Plastic Part Design Properties for Engineers - Water Uptake of Aliphatic Polyamides

Hello and welcome back to a new post. Today we discuss the water and moisture uptake of aliphatic short and long chain Polyamides. In a previous post I discussed the water uptake for high performance polymers - check it out here. Here you can find a collection of all my "Design Properties for Plastics Engineering" posts. 

Properties of Polyamides

In general, Polyamides are often used as engineering material due to their high thermal stability, very good strength and hardness, combined with high mechanical damping characteristics and good chemical resistance. However, all Polyamides are hygroscopic due to the polar amide groups which form hydrogen bonds with water. Water absorption (at a given temperature and relative humidity) is proportional to the amount of amorphous part of the Polyamide. As a consequence, the water acts as a plasticizer and lowers the mechanical properties. At higher temperatures, hydrolysis can take place too. 

How much is the water uptake of aliphatic Polyamides? 

Figure 1 shows the water uptake situation of the most used aliphatic Polyamides at equilibrium in 50% relative humidity and at equilibrium in complete saturation.

Figure 1: Water uptake data of most used aliphatic Polyamides

Long chain aliphatic Polyamides such as PA 6.10, PA 6.12, PA 11, and PA 12 show a lower water absorption compared to PA 6, PA 6.6, and PA 4.6.  Higher dimensional stability, together with low variation in the properties during ambient humidity changes are the result. Major reason for the lower water uptake is the relatively long hydrocarbon chain length (limiting the amide groups to form hydrogen bonds with water).

Important during material selection is the consideration of the  behavior of Polyamides when they are exposed to water (part immersion) or humid environment. The part dimensions need to be still kept within the specified tolerance. 

Thank you for reading and #findoutaboutplastics

Greetings, 

Herwig 

Interested to talk with me about your plastic selection, sustainability, and part design needs - here you can contact me 

Interested in my monthly blog posts – then subscribe here and receive my high performance polymers knowledge matrix.

New to my Find Out About Plastics Blog – check out the start here section

My YouTube channel

Literature:

[1] https://www.findoutaboutplastics.com/2020/12/design-properties-for-engineers-water.html

[2] https://www.sciencedirect.com/science/article/pii/S2590048X20300911

[3] https://www.hanser-elibrary.com/doi/book/10.3139/9783446437296

The Penguin Circle - A Symbol For Teamwork and Leadership

Hello and welcome to a new post. Today we have leadership and teamwork as the main topic, always in relation to the plastics industry. Read my leadership series here. 

The Penguin Circle - Teamwork and Leadership (Findoutaboutplastics.com / Herwig Juster)

Penguins - fighting the chilling freeze by huddling

Emperor penguins have their home in the Antarctic which is known to be a harsh environment with chilling temperatures. Penguins huddle together to heat up and stay warm. They also take turns to be in the center of the huddle. Researchers found it can get up to 37°C in the center of the huddle which can be too hot for the penguins. Also for breeding the circle formation is important since the male penguin takes care of the egg which is placed between the legs. 

Why is the Penguin circle so important?

What is valid for penguins is also valid for us: forming circles and huddling protects us from harsh cold conditions. It is better to be in the circle, otherwise you will freeze and face the danger of not surviving. The circle has several meanings. Most of us know the “Circle of Life” philosophy (life starts at the end and ends in the beginning), however the aforementioned penguin example shows the circle as a powerful symbol for teamwork and reaching goals together. 

Plastics industry - is the circle closed? 

In our plastics industry environment, tasks became complex and multi-leveled so that working together in teams is essential. It is in particular the interfaces between project stages, product development stages or production that bring challenges. It is well reported that other industries such as automotive, have to deal most of the time with interface challenges. Also, circular economy embraces to keep polymers in a loop.

Altogether, developing a feeling and empathy for the other working areas will help to close the circle and make the upcoming tasks more successful. 

Thanks for reading and #findoutaboutplastics

Greetings, 

Herwig 

#findoutaboutplastics

Interested to talk with me about your plastic selection, sustainability, and part design needs - here you can contact me 

Interested in my monthly blog posts – then subscribe here and receive my high performance polymers knowledge matrix.

