>> Sunday, 27 February 2011
The purpose of the primary blow air is to inflate the preform as much as possible to the final shape of the container. The setting of the primary blow pressure can be extremely critical with containers having flat panels although it is not normally so important for round containers.
If there is insufficient inflation in the primary blow, the extreme high pressure of the secondary blow may cause damage to the inflating preform such as pearlescence in the corners or splitting in the base.
Too much primary air pressure can cause uncontrolled inflation of the preform leading to splitting preforms or buckling of flat panels.
Turn off the Secondary Air and test the inflation of the preform at varying Primary Pressures.
Referring to Optimize Primary Blow Time, increase the time delay of Secondary Air to the same as the blow time. This will prevent the secondary air from starting so that the Primary Air inflation can be more easily observed.
Reduce the Primary Air Pressure to around 0.3~0.4 MPa (3~4 Kg/cm²), then start the machine.
Wait for the preform temperature to stabilize, then turn on the blow mold.
Collect a sample bottle, make a note of the pressure used, then increase the pressure by 0.1 MPa (1kg/cm²) and repeat the sample collection.
Continue this until the pressure has reached around 2.5 MPa (2.5 kg/cm²) or the inflation of the preform becomes uncontrolled.
If any other parameters such as injection or conditioning settings are changed, it may be necessary to re-optimize the pressure.