JP2005177887A - Vitrified silicon carbide grinding wheel and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To dissolve defects in manufacture in consideration of economical efficiency to stably supply to the market a vitrified grinding wheel using silicon carbide abrasive grains in a size range from F150 or finer than F150 up to #1500. <P>SOLUTION: The burning temperature of the grinding wheel is set to 800-1000°C, and the softening yield point of the grinding wheel is minus 0-200°C from the burning temperature. The specific softening yield point temperature is 600-800°C. Chemical components of a vitrified binder therefor are as the feature 40.0-55 wt% SiO2, 15.0-30 wt% Al2O3, 1.0-3.0 wt% CaO, 4.0-10.0 wt% Na2O, 1.0-2.0 wt% K2O and 10.0-25.0 wt% B2O3. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

The present invention relates to a vitrified silicon carbide grindstone using silicon carbide having a particle size range of up to # 1500 and finer than F150 or F150 bonded with a vitrified binder.

The main types of grinding and polishing wheels include vitrified wheels, resinoid wheels, metal wheels, and electrodeposition wheels when enumerated by binder.
Among them, vitrified grindstones with good sharpness, high durability and good dressing are mainly used. As abrasives used for vitrified grinding wheels, super abrasive grains such as CBN abrasive grains and diamond abrasive grains, alumina abrasive grains, and silicon carbide abrasive grains are used. Rougher than F120 and finer than F150 or F150 which is a finish grinding (or polishing) region.

  Among the abrasive grains used, silicon carbide abrasive grains are used for grinding and polishing non-metals, non-ferrous metals, cast iron, high-hardness brittle steel materials, superalloys, etc., among which vitrified silicon carbide-based abrasives In the particle size range of finer than F150 or F150 and up to # 1500, it is used as the above-mentioned finishing polishing grindstone and as a dresser for other grindstones.

  As a general method for producing a silicon carbide vitrified grindstone, it is described that a vitrified binder made of feldspar-ceramic stone-clay is fired at 1300 ° C. as described in P643 and 644 of fine ceramics. Has been.

Yoichi Motoki, “Sintered Ceramics General 4 Fine Ceramics”, pages 643-644, published on January 25, 1976 Tokyo Printing Center

However, when the method for producing a silicon carbide vitrified grindstone described in Non-Patent Document 1 is applied to a silicon carbide vitrified grindstone finer than F150 or F150, cracks often occur in the grindstone after firing. As the form of the crack, the crack form 1) described in P650 of Non-Patent Document 1 is mainly used, and cracks of other forms are also generated. As a cause of cracks described in Non-Patent Document 1 P649, measures were taken with attention paid to drying of a grindstone before firing, but good results were not obtained.

As a cause of the crack, oxidation of the abrasive grains in the firing temperature range of the silicon carbide-based abrasive grains was considered. It is known that when silicon carbide is heated at a high temperature, the bond between Si and C is decomposed and chemically changed to SiO2 and CO2. Looking at this in relation to the abrasive grain size, as the abrasive grain size becomes finer, the specific surface area of the abrasive grain increases, and the proportion of the abrasive grain surface oxidized and SiO2 formed increases. It was considered that the increase in weight at that time and the increase in the abrasive grain volume accompanying this increase in the volume of the grindstone and the occurrence of cracks after firing. As a countermeasure, firing under an inert atmosphere generally used in a method for producing a vitrified diamond grindstone is conceivable. However, since the production cost increases and it becomes unprofitable, finer silicon carbide vitrified grindstone than F150 or F150. Has not been adopted.

  Therefore, as a subject of the present invention, in vitrified grindstones using silicon carbide abrasive grains finer than F150 or F150 and having a particle size range of up to # 1500, manufacturing defects are eliminated in consideration of economic efficiency, and the market is stably obtained. It can be supplied.

As a result of intensive studies to solve the above-mentioned problems, the firing temperature of the vitrified silicon carbide grindstone is set to 800 to 1000 ° C., and the softening yield point of the grindstone is minus 0 to 200 ° C. from the firing temperature. The temperature is 600 to 800 ° C., and 40.0 to 55 wt% SiO 2, 15.0 to 30 wt% Al 2 O 3, 1.0 to 3.0 wt% CaO, 4.0 as chemical components of the vitrified binder for that purpose. It is characterized by being -10.0 wt% Na2O, 1.0-2.0 wt% K2O, 10.0-25.0 wt% B2O3.