New to my Find Out About Plastics Blog – check out the start here section

My YouTube channel

Literature:

[1] https://www.gizmodo.com.au/2015/12/the-social-dynamics-of-penguin-huddles-are-more-complex-than-we-thought/

[2] https://theconversation.com/curious-kids-how-can-penguins-stay-warm-in-the-freezing-cold-waters-of-antarctica-116831#:~:text=Male%20emperor%20penguins%20gather%20close,huddle%20is%20below%20%2D30%E2%84%83.

6 Major Benefits of Injection Moulding Simulation in Polymer Part Design and Material Selection

Hello and welcome to a new blog post. Today we have a closer look at how injection molding simulations support us in part design, polymer material selection and processing.

1. Injection point and gate placement

Finding the optimal injection point and gating is key to fulfill certain aesthetics or warpage requirements. Also, it helps to prevent flow line situations and as a consequence lower mechanical performance of your part. Nowadays most polymer injection molding simulations have gate placement tools integrated which can recommend you the optimal injection point. 

2. Placement and balancing of runners

Bringing the molten polymers towards the cavity, runners (thin channels) are needed. Aim is to ensure an even filling of your cavity. Runner analysis is hand in hand with the gating analysis from the previous point and most simulation software have a runner balance tool too. 

3. Warpage and shrinkage situation 

Analyzing the shrinkage and warpage situation is in particular needed when you use fiber-reinforced polymers which have an effect on the shrinkage and warpage of your part. Filling simulation can use the information of the velocity vectors to predict fiber behavior in the final part. And over this route, calculate the effect on shrinkage and warpage. 

4. Packing situation 

Analyzing the packing situation allows you to set the packing pressure and time for your part. There are several factors such as the material and mould shape which are influencing the packing. Packing analysis covers the prediction of the gate freeze time, clamping force needed in this phase, and predict areas where high volumetric shrinkage may appear. 

5. Cooling - mold 

There are injection moulding simulation tools which allow a design and optimization of the cooling channel layout of your moving and fixed moulding half. However, most tools simulate a uniform mould cooling at a set temperature.

6. Processing - identify critical shear rates

In case you work with polymers which are sensitive to mechanical stresses like shear rates then it is worth to have a plan of action how to locate critical areas and solve them by using simulation or in a simple way with analytic methods.

In the video I made you can see the perforated plate in the version of side gating and central gating. This applied method of shear rate tracer release is possible in the virtual molding package Sigmasoft.

In the following are the four steps of my procedure I use in the post-processing after I have done a process simulation:

1) Watch the shear rate contour plot to get the "big picture"

2) Activate the shear rate tracer

3) Analyze the release places and where the sheared material will end up in the part (to predict if there will be a decrease in the mechanical properties of the part)

4) Make geometry changes or process changes (melt temperature; inlet velocity profile)

The shear rate tracer method helps you to locate the punctual critical areas. So far, those are the advantages of such an approach. Another aspect is that the allover simulation will take more time and more memory as well as more working space.

In detail you can read here about my shear rate analysis. 

What are some of the most used injection moulding simulations?

There are several suppliers and often used are Autodesk Moldflow, SIGMASOFT Virtual Molding, Moldex3D, Vero VISI Flow, Simcon CadMould, and Solidworks Plastics.

Thanks for reading and till next time!

Greetings,

Herwig 

#findoutaboutplastics

Interested to talk with me about your plastic selection, sustainability, and part design needs - here you can contact me 

Interested in my monthly blog posts – then subscribe here and receive my high performance polymers knowledge matrix.

New to my Find Out About Plastics Blog – check out the start here section

My YouTube channel

Literature: 

[1] https://www.findoutaboutplastics.com/2015/04/injection-molding-filling-simulation-my.html

[2] https://www.findoutaboutplastics.com/2018/01/data-is-new-plastic-data-algorithms-in.html

[3] https://www.findoutaboutplastics.com/2021/03/the-future-of-plastics-manufacturing.html

[4]https://www.3erp.com/blog/how-injection-molding-simulation-software-helps-you-design-better-parts/

[5] https://www.downloadcloud.com/injection-molding-software.html