The working part of any abrasive tool, such as an grinding wheel or bar, contains classified particles of abrasive material, the hardness of which exceeds the hardness of the processed material and which is capable of cutting by grinding. Such abrasive materials after grinding, enrichment and classification are called grinding.
Natural and artificial abrasive materials for sharpening knives and tools, classification, characteristics, marking and symbols.
For sharpening knives and tools use natural and artificial abrasive materials that differ in chemical composition, physical properties and production technology. The following grinding abrasives are most commonly used:
Electrocorundum – normal (13A, 14A, 15A), white (23A, 24A, 25A), chromium (ZZA, 34A), titanium (37A), zirconium (38A).
Monocorund (43A, 44A, 45A).
Silicon Carbides – Black (53C, 54C, 55C), Green (63C, 64C).
Diamonds – synthetic (АС2, АС4, АС6, АС15, АС20, АС32, АС50), natural (А8, А5, A3, А2, А1 brands).
Cubic boron nitride, or elbor (LO, LP, LVM, LPM).
Synthetic polycrystalline diamonds (ARV ballads, ARC carbonado, ARS specs).
Depending on the grain size (μm), grinding abrasive materials are divided into four groups:
Shlifserno, 160-2000 microns.
Grinding powders, 40-125 microns.
Microsized powders, 14–63 microns.
Fine micropowders, 3-10 microns.
The grain size is determined by sieve analysis, microscopic or combined. When the sieve analysis is carried out the screening of samples of material into fractions in special plants equipped with a set of wire or nylon mesh with different sizes of holes of a square shape. The fraction prevailing in mass, volume or number of grains is called the main.
The characteristic of a specific set of grains, expressed by the size of the main fraction, is called granularity. Granularity of grinding powder and grinding grain is designated as 1/10 of the size of the side of the sieve cell (in the light), microns, on which the grains of the main fraction are retained.
Grinding abrasive materials are made of the following grit:
Shlifzerno – 200; 160; 125; one hundred; 80; 63; fifty; 40; 32; 25; twenty; sixteen.
Grinding powders – 12; 10; 8; 6; 5; 4.
Micropowders – M63; M50; M40; M28; M20; M14.
Thin micro-grinding powders – M10; M7; M5.
For diamond and elbor polishing powders, grain size is indicated by a fraction in which the numerator corresponds to the side size of the cells of the upper sieve, μm, and the denominator to the size of the side of the cells of the lower sieve, μm, for the main fraction. For example 400/250; 400/315; 160/100; 160/125. Elbor granularity is sometimes indicated traditionally by the size of the cells of only the lower sieve, for example L20, L16, L10.
Marking and symbols of grinding abrasive wheels.
The percentage of the main fraction is indicated by the indices B, P, H, D, which complement the designation of grain size. For example, for grit sizes from 200 to 8, the minimum content of the main fraction in accordance with the indices is as follows: P – 55%; H – 45%; D – 41%, for grain sizes M63 — M28, respectively, B – 60%; P – 50%; H – 45%; D – 43%.
Types of ligaments used for fixing grains of abrasive material.
A substance or a combination of substances (crushed to a given size and mixed to the required uniformity) used to fix the grains of the grinding material and filler in an abrasive tool is called a bunch. The filler in the bundle gives the tool the required physicomechanical, technological and operational properties, depending on the structure of the tool, on certain ratios between the volumes of grinding material, pores and ligaments.
The following ligaments are distinguished depending on the main substance:
Ceramic – K1, K5, K8 for fixing grains of electrocorundum materials and K2, KZ for fixing grains of silicon carbide.
Bakelite – B, B1, B2, BZ, B4, BU, B156, BP2.
Volcanic – В, В1, В2, ВЗ, В5.
Other ligaments – glyphthal, polyvinyl acetal, metal, epoxy, etc..
The structure of the abrasive tool is indicated by numbers from 0 to 20 (volumetric concentration of grains is 62 and 22%, respectively). When the structure is increased by one number, the grain content decreases by 2%. For diamond and elbor tools, indicate the relative concentration of grains (%), four times higher than the actual volumetric content of grinding material in the tool – 150, 100, 75, 50.
Marking and legend of diamond grinding wheels.
The value characterizing the property of an abrasive tool to resist adhesion between the grains and the bond while maintaining the characteristics of the tool within the established standards is called the hardness of the abrasive tool.
Depending on the hardness values determined by the method of a hole formed under the influence of a quartz sand jet of a certain characteristic, or by the method of indenting a ball under a given load, eight degrees of hardness of an abrasive tool are established:
Very soft – BM1, VM2.
Soft – M1, M2, MZ.
Medium soft – SM1, SM2.
Medium – C1, C2.
Medium hard – ST1, ST2, STZ.
Solid – T1, T2.
Extremely Solid — VT.
Extremely Solid – Th.
The numbers 1, 2, 3 characterize the increase in the hardness of the instrument inside the degree. The type of abrasive wheel or bar, its dimensions, grade of grinding material, grain size and its index, structure number, mark of bond, along with a number of other parameters make up the characteristic of the abrasive tool in the delivery state (static characteristic).
Based on materials from the book Sharpening and fine-tuning of a cutting tool.