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Original Question: Assuming steel is uniform which cavities will fill first?

Understanding Rheology

Facts about plastic flow that help explain shear imbalances:

• Plastic viscosity is affected by shear rate
• As shear rate increases, viscosity decreases (non-Newtonian)
• Plastic viscosity is also affected by temperature
• As temperature increases, viscosity decreases

• Plastic has a laminar flow. No turbulence!! Reynolds numbers are often less than 10. Full turbulence requires a Reynolds number of 4000. Transition zone 2300-4000. Highest Shear Rate is just inside the frozen layer
  
  
• Highest Shear Rate is just inside the frozen layer. Shear-thinning and shear-heating reduces viscosity in these laminates.
  
  
• Due to the laminar flow, when plastic encounters a feature such as a intersection in a runner system, the hotter, less viscous plastic hugs the corner and travels along the outside wall, creating a cavity to cavity imbalance.
  
• Cross sections of runner channels showing position of higher sheared, hotter, less viscous material in red. Material that has experienced less shear heating is marked with blue.
   
  

  Mold Number: LinkedIn
  Current Conditions:

• The red lines again represent the higher sheared, less viscous material; the blue lines shows the less sheared more viscous material.  Various melt properties will be distributed to and across the cavities.  The various melt properties will result in 2 Flow Groups (FG) as shown below.
  

  Expectations:

• Cavities that receive the high sheared, less viscous material will fill before the cavities that will receive the low sheared, more viscous material.
• Dimensional variations, due to volumetric and orientation induced shrinkage differences,  may result between the cavities as a result in the variation the melt distribution properties

Answer to

LinkedIn Mold:

Cavities 2,4,5,and 7