RU2835917C1 - Mass for making grinding wheel with minimum content of abrasive - Google Patents

Abstract

FIELD: performing operations.

SUBSTANCE: invention relates to production of abrasive tools with high structure numbers for grinding, in particular, to production of high-structure grinding wheels, in which content of abrasive grain is from 18 to 2% of its volume. Mixture for making a grinding wheel contains an abrasive, a ceramic binder, adhesive and wetting additives and a filler. Mixture consists of two mixtures: a mixture of abrasive grains with content of 2-18 vol.% and a filler in the form of aluminosilicate hollow spherical particles with size in range of 1-50 mcm with content of 42-60 vol.% and from a mixture of ceramic binder with content of 5-20 vol.% with filler in form of hollow spherical particles of low-melting glass in amount of 10-25 vol.% of ceramic binder.

EFFECT: production of high-structure fine-grained grinding wheels with increased hardness, improved processability.

2 cl, 4 tbl, 4 ex

Description

The invention relates to the production of an abrasive tool with high structure numbers for grinding, in particular to the production of high-structure grinding wheels in which the abrasive grain content is from 18 to 2% of its volume.

In accordance with the current GOST R 52781-2007 "Grinding and sharpening wheels. Technical conditions", the structure number is one of the main characteristic parameters that determines their performance and is included in their mandatory marking.

According to the generally accepted practice in the world of manufacturing grinding wheels, including Russia, the structure number is assigned in accordance with the classification proposed by Norton in 1920. The zero structure number according to the international classification is determined by filling the wheel volume with abrasive grain by 62%, followed by a 2% decrease in grain per structure number. According to the accepted classification, the abrasive content from 18 to 2% vol. corresponds to grinding wheel structures from No. 22 to the maximum possible No. 30.

There is no information in literature or advertising materials about the compositions of grinding wheels with a minimum abrasive content with structures from No. 22 and higher made of traditional abrasives (corundum, silicon carbide and their modifications) and superhard materials (diamond and cubic boron nitride), their production and application. It is only known about tools with structures in which the volume content of abrasive can be up to 12.5% of its volume. In particular, for grinding wheels made of superhard materials, it is envisaged to manufacture compositions with a relative abrasive concentration of 50% (for example, GOST R 53923-2010 "Diamond and cubic boron nitride (elbor) grinding wheels. Specifications"), which is 12.5% of the volume of the working layer of the tool.

Industrial experience of using tools with high structure numbers from No. 10 to No. 18-20 and more shows that with a decrease in the volume content of abrasive grains from 42% to 26-22%, its cutting ability improves significantly. The positive effect is achieved as a result of the redistribution of the functional participation of the remaining grains in the grinding process: their number increases, actively removing the material, and the proportion of those grains that only intensify the heating of the processing zone during friction and plastic deformation of the ground surface of the part decreases. The remaining grains are less densely distributed on the working surface of the circle, which creates favorable conditions for them to overcome the cutting threshold (by the thickness of the cut chip) and disperse the material being processed. With a decrease in the amount of abrasive, the volume porosity of the grinding wheel increases, which becomes an additional factor in its effective use. (Starkov V.K. Mechanism of influence of circle structure on grinding efficiency // see Bulletin of Moscow State Technical University "STANKIN". 2019. No. 1. P. 38-43).

Wheels with large structure numbers and increased porosity are in demand for profile pendulum and deep grinding of complex-shaped parts made of difficult-to-machine steels and alloys prone to the formation of burns and cracks on the surfaces being machined.

The application area of the tool with a minimum abrasive content can be grinding with wheels with a grain size of F150-F220 and finer and with a hardness of N-S and harder. Wheels with such a combination of grain size and hardness and at the same time with a high abrasive content are extremely difficult to manufacture due to the lack of free space in the molding mass for introducing a large amount of ceramic bond. The increased density of fine-grained abrasive with their strong fixation on the working surface of the tool also increases the risk of forming grinding defects on the processed surface of the part.

Known compositions of abrasive masses of high-structure grinding wheels cannot be used to manufacture tools with a minimum abrasive content. In their compositions, abrasive grains firmly connected by a ceramic bond are the basic volumetric framework that forms the working configuration of the tool with specified strength and cutting properties. The need to strengthen the framework with a decrease in abrasive grains and, accordingly, the bond bridges between them is compensated by introducing abrasive grain with a smaller grain size and special fillers.

