RU2543024C1 - Method of producing abrasive articles - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: abrasive powder of corundum is mixed with boron carbide powder in amount of 10-20% of abrasive powder bulk with grain size of 30-50% of that of abrasive powder. Produced abrasive charge is filled in the mould and subjected to heat treatment at 600-750°C for 45-80 min at simultaneous vibration of the charge with amplitude of 0.5-1.5 mm. Abrasive charge is formed at static stress and dynamic load of shock wave with subsequent heat treatment.

EFFECT: higher quality of abrasive tool owing to uniform distribution of abrasive grains.

1 tbl, 2 ex

Description

The invention relates to the production of abrasive tools mainly for finishing and can be used for the manufacture of abrasive tools.

A known method of manufacturing abrasive products [RF Patent No. 2227774, B24D 3/02, 18/00, publ. 04/27/2002, Bull. No. 12], in which the electrocorundum abrasive powder is formed under static and dynamic loading by a shock wave in a mold, then heat treatment is carried out, and the following order of filling the mold is observed: abrasive powder, which is a mixture of primary and secondary, is placed in its lower part fractions of electrocorundum powders. Powder of the main fraction is placed in the upper part of the mold. The ratio of volumetric filling of the mold parts is 1: (0.5 ÷ 0.7).

However, the stepwise filling of the mold with electrocorundum powders of different grain sizes and at different levels does not allow for a high uniformity of the distribution of grains and pores, since The shock wave, initially acting on the powder of the initial fraction, moves it along the mold and leads to the formation of conglomerates of grains, which form the so-called "arch connection" due to engagement, forming pores of various sizes and unevenly distributed over the volume of the tool, which reduces quality abrasive products.

There is also known a method of manufacturing abrasive products, in which a mixture of white electrocorundum powders of different grain sizes is pressed by an explosive shock wave and then subjected to heat treatment at a temperature of 1400-1800 ° C for 2-6 hours [RF Patent No. 673446, MKI B24D 17/00, 1993 ].

However, due to the gradual decrease in pressure in the front of the shock wave as it passes through the abrasive charge in the compact, an uneven distribution of large and small grains and pores is formed, which does not allow for uniform material removal and tool wear during finishing at elevated speeds and power modes and reduces the quality of the abrasive tool.

A known method of manufacturing abrasive products, comprising shaping an abrasive product in two stages, the first of which involves static pressing to ensure a density of 0.6 ÷ 0.7 of the density of the finished product. In the second stage, the resulting workpiece is exposed to a shock wave with a power of 0.75 ÷ 1.0 MW / g of powder, and heat treatment is carried out at a temperature of 1800-1850 ° C for 2-4 hours. The second stage is repeated 5-7 times, and dynamic loading can be carried out by an electro-hydraulic shock wave [USSR author's certificate No. 1364454, MKI B24D 18/00, 1988].

However, the multiple loading of the shock wave does not provide a uniform density of the product, depending on the uniform distribution of grains and pores throughout the volume, because this leads to a large number of micro- and macrocracks, which lead to uneven wear of the abrasive product and, accordingly, reduce its quality.

The closest is a method of manufacturing abrasive products [RF Patent No. 2293013, IPC B24D 18/00, publ. 02/10/2007, Bull. 4], which includes the formation of abrasive electrocorundum powder under static and dynamic loading by shock wave, followed by heat treatment, and boron carbide powder is additionally introduced into the abrasive powder of electrocorundum in the amount of 10-20% by weight of the abrasive powder and grit size 30-50% of the granularity of the abrasive powder.

The addition of boron carbide powder leads to additional crushing of large grains of electrocorundum powder and the formation of a significant number of pore sizes of various sizes after sublimation of boron carbide grains during heat treatment, which does not increase the uniform distribution of grains and pores throughout the product, leads to uneven metal removal and abrasive wear products and, accordingly, reduces its quality.

The objective of the invention is to obtain abrasive products of high quality with a uniform distribution of abrasive grains of a certain grain size and pores throughout the volume.

The technical result of the invention is to improve the quality of abrasive products.

The technical result is achieved by the fact that the electrocorundum abrasive powder is formed under static and dynamic loading by a shock wave, followed by heat treatment, boron carbide powder is introduced into the abrasive powder of electrocorundum in the amount of 10-20% by weight of the abrasive powder and grain size 30-50% of the granularity abrasive powder, and also carry out heat treatment at a temperature of 600-750 ° C for 45-80 min with simultaneous communication of vibrations of the abrasive mixture with an amplitude of 0.5-1.5 mm .

