Grooved-feed barrel for single-screw extruders: axial grooves in the feed section that stop pellets turning with the screw
Single-screw extruder barrels whose bore is grooved or faceted where the pellets enter · 6 or 8 axial grooves 1.5 mm deep fading out over 200 mm, pressure at the end of the grooved section up from 4.3 to 29.0 MPa, and the cooling the grooves need
In a smooth-bore single-screw extruder, pellets in the feed section are moved forward only if they grip the barrel harder than the screw; if they slip, they turn with the screw and output falls as head pressure rises. A grooved-feed barrel cuts shallow axial grooves into the first diameters of the bore, or faces it with flats, so the pellets lock against the barrel and are driven forward. The grooves have to be kept cool, and their number, depth and length decide how much pressure the feed section builds.
Barrels and feed bushings for single-screw plastics extruders with axial grooves or polygonal flats in the feed and solids-conveying section, compared with smooth bores: groove number, cross-section, depth and length, pressure build-up, output against head pressure and feed-section cooling. Bimetallic inlays and liners are covered on the Polymer extrusion barrel liner page, screws on the Polymer extrusion screw page, injection-unit barrels on the Injection unit barrel and screw page, co-rotating twin-screw extruders on the Co-rotating twin-screw compounding extruder page and barrel-zone heating and cooling equipment on the Barrel heating and cooling system for twin-screw extruder zones page.
CNFX editorial research · Sources checked October 12, 2026 · 3 sources
Six or eight trapezoidal grooves, 1.5 mm deep at the feed opening, gone after 200 mm
Sasimowski, Sikora and Królikowski at Lublin University of Technology fitted a 25 mm, L/D 24 extruder with exchangeable feed sleeves, smooth or with 6 or 8 longitudinal grooves, and ran low-density polyethylene pellets at 1.67 to 8.33 screw revolutions per second. [1]
Editorial calculation: 200 mm of grooving on a 25 mm screw is 8 diameters.
Mobil's 1989 patent describes the axial grooves of conventional grooved barrels as parallel-sided, about two pellet diameters wide, with an average depth about equal to their width; about 1½ times their width deep in the feed throat, tapering to nothing after 6 to 9 barrel diameters. It notes that the screw and barrel are water-cooled in the throat and feed zones because heat softens the pellets in the grooves and lets them turn with the screw, that such grooves are hard to clean when they plug or bridge from interrupted cooling or excessive back pressure, and that there appeared to be a practical screw-diameter limit of about 3½ inches. [2]
KraussMaffei's patent takes axial grooves further, into the melting zone of a barrier-screw extruder, with grooves equally spaced around the bore whose depth falls to zero toward the end of the melting zone; it warns that grooves cut too deep impair the function, and says the design lowers the pressure needed between feed and melting zones, so the transition area of the screw wears less and the feed zone may not need separate cooling. [3]
Sleeve detail in the study
Value
Groove cross-section
Trapezoid, 5 mm wide at the screw, 4.5 mm at the bottom [1]
Direct torque motor, 300 Nm, 15.7 kW, up to 8.33 rps [1]
Give the barrel maker the polymer and pellet size, the screw diameter, and whether the feed section can be water-cooled, so groove number, width, depth and length can be set.
02
Pressure at the end of the grooved section: 4.3 MPa smooth, 7.8 MPa with six grooves, 29.0 MPa with eight
At the lowest screw speed of 1.67 rps the Lublin authors measured polymer pressure at the end of the grooved section: [1]
The paper states these as increases of 2.8 times and 6.8 times; the editorial ratios from the quoted pressures are 7.8 ÷ 4.3 ≈ 1.8 and 29.0 ÷ 4.3 ≈ 6.7, so the six-groove figure should be checked against the original data. With six grooves the pressure rose to 16.2 MPa at 8.33 rps. Energy per unit mass with either grooved sleeve was clearly lower than with the smooth one between 1.67 and 3.33 rps and similar at higher speeds, and the grooves had no significant effect on the melt flow rate of the extrudate. The authors cite earlier studies reporting flow-rate increases of 20 to 100 %, sometimes more. [1]
Mobil's patent tested a smooth round barrel insert against a hexagonal one, with flats acting as axial recesses, on polystyrene with three screws, closing a valve at the outlet. [2]
Higher than 6 grooves, but only over part of the speed range [1]
Ask for measured output against head pressure for your polymer, with the grooved section at its set cooling temperature.
03
A faceted bore against a smooth one: output kept when the outlet is throttled
The average progressive cut-off head pressure was 208 psi for the smooth barrel and at least 13,350 psi for the hexagonal barrel with its vaulted screw, which the patent says was the limit of the test apparatus. [2] Editorial calculation: 13,350 psi ≈ 92 MPa; 208 psi ≈ 1.4 MPa.
Editorial note: these figures come from one patent's test rig with polystyrene and differ in geometry from axial-groove bushings; they show the direction of the effect rather than a rating for a production barrel.
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Compiled and source-reviewed by the CNFX editorial team.
Each manufacturer above links to the page on that company's own website where the product is listed, with the date we checked it. How we source and review
· Page last updated 13 October 2026
Buyer questions
How deep are the grooves in a grooved-feed barrel?
In the Lublin study, 1.5 mm at the feed opening, fading to zero over 200 mm; Mobil's patent describes conventional grooves about 1½ times their width deep at the throat, tapering out over 6 to 9 barrel diameters. [1][2]
How much pressure does a grooved feed add?
At 1.67 rps, pressure at the end of the grooved section was 4.3 MPa with a smooth sleeve, 7.8 MPa with six grooves and 29.0 MPa with eight. [1]
Why must the grooved section be cooled?
Heat softens pellets in the grooves so they turn with the screw instead of moving forward; the feed opening in the Lublin tests was held at 40 °C. [2][1]
Sources and what still needs a direct check
Sources checked 2026-10-12. Measurements come from a peer-reviewed study at Lublin University of Technology in Polimery; output against head pressure and conventional groove proportions from a Mobil Oil patent; groove placement in the melting zone from a KraussMaffei patent.