For example, a known composition is an abrasive mass with a cutting abrasive grain made of white electrocorundum grade 25A with a grain size of F70 and a size of 200 μm in an amount of 22% by volume (structure No. 20) with the addition of 22% by volume of microcrystalline corundum grains of grade SG with a grain size of F80 and a size of 160 μm as a filler and a filler in the form of aluminosilicate hollow spherical particles in the form of a mixture of particles with sizes from 85 to 560 μm in an amount of 4.5% by volume (RU Patent No. 2493956, priority dated 19.07.2012, IPC B24D3/18, B24D3/34, Published 27.09.2013 Bulletin No. 27).

When using such a composition, the cutting relief of the working surface of the tool, consisting of grains of two different sizes, is leveled out into a relief with an increased density of grain distribution of the same height as a result of its correction with a diamond pencil or roller during grinding. However, the risk of increased heating of the ground surface with the formation of burns and microcracks on it increases.

Also known is the composition of the mass for a grinding wheel with a volume content of 26% of grade 25A grain size F80, where aluminosilicate hollow spherical particles are introduced as a filler-compensator for abrasive grains in combination with expanded perlite, respectively, in 13 and 10% of the mass volume (RU Patent No. 2494853, priority dated 12/17/2012, IPC B24D3/18, published 10/10/2013 Bulletin No. 28).

The specified composition of abrasive grain fillers-compensators is unacceptable for filling the volume of abrasive mass for wheels with a grain finer than F80, since they cannot effectively provide their full cutting capacity during grinding.

The closest is the mass for the manufacture of an abrasive tool, including an abrasive, a ceramic bond and a filler containing hollow spherical particles of aluminosilicate, and hollow spherical particles of aluminosilicate in the form of a mixture of particles in the range from 5 to 560 μm in an amount of 2-200 vol.% of the abrasive (Patent of the Russian Federation No. 2152298, priority from 11.10.1999, IPC B24D3/18 3/14, published 10.07.2000 Bulletin No. 19). For example, composition No. 22: aluminosilicate hollow spherical particles are introduced into the mass of a circle with an abrasive grain content of 20 vol.% (structure No. 21) in an amount of 40% of the volume

In this solution, the filler-compensator in the form of a mixture of aluminosilicate particles of different sizes from 5 to 560 microns performs an additional function of creating a volumetric support frame of the tool together with abrasive grains. At the same time, the abrasive retains its priority purpose for the frame of the grinding wheel, since it has higher strength and density (almost 9 times more), as well as morphological properties and, above all, a developed microrelief of the surface in contrast to the smooth surface of the microspheres, which provide a reliable connection in the frame structure. Due to the content of aluminosilicate particles of large fractions in the composition, their use in the manufacture of fine-grained wheels with a grain size of F120 and less, as in the previous example, is impractical.

When the amount of abrasive in the molding mass is reduced to 2-18% by volume, its positive role in creating a volumetric design of the grinding wheel is leveled, and its compensation by aluminosilicate hollow particles in the amount of 2-200% by volume of abrasive is insufficient to form a mass with a dense volumetric loading of solid non-burning components to counteract its deformation during firing. In addition, the heterogeneity of the sizes of the mixture of abrasive grains and aluminosilicate particles in the composition of the tool is a factor in reducing its strength and, accordingly, the possible grinding speed.

Also, in the closest invention, the abrasive mass additionally contains a filler in the form of hollow spherical particles of low-melting glass in an amount of 0.5% by volume, which does not guarantee the necessary strength of adhesion of a large number of small-sized particles of abrasive and aluminosilicate.

The technical result of the claimed invention is the creation of highly structured fine-grained grinding wheels with increased hardness and improved manufacturing technology based on the minimum possible abrasive content of up to 2-18% by volume with structures No. 22-30.

The essence of the proposed invention is that the composition of the grinding wheel mass with a minimum abrasive content forms its volumetric framework mainly from aluminosilicate hollow spherical particles with sizes in a narrow range from 1 to 50 μm and with a content of 42-60% of its volume. The cutting ability of the tool is ensured by adding electrocorundum grains to its composition in an amount of 2-18% of the mass volume.

