Let’s keep it clean

With finance scarce and an uncertain economic outlook, converters are showing a keen interest in technologies that increase the productivity of existing converting lines. By reducing waste and cutting downtime, web cleaning systems fit this category perfectly. Dirt, debris and paper dust are an inevitable by-product of high speed webs, whose movement creates a boundary layer of air that holds contamination firmly on the surface of the substrate.

Web cleaning solutions break down the boundary layer and loosen and remove debris, delivering cost savings and productivity improvements in the process.

Meech has a customer who increased monthly sales by around £8,000 after investing in web cleaning on a 1,200mm width gravure web. The system reduced line stoppages from web breaks and poor quality output by almost 70%, and paid for itself in less than nine months.

Contact or non-contact?

Converters are able to choose from a variety of contact and non-contact web cleaning technologies – these are described below – but whichever technology is adopted should combine a method of breaking down the boundary layer and neutralising any static charges that are attracting particles to the web.

The choice between contact and non-contact cleaning is typically determined by the materials being run, the application, the level of ongoing flexibility required, and the available budget for the investment.

Broadly speaking, contact web cleaners employ either vacuum systems, adhesive rollers or brushes. In a vacuum system, a low-friction component of the cleaning manifold is in contact with the web, breaking down the boundary layer and releasing contaminants to be vacuumed from the surface.

These systems commonly incorporate active AC static control bars. For example, on Meech’s Tornado contact cleaner two highly polished stainless steel faceplates create turbulence to break down the boundary layer; the system also incorporates twin ionising anti-static bars to neutralise static charges on the web on entry and exit.

Adhesive roller systems such as the Meech TakClean use an elastomer roller, driven by contact with the web, to remove debris. The elastomer roller is in contact with a second adhesive roller which, in turn, takes up and traps the contaminants, preventing recontamination.

TakClean systems also incorporate active AC ionising bars to neutralise the web on exit from the system, again preventing recontamination. Excellent cleaning levels can be achieved, but these systems are not really suitable for webs with very high levels of contamination, as the consumable adhesive roll can quickly become contaminated.

Brush systems ‘scrub’ the web and are the least popular because, even if the substrate is not prone to marking, the process appears harsh.

There are three main technology options when it comes to non-contact web cleaning: ultrasonic, blow-and-vacuum, and boundary layer.

Ultrasonic systems act by blasting the web with ultrasonic pulses from either side of a vacuum slot, and usually employ static eliminator bars on the infeed. They are effective, but are also the most expensive solution.

Blow-and-vacuum systems use a combination of blowing and vacuum airflows to strip contamination from the substrate. These systems are efficient and typically quite compact. They require some initial set-up time to balance the blow and vacuum airflows, and then provide a good level of cleaning.

Boundary layer systems are the latest innovation. They create a powerful layer of air that breaks the boundary layer, which is then ‘sheared’ into a vacuum chamber.

These systems have low running costs and no consumable costs. As an example, Meech’s ShearClean system incorporates two cotton-covered rollers, positioned 0.5 to 1.0mm on either side of the web. The rollers spin at high speed – 4,000 rev/min and upwards – in the opposite direction to the travel of the web. This generates a high speed boundary layer of air, the greater energy of which destroys the boundary layer associated with the incoming web, exposing even the smallest particles resting on it to the powerful cleaning force.

Ionising bars ensure both neutralisation of static charges on the web and easy breakdown of the bonds holding contaminants to the web surface. The risk of re-attraction of contaminants to the cleaned web surfaces is also minimised.