Plasticating apparatus and screw therefor

A plasticating apparatus comprising:

• a barrel having inlet means for the introduction of resinous material into the barrel and outlet means for enabling discharge of plasticated molten extrudate;
• and
• screw means, rotatably mounted within said barrel and having a length extending between said inlet means and said outlet means for receiving the resinous material, plasticating the resinous material and discharging plasticated resinous material through the outlet means as a plasticated molten extrudate, said screw means having an infeed section with a helical flight with an outside diameter sized for rotatably engaging an inside surface of said barrel and a helical valley disposed between flight lands of said helical flight, said screw means comprising a metering section and a transition section, between said infeed section and said metering section, said transition section having a helical flight with helical valleys disposed between flight lands of the transition section helical flight, each valley having a rear root diameter and a corresponding forward root diameter, each rear root diameter being closer to said inlet means than the corresponding forward root diameter and each rear root diameter being greater than the corresponding forward root diameter proximate the inlet means, the forward root diameters linearly increasing in diameter between the infeed section and the metering section, said screw means comprising a pitch length greater than about 1.1 times the outside diameter throughout the infeed transition and metering sections, the pitch length being constant.

A screw for plasticating of resinous material, said screw comprising:

• a shank;
• a feed section having a helical flight with a helical valley disposed between flight lands of the feed section helical flight, said feed section having a pitch length greater than about 1.1 times the diameter of the feed section;
• a metering section;
• and
• a transition section disposed between the feed section and the metering section, said transition section having a helical flight with helical valleys disposed between flight lands of the transition section helical flight, each transition section helcial valley having a rear root diameter and a corresponding forward root diameter, each rear root diameter being closer to said feed section than the corresponding forward root diameter and each rear root diameter being greater than the corresponding forward root diameter proximate the feed section, the forward root diameters linearly increasing in diameter between the feed section and the metering section, said screw means comprising a pitch length greater than about 1.1 times the outside diameter throughout the feed, metering and transition sections, said pitch length being constant.