STF Maschinen und Anlagenbau GmbH
STF-Machine & Plant Construction | STF-Thermoforming Sheets  | STF-Recycling    

Sorting plants

Sorting plants made by the STF company have been developed specially for sorting PET bottles.

The use of different modern sorting technologies makes it possible to eliminate foreign materials like e.g. plastic sheets, PVC, wrong colours...


  Material introduction

The bottles which are compressed to bales are brought into the debaler with a forklift after the packaging wire has been removed. The PET bottles are untangled and fall into a discharging screw which transports them evenly to the elevating conveyor. By regulating the rotational speed of the screw, the plant capacity is determined. The elevating conveyor is equipped with a non-magnetic area that has a permanent magnet installed above it. It removes ferromagnetic materials contained in the input. The bottles are then transported to the foil separation stage.

  Foil separation

All parts smaller than 30 mm are separated from the material flow by a star screen. These parts are mainly labels that have already been removed from the bottles as well as caps, sand, stones and metals. A discharging screw transports the separated materials into a container that has to be provided by the customer. A vacuum belt separates foils like loose labels from the material flow. The vacuum is produced by two blowers. The material is then brought to the next stage by an elevating conveyor belt.

  Manual sorting

The sorting belt is mounted on a stage which is designed for 4 manual sorting places.

The built-in detection coil detects metals and stops the belt. So, it is possible for the sorting personnel to remove the metals and restart the belt. Conveyor belt for automatic sorting.

  Automatic sorting

The automatic sorting consists of three sorting stages. The colour fractions which have to be sorted are freely programmable.
The bottles are put onto a pneumatic vibrating chute which guarantees an even allocation of the material to the complete working width. The following acceleration belt increases the speed of the bottles to the speed that is necessary for sorting. Due to the exactly defined speed of the bottles, they move through the sorter on a predetermined trajectory. An optical system recognizes the colours and the bottles are imposed according to the programming with compressed air. Metals are also detected and are blown into a separate funnel.

The fractions that are produced this way are brought onto a further acceleration belt each and are then separated into more colours by colour sorting devices. By doing so, up to four fractions with different colours are produced.

Since the clear fraction is the most important raw material in practice, we recommend to sort only the clear bottles in the first stage and to sort them again in the second stage in order to get a particularly pure clear fraction.

The four fractions are collected in bins lying underneath and can then be transported with a forklift.