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Technology Development

Finite Element Analysis of Plastic Containers

At PTI, we have taken the output of Virtual Prototyping™ Modules one step further. Once we predict the thickness distribution of a blow molded container, we also know the mechanical properties of each section of the container as it is related to the degree of orientation that it has undergone. Using both of these outputs, we are now able to predict the performance of the container in a variety of test method simulations. Thus, it is possible to know quite accurately how your container would perform even before blowing a single bottle.

This technique allows you to review a variety of container shapes and geometric features for their efficacy in the performance characteristic that you are looking for.

Top Load Performance

One of the most common attributes that a container is tested for is its Top Load performance. The picture below shows how well the Empty Top Load performance of a 14g 500ml water bottle can be simulated.

Top Load

Container Top Load performance can be different if it is filled or empty. The above was a case where the Empty Top Load performance of the container was simulated. In some cases the container may be partially filled with a liquid and the bulk modulus of the water and increasing pressure of the headspace offers greater resistance to the deformation of the container. Such requirements arise in cases where the containers are filled in the same location they are blown and hence, the empty Top Load strength is not a specification.

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Thermal Stability Performance

A number of beverage containers, most carbonated soft drink containers are designed for withstanding internal pressure. The containers then typically expand slightly when pressurized to the initial carbonation level. However, they are then stored in a relatively hot climate (100°F) for 24 hours to determine if they would rocker (negative base clearance) or grow too much in height and diameter due to the increased pressure and the softer material property at the elevated temperature. With FEA techniques, the performance of the container can be simulated for similar conditions. The initial pressure can be a variable and so can be the storage temperature (as long as it is well within the Glass Transition Temperature of PET).

Thermal Stability

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Creep Performance

A slight variation of the above technique is evaluation of creep performance at elevated temperatures for extended periods of time. Regions of the container that are oriented are typically resistant to creep to a great extent. However, the amorphous regions of the base and finish are more prone to deformation under stress. Our mathematical models allow simulation of such performance characteristics for PET articles.

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Pasteurization Performance

In a number of cases, both carbonated containers (beer type products) and hot-fill products (juices, etc) are filled and then sent through pasteurization tunnels maintained at different temperatures. For beer, the product is typically filled cold and then taken through elevated temperatures. For juice, the product is typically filled hot, capped and cooled through different cooling chambers that allows for part of the headspace to condense and the liquid also changes in density causing development of vacuum that causes the container sidewalls to become prone to buckling. Different geometry and preform weights can be prescribed for determining optimum performance.

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Drop Impact Performance

Often, Containers are dropped accidentally and the last thing you want is to spill the contents after a rupture of the sidewall. With FEA, you can now estimate if a filled and possibly pressurized container is dropped from a range of heights, when failure would occur. The stress levels developed during the impact is linked to the break stress of the material at the contact location and its vicinity to determine if failure would occur. The graphic below shows denting of a petaloid base container upon impact.

Drop Test

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Burst Performance
Burst Failure

Containers that are blown with a preform of optimum weight and appropriate stretch ratio will have good orientation that will help it meet minimum burst specifications. This is also a failure method of performance testing where container geometry, sidewall thickness and mechanical properties play an important role in determining the failure condition. At lower pressures, it can help identify the regions where high stresses have developed and possibly address issues like delamination that occur at specific locations of a pressurized container.

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