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Created page with "{{Language_sel|LANG=ger|ARTIKEL=Einfallstelle}} {{PSM_Infobox}} <span style="font-size:1.2em;font-weight:bold;">Sink mark</span> In the injection moulding process of plastic components, a volume contraction ( shrinkage) occurs during cooling. In areas of mass accumulation or large wall thicknesses, this volume contraction of the melt is increased, whereby the reducing volume cannot be replaced by new melt as the injection channel has already so..."
 
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{{PSM_Infobox}}
{{PSM_Infobox}}
<span style="font-size:1.2em;font-weight:bold;">Sink mark</span>
<span style="font-size:1.2em;font-weight:bold;">Sink mark</span>
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In the injection moulding process of plastic components, a volume contraction ([[Processing Shrinkage | shrinkage]]) occurs during cooling. In areas of mass accumulation or large wall thicknesses, this volume contraction of the melt is increased, whereby the reducing volume cannot be replaced by new melt as the injection channel has already solidified. [[Tensile Mechanical Stresses Orientations | Tensile residual stresses]] are therefore built up inside. If there is a sufficiently thick surface layer, central cavities can form as a result of the internal tensile stresses. However, if the solidified surface layer is not yet stable enough to counteract the internal tendency to contract, the surface is deformed inwards and sink marks or depressions form on the surface of the moulded part.
==General information==


These sink marks occur in particular on larger mass accumulations or with greater wall thicknesses [3].
In the injection moulding process of plastic components, a volume contraction ([[Processing Shrinkage | shrinkage]]) occurs during cooling. In areas of mass accumulation or large wall thicknesses, this volume contraction of the melt is increased, whereby the reducing volume cannot be replaced by new melt as the injection channel has already solidified. [[Tensile Test Residual Stresses Orientations|Tensile residual stresses]] are therefore built up inside.
 
==Causes for formation==
 
If there is a sufficiently thick surface layer, central cavities can form as a result of the internal tensile stresses. However, if the solidified surface layer is not yet stable enough to counteract the internal tendency to contract, the surface is deformed inwards and sink marks or depressions form on the surface of the moulded part.
 
These sink marks occur in particular on larger mass accumulations or with greater wall thicknesses [1].
 
==Examples of plastic components==


Sink marks can be avoided by designing the construction to be plastic-compatible, i.e. by making the wall thickness as thin as possible, providing equal wall thicknesses and avoiding mass accumulations.
Sink marks can be avoided by designing the construction to be plastic-compatible, i.e. by making the wall thickness as thin as possible, providing equal wall thicknesses and avoiding mass accumulations.
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|- valign="top"
|width="50px"|'''Fig. 1''':  
|width="50px"|'''Fig. 1''':  
|width="600px" |Sink marks at injection moulded components in the range of material                accumulations, a) Example of [1], b) Example of [2] PA11-Clip
|width="600px" |Sink marks at injection moulded components in the range of material                accumulations, a) Example of [2], b) Example of [3] PA11-Clip
|}
|}


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==See also==
==See also==


*[[Shrink Voids | Shrink voids]]
*[[Failure Analysis – Basics|Failure analysis – Basics]]
*[[Tensile Mechanical Stresses Orientations | Tensile mechanical stresses orientations]]
*[[Failure Analysis Plastics Products, VDI Guideline 3822|Failure analysis plastics products, VDI Guideline 3822]]
*[[Shrink Voids|Shrink voids]]
*[[Weld Line | Weld line]]
*[[Weld Line | Weld line]]
*[[Gas Bubbles|Gas bubbles]]


 
==References==
'''References'''


