PETpla.net Insider 09 / 2017

BOTTLE MAKING 32 PET planet Insider Vol. 18 No. 09/17 www.petpla.net Figure 3.9 Linear ovens and blowing wheels have become standard in the design of rotary machines. Photo cour- tesy of KHS Corpoplast GmbH. The main difference to other machine types is in the design of the blow clamp. In a rotary machine each preform travels to its own blow clamp that is arranged on a blow wheel. All services to these clamps come through the centre of the blow wheel by means of rotary distributors. A massive drive gear sits underneath the wheel and a variable-speed motor drives it. The time between the end of oven section and the start of blowing is identical for each preform and this feature, combined with cam-controlled motions, allows rotary machines to deliver excellent quality, on a consist- ent basis. To familiarise the reader with the main machine components, the layout in Fig. 3.10 should prove to be helpful. Figure 3.10 Layout of typical rotary blow-moulding machine. Diagram cour- tesy of Krones AG. Preforms enter the machine at position #20. Injection moulders often pack their preforms in the so-called ‘gaylords’ (cardboard storage boxes of roughly 1m 3 volume). Resin compa- nies use these gaylords to ship resin and they are widely available. The unloading station might have a ‘gay- lord tipper’ that enables personnel to easily tilt gaylords to empty them (see Fig. 3.11). Position #19 is the storage bin, a simple metal enclosure open to the top. Figure 3.11 Storage bin and incline con- veyor to unscramble. Photo courtesy of Krones AG. Position #18 is the incline con- veyor that takes the preforms to the unscrambler. Incline conveyors are controlled by downstream switches that detect the amount of preforms in the line and only feed preforms when needed. Position #17 is the unscrambler. It orients the preforms onto the in-feed rails at position #16 with flexible pad- dles and the support of gravity. The preforms hang from their neck-support ring between two stainless steel rails (Fig. 3.12) and travel this way again by gravity to the in-feed star wheel at position #5. Figure 3.12 Preforms hanging from their neck-support rings on rails (upper left of the picture) on their way to the in- feed of the machine. Photo courtesy of Krones AG. In the in-feed section, preforms are transferred by various means onto mandrels (see Fig. 3.13). Figure 3.13 Machine using a star wheel to transfer preforms onto mandrels. Photo courtesy of KHS Corpoplast. These mandrels feature vari- ous spring-loaded devices to hold the preform in place and guarantee both alignment and secure assem- bly (Fig. 3.14). Most mandrels ride in tracks (position #6) and feature a sprocket on the top (in oven systems where the preforms ride upside down, the sprocket is at the underside). The sprocket engages with a chain that spins the mandrels and may also move the mandrels through the oven section at position #2. Spacing between mandrels on the track ranges from 38mm to about 50mm (1.5″–2″) and can be increased to double that figure for wide-mouth applications. The majority of soft drink and water bottles use necks of 28-33mm dia- meter, easily accommodated by the standard spacing. Figure 3.14 Mandrel using an innovative design with two rows of balls holding preforms firmly in place. Photo courtesy of KHS Corpoplast. Spinning with the mandrels, the pre- forms are exposed to infrared radiation. The machine shown in Fig. 3.15 has 14 heating ovens (position #12), ten on the way away from the blowing wheel position #1 and four on the return route. In the turnaround section as well as in between the last oven in the line and the blowing wheel, preforms undergo equilibration, i.e., a balancing of tem- perature differences inside the preform wall (see Chapter 6). Figure 3.15 In this machine preforms passing through the ovens upside down. Photo Courtesy of Sidel Inc.