Static Electricity in Conveyor Belts
Static electricity is defined as electrical charge at rest. It can be caused by the triboelectric effect and can be accumulated by inductive and conductive charging.
A static spark discharge can be dangerous in gaseous or dusty atmospheres as it can cause ignition, in grocery stores as customers and employees can be shocked regularly, and in electronic manufacturing settings. When two surfaces in close proximity are moved relative to one another, a static charge is generated (the triboelectric effect).
- A person walking across a carpet can generate more than 30,000 electrostatic volts at a relative humidity in the 10 – 20% range. The same person walking across the same carpet would exhibit less than 2,000 electrostatic volts if the relative humidity were 70% or more. This is due to the high bleed-off static charges by the humid air.
- When slitting conveyor belting that passes over a flat surface and through pinch rollers, a static electric charge can be generated, especially when humidity is low, causing the hair on the operator’s arm(s) to rise or cause the operator to feel a “zap” or jolt of electrical current.
On belt conveyors, the belt surface is continually leaving the pulley surface, generating static electricity. As the conveyor continues to operate, the static charge will continue to accumulate and increase unless it is bled off (or discharged) in some manner.
Static charge during installation
In a conveyor belt installation, we cannot control static by eliminating generations. However, the accumulation and storage of static electricity can be controlled.
Accumulation and storage of static charges can be controlled by making the entire system sufficiently conductive and contiguously and properly grounded. This means that the belt, pulley lagging, pulley, bearings, conveyor structure, and electrical ground must all be connected electrically.
Specific to the conveyor belt and in order to be sufficiently static conductive, the surface resistivity must be 300 meg-ohms or less. This is the ISO and OSHA standard.
What is 300 meg-ohms? 3 x 108 ohms … or 300 x 106ohms … 300,000,000 ohms.
One of the best ways to “ground” a conveyor system is to literally discharge the static charge through the framework of the conveyor… through the floor… into the ground/earth. If a conveyor system is not sufficiently grounded, a static conductive belt will not, alone, control the electrical charge.
What conveyor belts can be used to reduce static electricity?
Some Sparks products that meet or exceed the ISO and OSHA standards for static conductivity include:
- Wear Flex NSF 15 A/S @ 10,000,000 ohms
- Mono Flex LBU 210 @ 280,000,000 ohms
- Mono Flex WU 110 A/S, WU 210 A/S, BP 290
- BU 200 I @ 300,000,000 ohms
In manufacturing conveyor belting, static conductivity can be added to the textile, polymer, or both.
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A Sparks representative can help you determine the best conveyor belt to reduce static electricity in your application.Speak With Us Today