As an effect of the present invention, compared to F150 manufactured by the conventional manufacturing method or vitrified silicon carbide grinding stones with a finer particle size range up to # 1500 than F150, the problem of cracking after firing is eliminated, and the grinding stones are stable on the market. In addition, the grinding performance equivalent to or higher than that of the conventional grindstone is exhibited. The contribution of the present invention to the grinding industry is significant.

F150 or silicon carbide vitrified grinding wheel with a finer particle size range up to # 1500 than F150 used in the present invention is used for finish polishing of non-metal, non-ferrous metal, cast iron, high-hardness brittle steel, superalloy, etc. Used as a grindstone dresser.

  As a result of intensive investigations that should solve the problems of the present invention, it is possible to minimize the oxidation reaction of SiO2 generation of silicon carbide abrasive grains when the firing temperature is set to 800 to 1000 ° C., thereby minimizing the volume expansion of the grindstone. It has been found that production defects and cracks after firing are eliminated, and stable whetstone production can be achieved. The firing temperature is desirably 850 to 950 ° C, and more desirably 870 to 930 ° C.

The softening yield point defined in the present invention refers to a piece of a grindstone that has been fired, and a thermal expansion measured by TMA under a certain load. At a certain point, the vitrified binder in the vitrified silicon carbide grindstone decreases in viscosity due to heating. The expansion of the vitrified silicon carbide grindstone decreases in the negative direction. This characteristic is due to the thermal expansion of the abrasive grains themselves and the viscosity reduction of the vitrified binder that serves to buffer the distortion caused by the oxidation of the abrasive grains. It shows that the problem of crack generation during firing is eliminated by being less than the manufacturing method, and the vitrified binder is softened and melted at a predetermined firing temperature to hold silicon carbide abrasive grains well and to obtain good grinding performance Is.
In the present invention, a TMA / SS6300 manufactured by Seiko Instruments Inc. (SII) was used, a load of 20 g was applied to a rectangular parallelepiped test piece having a cross-sectional area of 1 mm2, and 20 ° C./min. The temperature was raised at The softening yield point is preferably minus 0 to 200 ° C., more preferably minus 50 to 200 ° C., from a predetermined firing temperature. Specifically, the temperature of the softening yield point is 600 to 800 ° C, preferably 650 to 800 ° C, and more preferably 700 to 800 ° C. In addition, the measurement of the softening yield point of this result may use the result measured by another model unless it greatly deviates from the conditions implemented in the present invention.

The chemical component of the vitrified binder for carrying out the present invention is SiO2 in the range of 40.0 to 55 wt%, and if it is less than 40 wt%, the main skeletal component of the vitrified binder is insufficient, so that the abrasive retention force decreases. Furthermore, the softening point of the vitrified binder is too low, causing problems such as gas generation during firing. If it exceeds 55 wt%, the softening point of the vitrified binder is increased and the holding power of the silicon carbide-based abrasive grains is reduced. Al2O3 in the range of 15.0 to 30 wt%, if less than 15 wt%, the main skeleton components are insufficient, so the abrasive grain holding power is lowered, the softening point is lowered too much, causing problems such as gas generation during firing, 30 wt% If it is more than%, the softening point of the vitrified binder will be high and the holding power of the silicon carbide abrasive grains will be reduced. When CaO is less than 1 wt% in the range of 1.0 to 3.0 wt%, the softening point of the vitrified binder increases and the holding power of the silicon carbide abrasive grains decreases. If it exceeds 3 wt%, the softening point of the vitrified binder will be too low, causing problems such as gas generation during firing. When the Na2O content is less than 4 wt% within the range of 4.0 to 10.0 wt%, the softening point of the vitrified binder increases and the holding power of the silicon carbide abrasive grains decreases, and when it exceeds 10 wt%, the vitrified binder softens. The point lowers too much, causing problems such as gas generation during firing, and the softening point of the vitrified binder is too low, causing problems such as gas generation during firing. When 1.0 to 2.0 wt% of K2O is less than 1.0 wt% in the range of 1.0 to 2.0 wt%, the softening point of the vitrified binder increases and the holding power of the silicon carbide abrasive grains decreases, If it exceeds 4.0 wt%, the softening point of the vitrified binder will be too low, causing problems such as gas generation during firing. When B2O3 is in the range of 10.0 to 25.0 wt% and less than 10 wt%, the softening point of the vitrified binder increases and the holding power of the silicon carbide abrasive grains decreases, and when it exceeds 25 wt%, the softening point of the vitrified binder This will cause problems such as gas generation during firing.
The adjustment of the vitrified binder can be made with a combination of commercially available materials, for example, a combination of clay, feldspar, porcelain stone and frit. Adjustments can be made as appropriate without departing from the spirit of the present invention.

