Types of grinding wheels and their markings

Classification of abrasive wheels

Disks are classified into the following types:

• with undercut (PV – for cylindrical grinding);
• double-sided conical (PVDK);
• straight profile (PP – universal circle);
• with a conical one-sided or two-sided groove;
• ring (K – suitable for flat grinding);
• disc-shaped (T);
• cup conical or cylindrical;
• with a double-sided conical profile (2P: scope of application – thread grinding, slot grinding, gear grinding).

Marking of grinding wheels

Grinding wheels can vary in geometric shape, type of abrasive material, as well as type of bond, wheel grit, hardness, etc. When choosing a grinding wheel, hardness and texture may weigh more heavily than the type of abrasive.

According to various editions of GOSTs, the marking of circles has different designation parameters. Almost every manufacturer labels their wheels differently.

Thus, the complete marking of the varieties of grinding wheels contains:

• circle type;
• grinding material;
• disk dimensions;
• degree of hardness;
• grain size;
• structure;
• binder;
• maximum rotation speed;
• accuracy class;
• imbalance class.

How to choose

The main criterion for choosing the disk size will be the nature of the work performed. In the household, these will be circles of smaller diameters; in a production environment, a tool of large diameter (230 mm) is used.

In addition to the dimensional characteristics, you should carefully check the compliance of the disc material with the material of the workpiece being processed.

Another determining factor is the power of the grinder. It is directly related to the weight and overall characteristics of an angle grinder. With approximately the same characteristics, preference should be given to a lighter specimen.

Type of abrasive material

The most popular and common materials used in the manufacture of grinding wheels include:

1. Electrocorundum. When purchasing such a circle, you can see white, titanium, chrome and zirconium options. The main disc used is white electrocorundum, which is highly self-sharpening. By working with it you can achieve a more even and smooth surface.
2. Silicon carbide. There are black and green tones, this circle differs in structure and degree of fragility - it is harder and more durable than the first type described above. Area of ​​application: working with hard alloys, porcelain and marble.
3. Elbor. This type of grinding wheel has the hardest abrasive material and high heat resistance. Elbor can be used for sharpening cutting tools and other parts that can be deformed by heat, as well as for working with hard metals.
4. Diamond. Another hard type of abrasive wheel. It is used when working with hard materials, glass and ceramic surfaces. It is self-sharpening, but cubonite and CBN have greater heat resistance without compromising strength.

Regardless of the type of abrasive material, all wheels are characterized by the parameters of strength, wear resistance and heat resistance, however, when choosing, you should take into account the main parameter - hardness. The hardness characteristic is prescribed in the standards of GOST 2424 and is calculated using special tables.

For example, the type of grinding material for the 25A F180 K 7 V wheel is white corundum. There are other types of known abrasives:

• normal electrocorundum (13-16A);
• white (23-25A);
• chromium (33 and 34A);
• titanium only one (37A);
• zirconium is also one (38A);
• monocorundum (43-45A);
• black silicon carbide (53 and 54C);
• green silicon carbide (62-64C).

Grinding wheel grit markings

When marking grinding wheels, manufacturers indicate only its width (MKM or F with a numerical indicator of grain size). The grain size not only indicates the wear resistance of the abrasive, but also plays an important role when grinding a particular surface.

The grain size of the wheel affects the quality and cleanliness of the surface finish. Consider the material you are working with. To get the cleanest possible surface, you should buy a wheel with the smallest grain size. However, a person working with such a wheel must understand that it quickly becomes greasy and the material being processed often gets burned.

According to GOST from 1980, units equal to 10 microns are used to measure the grain size of wheels. In the modern version of GOST R 52381-2005, circles are marked with the letter F with a certain number (as the number increases, the degree of grain decreases).

