One-stage or two-stage blowing of PET bottles in special forms using compressed air with a pressure usually above 30-35 bar. In order to obtain appropriate parameters, the bottle is first shaped in the so-called preform, only then it is blown to the expected size.
There are a variety of blow moulding processes and all of them require stable compressed air pressure delivered to the moulding machine to control quality and maintain productivity. In most blow moulding processes, compressed air is used to inflate the parison or “preform”. The parison is a tube-like piece of plastic with a hole in one end through which compressed air can pass. The compressed air also cools the part after inflation to final form, but prior to ejection from the mould. In PET bottle blowing, high speed rotary machines use 600 psig (40 Barg) compressed air to produce bottles at rates greater than 20,000 bottles per hour.
To inflate the parison, or blow the part, as quickly as possible leads to very high rates of flow in supply components which creates high pressure drop. A blow machine running 16 oz. bottles at 24,000 bottles per hour can consume 2,800 to 3,200 scfm depending upon process setup which creates significant pressure drop in the headers and filters delivering the air to the blow machine. Pressure drops from 50 psid to as high as 110 psid have been observed in the process. In order to make acceptable bottles with this level of pressure drop the system has to operate at dramatically higher than necessary pressure.
In view of this, substantial amount of artificial demand is present in the system and Flow Controllers with adequate storage help to reduce the energy losses in blow moulding operations.