JP2007256267A - Porosity valuation method of grinding stone using capacitance and dielectric constant - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for evaluating a porosity of grinding stone, to be more precise, method for easily evaluating a porosity of grinding stone, which is a porous structure with continuous pores. <P>SOLUTION: This is the method for evaluating porosity of grinding stone, characterized that database indicating correlation between porosity and dielectric constant on a standard sample of the grinding stone with its porosity known is built, capacitance of the grinding stone to be evaluated is measured, dielectric constant is computed from the above dielectric constant, and then the dielectric constant of the above grinding stone to be evaluated is compared with that of the standard sample to evaluate the porosity of the grinding stone as the object to be evaluated. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for evaluating the porosity of a grindstone. Specifically, for a grindstone that is a porous sintered body containing continuous pores, the pores are obtained using capacitance and dielectric constant. It relates to a method for assessing rates.

  A so-called porous sintered body having a large number of pores inside the sintered body is used in various industrial fields. Since the internal structure of the sintered body, particularly the pores, has a significant effect on the properties of the sintered body, it is important to measure and evaluate not only the presence or absence, but also the degree of presence, that is, the porosity.

  As a technique for evaluating the internal structure of an object to be evaluated, a method for inspecting ceramic electronic components such as a ceramic heater has been disclosed (see Patent Document 1). In this method, after removing bubbles adhering to the outer surface of the object to be evaluated, a voltage is applied in the electrolytic solution to measure the resistance value of the object to be evaluated, and the resistance value exists inside the object to be evaluated. This technology detects pinholes and internal defects.

  As another example, a method for evaluating the internal structure of a grinding wheel is disclosed (see Patent Document 2). A grinding wheel composed of a porous sintered body usually has a large number of continuous pores in its structure (a plurality of pores are connected to each other without being independently present). . In the grinding wheel, the pores have a great influence on the grinding characteristics because they function as a place to release the grinding heat generated during the grinding operation and to accommodate the grinding tips (grinding chips of the workpiece). It is a very important factor. This method is a technique for evaluating the relative density distribution of a grinding wheel using ultrasonic flaw detection.

As yet another example, a method for detecting a ceramic element including a porous part (see Patent Document 3) is disclosed. This method is a technique for non-destructively detecting a ceramic element including a porous portion by measuring the capacitance of the ceramic element.
JP 2002-48832 A JP 2006-10493 A JP 2001-165980 A

  Among the conventional methods described above, the method described in Patent Document 1 immerses the object to be evaluated in the electrolytic solution when measuring the resistance value, and therefore, it is necessary to remove fine bubbles on the outer surface before the measurement. Moreover, the work which removes electrolyte solution from a to-be-evaluated object is required after completion | finish of a measurement, and additional time and labor are required. Further, it is an inappropriate method when the object to be evaluated is not preferable to be in contact with a liquid.

  Nondestructive evaluation by ultrasonic waves is not limited to the evaluation of grinding wheels in Patent Document 2, and is a technique applied in a very wide range of fields. Since ultrasonic measurement in air is affected by the flow of air, it is usual to measure by immersing an object to be evaluated in a liquid such as water. Similar to the method described in Patent Document 1, such measurement in a liquid cannot be applied depending on the object to be evaluated, and is inconvenient because it requires an operation of removing the liquid from the object to be evaluated.

  The capacitance used in the method described in Patent Document 3 is a parameter whose value can vary depending on the measurement atmosphere, temperature, and humidity. Using the capacitance as an index for evaluating the internal structure of the object to be evaluated is sufficient for detecting the presence or absence of pinholes that are regarded as internal defects in the ceramic element as described in Patent Document 3. However, it is not sufficient to specify the porosity value of an object to be evaluated that is continuous pores and has a large pore volume ratio. Further, the object to be evaluated in Patent Document 3 is an electric element in which an electrode is embedded, and the internal electrode can be used for measuring the dielectric constant and the like, but the object to be evaluated does not have such an internal electrode. It cannot be applied to objects. In other words, the porosity can be specified to some extent by the dielectric constant calculated from the capacitance, but it is desired to specify the porosity with higher accuracy.

