KHS develops digital control systems for PET bottle production

Even on the most advanced machine there can be discrepancies in the distribution of PET bottle material in the stretch blow moulding process. This has an impact on the bottle quality and production efficiency. In order to optimise these parameters, KHS has developed Unit Mould Control in cooperation with US company Agr International. This digital, automated process control system, connected with the KHS controller, can individually regulates the respective blow stations in KHS’ InnoPET Blomax series, thus minimising any fluctuations in quality during stretch blow moulding. This results in improved bottle stability coupled with lower preform weights. This had proved something of a challenge to date, especially where containers with a high recycled PET content are used.

On a stretch blow moulder the amount of wear on the individual blow valves used can vary. This allows the bottles blown with the same also change throughout the service life of the stretch blow moulder depending on the station used. In the production process, this can cause discrepancies in the distribution of material and thus to differing thicknesses of bottle wall. To date, parameters could only be adjusted for the entire machine and not for each individual station. With the new digital Unit Mould Control system manufacturers optimise their blow moulding process by making individual settings for each station.

“This enables material distribution to be more precisely controlled per station, thus minimising variations in the wall thickness from mould to mould by more than 30%,” explained Frank Haesendonckx, head of technology at KHS Corpoplast.

Unit Mould Control adjusts settings fully automatically
To this end, Unit Mould Control inspection technology constantly measures the material distribution in each bottle and adjusts the settings for optimisation fully automatically.

“With this system deviations in the individual mould stations are identified. By applying an algorithm, the degree of variability is reduced without operator intervention and possible incorrect settings are avoided,” Haesendonckx stated.

Furthermore, the data captured from the individual mould stations provides valuable information for the condition-based maintenance of valves, stretching systems or mould shells, for instance. Unit Mould Control yields further benefits with regard to the growing percentage of recyclate used in PET bottles in particular.

“Process accuracy reaches its limits with containers such as these,” Haesendonckx said. “As the material quality varies when recycled PET is used, the bottle becomes less and less stable the less the preform weighs or manufacturers have to use heavier preforms to ensure stability.”

With the new system weights can be reduced while retaining bottle stability, he claimed. “Unit Mold Control effectively compensates for discrepancies by identifying any unwanted material displacement during wall thickness inspection and automatically counteracting this.”

Partner Agr is also convinced by the joint new development.

Robert Cowden, COO of Agr, said, “Our commitment to the global beverage market is to provide innovative process control solutions for the factory floor. In doing so we’re helping to constantly optimise processes and improve production line efficiency and productivity by reducing unplanned downtime, labour content per produced container and energy costs.”

Unit Mould Control is available as an option for KHS InnoPET Blomax Series IV and V stretch blow moulders and has already successfully proved itself on the market several times over. Furthermore, the new system – whose industrial property rights are held by KHS and Agr – can also be retrofitted into existing plant machinery.