Time : August 14, 2023
Abstract: Explore the detection techniques for surface characteristics of ceramic bearing parts, including optical methods, ultrasonic methods, acoustic emission, staining methods, and ray methods. Provide a detailed introduction to the advantages and disadvantages of these detection methods and the corresponding items that can detect the surface characteristics of ceramic bearing parts.
Keywords: ceramic bearings; Parts; Surface characteristics; detection
Engineering ceramic materials such as silicon nitride used in rolling bearings have advantages such as wear resistance, high temperature resistance, corrosion resistance, non magnetism, low density, low thermal expansion coefficient, and insulation. They are suitable for working in special environments such as high temperature, high speed, corrosion resistance, non magnetism, oil free lubrication, and light weight, and have attracted more and more attention from people. Due to the limitations of ceramic manufacturing technology and material characteristics, there are often various defects such as cracks, pores, inclusions, and additive segregation on the surface or inside of ceramic bearing parts (mainly referring to rolling elements and rings), as well as changes in the physical and mechanical properties of the surface layer. This not only reduces friction and wear performance, leading to a significant decrease in strength, but also seriously affects the service performance and fatigue life of bearings. Therefore, during the processing and operation tests of bearing related parts, it is necessary to strictly inspect their surface characteristics, which means that in addition to checking the size, shape accuracy, and surface roughness of the parts, the surface defect characteristics should also be detected. In order to promote the research of non-destructive testing methods for the surface characteristics of ceramic bearing parts, based on recent experiments and research on the rolling contact fatigue, wear, lubrication, and processing and surface coating of related parts of ceramic bearing performance both domestically and internationally, this article explores the corresponding main detection technologies.
1.1 Surface roughness and waviness
Like ordinary bearings, the measurement methods for surface roughness of ceramic bearing parts can be divided into two categories: contact type and non-contact type based on whether they are in contact with the measured surface. The most commonly used contact roughness tester currently is a stylus profilometer (such as the Talysurf -6 model).
Non contact detection techniques are used for measuring steel balls, such as interference microscopy and laser speckle method. They do not come into contact with the measured surface during the measurement process, so they do not affect the morphology of the measured surface. It is generally believed that evaluating surface roughness solely based on Ra is not enough, and Ry must also be added, as the latter has a significant impact on the surface of ceramic balls (such as scratches and pits). Therefore, to ensure the uniqueness of the measurement results, JB/T7051 93 stipulates that the Ra of the steel ball is based on the profiler, and Ry is based on the interferometer.
The measurement of spherical error of ceramic balls usually uses a bearing inspection instrument or a roundness meter (such as the Talyrond300 roundness meter). To reduce measurement errors, it is important to pay attention to the definition of spherical errors as much as possible during measurement, as well as the statistical rules during data collection.
It should be pointed out that there is currently little attention paid to the surface waviness of the ball, which is usually used to describe surface waviness that varies randomly or repeatedly between shape deviation and surface roughness. The waviness of the ball can cause high-frequency vibration, which is very detrimental to the use of high-speed ceramic bearings. Therefore, it is necessary to strengthen research in this area.
1.2 Microhardness
Usually, Vickers or Knoop hardness testers are used to measure the hardness of ceramic parts. Compared with other measurement methods, the indentation obtained by Vickers hardness has a similar geometric shape and high measurement accuracy. Compared with Vickers hardness, Knoop hardness has many characteristics: the indentation length of Knoop is 2 8 times, which can improve the accuracy of length measurement. Due to the shallow indentation of Knoop hardness, it is particularly sensitive to the surface of the sample and can be used to detect suspicious defects such as burnt areas, softened areas, hardened deformation scars, and uneven surface treatment areas on the sample surface. In addition, Knoop hardness can withstand larger indentation loads without cracking, but the advantage of Vickers hardness is that it can determine the fracture toughness Kv and KIC values of ceramic materials in a single simple test process.
Optical methods, ultrasonic methods, acoustic emission, staining methods, and ray methods can be used to detect defects such as holes, peeling, scratches, micro scratches or microcracks on the surface of parts, as well as internal delamination, porosity, and porosity.
2.1 Optical Microscope (OM)
Optical microscope is the most commonly used and simplest tool for directly observing and analyzing the microstructure and surface morphology of materials, with a resolution of about 200 nm and a magnification of about 1000 times. In order to fully utilize the resolution ability, replica metallography (or replica metallography) is sometimes used, but it can only intuitively reflect the organizational morphology at the 100 nm size level, and is powerless for smaller organizational structures and units (such as dislocations). It can also be used to inspect the failure and fracture morphology on worn surfaces, observe and analyze the morphological characteristics of cracks, surrounding conditions, hardness measurements, and fracture morphology.