  In particular, the grindstone to be evaluated by the present invention has a large number of continuous pores inside the sintered body, and it is important to specify the porosity. Since the grindstone itself is consumed by use, it is necessary to replace the grindstone with a new grindstone as necessary in the grinding / polishing process. In order to grind and polish the same workpiece, it is usual to use a plurality of grindstones by frequently exchanging them. Therefore, when the internal structure of the grindstone, specifically, the porosity, varies between the production lots of the grindstone, there is a disadvantage that the workpiece cannot be supplied with a certain quality. In a grindstone, since pores existing in a grindstone, which is a sintered body, have a significant effect on the performance of grinding and polishing, it is important to provide a method that can easily evaluate the porosity of a grinding wheel for grinding. .

  The present invention provides a method for evaluating the porosity of a grindstone, specifically, for easily evaluating the porosity of a grindstone that is a porous sintered body containing continuous pores. It is an object to provide a method.

  As a result of diligent research to solve the above problems, the present inventors measured the capacitance of the grinding stone being evaluated and the dielectric constant calculated from the capacitance as an index, and measured this under specific humidity conditions. Thus, a method capable of evaluating the porosity was found and the present invention was completed.

That is, the present invention is a method for evaluating the porosity of a grindstone,
(1) Select the grindstone to be evaluated,
(2) Select a grindstone standard sample containing the same abrasive grains as those contained in the evaluation target grindstone,
(3) For the grindstone standard sample whose porosity is known, the capacitance is measured in an atmosphere where the humidity is higher than 25% and lower than 30%, and the dielectric constant is calculated from the capacitance,
(4) By repeating the step (3) for a plurality of grindstone standard samples having different porosities, a database showing the correlation between the porosity and the dielectric constant of the grindstone standard samples is constructed,
(5) For the evaluation target grindstone, the capacitance is measured in an atmosphere where the humidity is higher than 25% and lower than 30%, and the dielectric constant is calculated from the capacitance.
(6) The porosity of the evaluation target grindstone is evaluated by comparing the dielectric constant of the evaluation target grindstone with the dielectric constant of the grindstone standard sample in the database.

  In another aspect of the present invention, in the above method, the grindstone to be evaluated includes a plurality of types of abrasive grains, and a plurality of types of whetstone standard samples are selected as the whetstone standard samples. One or more kinds of abrasive grains included in the evaluation target grindstone are included, respectively.

In this invention, it is preferable that the grindstone to be evaluated is a porous sintered body containing continuous pores.
Moreover, in this invention, it is preferable that the grindstone to be evaluated is a vitrified superabrasive grindstone.

  According to the method of the present invention, the porosity of a grindstone, which is a porous sintered body containing continuous pores, can be easily evaluated.

The present invention provides a method for evaluating the porosity of a grindstone to be evaluated using capacitance and dielectric constant.
The method of the present invention is a method for evaluating the porosity of a grindstone, wherein (1) a grindstone to be evaluated is selected, and (2) a grindstone standard including the same abrasive grains as those contained in the grindstone to be evaluated. Select a sample, and (3) measure the capacitance in an atmosphere where the humidity is higher than 25% and lower than 30%, and calculate the dielectric constant from the capacitance, with respect to the grindstone standard sample whose porosity is known. (4) The step (3) is repeated for a plurality of grinding wheel standard samples having different porosity, and a database showing the correlation between the porosity and the dielectric constant of the grinding wheel standard sample is constructed, and (5) the evaluation For the target grindstone, the capacitance is measured in an atmosphere where the humidity is higher than 25% and less than 30%, and the dielectric constant is calculated from the capacitance. (6) The dielectric constant of the evaluation target grindstone is calculated in the database. Invitation of standard grinding wheel samples By comparing the rate, it is characterized in evaluating the porosity of the grinding wheel is the evaluation target.

