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    * Sandpaper *

    کاغذ سمباده


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    (Wikipedia) - Sandpaper
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    Sheets of sandpaper with different grits (40, 80, 150, 240, 600).

    Sandpaper or glasspaper are generic names used for a type of coated abrasive that consists of a heavy paper with abrasive material attached to its surface. Despite the use of the names neither sand nor glass are now used in the manufacture of these products as they have been replaced by other abrasives. Sandpaper is produced in different grit sizes and is used to remove small amounts of material from surfaces, either to make them smoother (for example, in painting and wood finishing), to remove a layer of material (such as old paint), or sometimes to make the surface rougher (for example, as a preparation for gluing).

    Contents

    History

    The first recorded use of sandpaper was in 13th-century China when crushed shells, seeds, and sand were bonded to parchment using natural gum. Sandpaper was originally known as glass paper, as it was coated with particles of glass rather than sand. Glass frit has sharp-edged particles and cuts well whereas sand grains are smoothed down and do not work well as an abrasive. Cheap counterfeit sandpaper was often passed off as true glass paper; Stalker and Parker cautioned against it in A Treatise of Japaning and Varnishing published in 1688. Glass paper was manufactured in London by 1833 by John Oakey, whose company had developed new adhesive techniques and processes, enabling mass production. A process for making sandpaper was patented in the United States on June 14, 1834 by Isaac Fischer, Jr., of Springfield, Vermont. In 1921, 3M invented a sandpaper with a waterproof backing, known as Wet and dry. This allowed use with water, which would serve as a lubricant to carry away particles that would otherwise clog the grit. Its first application was automotive paint refinishing.

    Shark skin has also been used as an abrasive and the rough scales of the living fossil, Coelacanth are used for the same purpose by the natives of Comoros. Boiled and dried, the rough horsetail is used in Japan as a traditional polishing material, finer than sandpaper.

    Types320 grit silicon carbide sandpaper, with close-up view.

    There are many varieties of sandpaper, with variations in the paper or backing, the material used for the grit, grit size, and the bond.

    Backing

    In addition to paper, backing for sandpaper includes cloth (cotton, polyester, rayon), PET film, and "fibre", or rubber. Cloth backing is used for sandpaper discs and belts, while mylar is used as backing for extremely fine grits. Fibre or vulcanized fibre is a strong backing material consisting of many layers of polymer impregnated paper. The weight of the backing is usually designated by a letter. For paper backings, the weight ratings range from "A" to "F," with A designating the lightest and F the heaviest. Letter nomenclature follows a different system for cloth backings, with the weight of the backing rated J, X, Y, T, and M, from lightest to heaviest. A flexible backing allows sandpaper to follow irregular contours of a workpiece; relatively inflexible backing is optimal for regular rounded or flat surfaces. Sandpaper backings may be glued to the paper or form a separate support structure for moving sandpaper, such as used in sanding belts and discs. Stronger paper or backing increases the ease of sanding wood. The harder the backing material, the faster the sanding, the faster the wear of the paper and the rougher the sanded surface.

    Material

    Materials used for the abrading particles are:

    Sandpaper may be "stearated" where a dry lubricant is loaded to the abrasive. Stearated papers are useful in sanding coats of finish and paint as the stearate "soap" prevents clogging and increases the useful life of the sandpaper.

    The harder the grit material, the easier the sanding of surfaces like wood. The grit material for polishing granite slab must be harder than granite.

    Later abrading surfaces include long-life stainless steel sanding discs.

    Bonds

    Different adhesives are used to bond the abrasive to the paper. Hide glue is still used, but this glue often cannot withstand the heat generated during machine sanding and is not waterproof. Waterproof or wet/dry sandpapers use a resin bond and a waterproof backing.

    Sandpapers can also be open coat, where the particles are separated from each other and the sandpaper is more flexible. This helps prevent clogging of the sandpaper. Wet and dry sandpaper is more effective used wet because clogging is reduced by particles washing away from the grinding surface. Arguably there are also benefits due to lubrication and cooling.

    Shapes

    Sandpaper comes in a number of different shapes and sizes:

    Grit sizes

    Grit size refers to the size of the particles of abrading materials embedded in the sandpaper. Several different standards have been established for grit size. These standards establish not only the average grit size, but also the allowable variation from the average. The two most common are the United States CAMI (Coated Abrasive Manufacturers Institute, now part of the Unified Abrasives Manufacturers'' Association) and the European FEPA (Federation of European Producers of Abrasives) "P" grade. The FEPA system is the same as the ISO 6344 standard. Other systems used in sandpaper include the Japanese Industrial Standards Committee (JIS), the micron grade (generally used for very fine grits). The "ought" system ({0, 00, 000, ...} aka {1/0, 2/0, 3/0, ...}) was used in the past in the US. Cheaper sandpapers sometimes use nomenclature such as "Coarse", "Medium" and "Fine", but it is unclear to what standards these names refer.

    Grit size table

    The following table, compiled from the references at the bottom, compares the CAMI and "P" designations with the average grit size in micrometres (µm).

    Grit size table ISO/FEPA Grit designation CAMI Grit designation Average particle diameter (µm)
    MACROGRITS
    Extra Coarse (Very fast removal of material, hardwood flooring initial sanding) P12   1815
    P16   1324
    P20   1000
    P24   764
      24 708
    P30   642
      30 632
      36 530
    P36   538
    Coarse (Rapid removal of material) P40 40 425
      50 348
    P50   336
    Medium (sanding bare wood in preparation for finishing, for gentle removal of varnish, also used for skateboard grip tape)   60 265
    P60   269
    P80   201
      80 190
    Fine (sanding bare wood in preparation for finishing, not suitable for removing varnish or paint from wood, use for cleaning plaster and water stain from wood) P100   162
      100 140
    P120   125
      120 115
    Very Fine (sanding of bare wood) P150   100
      150 92
    P180 180 82
    P220 220 68
    MICROGRITS
    Very Fine (sanding finishes between coats) P240   58.5
      240 53.0
    P280   52.2
    P320   46.2
    P360   40.5
    Extra fine, start polishing of wood   320 36.0
    P400   35.0
    P500   30.2
      360 28.0
    P600   25.8
    Super fine (final sanding of finishes, final sanding of wood)   400 23.0
    P800   21.8
      500 20.0
    P1000   18.3
      600 16.0
    P1200   15.3
    Ultra fine (final sanding and polishing of thick finishes) P1500 800 12.6
    P2000 1000 10.3
    P2500   8.4
    P3000   6
    P6000   4

    Tags:China, Chromium, Comoros, ISO, Isaac, Japan, Japanese, London, Sandpaper, US, United States, Wikipedia


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