Compression molding of PET performs could challenge domination of injection molding process

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Compression molding of PET performs could challenge domination of injection molding

PET performs are predominantly manufactured by injection molding process. Compression molding offers higher quality, improved productivity and also an opportunity to make them lighter in weight. The new process based on principles of compression molding is called Preform Advance Molding (PAM), introduced at K 2007 by Sacmi Imola S.C. of Italy.
PAM starts with an extruder. It continuously extrudes a cylindrical parison, which descends from a vertical die and is cut by a knife into a slug or gob. The gob is grabbed by an insertion carousel and dropped into one of 48 mold cavities on a spinning carousel. As it turns (9.5-10.5 rpm), the cavities rise to meet the cores and thread splits and mold each preforms less than 2 tons of force. (PAM systems can be built with upto 5 tons/cavity.) The molding carousel processes standard 0.5 Liter carbonated soft-drink (CSD) preforms�23 gm weight, 120 mm long, PCO 1810 neck finish, at up to 450-500/hr. After a 6.5-sec molding cycle (approx. 90% of which involves actual pressing), the core and neck splits lift the preform out of the cavity and another robot transfers the preforms to a post-cooling carousel. The latter has 256 sleeves in which preforms are air-cooled inside and out for the equivalent of 5.3 molding cycles. The preforms leave the system aligned on a conveyor, which permits integration of 100% vision inspection (at up to 650 preforms/min with Sacmi's PVS-1 multi-camera system) or direct delivery to a stretch-blowing machine.
Some of the major benefits claimed by the Italian manufacturer are:

• Quality due to absence of gates in this process, required for injection molding process.	• Quality due to absence of gates in this process, required for injection molding process.
• Lower level of acetaldehyde content due to lower shear in extrusion process compared to injection molding.	• Lower level of acetaldehyde content due to lower shear in extrusion process compared to injection molding.
• Higher productivity due to lower melt temperatures requiring lower cooling as well as faster cooling cycles.	• Higher productivity due to lower melt temperatures requiring lower cooling as well as faster cooling cycles.
• Lower capital cost.	• Lower capital cost.
• Energy saving due to lower melting temperatures.	• Energy saving due to lower melting temperatures.
• Use of higher IV PET polymer, producing stronger performs and thereby reduction in wall thickness and subsequently weight.	• Use of higher IV PET polymer, producing stronger performs and thereby reduction in wall thickness and subsequently weight.