For example, the grain number according to the old GOST (M40-M5) and the new one (F280, F320, F360, F400-F600, F800). To decipher: such a disk is used for final finishing and honing of parts with an accuracy of 3-5 microns or less, as well as superfinishing. Or size 40, 32 according to the old GOST and F40, F46 according to the new one: wheels with this grain size are used for preliminary and final grinding of parts with surface roughness of 7-9 cleanliness classes, as well as for sharpening cutting tools.

How to replace

The grinder disc is a consumable item. Therefore, it has to be changed frequently. There is a simple algorithm in which an important role is played by the original design of the key supplied to the consumer along with the grinder.

1. — The protruding rods of a special key are installed in the grooves of the fastening nut.
2. — At the same time, press the lock button located on the gearbox housing. It will lock the rotor from turning.
3. — Turn the key counterclockwise to release the fasteners of the worn disk.
4. — The old disk is replaced with a new one of the same technical characteristics and size. The new disk is installed with the markings facing out to remind you of the disk parameters and for other good reasons (see explanation in the video above).
5. — The fastening nut is first tightened by hand and finally tightened with a special wrench.

The Bulgarian is ready to continue fulfilling its functional purpose.

Abrasive disc size

The marking of abrasive wheels by size is written as follows: DхТхН (where D is the outer diameter, T is the height, H is the diameter of the hole). The D parameter can reach a maximum size of 1100 mm, the H value can be up to 305 mm, and the T parameter varies from 0.18 mm to 250 mm.

The types of CBN and diamond discs are described in more detail in GOST 24747-90. The marking of the shape of such grinding wheels consists of three or four symbols indicating the cross-sectional shape of the body and layer, its location on the wheel, and also provides information about the design features of the body.

For example, 150x16x32 is the size of a 25A white electrocorundum abrasive wheel.

Reminder when choosing abrasive wheels:

• When choosing the diameter of the circle, you should take into account the number of spindle revolutions and the ability to provide optimal speed.
• The larger the diameter, the less specific wear of the circle. There are fewer grains on the working surface of small circles. So, during operation they wear out unevenly.
• When choosing a diamond wheel, you should take into account the width of the diamond-bearing layer. If used incorrectly, ledges may appear on the surface of the wheel.

Catalog >> News >> Marking and selection of cutting and grinding wheels

Marking and selection of cutting and grinding wheels

Grinding wheels are characterized by geometric shape (type), type of abrasive material, its grain size, bond type, hardness, etc. And when choosing a grinding wheel, such characteristics as the degree of hardness or structure may be more significant than the type of abrasive.

The complete markings for grinding wheels contain:

• circle type;
• its dimensions;
• type of abrasive material;
• grit number;
• degree of hardness;
• structure (the relationship between the abrasive, bond and pores in the body of the tool);
• type of ligament;
• maximum speed;
• accuracy class;
• imbalance class.

The marking of wheels, made in accordance with various editions of GOSTs, has some differences regarding the designations of grain size, hardness, grade of abrasive and binder. Manufacturers label their wheels differently, using old or new designations and excluding certain characteristics. Below are examples of deciphering the designations of grinding wheels.

Grinding wheel markings

1 - abrasive material: 25A - white electrocorundum; 2 - grain size (old marking): 60 (according to GOST it should be 63) - 800-630 microns; 3 - hardness: K - medium-soft; 4 - structure: 6 - average; 5 - ligament: V - ceramic; 6 — imbalance class: 2

Grinding wheel markings

1 - abrasive material: 25A - white electrocorundum; 2 - grain size (old marking): 60 (according to GOST it should be 63) - 800-630 microns; 3 - hardness: KL - depending on the circumstances, can be K or L - medium-soft; 4 - ligament: V - ceramic.

