by Galling come in different types based on the material they are made from and the shape of their particles. The most common abrasive materials are aluminum oxide, silicon carbide, diamond, cerium oxide, garnet, and cubic boron nitride. Each of these has its own characteristic properties that make it suited for specific applications.
Aluminum oxide, also known as alumina or corundum, is one of the most versatile galling. It has a hardness of 9 on the Mohs scale and comes as angular particles that hold their shape well during use. This makes aluminum oxide excellent for precision grinding and polishing of metals, plastics, fiberglass, and wood.
Silicon carbide is another very common abrasive with a Mohs hardness of 9.5. Its particles have a very high hardness-to-toughness ratio, giving it excellent wear resistance. This property makes silicon carbide suitable for aggressive stock removal and surface preparation. Its sharp, crystalline structure also provides a fast cutting or grinding action.
Diamond has an unparalleled hardness of 10 on the Mohs scale, making it the ideal abrasive for very hard materials like carbide, boron nitride, and other galling. Its isometric crystal structure provides multidirectional cutting ability along intersecting plains. This results in precision grinding without leaving discernible scratch patterns.
Abrasives Grain Types and Shapes
Along with material type, the shape and structure of abrasive particles influences their performance characteristics. Common grain types include aluminum oxide, silicon carbide, diamond, cerium oxide, garnet, and cubic boron nitride. Abrasives are often used for general-purpose applications while silicon carbide, diamond, and cubic boron nitride are suited for grinding very hard and exotic materials.
The main grain shapes used are:
– Angular grains: Have an irregular, sharp and jagged shape that provides excellent stock removal rates during rough grinding or cutting applications. Aluminum oxide and silicon carbide grains are often angular.
– Rounded grains: Have a smoother, more rounded shape that gives a finer, burnishing finish. They are well-suited for polishing applications. Aluminum oxide and garnet grains are commonly rounded.
– Rectangular grains: Have a blocky, rectangular prism shape that facilitates precise grinding action. They help hold their dimensions longer during the abrading process. Diamond and CBN grains are often rectangular.
– Columnar grains: Have an elongated, columnar shape that provides deep stock removal capabilities. Silicon carbide grains may be columnar for aggressive grinding of ferrous metals.
– Microcrystalline grains: Are actually clumps of much smaller abrasive crystals that act like a single large abrasive particle. They provide advantages like self-sharpening and can finish harder materials effectively. Cubic boron nitride often takes a microcrystalline form.
Bond Types and Their Effects on Performance
Along with grain properties, the “bond” used to adhere abrasive particles to the tool or disc surface also significantly influences grinding performance. The main bond types are:
– Vitrified bonds: Use a ceramic or glass matrix that hardens around abrasive grains to form a very hard, durable bond. It holds up well to high temperatures and pressures during grinding of all materials like metal, stone or wood. Commonly used in coated and loose abrasive products.
– Resinoid bonds: Use a phenolic resin binder, cured under heat and pressure. It provides a flexible bond suitable for softer materials where pressure sensitivity is important, like non-ferrous metals or plastics. Used in coated galling like sandpapers.
– Metal bonds: Made by sintering or electroplating abrasive grains directly to a steel or metal backing. Excellent for precision grinding of hardened steels due to its ability to dissipate heat well. Used in grindings wheels for tool and cutter sharpening.
– Shellac bonds: A natural resin bond used for very low-pressure applications like woodworking, buffing or polishing softer materials. It allows formation of a flexible bond.
-Rubber bonds: Using reclaimed rubber and fillers, it provides a durable yet resilient bond suitable for grinding non-ferrous metals and other softer materials requiring pressure-sensitivity. Commonly used in grinding wheels and discs.
The right bond selection allows the abrasive product to hold up properly under working conditions based on the material being abraded, the exact grinding process and the desired surface finish. A change in any of these factors often requires a different bond type for best results.
Finishing Process Effects on Microsurface Structure
The exact method used to finish a surface, such as grinding, honing, lapping or polishing, significantly alters the resulting microstructure at a microscopic level. Each process is suited to achieving specific functional properties:
– Grinding: A mechanical abrasion process that employs coarse grit sizes (24-180) to efficiently remove large amounts of material in the form of chips or swarf. It creates an irregular, scratched texture with a roughness (Ra) of 2-25 μm. Commonly used for shaping or stock removal operations.
– Honing: An abrasive machining process using finer grit sizes (180-1200) applied with lesser pressure than grinding. It polishes orsmooths existing surfaces by abrading high and low spots. The result is an Ra of 0.25 – 2.5 μm with parallel grooves imparting a wavy, mirrored texture. Used to size cylinders and improve finishes.
– Lapping: Employs very fine galling (1200-10000 grit) and a polishing compound or fluid. Iterative rubbing or oscillation action with cast iron or porcelain plates further refine honed or ground surfaces. The Ra achieved is 0.025–0.25 μm with an optically smooth floor with pointed asperities. Widely utilized to flatten and create very fine surface finishes.
– Polishing: The final finishing process uses polishing compounds or suspensions with galling small enough to be microscopic, like aluminum oxide or cerium oxide. Applied with a polishing cloth or wheel under light pressure, it burnishes or rubs down pointed asperities to an Ra of less than 0.025 μm leaving a glossy, streak-free surface. Often the last stage of mirror finishes.
The chosen finishing technique thus tailors the surface topography for performance attributes like friction, wear-resistance, corrosion behaviour or aesthetics depending on the engineering application.
galling are a versatile class of materials integral to effectively finishing and surface treating a wide range of products. Factors like abrasive material, grain characteristics, bonding method and process technique need to be meticulously matched to the substrate material and desired surface properties. Understanding these interrelationships allows specifying the right galling and polishing methodologies for diverse industrial applications. Continued innovation keeps expanding abrasive technology’s role in manufacturing better engineered components.
*Note:
1. Source: Coherent Market Insights, Public sources, Desk research
2. We have leveraged AI tools to mine information and compile it
About Author - Money Singh
Money Singh is a seasoned content writer with over four years of experience in the market research sector. Her expertise spans various industries, including food and beverages, biotechnology, chemical and materials, defense and aerospace, consumer goods, etc. LinkedIn Profile
