GB2143515A - Ceramic binder for making abrasive tools - Google Patents

Abstract

A ceramic binder designed for making abrasive tools comprises the following components, in wt.%: lithiumborosilicate frit 15 - 60 fireclay 0.1- 40 feldspar material 15 - 60 cryolite 5 - 15 The binder can bind various types of abrasive material e.g. corundum, cubic boron nitride, diamond or carboid-silicon and enables the strength and service life of the tools to be increased.

Description

SPECIFICATION Ceramic binder for making abrasive tools The present invention relates to the field of manufacture of abrasive tools and, more particularly, to ceramic binders used for making abrasive tools.

Abrasive tools made of an abrasive material with a ceramic binder are widely used in machine-building. Important parts of most diverse designations are subjected to abrasive working: blades of jet engines and hydraulic turbines, ruby rods of lasers, crankshafts and camshafts of cars and tractors, screw propellers of ships, parts of bearings, cutting tools, etc.

Abrasive tools are used in all the operations of grinding, polishing and finishing.

Depending on the type of the abrasive material and the requirements set forth to the tool operation characteristics, use is made of most diverse compositions of ceramic binders.

However, though possessing certain advantages, the conventional compositions of ceramic binders have a number of disadvantages: some ceramic binders are not chemically active enough and do not possess the required adhesion with respect to the abrasive grain, especially when making tools from alloyed electrolytically produced corundum, boron cubic nitride and diamonds; other ceramic binders have in their compositions expensive and rare materials, limiting their application.

Besides, the majority of conventional ceramic binders are multi-component, which does not provide them with the homogeneity required during thermal treatment of the abrasive tool.

There are ceramic binders for abrasive tools which are based on boron glass and mineralizing additives ("Raising the operation speed of grinding wheels" by S.G. Voronov, "Abrazivy" Journal, NllMASH, Moscow, No. 5, 1952; "Abrasive tools and their manufacture" by Lubomudrov V.N., Vasilyev N.N. and Falkovsky B.l., Mashgiz, Moscow, 1953; "Selection of characteristics of grinding wheels for various grinding operations" by Ivashinnikov V.T., Yuzhno Uralskoye Knizhnoye Izdatelstvo, Chelyabinsk, 1966).

For example, for making abrasive tools from electrolytically produced corundum use is made of a boron binder which has the following composition, in wt. %: boron glass- - 40, feldspar, used as a mineralizing additive - 20, fireclay - 30 and talc - 10.

The main disadvantages of the conventional binder include presence in its composition of a considerable amount of refractory components (feldspar, fireclay, talc) which cause its high refractoriness constituting 1140-1180"C. In the finished product, this binder is not homogeneous and often contains non-melted grains of the initial components, which reduces, to a certain extent, the mechanicals strength of the abrasive tool. Besides, it is characterized by a low ability to wetting the surface of the electrolytically produced corundum, and even at a temperature of 1 250 C. the final terminal angle of wetting the surface of the electrolytically produced corundum remains above 55 .

The comparatively low mechanical strength of the abrasive material manufactured on the basis of the conventional binder, which equals 1 2,5MPa, limits its use in high-speed operations of grinding articles.

It is also known to use a ceramic binder consisting of the following components, in wt. %: silica - 69, boron oxide - 13 and alkali metal oxides - 10, the latter including up to 3% by weight of lithium oxide (U.S. Patent No. 2,730,439). The binder of the afore-given composition is used for manufacturing a tool from electrolytically produced corundum in the amount of at least 50% by weight. The binder is prepared from the following ingredients, in wt. parts: silicon dioxide 750 feldspar 10 alumina 6 boric acid 262 cryolite 98 potassium nitrate 45 fluorite 3 talc 28 lithium carbonate 90 In order to increase the reaction properties of the binder of the above composition, it is necessary to make a complete frit therefrom, which raises the cost of the binder to a considerable extent.The abrasive tool made from this binder is characterized by a low strength.

In order to increase the strength, a metal reinforcement is added to the ceramic mass, which considerably complicates the technology of manufacture of the abrasive tool.

Also known in the art is a ceramic binder used for carbidesilicon grinding wheels, and comprising feldspar, silicon dioxide, wollastonite, fireclay, lithium kaolin magonite, lithiumborosilicate frit and molybdenum (U.S. Patent No. 2,977,206). In order to obtain the required properties of the binder, the frit was prepared from 45 parts by weight of silicon dioxide, 40 parts by weight of boric acid and 1 5 parts by weight of lithium carbonate. This ceramic binder is very intricate in its ingredient composition and its use is limited to carbide-silicon grinding wheels only, whose manufacture requires a high temperature of 1260"C. and under which temperature they have to be kept for a rather long time period of 24 hours.Large-size abrasive tools using this binder are to be kept at the above annealing temperature for a still longer time period.