Silicon carbide-based abrasive grains used in the present invention are black silicon carbide abrasive grains (hereinafter referred to as C abrasive grains) and green silicon carbide abrasive grains (hereinafter referred to as GC abrasive grains).
The application range of the silicon carbide-based abrasive grain size applied to the present invention is applied to finer abrasive grains than F150 or F150.
The fine grain lower limit range of the abrasive grain size can be satisfactorily applied up to # 1500, preferably # 1000, and more preferably F500.

The abrasive volume ratio applied to the present invention is 38 to 53 vol%. Moreover, the binder volume ratio applied to this invention is 3-35 vol%. The pore volume ratio is a value obtained by subtracting the abrasive volume ratio and the binder volume ratio from 100. These are appropriately determined depending on grinding conditions and the like.
Examples of the present invention will be described below together with comparative examples. However, these examples illustrate the feasibility and usefulness of the present invention, and are not intended to limit the configuration of the present invention.

Silicon carbide abrasive grains, confirmation of weight change by heating Abrasive grains used: GC abrasive grains Particle sizes to be tested: F60, F100, F220, F400, # 800
Test procedure: Using a TG / DTA6300 manufactured by Seiko Instruments Inc. (SII), 0.05 g of test abrasive grains were put into a platinum dish having a cup shape with a diameter of 5.2 mm and a height of 2.5 mm, and 20 ° C./min. . The temperature was then increased and the weight change was measured.

Test result (weight increase%)

As can be seen from the above results, the increase in weight increases as the grain size becomes finer. In particular, the weight increase under conventional firing conditions such as heating temperature of 1250 ° C or 1300 ° C with F220 and F220 finer is remarkable. large.
This increase in weight is considered to increase the volume of the grindstone during firing under conventional firing conditions, causing cracks after firing.

TMA measurement Vitrified binder chemical component Examples: SiO2: 48 wt%, Al2O3: 26 wt%, CaO: 1.0 wt%
K2O: 1.0 wt%, Na2O: 7.0 wt%, B2O3: 17.0 wt%
Comparative example: SiO2: 70 wt%, Al2O3: 20 wt%, K2O: 8.0 wt%,
Na2O: 2.0 wt%
The examples were adjusted to the above chemical components using clay, feldspar, and low temperature softening frit raw materials.
In the comparative example, clay, feldspar, and ceramic stone were used, and the above chemical components were prepared with reference to the No3 binder chemical components in Table-3.235 of Non-Patent Document 1P643.

Test piece preparation whetstone mixing ratio GC abrasive grains F320 100 parts by weight Binder 25 parts by weight Primary binder 6 parts by weight

After the above materials are uniformly mixed, a 42 × 5 × 10 rectangular parallelepiped square grindstone is prepared, and the input weights are abrasive volume fraction = 45%, binder volume fraction = 15%, pore volume fraction = 40 wt%. After adjustment and molding, the grinding wheel of Example 1 using the binder of the example dried at 60 ° C. for 12 hours was the maximum firing temperature of 900 ° C. The grinding stone of Comparative Example 1 using the binder of the comparative example was the maximum firing temperature. Firing was performed at 1250 ° C.

