PETpla.net Insider 04 / 2011

BOTTLE MAKING 28 PET planet insider Vol. 12 No. 04/11 www.petpla.net Research into energy-optimised stretch blow moulder Faster stretching, lighter bottle Improving energy efficiency in production processes is of great interest to bottlers and PET bottle makers alike. Every year the German Federal Ministry of Education and Research (BMBF) sponsors industrial projects in this field. In 2009, a group of stretch blow moulding experts jointly submitted a grant application under the title “ Increasing Energy and Resource Efficiency in the Manufacture of PET Bottles”. The team consists of KHS Corpoplast, the Institute for Plastics Processing (IKV), AdPhos Innovative Technolo- gies, and Okertaler Mineralbrunnen, a mineral water bottling plant. The project is schedule for completion in 2011. Weight, electricity, and compressed air Each year, around 25 billion PET bottles are made in Germany alone, and around 500 billion worldwide. The manufacture of 1kg of PET requires approximately 1.9kg (4.2 lbs) of oil and 23kWh of energy. In light of these facts the team focused on three main fields where the highest energy savings could be expected: weight of the preform/bottle; energy consumption during preform heating; and compressed air. Practical tests have been performed, analysed, and optimised on a KHS Corpoplast Inno- PET Blomax Series III, with 14 blow stations and up to 25,000 PET bph capacity. The machine is installed at Okertaler Mineralbrunnen. Fast stretching increases strength, allows weight reduction The material content offers the greatest potential for energy sav- ings and cost reductions. As a rule of thumb, 70% of the costs of a PET bottle can be attributed to the amount of material used. Preform produc- tion and actual production of the PET bottle account for a further 15% of costs. Reducing the weight of a PET bottle is important both for its eco- nomic competitiveness and in reduc- ing its energy consumption. Prduction of a PET bottle involves stretching in both axial and radial directions. The team analysed the way that the properties of the PET bottle changed when the biaxial stretch of the PET material was altered. The result: the material’s orientation is the highest when stretched at the high- est possible speed, i.e. the strength of the PET material increases when it is stretched rapidly. In this particular case, the faster stretching results in an improved PET strength of around 10% for the Okertaler bottle. This greater strength and higher orienta- tion allows the design of lighter PET bottles. If stretching at speed results in 10% increase in strength, then this would mean that future 1.5-litre PET bottles could become 3% lighter. The weight of each PET bottle would thus drop from the current 31g to 30g. 1g less material per bottle would lead to a considerable saving of 100,000kg (roughly 220,500lb) of material per annum, assuming approximately 100 million bottles are produced per year. At a market price of €1.20 for 1kg (2.2 lb) of PET, the annual amount saved would be €120,000. The design of the PET bottle is also important, as the specific shape can help to use less material. During the course of the project, the shape of the Okertaler PET bottle was rede- signed with the help of KHS Corpo- plast ‘Bottles & Shapes’ program . To date, the company has optimised around 9,000 PET bottles using this program. Optimised preform heating can reduce energy consump- tion 15 to 20% The second decisive factor was the amount of energy required to heat 1kg (about two pounds) of PET. An important consideration is the fact that the preform mouth is not heated in the stretch blow moulder and thus not altered, meaning its weight can be deducted from the weight of the overall preform when calculating the total weight to be heated. Thus if a preform weighs 25g and its mouth 5g, only 20g needs to be included in Development in the weight of 1.5l PET bottles over the last ten years Development in the amount of energy used for preform heating over the last ten years Development in the inflation pressure used to manufacture PET bottles over the last ten years.