In this case, heat treatment can significantly reduce the height of microroughnesses, since it is precisely at the tops of the microprotrusions that the energy is concentrated, which leads to their fusion. These processes lead to a weakening of the adhesion forces between the grains of electrocorundum and boron carbide, thereby reducing the "arched effect" of the interaction between them.

In this case, the message of oscillations of the abrasive mixture, filled in the mold, allows the latter to acquire mobility, which leads to a weakening of the adhesion forces between the grains. At the same time, they are closer to each other, their denser packing occurs and the abrasive charge is compacted.

Using a temperature of less than 600 ° C does not lead to the melting of microroughness protrusions on the surfaces of boron carbide grains and the adhesion forces between microroughness protrusions of grain surfaces of electrocorundum and boron carbide do not allow uniform distribution of grains and pores throughout the entire volume of the abrasive charge due to random arches ". As a result, the finished abrasive product does not have high quality, because cannot be used as an abrasive tool in finishing operations at high speed and power processing conditions.

Using temperatures above 750 ° C leads to the complete melting of the microroughness protrusions and the partial melting of the surfaces of boron carbide grains, which leads to the formation of durable compounds of the latter with electrocorundum grains. Such compounds increase the number of accidentally formed "arches", thereby enhancing the "arched effect", which does not allow to form a uniform distribution of grains of aluminum oxide, boron carbide and pores in the entire volume of the abrasive mixture. This does not lead to an increase in the quality of the finished abrasive product, because it does not allow using it as an abrasive tool in finishing operations at high speed and power modes.

Conducting heat treatment for less than 45 minutes does not allow the protrusions of microroughness on the surfaces of boron carbide grains to melt in sufficient quantities and a significant amount of unmelted protrusions of microroughness of the latter adhere to the protrusions of microroughness of the surfaces of grains of electrocorundum, forming random conglomerates - “arches” that do not allow creating abrasive charge uniform distribution of grains of electrocorundum, boron carbide and pores. In this case, the finished abrasive product does not have high quality, because it cannot be used in finishing operations with high speed and power parameters.

Conducting heat treatment for more than 80 minutes leads to the complete melting of all the protrusions of the microroughnesses of the surfaces of boron carbide grains and the partial melting of their surfaces. This leads to the formation of a significant number of random conglomerates - “arches” during fusion of the surfaces of boron carbide grains and electrocorundum.

This does not lead to a uniform distribution of electrocorundum grains, boron carbide and pores in the entire volume of the abrasive charge. The finished abrasive product is not of high quality, because does not allow it to be used as an abrasive tool in finishing operations at high speed and power loads.

Communication of vibrations of an abrasive mixture with an amplitude of less than 0.5 mm does not allow sufficiently uniform filling of the pores between the grains of electrocorundum and boron carbide, since the adhesion forces between the protrusions of the microroughnesses of their surfaces are quite large due to the large number of irregularities. This leads to the fact that the uneven distribution of grains of aluminum oxide, boron carbide and pores in the entire volume of the abrasive charge is sufficiently high, which does not allow to obtain a finished abrasive product of high quality, i.e. it cannot be used as an abrasive tool when finishing at high speed and power modes.

Using the vibration amplitude of more than 1.5 mm leads to the fact that the abrasive charge begins to lose contact with the working body (vibrator), the bonds between the grains are broken, circulation flows occur in the abrasive charge, so-called “drilling” occurs, i.e. the mixture comes into a state of "boiling". This leads to a significant loosening of the abrasive mixture and a decrease in its density, which causes refraction and intensive mixing of grains of various fractions of the abrasive mixture.

In this case, the uniform distribution of grains and pores throughout the entire volume of the product is significantly violated, which does not allow using it as an abrasive tool at high speed and power finishing conditions.

The proposed method for the manufacture of abrasive products includes the preparation of a mixture of white alumina powder and boron carbide, the mixture is subjected to heat treatment at a temperature of 600-750 ° C for 45-80 minutes, while vibrations of the abrasive mixture with an amplitude of 0.5 ÷ 1.5 mm are simultaneously reported. , subsequent static loading and dynamic loading by a shock wave, followed by heat treatment. Boron carbide powder is taken in an amount of 10-20% of the mass of abrasive electrocorundum powder and granularity of 30-50% of the granularity of electrocorundum powder, and dynamic loading is carried out by a shock wave with a power of 0.65 MW / g of corundum powder mass, followed by heat treatment at a temperature of 1800 ° C within 4 hours

The vibrations of the abrasive charge are reported on the UVG-200 vibroinstallation (the working chamber volume is 200 dm ³ , one working chamber, the oscillation amplitude is 0-7 mm, the vibrator drive electric motor power is 4.5 kW, the oscillation frequency is 33 Hz), and the preliminary thermal processing before shaping is carried out in a conventional muffle electric furnace.

