Um pouco sobre grãos para afiação

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Não sabia onde colocar o post. Moderador, sinta-se a vontade em

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Particularmente, achei est

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eu copiei para o wiki, secção de manutenção de navalhas

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Sinta-se a vontade, amigo..

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Um pouco dos termos usados em abrasivos
fonte:   http://www.uama.org/Abrasives101/101Glossary.html

Glossary of Terms Commonly Used in the Abrasives Industry

Acid Washed - Abrasive grain washed with acid to remove iron and/or impurities.

Angle of Repose - The greatest angle to the horizontal made naturally by the inclined surface of a pile of abrasive when poured from a designated height. Usually a measure of the ease with which the material will flow.

ANSI - American National Standards Institute - Organization maintaining standards used in the industry.

Apparent Specific Gravity - The ratio of a mass of solid or liquid to the mass of an equal volume of distilled water.

Aspect Ratio - The ratio of the length of a particle to its width.

ASTM - American Society of Test Materials - Organization maintaining technical standards for a wide variety of industries.

Ball Mill - Equipment used to reduce particle size by breaking agglomerations of particles into individual particles and larger particles into smaller ones, and to modify particle shape.

Bayer Process - A process for the purification of bauxite (aluminum ore). The ore is digested with a sodium hydroxide solution which dissolves the alumina and precipitates oxides impurities such as iron, silicon, etc. The solution is then filtered and the alumina precipitated as a hydroxide. This is used as a feed stock for white fused and calcined alumina.

BCI Test - Buck and Company Incorporated - Test equipment for analyzing abrasives for free iron.

Bolting Cloth - Mesh used for making sieves for sifting equipment.

Bonded Abrasives - Abrasive grain used in Grinding Wheel applications.

Bulk Density - Sometimes referred to as "density" or "loose packed density" (LPD). Weight (grams) per volume (cubic centimeters) of loose packed abrasive grain. Generally indicative of the shape of the grain.

CAMI - Coated Abrasives Manufacturing Institute - Organization of coated abrasive manufacturers.

Capillarity - Ability of abrasive grain to be wetted by capillary action. Usually an indication of grain cleanliness.

Cerium Oxide (CeO2) - Naturally occurring deposits are usually a mix of Cerium and other rare earth oxides (REO's), such as Rubidium Oxide and Tantalum Oxide. Color varies from off-white (buff) to reddish brown, depending on the chemical content. Softer than Alumina and Silicon Carbide; primarily used for polishing glass, quartz crystals, etc.

Chemical Composition - A chemical analysis of an abrasive.

Coarse - Composed of comparatively large particles.

Coarse Grading - Abrasive grain with too many large particles. A sieve analysis with too much material retained on the largest opening sieves in the specification.

Coarse Grits - Generally particles extremely large for the abrasive grain size.

Coated Abrasives - Abrasive grain used in the sandpaper industry.

Colloid - A finely divided dispersion of one material in a second continuous phase (usually a liquid) in which the particles range in size from one nanometer to one micron. May be used for very fine polishing or as a feedstock for non-fused abrasive manufacture.

Coning and Quartering - A method for getting a smaller representative sample usually from a larger sample. The grain is arranged into a conical pile and divided into quarters. Alternate quarters of the pile are combined, piled and quartered similarly until a small representative sample is obtained.

Corundum - Naturally occurring Aluminum Oxide.

Crude - Large pieces of abrasive in an ingot form (after furnacing) or after primary crushing.

Crusher - Size reduction equipment causing the separation of a solid into pieces. Some examples are jaw, gyratory, roll, and hammermill.

Crystallography - Description of the size or shape of a crystal. For fused abrasives, usually determined by degree of cooling an ingot after furnacing. For SiC, alpha silicon carbide forms hexagonal crystals. NOTE: Crystallography refers to the shape of the crystal formed, and is distinct from the shape of the actual abrasive granules, which may be modified by crushing, milling, etc.

Density - Sometimes used to describe apparent specific gravity or bulk density.

