Effect of foam processing parameters on bubble nucleation and growth dynamics in high-pressure foam injection molding

2016 ◽  
Vol 155 ◽  
pp. 27-37 ◽  
Author(s):  
Vahid Shaayegan ◽  
Guilong Wang ◽  
Chul B. Park
Keyword(s):  
High Pressure ◽  
Injection Molding ◽  
Growth Dynamics ◽  
Processing Parameters ◽  
Nucleation And Growth ◽  
Bubble Nucleation ◽  
Foam Injection Molding

Process comparison on the microstructure and mechanical properties of fiber-reinforced polyphenylene sulfide using MuCell technology

2018 ◽  
Vol 37 (15) ◽  
pp. 1020-1034 ◽  
Author(s):  
Christoph Lohr ◽  
Björn Beck ◽  
Frank Henning ◽  
Kay André Weidenmann ◽  
Peter Elsner
Keyword(s):  
Mechanical Properties ◽  
High Pressure ◽  
Injection Molding ◽  
Fiber Orientation ◽  
Polyphenylene Sulfide ◽  
Injection Molding Process ◽  
Fiber Reinforced ◽  
Molding Process ◽  
Glass Fiber Reinforced ◽  
Foam Injection Molding

The MuCell process is a special injection molding process which utilizes supercritical gas (nitrogen) to create integral foam sandwiches. The advantages are lower weight, higher specific properties and shorter cycle times. In this study, a series of glass fiber-reinforced polyphenylene sulfide foam blanks are manufactured using the MuCell injection molding process. The different variations of the process (low-pressure also known as structural foam injection molding) and high-pressure foam injection molding (also known as “core back expansion,” “breathing mold,” “precision opening,” decompression molding) are used. The sandwich structure and mechanical properties (tensile strength, bending strength, and impact behavior) of the microcellular and glass fiber-reinforced polyphenylene sulfide foams are systematically investigated and compared to compact material. The results showed that the injection parameters (injection speed, foaming mechanism) played an important role in the relative density of microcellular polyphenylene sulfide foams and the mechanical properties. It could be shown that the specific tensile strength decreased while increasing the degree of foaming which can be explained by the increased number of cells and the resulting cell size. This leads to stress peaks which lower the mechanical properties. The Charpy impact strength shows a significant dependence on the fiber orientation. The specific bending modulus of the high-pressure foaming process, however, surpasses the values of the other two processes showing the potential of this manufacturing variation especially with regard to bending loads. Furthermore, a high dependence of the mechanical properties on the fiber orientation of the tested specimens can be found.

Preparation of open microcellular polylactic acid foams with a microfibrillar additive using coreback foam injection molding processes

2018 ◽  
Vol 54 (4) ◽  
pp. 765-784 ◽  
Author(s):  
Shota Ishihara ◽  
Yuta Hikima ◽  
Masahiro Ohshima
Keyword(s):  
Injection Molding ◽  
Polylactic Acid ◽  
Bubble Nucleation ◽  
Number Density ◽  
Cell Content ◽  
Open Cell ◽  
Cooling Conditions ◽  
Nucleation Sites ◽  
Fast Cooling ◽  
Foam Injection Molding

Open microcellular polylactic acid foams with a fibrous polytetrafluoroethylene additive were prepared by a coreback foam injection molding technique. The effects of this fibrous additive on the foam cell structure were investigated. Fibrous polytetrafluoroethylene forms a network structure in polylactic acid in metering and mixing processes. The fibrous polytetrafluoroethylene network increased the viscoelasticity of polylactic acid and provided polylactic acid with a strain-hardening property. The network also provided heterogeneous bubble nucleation sites for physical foaming. However, because of the slow crystallization rate of polylactic acid, the fibrous polytetrafluoroethylene additive did not promote the nucleation of polylactic acid crystals under fast cooling conditions. During fast cooling, such as injection molding cooling conditions, the crystals induced by the fibrous polytetrafluoroethylene network could not behave as bubble nucleation sites. Thus, changes in rheological properties and the increased number of heterogeneous sites contributed to the decrease in cell size, the increase in the number density of cells and the increase in the open cell content. As the number density of cells increased, the cell walls with the fibrous polytetrafluoroethylene fibrous additive became so thin that they could be easily fibrillated by a stretching operation during the coreback operation, while their strain-hardening property prevented the walls from complete breakage. Synergistically conducting cell reduction and stretching (coreback) operations, high expansion ratio foams with high open cell content were prepared. When we adjusted the foaming temperature and holding time, five-fold expansion (i.e. 80% void ratio) foams with cell diameters less than 25 µm and open cell contents (OCC) higher than 80% were produced.

