Thursday 27 August 2020

Design Properties for Engineers: Transition Temperatures (Tg, Tm, CUT) of High Performance Polymers

Today we discuss the major thermal transition temperatures of high performance polymers. Details on alpha, beta, gamma and delta transitions are explained in this blog post. Amorphous thermoplastics show a linear behavior up to the glass transition temperature. Semi-crystalline polymers have a two-step behavior: the first drop in mechanical values can be observed at the Tg, followed by the second drop at the crystal melt temperature. The structural crystal elements can resist much more the temperature increases. 

In the graph below, the glass transition and crystal melt temperature of different high performance polymers are shown. It can be seen that polyimides (PI, PAI, PBI) outperform other polymers. Checking the glass transition temperature is important during the material selection when you decide on the suitability of the polymer to fulfill the application service temperature. Thermoplastics show already a drop in mechanical performance at the glass transition area. 

Transition Temperatures of High Performance Polymers

PTFE, PAI, PBI, and PI are not melting when the glass transition or crystal melt temperature is reached. These polymers show a particular molecular structure (thermoset-like). Nevertheless, using such polymers above their continuous use temperature is not good since thermal-oxidative degradation starts.

Thank you for reading and #findoutaboutplastics

Herwig Juster

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Wednesday 12 August 2020

Design Properties for Engineers: Thermal Conductivity of High Performance Polymers

 In this blog post we discuss the thermal conductivity of filled and unfilled high performance polymers.

Thermal conductivity is a key figure to show the thermal transfer of different materials. Polymers have compared to metals (45 W/mK average value) a very low thermal conductivity. Semi-crystalline polymers have a higher thermal conductivity compared to amorphous polymers since the crystalline regions allow a better heat transfer. In amorphous polymers, polymer chains are unstructured and this leads to a lower thermal conductivity. Furthermore, thermal conductivity is higher in processing (= orientation) direction than perpendicular to it. This can be observed in injection moulding parts with thin wall thickness.

Unfilled high performance polymers behave similar in their thermal conductivity and not many differences can be observed (Table 1). Thermal conductivity can be immediately increased by adding carbon fiber or graphite (Table 2). Improved thermal conductive plays an important role in high temperature applications, where an improved heat transfer between metal housing and plastic part leads to better mechanical part endurance. Therefore it is important to consider such a requirement during the polymer material selection process.

Table 1: Thermal conductivity of unfilled high performance polymers

Table 2: Thermal conductivity of filled high performance polymers

Thank you for your attention and #findoutaboutplastics
Best regards, 

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Friday 7 August 2020

What is the Difference Between an Industrial Designer and a Design Engineer? incl. Polymer Part Design Checklist [Guest Post]

Our guest author and polymer design engineer Vatsal Kapadia presents in this post the difference between an industrial designer and design engineer. This post reflects his personal experiences in this area and he wants to share them with us. 
As an engineering tool for your next plastics part project, we worked on a Polymer Part Design Checklist which can be found in the end of this post.

What is the difference between an Industrial Designer and a Design Engineer? 

An Industrial Designer creates the concept for a part with major emphasis on aesthetics and innovation. A Design Engineer designs a part considering functionality. Thus, dimensions, tolerances and limits are established according to the technical requirements of the envisaged product. 

A refined part is the one which satisfies all expectations including performance and appearance and is commercially economical to produce. Different other factors contribute to the dimensions and properties of a part, i.e. utilized machines, processes and skill level of workers. 

Dimensions and tolerances are fundamental for manufacturing any polymer-based part. This leads us to the following question: How do you choose a tolerance? You should start by consulting the tolerance chart available for the materials you want to produce your part with and review these together with the manufacturing team. Resulting manufactured prototypes shall subsequently be inspected for obtained dimensions. In the final drawing sheet, all the tolerances along with the dimensions in an orthographic view are necessary. Such process is crucial for concept to completion or design to manufacture. Concepts of GD&T (Geometric Dimensioning and Tolerance system) have allowed designers to work more precisely with datum points facilitating efficient exchange of part’s design data between involved parties as well. 

A foolproof design engineer and/or tool designer shall also be thorough when it comes to material selection as the choice of the right material is crucial for part design and manufacturing. Important material properties influencing part’s design include e.g. mechanical, thermal, electrical and chemical properties, shrinkage factor, surface finish and material recyclability. Selection of a suitable processing technique accordingly completes the whole part design process. 

Finally, I would like to share a non-technical experience: Cooperation and communication between industrial designers, design engineers and tool designers can save time by ensuring that the product is not only accurately designed to accomplish its functionality, but also that it can be molded and assembled. 

The following Polymer Part Design Checklist will allow you to gather all necessary information about the part. Having such a checklist not only allows the present job work to be systematic, but it should also help in the future when a part failure occurs in any real life application.

Thank you and #Findoutabouplastics!
Vatsal & Herwig 

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