The term “porosity” used in the present specification refers to the volume ratio of pores in the grindstone when the volume of the grindstone to be evaluated is 100%.
As used herein, “dielectric constant” is a coefficient (ε) that indicates the relationship between charge and the force provided thereby in a substance. Each material has a specific dielectric constant, and this value is determined by how the atoms (or molecules) in the material respond (dielectric polarization method) when an electric field is applied from the outside. The coefficient ε ₀ is called the dielectric constant of vacuum, and ε ₀ = 8.854 × 10 ⁻¹² F / m.

The ratio ε / ε ₀ = ε _s between the dielectric constant and the vacuum dielectric constant is called the relative dielectric constant. The relative dielectric constant is a dimensionless quantity and takes a constant value regardless of the unit system used. The relative permittivity of main materials is as follows. Water: 81, Diamond: 5.4 to 9.9, Alumina: 8.5, Mica: 7.0, Quartz: 3.8, Asphalt: 2.7, Air: 1.0059.

  In the present invention, with respect to a grindstone standard sample with a known porosity and a grindstone to be evaluated, the capacitance is measured, and the dielectric constant is calculated from the measured capacitance. FIG. 1 shows a conceptual diagram of an apparatus for measuring the capacitance of an object to be evaluated. The apparatus of FIG. 1 is for sandwiching an object to be evaluated 2 between a pair of opposing electrodes 1 and applying an AC voltage to the object to be evaluated by an AC power supply 4 to measure the capacitance. Since the dielectric constant of the object to be evaluated is known to change relatively depending on the frequency of the AC power source, the capacitance is measured by applying a plurality of AC frequencies from the range of 100 kHz to 1 MHz. Do.

Next, the intrinsic dielectric constant ε _s of the measurement target is calculated from the measured capacitance C. The calculation formula is shown below.

  By comparing the dielectric constant of the grindstone standard sample obtained by following the above procedure and the grindstone to be evaluated, the correlation between the dielectric constant and the porosity is used to determine the relative porosity of the grindstone to be evaluated. Can be evaluated.

  The dielectric constant of the grindstone can vary depending on the type of abrasive grains contained since the inherent dielectric constant of the abrasive grains is different. Therefore, in the method of the present invention, it is preferable that the abrasive grains contained in each of the evaluation target grindstone and the grindstone standard sample are the same regardless of whether the abrasive grains are a single kind or plural kinds. Alternatively, when the grindstone to be evaluated includes a plurality of kinds of abrasive grains, a plurality of kinds of grindstone standard samples are selected as the grindstone standard samples, and one or more kinds of these grindstone standard samples are included in the grindstone to be evaluated. It is preferable that each contains an abrasive grain.

  That is, it is important to select a grinding wheel standard sample and accumulate porosity data so that the grinding wheel standard sample database includes abrasive grains contained in the grinding stone to be evaluated and porosity data thereof.

  Since the humidity conditions in the atmosphere to be measured have a significant effect on the capacitance measurement, the inventors have found that the capacitance measurement value varies, and that the dielectric constant and the porosity are constant. It was found that no correlation was shown. Therefore, in the method of the present invention, the capacitance is measured under specific humidity conditions in order to eliminate the variation in capacitance due to humidity and establish a correlation between the dielectric constant and the porosity. . Specifically, in the present invention, the capacitance is measured in an atmosphere where the humidity is higher than 25% and lower than 30%. In addition, the temperature condition during the measurement of the capacitance does not have a significant influence that causes variations in the capacitance value. In the humidity condition described above, the temperature condition is not particularly limited, and the room temperature There is no problem with measurement in the vicinity.

  The method of the present invention described above can be applied to a porous sintered body containing continuous pores, and can be applied particularly well to a grindstone having a porous sintered body structure. it can. According to the present invention, the porosity can be satisfactorily evaluated in a grindstone in which the presence of pores greatly affects the characteristics.

  A grindstone generally has a structure formed by fixing hard inorganic particles called abrasive grains with a substance called a binder. Examples of the binder include vitrified as the inorganic binder, resinoid as the organic binder, and metal and electrodeposition as the metallic binder.

