DuPont Engineering Design Electronic Magazine
Global choice for thermostat housings
By Andreas Oldeweme, DuPont Engineering Polymers, Germany
and Gwon Sul, DuPont Engineering Polymers, Korea
As illustrated by two recent applications spanning the globe, DuPont™ Zytel® HTN polyphthalamide (PPA) has what it takes to deliver higher performance for today’s automotive thermostat housings.
When seeking a material for the housing of a map-controlled thermostat, to be installed in BMW’s N43 series four-cylinder petrol engines, Behr Thermot-tronik of Germany concluded their requirements exceeded the capabilities of conventional polyamides used in under-the-bonnet applications. “As the thermostat is next to the cylinder block, it is exposed to temperatures anywhere between -40 °C to +150 °C (-40°F to 300°F),” says Barbu Frunzetti, project leader at Behr Thermot-tronik. “In addition, the exterior surface is exposed to typical motor-compartment media, such as oils, greases, fuel and road salts. Inside the thermostat housing, coolant flows at up to 140°C (284°F) and creates an interior pressure of up to 2.5 bar. Moreover, when in operation the whole system is constantly under vibrational stress.”
“In extensive comparative tests, DuPont™ Zytel® HTN met our demanding requirements best,” Frunzetti continues. “Reinforced with 35 % glass fiber, it has the required high static and dynamic strength, the dimensional stability over a broad temperature range essential for this application, high chemical and hydrolysis resistance, good flowability and high compatibility with PA 66 for overmolding of additional plastic parts.”
Replacing aluminum in Korea
On the other side of the globe, design engineers at INZI Controls Inc. in Korea – a first tier supplier to Hyundai – had come to the same conclusion. They were looking to replace aluminum for the housing of a new thermostat installed in Hyundai’s Theta four-cylinder petrol engine from the end of 2007 onwards, thereby achieving a weight saving of around 40 percent and a more integrated design. As with the German application, INZI Controls selected Zytel® HTN PPA with 35 % glass fiber reinforcement.
“We were particularly impressed by the thermoplastic’s retention of key properties, such as creep resistance and toughness, despite long-term exposure to today’s more aggressive long-life coolants.” comments JS Kim, R&D team manager at INZI Controls. Subsequent testing, including an ‘engine full load test’ at 6000 rpm over 300 hours without any crack or leakage, confirmed the material’s performance. According to INZI Controls, assistance provided by DuPont’s technical center in Korea, which was involved from the initial design stage and assisted with NVH (noise, vibration, harshness) simulation to analyze the vibrational stress placed on the part, was essential to the project’s success.