Sandpaper

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

Sandpaper or glasspaper[1] are names used for a type of coated abrasive that consists of sheets of paper or cloth with abrasive material glued to one face. Despite the use of the names neither sand nor glass are now used in the manufacture of these products as they have been replaced by other abrasives.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 a range of grit sizes and is used to remove 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). It is common to use the name of the abrasive when describing the paper, e.g. "aluminium oxide paper", or "silicon carbide paper".

Grit refers to the average particle diameter. The larger the grit, the smaller the particle size. The smaller the grit, the coarser the particles are.

History

The first recorded use of sandpaper was in 1st-century China when crushed shells, seeds, and sand were bonded to parchment using natural gum. Shark skin (placoid scales) 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.[2] Boiled and dried, the rough horsetail plant is used in Japan as a traditional polishing material, finer than sandpaper. Glass paper was manufactured in London by 1833 by John Oakey, whose company had developed new adhesive techniques and processes, enabling mass production. Glass frit has sharp-edged particles and cuts well whereas sand grains are smoothed down and do not work well as an abrasive. Cheap sandpaper was often passed off as glass paper; Stalker and Parker cautioned against it in A Treatise of Japaning and Varnishing published in 1688.[3] In 1921, 3M invented a sandpaper with silicon carbide grit and a waterproof adhesive and 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 in automotive paint refinishing.[4]

Types

320 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.

Type of abrasive

Types of abrasive materials include:

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.

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 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 Manufacturer's 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

See also

Similar to sandpaper

Tools used with sandpaper

Miscellaneous

References

  1. ↑ E. M. Kirkpatrick, ed. (1983). Chambers 20th Century Dictionary. Edinburgh: W & R Chambers Ltd. p. 532. ISBN 0-550-10234-5.
  2. ↑ Thomson, Keith Stewart (1992). Living Fossil: The Story of the Coelacanth. W. W. Norton & Company Limited. ISBN 978-0-393-30868-6.
  3. ↑ Stalker & Parker (1971) [1688]. A Treatise of Japaning and Varnishing. Tiranti.
  4. ↑ Jeffrey, Kirk (1989). "The Major Manufacturers: From Food and Forest Products to High Technology". In Clark, Clifford Edward. Minnesota in a Century of Change: The State And Its People Since 1900. Minnesota Historical Society Press. p. 234. ISBN 978-0-87351-238-1.

Further reading

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