  Examples of the inorganic particulates used as the abrasive grains include alumina-based abrasive grains, silicon carbide-based abrasive grains, zirconia-based abrasive grains, cerium oxide, silica, chromium oxide, CBN abrasive grains, and diamond abrasive grains. The combination of the binder and the abrasive is appropriately determined in consideration of grinding conditions and the like.

  As a grindstone, there is a so-called vitrified grindstone using an inorganic binder. Vitrified grindstones are particularly simple because pores are easily formed in the structure, and they have good sharpness, high holding power of abrasive grains, high durability and good dressability (the abrasive blades can be projected well). Has characteristics. FIG. 2 shows an example of the structure of the vitrified grindstone. In FIG. 2, the structure of the vitrified grindstone is usually a structure in which a large number of pores 7 are not independent but continuously formed in a structure in which abrasive grains 5 are held by a binder 6. This continuous pore body functions as a place for releasing the grinding heat generated during the grinding operation and accommodating the grinding tip (grinding residue of the workpiece).

  Recently, vitrified superabrasive grindstones using vitrified superabrasive grindstones that employ particularly hard abrasive grains such as CBN abrasive grains and diamond abrasive grains are particularly highly durable, and a large number of single grindstones are used. The workpiece can be processed. Since the abrasive grains used in the vitrified superabrasive grindstone are more expensive than other abrasive grains, quality control in the manufacturing process is particularly important.

  The porosity of the vitrified superabrasive grindstone is generally 5 to 80%. When used for special applications, the porosity may be greater than 50%, for example 70% or more, but when used for normal applications, the porosity is 20-35%. On the other hand, when detecting defects such as pinholes in the prior art, as shown in Patent Documents 1 to 5, the object to be evaluated is basically a sintered body that does not allow the presence of pores, and its pore volume% Is at least less than 5%. On the other hand, in the present invention, a grindstone having a continuous multi-pore structure can be evaluated, and a grindstone having a porosity of at least 5% can be evaluated.

  Hereinafter, examples of the present invention will be described together with comparative examples. However, these examples illustrate the feasibility and usefulness of the present invention, and do not limit the configuration of the present invention.

Example 1
A vitrified CBN grindstone having a known porosity was used as an object to be evaluated, and the dielectric constant was measured to examine the relationship with the porosity.
1-1. Composition of vitrified CBN grinding wheel Evaluated object 1 CBN abrasive grains 40% by volume
Silicon carbide abrasive grains 10% by volume
Vitrified binder 17.5% by volume
Porosity 32.5% by volume
Product 2 CBN abrasive grains 40% by volume
Silicon carbide abrasive grains 10% by volume
Vitrified binder 22.5% by volume
Porosity 27.5% by volume
Product 3 CBN abrasive grains 40% by volume
Silicon carbide abrasive grains 10% by volume
Vitrified binder 27.5% by volume
Porosity 22.5% by volume
1-2. Manufacturing procedure of vitrified CBN grindstone The charging ratio of CBN abrasive grains, silicon carbide abrasive grains, and vitrified binder is determined so as to have the above-described configuration, and the primary binder (liquid glue, shape of sintered body from molding to firing) And disappear after firing.) Was added and mixed uniformly, and the mold was filled and cold-molded to form a rectangular parallelepiped having a length of 43 mm, a height of 5 mm, and a width of 12 mm. . The obtained molded body was dried at 60 ° C. for 12 hours and then calcined at 900 ° C. for 7 hours. After firing, the surface of the obtained grindstone was polished for the purpose of eliminating extreme irregularities.
1-3. Dielectric Constant The dielectric constant was calculated by measuring the capacitance of the evaluation objects 1 to 3. The apparatus used to measure the capacitance is shown in FIG. In FIG. 3, an object to be evaluated 11 was placed between the fixing jigs (including electrodes) 10, and the thickness was measured with a micrometer 8. The switch of the alternating current power supply installed in the back surface was input, and the alternating current of frequency 100kHz, 200kHz, 300kHz, 400kHz, 500kHz, 600kHz, 700kHz, 800kHz, 900kHz, and 1MHz was each given for 10 second by the voltage of 1V. The capacitance was measured with an LCR meter (Agilent, 4284A), and the dielectric constant was calculated according to Equation 1.

