Material Selection Considerations for Electric Vehicles (EV’s) - Thermal Management Systems

In this post, we will have a closer look at the key considerations for thermal management systems used in electric and hybrid cars. This can support an optimal selection of plastic materials.

Traditionally, in internal combustion engine cars a powertrain thermal management and a passenger cabin thermal management system are present. Here, it well understood which type of plastic materials can be used depending on the application requirements.

In EV’s, thermal management systems support additional systems such as:

• Lithium battery: Thermal management systems need to ensure operating temperatures of 40-45°C to maximize battery service life. Composing parts need to retain material properties after 6.000-10.000 hours to ensure safe handling. Thus, precise control of temperature deltas is crucial.

• Traction motor: Thermal management systems need to ensure operating temperature of coils up to 190°C to allow high torque at small size.

• Power electronics: For high power electronic controllers, liquid cooled systems are favored and plastic materials used in housing need to have a thermal conductive role.

• Hybrid EVs: Downsizing of the combustion engine leads to local hot spots, which thermal management systems need to be able to handle.

What are the market trends and emerging needs?

For internal combustion engines increased temperatures due to downsizing of engines are expected. Simultaneously, more and more turbocharging systems need to be used to compensate the missing engine performance. EV’s have a system temperature ranging from 70°C to 80°C. The latter makes polyolefins accessible for thermal management applications.

Furthermore, in battery EV’s an increased aging exposure to water glycol coolant from 3.000 up to 6.000 till 10.000 hours is expected. Thermal management systems need to be active during charging time as well as when the surrounding temperatures are extremely low. Also, when the EV is not operating, temperature is monitored and in case extreme temperatures are reached, thermal management systems have to be activated too.

All this leads to ongoing discussions at the OEM and Tier-1 level on the requirements, which can be summarized as follows:

1) Coolant fluid temperature: ranging from 80°C to 110°C

2) System pressures: can reach up to 3 bar

3) Increased lifetime: up to 10.000 hours

4) Use of dielectric conductive coolant fluids

New design challenges

As mentioned in the beginning, having additional systems such as the battery, traction motor and power electronics for monitoring tasks require higher complexity thermostat valves which need to fulfill a more precise control. Temperature deltas between one battery module and the next module can be as stringent as 1°C.

Since available space for battery module placement is limited, the design of thermal management systems must be compact. Long operation times (during driving, charging and parking) and chemical resistance of water glycol coolant fluids represent another design challenge. One of the most critical challenges is the material strength which includes the weldline strength, especially after long term aging exposure.

Weldlines represent always the weak point of the plastic application, since the connection is weakened due to random orientation of glass fibers in the connection area. In addition, weldline strength is further weakened by water glycol aging. Since we will be dealing with more complex parts, weldlines are unavoidable and need to be taken care of.

Can all this be handled by plastics? - Yes, but only with the proper material selection

Let us summarize the key considerations for our material selection and give suitable polymer examples:

1. Aging temperature: 120-150°C: Polyphenylene sulfide (PPS); 120-135°C: Polyphthalamide (PPA)

2. Aging time: 1.000 – 3.000 hours: PPS and PPA; > 6.000 hours: PPS or PPA based on required temperature.

3. Increased chemical degradation due to different coolants: PPS has best in class chemical resistance.

4. Dimensional stability for sealing tasks: PPS and PPA.

5. Secondary operations such as laser welding: PPA has good laser welding capabilities.

PPS and PPA show promising mechanical behavior even when exposed to high temperatures, water-glycol coolant and long aging time.

Figure 1 shows mechanical data of PPS after exposure to water-glycol coolant (Ryton® R-4-220BL, Solvay). Figure 2 shows the mechanical data of a suitable PPA for water-glycol applications (Amodel® A-1933 HSL, Solvay).



Figure 1: Mechanical data of PPS after exposure to water-glycol coolant (Ryton® R-4-220BL, Solvay).

Figure 2: Mechanical data of a suitable PPA for water-glycol applications (Amodel® A-1933 HSL, Solvay).

