Static conductive belts

There is always a demand for belts and other rubber products to be used in the presence of explosive gases, liquids, powders, dusts, etc., where the possibility of static sparks must be kept to a minimum.

Any material can be electrified to some extent. If the material is a conductor, it may be discharged by connecting any point with the ground. If it is a nonconductor, the charge must be removed at the point where it is generated.

The term “resistivity” applies to the specific resistance of the substance of which the conductor is made. It is numerically equal to the resistance between the opposite faces of a cube of the substance whose edge is one centimetre. The unit of resistivity is the Ohm-Centimetre. The specific resistivity of most rubber compounds is approximately 1015 (10 followed by 14 zeros) ohm-cm. For all practical purposes, it is sufficient to know that the resistivity of rubber is very, very high and that it is a good insulator. It is possible, however, to make a rubber compound having a resistivity of 100 ohm-cm or less. Thus compared to ordinary rubber compounds, these stocks may be classed as conductors. However, when compared to copper, which has a resistivity of 0.0000017 ohm-cm, the very best of conducting rubber compounds, would still be classed as insulators. The ProTorque wrapped belts are produced antistatic according to corresponding ISO standards (ISO 1813 for friction belts and ISO 9563 for Synchronous belts). If special customers insist on tighter static conductive limits than required by ISO, such limits should be carefully noted and emphasized on the order so that these belt orders can be specially processed through the plant. However, merely using a conductive belt does not eliminate the static problem entirely. The entire system must be grounded since, if no ground is provided, the belt or other parts of the system may by charged either by conduction or induction from some outside source. 

Belt and pulley surfaces should be kept free of foreign substances, which are not themselves conductors (dirt, dust, belt dressing, etc.). The pulleys must be made out of a conductive material which rules out most nonmetallic materials unless they are specially designed and treated.  

Drive conditions and service variables in combination with time in operation can result in a loss of static conductivity. It is recommended that a conductivity check be added to drive preventive maintenance programs where belt static conductivity is a requirement.