The capacitance measurement atmosphere was a temperature of 33 ° C. and a humidity of 28%.
1-4. Results The dielectric constant results are shown in Table 1.

  The dielectric constants of the three types of evaluation objects having different porosities are proportional to the porosity at any AC frequency, the evaluation object 1 having the highest porosity has the lowest value, and the evaluation object having the lowest porosity. 3 showed the highest value.

The difference in the porosity of the objects to be evaluated 1 to 3 is 5.0% by volume, but the measured dielectric constant has a clear difference according to the difference in the porosity, and the porosity of the object to be evaluated is It was shown that relative evaluation can be easily performed. In this example, since the object to be evaluated was placed on a simple jig and measurement was possible by applying a voltage for 10 seconds, the evaluation method of the present invention can be carried out simply and in a short time.
(Example 2)
We investigated the influence of the humidity conditions of the atmosphere when measuring the capacitance on the correlation between the dielectric constant and the porosity. Dielectric constant values were compared in the same manner as in Example 1 by changing the humidity conditions of the capacitance measurement atmosphere.

2-1. Structure of vitrified CBN grinding wheel Evaluation object 1 CBN abrasive grains 50% by volume
Vitrified binder 17.5% by volume
Porosity 32.5% by volume
Product 2 CBN abrasive grains 50% by volume
Vitrified binder 22.5% by volume
Porosity 27.5% by volume
Product 3 CBN abrasive grains 50% by volume
Vitrified binder 27.5% by volume
Porosity 22.5% by volume
2-2. Manufacturing procedure of vitrified CBN grinding wheel It was manufactured in accordance with item 1-2 of Example 1.
2-3. Dielectric constant The capacitance was measured according to the paragraph 1-3 of Example 1 to obtain the dielectric constant. The measurement atmosphere of the capacitance was 25 ° C., and the humidity was changed to (1) 70%, (2) 50%, (3) 30%, (4) 27%, (5) 25%.
2-4. Results The results of dielectric constant are shown in Tables 2-6.

  In Table 2, when the humidity was 70%, the value of dielectric constant tended to increase from 500 kHz to 600 kHz for the object to be evaluated 1 and from 300 kHz to 400 kHz for the object to be evaluated 2.

  In Table 3, when the humidity was 50%, the value of dielectric constant tended to increase from 300 kHz to 400 kHz, from 2 kHz to 300 kHz, and from 3 kHz to 400 kHz.

In Table 4, when the humidity was 30%, the to-be-evaluated object 2 showed an increasing tendency in the value of the dielectric constant from 300 kHz to 400 kHz.
In Table 6, when the humidity was 25%, the to-be-evaluated object 1 showed an increasing tendency in the value of the dielectric constant from 300 kHz to 400 kHz.

  From the results of Example 1 described above, the value of the dielectric constant is inversely proportional to the grinding wheel porosity, and the dielectric constant tends to increase as the grinding wheel porosity decreases. This is because the density of the grindstone that is the object to be evaluated is increased.

  However, in the above four humidity atmospheres (humidity 70%, 50%, 30%, 25%), such a relationship is not formed, and the dielectric constant varies and a stable measured value of the dielectric constant is obtained. There wasn't.

  On the other hand, in Table 5, when the humidity was 27%, the phenomenon that the dielectric constant increased at a certain frequency as seen in other humidity conditions was not observed. Further, in any object to be evaluated, there is an inversely proportional relationship between the grindstone porosity and the dielectric constant, and the value of the dielectric constant tends to increase as the grindstone porosity decreases between objects to be evaluated. It was.

  In Example 1, the humidity of the capacitance measurement atmosphere was 28%, and the same tendency as the measurement result at the humidity of 27% was observed. Therefore, the humidity should be higher than 25% and less than 30%. It was confirmed that a stable dielectric constant value can be obtained without variation. This indicates that the porosity can be specified from the dielectric constant which is the object of the present invention under such humidity conditions.

