Screw and plasticating apparatus and method

A screw for a plasticating apparatus, the plasticating apparatus having a heatable barrel with an inner wall and inlet and output ports, the screw comprising:

• a) a helical flight which cooperates with the inner wall of said heated barrel;
• b) a helical valley extending along said flight;
• c) said screw having a metering section for working resinous material at high temperature, the bottom surface of said helical valley in said metering section having a groove relatively deeper than said valley so that there is a depth differential between the bottom of the groove and said bottom surface of said valley, said channel extending in a helical path through said valley bottom surface;
• d) said helical path having a different pitch than the pitch of said helical flight so that the helical flight periodically interrupts said helical path;
• and
• e) a transit channel in said metering section having a reverse helical direction in relation to the helical direction of the helical flight, said transit channel continuously cutting through said helical flight and helical valley at intersections with said transit channel so that portions of molten resinous material in the transit channel can flow through the helical flight and helical valley.

A process of plasticating resinous material in a molten state under pressure comprising:

• a) feeding solid resinous material to a rotating screw in a barrel having a cylindrical inner surface, said screw having a helical flight with said flight cooperating with said inner surface to move said material along a helical path;
• b) applying heat to said barrel and said material while working the material between the barrel and the screw to convert the solid material to a molten state with only a minor amount of unmelted particles;
• c) passing said molten material through a metering section having a helical valley defined by said helical flight, the bottom surface of said helical valley defined by a relatively shallow level and relatively deep level extending in side by side helical paths having a depth differential therebetween, said helical valley and helical flight being periodically interrupted by a transit channel having a reverse helical direction in relation to the helical direction of the helical flight, said transit channel passing through said helical flight and valley;
• d) portion of said molten material in the metering section is continuously and unobstructively advanced by the helical flight toward the outlet port, said advancing portion of molten material mixing by passing between said relatively shallow and deep levels with some of said molten material passing into the transit channel and regressing from the advancing stream thereby being recirculated through the mixing section.