PPS and PPA: not all grades are equal

PPS has unbeatable chemical performance due to the benzene sulfide group in the backbone. When exposed to water-glycol coolant, the PPS polymer matrix can withstand long aging times. However, attention needs to be payed to the glass fiber sizing. The same applies to PPA grades as well.

Interfacial adhesion of the polymer to the glass fiber is achieved over the sizing which is coated onto the glass fiber. Standard glass fiber sizings are cleaved when exposed to glycol and thus the mechanical values drop. Therefore, special sizings are used when the final compound is exposed to glycol. When your application is exposed to coolants, using of glycol resistant glass fillers is a must. The compounds shown in Figure 1 and 2 use such glycol resistant glass fiber fillers.

Material recommendations

Table 1 shows a recommendation concerning material selection for EV’s thermal management system based on existing data.

Table 1: Comparison of PPS and PPA for EV thermal management systems

Comparison PPA and PPS for thermal management systems

Overarching, high performance and engineering plastics will find more and more applications in EV thermal management systems.

If you would like support in the material selection of thermal management systems (from polymer to supplier) for ICE and/or EV feel free to get in contact with me. We can discuss your project.

Thanks for reading & till next time!

Greetings,

Herwig Juster

If you liked this post, share and like!
Interested in my monthly blog posts – then subscribe here.
New to my Find Out About Plastics Blog – check out the start here section
Check out also my personal webpage.

Literature
[1] https://www.solvay.com/en/brands/ryton-pps#Design-Guidelines
[2] https://www.solvay.com/en/brands/amodel-ppa#Grades

Plastics Part Design: Coefficient of Linear Thermal Expansion (CLTE) of 136 Polymers

Topic of this blog post is the coefficient of linear thermal expansion (CLTE).

CLTE is often presented with the letter “α” and is calculated using the following equation:

α = ΔL / (L0 * ΔT).

L0 is the length of the part at room temperature; ΔL is the length variation of the specimen when it is heated up, and ΔT is the temperature difference between start and end. More details can be found in the standard ASTM D696.

Polymers in applications such as bus bars, which are used in traction motors, battery modules and power electronics, need to pass thermal shock tests. In such tests, metal bars are overmoulded. Thermal cycles between -40°C (1 hour) and +150°C (1 hour) of the overmoulded bars are done. The cycles are counted until cracking of the polymer layer occurs. The similar the CTLE value of both materials and the better the elongation at break of the overmoulded polymer are, the easier the selected material will pass such tests.

In the table below you can find the maximum CLTE of 136 polymers. Furthermore, I added a factor which shows how similar the polymer is to copper in terms of thermal expansion. This is useful for overmoulding of copper elements.



You can add this table to your part design library. Here, you can find some more part design related data: continuous use temperature and thermal conductivity.

Thanks for reading & till next time!

Greetings,
Herwig Juster

Literature:
[1] https://omnexus.specialchem.com/polymer-properties/properties/coefficient-of-linear-thermal-expansion

Reviewing Key Engineering Plastics – Polycarbonate [incl. Video]

Hello and welcome to this post on reviewing key engineering plastics. Today, we have a closer look at polycarbonate (PC).

Similarly to the last review on the aliphatic polyamides PA 6 and PA 6.6, we review the chemistry including the simplified petrochemical flowchart, discuss the properties and applications of polycarbonate and look at their global demand and producers.

Here you can find the youtube video of the review:

Before we start with the chemistry I would like to uncover the history of polycarbonate. In 1953, Mr. Fox from GE Plastics prepared the first sample of polycarbonate in his lab. At the same time, Mr. Schnell from Bayer AG discovered polycarbonate too. A patent fight between the two inventors started. This could luckily be settled, which allowed the start of the high volume production of polycarbonate.

General properties and chemistry

Polycarbonate is an amorphous polymer with a glass transition of 147°C and a melting temperature of 160°C. It is transparent and has a density of 1.2 g/cm3.

