Sandpaper grit, types, markings, tables

For grinding, leveling wood, metal, stone, plastic, abrasive materials are used. For hand finishing or using hand grinders, sandpaper is needed. This is a material with a rough surface. The degree of “roughness” determines the graininess of the sandpaper. What is it and how is it chosen, what other types of sandpaper can be, how to choose it. Read more about all this.

What is sandpaper

Emery, sandpaper (or just sandpaper), sandpaper, abrasive or sandpaper are all names for the same material. This material is a flexible abrasive for manual or machine processing of various materials. There is an emery for metal, wood, plastic, glass. They are sometimes used for processing plaster and putty, but for these purposes a grinding mesh may be more convenient. She doesn’t clog up like that.

Sandpaper abrasive is small particles of hard materials of different sizes. These particles are called grains, and their size is called granularity. They are glued to a flexible base. Sanding / abrasive paper-based paper is more common. This is the cheapest type, but not the most durable. The fabric base is more reliable, but it can stretch, which is also not always convenient when working. Polyethylene-based emery is a waterproof sanding material. This is the most expensive type, but you can even work in water. For wet processing, sandpaper on waterproof paper is also used.

Sandpaper is used to eliminate irregularities and defects, to obtain a smooth surface, grinding and polishing. So sanding can be coarse or fine. Under the rough understand the removal of paint or rust, burrs, primary leveling of the surface. For this work, material with large (from 500 microns to 1 mm or more) and medium (from 200 microns to 500 microns) grains is used. Obtaining a flat and smooth surface – grinding, polishing – this is already a fine or finishing treatment. For this type of work, a skin with a fine grain (less than 200 microns) is used.

Release forms and types

The usual form of release is in rolls or sheets. The sheet can be based on cardboard, or it can be on thick paper. Most often it is more rigid than rolled. Roll is more often used on belt grinders, and for manual use too. In addition, there are the following types of abrasive materials:

• abrasive circles. Used for installation on nozzles for special machines. These can be grinders, drill bits, angle grinders. There are different types:
  • Ordinary circles of different diameters and different grain sizes.
  • With Velcro glued on the back.
  • Petal – this is when strips of sandpaper are glued to the base. They can be of different grain sizes. They are used for rough processing of metals (usually), for removing paint (including from concrete).
    

• Belts for belt grinders. They have a certain length and width – for the most common sizes.
• Net. Thin wire, interwoven in the form of a cloth. Abrasive particles are glued to the wire. Such material is convenient for grinding plaster, since most of the resulting dust wakes up through the mesh cells and the abrasive does not clog. It is this material that is used to level gypsum plaster for painting.

There are also sanding pads. This is an abrasive that is applied to polyurethane foam. This type of abrasive is used to smooth surfaces with grooves, threads, recesses. Abrasive particles can be applied to one, two or four sides of the sponge. They can be the same size or different. But usually, this is a fine grain, just a different degree of “fineness”. Sponges are more convenient, as they take any shape, in addition, they can be washed from dust and dried. The number of washes is not limited. They do not suffer from washing, they can be used until the grain has crumbled. And it depends on the quality.

Types of grit sandpaper

As already mentioned, the grit size of the sandpaper is the size of the abrasive fragments. They are measured in micrometers. The smallest grain that is found in sandpaper is only 3-5 microns, the largest is 1000 microns (this is 1 mm). According to the grain size, fine-grained and coarse-grained abrasives are distinguished.

Russian standards

In order to be able to understand what specific material is in front of you, the dimensions of the abrasive grain are indicated in the marking. But it’s not so easy for her. During the Soviet era, GOST (3647-80) was introduced, the designation according to which still exists, although in 2005 a new standard (GOST R 52381-2005) was introduced, which was developed on the basis of common European standards. The difference between the old and new GOST is significant.

• According to the old standard the minimum grain size is prescribed. That is, the larger the number, the larger the grain. But it must be borne in mind that some of the grains are smaller. In addition, the marking (letter designation) for large and small grains is different. It’s worth remembering.
  • For coarse-grained emery, the grain size of the sandpaper is indicated in microns, and after it they write the letter H with a hyphen in front of it – “H”. For example, 63-HThis means that the minimum grit size on the emery will be 63 microns or 63 micrometers (µm). But there will also be particles of a larger size. How much bigger? Slightly smaller than the previous brand. In this case, only 63-H is larger than 80-H, that is, the grain will be slightly less than 80 microns. The second example is 6-H. The grain size is no more than 6 microns or 60 microns, and the largest will be no more than 80 microns (since the previous grade is 80-H).