Grinding wheel designation

1 - abrasive material: 25A - white electrocorundum; 2 - grain size (old marking): 25 - 315-250 microns; 3 - hardness (old marking): SM2 - medium-soft; 4 - structure: 6 - average; 5 - bond (old marking): K - ceramic; 6 — accuracy class: B 7 — imbalance class: 3

Marking of abrasive wheel

1 - abrasive material: 25A - white electrocorundum; 2 - grain size: F46 - average size 370 microns; 3 - hardness: L - medium-soft; 4 - structure: 6 - average; 5 - ligament: V - ceramic; 6 — peripheral speed: 35 m/s; 7 — accuracy class: B 8 — imbalance class: 3

Grinding wheel designation

1 - abrasive material: 14A - normal electrocorundum; 2 - grain size: F36-F30 - extended range including F36 (average size 525 microns) and F30 (average size 625 microns); 3 - hardness: QU - depending on the circumstances, it can be medium-hard, hard, very hard; 4 - bond: BF - bakelite with reinforcing elements; 5 — imbalance class: 1

The choice of grinding wheel brand should be made taking into account all its characteristics.

Types of grinding wheels and their sizes

The following types of grinding wheels are produced (in parentheses the designations according to the old GOST 2424-75 are given):

• 1 (PP) - straight profile;
• 2 (K) - ring;
• 3 (3P) - conical;
• 4 (2P) - double-sided conical;
• 5 (PV) - with one-sided groove;
• 6 (ChTs) - cup cylindrical;
• 7 (LDPE) - with two grooves;
• 9 - with double-sided groove;
• 10 (PVDS) - with double-sided groove and hub;
• 11 (CHK) - conical cup;
• 12 (T) - disc-shaped;
• 13 - disc-shaped;
• 14 (1T) - disc-shaped;
• 20 - with one-sided conical groove;
• 21 - with double-sided conical groove;
• 22 - with a conical recess on one side and a cylindrical recess on the other;
• 23 (PVK) - with conical and cylindrical grooves on one side;
• 24 - with conical and cylindrical recesses on one side and a cylindrical recess on the other;
• 25 - with conical and cylindrical recesses on one side and conical on the other;
• 26 (PVDK) - with conical and cylindrical recesses on both sides;
• 27 - with a recessed center and reinforcing elements;
• 28 — with a recessed center;
• 35 - straight profile, working with the end;
• 36 (PN) - with pressed-in fasteners;
• 37 - ring with pressed fasteners;
• 38 - with one-sided hub;
• 39 - with a double-sided hub.

Some types of grinding wheels

All types are described in GOST 2424-83.

In addition to the profile shape, circles are characterized by the size DxTxH, where D is the outer diameter, T is the height, H is the diameter of the hole.

Types of diamond and CBN wheels are regulated by GOST 24747-90. The marking of the shape of CBN and diamond wheels consists of 3 or 4 characters that carry information about the cross-sectional shape of the body, the cross-sectional shape of the CBN-containing or diamond-bearing layer, the location of the latter on the wheel, and the design features of the body (if any).

Designation of a grinding wheel with the shape of the body 6, the shape of the diamond-bearing or elboron-containing layer A, with the location of the diamond-bearing or elboron-containing layer 2, with the design features of the body C.

Designation of diamond or CBN grinding wheels

All types are described in GOST 24747-90.

The type and size of the wheel are selected based on the type and configuration of the surfaces being ground, as well as the characteristics of the equipment or tool used.

The choice of wheel diameter usually depends on the spindle speed on the selected machine and on the ability to provide an optimal peripheral speed. Specific wear will be the least with the largest diameter circle size. Smaller wheels have fewer grains on the working surface, each grain has to remove more material, and therefore they wear out faster. When working with small diameter wheels, uneven wear is often observed.

When choosing a diamond wheel, it is advisable to pay attention to the width of the diamond-bearing layer. When working “on the pass” it should be relatively large. When grinding using the “plunge” method, the width of the diamond coating should be commensurate with the width of the surface being processed. Otherwise, ledges may appear on the surface of the circle.

Abrasives

The most commonly used abrasive materials for grinding wheels are: electrocorundum, silicon carbide, CBN, diamond.