Dust Fines/Extreme Fines - Particles much too fine for the abrasive grain size.

Electrical Resistance - A method of measuring particle size distribution, used especially for microgrits.

Emery - Naturally occurring mineral, an intimate mixture of corundum and mineralized iron oxide.

FEPA - Federation of European Producers of Abrasives - European organization which maintains abrasive specifications (FEPA F - Bonded) (FEPA P - Coated).

Fine - Composed of comparatively small particles.

Fine Grading - Abrasive grain with too many small particles as specified on a sieve analysis.

Flint - A silica-based mineral often used as an abrasive.

Free Iron - Iron in abrasive grain usually originating from the crushing equipment.

Friability - Relative breakdown of the abrasive grain through attrition (grinding, blasting, milling)

Furnacing - General method for producing abrasive crude either by fusion (alumina based) or electro chemical reaction (Silicon Carbide).

Fusion - Melting of raw materials (generally in an electric arc furnace) to make an abrasive ingot. Generally associated with Alumina based abrasive grains.

Garnet (Al2O3.3FeO.3SiO2) - A naturally occurring abrasive, reddish brown in color, blocky to sharp in shape, slightly softer than Alumina (8 on Mohs scale). Used in a variety of industrial applications.

Grade - Definition of size of abrasive grain.

Grit - Similar to grade.

Hardness - Resistance to denting or scratching usually measured the Moh's scale or Knoop.

Heat Treating - Heating an abrasive grain to impart a certain property (harder, tougher, cleaner)

ISO - International Organization for Standardization- International organization involved with specifications and quality systems.

JIS - Japanese Industrial Standard, published by the Japanese Industrial Standards Committee in conjunction with the Japanese Standards Association.

LPD - Loose packed density. Same as bulk density.

Macrogrits - Generally abrasive grain sizes coarser than 240 or 280 grits.

Mag (Magnetic) Treat - Passing abrasive grain through a magnetic field to remove free iron.

Melting Point - The temperature at which a solid turns to a liquid.

Mesh - Generally interwoven wire screening used to sift or test abrasive grain. Sometimes wrongly used to describe abrasive grain size.

Microgrits - Generally abrasive grain sizes finer than 220 or 240 grits.

Micron - One millionth of a meter. Generally used to define average particles size of microgrits (powders).

Mixed Grits - Generally a condition where two grit sizes are unintentionally mixed together.

Nanometer - One billionth of a meter (one thousandth of a micron).

Netronics - Instrument (Buck and Company, Inc.) Used for measuring free iron.

Packed Density - Another term for tap density.

Particle Size - Average diameter of an abrasive grain.

Pour Density - Bulk density.

Pycnometric Density - Apparent specific gravity tested with a pycnometer.

Refractories Abrasive - Abrasive grain manufactured for the Refractory industry.

Riffle - A sample splitting device used to separate a large sample into a small representative sample.

Rotap - Instrument used to sift abrasive through sieves to obtain a particle size distribution measurement.

Sample Thief - A tubular instrument with a closed, pointed end having holes down one surface used for procuring a representative sample of abrasive grain.

Screen: 1) A sieve. 2) A machine with screening surface(s) used to classify materials by size.

Screen Sizes - Another term for macrogrits.

Sedimentation Sizes - Another term for microgrits.

Sedimentometer - A device for measuring particle size distribution using the time it takes a sample of material to settle a given distance, using Stokes Law.

Sieve - Generally, interwoven mesh mounted on a frame and used for testing or sifting abrasive grain.

Sieve Sizes - Another term for macrogrits.

Sinter - To coalesce into a single mass without actually melting.

Size Distribution - A measured size range of abrasive particles.

Spherical Equivalent - A means of reporting the size of particles regardless of shape based on their volume, in which the particle size is reported as the diameter of a sphere of the same volume.

Standard Sand - An abrasive of a known particle size distribution when tested on a calibrated instrument; used to verify calibration of other test instruments (such as sieves; see Appendix 3).

Surface Treatment - Coatings added to abrasive particles to impart certain characteristics (wetability, flowability, retention).