• • RџSЂRё marking of fine-grained abrasive paper grain size is indicated in micrometer, and after the number put the letter “М» (no hyphen). Example: 14M. This means that the maximum grit of sandpaper is 14 micrometers, but there are also finer grains up to 10 microns in size.
• According to the new standard (GOST R 52381-2005) the grain size of the sandpaper is indicated by the number of sieve fibers through which the abrasive is sieved. It turns out here that the smaller the number, the larger the grain. The number is preceded by the letter “R”.

As you can see, it’s already quite confusing. It is also worth mentioning that, according to the old standard, fine-grained emery can have a double designation – with the letters M and H – as in the table. Moreover, more often it was the options in microns that were in use. Therefore, the smallest grain – 5M or 00-N – is often called zero. This is because it has a size of 3-5 micrometers. According to the rounding rules, this can be considered zero. This is where the name came from.

Compliance tables for other countries

As you can see, the situation is not easy. And there is also American ANCI (USA and Canada), European FEPA or its other name ISO 6344, Japanese JIS and Chinese GB2478. Moreover, on the market you can find material from almost all of these countries / parts of the world. So it is desirable to have at least some data. The most common ones are shown in the tables.

Please note that next to each column are the grain sizes in micrometers (µm). The sizes are different. For work, this can be important.

Sandpaper marking

Sandpaper marking is a set of letters and numbers that encodes complete information about the type of base, abrasive, application method, composition and grain size. We have already considered graininess. This parameter is at the end of a series of letters and numbers. It’s more or less clear to him. In general, sandpaper marking displays the following data (starting from the first character):

• what material is the grain made of;
• the base of the skin;
• a binder with which the grain is glued to the base;
• methods of applying grain;
• type of base (paper or fabric);
• water resistance (if not waterproof, there is no icon);
• sandpaper grit.

Let’s deal with the rest of the characteristics that are encrypted in the marking. The letters are in Latin. For example, let’s take a look at what the following marking means: KK19XW. So:

• the first K is the type of abrasive – normal electrocorundum;
• second K – base – cotton fabric;
• 1 – two-layer application of a binder (resin + resin).
• 9 — type of application unclear;
• X – type of textile – hard.
• W – indicates that the material is waterproof.

Next should be the letter P and the numbers by which the graininess of the emery is determined.

Types of abrasive

The first letter in the marking indicates the material from which the abrasive is made. It is the abrasive material that is responsible for how much effort must be applied during processing. The stronger it is, the longer you can work with one piece of skin. Unfortunately, the rule here is true – the better, the more expensive.

• K – “normal” electrocorundum. The abrasive has a brown color (shades may vary). The most common and relatively inexpensive material.
• C is silicon carbide. Very durable material. For a long time it is not erased and clogs a little. For processing glass and plastic, for finishing metal polishing.
  

• G – zirconium electrocorundum. It has a brick-red color due to the addition of zirconium. Differs in the increased wear resistance, but is more expensive than “usual”.
• A – doped electrocorundum. It has an additive of titanium, which gives it a blue color. Probably the most durable. Recommended for grinding difficult-to-machine materials.
• V – white electrocorundum. Differs in white color due to a large amount of aluminum.
• S – ceramic electrocorundum.

If looking at the photo, you decide that the emery is tinted, then in vain. Different colors are given to it by various additives used in the manufacture of abrasive substances. Another thing is that most often we see brown, gray or dark gray sandpaper. They are simply the cheapest and most popular.

Base types

The basis of the abrasive skin is the material on which the abrasive is glued. This material determines the degree of flexibility, resistance to deformation. It also depends on the base whether this type of sandpaper can be used for dry or wet grinding.

In the marking, the type of base is encrypted with the second letter.

• Woven base. Cloths are woven from cotton and synthetic fibers:
  • K – cotton fabric. High strength, wear resistance, not afraid of getting wet. Of the disadvantages – it can lengthen during operation. For belt grinders, this is bad.
  • X – polyester textile. Compared to cotton, it is more durable. Used to make ribbons of various widths. The base is dense. It can be slightly stretched when refueling in grinders and at the same time does not deform for a long time.
    

  • Y – synthetic. It is applied in the furniture industry to polishing of wooden boards. Withstands very heavy loads.
  • J – elastic cotton fabric. It is applied to processing of an insignificant relief.
  • JJ or F – cotton fabric with increased elasticity. These types of bases are for narrow tapes, for processing deep relief. Very good stretch and bend.
• P – paper base. Inexpensive, even very fine grain can be applied. Nulevka and other abrasives with fine grains are based on this basis. Without additional impregnation, it cannot be used for wet grinding (with water supply). Emery paper comes in different densities. A fine abrasive is applied to a less dense one, a large abrasive is applied to a denser one. These types of sandpaper are:
  • A – density 90 g / m², B – 110 g / m². for chalkwhom grain. Flexible, bends wello facilitates finishing.
    

