Screw Terminology

Screw: 

a helically flighted shaft that when rotated within the barrel mechanically works and advances the material being processed.

screw

Screw Flight:

the helical metal thread of the screw.

Screw Root:

the continuous central shaft, usually cylindrical or conical in shape.

Flight Land:

the surface at the radial extremity of the flight constituting the periphery or outside diameter of the screw.

Screw Shank:

the rear protruding portion of the screw to which the driving force is applied.

Feed Section of Screw:

the portion of a screw that picks up the material at the feed opening (throat) plus an additional portion downstream. Many screws have an initial constant lead and depth section, all of which is considered the feed section.

Transition Section of Screw:

the portion of a screw between the feed section and metering section in which the flight depth decreases in the direction of discharge.

Metering Section of Screw:

a relatively shallow portion of the screw between the feed section and metering section in which the flight depth decreases in the direction of discharge.

Screw Diameter:

the diameter developed by the rotating flight land about the screw axis.

Helix Angle:

the angle of the flight at its periphery relative to a plane perpendicular to the screw axis.

Axial Flight Land Width:

the distance in an axial direction across one flight land in a direction perpendicular to the flight.

Flight Lead:

the distance in an axial direction from the center of a flight at its outside diameter to the center of the same flight on turn away. The location of measurement should be specified.

Full Flighted Length os screw:

overall axial length of the flighted portion of the screw, excluding non-return valves, smear head, etc.

Screw Channel: 

with the screw in the barrel, the space bounded by the surface of flights, the root of the screw, and the bore of the barrel. This is the space through which the stock is conveyed and pumped.

Enclosed Volume of Screw Channel:

the volume of screw channel starting from the forward edge of the feed opening to the discharge end of the screw channel.

Screw Efficiency: 

the volume of material discharged from the machine during one revolution of the screw expressed as a percentage of the developed volume of the last turn of the screw channel.

Screw Speed:

the number of revolutions of the screw per minute.

 

 

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