Automatic Particle Identification and Counting in Greases Rich Wurzbach, Evan Bupp, Lisa Williams MRG Labs, York, PA, USA Tod Canty, JM Canty, Buffalo, NY, USA ABSTRACT
Particle counting is a well-established and important consideration in the quality control of new oils and hydraulic fluids. Particle counting is used to monitor the effectiveness of equipment cleanliness protection and particle removal equipment. For greases, the limited ability to filter once obtained by the end-user customer has generally resulted in this focus on particle counting and cleanliness to be overlooked. Additionally, the flow limitations of greases have prevented the use of typical oil particle counting tools from being applied in like manner to grease as a cleanliness verification and evaluation tool. Methods utilizing the preparation of a thin-film of grease for inspection, coupled with new imaging, identification and measurement tools are being developed to automate and standardize an approach to particle counting. Since the impact of abrasive contaminants can be equally destructive in grease lubricated components, tools that enable the monitoring of particulate may allow intervention to minimize abrasive and fatigue wear due to particulate initiated damage.
CURRENT PARTICLE CHARACTERIZATION METHODS FOR IN-SERVICE GREASE
Metal spectroscopy and ferrous debris monitoring techniques are typically used to evaluate wear and contaminant ingress in greases. There are many ways to determine the elemental content of in-service greases – including Rotating Disc Electrode spectroscopy, Inductively Coupled Plasma spectroscopy, Atomic Absorption spectroscopy, and X-Ray Fluorescence Spectroscopy. These metal spectroscopy techniques are used to detect mixing of different thickeners, wear metals, and anti-oxidant elements remaining by determining the elemental make up of the samples. Ferro-magnetic material is detected using ferrous debris monitoring instrumentation. A sensor is used to measure
disturbances in the electromagnetic field caused by ferro-magnetic particles – allowing a quick and nondestructive way to analyze the total ferro-magnetic content in a sample. Microscopic techniques, including analytical ferrography, can be used to look at the wear particle surfaces and determine nature and origin of the wear particle. Most of these methods is well-known and proven in the industry as effective ways to look at wear particles. However there have been limited techniques to test total particulate in grease, or reliably evaluate new greases for dirt and other contaminant particles. Methods that have been used include “Federal Standard 791D, Method 3005.4, Dirt Content of Grease”, which is a microscopic evaluation using glass plates, and the Hegman gage. The Hegman gage is a sloped channel in a metal block, where a scraper is used to drag the particles to the narrow end. Another method is ASTM D1404 “Deleterious Particles”, which involves placing grease between two plastic plates and rotating them under load. The resulting scratches are counted as an indication of the destructive potential of the grease. These manual methods for grease particulate evaluation are time consuming and subjective. New technology has been developed using particle imaging as a screening tool for potential damaging wear and contaminant particles present in the grease. This new method allows for a nonsubjective, quantitative and qualitative evaluation of new and used greases to help address the destructive potential of particles in greases.
NEW PARTICLE CHARACTERIZATION METHODS FOR IN-SERVICE GREASE
The Grease Thief Analyzer is a device used to measure the consistency of greases using the die extrusion
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