Viscosity of the material in moldflow database for Injection pressure calcuation

[kulandaivel_palanisamy]

 Dear all,

I am comparing three different grades of PA66 with the uniform melt (295 C) and mold (100 C) temperatures.

Material 1: Technyl A 218 V30 (PA66 GF30)

Material 2: Zytel 70G50HSLA BK039B (PA66 GF50)

Material 3: Grivory GV-5H (PA66+PA6I/6T GF50),

I am getting the injection pressure result as

Material 1: 41 MPa

Material 2: 59 MPa

Material 3: 91 MPa

Although viscosity of the material 2 and 3 are almost same as shown in the viscosity curve as attached, Please let me know why the injection pressure of the material 3 is high? Which is the main factor taken in to account to calculate the injection pressure? Is the viscosity curve of material 3 is correct?

Thank you very much in advance.

Regards

JK

[petr_AL]

Hi,

in my opinion you should check Shear rate result.

When Shear rate is higher, higher is also Viscosity difference of material 2 and 3.

[abakharev]

Pressure drop in the runners is a complicated thing that depends upon rheology and thermal properties. That is because a part of the runner crossection is frozen and only part is melted. The thickness of the frozen layer depends upon thermal properties of the polymer, temperature of the melt and of the mold, shear heating, etc. Sometimes there might be weird effects like higher viscosity of plastic causing more shear heat and so thinner frozen layers and higher temperature in the shear zone, thus eventually leading to lower pressure drop.

But in this case the result seems to be caused by the material 3 having higher viscosity at high shear rate. At shear rate of ~1000 1/sec the third material has approximetely twice as much viscosity as the second material. Check your maximal shear rate graph during filling and you will probably see shear rates of ~1000 1/sec

[kulandaivel_palanisamy]

Hello Abakharev and Petr,

Thanks for your response.

I accept the viscosity of the 03rd material is higher than the 2nd material (thanks for your picture showing the viscosity)

Attached is shear rate maximum result of 3 materials as given in the result plot.

01st material: 97979 1/s

02nd material: 110400 1/s

03rd material: 49845 1/s

I guess, higher the shear rate will lead to lower the viscosity (in general) so in the case of option 3, lower the shear rate leading to higher viscosity and inturn high injection pressure?

Let me know, my interpretation about shear rate result with the viscosity and the injection pressure is correct?

Regards

JK