Tap Density - Generally a bulk density of a packed sample. Generally used for powders.

Test Sieve - A specially manufactured sieve used for testing particle size.

Toughness - Resistance to abrading of abrasive grain.

Viscosity - The resistance of a liquid to shear forces, and thus its resistance to flow.

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Common Types of Manufactured Abrasives
   
   
Naturally Occurring vs. Manufactured Abrasives

Throughout history, humans have used as abrasives everything from beach sand to walnut shells to paper bags. This section covers some of the most widely used types of manufactured abrasives. By manufactured abrasives, we mean primarily those materials that are created through a manufacturing process as opposed to being mined from the earth. Some naturally occurring materials are also produced artificially (such as aluminum oxide and diamond), so it is impossible to draw a hard and fast line between these two categories. Additionally, naturally occurring abrasives are often used in the same applications as manufactured abrasives. Thus, some naturally-occurring abrasives are mentioned briefly and listed in the glossary.

Widely-used naturally occurring abrasives include garnet, cerium oxide, flint, emery, corundum (aluminum oxide), and diamond. These materials may have varying characteristics and chemical compositions depending on the specific geological source. Manufactured versions of these materials are usually more consistent in chemical composition and other characteristics.
Manufactured Abrasives

Abrasives can be distinguished in a variety of ways- their hardness, color, chemical composition, crystal shape, and friability, to name but a few. Since the chemical composition- that is, the type of material- determines many of the other characteristics, we use that as the primary means of distinguishing one type of abrasive from another.

1. Chemical Composition

a. Alumina Based ( Aluminum Oxide, Al2O3) (9.0 on Mohs hardness scale)

White Fused Aluminum Oxide - High chemical purity (>99% Al2O3); generally used for applications where high purity is important (medical, dental or other industrial uses); generally softer or more friable than other abrasives; used in grinding applications where a more friable product is desired. Granules typically are blocky shaped (see below, Shape), with an aspect ratio of approximately 1:1 to 3:1.

White Calcined Aluminum Oxide - High purity aluminum oxide (>99.5% Al2O3), manufactured by growing individual crystals from seed crystals at high temperature. Crystals are hexagonal platelet shaped with an aspect ratio of 5:1. Used in a variety of lapping, buffing and polishing applications, incorporated into bars and pads, and used in ceramics.

Aluminum Oxide with Chrome - White Aluminum Oxide fused with Cr2O3 to enhance grinding; a pink abrasive used in grinding applications requiring slightly more toughness than White Fused Aluminum Oxide.

Brown Fused Aluminum Oxide - Abrasive with a content of 2-4% TiO2 to further enhance toughness; the "workhorse" of the industry; used in a wide variety of uses including Bonded, Coated, Refractory and Industrial markets; probably the most widely used abrasive.

Low Titania Brown Fused Aluminum Oxide - Abrasive with a content of 1-2% TiO2 to enhance toughness of the grain; generally used in Bonded or Coated applications requiring an abrasive slightly tougher than White Aluminum Oxide.

Zirconia-Alumina - The toughest of the alumina based products; used in Bonded, Coated and Sandblasting applications requiring an extra tough abrasive.

Hydrated Alumina - Aluminum oxide with water chemically bonded to the alumina. Crystals are small (typically 1 mm or less in size) and very soft; typically used for fine polishing applications and as a raw material for ceramics.

Ceramic Aluminum Oxide - A high-purity fine-grained alumina obtained from sintering dispersed colloidal alumina. This provides a tough product primarily used for precision grinding of steels and hard alloys.

b. Silicon Carbide (SiC) (9.3 on Mohs hardness scale) - Silicon Carbide is a man-made abrasive material formed by a series of vapor-phase reactions of carbon and silicon dioxide at high temperature in an Acheson furnace. Alpha phase silicon carbide, in the form of hexagonally shaped platelets, is the most common form observed in the abrasives and refractories industries. The character of alpha silicon carbide is dependent on a number of factors such as purity of raw materials used in the Acheson furnace, and the reaction time and temperature. (see below, p. 9, Furnacing Silicon Carbide.)