Also known the art is a ceramic binder of Japanese authors Terada Sedzi and Yamara Hirosi (the technology of manufacture of the binder is published in "Nagoya Koge gidsuzu Sikense Hokoku", v. 12, No. 7, pp. 348-358, 1964). The authors studied the possibility of making grinding wheels by using binders of the spodumene-feldspar-toseki system. They selected an optimum composition of the binder for the grinding grain from silicon carbide, comprising 30% by weight of spodumene, 40-50% by weight of feldspar and 10-20% by weight of toseki. At an annealing temperature of articles of up to 1 35'C. the Japanese authors obtained a vitrified binder which reacts, to a certain extent, with the grinding grain and, as a result of a change in its chemical composition, causes reduction in the operation properties of the abrasive articles.

Besides, the abrasive tool made on the basis of the binder is characterized by a low thermal resistance, as just only one cycle of heating articles up 300 C for 1 5 minutes and cooling-down in water to 0 C. decreases the tensile strength of the articles by almost 2 times, which is not a desirable factor during operation of abrasive articles.

Known is a ceramic binder (USSR Inventor's Certificate No. 218,699, Int. Cl. B24D 3/14 for "A Method of Manufacturing Abrasive Tools"), comprising lithium-boron containing frit, or a mixture thereof with fireclay, the latter being used in the amount of up to 1 5% by weight from the total weight of the binder, the composition of frit containing lithium and boron including 40-60% spodumene concentrate and 60-40% boron glass.

A disadvantage of the above binder is its insufficient ability to react with abrasive materials (electrolytically produced corundum, cubic boron nitride), as a result of which the mechanical strength of the abrasive tool based on it does not provide for its effective use in high-speed and power grinding.

Use in the metal-working industry of grinding machines requiring use of abrasive tools for power and high-speed grinding at an operating speed of 60-80 m/sec, necessitates development of a binder providing for a higher mechanical strength of the tools to be used at such speeds.

It is an object of the present invention to provide such a ceramic binder for abrasive tools, that would be applicable for binding various types of the abrasive material and would allow to improve the strength characteristics of the abrasive tool and to increase its service like during power and high-speed grinding.

The present invention provides a ceramic binder for the abrasive tool, comprising the following components, in % by weight: lithiumborosilicate frit 15 -60 fire clay 0.1-40 feldspar material 15 -60 cryolite 5 -15.

The invention also provides a tool as set forth in Claim 4.

The lithiumborosilicate frit preferably has the following chemical composition, in % by weight: silicon dioxide 64 -75 boron oxide 10 -18 aluminum oxide 2 -8 magnesium oxide 1 -2 sodium oxide 3.5-6.4 potassium oxide 3.5-4.6 lithium oxide 4.6-6 adiixtures: ferric end calcium oxides not nore than 1.5.

The chemical composition of the lithiumborosilicate frit, which is essentially the main glassforming component of the binder, provides the latter with such important physical and chemical properties as reaction capability, wetting capability, viscosity, initial temperature of formation of the liquid phase, and the coefficient of thermal linear expansion.

The quantitative content (15-60% by weight) of the lithiumborosilicate frit basically depends on the type of the abrasive material used, the upper limit preferably being used for manufacturing the tool from cubic boron nitride in order to impart to the binder greater wetting and reaction capability in relation to the abrasive material and to bring the annealing temperature of the articles down to 1100 C. and the lower limit of the lithiumborosilicate frit preferably being basically used for binding the electrolytically produced corundum materials since annealing of the articles in this case is carried out at a temperature of 1250"C. and, therefore, the above-mentioned physical and chemical properties of the lithiumborosilicate frit are not that necessary.A content of the lithiumborosilicate frit, that exceeds 60% by weight or is below 15% by weight is of a low efficiency as it results in the both cases in a lower mechanical strength of the abrasive articles.

Introduction of fireclay (in 0.1 -40% by weight) is basically aimed at improvement of plasticity and shaping ability of the abrasive mixture. The upper limit of the fireclay content in the binder is preferably basically used when manufacturing tools from the electrolytically produced corundum materials and when the annealing temperature of the articles is 1 250'C., whereas the lower limit of the fireclay content in the binder is preferably used for making an abrasive tool from cubic boron nitride when lower annealing temperatures are required, in which case the plasticity of the abrasive mixture is provided by introduction into it of not fireclay but liquid bakelite.

Introduction of fireclay into the composition of the ceramic binder in amounts exceeding 40% by weight makes it hard to bake at the annealing temperature of 1250"C., which results in a sharp reduction of the mechanical strength of the abrasive articles, whereas introduction of fireclay into the ceramic binder composition in amounts lower than 0.1% by weight is of a low efficiency.

