To optimize the plasticizing of a specific polymer (or a small group of polymers) it is possible to develop a 3-zone screw by redesign the compression ratio, the length of the three zones, radius on both side of the flight and other construction details.
Plasticizing screws with a too low compression ratio creates the risk of unmelted particles in the product. If the compression ratio is too high it can trigger the degradation processes in the compression zone and generate blacks spots, worse mechanical properties and other defects which result in more scrap.
Standard screws, which are supplied with the press, or as spare parts, are often screws with an average compression ratio capable of plasticizing all polymers, but in practice they are unsuitable for the job they have to do.
If you do not want to buy a 3 phase MAXI MELT screw we can offer you alternative the option to develop a profile dedicated to your plasticizing of a specific type of polymer or to a group of polymers with similar characteristics. The screw profile redesign will review following aspects:
- The lengths of the three zones(feeding, compression and metering)
- The height of the flight in the feeding zone and metering
- The radius on both sides of the flight.
- The flight pitch.
- The flight width
- Material selection
- Surface treatment
A redesigned screw has a better and efficient plasticizing of a polymer or group of polymers for which it is designed for and therefore is not a universal screw!
For example, a screw with a high compression ratio can solve the problem of unmelts with semi-crystalline polymers but is not suitable for plasticizing an amorphous material as it easily causes overheating and therefore streaks, deposit of the screw and molded parts.
On the contrary, a low compression ratio screw is suitable for the plasticizing of amorphous polymers or sensitive to overheating, but is not suitable for the plasticizing of semi-crystalline. In those cases we often observe poor mixing, poor mechanical properties, and difficulties to keep the product tolerances under control.
The company MAXI MELT has a long experience in developing optimized geometries to increase the efficiency of your production.