Electrocorundum

Available in the following grades: white -
22A
,
23A
,
24A
,
25A
(the higher the number, the higher the quality);
normal - 12A
,
13A
,
14A
,
15A
,
16A
;
chromium - 32A
,
33A
,
34A
;
titanium - 37A
;
zirconium - 38A
and others.

Silicon carbide

.
Two types of silicon carbide are available: black - 52С
,
53С
,
54С
,
55С
and green -
62С
,
63С
,
64С
, differing from each other in some mechanical properties and color. Green carbide is more fragile than black carbide.

Diamond

widely used for the manufacture of diamond grinding wheels used for finishing and sharpening carbide tools, processing parts made of hard alloys, optical glass, ceramics, etc. It is also used for dressing grinding wheels made of other abrasive materials. When heated in air to 800°C, diamond begins to burn.

Diamond grinding wheels

Elbor

(CNB, CBN, borazone, cubonite) is a cubic modification of boron nitride. Having the same hardness as diamond, it is significantly superior to the latter in heat resistance.

CBN wheels for full-profile sharpening of band saws

Abrasive materials are characterized by hardness, granularity, abrasive ability, strength, heat and wear resistance. High hardness is the main distinguishing feature of abrasive materials. Below are comparative characteristics of microhardness and heat resistance of the main abrasive materials.

The choice of one or another abrasive material is largely determined by the characteristics of the material being processed.

Diamond wheels are capable of processing material of any hardness. However, you need to keep in mind that diamond is very fragile and does not withstand shock loads well. Therefore, it is advisable to use diamond wheels for final processing of carbide tools, when it is necessary to remove a small layer of material and there is no shock load on the grain. In addition, diamond has relatively low heat resistance, so it is advisable to use it with a coolant.

Grain

Abrasive grain size is a characteristic of grinding wheels that determines the cleanliness of the resulting surface. The grain is either an intergrowth of crystals, or a separate crystal, or its fragments. Like all solids, it is characterized by three dimensions (length, width and thickness), but for simplicity we operate with one - width. Many parameters depend on the grain size - the amount of metal removed in one pass, the cleanliness of the processing, grinding performance, wheel wear, etc.

According to GOST 3647-80, in the designation of the grain size of grinding wheels, the grain size is indicated in units equal to 10 microns (20 = 200 microns), for micropowders - in microns with the addition of the letter M.

In the new GOST R 52381-2005, which basically corresponds to the international standard FEPA, the grain size of grinding powders is indicated by the letter F with a number. The higher the number, the finer the grain and vice versa.

Diamond and CBN wheels have their own grain size designations. Their grain size is indicated by a fraction, the numerator of which corresponds to the size of the side of the upper sieve in microns, and the denominator corresponds to the size of the lower sieve.

The table below shows the ratios of grinding wheel grit according to old and current standards.

The choice of wheel grain size should be determined by a number of factors - the type of material being processed, the required surface roughness, the amount of allowance to be removed, etc.

The smaller the grain size, the cleaner the processed surface is. However, this does not mean that finer grain size should be preferred in all cases. It is necessary to choose the grain size that is optimal for a particular processing. Fine grain gives a higher surface cleanliness, but at the same time can lead to burning of the processed material and clogging of the wheel. Using fine grains reduces grinding performance. In general, it is advisable to choose the largest grain size provided that the required cleanliness of the treated surface is ensured.

If it is necessary to reduce surface roughness, the grain size must be reduced. Larger allowances and increased productivity require larger grits.

In general, the harder the material being processed and the lower its viscosity, the higher the wheel grit can be.

Hardness of grinding wheels

The hardness of the grinding wheel should not be confused with the hardness of the abrasive material. These are different concepts. The hardness of the grinding wheel characterizes the ability of the bond to hold abrasive grains from being torn out under the influence of the material being processed. It depends on many factors - the quality of the bond, the type and shape of the abrasive, and the wheel manufacturing technology.

