Their advancements have also allowed their finite element analysis (FEA) software to improve. The primary software used during their years of research has been Abaqus FEA software. “No matter what the product, the behavior of the polymer material is the most difficult aspect to model when you are trying to simulate how it inflates,” said Menary. “Abaqus gave us the ability to code our own material models and customize our analysis. Abaqus simulations provided the necessary scientific approach that takes material characteristics into account when creating and evaluating designs.”
Overall, the team now has a deeper understanding of blow molding. Experiments have helped them calibrate and fine-tune their software models and better understand the distribution of pressure. However, there are still areas Menary would like to improve upon.
Free blow experiment on an instrumented, marked PET bottle prototype allowed a perfect synchronization between force, displacement, and pressure measurements of the stretching and blowing stages of the bottle blowing process. Above are results from image capture using a high-sampling rate video camera and the corresponding predictions from the Abaqus FEA simulation. Contours are of axial strain. (Source: Queen’s University Belfast)
“There are still things we don't fully understand, such as the contact issues between the PET and the mold, and the heat transfer conditions,” Menary said. “When the hot polymer touches the cold mold there is a heat transfer as well as a frictional behavior. There's also temperature-dependent slippage between the polymer and the mold. All these are the focus of our simulation work at the moment.”
In the future, the team hopes they can expand their knowledge to more applications beyond plastic molding such as with the medical devices. As for now the team is continuing to develop and better understand technologies associated with bottle molding and other related materials. It is amazing to see how much work can go into something we use so often.
Yeah, I think they got the blow-balance perfected, and have not changed it. Think how long you've been seeing the same bottles on the store shelves.
Altho, I specifically recall a time when the clear bottles ALL had a BLACK or GREEN or RED opaque base element, glued to the bottom to avoid wobble or tip-over. I guess those extra parts were phased-out after the first 20 million or so bottles proved to be "stable enough".
I remember, (probably 25 years ago – perhaps 1987), when a designer associate of mine returned from visiting a potential New supplier, who did Plastic injection molding. He brought back a sample part, which was the molded slug used for placement into the blow-molding application you have showcased here. This injection molded part had the molded-in threads for the bottle cap, and the precise volume and shape of the material needed to 'seed' the blow-molding operation, as you have described. As my associate passed around this clear, threaded, solid, phallic-looking slug, several 'guesses' were offered as to what it was – but no-one guessed correctly; that it was the seed-part for a blow-molded Coke Bottle!!
TJ, it is also possible that there are others who read this blog, or write for Design News, or read it, who may be in a position to do such a write up. and it may be possible that the bottling company wouldlike a chance to show off their superior technology.
And there also exists the possibility that some automation company that produces bottling equipment or bottle producing equipment wouldappreciate a chance to tell a lot of folks how great their systems are.
TJ, the first machine that I worked on had a cycle timeof ten seconds, for a gallon PE bottle. My guess is that the soft drink machines are a whole lot different. That wold make a good writeup, if anybody is seeking hints for topics.
Like most folks,Ihad not considered the complexity of the blowmolding process until I was called upon to do a major upgrade replacement oof the parison controllers on some blowmolding machines. The process is quite complex, since that glob of hot plastic, ( called the parison), is extruded with a variable thickness from a carefully controlled size shot of hot plastic, which is delivered by a mechanism sort of similar to an injection molding machine. The thickness is set at close intervals, either by time or by the displacement of the injector piston. At each point the opening of the injection control valve poppet is monitored and set according to the program. And that setting can be set, typically for every 2% to 5% of the bottles height. And since the control is done before the bottle mold is closed, the process is often iterative, starting with an educated "best guess", at least in some bottle plants. so the whole process would certainly benefit from greater understanding, and possibly closer control.
Nice discussion of all the multiple process variables encountered during bottle molding. Its amazing how we take for granted these everyday processes and don't realize just how much engineering goes into them. Did not consider that frictional heat effects could also have a significant influence on this process.
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