Friction, Wear, and Abrasion Resistance Tests & Observation, Analysis, and Measurement
Friction occurs between moving parts. For example, the power train that transmits power in automobiles and trains uses many parts—including a clutch, a transmission, and drive shafts—and these are referred to as contact engagement parts.
The friction causes heat generation and wear in these parts. Heat generation and wear derived from friction account for most mechanical system failures, and economic losses due to such failures are not small. To reduce such losses, tribological tests are conducted to evaluate parts and the properties of the materials used for such parts through friction, wear, abrasion resistance tests.
This section introduces the testing and measurement methods along with the latest examples of solving problems using KEYENCE’s 4K Digital Microscope from the perspective of tribology—the science of wear and friction between interacting surfaces in relative motion.
- Friction, Wear, and Abrasion Resistance Tests
- Friction, Wear, and Abrasion Resistance Testing Methods
- Tribological Tests
- Latest Examples of Observation for Friction, Wear, and Abrasion Resistance Tests
- The Latest Tool for Quickly Responding to Market Demands
Friction, Wear, and Abrasion Resistance Tests
In this test, a test piece and an interfacing surface are subject to interaction in relative motion to measure the coefficient of friction* and the wear volume.
In industries where contact engagement parts are used, there are many cases of evaluating changes in the material by means of friction, wear, and abrasion resistance testing as part of product quality assessment, commissioned analysis, and research and development of new products. Such cases are seen as necessary testing for quality assurance in a wide range of industries that involve contact engagement parts such as lubricant and grease manufacturers; suppliers of bearings, pulleys, and other parts; and motor manufacturers.
Coefficient of friction: A value that shows the impact of the contact surface on frictional force. It does not have any unit and is represented by μ (mu). Classified into coefficient of dynamic friction and coefficient of static friction, the value varies depending on the object and surface treatment.
Friction, Wear, and Abrasion Resistance Testing Methods
A friction test measures the frictional characteristics together with an abrasion resistance test, and the result is generally calculated using the coefficient of friction. On the other hand, a wear test measures the changes in conditions caused by friction, and the result is obtained from deformation, scratches, and indentations on the interacting surfaces.
There are several ways to measure the coefficient of friction: by measuring the frictional force with a gauge, by measuring and converting the load power of the driving motor, by calculating from the behaviour of vibration damping* by friction, and by calculating the maximum static frictional force* based on the angle at which an object placed on a slanted surface starts sliding. These tests check not only for wear and friction but also for the effectiveness and deterioration of lubricants.
Vibration damping: Vibration decreasing with time. Also called vibration attenuation.
Maximum static frictional force: Frictional force generated when a stationary object is moved. In contrast, the frictional force that arises during movement is called dynamic friction, and the friction that occurs on balls and needles in bearings is called rolling frictional force.
Tribological Tests
Frictional resistance is a big load and loss for contact engagement parts for which bearings are a great example. This resistance must be comprehensively minimised by taking a multi-faceted approach that includes material mechanics (such as the mechanical properties of the parts), the fluid mechanics of lubricants, and thermodynamics that measure the surface conditions affected by heat.
Tribology is the science of examining and evaluating the impact of friction from a wide-ranging perspective. The tests conducted to evaluate the relevant properties are called tribological tests.
The need for tribological tests
The heat generated by friction and loss of material caused by friction that occur in mechanical systems lead to mechanical resistance, which is said to be the largest contributor to machine faults and failure. Reducing and controlling friction and wear is not merely a problem prevention approach, but a core technique for improving the reliability and performance of mechanical systems and therefore reducing economic loss.
Characteristics of tribological tests
Wear and friction tests are said to often give completely different characteristic values when the shape of the specimen, test method, and atmospheric conditions change, even when testing the same material. Therefore, for wear and friction tests, it is necessary to understand the conditions under which the actual target impact is caused and conduct the tests using similar conditions. The performance of a lubricant depends significantly on the physical properties of the lubricant and the chemical properties of the interface. In particular, solid lubricants* have a higher load capacity than oil and grease and therefore are also used as additives to oil and grease.
Tribological tests are conducted under conditions close to the usage conditions, reproducing the actual environment the friction to be observed occurs in. The materials used in the contact engagement parts as well as the lubricants and the part shape-derived characteristics are all evaluated.