Investigation of the mold-filling phenomenon in high-pressure foam injection molding and its effects on the cellular structure in expanded foams

Polymer ◽  
2019 ◽  
Vol 160 ◽  
pp. 43-52 ◽  
Author(s):  
Mike Tromm ◽  
Vahid Shaayegan ◽  
Chongda Wang ◽  
Hans-Peter Heim ◽  
Chul B. Park
Keyword(s):  
High Pressure ◽  
Injection Molding ◽  
Cellular Structure ◽  
Mold Filling ◽  
Foam Injection Molding

The critical requirement for high-pressure foam injection molding with supercritical fluid

Polymer ◽  
2021 ◽  
pp. 124388
Author(s):  
Chongda Wang ◽  
Vahid Shaayegan ◽  
Franco Costa ◽  
Sejin Han ◽  
Chul B. Park
Keyword(s):  
High Pressure ◽  
Injection Molding ◽  
Supercritical Fluid ◽  
Critical Requirement ◽  
Foam Injection Molding

scholarly journals Can nanolites enhance eruption explosivity?

Geology ◽  
2020 ◽  
Vol 48 (10) ◽  
pp. 997-1001 ◽  
Author(s):  
Francisco Cáceres ◽  
Fabian B. Wadsworth ◽  
Bettina Scheu ◽  
Mathieu Colombier ◽  
Claudio Madonna ◽  
...  
Keyword(s):  
Volcanic Rocks ◽  
Growth Dynamics ◽  
Nucleation And Growth ◽  
Bubble Nucleation ◽  
Magma Ascent ◽  
Primary Control ◽  
Number Density ◽  
Starting Conditions ◽  
Bubble Number ◽  
Bubble Number Density

Abstract Degassing dynamics play a crucial role in controlling the explosivity of magma at erupting volcanoes. Degassing of magmatic water typically involves bubble nucleation and growth, which drive magma ascent. Crystals suspended in magma may influence both nucleation and growth of bubbles. Micron- to centimeter-sized crystals can cause heterogeneous bubble nucleation and facilitate bubble coalescence. Nanometer-scale crystalline phases, so-called “nanolites”, are an underreported phenomenon in erupting magma and could exert a primary control on the eruptive style of silicic volcanoes. Yet the influence of nanolites on degassing processes remains wholly uninvestigated. In order to test the influence of nanolites on bubble nucleation and growth dynamics, we use an experimental approach to document how nanolites can increase the bubble number density and affect growth kinetics in a degassing nanolite-bearing silicic magma. We then examine a compilation of these values from natural volcanic rocks from explosive eruptions leading to the inference that some very high naturally occurring bubble number densities could be associated with the presence of magmatic nanolites. Finally, using a numerical magma ascent model, we show that for reasonable starting conditions for silicic eruptions, an increase in the resulting bubble number density associated with nanolites could push an eruption that would otherwise be effusive into the conditions required for explosive behavior.

Influence of supramolecular additives on foam morphology of injection-molded i-PP

2011 ◽  
Vol 47 (6) ◽  
pp. 519-534 ◽  
Author(s):  
Marieluise Stumpf ◽  
Andreas Spörrer ◽  
Hans-Werner Schmidt ◽  
Volker Altstädt
Keyword(s):  
Mechanical Properties ◽  
Injection Molding ◽  
Control Cell ◽  
Large Cell ◽  
Processing Parameters ◽  
Expansion Ratio ◽  
Foam Formation ◽  
Nucleating Agents ◽  
Foam Morphology ◽  
Foam Injection Molding

Foaming isotactic polypropylene (i-PP) by foam injection molding usually results in inhomogeneous, large cell structures. Possibilities to realize more homogeneous and finer foam morphologies are adjusting processing parameters or adding nucleating agents. Often, inorganic nucleating agents such as talc in concentrations of about 2 wt% are used to influence the foam morphology. This article discusses the use of two benzene trisamide-based nucleating agents to control cell nucleation during foaming of i-PP. These additives form supramolecular nanostructures in the polymer melt acting first as nucleating sites for foam formation and second as nuclei for the polymer crystallization. Foaming was performed by foam injection molding with nitrogen as physical blowing agent. A specially designed variotherm mold technology was utilized to exactly control the foaming temperature, foaming pressure, and expansion ratio. Foamed i-PP samples were prepared with a density reduction of 50% and analyzed with respect to foam structure and mechanical properties. We demonstrate that the benzene trisamide additives have a strong influence on the foam morphology at very low additive concentrations. Only 0.02 wt% of an additive is sufficient to obtain a remarkable reduction of the cell sizes. It appears that the cell struts, those dimensions can be influenced by the additives as well, leads to a significant improvement of the mechanical properties.

scholarly journals Development of Foam Injection Molding Technology without High Pressure Equipment

Seikei-Kakou ◽  
2018 ◽  
Vol 30 (6) ◽  
pp. 234-238
Author(s):  
Atsushi Yusa ◽  
Satoshi Yamamoto ◽  
Hideto Goto
Keyword(s):  
High Pressure ◽  
Injection Molding ◽  
Foam Injection Molding ◽  
High Pressure Equipment

Accurate theoretical modeling of cell growth by comparing with visualized data in high-pressure foam injection molding

2019 ◽  
Vol 119 ◽  
pp. 189-199 ◽  
Author(s):  
Chongda Wang ◽  
Vahid Shaayegan ◽  
Mohammadmehdi Ataei ◽  
Franco Costa ◽  
Sejin Han ◽  
...  
Keyword(s):  
High Pressure ◽  
Cell Growth ◽  
Injection Molding ◽  
Theoretical Modeling ◽  
Foam Injection Molding
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