Efficient cooling of components during transport

There are many different types of belts made from different materials, such as PU, PVC, felt, polyester fabric, silicone, rubber, etc. In most cases, conveyor belts are made up of different layers and often have a fabric that serves as a carrier layer.

Most of the above-mentioned belt materials are insulators (e.g. PU, PVC), i.e. they do not conduct any static charges. Nevertheless, many belts are described as "antistatic" by their manufacturers. This refers to the running side of the belt, i.e. the inside that comes into contact with the conveyor belt. In this context, "antistatic" means that the running side of the belt is equipped with electrically conductive threads (usually carbon threads), which prevent the belt from charging itself as it slides over the belt body. Any charges that arise during the sliding process are dissipated directly via the aluminium frame of the conveyor belt.

However, this does not indicate whether, for example, the surface of the conveyor belt, known as the carrying side, also becomes charged over time due to constant exposure to electrostatically charged conveyed goods. This can cause parts to "stick" to the belt during the conveying process.

For special applications, such as the transport of highly sensitive circuit boards in the electrical industry or applications in potentially explosive areas (ATEX), even higher requirements must therefore be met in some cases. MTF Technik offers belt no. 44 for this purpose. According to the manufacturer's data sheet, this belt has a surface resistance of less than 3 ∙ 10⁸ Ω and a tracking resistance of less than 1 x 10⁹ Ω. According to EN 13463-1, it can be assumed that electrostatic charging is prevented if the surface resistance is less than or equal to 1 x 10⁹ Ω.

We can illustrate the difference using an installation tester, for example. Even though electrostatic charges can easily reach tens of thousands of volts, a test with an installation tester and a maximum voltage of 500V already shows clear differences. For example, we measured the surface of MTF belt no. 44 and belt no. 45. Belt no. 44 shows that a test voltage of 116 volts already results in a measurement of 0.04 MΩ. With belt no. 45 (PU surface), no resistance can be measured despite a maximum test voltage of 535V, i.e. this is an insulator. Even though the test setup in this form does not comply with any standard, it nevertheless impressively demonstrates the difference in the conductive behaviour of different belt materials.

The conveyor belts from MTF Technik are generally equipped with standard-compliant earthing. In most cases, this is achieved via the electrical connection cables and/or additional earthing lugs. In special applications, e.g. the transport of plastic parts with a high electrostatic charge, additional earthing can help to dissipate the charges.

To remove unwanted charges from the carrying side of a belt, electrically conductive brushes can be used, for example, which are mounted at the belt inlet. These pick up any charges on the belt and dissipate them so that a "neutral" belt is available in the area where the parts are fed. The belt is thus grounded again with each rotation. Fibres made of carbon or stainless steel, for example, are used for this purpose.

Problems caused by static charges on separated material can also occur in separation drums. Here, there is a risk that the charges will be transferred to the PVC rollers of a roller separation drum during separation.

In addition to using ionisation bars above the separation drum cages (see above), a thin, additionally earthed stainless steel foil can also be placed on the rotating drum cage. This is offered by as an optional clip-on device for the base frame and can also be retrofitted to existing systems. The stainless steel foil then sweeps over the drum cage and dissipates the charges.

The steel hinge plate belts and steel mesh conveyor belts from MTF Technik are perfectly suited for dissipating static charges on components thanks to their electrically conductive properties. The hinge plates are earthed via contact with the belt body and the drive grounding.

However, the costs here are significantly higher than for a belt conveyor, so in practice belt conveyors with the appropriate equipment are more commonly used.