{|
{|
|-valign="top"
|-valign="top"
|[1]
|[1]
|VDI 3822, Part 2.1.2 (2012-01): Failure Analysis – Defects of Thermoplastic Products made of Plastics caused by Faulty Processing and Corrigendum Concerning Guideline Part 2.1.2 (2012-04)
|Ezrin, M.: Plastics Failure Guide – Cause and Prevention. Carl Hanser Munich, 2nd Edition (2013) (ISBN 978-1-56990-449-7; see [[AMK-Library]] under D 7)
|-valign="top"
|-valign="top"
|[2]
|[2]
|Kurr, F.: Praxishandbuch der Qualitäts- und Schadensanalyse für Kunststoffe. Carl Hanser Verlag, München (2014) (ISBN 978-3-446-43775-3; see [[AMK-Büchersammlung | AMK-Library]] under D 6-2)
|VDI 3822, Part 2.1.2 (2012-01): 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"
|-valign="top"
|[3]
|[3]
|Ezrin, M.: 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)
|Kurr, F.: Praxishandbuch der Qualitäts- und Schadensanalyse für Kunststoffe. Carl Hanser Verlag, München (2014) (ISBN 978-3-446-43775-3; see [[AMK-Library]] under D 6-2)
|}
|}


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


*[[Ehrenstein,_Gottfried_W.|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,_Gottfried_W.|Ehrenstein, G. W.]]: Kunststoff-Schadensanalyse – Methoden und Verfahren. Carl Hanser Munich, Vienna (1992) (ISBN 978-3-446-17329-3; see [[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)
*Ehrenstein, G. W.: SEM of Plastics Failure – REM von Kunststoffschäden. Carl Hanser Munich (2010)(ISBN 978-3-446-42242-1; see [[AMK-Library]] under D 5)
*Engel, D., Klingele, H., Ehrenstein, G. W., Schaper, H.: Rasterelektronenmikroskopische Untersuchungen von Kunststoffschäden.  Carl Hanser Munich, Vienna (1978) 1. Edition (ISBN 978-3-446-12560-5, see [[AMK-Büchersammlung | AMK-Library]] under D 8)
*Engel, D., Klingele, H., Ehrenstein, G. W., Schaper, H.: Rasterelektronenmikroskopische Untersuchungen von Kunststoffschäden.  Carl Hanser Munich, Vienna (1978) 1. Edition (ISBN 978-3-446-12560-5, see [[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)
*Brostow, W., Corneliussen, R. D.: Failure of Plastics. Carl Hanser Munich, Vienna (1986) (ISBN 978-3-446-14199-5; see [[AMK-Library]] under D 10)


[[Category:Surface Testing Technology]]
[[Category:Surface Testing Technology]]
[[Category:Damage Analysis_Component Failure]]
[[Category:Damage Analysis_Component Failure]]

Latest revision as of 10:47, 7 September 2026

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Sink mark


General information

In the injection moulding process of plastic components, a volume contraction ( shrinkage) occurs during cooling. In areas of mass accumulation or large wall thicknesses, this volume contraction of the melt is increased, whereby the reducing volume cannot be replaced by new melt as the injection channel has already solidified. Tensile residual stresses are therefore built up inside.

Causes for formation

If there is a sufficiently thick surface layer, central cavities can form as a result of the internal tensile stresses. However, if the solidified surface layer is not yet stable enough to counteract the internal tendency to contract, the surface is deformed inwards and sink marks or depressions form on the surface of the moulded part.

These sink marks occur in particular on larger mass accumulations or with greater wall thicknesses [1].

Examples of plastic components

Sink marks can be avoided by designing the construction to be plastic-compatible, i.e. by making the wall thickness as thin as possible, providing equal wall thicknesses and avoiding mass accumulations.

Fig. 1: Sink marks at injection moulded components in the range of material accumulations, a) Example of [2], b) Example of [3] PA11-Clip

Fig. 2: Sink marks at injection moulded components of PC/ABS in the range of material accumulations (rips)

See also

References

[1] Ezrin, M.: Plastics Failure Guide – Cause and Prevention. Carl Hanser Munich, 2nd Edition (2013) (ISBN 978-1-56990-449-7; see AMK-Library under D 7)
[2] VDI 3822, Part 2.1.2 (2012-01): Failure Analysis – Defects of Thermoplastic Products made of Plastics caused by Faulty Processing and Corrigendum Concerning Guideline Part 2.1.2 (2012-04)
[3] Kurr, F.: Praxishandbuch der Qualitäts- und Schadensanalyse für Kunststoffe. Carl Hanser Verlag, München (2014) (ISBN 978-3-446-43775-3; see AMK-Library under D 6-2)

Additional literature references on plastic diagnostics/damage analysis

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