blow-and-Vacuum' systems employ air knives on either side of the web to strip the boundary layer and all traces of contamination from the web’s surface. The presence of vacuum airflows ensure that the contamination is captured and subsequently removed. It is an eficient method, and the systems are typically compact, which makes integration into existing web lines more straightforward. Boundary layer systems are a relatively recent
development. High-speed, non-contact rollers rotate at a distance between 0.5 and 1mm from the surface, and in the opposite direction. The roller design is optimised to generate its own boundary layer that is substantially greater than the boundary layer on the web. The greater energy of which destroys the boundary layer
8 March 2017
Contact or non-contact? C
web cleaning technologies — the system chosen depends on the materials being processed, the application, the flexibility required by the converting line and, of course, the budget. Contact cleaning systems typically take one of
The gravure coating process
Reverse roll coating
carried by the incoming web. This exposes even the smallest particles on the web to a very powerful cleaning force. The low-pressure, high- velocity region created by the roller lifts and removes the contamination from the web and carries them to a vacuum extraction chamber.
CONTROLLING STATIC In order to guarantee a spotless web, a cleaning system must be combined with an effective static control solution to counter the charges on the web’s surface that attract contamination. All Meech web cleaning systems incorporate the latest shockless AC static control as standard. For example, a static charge can be generated
when the web unwinds, or by friction as the web travels over non-conductive nip rollers. Such charges are more likely to occur when
processing film and, if not neutralised, will pull airborne contamination to the surface of the web. Charges can be positive or negative in polarity; paper is usually positive and film negative. Active static control provides the most effective means of neutralising charges. The technology uses ionisation. A voltage is fed to an array of emitter pins mounted on an ionising bar, creating a high-energy ‘cloud’ of positive and negative ions. Any statically-charged surface, of either polarity, passing close to the cloud is quickly neutralised.
CONCLUSION Converters must be able to meet constantly changing demands, and do so profitably. Installing a web cleaning solution can increase the productivity of the converting line, and ensure products are processed to a consistently high quality. Arriving at the right choice of web cleaning system, however, means considering a wide variety of factors before deciding which web cleaning technique is right for you.
uwww.meech.com www.convertermag.co.uk
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