The temperature of the capacitance measurement atmosphere was 33 ° C. in Example 1 and 25 ° C. in this example. Therefore, if the humidity is in the range of more than 25% and less than 30%, the temperature condition is the dielectric constant. It is judged that there is no significant effect on the results of.
(Example 3)
For a vitrified grinding wheel containing different types of abrasive grains, the correlation between dielectric constant and porosity was verified, and a database was constructed. Furthermore, the applicability of the present invention was examined using a vitrified grindstone containing two types of abrasive grains as an evaluation target.
3-1. Composition of grinding wheel standard sample Three kinds of standard samples using (1) CBN abrasive grains, (2) GC abrasive grains, and (3) diamond abrasive grains are prepared as the grinding stone standard samples. Was changed to 32.5 vol%, 27.5 vol%, and 22.5 vol%, and the dielectric constant was measured, and a database showing the correlation between the dielectric constant and the porosity was constructed.

Standard Sample 1 Vitrified CBN grinding wheel a) CBN abrasive grains 50% by volume
Vitrified binder 17.5% by volume
Porosity 32.5% by volume
b) CBN abrasive grains 50% by volume
Vitrified binder 22.5% by volume
Porosity 27.5% by volume
c) CBN abrasive grains 50% by volume
Vitrified binder 27.5% by volume
Porosity 22.5% by volume
Standard sample 2 Vitrified GC grinding wheel a) GC abrasive grains 50% by volume
Vitrified binder 17.5% by volume
Porosity 32.5% by volume
b) GC abrasive grains 50% by volume
Vitrified binder 22.5% by volume
Porosity 27.5% by volume
c) GC abrasive grains 50% by volume
Vitrified binder 27.5% by volume
Porosity 22.5% by volume
Standard sample 3 Vitrified diamond wheel a) Diamond abrasive grains 50% by volume
Vitrified binder 17.5% by volume
Porosity 32.5% by volume
b) Diamond abrasive 50% by volume
Vitrified binder 22.5% by volume
Porosity 27.5% by volume
c) Diamond abrasive 50% by volume
Vitrified binder 27.5% by volume
Porosity 22.5% by volume
3-3. Manufacture procedure of whetstone standard sample It manufactured according to 1-2 item of Example 1.
3-4. Dielectric constant The dielectric constant was determined by measuring the capacitance using the apparatus described in the paragraph 1-3 of Example 1. The measurement was performed at a frequency of 1 MHz. The measurement atmosphere was the same as in Example 1.
3-5. Measurement result

As shown in Table 7, with respect to a grindstone standard sample having the same porosity, a result that the value of the dielectric constant greatly differs depending on the kind of abrasive grains was obtained. This is a result of reflecting the value of the specific dielectric constant of each abrasive grain. From this, even if it is a case where a grindstone containing two or more kinds of abrasive grains is an object of evaluation, if the kind of abrasive grains is known, the dielectric constant and porosity of the grindstone standard sample containing the corresponding abrasive grains We thought that it was possible to evaluate the porosity of the evaluation target grindstone by constructing a database showing the correlation of Of the three types of abrasive grains used in the standard grinding wheel samples, the evaluation is a grindstone in which two types of abrasive grains are mixed. Refer to the dielectric constants of the standard grinding stone samples that have different values depending on the specific dielectric constant of the abrasive grains. Thus, the porosity of the evaluation target grindstone was evaluated, and the applicability of the present invention was examined.
3-6. Evaluation object Evaluation object 1
a) CBN abrasive grains 25% by volume
GC abrasive grains 25% by volume
Vitrified binder 17.5% by volume
Porosity 32.5% by volume
b) 25% by volume of CBN abrasive grains
GC abrasive grains 25% by volume
Vitrified binder 22.5% by volume
Porosity 27.5% by volume
c) CBN abrasive grains 25% by volume
GC abrasive grains 25% by volume
Vitrified binder 27.5% by volume
Porosity 22.5% by volume
Evaluated object 2
a) Diamond abrasive 25% by volume
GC abrasive grains 25% by volume
Vitrified binder 17.5% by volume
Porosity 32.5% by volume
b) Diamond abrasive 25% by volume
GC abrasive grains 25% by volume
Vitrified binder 22.5% by volume
Porosity 27.5% by volume
c) Diamond abrasive 25% by volume
GC abrasive grains 25% by volume
Vitrified binder 27.5% by volume
Porosity 22.5% by volume
3-7. Product to be evaluated Manufactured in accordance with item 1-2 of Example 1.
3-8. Measurement of dielectric constant The dielectric constant was measured using the apparatus described in Section 1-3 of Example 1. The measurement was performed at a frequency of 1 MHz. The measurement atmosphere was the same as in Example 1.
3-9. Measurement result