There are two processes to obtain polycarbonate:

1. Phase transfer process

2. Melt process route

The phase transfer process involves an interfacial polycondensation between phosgene (COCl2) and bisphenol A (BPA) in an organic solvent. It is a batch process suitable for specialty polycarbonate grades.

The melt process has been developed as an alternative to the utilization of phosgene due to environmental concerns. It consists of melt transesterification of BPA and diphenyl carbonate (DPC). DPC is obtained from dimethyl carbonate and phenol or directly over carbonylation of phenol. In a next step, DPC reacts with BPA to form polycarbonate precursors. With the precursors at hand, polycondensation takes place to obtain high molecular weight polycarbonate.

The melt process has been developed as an alternative to the utilization of phosgene due to environmental concerns. It consists of melt transesterification of BPA and diphenyl carbonate (DPC). DPC is obtained from dimethyl carbonate and phenol or directly over carbonylation of phenol. In a next step, DPC reacts with BPA to form polycarbonate precursors. With the precursors at hand, polycondensation takes place to obtain high molecular weight polycarbonate.

Simplified flow chart: Where does PC has its chemical roots?

As already mentioned, bisphenol A (BPA) is a major building block for PC. The simplified chemical flow chart helps us understand how BPA is produced. BPA production needs phenol which is obtained by the so called cumene process. Benzene and propylene are required in the cumene process too. In detail, benzene is alkylated with propylene which results in cumene. In a next step cumene is oxidized to obtain phenol and acetone. Acid catalyzed condensation of phenol and acetone leads to BPA. In a next step, BPA reacts with diphenyl carbonate to form polycarbonate.

Polycarbonate properties

Impact resistance, ductility, clarity, and dimensional stability are the major advantage properties of PC which makes it an excellent engineering plastic. Furthermore, PC has inherent flame resistance, good electrical properties and can be used at elevated temperatures up to 120-140°C. PC has a poor solvent resistance, limited hydrolytic stability and notch sensitivity. This needs be taken into account during your material selection.

PC global demand

In 2016, global PC demand was 4 million tons. The electrical and electronics markets make up for 27% of the total PC consumption. Next in line for PC consumption are the construction and the automotive markets, respectively. Geographically, one can state that Asia is the largest market for PC with 59% of its global consumption.

 
PC Price to performance
Polycarbonates form the base of amorphous engineering thermoplastics with a price of ca. 2.5 €/kg for base grades. High heat modified grades cost in the range of 3 to 3.6 €/kg.

PC end uses

PC covers a wide range of applications in different markets:

- Electronic components: good electrical insulator; heat-resistant and flame-retardant properties

- Construction materials: domelights, flat or curved glazing, and sound walls

- Data storage: Compact Discs, DVDs, and Blu-ray Discs.

- Transportation (Automotive, aircraft, railway, and security components): headlamp lenses, decorative bezels and optical reflectors

- Medical applications: complies with both ISO 10993-1 and USP Class VI standards

- Smartphones: cases, battery covers.

A new application field is battery cage housings and battery management systems components in electrical vehicles, including hybrid electrical cars.

A famous application was the use of Lexan® PC for the helmet visor of the Apollo moon mission 50 years ago.
I wrote a separate post on this topic which you can find here.


This was the review on polycarbonate, a versatile amorphous engineering thermoplastic used in many applications.

Thanks for reading & till next time!


Greetings,
Herwig Juster


If you liked this post, share and like! 
Interested in my monthly blog posts – then subscribe here. 
New to my Find Out About Plastics Blog – check out the start here section 
Check out also my personal webpage.
Literature
[1] https://pubs.acs.org/doi/10.1021/ie034004z
[2] https://nexant.com

Second Wave of Digitalization: From Plastics Machine Manufacturer to Platform Provider?

Second Wave of Digitalization

Thinking back to the last K-Show held in 2016 in Düsseldorf, Industry 4.0 and Industrial Internet of Things (IIoT) were all over the booths. This year at the K-Show we will see a lot about topics such as sustainability, circular economy, and recycling.

