Full throttle with flame-retardant polycarbonates in electric race car

Electric vehicles not only prevent local emissions, but they can also be fun. Founded in 2012, the E.Stall Esslingen is participating in various international events of Formula Student with an electrically powered racing car. One of the biggest events is the Formula Student Germany, which takes place every year at Hockenheim Ring.

The design of the racing car's traction battery is demanding – it is one of the most important components for the course of the race: It determines whether the driver has enough power to beat the competition.

PC/ABS sheet is used to produce frames and brackets for the battery modules in the E.Stall Esslingen racing car.

Since the 2018 racing season, Covestro has supported the E.Stall Esslingen team with flame-retardant materials for the construction of the battery. In its Leverkusen pilot plant, the plastics manufacturer extrudes sheets from the Bayblend PC/ABS (polycarbonate/acrylonitrile-butadiene-styrene) alloy to produce frames and brackets for its battery modules. These modules are based on lithium-ion battery cells in the so-called pouch format.

In the design department for the battery, the various disciplines of the students at Esslingen University of Applied Sciences complement each other – from electrical engineering to electronics and mechanical engineering. In addition, the Formula Student specifies certain design requirements for the students in its rules and regulations, among others with regard to safety in handling lithium-ion cells. Apart from active monitoring and control of the battery, the Formula Student regulations explicitly require the use of flame-retardant materials in accordance with the Underwriters Laboratories' flame-retardant standards according to category UL 94 V-0 in the General Technical Requirements.

“We are delighted that Covestro is supporting us again in the 2019 season with polycarbonate blend sheets, which we can process easily,” explains Raphael Raff, who is currently in charge of the high-voltage sub-project at E.Stall Esslingen. Compared with the previous year, a PC/ABS blend with around 10 percent lower density and high mechanical, electrical and thermal properties was selected for the racing team together with the Bayblend product experts from Covestro in order to remove even more weight from the racing car's battery.

For mass production, designers are looking for materials that meet the strict requirements of car manufacturers in-vehicle operation but which are also easy to process. Compared to semi-crystalline materials, amorphous plastics such as polycarbonates have the advantage that they are virtually shrinkage-free in the injection molding process and have very low water absorption. This facilitates being able to design thin-walled, distortion-free components. Also, polycarbonates can be provided very well with flame protection. The Covestro product portfolio includes a large selection of flame-retardant materials that meet the standards of the Underwriters Laboratories of category UL 94 V-0.

Covestro continues to develop its portfolio for battery applications. For cell holders to hold cylindrical battery cells, pouch cell frames, battery housings, and similar applications, the focus is on both unfilled (Bayblend FR3010, Bayblend FR3040) and mineral-filled (Bayblend FR3020, Bayblend FR3021), along with glass-fiber-reinforced Bayblend FR3060 EV) flame retardant Bayblend products. Covestro also offers thermally conductive polycarbonate grades of the Makrolon TC product family that can contribute to battery thermal management.

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