Static control for the converting industry
The converting industry is driven by many processes where static electricity is a major problem. These include slitting, sheeting, coating, die cutting and many other areas. The problems can be product misbehaviour, dust attraction, shocks to operators or even fires.
To attempt to control static during the converting process a basic understanding of electrostatic fields is required. If an electrostatic charge is present on a material then the field generated by this charge will automatically seek out an opposing charge in order to restore balance. In the case of converting, if a grounded roller is present or a grounded part of any machine is present, the electrostatic field will automatically attract the non-conductor. When this occurs what commonly follows is a web wrapping itself around conductive rollers, misfeeding or jamming the process. Ironically it is the same electrostatic field principle that enables static eliminators to effectively treat the static problem.
Typical Static Control Equipment for Converting Applications
Due to the speed of converting processes and the volume of the charges that build on the surface of the material being converted it is common to see a powered ionising bar instead of a passive static eliminator on a converting machine. Powered static eliminators come in many forms ranging from AC to DC with outputs varying to allow different proximity to the charge being neutralised. Having the correct static control bar in relation to the proximity of the material being neutralised is very important, this is partly due to the nature of converting processes which don't always allow for convenient close range static control bar mounting.
Fraser 1250 AC Static Eliminator Fraser 3024 DC Static Eliminator
The issues with AC Static Eliminators on high speed converting equipment.
While alternating current ionising bars provide an excellent and viable static control solution in most instances, in high speed converting applications they have a tendency to be "over run". AC ionisers have a single row of emitters as seen above and these will change polarity in a cycle of once every 1/120 of a second and generate both positive and negative ions. If the speed of the web traveling past the ioniser exceeds 300 meters per minute a condition will arise in which certain sections of the web will not be neutralised, this is commonly referred to as "striping". This can be overcome by placing multiple AC ionisers on either side of the web or simply by utilizing a DC anti-static bar.
The Coupling Effect or how a static charge can be masked.
It is important to appreciate that a charged material must be located in "free space" in order for a static neutraliser to do its job. If the non-conductive, charged material is placed against any surface, the electrostatic field is collapsed and, hence, the material appears neutral. For example, as a web of charged material passes over a grounded roller, the electrostatic field will look as follows:
The electrostatic charge has not been removed or neutralised and is merely being masked by the roller.
Fraser has become the static control supplier of choice for many of the world`s leading converters and converting machinery manufacturers because it offers modern cost-effective solutions to these problems.
For specific advice, or to discuss general applications in the converting industry call our team of engineers today.