Selecting Injection Molding Screws
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is usually between 2 and 3 for plastics such as PP and PE. The length of the transition zone is typically 4 to 7 x the screw diameter in a general purpose screw.
Another aspect of screw design is the length to diameter ratio (L/D) meaning how long it is compared to its diameter. As an example, the L/D ratio for PP and PE is in the range 20-30:1.
When it comes to general purpose screws, longer screws are usually preferred because they will produce a better quality melt and therefore produce better quality parts
The disadvantage is that, for some materials, part quality and productivity rates will be lower compared to more advanced injection molding screw designs such as the barrier screw.
The exact design chosen must be in line with the application.
Another aspect of screw design is the length to diameter ratio (L/D) meaning how long it is compared to its diameter. As an example, the L/D ratio for PP and PE is in the range 20-30:1.
When it comes to general purpose screws, longer screws are usually preferred because they will produce a better quality melt and therefore produce better quality parts
General Purpose Screws (GPS)
The advantage of a GPS is that they can be used with most plastic materials such as PP, PE, Nylon, PET and PC so they are very flexible and good for moulding companies that mould a variety of different materials. The disadvantage is that, for some materials, part quality and productivity rates will be lower compared to more advanced injection molding screw designs such as the barrier screw.
Barrier Screws
This type of screw provides a better quality melt at a faster rate compared with a GPS. There are many different designs of barrier screws, the difference being in the varying of the flight depths and channel widths. The exact design chosen must be in line with the application.
Double Flight Screws
Although double flight