  • C – density 125 g / m², for an abrasive of medium size. This type is the most popular. May be in the form of rolls or thin sheets.
  • Paper weight D – 150-180 g/m², type E – 220-250 g/m². This is the basis for coarse grain. Usually available in the form of sheets (manual application) and narrow belts, discs for orbital grinders.
  • Rigid paper F (270 g/m²) and T (300 g/m²) – the basis for very coarse grain. It is used to make wide belts for large grinders.
• F – fiber. Thick and durable fabric. Used for discs. Absorbs water and therefore not suitable for wet sanding.
• C – combined basis. This is heavy paper, glued with fabric on one side. The fabric makes the paper more resistant to deformation, it lasts longer. Usually used for large grains.
• T – latex paper. This is a specialized type of foundation that home craftsmen do not use due to its high cost.

If we talk about the base, then the cheapest paper-based emery. It is usually used for manual processing or fixed on a hand holder. For grinders, a woven base is often taken. Cotton or polyester is your choice. Who likes what.

Binder

In the third position in the marking of the abrasive skin there is a number that encodes the method of fixing the abrasive on the base. Use glue or polymer resins, their combinations. The glue adheres well to the abrasive and the base. A single-layer application of a binder (marked with the number 2 in the corresponding position) is used where the emery is not subjected to heavy stress.

For a stronger hold of the grains, a second layer is poured over the glue. Most often it is a resin (phenolic or any other). It turns out a bunch – glue + resin (number 3 in the marking). The second layer of binder makes the emery more resistant to abrasion.

There is another option – resin + resin (this is 1 in the encoding). That is, both the first and second layers are made of bakelite resin. The cost of this option is higher, which determined its area of ​​​​use – production.

Method of applying and pouring grain

There are two ways to apply grain to the primary binder layer: free and electrostatic. When free, abrasive particles are simply poured. They lie in a free order, their direction is random. With the electrostatic method of filling the grain, the paper is passed through an electric field. As a result, the grains have the same orientation, which makes the surface rougher.

In addition, there are two types of grain filling: open and closed. They differ in the number of particles per unit area. With open filling, sharp fragments are located at a distance from each other, the base is visible (open). Such paper is good when working with loose materials. For example, with wood. Wood dust wakes up, the abrasive is not clogged.

Closed filling of grain on emery is denser. The abrasive particles lie one next to the other, the base is practically closed, not visible. This type of sandpaper is good for tough materials (steel, for example).

What should be the grit of sandpaper for work

As you understand, different sanding papers are used for different processing of materials. This is not about the form of release, but about the size of the grain, the method of its application. The type of abrasive and method of application is of secondary importance. They have a greater impact on the durability of the material. But as usual, better means more expensive. Here everyone already chooses for himself. But the grain size is better to choose for specific tasks.

What sandpaper to sand wood

In order for the skin not to clog, the grain must be applied at intervals. This is an open type of application. In this case, you do not often have to “knock out” or change it. Base type – paper or fabric. Paper is cheaper, fabric is more expensive. If there is a grinder, see the recommendations for it. For manual processing, you can fix a piece on a special holder or nail it to a bar.

Recommendations for choosing grit size are given in the table. For primary processing, there is a sanding sheet from P40 to P80. This is shaping, removing a thick layer. With the same materials we remove varnish and paint from wood. To prepare the wood for painting, P100 to P240 is already needed. For sanding after applying the first coat of varnish, take P360 or P400. And bringing to smoothness – actually polishing and varnishing – these are already quite small P500 and above. In general, polishing is a separate issue, and there you need to grind step by step and apply paint or varnish. And each time the grain is taken more and more thin. And they complete the polishing, generally with a soft polishing (felt) material.

What emery to process metal

For metal processing, you will have to take harder abrasive materials, and therefore more expensive ones. Ordinary corundum will cope with aluminum and its alloys. They also process cast iron, bronze and black steel. For brass, at least zirconium is needed, but titanium or alloyed electrocorundum is better. Better yet, ceramic. Also note that the method of application must be closed.

The principle of grit selection is the same: for rough processing, the increased “roughness” of large grains, the finer the processing, the finer the abrasive. To remove rust and level the main roughness, take the coarsest sandpaper. The thinner the layer, the smaller the grain size. So everything is logical here. But note that there are two or three grit sizes for each type of work. This does not mean that you need to take any of the above. This means that to get a good result, you need to process each size. Although, if the appearance is not so important to you, then you can use one of the recommended sizes.

Sandpaper for plastic, stone, ceramic and glass

According to the type of abrasive and its application, the recommendations are the same: stronger, more dense arrangement. But sanding is recommended with water supply, so a water-resistant modification of the emery is required.

For finishing plastic and glass, sanding paper with even the smallest grit – the same zero or P800 – will be too rough. It will leave visible scratches. These materials are brought to smoothness with the help of GOI paste and even finer grinding compounds. But this is a separate story and its own technologies.