Definitions

sandpaper

sandpaper

[sand-pey-per]
sandpaper, abrasive originally made by gluing grains of sand to heavy paper sheets. Today sandpaper is made primarily with quartz, aluminum oxide, or silicon carbide grains, and is graded according to the size of the grains. It is used for smoothing and polishing, for removing old paint or varnish, and for otherwise preparing wood surfaces for refinishing or other treatment.
Abrasive Paper is a form of paper where an abrasive material has been fixed to its surface.

Abrasive Paper is part of the "Coated abrasives" family of abrasive products. It is used to remove small amounts of material from surfaces, either to make them smoother (painting and wood finishing), to remove a layer of material (e.g. old paint), or sometimes to make the surface rougher (e.g. as a preparation to gluing).

History

The first recorded instance of sandpaper was in 13th century China when crushed shells, seeds, and sand were bonded to parchment using natural gum.

Shark skin was also used as a sandpaper. The rough scales of the living fossil Coelacanth are used by the natives of Comoros as sandpaper.

Abrasive paper was originally known as glass paper, as it used particles of glass. Glass frit has sharp-edged particles and cuts well, sand grains are smoothed down and work less well. Cheap counterfeit sandpaper has long been passed off as true glass paper; Stalker and Parker cautioned against it as far back as the 17th century. Although neither medium has been used for quality sandpaper for years, some authorities (notably school woodwork teachers) still practice an obsession that glasspaper is the "correct" title and sandpaper a misnomer. Neither is any more appropriate today.

Glass paper was manufactured by John Oakey's company in London by 1833, who had developed new adhesive techniques and processes that could be mass-produced. A process for making sandpaper was patented in the United States on June 14 1834 by Isaac Fischer, Jr., of Springfield, Vermont.

In 1916, 3M invented a type of sandpaper with a waterproof backing, known as Wetordry. This allowed use with water as a lubricant, and to carry about particles that would otherwise clog the finest grades. Its first application was for automotive paint refinishing.

Sandpaper has occasionally been used as a surface for painting, as by Joan Miro. Sandpaper was even used as a musical instrument, in Leroy Anderson's Sandpaper Ballet.

Types of sandpaper

There are countless 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". Cloth backing is used for sandpaper discs and belts, while mylar is used as backing with 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 rounded contours of a given workpiece; relatively inflexible backing is optimal for regular rounded or plane 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.

Material

Materials used for the abrading particles are:

  • flint — no longer commonly used
  • garnet — commonly used in woodworking
  • emery — commonly used to abrade or polish metal
  • aluminium oxide — perhaps most common in widest variety of grits; can be used on metal (i.e. body shops) or wood
  • silicon carbide — available in very coarse grits all the way through to microgrits, common in wet applications
  • alumina-zirconia — (an aluminium oxide - zirconium oxide alloy), used for machine grinding applications
  • chromium oxide — used in extremely fine micron grit (micrometre level) papers
  • aluminum oxide — used in high pressure applications, commonly known as CubitronTM a 3M Corp. Trademark who invented sol gel ceramic grains. Used in both coated abrasives, as well as in bonded abrasives.

As well, 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. Aluminium Oxide with stearate is also known as PS33.

Innovative abrading surfaces now 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 paper often cannot withstand the heat generated when 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. The wet and dry sandpaper is best used when wet and when using material like acrylic where it leaves a nice smooth feel afterwards.

Shapes

Sandpaper comes in a number of different shapes and sizes.

  • sheet — usually 9 by 11 inches, but other sizes may be available
  • belt — usually cloth backed, comes in different sizes to fit different belt sanders.
  • disk — made to fit different models of disc and random orbit sanders. May be perforated for some models of sanders. Attachment includes Pressure sensitive adhesive (PSA) and "hook-and-loop" (similar to velcro).
  • rolls

Grit sizes

Grit size refers to the size of the particles of abrading materials embedded in the sandpaper. A number of 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 Japan Industrial Standards Committee (JIS), the micron grade (generally used for very fine grits). The "ought" system was used in the past in the United States. Also, cheaper sandpapers sometimes are sold with nomenclature such as "Coarse", "Medium" and "Fine", but it is not clear 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) 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)   60 265
P60   269
P80   201
  80 190
Fine (sanding bare wood in preparation for finishing) P100   162
  100 140
P120   125
  120 115
Very Fine (final 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   320 36.0
P400   35.0
P500   30.2
  360 28.0
P600   25.8
Super fine (final sanding of finishes)   400 23.0
P800   21.8
  500 20.0
P1000   18.3
  600 16.0
P1200   15.3
Ultra fine (final sanding of finishes) P1500 800 12.6
P2000 1000 10.3
P2500   8.4

See also

References

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