The composition of aluminosilicate particles that do not burn out and do not melt at the tool firing temperature of up to 1250°C contains up to 58% by weight of silicon dioxide SiO₂ and up to 26% of aluminum oxide Al₂O₃, which is what electrocorundum consists of. Both components are the basis of the K5 ceramic bond (up to 66 and 17%, respectively), which ensures chemical affinity of the basic components of the grinding wheel composition and, as a result, a strong adhesive connection by the ceramic bond of a large number of hollow aluminosilicate particles with electrocorundum grains.

Hollow spherical particles of low-melting glass are introduced into the ceramic bond in the amount of 5-20% by volume of the mass in the amount of 10-25% by volume of the bond. The glass particles, melting during the high-temperature firing of the tool, increase the amount of glassy mass in the ceramic bond and, accordingly, its strength properties. This ensures a more reliable connection of the non-burning components of the molding mass of the tool - abrasive and hollow spherical aluminosilicate particles.

The declared composition of the grinding wheel mass with a minimum abrasive content has increased volume porosity, including natural porosity and porosity that is formed during the firing of the tool after the burning out of ground fruit pits introduced into the molding mass as a burnout filler-porogen in an amount of 2-10% by volume, as well as adhesive and moisturizing additives.

The priority area of application of the declared weight of the grinding wheel with a minimum abrasive content is grinding with wheels with a hardness from N to S and harder with an abrasive of grain size F120-F150 and finer. It is almost impossible to manufacture high-quality wheels with such a characteristic according to known compositions, and their analogues with increased hardness and structures of 10-14 "burn" the ground surface of the part. The main purpose of high-structure wheels with a minimum abrasive content in the future is high-speed grinding at speeds up to 100-120 m/s, including without cooling with cutting fluids.

Examples of using the stated weight of a grinding wheel with a minimum abrasive content are given below.

Example 1

The mass of a grinding wheel with a minimum content of abrasive made of white electrocorundum grade 25A with a size of 106 µm (grain size F120) with structure No. 22 for characteristic 25A F120 G 22 V consists of the following components vol.% according to Table 1.

Table #1 – Example #1

Index, vol.% Meaning Abrasive grain made of white electrocorundum grade 25A with a size of 106 microns (grain size F120) 18 Aluminosilicate hollow spherical particles (filler) in the form of a mixture of particles with sizes from 1 to 50 microns 42 Ceramic bond K5 5 Hollow spherical particles of low-melting glass (filler) 0.5 The ratio of the content of hollow spherical particles of low-melting glass to the content of ceramic binder K5 10 Ground fruit pits (burnout filler) 10 Adhesive and moisturizing additives 10.5

Example 2

The mass of a grinding wheel with a minimum abrasive content made of white electrocorundum grade 25A with a size of 63 µm (grain size F220) with structure No. 26 for the characteristic 25A F220 S 26 V consists of the following components vol.% according to Table No. 2.

Table #2 - Example #2

Index, vol.% Meaning Abrasive grain made of white electrocorundum grade 25A with a size of 63 microns (grain size F220) 10 Aluminosilicate hollow spherical particles (filler) in the form of a mixture of particles with sizes from 1 to 50 microns 48 Ceramic bond K5 20 Hollow spherical particles of low-melting glass (filler) 3.6 The ratio of the content of hollow spherical particles of low-melting glass to the content of ceramic binder K5 18 Ground fruit pits (burnout filler) 5 Adhesive and moisturizing additives 10.5

Example 3

The mass of a grinding wheel with a minimum abrasive content made of white electrocorundum grade 25A with a size of 75 µm (grain size F150) with structure No. 30 for characteristic 25A F150 P 30 V consists of the following components in vol.%, according to Table 3.

Table #3 - Example #3

Index, vol.% Meaning Abrasive grain made of white electrocorundum grade 25A with a size of 75 microns (grain size F150) 2 Aluminosilicate hollow spherical particles (filler) in the form of a mixture of particles with sizes from 1 to 50 microns 60 Ceramic bond K5 12 Hollow spherical particles of low-melting glass (filler) 3 The ratio of the content of hollow spherical particles of low-melting glass to the content of ceramic binder K5 25 Ground fruit pits (burnout filler) 2 Adhesive and moisturizing additives 10.5

For experimental verification of the proposed technical solutions, 3 masses were produced for experimental grinding wheels in accordance with the examples presented above (Table 4).

