Test Before You Launch
Lubricants are required to ensure the reliability of space mechanisms, but the wrong lubricant may result in premature failure and contamination. Lubricant outgassing and particle generation can contaminate optical components including sensors, lenses, and solar cells. Space mechanisms require lubricants that ensure longer expected life and durability, as the ability to service or replace components during extended voyages will be very limited or non-existent. To avoid these issues, it is critical to select high performance, long-lasting greases with low outgassing and particle generation properties.
To reduce risk for our customers, Nye’s vacuum greases are validated in our state-of-the-art laboratory dedicated to in-vacuum testing. Nye's Vacuum, Aerospace, and Semiconductor Testing (VAST) Laboratory allows us to test our lubricants under simulated environmental operating conditions (i.e., vacuum, extreme temperatures) and provide our customers with performance data that helps them understand how our lubricants will perform in their application. Ultimately, this service helps our customer make the most informed lubricant choice.
Here are some of the properties that can be measured in the VAST Lab:
- Friction & Wear
- Particle Generation
- Vapor Pressure & Outgassing
- Relative Life
Friction & Wear
It is important to consider a lubricant’s ability to protect components against friction and wear under specific loads, speeds, and geometries.
The SRV (Oscillating, Friction & Wear) test rig can run custom tests with options that include: rotational and linear oscillatory motion, tests up to 2,000 N load, 2,000 RPM, and a maximum temperature of 180 °C. Specimens include ball on disc, pin on disc, cylinder on disc, and custom geometries.
The Mini Traction Machine measures friction in a mixture of rolling/sliding contacts to simulate applications, like rolling element bearings and gears. Unlike other tribological tests where speed is either measured as the number of rotations during a period of time or the oscillatory frequency, the MTM allows for the speed element to be a combination of sliding and rolling speed to produce the entrainment speed. The MTM provides a very good testing method for scuffing and galling of metal surfaces by allowing for the ball and disc to be driven in different directions (contrarotation). This produces a tribological test that can operate with high sliding / rolling speeds and low entrainment speed.
Particle Generation
The term dynamic particle generation describes what happens when contaminants are created by being forced or expelled from a lubricated ball-screw, bearing, or gear system into the operating environment. These contaminants could include base oil constituents, thickener particles, additives, etc. and are freed from the grease through dynamic mechanical action whether it be rolling, sliding, or a combination of both.;
The Dynamic Particle Generator is used to classify lubricant particle generation into ISO and Federal cleanliness levels for Aerospace applications. It utilizes an ISO 3 clean air system, precision ball screw, and particle counter to characterize the number of particles down to 0.1 micron produced by various greases as the test is run. The ability to run Residual Gas Analysis on the materials released from the lubricant is also available. Test provides ISO and Federal cleanliness levels on your lubricant.
Vapor Pressure & Outgassing
When a lubricant outgasses it releases condensable material that can contaminate optics and other sensitive components. Vapor Pressure (VP) is defined as the pressure exerted by a vapor in thermodynamic equilibrium with its condensed phases at a given temperature in a closed system. The higher a material’s VP, the more likely it is to outgas at pressures nearing atmospheric. Therefore, it is essential that all materials used in aerospace applications possess low vapor pressures to ensure that they will be able to endure low pressure environments without outgassing and contaminating the surrounding surfaces and environment.
Outgassing testing (per ASTM E595 Vacuum Stability) is designed to screen materials for volatile contamination. This test provides percent Total Mass Loss (TML) and percent Collected Volatile Condensable Materials (CVCM) data for our lubricants. Nye engineers can monitor the outgassing via Residual Gas Analysis to determine the elemental species contained in the outgassing material. This testing provides customers with a better understanding of the stability of our materials in a static vacuum environment and the ability to identify what materials are outgassing. Additionally, this test can show how much of the outgassing is condensable to give an indication of the lubricant’s material suitability within sensitive mechanisms in a vacuum environment.
Nye Lubricants employs the Knudsen method of determining the vapor pressure (VP) of lubricants. This method requires a very small sample, which reduces testing costs and increases testing efficiency. The sample is placed in a small, capped cell with an orifice in the cap of known diameter. The cell (containing lubricant) is then placed in one of the vacuum chambers, at a desired temperature and for a desired duration. The mass loss from the lubricant within the cell is factored into the Knudsen equation, along with the other known variables of temperature and time, to calculate the Knudsen VP of that material at that particular temperature.
Relative Life
Depending on the application and operating conditions, there are many benefits that a given lubricant may offer, but its’ primary purposes are to reduce direct metal-on-metal contact between the rolling elements, raceways and cage to minimize friction and wear. Other benefits of a lubricant can include, dampening, corrosion resistance, wash out resistance, low particle generation, low outgassing, thermal conductance, electrical conductance and assembly aids. However, the ideal bearing lubricant will help a bearing achieve the calculated bearing L10 fatigue life, in hours or revolutions, before experiencing fatigue failure.
Originally developed by NASA to evaluate space applications, the Spiral Orbit Tribometer (SOT) is a method of tribometry designed to bridge the gap between tribo-contact testing and longer-term bearing tests. The SOT produces relative lifetime calculations based on the number of orbits made below a friction level which is normalized to the amount of lubricant on the ball bearing. The testing is a simulation of a thrust bearing and provides results that indicate the lubricant consumption, degradation, and life. As this test is done in ultra-high vacuum and the materials in contact can be customized, the SOT can provide insight into the performance of application critical lubricants.
The Vacuum Bearing Test apparatus will offer engineers data that can be used to determine the realistic life expectancy of our lubricants test on angular contact bearings in high vacuum environments. This rig can support customer supplied bearings to simulate how a lubricant will perform in a specific application. Our high vacuum test can assess how our lubricants will perform at temperatures up to 200 °C and determine mass loss under specific operating conditions. The rig also uses electrical resistance across the bearing to determine which lubrication regime (boundary, mixed or elasto-hydrodynamic) our products qualify under, given the test parameters.
