Reduced emissions with high-performance polymers

  • 19-Mar-2010 09:53 EDT
fig 2_Metaldyne Balance Shaft Gear.jpg

This balance shaft module gear from Metaldyne is based on Victrex PEEK polymer.

With environmental pollution increasing worldwide and the foreseeable climate change, the European Commission has legally demanded that manufacturers reduce automobile emissions. The associated reduction of CO2 creates many challenges for technical designers in the automobile industry, where it is an objective not only to reach the emissions goal of 130 g/km by 2012 but to remain competitive at the same time.

The automotive industry has been pursuing numerous solutions to reduce emissions that are primarily focused on increasing the performance of the vehicle while minimizing fuel consumption and weight. For example, the hybrid engine can save up to 20% of the CO2 emissions that typical combustion engines create today through engine optimizations and braking systems. Besides reducing vehicle weight, the miniaturization of components as well as function integration are at the forefront of the automotive industry, leaving these fields open to new and innovative ideas. Legislative requirements, operating in tight tolerances, and rising overall costs are pushing OEMs to identify materials that provide higher performance at lower weights.

Plastics have played a crucial role in the automobile industry when it comes to weight reduction and design flexibility. In Europe, about 50% of plastics used are found in the interior of an automobile, approximately 22% externally, and about 11% in electrical connection and lighting applications. There are also many opportunities for under-the-hood components.

Smaller, more reliable components made from high-temperature materials with excellent strength and flow characteristics have risen in demand. This demand can be met by producing thinner-wall parts made from high-performance thermoplastics. The industry standards for materials today need to perform at 150°C (302°F) or higher depending on the application, whereas years ago temperature-range requirements were 100 to 120°C (212 to 248°F). OEMs, for example, are searching for materials that can perform up to 180°C (356°F) in lower steering columns and 220°C (428°F) in turbocharger components. With these requirements in mind, it may not be feasible to use traditional plastics in these environments as well as light alloys, which show a loss in mechanical strength at temperature ranges around 200°C (392°F).

Victrex Polymer Solutions, a division of Victrex plc, manufactures materials that meet automotive requirements without considerable property loss at continuous operating temperatures beyond 150°C. A recent study concludes that Victrex PEEK polymers maintained their original stiffness, stretch behavior, and impact strength after 5000 h of use; conventional materials registered property losses up to 50% in the same conditions.

A new high-performance line, Victrex ST polymer, has a melting temperature of 389°C (732°F) and a glass transition temperature of 164°C (327°F) that can perform in the most aggressive environments. Dimensional stability and long-term stress performance showed improvements when compared to other materials in temperature ranges over 150°C. This thermoplastic also possesses all of the well-known properties of Victrex PEEK polymer such as high purity, excellent electrical properties, high chemical resistance to fuels and other fluids, and low thermal expansion.

For example, using Victrex’s high-performance polymer for gear wheels in demanding environments results in minimal thermal expansion where temperatures and chemicals can heavily influence performance. The gear wheels exhibited higher load-carrying capacity than those made from standard materials when comparing tooth strength. Molders will reduce the size of gear wheels by placing a higher load on the teeth for that very reason. Thermoplastic gear wheels also offer reduced noise levels compared to gear wheels made from metal.

If traditional materials such as PPA, PPS, and PPSU do not meet the increased requirements for automobile applications, it must be determined whether high-performance thermoplastics can be processed in the equipment as well as spray casting tools and manufacturing equipment used for treating the materials. One of the benefits of using Victrex PEEK polymer is that it is capable of being processed on conventional thermoplastic equipment in both pellet and powder form.

The use of high-performance thermoplastics has a promising future in the automotive industry. High-performance polymers may have higher material costs, but the ease of processing, shorter production times, and reduced risk of downtime can certainly outweigh the price of the material. These overall cost savings allow customers to view the benefits of using such a product as advantageous for them and their customers.

Jürgen Reinert, Senior Market Development Manager of Victrex Polymer Solutions, Victrex Europa GmbH, wrote this article for SAE Magazines.

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