Method for recycling energy in a blow moulding machine for blow moulding containers

A method for recycling blowing air from a blow moulding apparatus for blow moulding plastic material containers, said apparatus including:

• moulds provided with blowing cavities,
• first blowing means for blowing primary air in the cavities of said moulds, comprising a primary air tank,
• second blowing means for blowing secondary air in the cavities of said moulds, comprising a secondary air tank,
• first recycling means for recycling the blowing air exiting from said cavities, in a first step of discharging the air from the containers, wherein said first recycling means are configured so as either to allow an input of primary air into a first blowing stage within the cavities of said moulds or to allow an input of a part of secondary air into a second blowing stage,
• said method comprising the following stages:
• a) at a predetermined starting time t0 of a blowing cycle, blowing the air into the containers contained in the cavities of the moulds at a first predetermined pressure P1, by means of the first blowing means, and maintaining the air at such a first pressure in the containers contained in the cavities up to a first time t1, in which said air is defined primary;
• b) blowing the air into the containers contained in the cavities of the moulds at a second predetermined pressure P2, by means of the second blowing means, said second predetermined pressure being higher than the first pressure P1, and maintaining the air at said second pressure up to a second time t2, in which said air is defined secondary;
• c) discharging the air from the containers contained in the cavities until a third pressure P3 is reached in the containers, such a third pressure having a value comprised between said first pressure P1 and second P2 pressure, and recycling the air at said third pressure P3 by means of the first recycling means, wherein said third pressure P3 has a value in the range between 20 and 28 bar, this stage having a duration in the range between 0.05 and 0.15 sec,
• c′) discharging and recycling the air from the containers contained in the cavities until a fourth pressure P3′ is reached in the containers with a value between 12 and 14 bars, and transferring the recycled air in a recycling tank or other dedicated storing means, this stage having a duration in the range between 0.05 and 0.10 seconds;
• and
• d) discharging the remaining air contained in the containers contained in the cavities at atmospheric pressure.