  The test piece softening yield point was measured by using a TMA / SS6300 manufactured by Seiko Instruments Inc. (SII), applying a 20 g load to a rectangular parallelepiped test piece having a cross-sectional area of 1 mm2 and a test piece length of 17.0 mm. / Min. And the change in thermal expansion was observed.

Measurement Result As shown in the results of FIG. 1, the grindstone using the binder of Example 1 turned from expansion to contraction at a peak at 755 ° C. This is because the grindstone was not actually shrunk, but the binder softened and the viscosity decreased, so that it did not expand due to the load applied to the grindstone, and it can be said that the binder softened below the predetermined firing temperature. In contrast, the grindstone using Comparative Example 1 turned from expansion to contraction at a temperature of 1467 ° C. This was a temperature above the predetermined firing temperature.

Grinding wheel production test A 1A type grinding wheel was produced, and the presence or absence of cracks after firing was confirmed. As the vitrified binder to be tested, the binder described in Example 1 is used, the grindstone using the binder of the example is the grindstone of Example 2, and the grindstone using the binder of the comparative example is grindstone of Comparative Example 2.

Test whetstone dimensions: φ205 mm × t15 mm × h 31.75 mm 1A type whetstone whetstone mixing ratio (both Example 2 and Comparative Example 2)
C abrasive grains F220 100 parts by weight Vitrified binder 10 parts by weight Primary binder After uniformly mixing 3 parts by weight or more of materials, the input weight is abrasive volume fraction = 47%, binder volume fraction = 6%, pore volume fraction = 20 wt. Grindstones adjusted to 47 wt% and prepared as described above, molded and dried at 60 ° C. for 12 hours, and the grindstone of Example 2 using the binder of the example has a maximum firing temperature of 900 ° C. The grindstone of Comparative Example 2 using the binder of Comparative Example was fired at a maximum firing temperature of 1250 ° C.

test results

As described above, in the grindstone of Example 2, no cracks occurred in the grindstone after firing. On the other hand, in Comparative Example 2 grindstone, 6 out of 20 cracks as shown in FIG.
First, the firing temperature of Comparative Example 2 is higher than that of Example 2. This is because silicon carbide abrasive grains are oxidized more than the grinding wheel of Example 2, and it is considered that the grinding stone of Comparative Example 2 has a large volume expansion, and cracks are generated due to the distortion, and as confirmed in Example 2. The softening yield point is higher than the predetermined firing temperature, which is because the viscosity reduction of the vitrified binder that plays a role in buffering distortion such as thermal expansion of the abrasive grains and volume expansion due to abrasive oxidation is small. Conceivable.

  From the above, the oxidation of the abrasive grains is less than that of Comparative Example 2 and the softening yield point is lower than the predetermined firing temperature as confirmed in Example 2, and this is because of the abrasive grains themselves. The viscosity of the vitrified binder that serves to buffer strain such as thermal expansion and abrasive volume expansion due to abrasive oxidation occurs sufficiently, and since the firing temperature is lower than that of the comparative example 2, the thermal expansion of the abrasive itself Comparative Example 2 It is considered that a good production result was obtained by adding a factor that it was less than that of the grindstone.

Grinding test In order to confirm the grinding performance of the vitrified silicon carbide grinding wheel of the present invention, a comparison with a conventional product is performed.
The binder described in Example 1 is used as the vitrified binder to be tested, and the grindstone using the binder of the example is Example 3, and the grindstone using the comparative binder is Comparative Example 3.

Grinding wheel dimensions to be tested : φ205mm × t15mm × h50.8mm 1A type grinding wheel

Grinding wheel mixing ratio (both Example 3 and Comparative Example 3)
GC F150 100 parts by weight Vitrified binder 13 parts by weight Primary binder 4 parts by weight

After uniformly mixing the above materials, the input weight was adjusted so that the abrasive grain volume ratio = 47%, the binder volume ratio = 8%, and the pore volume ratio = 45 wt%, and 20 grinding wheels having the dimensions described above were prepared. After grinding and drying at 60 ° C. for 12 hours, the grinding wheel of Example 3 using the binder of the example has a maximum firing temperature of 900 ° C., and the grinding wheel of Comparative Example 3 using the binder of the comparative example has a maximum firing temperature of 1250. Baked at ℃.

