Extruder Drag Flow
Calculate the drag flow of a single-screw extruder, Q_d = ½·π²·D²·N·H·sin(φ)·cos(φ), from the barrel diameter D (m), screw speed N (rev/s), metering-zone channel depth H (m) and helix angle φ (degrees). Drag flow is an extruder's main pumping mechanism: the melt is dragged forward by the relative motion between the rotating screw and the fixed barrel, like a screw pushing a nut that cannot turn. This viscous drag is proportional to screw speed and channel geometry, and would be the maximum theoretical flow with no back-pressure. In practice the net flow is the drag flow MINUS the pressure flow (the backflow from die/head resistance). The balance between drag and pressure sets the extruder's operating point on its characteristic curve. Drag flow is the basis of extrusion screw design, the process that makes pipes, profiles, films, sheets, wire and the pellets of nearly all transformed plastic. Enter the diameter, speed, channel depth and helix angle.
Resultado
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Vazão de arraste da extrusora
A vazão de arraste (drag flow) é o mecanismo principal de bombeamento de uma extrusora monorrosca, Q_d = ½·π²·D²·N·H·sen(φ)·cos(φ), a partir do diâmetro do barril D, da rotação da rosca N, da profundidade do canal na zona de dosagem H e do ângulo de hélice φ. O fundido é arrastado para frente pelo movimento relativo entre a rosca, que gira, e o barril, que fica parado — exatamente como um parafuso empurraria uma porca impedida de girar. Esse arraste viscoso é proporcional à rotação e à geometria do canal, e seria a vazão máxima teórica se não houvesse contrapressão. Na prática, a vazão líquida é a vazão de arraste menos a vazão de pressão (o refluxo que a resistência do cabeçote e da matriz empurra de volta canal acima). O equilíbrio entre arraste e pressão define o ponto de operação da extrusora na sua curva característica, e a vazão de arraste é a base do projeto e do dimensionamento de roscas — o processo que produz tubos, perfis, filmes, chapas, fios e os próprios pellets que alimentam quase toda a transformação de plástico do mundo. Informe o diâmetro, a rotação, a profundidade do canal e o ângulo de hélice.
Related Tools
Screw Compression Ratio
Calculate an extrusion screw's compression ratio, CR = H_feed ÷ H_metering, from the channel depth in the feed zone H_feed and the metering zone H_metering. An extrusion screw has three zones: feed (deep channel, receiving solid pellets), compression (transition, channel tapering) and metering (shallow channel, homogenizing and pumping the melt). The compression ratio is how much the channel narrows from inlet to outlet — typically 2:1 to 4:1. This compression is essential: by reducing channel volume it compacts the pellets, expels trapped air (which must vent back through the feed, not go forward) and generates the shear and pressure that melt the polymer by viscous heating (plus barrel heat). The right ratio depends on the polymer: materials melting with large volume reduction and amorphous ones need different ratios from semicrystalline. A wrong ratio causes incomplete melting, air pumping, flow instability (surging) or degradation. It is one of the parameters that define whether a screw suits a given material. Enter the feed and metering channel depths.
Screw Channel Shear Rate
Calculate the average shear rate in an extrusion screw channel, γ̇ = (π·D·N) ÷ H, from the barrel diameter D (m), screw speed N (rev/s) and channel depth H (m). Shear rate is the velocity gradient the molten polymer experiences between the moving screw surface and the fixed barrel, and it is central to plastics processing for a key reason: molten polymers are NON-Newtonian pseudoplastic fluids whose viscosity DECREASES as shear rate rises (shear thinning). Knowing the shear rate lets you estimate the material's real viscosity in the machine (via the power law) and thus pressure, power and viscous heating. Very high shear can degrade the polymer (chain scission by shear and heat); too low leaves melting incomplete. Each polymer has a suitable range. This screw-channel shear rate differs from the (much higher) die shear rate at the exit restriction. It is a basic processing-rheology calculation. Enter the diameter, speed and channel depth.
Screw L/D Ratio (Injection)
Compute the L/D (length/diameter) ratio of an injection or extrusion screw by dividing the effective length by the diameter. It is a central parameter of the plasticizing design: long screws (L/D 20–24) give better melt mixing and homogenization; short ones (L/D < 18) plasticize less but are more robust. It defines melt quality and the ability to process different materials. Enter the screw length and diameter.
Screw Degree of Fill
Calculate an extrusion screw's degree of fill, η = (actual flow ÷ drag flow) · 100, from the actual production flow and the screw's theoretical drag flow. Degree of fill measures how much of the screw's theoretical pumping capacity (the drag flow, which would occur with no back-pressure) is actually delivered as real flow — the difference is 'lost' to pressure flow (backflow from die resistance). It is thus a measure of the extruder's volumetric EFFICIENCY and operating point on the characteristic curve: a high fill (near 100%) means little back-pressure (open die, simple product); a low fill means strong back-pressure (restrictive die), with much internal backflow. In gravity-fed (flood-fed) extruders the screw runs full, and degree of fill reflects the drag-pressure balance; in metered-feed (starve-fed, common in twin-screw) extruders, degree of fill is deliberately controlled by the feed rate, decoupling flow from speed and giving independent control of residence time and shear. Knowing the degree of fill helps diagnose the process and optimize productivity. Enter the actual flow and the drag flow.
Extruder Head Pressure
Estimate an extruder's head pressure, ΔP = (Q·μ) ÷ K, from the volumetric flow Q (m³/s), the melt viscosity μ (Pa·s) and the die conductance constant K (m³, summarizing the head+die flow-resistance geometry). Head pressure is the pressure the melt reaches at the screw end, before being forced through the die that gives the product its final shape. It results from the balance between the screw's pumping capacity (drag flow) and the die's resistance: more restrictive dies (smaller orifices, longer narrower channels) need higher pressure for the same flow. Extrusion pressures are very high — typically 100-400 bar (10-40 MPa) — and measuring and controlling them is essential: pressure indicates process state (blockages, viscosity changes from temperature, screw wear), governs flow and product uniformity, and has safety limits (excessive pressure can rupture the head or trigger burst disks). The screw-die balance, shown in the extruder's characteristic curve, is the heart of process control. Enter the flow, viscosity and die constant.
Blow-Up Ratio (Blown Film)
Calculate the blow-up ratio (BUR) in blown-film tubular extrusion, BUR = D_bubble ÷ D_die, from the film bubble diameter D_bubble and the annular die diameter D_die. Blown-film extrusion makes most of the world's plastic films (bags, packaging, sacks, sheeting): the melt is extruded through an annular die forming a tube, which is then INFLATED with compressed air like an elongated balloon and pulled upward at once, stretching the film in two directions to its final thickness (a few micrometres). The blow-up ratio is how much the tube is inflated relative to the die diameter — typically 1.5:1 to 4:1. It controls molecular orientation in the TRANSVERSE (circumferential) direction: a higher BUR stretches the film more in width, balancing its properties in both directions (transverse by blowing and longitudinal by pulling). The balance between blow-up and draw (pulling) sets the biaxial orientation, which determines the film's strength, stiffness, clarity and tear behavior. Adjusting BUR is a main control variable in making blown films with the desired properties. Enter the bubble diameter and the die diameter.
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