Among the different parts of a pelletizer (granulation chamber, pumps, nozzles for water, blades and blades-holder, centrifuge, steam-suction fan etc.), the die plate is the most important one. Considering the pelletizer as a human body, you could say that the die plate is both the “heart” and the “brain” of the system.
Filtec take special care in each and every part, nonetheless the study and the actual production of the die plates are object of even greater care.
Due to our company policy, we would not like to have a big number of “standard” die plates in stock. We want to study and develop them in accordance to the actual information provided by the customers and to the rheological features of the plastic materials. Our die plates have different features of:
- diameter of the holes
- depth of the hole (L/D ratio, i.e. Length of the straight hole compare to the Diameter)
- number of holes
This approach is needed because the molten plastic material coming out from the die plate must have the correct speed to form the strands that will be immediately cut by the blades. In case of too low speed, the molten plastic material will not be cut by the blades: it will smear inside the granulation chamber. In the same time, the machine must not be too fast in order to avoid both dangerous pressure surge and insufficient blades speed. The aim is to have pellets in form of small cylinders.
The L/D ratio is needed to give a direction to the molten plastic material and shape it before to be cut by the blades. Materials with low MFI may need the L/D at 3 or 4, while the materials with high MFI may need L/D up to 16 or 20.
The number of holes in the Filtec die plates depends on the hourly throughput. While the diameter of the holes and their L/D depend on the features of the plastic material, first of all the MFI.
The diameter of the holes depends on how the plastic material “holds” the heating and how the cooling water can dissipate it. For instance, the PP holds much heat and its pellets must not be big, otherwise it would need a long cooling time in water.
By studying and developing the die plates as above explained, our company is in condition to arrange highly customized technical proposals in the different pelletizing situations. The target is produce pellets with even shape and with no faults.