2.2 Ultrasonic testing
Scanning Acoustic Microscope (SAM) ultrasonic testing utilizes the directionality and other characteristics of ultrasound to collect and analyze reflected sound waves from a given depth of bearing parts to display images of their microstructure, thereby quantitatively determining the size, depth, shape, and distribution of defects. It can also measure the viscosity, temperature, and hardness of component materials. The most commonly used frequency for ultrasound is between 500 kHz and 20 MHz.
The scanning acoustic microscope, developed based on ultrasonic technology, is a non-destructive testing technology that reveals internal micro defects. Its working principle is to send a signal with a sound frequency of about 200 MHz, collect reflected waves, and convert them into electrical signals to obtain images. It can not only detect defects, but also accurately determine the location of defects and provide quantitative values for the size and depth of defects. Suitable for confirming the observation of optical mirrors and quantitatively detecting cracks and subsurface damage that cannot be observed by optical microscopes, with a scanning width of 0 5-3.75 mm, detectable depth 5-30 μ The surface defects of m (which have exceeded the limit that conventional ultrasonic testing can solve), and the characteristics of the fiber matrix interface can be determined in composite ceramic materials.
2.3 Staining method (FDP)
The use of high-resolution penetrants and advanced lighting technology and detection methods can effectively detect very small defects on the surface of parts (which have been successfully used in mass production of silicon nitride balls), which are usually invisible to the naked eye. If ceramic bearing parts are immersed in highly sensitive fluorescent dye penetrant, it is easy to observe the penetrant that has penetrated below the surface of the component, thus obtaining the range and shape image of very small surface cracks and peeling. The disadvantage of dyeing method is that it cannot reliably detect small cracks, especially when detecting porous materials, the background differences may obscure the differences in defects. In addition, it is not suitable for rapid automatic detection and places with chemical pollution issues.
Also known as electron microscopy or analytical electron microscopy (AEM), it is a comprehensive detection technology. Especially by using a high-energy electron beam as a light source to irradiate the sample to be analyzed, and using a magnetic field as a lens, various signals (such as secondary electrons, Auger electrons, etc.) that reflect the local information directly irradiated by the sample can be collected and analyzed using different methods. Not only can high-resolution and high magnification surface morphology of small areas in the part sample be obtained, Data related to crystal structure, defects (crystallographic parameters), and chemical composition can also be obtained. It mainly includes the following types: scanning electron microscopy (SEM), transmission electron microscopy (TEM), Auger spectroscopy (AES), X-ray photoelectron spectroscopy (XPS), electron probe microscopy (EPMA), and atomic force microscopy (AFM).
Surface residual stress is a very important indicator in the surface characteristics of ceramic bearing parts. Currently, a widely used non-destructive non-contact testing method is X-ray diffraction technology (XRD). The disadvantage is that it is not as intuitive and visible as an optical microscope, which makes it impossible to combine morphology observation with crystal structure analysis microscopically; The measurement depth is only a few micrometers to tens of micrometers below the surface of the sample, and it is necessary to use appropriate means (such as electrolytic polishing) to layer by layer exfoliate the sample in order to measure the residual stress at a certain depth; The detection results are greatly affected by surface conditions (such as collisions), thus requiring high requirements for the detected surface (to avoid damaging the original surface and maintain cleanliness). The advantages are simple principle, convenient measurement, high accuracy, and small measurement area (usually 5 mm) × 10 mm to 2 mm × 2 mm) can be used to create stress distribution maps on a fine scale, and can also infer contact stress and fracture stress. It is suitable for harsh environments such as high temperatures, as well as for qualitative and quantitative phase analysis, structural analysis, crystallinity analysis, and determination of lattice parameters. It should be pointed out that due to the particularity of ceramic materials and the shape of rolling elements, there is currently no satisfactory method for measuring residual stress on the surface of ceramic balls. Therefore, various experimental studies have been conducted, such as indentation crack method and scanning electroacoustic microscopy (SEAM).
More about XZBRG Ceramic Balls：
Full ceramic ball bearings constructed entirely of ceramic material. Inner/outer races and balls are made of either Silicon Nitride (Si3N4), Zirconium Oxide (ZrO2) or Silicon carbide (SiC). They are available as full complement (no cage) or with a cage made from PEEK or PTFE. Full ceramic bearings are for medium load and medium speed applications. It is not possible to achieve the inner and outer ring roundness that is found with precision steel bearings so full ceramic bearings have lower speed ratings.
Xinzhou Bearing provide a wide range of ceramic ball options across a variety of sizes. Material options include Silicon nitride (Si3N4), Zirconia (ZRO2), Alumina (Al2O3) and Silicon carbide (SIC) from 0.4mm to just over 115mm in diameter with the most common sizes in between. Precision grades provided are 5, 10, 16, 25 and 100.
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