The pressure loss of the material in the barrel is mainly reflected in two aspects: the internal friction of the material and the external friction of the cylinder wall and the die cavity and the compaction material. 

 

Injection rate, the diameter of the barrel (nozzle), the length of the barrel (or nozzle) and the temperature of the material are main factors that affecting the pressure loss.

 

I. Pressure Loss

1, Pressure loss in cylinder - loss of friction (as shown above)

For a plunger injection system, the pressure drop loss value p of a compact pellet can be approximately obtained:

 

ΔPg=p0（1-e-4fL/R）（1）

Where, p0... Injection pressure;

R... Inside diameter of cylinder wall;

L... Material area length;

F... Friction coefficient between grain and cylinder wall.

 

 

2. Pressure Loss in Cylinder-Compression Pressure Loss

When the screw or plunger presses the material to the nozzle, the pressure drop of the melt through the barrel can be estimated by the formula of the volume flow rate of Newton fluid:

 

qv=πΔpR4/8ηL （2）

ΔPl=8ηLqv/πR4（3）

Where, qv... volume flow rate of the melt through the cartridge;

       R... Inner radius of material barrel;

       η... Shear viscosity of Newton fluid;

       L... The length of the melt in the barrel.

 

The pressure loss of material in the cylinder: ΔP=ΔPg+ΔPl, Mechanism of the pressure loss in the nozzle is similar to that in the barrel, and the calculation process is the same.

 

Ⅱ. Influencing Factors

1, The injection rate, the formula (2) shows that the injection rate increased, qv increased, and ΔPl increased;

2, Material cylinder (or nozzle) diameter, by formula (1) (3) can be seen, R increases, ΔPg and ΔPl also increases;

3, When other conditions are constant, the nozzle length increases, and the delta Pg and delta Pl increase as well;

4. Temperature mainly affects the pressure loss by changing the shear viscosity of the melt. And the change of injection pressure also results in the change of melt temperature