Advanced Test Methods for Motion Control Applications
Grease is often used to control motion, provide a quality feel, reduce noise and vibration; friction and wear reduction come as an added benefit. Many automotive OEMs can struggle to find a non-silicone lubricant that performs consistently over a wide temperature range.
Chemists at Nye Lubricants have developed a series of test methods to quantify the reliability of our motion control lubricants under various temperature and shear conditions to ensure your application has the same feel, every time, at any temperature.
A hand-operated component, such as a shifter or sun visor, must provide the same actuation force regardless of temperature to give the user the same quality feel. Nye’s custom rheological test evaluates the ability of a grease to maintain its viscosity at extreme temperatures. During this test, the grease is sheared from -40 to 120 °C. The viscosity of the grease is recorded at each temperature point and is used to create a viscosity ratio (VR).
The VR shows the viscosity consistency of a grease from -40 to 120 °C; a VR of 1 would be ideal. If a grease has a smaller VR it means that the grease is more likely to maintain the same quality feel when sheared over a wide temperature range. Nye has the capability to measure the shear response at different strains to simulate a customer’s application. For example, the strain ratio can demonstrate how a grease will behave in a dial; rotating a dial should feel the same, regardless of the turning speed.
A mechanism must provide a reliable feel or actuation even if the mechanism is used frequently over a short period of time. If a grease loses its structure after repeated motion, tolerance could be affected. In these applications, you want the lubricant to shear and recover its structure as quickly as possible so that the next actuation feels the same. Nye’s custom rheological test method measures the percent recovery of the grease to quantify the stability of its structure after repeated use; if a grease cannot recover its structure, the performance will be inconsistent. A 100% recovery percentage is ideal.
Mechanisms operating under dynamic conditions, like seat tracks, will wear at a different rate than applications operating at a constant speed or duration. The mini-traction machine (MTM) wear test simulates how a lubricant will perform within the different lubrication regimes: boundary, mixed or hydrodynamic. The wear scar is analyzed through profilometry and a wear rate is calculated. This allows us to compare oils or greases within the same lubrication regime and rank their performance. The smaller the wear rate, the better protected your components are in dynamic conditions.
This industry standard test is a useful measurement of how grease affects start-up and running torque at low temperatures. The test quantifies the amount of force required to rotate a bearing at the initial start-up and then after 60 minutes of running at -40 °C. This test is used to indicate the degree to which grease inhibits motion and can be particularly important for low-powered mechanisms such as those found in automotive interiors.
This data is not readily available for all our products but can be produced upon request.
