The abrasive material reduced to fragments is called grinding material. The fraction means the totality of the abrasive granulations in the established interval of the size. The fraction predominated over the mass, volume and quantity of the granules is called the general.
The granularity characterize the size of the cutting granules of the general fraction in this instrument. Concerning to a size of granules the grinding instruments are divided into following groups: grinding grain from №200 to №16; grinding powers from №12 to №4; grinding micro-powers from M63 to M14; fine grinding micro-powers- from M10 to M5. The grinding grain and powers are received by the screen sizing, micro-powers- by the hindered settling in a liquid. The similarity of the grain composition, which influences essential the granularity of the processing surface, the cutting properties and the solidity of the grinding instruments are characterized of the rated keeping of the general fraction. Also they add to the conventional designation of the granularity the letter code according to this rate keeping: B- high; П- raised; Н- nominal; Д- permissible.
Concerning to the group of the materials the granularity is designated in such a way:
for the grinding grain and grinding powers- 0.1 of the size (mkm ) in the side- light of the sieve mesh, where the grains of the general fraction are delayed e.g. 40, 25, 16 (accordingly 400, 250, 160 mkm );
for the micro-powers - with the top limit of the grain s size of the general fraction with addition of the code letter M, e.g. M40, M28, M10 (accordingly 40, 28, 10 mkm );
for the diamond grinding powers - the fraction, which numerator corresponds to the size of the top sieve mesh s side, and the denominator- to the size of the low sieve mesh s side of the general fraction e.g. 400/250, 400/315, 160/100, 160/125;
for the diamond micro- powers and sub- micro- powers- the fraction, which numerator corresponds to a larger and the denominator to a smaller size of the general fraction s grains, e.g.40/28, 28/20, 10/7;
for the grinding grain and grinding powers in depending of the control s method: the sieve method- 0,1 of the size in the side- light of the sieve mesh, where the grains of the general fraction are delayed e.g. Л20, Л16, Л10; the microscopic method- analogous to the designation of a granularity of the grinding grains and grinding powers, e.g. 250/200, 200/160, 125/100.
The composition, which is demanded in the GOST for the grinding materials 3647- 80, in the GOST 9206- for the diamonds powers.
A granularity of the grinding grain and powers (GOST 3647- 80 and ISO 8486(FEPA))
GOST 3647-80
ISO 8486-86 FEPA 42-D Row F (The hard abrasives)
GOST 3647-80
ISO 8486-86 FEPA 42-D Row F (The hard abrasives)
80
F24
М63
*
63
F30
*
F230
50
F36
М50
F240
40
F40
*
*
*
F46
М40
F280
32
F54
*
F300
25
F60
М28
*
20
F70
*
F360
16
F80
М20
F400
*
F90
*
*
12
F100
М14
F500
10
F120
М10
F600
8
F150
М7
F800
6
F180
М5
F1000
The hardness of the abrasive instruments
The notion "the hardness of the abrasive materials" doesn't coincide with the analogous notion, which determines the properties of the metals and other hard substance. The hardness of the grinding instruments characterize the bond s solidity of the abrasive grain s with each other. That is why it is possible to manufacture the mild abrasive instruments of the hard and hard abrasive instruments of the mild. The mild abrasive instruments are called such items, of which the grains fall away easily.
The hardness of the abrasive instruments has an influence upon the cutting properties and border-durability of the abrasive instruments, also upon the term of their wearing property during the cutting process. If the fastening durability of the grains in the abrasive instrument is lower, than the abrasive grain s solidity (a mild abrasive instrument ) , the wearing process goes on owing to fall away of the grains and the item works in the regime of the self-sharpening. If the durability of the abrasive grains is lower than of their fastening in the instrument (a hard abrasive instrument), the wearing process goes on partial owing to the grain s shearing and partial to the rubbing-of with the formation of the wearing s areas on the grain.
In the plate 1 you can sea a classification of the abrasive instruments hardness and field of use of the abrasive instruments according to their hardness.