Solid lubricant: Solid substance that protects the material surface from friction and reduces wear and friction. Examples of solid lubricants include molybdenum disulphide, graphite, and PTFE (Polytetrafluoroethylene).
Latest Examples of Observation for Friction, Wear, and Abrasion Resistance Tests
Test pieces and interacting parts in wear and friction tests are generally three-dimensional and can have strongly reflective surfaces. In the corresponding measurements and analyses using microscopes, the operator must be highly skilled in order to find proper focus and mitigate the reflection from the surface.
Thanks to technological advancements, digital microscopes have significantly improved the efficiency of friction and wear tests.
Efficient observation of deep indentations in bearings
Indentations occur when some sort of impact is applied to the bearing. When the observation surface on the bearing is not flat, time-consuming focus adjustments must be performed during high-magnification observation with a microscope.
The high-resolution lenses and the motorised revolver of the VHX Series 4K Digital Microscope enable a seamless zoom function that quickly switches between lenses according to the magnification in the range of 20x to 6000x, eliminating the need for lens replacement.
- A: Observation using a digital microscope
- B: Observation without depth composition
- C: Observation of an indentation on the front surface
- D: Observation of an indentation on the back surface (500x)
The real-time composition function automatically performs depth composition to bring the entire target into focus. With this function, you can easily perform accurate, efficient magnified observation, appearance inspection, and evaluation using ultra-high definition images fully focused from close up to far away.
Additionally, the VHX Series automatically detects the connected lens and can manage magnification data together with captured images.
This digital microscope contributes to improved inspection efficiency with excellent data management along with an observation function that can seamlessly zoom into a magnified image of a part of the entire image while maintaining the high definition.
Observing and measuring damage on friction surfaces with a single machine
When performing observation and measurement, previously testers needed to switch instruments, leading to long test times.
The VHX Series 4K Digital Microscope can not only perform clear magnification and observation but measurements and quantification as well. A whole range of tasks—from post-wear test observations of flaking*, pitting*, and other damage to the interacting surfaces to 2D measurements and roughness measurements that are useful for roughness inspections—can be readily executed from a single machine using easy mouse operations.
Flaking: Rough and coarse texture caused by peeling in the raceway surface and the rolling element surface that occurs due to the rolling fatigue of the material.
Pitting: Speckle-like holes with an approximate depth of 0.1 mm that appear on the raceway surface.
Observing wear and friction with reduced reflected light from glossy surfaces
Test pieces that are worn due to friction typically have a highly reflective surface, making observation and imaging difficult.
The VHX Series 4K Digital Microscope has glare removal and ring-reflection removal functions that eliminate reflected light. This enables clear image capturing, preventing glare on an interacting surface having increased glossiness due to friction. The new 4K Digital Microscope distinguishes between fine hairline scratches, friction-inflicted dents, and adhesions to allow for a more accurate understanding of the wear and friction conditions.
A single microscope for everything from observation to 2D and 3D measurements
During appearance observation, testers need to focus on multiple different parts of three-dimensional targets, which can lead to damage being overlooked and different operators obtaining different results. Moreover, there was no other way than to use 2D measurements even for three-dimensional targets.
The VHX Series 4K Digital Microscope not only allows for magnified observation and 2D measurements using clear 4K images but also is capable of capturing 3D shapes and performing 3D measurements and profile measurements of selected cross-sections. Irrespective of the skill level of the tester, the VHX Series offers analysis and measurement of 3D shapes with easy operation, thereby streamlining tasks in addition to providing sophisticated and quantified evaluation of the friction surfaces
The Latest Tool for Quickly Responding to Market Demands
To respond to tribological evaluation needs, in addition to the expanding demands in wear and friction tests, it is necessary to establish R&D, quality improvements, and manufacturing processes based on fast and accurate inspection data.
The VHX Series high-definition 4K Digital Microscope offers excellent efficiency and ensures high-accuracy observation, analysis, measurement, and evaluation with just one machine. Equipped with many other advanced functions, the VHX Series can be an effective tool for industries that require both quality and speed.
For details on the VHX Series, click the button shown below to download the catalogue. For inquiries, click the other button shown below to contact KEYENCE.
