The Lab · Rheology

Viscosity Curve

Enter your velocity and pressure readings across the fill range. The tool plots relative viscosity, finds the shear-thinning plateau, and recommends an injection velocity.

Measured points
Material
Melt °C
Mold °C
Velocity (in/s)Pressure (psi)Fill time (s)opt

Enter at least two velocity / pressure points to plot the curve.

  • Each row is one shot at a different injection velocity.
  • Read the peak injection pressure at transfer for each velocity.
  • Add fill time to analyse on relative viscosity rather than pressure ÷ velocity.
  • Five or more velocities, evenly spaced, make the plateau easy to find.
Predicted · not measuredViscosity from your coefficients

If you have your grade's Cross-WLF card (from a simulation seat or the supplier) or a power-law fit, enter it to see the melt's flow curve at this study's melt temperature. It is a separate check on the material, not a fit to the shots above: a press study cannot recover these coefficients, because it never measures the true shear rate.

Your viscosity coefficients

Stays in this tab: not in the share link, not in saved studies, never sent to us. The Lab ships no default coefficients — fitted cards are licensed data we cannot redistribute — and a press study cannot fit them either: it never measures the true shear rate.

Enter all seven coefficients — missing n, τ*, D1, D2, D3, A1, Ã2.

How to run this study

Find the optimal injection velocity by characterizing how the material’s viscosity responds across a range of fill speeds. This sets the velocity setpoint for every study that follows and identifies the shear-thinning plateau where viscosity is low and the process is robust.

Procedure

  1. 01Set all parameters to recommended starting conditions (barrel temps, clamp, cooling). Disable pack/hold — first stage only.
  2. 02Start at a low injection velocity (e.g. 0.5 in/s) and mold 5 shots to stabilize.
  3. 03Record peak injection pressure and fill time for the stabilized shot.
  4. 04Increase velocity by a fixed increment (e.g. 0.5 in/s), stabilize 5 shots, and record again.
  5. 05Continue through 8–12 setpoints until you hit machine pressure limits or see flash.
  6. 06Enter each velocity/pressure pair — the tool plots relative viscosity (pressure × fill time) and finds the plateau.
  7. 07Take the optimal velocity from the middle of the plateau, where viscosity is lowest and most stable.