Fluid-free lubricated spur gears – Contour-matched coating design and tribological evaluation of performance limits
Research Topic
| Short Title | Fluid-free gears II |
| Start of Project | Q2/2022 |
| Funding | DFG-Nr. 357505886, SPP 2074 II, STA 1198/17-2 German Research Foundation, DFG |
| Contact | Dr.-Ing. T. Lohner |
Project Description
Conventional spur gears exposed to high mechanical loads without lubrication by a fluid lubricant (“fluid-free") show damages such as wear, scuffing and overheating after short operation period (see Fig. 1). For reliable operation of fluid-free lubricated gears, the system-dependent thermal performance limit, which depends on power losses and heat dissipation, may not be exceeded. Below the thermal performance limit, wear in fluid-free gear contact due to continuous material removal is life-limiting.
The overall objective of this research project in the priority program 2074 is to design a fluid-free lubricated spur gear with a durable coating that withstands high mechanical loads reliable. In addition to adaptation of gear geometry triboactive physical vapor deposition (PVD) coatings are applied in order to reduce friction and wear in tribological contacts. The solid lubricants elements are provided by out of the triboactive coatings via depots consisting of metal and sulfur and are synthesized in-situ in the contact. By designing the gear structure to promote heat dissipation, the thermal load of coated gears in fluid-free contact is decreased.
The aim of the second funding period is to adjust the coating properties by process design and the gear geometries as well as to transfer the knowledge of the first funding period regarding the supply mechanisms from model contact to gears. A quantitative evaluation of the thermal performance limit and wear behavior of coated spur gears enables the design calculations of fluid-free gear systems.
The work program is divided into three phases. In phase I, the compound adhesion of triboactive coatings on gears and a uniform coating thickness distribution over the tooth height on gears is focused. Simultaneously, the integration of heat-dissipating support structures will be analyzed. In phase II, experimental analyses of the thermal performance limit of gears in the gear efficiency test rig and numerical calculations of the power loss and temperature distribution will be performed. In addition, the supply and transfer mechanisms of elements from the triboactive coatings will be analyzed as a function of different thermal and mechanical loads. Based on this, the wear durability below the thermal performance limit will be investigated in phase III using experimental analyses and numerical calculations to identify failure criteria of coated spur gears. At the end of the project, guidelines for the design of durable coated spur gears under high loads in fluid-free lubricated contacts will be derived based on these results.
Keywords: PVD, triboactive coating, fluid-free lubrication, friction and wear, gears, contact simulation, DLC, (Cr,Al)N+X:S (X = Mo,W), mechanisms of action, supply mechanism, Raman, XPS, ESMA , thermal performance limit