PETpla.net Insider 11 / 2018

BOTTLE MAKING 17 PET planet Insider Vol. 19 No. 11/18 www.petpla.net BOTTLE MAKING 17 Figure 4.18 This tool-less system allows mould changeover in less than 1min/cavity. Picture courtesy of Sidel Inc. Taken all measures together may reduce changeover time from 5min/cavity to less than 1min/cavity. On a 20-cavity system, this would result in time savings of 80min/changeover, allow- ing an additional production of over 53,000 bottles if the machine runs at a speed of 2,000 bottles/ cavity per h (b/c per h). Even if the margin was only 0.5 cents/bottle, an additional revenue of $250 per changeover could be achieved. Air consumption Another important feature is air consump- tion and more specifically the so-called dead air volume. Air is the single-most costly part of blow- ing bottles besides the preforms and users do well to pay close attention to this issue. Air consumption is driven by the air pressure, the actual volume of the bottles produced, and the air that is not used in the blow process but needs to be exhausted every blow cycle. This air “hides” in the connection pieces between the blow valves and the cavity. When the exhaust valve is energised, all air that is between it and the cavity must be exhausted besides the actual bottle volume to make sure there is no pressure left in the blown bottle. Many manufacturers of blow machines do not publish this important information but users can calculate it by looking at the machine specifications. Let us assume a manufacturer specifies blow air consumption of 1300Nm 3 /h for the production of 20,000 b/h of 1.5 l volume at 35 bar. The volume that is actually inside the bottles is 20,000 b/h × 1.5 l × 35 bar/1,000 l/m 3 = 1,050Nm 3 /h. The differ- ence of 1300 − 1050 = 250Nm 3 /h is the dead air volume. This in turn is 367ml/bottle (250Nm 3 /h × 1000 l/Nm 3 /h/20,000 b/h/35 bar). It is important to calculate this as a fixed number rather than a percentage as this lost air is present for bottles of each size. A 500ml bottle has the same losses as a 1.5 l bottle; however, in the case of the smaller bottle 73% more blow air is needed than would be if just the bottle needed to be supplied. Smaller dead air volumes will save significant money over the lifetime of the machine. Small machines particularly often feature high dead air losses and users should carefully examine manufacturers’ offerings (Fig. 4.19). SDWHQWV UHVHDUFKHUV DQG WHFKQLFLDQV LQVWDOOHG SODQWV EUDQFKHV ZRUOGZLGH ,I ZH KDGQêW JRQH VR IDU ZH ZRXOGQêW EH VR QHDU <RXU IXWXUH VHHQ IURP QHDU