Static occurs throughout the year, of course, and is a perfectly natural phenomenon that happens when two or more surfaces come into close contact with each other and are then separated. We’ve all experienced that little shock from the door handle; it’s mildly irritating, but that’s all. In the converting environment, however, static can cause serious problems and, in extreme circumstances, endanger life.
Converting, with its fast moving webs of materials, is a perfect breeding ground for static. It’s unlikely to rear its head at the start of a process, but subsequent operations provide ample opportunity for static generation.
An automatic bag-making line might involve the high-speed merging of twin webs; in this case, uncontrolled static can make it almost impossible to align the two webs. A possible remedy – using wider webs than necessary – might solve the problem, but only at the cost of increased wastage.
On a rewinding unit, static can have such an impact on the tension of the web that it comes into contact with another surface and becomes contaminated with dirt – a production nightmare if your customer is a pharmaceutical manufacturer. The variations in tension can be so extreme that in some cases the core of the web has been crushed.
Lastly, using a corona discharge unit to increase the receptivity of plastic substrates to ink can create static as an unwelcome by-product, causing problems with ink transfer further downstream. To these production problems we should add the very real health and safety issues that uncontrolled static gives rise to, including the possibility of fire or explosions when solvents are involved. Meech consultants have also come across situations where operators have such high levels of static in their bodies that simply by cleaning equipment they have caused solvents to ignite.
There are measures you can take to reduce the chances of static build-up, such as storing materials in the right environment. For paper, for example, the ideal conditions are 52 percent relative humidity and a temperature of 21oC; at a relative humidity of less than 35 percent, the conductivity of absorbent materials falls considerably and static increases.
However, not everyone has the luxury of a climate-controlled warehouse, so if prevention of static is difficult, what’s the cure? Fortunately, the solution is usually straightforward, and involves fitting an ionising bar to neutralise static in the materials. This simple remedy can increase productivity by up to 12 percent per day through faster line speeds, improved quality and reduced maintenance.
Even higher productivity is possible using the latest developments in static control. Take Meech’s new 977CM Pulsed DC controller, for example, which helps overcome the problem of ionising bars becoming contaminated during use and needing cleaning to maintain efficiency. Depending on the application, cleaning might be necessary once a week.
Not only is the 977CM the first closed-loop pulsed DC static control system, it also incorporates features that make it easier to sustain optimum performance and extend cleaning intervals. The 977CM continuously monitors output from the ionising bars and will automatically adjust the input voltage to compensate for the adverse effects of contamination. When this reaches a preset level (typically +25 percent), further deterioration in bar performance alerts the operator to the need to clean the bars via local audible and visible warnings and remote alarm signals.
The fully-automated closed-loop feedback system incorporates a sensor bar that detects residual voltages on web paths and rewinds and instructs the 977CM unit to tune its output to ensure the best possible charge neutralisation for the current operating conditions. The closed loop facility means that current information about residual electrostatic charge in the material is always available on the clear LCD display, and can be transmitted to allow remote monitoring and logging for quality assurance purposes.
The 977CM can be set to provide accurate neutralisation of static charge regardless of any changes to the material being handled, running speeds or ambient humidity, which is vital for improving throughput in any subsequent processes. The system is straightforward to install and can be quickly connected to existing Meech Pulsed DC static elimination systems. Other features include an easy-to-use keypad on the front of the unit which enables the 977CM to be set up to maintain the optimum output of the ionising equipment, and a lock facility that prevents unauthorised or accidental alteration of the desired settings.
For evidence of the benefits of fitting a static control system, take Buckinghamshire-based adhesive tape manufacturer Technibond. Technibond specialises in technical adhesive tapes; in particular, in double-sided bonding tapes of a bespoke laminated construction. To counter the excessive static that was destroying the interleaving silicone layer in the tape, the company was forced to run its slitters and rewinders at reduced speeds.
In Technibond’s case a sensor bar and feedback controller used in conjunction with a Meech 977v3 Pulsed DC controller and 976 ionising bar. The feedback controller registers the residual static charge on the target material via the sensor and the ionising bar, and automatically optimises the removal of the charge. The operator can check the achieved static control level at any time via an illuminated display, and the equipment can also be connected to a remote alarm system or to data logging and records management systems.
MEECH STATIC ELIMINATORS:
T: +44 (0) 1993 706700