Wheel hardness is closely related to self-sharpenability—the ability of an abrasive wheel to regain its cutting ability by breaking down or removing dull grains. During operation, the wheels intensively self-sharpen due to the splitting of the cutting grains and their partial chipping out of the bond. This ensures that new grains enter into the work, thereby preventing the appearance of burns and cracks in the material being processed. The lower the hardness of the wheel, the higher the self-sharpening ability. Based on hardness, circles are divided into 8 groups.

The choice of grinding wheel hardness depends on the type of grinding, the accuracy and shape of the parts being ground, the physical and mechanical properties of the material being processed, the type of tool and equipment.
In practice, in most cases, medium-hard wheels are used, which have a combination of relatively high performance and sufficient durability. A slight deviation of the wheel characteristics from the optimal one leads either to burns and cracks of the sharpened surface, when the hardness of the wheel is higher than required, or to intense wear of the wheel and distortion of the geometric shape of the sharpened tool, when the hardness of the wheel is insufficient. Wheels for sharpening tools with inserts made of hard alloys must be selected with particular precision in terms of hardness.

Here are some recommendations that may be useful when choosing grinding wheels based on hardness. When sharpening tools with carbide cutters, the wheel must have high self-sharpenability. Therefore, when sharpening them, wheels of low degrees of hardness are used - H, I, J (soft), less often K. The more tungsten or titanium carbides in the hard alloy, the softer the grinding wheel should be.

When it is required to maintain high precision of shape and size, preference is given to those types of grinding wheels that have increased hardness.

When using cutting fluids, grinding uses harder wheels than when grinding without cooling.

Wheels on a bakelite bond should have a hardness 1-2 levels higher than wheels on a ceramic bond.

To prevent burns and cracks, softer circles should be used.

Structure

The structure of a tool is usually understood as the percentage of the volume of abrasive material per unit volume of the tool. The more abrasive grain per unit volume of the wheel, the denser the structure of the tool. The structure of the abrasive tool affects the amount of free space between the grains.

When sharpening cutting tools, it is advisable to use wheels with more free space between the grains, as this makes it easier to remove chips from the cutting zone, reduces the possibility of burns and cracks, and facilitates cooling of the tool being sharpened. For sharpening cutting tools, wheels on a ceramic bond of 7-8th structure are used, and wheels on a bakelite bond - 4-5th structure.

Bunch

In the manufacture of grinding wheels, abrasive grains are bonded to the base and to each other using a bond. The most widely used binders are ceramic, bakelite and vulcanite.

Ceramic bond

It is made from inorganic substances - clay, quartz, feldspar and a number of others by grinding them and mixing them in certain proportions.
Ceramic bonded grinding wheels are marked with the letter ( V
).
Old designation - ( K
)

The ceramic bond gives the abrasive tool rigidity, heat resistance, shape stability, but at the same time increased fragility, as a result of which it is undesirable to use wheels with a ceramic bond under shock loads, for example, during rough grinding.

Bakelite bond

mainly consists of an artificial resin - bakelite.
The marking of circles with bakelite has a Latin letter ( B
) in its designation.
The old designation is ( B
). Compared to ceramic, bakelite binder has greater elasticity and elasticity, heats the metal being processed less, but has lower chemical and temperature resistance, and worse edge resistance.

Bakelite bond can be with reinforcing elements ( BF

, old designation -
BU
), with graphite filler (
B4
, old designation -
B4
).

Vulcanite bond

is a vulcanized synthetic rubber.
The abrasive wheel is marked with the letter ( R
).
The old designation is ( B
).

In most cases, abrasive wheels on ceramic or bakelite bonds are used. Both have their own characteristics, which determine their choice for a particular job.

The advantages of a ceramic binder include strong fixation of grain in the binder, high heat and wear resistance, good preservation of the working edge profile, and chemical resistance. The disadvantages are increased fragility, reduced bending strength, high heat generation in the cutting zone, and, consequently, a tendency to burn the material being processed.

