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.
Resultado
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Taxa de cisalhamento no canal da rosca
A taxa de cisalhamento média no canal de uma rosca de extrusão é γ̇ = (π·D·N) ÷ H, a partir do diâmetro do barril D, da rotação N e da profundidade do canal H. É o gradiente de velocidade que o polímero fundido sofre entre a superfície da rosca (que se move) e o barril (parado), e é um parâmetro central no processamento por uma razão fundamental: os polímeros fundidos são fluidos não newtonianos pseudoplásticos, cuja viscosidade diminui quando a taxa de cisalhamento aumenta — o fenômeno do shear thinning (afinamento por cisalhamento). Conhecer a taxa de cisalhamento permite estimar a viscosidade real do material dentro do equipamento (pela lei das potências) e, com ela, calcular a pressão, a potência e o aquecimento viscoso. Taxas muito altas podem degradar o polímero (quebra de cadeias por cisalhamento e calor); muito baixas deixam a fusão incompleta. Cada polímero tem sua faixa adequada. Esta taxa, no canal da rosca, é distinta da taxa de cisalhamento na matriz (muito mais alta, no estreitamento de saída). É um dos cálculos básicos da reologia de processamento. Informe o diâmetro, a rotação e a profundidade do canal.
Related Tools
Shear Rate (Injection)
Compute the shear rate of the molten plastic in a rectangular channel, γ = 6Q/(W·H²), from the flow rate (Q), the channel width (W) and height (H). It is a critical parameter of polymer processing: thermoplastic viscosity drops with shear rate (pseudoplastic behavior), and excessive rates degrade the material. It guides the design of runners and gates. Enter the flow rate, the width and the height of the channel.
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 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.
The results provided by this tool are for general informational and educational purposes only and do not constitute professional, financial, medical, legal, tax or accounting advice. Always confirm important decisions with a qualified professional and official sources.