hydraulic pressure - specific

[Andrea Martinelli]

Good evening!
Can someone explain to me in words "poor" the difference between hydraulic pressure and specific in injection molding?
hydraulic = read or set value of the press?
specific = real pressure on the piece?
formula to calculate it?
Thank you!

 

[Fabietto]

hi gorea, in words "poor." .
pi= hydraulic pressure -> value you impose on press and that is the pressure you exert on the inject cylinder case.
psi= specific injection pressure -> pressure value in the dosing area of the material (and not on the piece) that you get by multiplier effect given by the ratio between the cylinder area and the screw.

the machine manufacturer should indicate:
- maximum hydraulic pressure (pi) of operation of the press
- the specific pressure obtainable (psi) at maximum hydraulic pressure.
you need to calculate the specific and hydraulic pressure ratio (psi/pi) and multiply it by the hydraulic pressure you impose in the press, so you will have the specific pressure value applied to the dosing zone during injection.

example of our 400 ton
maximum hydraulic pressure (pi) = 140 bar
maximum specific pressure (psi) = 2040 bar
psi/pi ratio = 2040/140 = 14,57
therefore, if imposed 100 bar on the press, in the dosing area the material will undergo a pressure of
100*14,57=1457 bar.

as mentioned above, to the psi/pi report, you can get there by making the relationship between
Cylinder Background / Screw Injection Area
but usually the press manufacturer does not give you the diameter of the injection cylinder. .

from the above you can get a chart that binds the hydraulic pressure set to the specific pressure obtained and hang it on the press board, so you do not always have to count. .


ciao

 

[Andrea Martinelli]

perfect, very kind!thanks for the very detailed answer!