Green Silicon Carbide - The highest purity Silicon Carbide manufactured; typically containing 99% or greater SiC; generally used in grinding wheels for particular grinding properties or in industrial applications requiring a high purity SiC (coatings); generally more friable than black SiC.

Black Silicon Carbide - Lower purity (95-98%), tougher Silicon Carbide; generally used in Bonded, Coated, Refractory and Industrial markets for a wide variety of applications.

c. Other Manufactured Abrasives -
Including Boron Carbide (B4C), Cubic Boron Nitride (CBN), and Diamond; used for special applications requiring very hard materials for grinding and polishing. CBN and Diamond are also known as "Superabrasives."
Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

2. Shapes

Particle shape affects the performance of the abrasive in a variety of ways, such as the rate of stock removal and level of subsurface damage. Some specialty applications require unusual shapes. For fused alumina and many other abrasives (such as silicon carbide), the aspect ratio (length to width) is a primary descriptor of shape. For others, the aspect ratio is irrelevant or misleading. Thus, fused aluminum oxide tends to have one long dimension and two smaller, roughly equal dimensions; i.e., the thickness is roughly equal to the width. Calcined alumina tends to have two long dimensions and one much smaller one; i.e. the length and width are roughly equal, but the thickness is about one-fifth the length. (For calcined alumina, this ratio, length to thickness, is often referred to as the aspect ratio). For more exotic shapes, aspect ratio may vary with the size of the particle and thus can only be given as a range.

a. Blocky Shape (High Bulk density) - The abrasive grain is "rounded" by abrading equipment to remove very sharp, weak grain. Depending on application, the grain shape can vary from "mulled" to blocky with sharp edges. The blocky shape enhances toughness and bulk density of the grain. Applications include tougher grinding or sanding applications, longer life for sandblasting and increased density for refractory or ceramic applications. Aspect ratio is approximately 1:1. (See Figure 1)

b. Blocky Shape (Medium Bulk density) - The abrasive grain is shaped to yield particles which are sharp but do not contain weak, platey or needlelike particles. Uses include general grinding, sanding, sandblasting and refractory applications. Aspect ratio is approximatley up to 1.5:1. (See Figure 2.)

c. Sharp Shape (Low Bulk density) - Abrasive grain that has been specially crushed to yield very sharp grain. This is generally required by the Coated abrasives industry and some grinding wheel applications to produce an aggressive, fast cutting product. Aspect ratio ranges from 1.5:1->3:1. (See Figure 3.)

d. Platelet Shaped - Generally found in calcined aluminas. (See Figure 4.)

e. Extreme Shapes - A variety of highly unusual shapes are possible through different manufacturing processes for specific applications. Figure 5 shows one of these, extruded abrasives.

3. Heat Treatments

Heat treatments are often applied to Brown Aluminum Oxides. These may be either high heat or low heat; both enhance toughness, high heat more so than low heat. High heat treatment imparts a bluish color to the grain. Low heat is used to improve cleanliness and capillarity. Uses of heat-treated abrasives include grinding wheels, coated abrasives, and specialized industrial applications.

4. Surface Treatments

A. Silane Treatments - Generally applied to enhance bonding of the abrasive grains to organic resins or epoxies. Applications include grain used for grinding wheels and industrial uses.

B. Projectivity Enhancing Treatments - A variety of coatings can be applied to abrasive grain for the Coated abrasives industry. These coatings enhance the electrostatic properties of the grain to improve projection during the making of sandpaper. (Grain on a conveyor belt passes through an electrostatic field. It "jumps up" or projects onto a sandpaper belt containing a resin. The electrostatic field polarizes each grain so that elongated ends stick up and improve cutting ability.)

C. Iron Oxide Coatings - Applied to improve bonding to resins for grinding wheel and sandpaper applications.

D. Others - Other specialized treatments may be applied to improve "wetability", flowability, suspension in water or oil, or to improve other characteristics.

Please Note: This is a very general report which does not include all applications.