Explosion hazard zones
Moving appliances can become electrostatically charged due to friction on slipping or by micro-friction when rolling forward. These electrostatic charges can be dangerous to electronic components and give a spark upon a sudden discharge.
Appliances which are fitted with plastic or rubber wheels are isolated electrically from the ground because plastics and rubbers are, by nature, good electric isolators.
In fields of application where electrostatic charging should be avoided, some solutions are already available. These solutions include the mounting of earth straps or wheels that allow the electrostatic charge to dissipate, in any case, to the ground, thus eliminating any voltage difference.
Antistatic ⇔ electrically conductive
Depending on the application, antistatic or electrically conductive wheels are chosen. A wheel or roller is, according to the wheel-roller standards (EN 12530 – EN12533) electrically conductive, if the ohmic resistance is less than 104 Ω. A wheel or roller is antistatic if the volume resistance is less than 107 Ω. The measurement must be taken under controlled conditions, as stipulated in the aforesaid standard.
The high standards that workplaces in the electronics industry have to meet and the requirements, via the ATEX-guideline, for zones with an explosion hazard have led to the development of electrically conductive polyurethane, to meet the standards EN12527 thru’ EN12533.
The electrically conductive properties of wheels can be improved in two ways:
- by using additives, the surface of the polyurethane is made hydrophilic, causing water molecules to adhere to the surface. Water is a good electrical conductor, thus allowing electrostatic charges to dissipate via this thin water film. Obviously, climatological conditions and the state of the wheel surface will greatly influence the electrical conductivity.
- a second way consists in creating an electroconductive path in the elastomer to channel away the electrostatic charges.
This is achieved by adding electroconductive fillers to the elastomer. At just the right concentration the ‘percolation point’ is obtained. This is the point at which sufficient electric micro-paths are formed in the matrix so that an electric current can flow. The type of filler, the general condition of the wheel, the applied load, etc. will largely determine the electrical properties of the wheel. A widely used filler is soot. Besides inferior mechanical properties, wheels with such formulations are also no longer ‘non-marking’.
Electrically conductive Vulkollan®
After research and rigorous testing, Vulkoprin has succeeded in optimizing the properties of its electrically conductive polyurethane Printhane-C™.
The key characteristics of Printhane-C™ are:
- NDI-based polyurethane => high load capacities + a good abrasion resistance
- 92 – 94 Shore A
- electrically conductive, according to standard EN 12527-12533
- a low rolling resistance
- the new formulation allows us to make wheels in smaller sizes.
Contact us for more information!