The test of the abrasive product obtained by the described method was carried out when processing 40X steel in a normalized state (HB 229) by honing under the following conditions: peripheral speed of the head trap - 60 m / min, speed of its reciprocating movement - 18 m / min, bar expansion pressure - 0.4 MPa.

Example 1. For the manufacture of an abrasive product, an abrasive mixture is prepared from electrocorundum and boron carbide powders, the amount of boron carbide powder in the charge being 10% by weight of the electrocorundum abrasive powder, and its granularity is 30% of the granularity of the electrocorundum powder, it is heat treated at a temperature 600 ° C for 45 minutes while simultaneously reporting vibrations to the abrasive charge with an amplitude of 0.5 mm. Then produce static pressing and, without removing the static load, conduct dynamic loading with an electro-hydraulic shock wave. After pressing, the preform is removed from the mold, placed in an electric vacuum furnace and heat treated. The resulting abrasive product has a compressive strength of 70 MPa, when honing in these modes, the processing productivity is 134% compared to the known tool, wear is reduced by 1.51 times, the arithmetic average deviation of the processed surface profile is Ra = 0.32 μm, which is less after processing with a known tool 1.97 times. A study of the thin sections of the proposed abrasive tool showed that the distance between the pores lies within 15 ÷ 45 μm, and the average distance is 25 μm.

Example 2. For the manufacture of an abrasive product, an abrasive mixture is prepared from electrocorundum and boron carbide powders, and the amount of boron carbide powder in the charge is 20% by weight of the electrocorundum abrasive powder, and its granularity is 50% of the granularity of the electrocorundum powder, it is heat treated at a temperature 750 ° C for 80 minutes while simultaneously reporting vibrations of the abrasive mixture with an amplitude of 1.5 mm. Then produce static pressing and, without removing the static load, conduct dynamic loading with an electro-hydraulic shock wave. After pressing, the preform is removed from the mold, placed in an electric vacuum furnace and heat treated. The obtained abrasive product has a compressive strength of 73 MPa, when honing in these modes, the processing productivity is 141% compared to the known tool, wear decreased by 1.57 times, the arithmetic average deviation of the processed surface profile Ra = 0.25 μm, which is less after processing with a known tool 2.52 times. A study of the thin sections of the proposed abrasive tool showed that the distance between the pores lies within 15 ÷ 45 μm, and the average distance is 35 μm.

Examples of abrasive products are shown in table 1.

Table 1 Examples
parameter Examples
parameter Granularity of boron carbide powder in% of granularity of electrocorundum powder Heat treatment temperature, ° C Duration of heat treatment, min Amplitude of vibrations, mm The limit of compressive strength, MPa Processing productivity,% Tool wear reduction, krat Parameter Ra of the processed surface, microns The average distance between pores by volume, microns The distance between the pores, microns 1.25A 12H ST1K5 - - - - - 55 one hundred 1,0 0.63 thirty 20 ÷ 80 2. Example 1 10 thirty 600 45 0.5 70 134 1.51 0.32 25 15 ÷ 45 3. Example 2 twenty fifty 750 80 1,5 73 141 1,57 0.25 35 15 ÷ 45 4. Example 3 5 twenty 500 35 0.3 58 125 1.21 0.48 fifty 5 ÷ 115 5. Example 4 5 twenty 500 35 1.7 64 121 1.40 0.41 55 10 ÷ 110 6. Example 5 5 twenty 500 90 0.3 66 115 1.33 0.52 45 5 ÷ 125 7. Example 6 25 60 850 35 0.3 56 120 1.37 0.44 65 15 ÷ 140 8. Example 7 25 60 850 35 0.7 61 110 1.15 0.38 60 10 ÷ 130 9. Example 8 25 60 850 90 0.3 63 128 1.28 0.50 70 15 ÷ 120

As follows from the table, the optimal parameters of the method of manufacturing technology of abrasive products of high quality are the following:

- heat treatment temperature: 600-750 ° C;

- duration of heat treatment: 45-80 min;

- amplitude of oscillations: 0.5-1.5 mm.

Claims (1)

A method of manufacturing abrasive products, including the preparation of an abrasive mixture of abrasive electrocorundum powder and an additionally introduced boron carbide powder in an amount of 10-20% of the mass of abrasive electrocorundum powder and a grain size of 30-50% of the granularity of abrasive electrocorundum powder and its shaping under static loading and dynamic loading by a shock wave followed by heat treatment, characterized in that prior to shaping the prepared abrasive charge is subjected to preliminary ermoobrabotke at 600-750 ° C for 45-80 min with simultaneous message it oscillations with an amplitude of 0.5 ÷ 1.5 mm.