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.
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Taxa de cisalhamento (injeção)
Quando o plástico fundido é forçado por um canal estreito, as camadas de fluido deslizam umas sobre as outras — esse deslizamento é o cisalhamento, e sua intensidade é a taxa de cisalhamento γ. Para um canal retangular, γ = 6Q/(W·H²), função da vazão e da geometria. Por que isso importa tanto? Porque os termoplásticos são pseudoplásticos: sua viscosidade cai à medida que a taxa de cisalhamento aumenta — o material fica mais 'fino' e flui mais fácil quanto mais rápido é empurrado (o mesmo princípio do ketchup que escorre ao ser sacudido). Isso é ótimo para preencher o molde, mas tem limite: taxas excessivas geram calor por atrito viscoso e degradam as cadeias poliméricas, manchando e fragilizando a peça. Cada material tem uma taxa máxima recomendada, que orienta o dimensionamento dos canais e do gate. Informe a vazão, a largura e a altura do canal.
Related Tools
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.
Plastic Injection Flow Rate
Compute the injection flow rate by dividing the injected volume by the fill time, in cm³/s. It is the speed at which the molten plastic enters the mold — a parameter that controls the shear rate, molecular orientation, surface finish and defects such as jetting or flow marks. High flow fills fast but may degrade; low flow may solidify before filling. Enter the injected volume and the fill time.
Injection Shot Volume
Compute the shot volume of a plastic part by dividing the injected mass by the molten material density. The shot is the total volume of plastic injected per cycle (parts + runners), a parameter that must fit the injection barrel capacity. Together with the machine capacity, it defines how many cavities can be filled per cycle. Enter the injected mass (g) and the material density (g/cm³).
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.