PETpla.net Insider 12 / 2018

BOTTLE MAKING 22 PET planet Insider Vol. 19 No. 12/18 www.petpla.net Virtually engineering bottles of the future Something big is happening in a small corner of Northern Ireland which is making a global impact among its Fortune 500 clients. Blow Moulding Technologies (BMT), who envi- sion ‘a scientific approach to Stretch Blow Moulding’ has emerged as a market leader in virtual engineering and test- ing bottles of the future. As the world scrambles in its search for the optimum bottle with the least material, yet with the same performance and at a lower cost, BMT provides a missing tools and the knowledge required to test these applications that a confident and seamless shift towards more sustain- able and alternative polymer contain- ers can be made. Using advanced data-driven tools and validated techniques, BMT’s team of qualified doctorate engineers from Queen’s University Belfast are enriching the SBM industry with the much-needed insight data which allows its clients to accurately predict the character- istics of new and recycled materials, preforms and bottles. Whereas the industry is predominately vested in PET, the seismic global shift towards new materials has created an intense focus on the application of recycled materials, new additives, bio-blends and bio-materials to the mass pro- duction of polymer containers. In light of the negative global trends against plastic, BMT’s highly optimised solu- tions have rapidly emerged into the limelight with what is, quite simply, the right solution at the right time. BMT offer a suite of technologies which facilitate this scientific approach to bottle engineering. The solution involves a consolidated stepped pro- cess which has been refined and opti- mised with over 20 years of research from leading experts in this field. Step 1 involves the characterisa- tion of the material by using a state- of-the-art bi-axial machine which is specifically designed to replicate the processing conditions and understand its behaviour during stretch blow moulding. It generates data by bi-axi- ally stretching the material to break- ing point using different temperatures, strain rates and stretch ratios. Figure 1: 6-step process Figure 2: Bi-axial characterisation Step 2 involves measuring the temperature dependent mechanical properties post deformation using DMA and tensile testing. This creates a database of elastic modulus, for dif- ferent processing histories, which is used in the design process. Step 3 involves the use of a state- of-the-art instrumented free-blow machine. This provides data for vali- dating the material model for simula- tion by enabling critical outputs from the free-blow process to be measured and compared. Free-blow experi- ments are conducted over a large process window, where the cavity pressure, stretch rod force, surface strain, the evolving bottle shape and material behaviour (stress / strain) are measured. Figure 3: Preform characterisation using free-blow and digital image cor- relation to give stretch ratio map over time for various conditions Step 4 involves analysing the biaxial test data and free blow data to generate material parameters for the user material model of PET for the stretch blow moulding simulation. This will include simulation of the freeblow tests from Step 3 which will validate the material model for the resin. As well as fitting the material parameters for the PET material model, the linear viscoelastic parameters need to be derived from the DMTA data. This will include the generation of the master curves assuming time temperature superpostion along with Prony series parameters. Figure 4: Free-blow validation - strain results and process results Step 5 involves working with clients to produce validated simula- tions of their manufacturing process.