Grinding conditions Work material Material: SKD11 (62HRc)
Dimensions: 5 x 100 x t mm
Grinding machine Type: Okamoto horizontal axis grinding machine
Model: CNC-52B
Grinding fluid Product name: Crekat NET-500B (Soluble type)
Concentration: 2%
Flow rate: 27 liters / min
Dress condition Dresser: 3 prismatic dresser
Wheel peripheral speed: 33.3 m / s
Dress cutting: 10Rμm / pass × 10pass
Dress lead: 0.1mm / rev
Grinding conditions Grinding type: Surface grinding Grinding conditions: Wet plunge grinding
Wheel peripheral speed: 33.3 m / s
Table speed: 0.155 m / s
Grinding depth: 5μm / pass
Stock allowance: 1.25mm
Characteristic to evaluate Grinding wheel hardness (HRL)
Grinding ratio (GR)
Grinding power (Ft)
Finished surface roughness (Rz)

Characteristic value evaluation procedure
Wheel hardness (HRL)
The Rockwell hardness is in accordance with JIS standard (Rockwell hardness test B7726, 1998). When a reference load of 10 kgf is applied, and then a constant test load is applied and then returned again, the intrusion depth h of the indenter at two reference loads before and after Desired. In this example, a 1/4 inch steel ball (diameter 6.35 mm) was used, and the test load was 60 kgf, and the calculation formula of 130-500 h was used.

Grinding ratio (GR)
Calculated by the material removal volume / grinding wheel consumption volume.

Grinding power (Ft)
It is calculated | required as 612 * W / peripheral speed (60/100) where W is the power consumption of the grinding wheel shaft motor. In addition, the said grindstone peripheral speed was used as a peripheral speed.

Finished surface roughness (Rz)
The surface roughness Rz is measured as a ten-point average roughness.
The ten-point average roughness Rz is extracted from the roughness curve by the reference length in the direction of the average line, measured in the vertical magnification direction from the average line of the extracted portion, and the altitude Yp of the highest peak from the highest peak to the fifth. And the average value of the absolute values of the altitudes Yv of the lowest valley floor to the fifth valley floor. In this example, the measurement was performed at an evaluation length of 25 mm.

The hardness of the grindstone was almost the same in both Example 3 and Comparative Example 3.
The grinding ratio of Example 3 was superior. On the other hand, the grinding power of Comparative Example 3 was lower. The finished surface roughness was smaller in Example 3. From this result, it can be said that the invention product exhibits a grinding performance equivalent to or higher than that of the conventional product.

The product of the present invention can be applied to various types of grinding such as internal grinding, surface grinding and cylindrical grinding, and the work material is also suitable for grinding, polishing, especially finish polishing of non-metal, non-ferrous metal, cast iron, high hardness brittle steel, superalloy etc. Can be used for

3 is a graph showing thermal expansion of Example 1 and Comparative Example 1. The form of crack generation after grindstone firing is shown.

Explanation of symbols

1: Grinding wheel after firing 2: Crack

Claims (4)

A vitrified silicon carbide grindstone that is bonded by a vitrified binder and uses silicon carbide abrasive grains having a particle size range of F150 or finer than F150 and up to # 1500, wherein the vitrified silicon carbide grindstone is fired at 800 to 1000 ° C. A method for producing a vitrified silicon carbide grindstone. The method for producing a vitrified silicon carbide grindstone according to claim 1, wherein the softening yield point of the grindstone is minus 0 to 200 ° C from the firing temperature. The method for producing a vitrified silicon carbide grindstone according to claim 1 or 2, wherein the softening yield point of the grindstone is in the range of 600 to 800 ° C. The vitrified binder is 40.0 to 55 wt% SiO2, 15.0 to 30 wt% Al2O3, 1.0 to 3.0 wt% CaO, 4.0 to 10.0 wt% Na2O, 1.0 to The vitrified silicon carbide grindstone according to claim 1, which is 2.0 wt% K 2 O, 10.0-25.0 wt% B 2 O 3.

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