1. The using fields of the abrasive instruments according to their hardness
The hardness grade of the abrasive instruments
A designation of the hardness
The using field of the abrasive instruments
Mild (М)
Medium mild (СМ)
М1...М3
СМ1, СМ2
The grinding with the intensive self-sharpening of the instruments, surface, internal grinding; sharpening and finishing of the cutting instruments, non-ferrous metals, hard-processing and viscous metals, cooled metals and of the high grade of the hardness, witch have an inclination to cracks; teeth-grinding; thread grinding; cleaning grinding and superfinishing.
Medium (С)
Cl, C2
The finish grinding, cleaning(round, centreless and internal); the surface grinding, the thread grinding; the grinding of the irons; the rough grinding.
Mid-hard
(СТ)
СТ1...СТЗ
The round and centerless in feed grinding, the processing of the disconnected surfaces, the rough grinding of the irons.
Hard (Т)
Т1, Т2
The rough grinding, barb dressing on the forgings and casting; the manufacturing of the cutting wheels and leading wheels for the centerless grinding; honing of the cooled steals; in feed profile grinding with a large volume of metal.
Very hard (ВТ)
Extremely
hard (ЧТ)
BT1, BT2
ЧТ1, ЧТ2
The rough grinding and the dressing in the industry and the forge-and-casting producing; the straightening of the grinding wheels; the grinding with a strong cutting pressure.
The structure of the grinding instruments
The structure of the abrasive instruments is characterized by contents of the abrasive material in the unit of it s volume, expressing in percents.
VЗ + VС + VП = 100 %,
The abrasive instruments, which have the same granularity and hardness, but various structures, differ from each other in the converning s grade of the abrasive granules. The structure №1...4 is used to be called closed(dense), №4...8- medium, №9...12- open. With growing of the structure s number the distance between granules grows.
There are few recommending using fields of the abrasive instruments:
№1...3-manufacturing of the instruments of the ceramic and: bonds by the grinding with small output, in advantage for processing of the sphere bearing;
№ 3,4 - the profile grinding, grinding with the variable load, cutting;
№ 4...6 - the round outside, centerless, surface grinding of the wheels periphery;
№ 7...9 - the surface grinding of the wheel s face plane, internal grinding, sharpening of the instruments;
№ 8...10 - grinding and sharpening of the instrument, being equipwith with a hard alloy;
№ 8...12 - the profile grinding by means of the small graining wheels(thread grinding).
The abrasive instruments of the open structure have better conditions for the cutting s branch and less heat-evolution. It is effective their use by the processing of the viscous metals, and also metals inclined to cracks.
We manufacture the wheels on the ceramic bunch, they have an increasing size of pores(2,3 mm) and are called the high-pore wheels.
The volume mass of the high-pore wheels is considerably less, than of the common, as a result they have the same size, but are lighter and need less energy expense for rotation.
The high-pore wheels get cool by mean of the during the working process joined air. The air s speed in the cutting area during the rotation of a high-pore wheel is by 23-35% bigger, than during the rotation of the common wheel, so you get a possibility to work with a bigger intensity of cutting. A big quantity of the large pores and the increased speed of the air jet during the work of the abrasive instruments make better conditions for the cuttings removal and diminish the possibility of it s decrease in the pores. During the working of the mild and viscose materials (plastic, wood, rubber, leather) the surface of the high-pore abrasive instruments has higher capacity for work and needs straightening more seldom. The specific wearing of the high-pore wheels is 1,5 times less comparatively to the common wheels.
If you claim for the high-pore wheels, you should let know the producing factory of the conditions of their use and claims to the operations. You should claim for the high-pore of the granularity smaller by 1-3 numbers, as usual. For example, if you use the structure wheels of the granularity 40, you should claim for the high-pore wheels of the granularity 25 or 16.
The fit of grade of the abrasive instruments
The fit of grade and of the geometrical form of the abrasive instrument have 3 classes : AA, A and B. They use the abrasive instrument of the class B for the not very responsible operations. The instruments of the class B are more exact and qualitative. They use the abrasive instruments of the class AA on the high-exact and multi-wheel machines. These instruments have more exacting of the geometrical parameters, more homogeneity of the grain s composition, more steady of the abrasive mass. The instruments of the class AA are manufactured of the best sorts of the grinding materials.
