Today's KNOWLEDGE Share:Mold Coatings:

-

Today's KNOWLEDGE Share:

Mold Coatings:

If you browse through the documentation of mold coating suppliers (PVD, WS2, others) they all claim better flow (i.e. lower pressure to fill) after coating the mold with just a few microns of their coating (typically a metal oxide, salt, or some other complex).





These layers do impart lubricity indeed, which is great to help ejection of the molded part.

But in Injection Molding there is no slip against the wall. Actually if/when you get some, you invariably end up with a surface defect !

So improved lubricity, as claimed by suppliers, DOES NOT explain better flow.


What is most probably happening is that the added layer, which is not "metallic" has always a lower Thermal Effusivity.

Effusivity is the material property that controls interfacial temperature.

So what we really have here is a slightly thinner frozen skin resulting from a somewhat higher interfacial temperature between plastic and coated steel. In a flat flow, effective available thickness for flow has a quadratic effect on pressure drop. For a runner/gate (cylinder) it is even a cubic dependence.

So the smallest reduction in the frozen layer, especially for thin cavities, can immediately explain the observed 5-10 % decrease in pressure drop (or, conversely, increase in flow length).


Source:VITO LEO

Visit MY BLOG http://polymerguru.blogspot.com


#plastics #injectionmolding #runner #gate #moldflow #coatings #lubrication #polymerscience #moldfilling #frozen #lowcoeffient

Comments

Post a Comment

Popular posts from this blog

Today's KNOWLEDGE Share:PLA BOTTLE

-
Image
Today's KNOWLEDGE Share Ever wondered how we can reduce plastic pollution in India? The Mysuru-based Defence Food Research Laboratory (DFRL), affiliated with the DRDO, has launched an eco-friendly remedy with the introduction of biodegradable water bottles. Crafted from sustainable Polylactic acid (PLA) material, these bottles not only combat plastic waste but also contribute to reducing the overall carbon footprint. The best thing about this bottle is its all-encompassing sustainability approach – the bottle, cap, and label are all compostable. This innovation, derived from 100% bio-based and renewable sources, sets us on a path towards environmental conservation and fosters a greener and more sustainable future. Source:The Better India #polymers #bioplastics #pla   #compostable   #ecofriendly   #sustainability
Read more

Today's KNOWLEDGE Share:High and low shear rate changes in Rheology

-
Image
Today's KNOWLEDGE Share If a relatively high Mw grade flows from thin to thick, as shown in the picture, and if the time needed to fill the thick section is way shorter than the average polymer relaxation time, the polymer will not be able to reach its higher viscosity (corresponding to higher thickness/lower shear-rate). I am assuming here the polymer reached equilibrium low viscosity in the thin section, say for instance because it is much longer. Any pressure prediction not accounting for transient rheology would then overpredict the pressure to fill.Of course the diverging flow will further complicate the situation and mess with the molecular orientation created in the thin section, but to what extent ? Since this is more of a reasonable "conjecture", don't take this for granted, and discuss or share your opinion in the comments. There are hundreds of Rheology papers on the "4:1 contraction flow". Not sure I have ever seen any on the..."1:4 expansio
Read more

Today's KNOWLEDGE Share : biobased content of polycarbonate diols

-
Image
Today's KNOWLEDGE Share MCG increases biomass content of polycarbonate diols Mitsubishi Chemical Group (MCG) has introduced grades of its Benebiol biomass-based polycarbonate diols that have a higher biomass content. The product is primarily used in the manufacture of polyurethane resins for coatings in sectors such as automotive, furniture and outdoor products. It is also used in the production of artificial leather. Existing Benebiol grades had a bio-based content of 20-50%, but the new HSS and NLDS grades have a biomass content in excess of 80%. Some of its previous petroleum-derived grades have also been converted to biomass, as the NLS grades. This, the company said, allows it to offer bio-based grades of all its Benebiol products. The shift to biomass-based raw materials while maintaining high-quality functions will contribute to our customers’ efforts to achieve sustainable manufacturing. source:MCG/www.utech-polyurethane.com
Read more