However, how did the Industry 4.0 story continue?

In the past three years, machine and equipment manufacturers, tool makers and plastic convertors connected their devices and started collecting data while making their products. This data allowed them to gain insights into their operations and make them more profitable. A major step stone was the introduction of Euromap 77 in 2018. This allowed data exchange between plastics converting machines e.g. injection moulding machines and manufacturing execution systems (MES). In this way, Euromap 77 enables a standardized way of connecting the entire production chain. Altogether, this first wave can be summarized under the term “efficiency innovation”. This was mainly driven to streamline internal processes and obtain cost reductions.

How does digitalization follow up?

Starting last year already, the second wave of digitalization [2] has arrived in Europe. In this second wave, investors focus on three main topics:

1. Artificial Intelligence (AI)

2. Platform based business models („platform economies“)

3. Mobility solutions

Artificial intelligence is the main game changer and impacts major traditional sectors such as banks and funds management. Adapting and changing your operations is major key to remain in business. For example, the most successful hedge funds managers, Ray Dalio with his Bridgewater Associates and Jim Simons with Renaissance Technologies have used sophisticated algorithms since the founding of their businesses. Now, the utilization of AI has enabled them to reach new levels of profitability.

Platform-based business models where profit is made by matching customers and producers belong to the most successful business models in the New Economy. There are several platform companies which are close or have already a stock valuation of 1 trillion USD. Microsoft (1.08 trillion Dollar) is the most valuable platform business followed by Amazon (961 billion Dollar), Apple (956 billion Dollar) and Alphabet (865 billion Dollar) [5].

Especially the third point “mobility solutions” is pushed by companies such as Amazon, which clearly places effort on having more vertical integration operations. For example, Amazon invested in the startup FlexPort to optimize its logistics so that the end consumer can be reached faster [3].

How is the plastics industry reacting to these three major drivers?

Plastic Industry 4.0 was and is all about making the use of things more efficient following the moto “faster, better, and cheaper.”

Apart of the efficiency steps, we see now first steps toward platform business models. For instances, the plastics machine manufacturer company, KraussMaffei, based in Munich set up his own market platform to tap into the material manufacturer pond. The platform is called “Polymore”. It represents a B2B marketplace to support sustainability in the plastics industry. It focuses mainly on compounds, recyclates and post-industrial waste, which serves plastic processors as well compounders. It will be launched at the K-Show in October later this year [1]. Although KraussMaffei is not producing resins or compounds, it can link polymer manufacturers and plastics convertors together and profit of the exchange. A similar platform is made by the company Matmatch (also Munich-based) which named its platform matmatch.com [4].

My interim conclusion

Plastics converting companies did not show exponential growth rates either, since fundamentally there was no change in their business models. Time will tell us, how the KraussMaffei approach will shake up the plastics industry. Creating a marketplace which not only offers materials, but also more and more plastics machinery, moulds and services combined with smart logistics and AI for sure hits the trend of second digitalization wave. With such platforms, companies gain access to customers and can leverage material capacities of other companies without having to own them. Market trends can be faster anticipated and customers better served. Traditional companies all along the plastics supply chain need now to re-think their business models.

Thanks for reading!

Till next time!

Best regards,

Herwig Juster

If you liked this post, share and like!
Interested in my monthly blog posts – then subscribe here.
New to my Find Out About Plastics Blog – check out the start here section
Check out also my personal webpage.

Literature:
[1] https://www.polymore.com/en/home
[2] https://www.netzoekonom.de/2019/03/27/endspiel-um-die-digitalmaerkte/
[3] https://www.cnbc.com/2019/02/21/softbank-leads-1-billion-investment-in-logistics-start-up-flexport.html
[4] https://go.matmatch.com/materials-marketing-platform?utm_source=linkedin&utm_medium=paid+social&utm_campaign=Supp_Demo_SuppListsAll_EuropeNorthAmerica
[5] https://www.netzoekonom.de/plattform-index/