The manufacturing technology of experimental grinding wheels of size 1,200 × -25 × 32 on the declared compositions of molding masses, 3 pieces of each composition, was compared with the manufacturing technology of a prototype wheel with structure No. 21 of a similar size.

Experimental wheels and wheels with the prototype mass composition were manufactured using serial technology for producing high-structure grinding wheels. The results of a comparative assessment of their manufacturing processability based on its key parameters - the strength of the green mass (mass for forming the wheel blank) and the volumetric deformation of the tool during high-temperature firing - are given in the table.

The strength of the green mass was measured using the Watti method on pre-formed bars from the mass under study. The method is based on measuring the part of the bar that broke under its own weight when the bar was cantilevered (Fundamentals of Design and Manufacturing Technology of Abrasive and Diamond Tools / Yu. M. Kovalchuk, V. A. Bukin, B. A. Glagovskiy et al. Under the general editorship of Yu. M. Kovalchuk. Moscow: Mashinostroenie. 1984 – 288 p. P. 157).

The volumetric deformation of the circles was determined by the difference in their volumes before and after firing.

Table No. 4 – Comparison of technical indicators

Declared weight by examples Weight of the circle according to the prototype
with structure #21 No. Strength of green mass, kPa Volumetric deformation, % Strength of green mass, kPa Volumetric deformation, % 1 49.1 4.8 46.9 5.2 2 61.3 8.5 3 58.4 27.6

When analyzing the results of assessing the manufacturability of manufacturing masses with increased structure presented in Table 4, it is necessary to take into account an important feature caused by the minimum amount of abrasive. With a decrease in the amount of abrasive in the wheel, the permissible threshold of its volumetric deformation during firing increases, at which the specified volumetric concentration of abrasive grain by structure number is maintained. For example, for a tool with structure No. 22, with a decrease in its volume by 5.26%, the concentration of abrasive grain is maintained practically at the initial level of 18±1%. To maintain structure No. 26 after firing, a volumetric deformation of the wheel of up to 9.09% is allowed, and for No. 30, volumetric deformation of the wheel is possible up to a maximum of 33.3%. At the same time, the concentration of abrasive remains within the tolerance of 10±1% and 2±1% vol., respectively. (Starkov V.K. Grinding with highly porous wheels. Moscow: Mechanical Engineering. 2007.688 p. pp. 665-670).

The obtained experimental results indicate that in terms of the strength of the raw material, the declared compositions of the masses with a minimum abrasive content are stronger than the raw material from the molding mass according to the prototype, and the volumetric deformation of the tool after firing corresponds to the permissible limits.

Thus, the claimed set of features, set out in the formula of the invention, makes it possible to ensure the strength of the raw material necessary for forming grinding wheels with a minimum abrasive content and their resistance to volumetric deformation during the firing process with a guarantee of manufacturing a tool of a given characteristic.

An analysis of the claimed technical solution for compliance with the patentability conditions showed that the features specified in the independent claim of the invention are essential and interconnected with each other to form a stable set of necessary features unknown at the priority date from the prior art, sufficient to obtain the required synergistic (super-sum) result.

The properties regulated in the claimed compound by individual features are well known from the state of the art and do not require additional explanations.

Thus, the above information indicates that the following set of conditions are met when using the declared technical solution:

- an object that embodies the declared technical solution, when implemented, is intended for the manufacture of grinding wheels;

- for the claimed object in the form in which it is characterized in the independent claim of the invention, the possibility of its implementation using the means and methods described above in the application materials, known from the state of the art as of the priority date, is confirmed;

- an object that embodies the declared technical solution, when implemented, is capable of ensuring the achievement of the technical result envisaged by the applicant.

Claims (2)

1. A compound for producing a grinding wheel containing an abrasive, a ceramic bond, adhesive and moisturizing additives and a filler, characterized in that it consists of two mixtures: a mixture of abrasive grains with a content of 2-18 vol.% and a filler in the form of aluminosilicate hollow spherical particles with sizes in the range of 1-50 μm with a content of 42-60 vol.% and a mixture of a ceramic bond with a content of 5-20 vol.% with a filler in the form of hollow spherical particles of low-melting glass in an amount of 10-25 vol.% of the ceramic bond. 2. The mass according to item 1, characterized in that it additionally contains a burnable filler in the form of ground fruit pits with a content of 2-10 vol.%.