Author name: honway

RA與SA的差異
Science Classroom

Differences Between RA and SA

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RA (Roughness Average) and SA (Surface Area) are two measurement indicators of surface roughness. RA is the most commonly used two-dimensional roughness parameter, evaluating surface smoothness by calculating the arithmetic mean of the absolute deviations of all points on the surface profile line from the reference line over the measured length. It is typically used for roughness detection on flat surfaces. On the other hand, SA is a three-dimensional surface roughness indicator that takes into account the height variations and other features of the surface profile. It is often used for more complex surface analyses, such as high-precision manufacturing or optical surface treatments. SA provides a more comprehensive view of surface roughness, making it suitable for applications that require detailed three-dimensional data.

Science Classroom

What is surface roughness?

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“Surface roughness” plays a crucial role in engineering and manufacturing. Surface roughness describes the smoothness of a surface, which affects various aspects of workpiece characteristics such as airtightness, mating performance, rigidity, and more. Unlike “surface flatness,” surface roughness measures the degree of surface irregularities, making it especially important for parts that require precise fitting or contact. Understanding the need to pursue “appropriate surface roughness” rather than extreme smoothness is essential to meet different application requirements.

鑽石砂輪與CBN砂輪怎麼選擇？
A complete guide to grinding wheel technology, Knowledge Column, Science Classroom

How to Choose Between Diamond Wheels and CBN Wheels?

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Grinding wheel abrasives can be categorized into general and super types, with diamond and CBN belonging to the super abrasives due to their extremely high hardness, making them suitable for grinding high-hardness materials. Diamond wheels should not be used on iron-containing workpieces, as they can catalyze the transformation of diamond into graphite, affecting performance and wearing down the wheel. When grinding temperatures exceed 600°C, diamonds are prone to melting or forming carbides, making them unsuitable for high-temperature processing. In contrast, CBN wheels are suitable for high-speed and iron-containing material processing, such as tool steel and mold steel, showcasing their unique advantages. With the advancements in technology raising precision requirements in manufacturing processes, selecting the most suitable grinding wheel is crucial. The most expensive option is not necessarily the best; rather, the most appropriate one is the optimal choice.

石榴石
Gemstones

Garnet—A Gemstone and High-Tech Material?

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Garnet is a versatile and colorful gemstone. Its name comes from the Latin word for pomegranate, due to its color and shape resembling pomegranate seeds. Garnet is a group of silicate minerals that have been used as gemstones and abrasives since the Bronze Age. There are many types of garnet, including pyrope, spessartine, and almandine each with unique chemical compositions and color characteristics. In addition to its use as a precious gemstone, garnet has extensive industrial applications, such as in water jet cutting, mechanical polishing, and optical equipment. In summary, garnet’s diverse uses and unique physical properties make it valuable in various fields with promising application potential.

青金石
Gemstones

Lapis Lazuli – A gemstone of higher status than gold

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Lapis Lazuli is a rock contains a variety of minerals, mainly composed of lapis lazuli, sodalite, etc., the white part is calcite, and the golden part is pyrite. The range of its colors includes teal, blue, indigo and blue-violet, the ones with more sky blue stone display brightly azure color. Lapis Lazuli has a long-standing history as a symbol of imperial power and wealth, and its status was valued in ancient Egypt, Babylon and other cultures. Ancient China called it “Emperor blue”, and the West called it “Ultramarine”, which is the emblem of nobility and majesty. Lapis Lazuli is often used in jewelry, pigments and medicines, and has high commercial value, the less white and golden part the better when buying.

天河石
Gemstones

A gemstone with mysterious river-colored — Amazonite

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Amazonite is a blue-green or green-blue variety of microcline feldspar, first discovered in the Amazon River basin. Its name comes from the Japanese “Tengaishi,” which means “river in the sky.” The distinct characteristic of Amazonite is its grid-like structure of blue-green and white squares caused by its twinning structure. High-quality Amazonite can be used as gemstones, while lower-quality stones are used for carving. Common imitations include copper-containing blue-green quartzite from China, known as “Guizhou Jade,” which differs from Amazonite in its higher hardness, lack of cleavage, and absence of the grid structure. When selecting Amazonite, look for pure color, transparency with few inclusions, and evenly distributed or inconspicuous grids. It is essential to avoid impact to prevent cracking. Some sellers use acid treatments to remove impurities, which may increase transparency but damage the structure. Methods to identify Amazonite include weight comparison and observing the stone’s pattern.

光譜石
Gemstones

A gems with unique optical effects – Labradorite

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Labradorite gets its name from the Labrador region in Canada, where it was first discovered. The stone contains a variety of metal element crystal minerals, giving it a unique play of colors known as labradorescence. This phenomenon causes the stone to shimmer with vibrant colors. Labradorites that display a full spectrum of colors are called “Spectrolite,” which is especially rare and valuable. Labradorite typically appears in gray, brown, or black, while gemstone-quality labradorite can exhibit iridescent colors such as red, yellow, blue, and green. When choosing labradorite, stones with a beautiful and large area of labradorescence are the most desirable. Due to its well-developed cleavage, labradorite is prone to breakage, so it should be set in jewelry with protective designs and handled carefully to avoid impact. There are almost no imitations of labradorite, but syenite rocks have a similar luster and are often counterfeited, but the quality is not as good as gem-grade labradorite.

日長石
Gemstones

A sparkling gemstone – Sunstone

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Sunstone, discovered by mineralogists in 1837, is primarily composed of oligoclase from the plagioclase series. Initially, it was very expensive due to its rarity, but it became more widely available after new deposits were discovered in Norway and Siberia. Its name comes from the fact that when viewed from a certain direction, the gemstone will shine with a bright golden brillience, which is a phenomenon known as “Aventurescence”. This shimmer is due to the presence of fine mineral inclusions within the gemstone, such as chalcopyrite, native copper, annite, goethite or hematite, which reflect golden to brownish-yellow light. The color of the gemstone is influenced by the amount of inclusions; the more inclusions it has, the deeper the color. When selecting sunstone, it is best to choose one that is evenly covered with metallic shimmer. To maintain it, avoid impacts to prevent damage along the cleavage planes.

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