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Plastic flow undergoes shear effects during filling. Shear effects are relative to flow rate and pressure drop. With too high shear stress or shear rate, degradation and cracking may happen to the part. The cross section area of the gate is often the smallest over the part, and thus the shear around this area is the highest.
Shear rate at the gate is relative to gate dimension and flow rate. It can be obtained using Moldex3D. Meanwhile, most of material manufacturers provide shear rate limits on the plastics. As shear rate is under the limits, product defects and problems can be reduced.
The below table is the Maximum shear stress limits applying to products and Maximum shear rate limits applying to gates.
Maximum of shear stress and shear rate

Maximum of Shear Stress, (MPa) 
Maximum of Shear Rate, (1/sec) 

PP 
0.25 
100,000 
HDPE 
0.08 
40,000 
LDPE 
0.08 
40,000 
EVA 
0.30 
30,000 
PS 
0.25 
40,000 
HIPS 
0.30 
40,000 
SAN 
0.30 
40,000 
ABS 
0.30 
50,000 
ABS (Platting Grade) 
0.30 
30,000 
PMMA 
0.40 
40,000 
PPS 
0.50 
50,000 
PA6 
0.50 
60,000 
PA66 
0.50 
60,000 
PA612 
0.50 
60,000 
PA12 
0.50 
60,000 
POM 
0.45 
40,000 
PET 
0.50 
50,000 
PBT 
0.40 
50,000 
PPO 
0.50 
35,000 
PC 
0.50 
40,000 
PC/ABS 
0.40 
40,000 
TPU 
0.40 
20,000 
PC/TPU 
0.40 
10,000 
PUR 
0.25 
40,000 
sPVT 
0.30 
20,000 
rPVT 
0.30 
20,000 
PSF 
0.50 
50,000 
PES 
0.50 
50,000 
LCP 
0.50 
60,000 