Conveyor technology - Flat belts, conveyor belts and material chutes

Conveyor design and configuration play an important role in material handling. Physical parameters such as the coefficient of friction between the belt and the transport material as well as the surface structure of the transport material determine the maximum inclination angle. This article explains the relevant physical relationships and presents field-proven optimization measures for long-lasting systems.

Fundamentals of Inclined Conveying

Belt conveyors are mechanical transport systems that continuously transport material over a movable belt surface (see here for more information on the basic structure). Its operation is based on the friction between the conveyed material and the belt that transports the material through the conveying section. For belt conveyors with an incline (i.e. vertical or inclined systems), additional forces such as gravity must be taken into account compared to horizontal conveyors. The adhesive and sliding friction between the conveyed material and the belt determine the maximum possible inclination angle at which safe transport is still guaranteed. In addition, sufficient drive force must be ensured by the motor and, if necessary, the gearbox. Where low friction is desired (e.g. between belt and belt support), the belt should be able to slide over the conveyor as easily as possible. At the same time, sufficient friction must be ensured between the drive roller and the belt so that the drive roller does not slip.

Factors influencing the maximum inclination angle

When determining the maximum inclination angle within a conveyor system, various factors must be considered.

Conveyed Material

The physical properties of the conveyed material have a significant influence on the maximum permissible inclination angle. This includes in particular shape, component size, density and aggregate state.

In principle, the following applies: Round components or elements that roll well, such as bolts or batteries, are more likely to slip back compared to angular or rough material. Viscous or semi-liquid substances are more difficult to convey in a controlled manner than solid material. The deposition angle of the material also influences the flow behavior and thus the inclination limit.

Conveyor Belt Properties

The material and surface finish of the conveyor belt significantly influence friction. Smooth surfaces such as PVC lead to slipping of the conveyed material more quickly with low coefficients of friction. Profiled belts with transverse ribs or dimpled structures usually allow significantly higher inclination angles depending on the conveyed material. A selection aid for the different conveyor belts can be found in our article about specifications and selection of conveyor synchronizing belts. The belt width, stiffness and use of attachments such as drivers influence the conveying behavior and ultimately the possible inclination angle.

Inclined conveyors and vertical conveyors

Inclined and vertical conveyors play a central role in the automated transport of components between processing stations in mass production. Their design differs fundamentally, especially with regard to carrier units, guide elements and drive technology. For inclined conveyors, the design depends mainly on the component weight, the surface properties and the inclination angle. Standard belt conveyors with a slight incline are often sufficient for stable, non-slip parts. However, as the incline increases or the conveyed material rolls or slides slightly (e.g., cylindrical turned parts, battery modules, housing parts), dimpled belts or other suited conveyor belts are required.

Vertical conveyors (e.g. steep conveyor belts with pockets or carriers) are used when components must be transported across several levels in a space-saving manner. Significantly higher tensile forces affect the belt and support structure, which is why robust frame structures and precise drive technology are necessary. Alternatively, chain-driven lifting systems or vertical conveyors with grippers, pallets or carrier devices are used to convey sensitive components in a position-accurate and synchronized manner.

As with chain-operated systems, where chain tension is important, belt tension in belt conveyors must be accurately calculated and the conveyance speed must be adjusted for safe start-up and stopping, as well as continuous conveyance.

Material chutes

In particular, in addition to belt conveyors, material chutes and baffle plates are used for short conveyor routes or in gravity-based systems (similar solutions with roller conveyors can be found here). Conveyor chutes and baffle plates use gravity to move material, with a small coefficient of friction between the sliding surface and the conveyed material playing an important role. Particularly with wet or sticky material, precise coordination with the conveyed material is necessary. Material chutes are often made of stainless steel, plastic or coated steel sheets.

Additional influencing factors

In addition to the physical parameters, a few other factors must be considered in practice.

Influence of moisture and contamination

Contamination from dust, slurries, oils or moisture changes the friction conditions considerably. A water film can cause a material that actually adheres well to suddenly slip or cause goods with smooth surfaces to virtually stick to the conveyor belt. This also applies to the belt surface itself, because worn or contaminated belts show altered friction values. It is therefore important to regularly maintain and clean conveyor systems and, in particular, belts.

Lateral slope and belt centering

On inclined conveyors, uneven loading, material accumulations or cross-gradients can lead to a lateral inclination of the belt and thus to the skewed operation of the conveyor belt. Faulty belt centering will not only cause wear, but can in extreme cases cause damage to support rollers, side guides or even cause the system to shut down. Modern systems rely on automatic belt centering rollers, sensor technology with feedback loops for control and active steering of the belt guide via pneumatic or hydraulic actuators. However, in general, it is necessary to try to prevent lateral inclination during installation or assembly. For this purpose, the conveyor belt supports or adjustable legs are usually equipped with leveling feet or articulated feet. When these levelling feet and adjustment elements are correctly set, they can compensate for uneven surfaces of the floor to prevent lateral inclination.

Practical examples

Inclined conveyors are primarily used in modern production systems when parts and components must be automatically moved between production steps. Typical applications include battery production for electric vehicles, where sensitive cell modules or housing parts are conveyed safely and by synchronized processes. Mass production with workpiece carriers or assembly lines for mechanical and electronic assemblies likewise make use of precisely designed inclined conveyors to ensure trouble-free material flow. Precision engineering employs perfectly calibrated inclined conveyors. Further industry examples can be found here.