The advantages of the bakelite bond are elasticity, good self-sharpening of the wheel due to the reduced strength of grain fixation in the bond, and reduced heat generation. The disadvantages are more intense wear compared to a ceramic bond, reduced edge resistance, low resistance to coolants containing alkalis, low heat resistance (bakelite begins to become brittle and burn out at temperatures above 200°C).

Accuracy class

The accuracy of the dimensions and geometric shape of abrasive tools is determined by three AA

,
A
and
B.
_
For less critical abrasive processing operations, class B
.
A
tool is more accurate and of higher quality .
For work in automatic lines, on high-precision and multi-circuit machines, high-precision AA
. It is distinguished by higher accuracy of geometric parameters, uniformity of grain composition, balance of abrasive mass, and is made from the best grades of grinding materials.

Unbalance class

The imbalance class of a grinding wheel characterizes the imbalance of the wheel mass, which depends on the accuracy of the geometric shape, the uniformity of mixing of the abrasive mass, the quality of pressing and heat treatment of the tool during its manufacturing process. Four classes of permissible imbalance of the mass of circles have been established ( 1

,
2
,
3
,
4
). Unbalance classes have nothing to do with the accuracy of balancing the wheels and flanges before installing them on the grinding machine.

Catalog >> News >> Marking and selection of cutting and grinding wheels

Structure and hardness index

The density of the structure of grinding wheels is indicated by the percentage of the volume of abrasive grains per unit volume of the wheel. The more abrasive, the denser the structure of the grinding wheel will be.

When sharpening a tool, a wheel with a less dense structure is better able to clean the surface of material particles, poses less risk of deformation and cools faster.

Often, specialists use disks of medium hardness, but it all depends on the type of work being performed, the coating being processed and the tool itself.

What are the structure numbers and volumes of abrasive in the grinding wheel:

• dense structures include units of measurement from 1 to 4;
• Average density includes numbers 5-8;
• to open – from 9 to 12;
• a highly porous structure is observed in circles with indicators 13, 14>.

However, do not confuse wheel hardness with abrasive hardness. According to GOST 2424, the hardness of a grinding wheel is distinguished by a capital letter.

According to GOST R 52587-2006, there are the following designations:

• very soft - letters F and G;
• to soft circles – H, I, J;
• medium softness includes markings K, L;
• averages are M, N;
• circles of medium hardness are designated by the letters O, P, Q;
• solids are designated as R and S;
• very hard – T, U;
• Extremely hard ones include V, W, X, Y, Z.

What grinding wheel hardness should I choose? This depends on many parameters - the characteristics of the material or surface being processed, physical properties, and, of course, the power of the grinding machine. If you need to maintain the exact shape of the material being processed, you should purchase a wheel with a high degree of hardness. Soft ones are used to prevent cracks and burns, also when grinding without additional liquid-lubricant cooling of the surface.

For example, let's take the same 25A grinding wheel, which has a hardness class of K and a structure of 7. This means that this disc is medium-soft and has a medium abrasive structure.

Bundle type

The bond is an indicator of the bonding of abrasive grains to each other. Modern grinding wheels have three types of bonds:

• V (ceramic, previously marked with the letter K);
• B (bakelite, formerly known as B4 and BU);
• R (volcanic, previously designated by the letter B).

Ceramic marked wheels have materials such as quartz, sand, clay, etc. mixed and ground in various proportions. Such circles are quite high-strength. However, they should not be used for power grinding of metal.

Bakelite or artificial resin wheels are highly elastic and heat resistant. Bakelite is often mixed with reinforcing elements, such as graphite.

The volcanic binder consists mainly of rubber; such wheels are used in certain processing industries.

Using the example of the 25A F180 K 7 V grinding wheel, we will consider the type of bond, where the designation V refers this disc to a ceramic bond.

Where can I buy

You can purchase wheels of various types and sizes from employees of companies that sell spare parts and consumables for grinders. Some component suppliers are presented in the corresponding section of our website.

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