Understanding static electricity
Static electricity is a surface phenomenon, that is generated when two or several surfaces come into contact and are then separated. There is then a kind of unfolding, during which negative electrons are transmitted from one atom to the other. The power of the charge depends on several factors: the material, its physical and electric properties, the temperature, the moisture of the air, the force and velocity of separation. The higher the force or speed, the more significant the charge will be.
These electric charges are electrons, positive ions, or negative ions. Whether the material allows for the mobility of charges or not, will determine whether it is a conductor or insulator. For solid materials, the atoms are bonded to each other. In the case of insulating materials, the electrons are strongly bonded to the atoms. They are stuck where they are and cannot move. Such plastics as PVC (polyvinyl chloride), polyethylene, or Teflon are insulating materials.
In the case of conducting materials, the electrons circulate freely. Nevertheless, this cloud of free electrons remains “bonded” to the positive ions which themselves are bonded to the atoms of the matter. Therefore, they cannot disperse anywhere. Under the impulse of external electric forces, the electrons can move. This medium is thus conductive, because the negative and positive charges can be easily separated. Solid materials that are typically conducting are metals like iron, copper, etc.
Static electricity in the industrial production process
In the various processes of production, the static charge represents an important factor of disturbances. Indeed, in some contexts, production involves the use of several materials in close contact or in contact with production machines. In addition, surrounding dust is attracted by static charges. In such contexts there is a considerable risk of explosion or fire, which can be caused by a simple spark produced by a static discharge. What are the principal factors of accidents of an electrostatic nature?
- The transfer of liquid from tankers (for example, the transfer from one tank to another).
- The cleaning of cisterns
- Disruptive phenomena as a result of electrically charged personnel
- The use of certain solvents on installations comprising of metal parts
Such accidents can cause death or inflict serious wounds, burns particularly. Material damage is also often significant. To improve employee safety, various regulations as well as preventative measures were put into place.
For example, the TR 22/49 circular of November 15, 1949 specifically treats the precautions that are to be taken into account for the prevention of the dangers of static electricity. The general measures of protection of goods and persons are rather complete. They recommend the integration of safety right from the conception of an installation. In the case of an already operating installation, the concern of safety must be permanent and must match the evolution of the equipment.
Solutions to measure and control static electricity
Controlling static electricity has become an important challenge for the optimization of the manufacturing process, and the limitation of risks. There are solutions that also allow for the neutralization of static, which utilize static electricity to facilitate the manufacturing process.
In order to improve manufacturing processes that are riddled with problems due to static electricity, it is necessary to be able to measure them. Electrostatic field measuring devices enable this: these devices are portable, compact, and are able to measure and record the value of the electrostatic field.
The neutralization of static charges in non-conductive materials is obtained with the help of active ionization. In regards to high voltage transmitters of devices equipped with this technology; air molecules are separated into negative and positive ions. The static charge then attracts the ions of opposed polarity, which re-establishes the material’s neutrality. A vast range of equipment uses this technology:
The anti-static bar: This equipment creates an electric field which transforms the air molecules around the bar into positive and negative ions thanks to the high-voltage contained in emitter tips. All charged materials in the vicinity attract opposing ions, until they are electrically neutralized. The risk of attraction of dust, fire or the exposure of personnel to electric shocks is thus removed.
Ionizing air blower: Plastic material, that has been statically charged, attracts dust. These particles adhere to the surface and form a grey film that is very difficult to remove. In the case of products that have various forms, neutralization must be done remotely. In this context, ionizing air blowers are recommended. The ionizing tips ionize the air, so that the ions are projected onto the statically charged product, and thus the static charge is neutralized.
Ionized air gun: Ionizing guns neutralize the electrostatic charges of various materials and clean the surface with ionized compressed air. The neutralization of static charges simplifies cleaning the surface and removes the attraction of dust to the cleaned material. The guns are plugged into high voltage outlets. By using the compressed air that they ionize, ionized air guns also allow for the neutralization of the electrostatic charges and for the removal of dust from surfaces.
Ionized air nozzle: Ionized air nozzles diffuse the flow of powerful ionized air intended to clean and neutralize a surface at the same time. The nozzles are supplied with compressed air and generate an air blast strongly concentrated for special applications. Ionized air nozzles adapt to many configurations.
Principal applications of anti-static solutions
The plastic industry sector is a large consumer of solutions for the neutralization or controlling of static electricity. On extrusion lines for example, an ionizing blower installed above the sheet directs the ionization towards this sheet. The electrostatic charges are eliminated which prevents the surrounding dust from sticking to it. Thus the materials remain clean, and the employees do not receive more electric shocks.
The packing industry is also particularly concerned with anti-static treatments, on a machine for labelling plastic bottles. The static electricity present on the bottles to be labeled can generate a bad placement of the labels on the support. Well positioned anti-static bars can eliminate static charges and allow for better productivity.
Even the printing industry shares this concern. For example, in the case of printing machines, the stack of paper at the entrance of the machine can cause an electrostatic charge, thus making the paper stick. The consequence of this is the paper not properly entering the machine. Therefore, it is possible to limit the amount of times the machine is stopped with the help of anti-static solutions.
In conclusion, measuring and controlling static electricity within the framework of industrial manufacturing processes is a major concern. For the safety of the goods and personnel, and for the improvement of quality and output. The implementation of any anti-static solutions requires that the professionals in the field be addressed.
Questions with Joel RACK (PRONIX)
What advice can be given to professionals who wish to solve their electrostatic charge problems during production?
The choice and the positioning of the ionizers are important in order to ensure an optimal resolution of the observed electrostatic problems. Therefore, they will have to be installed on your machine at the place where the static electricity generates disturbances. Maintenance and regular control of the anti-static equipment will prolong their effectiveness on the long term.