Feldspar material (15-50% by weight) is used in the ceramic binder of the composition of the present invention for two reasons: firstly, the feldspar material takes part in the formation of the glass-like state of the binder during annealing of the tool, and, secondly, being a mineralizing agent, it provides for creation of the structural skeleton of the glass-forming binder, thereby raising its microhardness and mechanical strength. Use of a greater amount (over 60% by weight) of the feldspar material in the binder results in a higher refractory capability of the latter and a lower strength of the abrasive articles. Use of the feldspar material in amounts below 15% results in production of a binder of a lower microhardness and reduction of the mechanical strength of the abrasive articles.

Cryolite (5- 15% by weight) is used in the ceramic binder of the composition of the present invention to bring down the temperature of formation of the liquid state and to improve its reaction and wetting capabilities.

Use in the ceramic binder of cryolite in amounts less than 5% by weight is irrational as it would not substantially affect its properties, whereas use of cryolite in amounts exceeding 15% by weight will be useless, as in the course of annealing of the abrasive tool the greater part of cryolite gets decomposed to form fluorine compounds that volatalize into atmosphere, are not absorbed by the ceramic binder and the abrasive grain, contaminate the environment and destroy the lining of the firing kilns.

Depending on the components it comprises, the ceramic binder of the present invention has a melting point in the range of 750-1000"C. and a final terminal angle of wetting the surface of electrolytically produced corundum of 10-35" at 1250"C. and 20-40' at 1000'C.

The ceramic binder of the present invention is characterized by low viscosity, homogeneity, higher wetting ability and a necessary chemical activity relative to the abrasive grain during annealing. An important advantage of the ceramic binder is its ability to bind various types of electrolytically produced corundum materials, as well as cubic boron nitride.

The ceramic binder of the present invention provides the abrasive tool with the following advantages: the mechanical strength of the abrasive tool can be raised up to 24.5MPa, and its service life can be 3-4 times longer than that of the tool manufactured from the conventional ceramic binder based on boron glass. The binder of the invention provides the tool with good self-sharpening, a light pink colour, and makes it look aesthetic. An abrasive tool manufactured on the basis of this binder is capable of operating at a working rate of grinding of up to 80 m/sec, whereas the abrasive tool manufactured from the conventional boron binder can operate at a grinding rate of only up to 60 m/sec.

The above advantages of the abrasive tool make it commercially advantageous over all other conventional abrasive tools.

The ceramic binder of the present invention consists of available components. The technology of its manufacture is simple and can be easily realized under industrial conditions.

The lithiumboronsilicate frit which is one of the components of the ceramic binder of the present invention can be prepared by way of melting a charge of raw components at a temperature of 1370-1410'C. A charge comprising the initial raw components is melted at a temperature of 1370-1410"C.

Use is made of lithiumborosilicate frit of the following composition, in % by weight: silicon dioxide 64 -75 boron oxide 10 -18 aluminum oxide 2 - 8 magnesium oxide 1 - 2 sodium oxide 3.5-6.4 potassium oxide 3.5-4.6 lithium oxide 4.6-6 azures of ferric and calciun not not more than 1.5.

The frit is ground to the powder-like state and is screened through a sieve with the cell size of 0.06-0.10 mm. The other components, namely, fireclay, feldspar, perlite, nepheline and cryolite are also ground separately to the powder-like state and are screened through a sieve having cells of the above-said size. Thereupon, these components are mechanically mixed up in the following ratio, in % by weight: lithiu=borosilicate frit 15- 60 fireclay 0.1-40 feldspar arterial 15 - 60 cryolite - 5-15 The ceramic binder thus prepared is ready to be used for making the abrasive tool. To do this, an abrasive mixture can be prepared by mixing up 8-25% by weight of the ceramic binder with dextrin, and 100% by weight of the abrasive grain is wetted by 3-6% by weight of liquid glass.

Then, the two mixtures are carefully mixed up. The abrasive mixture this prepared is pressed to take the shape of the abrasive tool, dried up and annealed at a temperature selected within the range of 1000-1300"C., depending on the binder composition used and the type of the abrasive material.

In order to more readily understand the present invention, given below are specific examples of its embodiment.

Example 1.

To prepare the ceramic binder of the invention, lithiumborosilicate frit, fireclay, perlite and cryolite are used.

The lithiumborosilicate frit is prepared by way of melting at a temperature of 1390"C. from a charge of the following composition, in % by weight: quartz sand 65.00 alunina 4.00 magnesium carbonate 2.09 soda 5.10 potash 5.90 lithium carbonate 12.30 boric acid 31.00 The lithiumborosilicate frit, fireclay, perlite and cryolite are ground separately to the powderlike state and are screened through a sieve with the cell size of 0.08 mm. The ground components of the binder are taken in the following ratio, in % by weight: lithiumborosilicate frit 30 fire clay 20 perlite 40 cryolite 10 and are carefully mixed up.The ceramic binder is ready for making an abrasive mixture, it has a melting point of 920"C. and a final terminal angle of wetting the surface of electrolytically produced corundum of 25t at 1250"C.

