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

Cutting plants

The cutting plants made by the STF company have been specially developed for pulverizing / fine grinding of plastics in the recycling industry. The main application area is the cutting of PET bottles. Due to the sturdy construction of our components, we can guarantee a maximum of plant availability to our customers. The high cleaning effect together with low effort provides the highest value creation.

  The process

The debaler uses a lengthwise running screw with ripping blades. The bales are broken during transport to the material exit. The material is circulated until it is ideally separated. At the same time, the ripping blades remove most of the labels from the bottles. The throughput is controlled by a pneumatic gate at the exit opening.

The material is transported by standardized conveyor belts which are equipped with different systems for metal detection and separation. Depending on the application area, these can be overbelt magnets, magnetic drums or metal detection coils that are mounted below the belt.

The cutting mill is a wet-shredding and cutting mill. With the help of adding an abundant amount of water, the friction produced by the cutting process can be used for intensive cleaning. At the same time, the wet-shredding process prevents the sieves from sticking down and protects the material from thermal impacts as well as from new contamination by dirt that has been squeezed into the cutting edges.

The material is dried in a friction cleaner (centrifuge). Water and removed dirt are removed from the material. The housing of the friction cleaner is a stable all steel welding construction that contains the rotor shaft with the fixed stainless steel rotor blades. Bearing is made by ball-joint bearings which are outside of the housing. So, dirt is prevented from getting into the bearings and bearing grease cannot get into the centrifuge. The shaft is sealed by stuffing boxes. The friction cleaner is equipped with a hand wheel that can be used for comfortably opening the cover for changing sieves and cleaning. A big container is integrated into the base frame which is very useful for the excellent separation performance. The friction cleaner is also equipped with a platform that provides an optimal access for maintenance work. Our friction cleaners are galvanized in order to protect them from corrosion.

The vertical air-stream separator is the main part of the air-stream separation stage. A cyclone with rotary valve guarantees for a pressure-free material introduction into the air-stream separator. A suction blower produces low pressure which removes lightweight particles like dust and pieces of foil from the grained mill material. A continuous mixing is achieved by the zig zag form. The cleaned material is transported by a blower.

The filling station consists of a construction that has been designed to hold two big bags. Above it, a storage silo is mounted that contains a discharging screw for each big bag. The material is introduced via a cyclone. The silo and the filling funnels for the big bags contain sensors which control the filling level. The filling station has an additional pneumatic vibration unit. 

  Material introduction

After the packaging wire has been removed, a forklift puts the bottles that have been compressed to bales or briquettes into the debaler. Inside, the bottles are detangled and fall into a dosig screw which transports them evenly and continuously to the elevating belt. The plant capacity is determined by adjusting the screw speed. The elevating belt transports the bottles to the sorting stage. It is equipped with a magnetic drum that removes ferromagnetic materials from the input.

  Manual sorting

The sorting belt is mounted on a stage construction and is designed for 4 manual sorting places. Below the stage sorting bunkers are mounted that make it possible to mount big containers under the chutes. The detection coil built into the belt recognizes metals and stops the belt. The sorting staff then has the possibility to remove the metals and to restart the belt. Afterwards, the material directly gets into the mill.

  Cutting and pre-cleaning

The cutting mill is essentially a wet-shredding and cutting mill. With the help of adding an abundant amount of water, the shredding process in this stage provides a combination of cutting and cleaning effects. During shredding, around 95% of the paper labels are resolved and dissolved in the water. The cut material then gets into a friction cleaner where the dissolved paper and other dirt is removed and pumped to the fibre separator of the corresponding circulatory container. The material then is blown to the next air stream separator.

  Air stream separation

The vertical air stream separator removes particles like labels, paper, dust and other suspended solids from the grained PET and PO flakes. The material gets into the air stream separator via cyclone with rotary valve. The flakes sink to the bottom and are then blown to the cyclone of the separation stage.
The contained fine particles are vacuumed off the top and are blown to the labels filling station. The selectivity can be adjusted over the label blower.

  PET filling station

This station continuously fills the PET flakes into the big bags. A full bag is detected automatically and the filling process is switched to the second bag. Now the full one can be replaced. The pneumatic shaking unit achieves an ideal compacting of the material, which reduces shipping costs considerably.
The labels filling station is identical to the PET filling station.