Oluschinski: Created page with "{{Language_sel|LANG=ger|ARTIKEL=Vakuolen}} {{PSM_Infobox}} Schrink Voids FORCETOC ==General information== The terms “vacuoles”, “shrink holes” and “vacuences” are also used synonymously in Anglo-Saxon literature. During the injection moulding process, a volume contraction (shrinkage) occurs when the moulded part (see: moulding compounds) cools in t..."

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Created page with "{{Language_sel|LANG=ger|ARTIKEL=Vakuolen}} {{PSM_Infobox}} <span style="font-size:1.2em;font-weight:bold;">Schrink Voids</span> __FORCETOC__ ==General information== The terms “vacuoles”, “shrink holes” and “vacuences” are also used synonymously in Anglo-Saxon literature. During the injection moulding process, a volume contraction (shrinkage) occurs when the moulded part (see: moulding compounds) cools in t..."

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{{Language_sel|LANG=ger|ARTIKEL=Vakuolen}}
{{PSM_Infobox}}
<span style="font-size:1.2em;font-weight:bold;">Schrink Voids</span>
__FORCETOC__

==General information==

The terms “vacuoles”, “shrink holes” and “vacuences” are also used synonymously in Anglo-Saxon literature.

During the injection moulding process, a volume contraction ([[Processing Shrinkage|shrinkage]]) occurs when the moulded part (see: [[Moulding Compound|moulding compounds]]) cools in the mould, whereby a residual compressive stress is built up in the edge areas and a [[Tensile Test Residual Stresses Orientations|residual tensile stress]] in the interior. This volume contraction of the melt is increased in areas of mass accumulation, as the reducing volume cannot be replaced by new melt.

==Process of shrink voids (vacuoles) formation==

Shrink voids (vacuoles), also known as blowholes (cavities) in [[Non-destructive Testing (NDT)|non-destructive testing (NDT)]], occur when the solidified surface layer has sufficient stability to counteract the internal tendency to contract. Due to the [[Tensile Test Residual Stresses Orientations|residual tensile stresses]] acting internally, the [[Moulding Compound|moulding compound]] tears open in the centre of material accumulations and [[Hole Formation Plastics|holes]] are formed ('''Fig. 1'''). As a result of the negative pressure, the holes have a jagged surface and are irregularly shaped. They differ very clearly from the [[Gas Bubbles|gas bubbles]] ('''Fig. 2''').

Shrink voids are formed in particular when the processing conditions or the mould and/or component design are not optimal. The main causes for the formation of shrink voids are too low a mould temperature, too low an effective holding pressure, a holding pressure time that is too short, bottlenecks in the flow path, an incorrect gate position (in the thin-walled area) or a gate that is too small [1, 2].

[[file:Shrink Voids 1.jpg|500px]]
{|
|- valign="top"
|width="50px"|'''Fig. 1''':
|width="600px" |Shrink voids at injection moulded [[Plastic Component|components]] in the range of material accumulations, a) Example of [2] PBT-GF, b) Example of [3] PA/PTFE-piston ring
|}

[[file:Shrink Voids 2.jpg|500px]]
{|
|- valign="top"
|width="50px"|'''Fig. 2''':
|width="600px" |Shrink voids on the [[Fracture Surface|fracture surface]] of a clip of polyoxymethylene ([[Plastics – Symbols and Abbreviated Terms|abbreviation]]: POM), a) light microscopical picture, b) [[Scanning Electron Microscopy|REM]] picture
|}

Very small shrink voids (vacuoles) are called [[Micropores | micropores]].

==See also==

*[[Sink Mark | Sink mark]]
*[[Micropores]]
*[[Hole Formation Films|Hole formation films]]
*[[Hole Formation Plastics|Hole formation plastics]]
*[[Failure Analysis Plastic Products, VDI Guideline 3822|Failure analysis plastic products, VDI Guideline 3822]]
*[[Weld Line | Weld line]]

'''References'''

{|
|-valign="top"
|[1]
|VDI 3822, Blatt 2.1.1 (2024-06): Failure Analysis – Defects of Thermoplastic Products Made of Plastics Caused by Faulty Design
|-valign="top"
|[2]
|VDI 3822, Blatt 2.1.2 (2024-06): Failure Analysis – Defects of Thermoplastic Products; Made of Plastics caused by Faulty Processing and Corrigendum Concerning Guideline Part 2.1.2 (2012-04)
|-valign="top"
|[3]
|Kurr, F.: Praxishandbuch der Qualitäts- und Schadensanalyse für Kunststoffe. Carl Hanser Munich (2014), (ISBN 978-3-446-43775-3; see [[AMK-Büchersammlung | AMK-Library]] under D 6-2)
|}

'''Additional literature references on plastics diagnostics/damage analysis'''

* [[Ehrenstein,_Gottfried_W.|Ehrenstein, G. W.]]: Präparation. Unverstärkte, hochgefüllte und verstärkte Kunststoffe – Ätzen für Strukturunterbrechungen. Erlanger Kunststoff-Schadenanalyse. Carl Hanser Munich (2019) (ISDN 978-3-446-40382-6; e-Book ISBN 978-3-446-46054-6; see [[AMK-Büchersammlung | AMK-Library]] under F 27)
* Ehrenstein, G. W.: Kunststoff-Schadensanalyse – Methoden und Verfahren. Carl Hanser Munich, Vienna (1992) (ISBN 978-3-446-17329-3; see [[AMK-Büchersammlung | AMK-Library]] under D 2)
* Ehrenstein, G. W.: SEM of Plastics Failure – REM von Kunststoffschäden. Carl Hanser Munich (2010) (ISBN 978-3-446-42242-1; see [[AMK-Büchersammlung | AMK-Library]] under D 5)
* Engel, L., Klingele, H., Ehrenstein, G. W., Schaper, H.: Rasterelektronenmikroskopische Untersuchungen von Kunststoffschäden. Carl Hanser Munich, Vienna (1978) 1st Edition (ISBN 978-3-446-12560-5, see [[AMK-Büchersammlung | AMK-Library]] under D 8)
* Brostow, W., Corneliussen, R. D.: Failure of Plastics. Carl Hanser Munich, Vienna (1986) (ISBN 978-3-446-14199-5; see [[AMK-Büchersammlung | AMK-Library]] under D 10)
* Ezrin, Myer: Plastics Failure Guide – Cause and Prevention. Carl Hanser Munich, 2nd Edition (2013) (ISBN 978-1-56990-449-7; see [[AMK-Büchersammlung | AMK-Library]] under D 7)

[[Category:Damage Analysis_Component Failure]]

Shrink Voids - Revision history