Rising temperatures, higher pressures raise the bar for automotive nylon

New car engine designs are driving developments at materials suppliers keen to offer the right combination of properties to help limit fuel consumption, weight and CO₂ emissions. For supplier Lanxess (Leverkusen, Germany), these new designs are placing new demands on the polyamide (PA) 6 and 66 it offers. The company’s Ludger Meinering and Jürgen Selig, both working in Lanxess’s semi-crystalline products business unit in Dormagen, Germany, see a trend towards supercharged engines with special air and cooling management, and towards engines with a higher exhaust gas recirculation rate. The aim of these changes is to generate more power with a smaller piston displacement and lower fuel consumption.

Lanxess’s Technical Service Center at its Dormagen plant carries out practically every single test procedure relevant to engine components.

These developments create some new challenges for PA 6 and 66, which see use for example in pipe systems found in engines for airflow management, oil and cooling circuits, and fuel supply. Enhanced heat aging resistance and temperature performance are two of the challenges faced, as well as the need for improved chemical resistance.

Processing developments such as water and gas injection technology (WIT, GIT)) place demands on the polyamides’ rheological properties.

The two men have overseen recent developments at the supplier of additional PA 6 and 66 grades in its Durethan-brand range for a number of under-the-hood applications. One example is a coolant pipe for four-cylinder diesel engines made of Durethan DP AKV 30 X HR EF, in series production as a WIT-molded part. Special glass-fiber reinforcement developed in-house by the plastics supplier helps ensure a smooth pipe interior. According to Lanxess, the material’s long-term chemical resistance has been proven at a pressure of 5 bar and temperatures ranging from -40 to 135°C, with mechanical properties virtually unchanged. In tests, the coolant pipe withstood constant media temperatures of 125°C and brief temperature peaks of 143°C.

Blowmolding grades get revamped too

The supplier also has been developing grades suitable for blowmolding, including some filled and unfilled PA 6 and 66 grades. Because of their high viscosity at low shear rates, they can be processed using both conventional extrusion blowmolding and 3D methods, such as suction blowmolding and blowmolding with parison manipulation. Parisons with a weight of up to 8kghave been formed and processed from Durethan AKV 325 H2.0, reinforced with 25% glass fibers. One example of a series application is a clean-air line for the Mercedes-Benz C 320 CDI engine, which is extrusion blowmolded of the PA 6 Durethan BKV 315 Z (15% glass fibers). These grades also are suitable for injection molding because, at high shear rates, their viscosity drops almost to the level of standard PA grades.

One special product in the range is the non-reinforced PA 6 Durethan DP BC 600 HTS, specifically developed for processing as a single material, via suction blowmolding, for the charge-air tubes with integrated bellows that are used in supercharged engines. As the bellows compensate for the relative movements of the engine and tolerances during assembly, they have to be flexible and elastic. This PA 6 satisfies this requirement thanks to an elasticity modulus of no more than around 350 MPa (conditioned). This solution is billed as a lower-cost alternative to the sequential coextrusion of two polyamides of differing hardness. The supplier says it has carried out successful prototype tests on a customer mold.  —[email protected]