The ceramic binder thus prepared is mixed up with dextrin and, then, with the electrolytically produced corundum which is preliminarily wetted with liquid glass, the ratio of the components, taken in weight parts, being as follows: electrolytically produced corundum 100.0 ceramic binder 9.4 liquid glass 4.1 dextrin 1.0 In order to determine mechanical tensile strength, samples are made from the binder of the invention and from the conventional boron binder. Use is made of the electrolytically produced corundum of grain size No. 40 of the following types: I - ordinary electrolytically produced corundum; 2 - white electrolytically produced corundum; 3 - electrolytically produced corundum alloyed with chromium; 4 - electrolytically produced corundum alloyed with titanium; 5 monocorundum.The samples of the above types had hardness CM2, structure No. 6 and a pleasant light pink colour. The results of tests of the mechanical tensile strength of the annealed samples are given in Table I.

Table 1 Denomlnation Tensile strength, n UPa of binder I 2 3 4 5 Binder according to the invention 16.0 21.0 21.0 18.5 17.5 Conventional boron binder 12.5 15.0 13.0 13.5 13.5 Example 2.

A ceramic binder of the following composition, in % by weight, is prepared by way of careful mechanical mixing up of the same ground components as in Example I, i.e. lithiumborosilicate frit, fireplay, perlite and cryolite: lithiumborosilicate frit fire clay 20 perlite 15 cryolite 5 The binder thus produced has a melting point of 790"C. and a final terminal angle of wetting the surface of electrolytically produced corundum of 32 at 1 000'C.

Abrasive samples are manufactured from the binder of the invention and the conventional boron binder. Use is made of white electrolytically produced corundum of grain sizes 16, 1 2 and 8. The manufactured samples had hardness C2 and structure No. 8. These technical characteristics of the tool correspond to those of the abrasive tool made from electrolytically produced corundum in combination with cubic boron nitride. The results of tests of the mechanical tensile strength of the samples are given in Table 2.

Table 2.

Iienomination Tensile strength of samples, in lIPs of binder Grain sizes 16 12 8 Blinder according to the invention 23.0 24.0 24.5 Conventional boron binder 15.0 17.0 18.0 Example 3.

The ceramic binder is prepared as described in Example 1, with the ratio of the components, taken by weight %, being as follows: lithiumborosilicate frit 15 fire clay 20 perlite 50 cryolite 15 The mechanical strength of the abrasive samples made with the aid of this binder is analogous to the one in Example I.

Example 4.

The ceramic binder is prepared as is described in Example I, with the ratio of the components, taken in % by weight, being as follows: lithiumborosilicate frit 60 fireclay 15 perlite 15 This ceramic binder is used for binding electrolytically produced corundum materials in combination with cubic boron nitride.

The mechanical strength of the abrasive samples prepared with the aid of the binder is analgous to the one in Example 2.

Example 5 The ceramic binder is prepared as described in Example 1, with the ratio of the components, taken by weight %, being as follows: lithi'wnborosilicate frit 60 fire clay 0.1 feldspar material 29.2 cryolite 10 The binder thus produced has a melting point of 750 C. Abrasive mass for press-moulding the samples as blocks and wheels contains by % weight: white electrical corund 43.3 cubic boron nitride n8.9 ceramic cinder 13.2 liquid bakelite 4.6 The results of mechanical strength tests of the 5 x 5, 5 X 50 mm blocks for bending and of 12 x 16 X 4 mm wheels for complete wear when polishing sleeves manufactured from chromir steel are given in Table 3.

liable 3 Description Hardness Bending resistance to of strength complete wear binder of blocks, of wheels (nXlm- BUPa ber of worked sleeves, pcs) Binder of the present inven- tion CTI 56 250 Described in the Inventors Certificate No.218699 CT2 43 220

Claims (5)

1. A ceramic binder for making abrasive tools, comprising the following components, taken in wt.%: lithiu:borosilicate frit 15- 60 fireclay 0.1-40 feldspar material 15- 60 cryolite 5-15

2. A ceramic binder according to Claim 1, in which the lithiumborosilicate frit has the following composition, in wt.%: silicon dioxide 64 - 75 boron oxide 10= aluminum oxide 2- 8 magnesium oxide 1 - 2 sodium oxide 3.5-6.4 potassium oxide 3.5-4.6 lithium oxide 4.6-6 adiixtures: calcium oxide and ferric oxide not more than 1.5

3. A ceramic binder substantially as hereinabove described in any one of Examples 1-5.

4. An abrasive tool having abrasive material bound by the binder of any one of the preceding Claims.

5. The tool of Claim 4, wherein the abrasive material is electrolytically-produced corundum, cubic boron nitride, diamond or carboid-silicon.