Fondarex - Calculation of the vacuum build-up in the mould cavity

Description of the parameters:

Volume of the vacuum tank:
Volume of the vacuum tank in litres.

Initial air pressure in the vacuum tank:
Air pressure in the vacuum tank at the time the vacuum build-up begins,

Hose diameter:
Inner diameter of the hose line to be evacuated from the vacuum valve or chill block to the CCAB.

Hose length

Length of the hose line to be evacuated from the vacuum valve or chill block to the CCAB.
Note: The volume of the two air filters located on this section is calculated internally by  adding an additional 1 litre.

Die temperature:
The "mould temperature" is the average temperature to which the air heats up before the plunger movement begins.
In addition to the air in the mould cavity, we also consider the air in the casting chamber, which has been heated by the molten metal flowing into it.

Shot weight (aluminium):
Weight of the aluminium dosed into the shot sleeve in kg.
If other alloys are used, the actual shot weight must be converted to the density of liquid aluminium (2.6 g/cm³).

Active shiot sleeve length:
Length of the shiot sleeve over which the melt spreads during dosing.

End of poring hole:
Plunger position from which the pouring hole is closed by the pplunger.
Reaching this position is the starting point for the vacuum build-up (VACUSTART).

Plunger velocity of the 1st phase:
Average speed of the plunger in the range "End of pouring hole" to "Shot sleeve full"

Number of vacuum channels:
Number of vacuum channels used. In this simulation all vacuum channels are granted for beeing identical:
Same venting unit, same venting cross-section, same hose diameter, same hose length.
If, for example, several chill blocks are connected in parallel to 1 channel, only 1 channel is counted, but the venting cross-section is increased accordingly.

Venting cross-section per channel:
The narrowest flow cross-section in the chill block or vacuum valve used.

Venting device:
Depending on the type of venting device selected, different flow resistance is calculated for the same venting cross-section.

Venting capacity:
Hydraulic vacuum valve:                 100%
Mechanical vacuum valve:              95%
Chill block:                                       75%

Vacuum start delay:
Delay of vacuum activation in seconds from VACUSTART ( = plunger has "closed" the pouring hole)

Vacuum valve closes after [s]:
Time at which the vacuum valve located in the die casting mould is closed. The vacuum suction behind the valve up to the tank remains active.
This parameter is generally only of interest when evaluating hydraulic vacuum valves.

Vacuum reduction:
During vacuum reduction, the flow cross-section in the area of the CCAB is reduced to the percentage specified here at the start of the vacuum build-up.
(0% = closed, 100% = max. flow ).

Duration of the vacuum reduction:

Time in seconds that the vacuum reduction is maintained. The time is measured from the time (VACUSTART) at which the pouring hole is closed by the plunger.

Leakage cross-section:
The leakage cross-section is the sum of all gaps and openings on the die casting mould through which air can flow in from outside during vacuum build-up.

Essentially, these are
- Vacuum valves / chill blocks that do not seal properly
- dirty, non-parallel dividing surface,
- slide guides,
- ejector allowance and
- gap between the shoit sleeve and  plunger.

Time of evaluation:

The calculated values for pressures and extracted air volume are specified for the evaluation time (in seconds after vacuum start).
If the specified evaluation time is after the end of the first phase ("shot sleeve full"), the values for the time of evaluation is set to the end of the 1st phase.