Measuring and modelling air mass flow rate in the injection stretch blow moulding process

Abstract

The injection stretch blow moulding process involves the inflation and stretching of a hot preform into a mould to form bottles. A critical process variable and an essential input for process simulations is the rate of pressure increase within the preform during forming, which is regulated by an air flow restrictor valve. The paper describes a set of experiments for measuring the air flow rate within an industrial ISBM machine and the subsequent modelling of it with the FEA package AbaqusABAQUS. Two rigid containers were inserted into a Sidel SBO1 blow moulding machine and subjected to different supply pressures and air flow restrictor settings. The pressure and air temperature were recorded for each experiment enabling the mass flow rate of air to be determined along with an important machine characteristic known as the 'dead volume'. The experimental setup was simulated within the commercial FEA package AbaqusABAQUS/Explicit using a combination of structural, fluid and fluid link elements that idealize the air flowing through an orifice behaving as an ideal gas under isothermal conditions. Results between experiment and simulation are compared and show a good correlation.

Finite element simulations of stretch-blow moulding with experimental validation over a broad process window

“…In previous research by the authors [10,25], the amount of air flow rate governing the rate on inflation of the preform was shown to be an important variable. In these experiments the air flow rate could be varied by adjustment of the line pressure and adjustment of a flow restrictor which had dimensionless settings 0 to 6 i.e.…”

“…For the purposes of these trials the line pressure was fixed to 8 bar and the flow restrictor input was set to 2, 4 and 6, corresponding to an air mass flow rate of 9, 23 and 36 g/s respectively. In previous research the evolving cavity temperature was recorded and revealed a quasi-adiabatic 'polytropic' process [25] and it was shown that assuming isothermal conditions was appropriate for accurately capturing the air flow behaviour. Understanding this air flow is critical when forming a suitable FEA simulation.…”

“…This series of pipes, bends and orifices located between the flow control valve and the preform is defined as the 'dead volume' [6,27] and must be accounted for when supplying mass flow values to the simulation. The dead volume for the lab scale SBM machine used for these experiments was measured to be 85 ml using the approach outlined in previous research [25]. The process data collected from experiment trials determined the flow rate characteristics; Fig.…”

Experimental characterisation on the behaviour of PLLA for stretch blowing moulding of bioresorbable vascular scaffolds

“…Based on the successful investigation of stretch blow moulding by free stretch blow for PET bottles [32][33][34][35][36], this article describes a technique for characterising the behaviour of PLLA tubes for stretch blow moulding of BVS. A novel experimental setup by processing tubes within a water bath has been introduced to ensure isothermal conditions, overcoming the surface cooling problems from exposure in the atmosphere during transfer from heating station to blow station.…”

Extrusion Blow Molding Simulation using Cross-Section Technique for Complex Shape Bottles

“…It was hard to control the final thickness of the plastic bottle. Some blow molding methods such as the stretch-blow modling had been simulated using FEM [10][11][12][13]. They had used a preform which was controlled its thickness using the plastic injection method.…”