Is static standing in the way of quality and productivity in your shop? This discussion will help you identify sources of static electricity as well as the types of systems available to eliminate it from your production process.
By David Rogers
Three main conditions are responsible for causing static electricity: friction, separation, and induction. The friction of two materials rubbed together causes the electrons associated with the surface atoms on each material come into very close proximity with each other. These surface electrons can move from one material to another. The harder the two materials are pressed together, the greater the exchange of electrons and the higher that charge that is generated. The speed of the rubbing action also has that effect on the level of charge—the faster the rubbing, the higher the level of charge. Surface electrons gain heat energy generated by the friction, and this extra energy allows them to break their atomic bonds and transfer to other atoms.
The method of charging by separation is similar to that of friction. When two materials are in contact, the surface electrons are in close proximity to each other and upon separation have a tendency to adhere to one material or the other. The faster the separation of the materials, the higher the charge generated and, conversely, the slower the separation, the lower the charge.
Factors that affect static electricity
Many factors affect the generation and maintenance of a static charge. Among them are humidity, the type of material, repetition, and change in temperature.
Type of material Some materials are more readily charged than others. For example, materials such as acetate gain a charge very readily, while glass gains a charge less readily. Also the relative position of materials on the triboelectric series (Figure 1) will determine whether a material charges positively or negatively dependent on the other material with which it has come into contact. For example, hard rubber, when rubbed against nylon, will become negatively charged but will become positively charged when rubbed against polyethylene.
Humidity Generally speaking, the dryer the environment, the higher the level of static charge and, conversely, the higher the humidity, the lower the static charge. In relative terms, water is a significantly better conductor of electricity than most plastics. Atmospheric humidity deposits small quantities of water on all surfaces in the environment; therefore, surface static charges on materials have a tendency to dissipate to earth by current flow through the surface moisture.
Did you enjoy this article? Click here to subscribe to the magazine.