MODIFICATION | WEAR RESISTANCE
vibration issues,” he says. “Today sintered metal gears are being replaced with high-performance plastic gears in automobiles because (of) the demand to lightweight vehicles and increase fuel efficiency (…) driven by meeting new and upcoming legislation to reduce emissions — so the research and testing to improve gear design continues.”
Hasanovic cites the start-stop motor as an
important application. These may perform as many as 350,000 starts over the lifetime of a vehicle, or up to 45m load cycles per annulus gear tooth. “DSM’s Stanyl (PA46) meets these tough material require- ments across a range of power ratings,” he says. To understand the theoretical and practical
Figure 6: Witcom is working on improving the CoF over time of compounds as making CoF more stable reduces noise for both gears and bearings Source: Witcom
remains extremely constant. This ensures very smooth-running bearings which are extremely silent,” says Business Development Manager Christine Van Bellingen. The product range, recently extended, includes grades based on a wide range of polymers. “Demand for these products has skyrocketed over the last few years, particularly because the automotive interior for electric vehicles is much quieter than before,” Van Bellingen says. “The noise of an internal combustion engine would drown out sounds which have now become clearly audible.” Another growth area for Witcom is gear materi-
Right: Gear testing on DSM’s test rig allows materials and gear wheel design to be optimised
als. Pieter Janssen, Chief Scientist Lubricated Materials, says: “Unlike traditional solutions, gears manufactured out of these materials have extreme- ly low wear when paired against themselves. This means the entire gear train can be made out of a single material, reducing manufacturing cost and simplifying design.” Gear designers do need to be careful, though. As was noted several times at the AMI conference, POM components do not perform so well when paired with other POM parts in such applications.
Shifting a gear Adnan Hasanovic, Technical Manager for Gear Actuators at DSM, explained recently in a blog how plastic gears can help to cut weight in vehicles. “For decades, scientists and engineers have focused on improving the materials used for gears while attempting to overcome several challenges, such as gear teeth breaking at the root due to fatigue, wear of the teeth at the flank, local overheating, too much noise, shock loading or hard stops, and noise
32 COMPOUNDING WORLD | February 2020
www.compoundingworld.com
relationship between the application and the material’s wear and friction properties, DSM runs various interfacial and environmental temperature tests. Its onsite gear tester validates material perfor- mance at an application level and correlates it with basic material properties, such as tensile strength, fatigue resistance and tribological properties. Eurostar Engineering Plastics has been working with French automobile group PSA and with research outfit Cetim to minimise gear noise. Alexis Chopin, Technology Engineer at the com- pany, explained at the AMI conference how “auto-lubrified” polymers can help reduce airborne noises in vehicles, which are typically generated by vibration of the surfaces as they rub against each other in, for example, mechanical joints. The sound waves are produced by variation in the frictional force generated at the contact between two surfaces. “The variations in force of each contact and the number of contact asperities as a function of space and time are specific in the resulting friction force,” said Chopin. “In the case where the other param- eters are fixed, these variations are therefore
IMAGE: DSM
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