PLASTICATING APPARATUS SCREW HAVING GROOVES OF VARYING ANGLES AND DEPTHS

1 . A screw for a plasticating apparatus, the screw comprising:

a longitudinal axis, the screw being rotatably supportable in a barrel for rotation about the longitudinal axis, the screw having a core and at least one helical flight extending along a length of the screw, the helical flight having a radially outermost flight surface, the helical flight extending in a first threaded direction and defining a first helical path of a first helix angle measured relative to a reference line perpendicular to the longitudinal axis, the first helix angle being less than ninety degrees; the helical flight defining a helical channel; and

a longitudinal portion of the screw having a plurality of advancing grooves with each advancing groove having at least one closed-end, the advancing grooves being arranged in a noncontinuous helix cut in the screw core in the helical channel of the screw, each of the plurality of advancing grooves forming a second helical path in the helical channel and being arranged entirely between adjacent helical flights and extending substantially parallel to the helical flights, and the plurality of advancing grooves being dimensioned to receive material therein as the material is conveyed forward through the helical channel;

the longitudinal portion further having at least one undercut surface located radially inwardly from the radially outermost flight surface, wherein the undercut surface has a depth that varies at least one of:

in a longitudinal direction parallel to the plurality of advancing grooves; and

in a direction traverse to the longitudinal direction.

2 . The screw of claim 1 , wherein the at least one undercut surface includes one or more first undercut surfaces adjacent to the helical flight.

3 . The screw of claim 2 , wherein:

the at least one undercut surface further includes a second undercut surface located on an opposite side of a first advancing groove, among the advancing grooves, from one of the first undercut surfaces, and

the one of the first undercut surfaces has a first depth.

4 . The screw of claim 3 , wherein:

the second undercut surface has a second depth that is less than the first depth, and

the second undercut surface is located radially inwardly from the radially outermost flight surface.

5 . The screw of claim 4 , wherein the at least one undercut surface further includes a third undercut surface located on an opposite side of a second advancing groove, among the advancing grooves, from the second undercut surface.

6 . The screw of claim 5 , wherein:

the third undercut surface has a third depth that is greater than the second depth, and

the third undercut surface is located radially inwardly from the radially outermost flight surface.

7 . The screw of claim 6 , wherein the third undercut surface is located on an opposite side of a third advancing groove, among the advancing grooves, from another one of the first undercut surfaces.

8 . The screw of claim 1 , wherein:

the at least one undercut surface includes a first portion having a first depth, and

the first depth is substantially constant along the longitudinal direction.

9 . The screw of claim 8 , wherein:

the at least one undercut surface further includes a second portion adjacent to the first portion,

the second portion has an increasing depth taper along the longitudinal direction, and

a portion of the increasing depth taper has a second depth that is greater than the first depth.

10 . The screw of claim 9 , wherein:

the at least one undercut surface further includes a third portion adjacent to the second portion,

the third portion has a third depth, and

the third depth is substantially constant along the longitudinal direction and is greater than the second depth.

11 . The screw of claim 10 , wherein:

the at least one undercut surface further includes a fourth portion adjacent to the third portion,

the fourth portion has a decreasing depth taper along the longitudinal direction, and

a portion of the decreasing depth taper has a fourth depth that is less than the third depth.

12 . The screw of claim 11 , wherein:

the at least one undercut surface further includes a fifth portion adjacent to the fourth portion, and

the fifth portion has a fifth depth that is less than the fourth depth.

13 . A screw for a plasticating apparatus, the screw comprising:

a longitudinal axis, the screw being rotatably supportable in a barrel for rotation about the longitudinal axis, the screw having a core and at least one helical flight extending along a length of the screw, the helical flight having a radially outermost flight surface, the helical flight extending in a first threaded direction and defining a first helical path of a first helix angle measured relative to a reference line perpendicular to the longitudinal axis, the first helix angle being less than ninety degrees; the helical flight defining a helical channel; and

a longitudinal portion of the screw having a plurality of advancing grooves with each advancing groove having at least one closed-end, the advancing grooves being arranged in a noncontinuous helix cut in the screw core in the helical channel of the screw, each of the plurality of advancing grooves forming a second helical path in the helical channel and being arranged entirely between adjacent helical flights and extending substantially parallel to the helical flights, and the plurality of advancing grooves being dimensioned to receive material therein as the material is conveyed forward through the helical channel;

the longitudinal portion further having at least one undercut surface located radially inwardly from the radially outermost flight surface, wherein the undercut surface has a depth that varies.