3-10. FIG. 4 shows the relationship between the dielectric constants of the evaluation object 1, the grindstone standard sample 1, and the grindstone standard sample 2. The grindstone standard sample 1 contains only CBN abrasive grains, the grindstone standard sample 2 contains only GC abrasive grains, and the binder is the same. All the standard samples showed a relationship in which the dielectric constant was directly proportional to the porosity.

The object to be evaluated 1 contains CBN abrasive grains and GC abrasive grains in the same volume%, and the result of dielectric constant is a graph of a direct proportional relationship between the standard sample 1 and the standard sample 2. .
That is, from this, even if the CBN abrasive grains and the GC abrasive grains have different contents, the dielectric constant is a graph of a direct proportional relationship between the standard sample 1 and the standard sample 2 according to the amount ratio. It turns out that it becomes.

  Since the amount relation of the abrasive grains is determined by the specifications at the time of manufacturing the grindstone, if the dielectric constant of the object to be evaluated is measured in consideration of it, the theoretical value of the porosity of the object to be evaluated can be obtained from the above graph. it can. If a deviation occurs in the measured dielectric constant, the deviation can be obtained from the graph to obtain the measured porosity.

  In FIG. 5, the relationship between the to-be-evaluated object 2, the grindstone standard sample 3, and the grindstone standard sample 2 is shown. The grindstone standard sample 3 contains only diamond abrasive grains, the grindstone standard sample 2 contains only GC abrasive grains, and the binder is the same. All the standard samples showed a relationship in which the dielectric constant was directly proportional to the porosity.

In the object 2 to be evaluated, the diamond abrasive grains and the GC abrasive grains have the same volume%, and the result of the dielectric constant is a graph showing a directly proportional relationship between the standard sample 3 and the standard sample 2.
That is, from now on, even if it is a to-be-evaluated object from which the content of a diamond abrasive grain differs from GC abrasive grain, a dielectric constant may become a graph of a direct proportional relationship between the standard sample 3 and the standard sample 2 according to the amount ratio. Recognize.

  From the above, if the value of dielectric constant is measured in advance according to the type of abrasive grains and made into a database, for example, even if it is a grindstone in which two or more kinds of abrasive grains are mixed, an accurate porosity is calculated. Is possible.

  When many kinds of grinding stone products are shipped, it can be used for quality control by carrying out the evaluation method according to the present invention for those with a large shipment amount.

FIG. 1 is a conceptual diagram showing an apparatus for measuring the capacitance of an object to be evaluated. FIG. 2 is a photomicrograph showing an example of the structure of the vitrified grindstone. FIG. 3 is a diagram showing an apparatus used for measuring the capacitance. FIG. 4 is a graph showing the relationship between the dielectric constants of the evaluation object 1, the grindstone standard sample 1, and the grindstone standard sample 2. FIG. 5 is a graph showing the relationship between the dielectric constants of the evaluation object 2, the grindstone standard sample 3, and the grindstone standard sample 2.

Explanation of symbols

1: Electrode 2: Evaluation object 3: Thickness of evaluation object 4: AC power supply 5: Abrasive grain 6: Binder 7: Pore 8: Micrometer 9: Electric wire 10: Fixing jig (including electrodes)
11: Object to be evaluated

Claims (4)

A method for evaluating the porosity of a grindstone,
(1) Select the grindstone to be evaluated,
(2) Select a grindstone standard sample containing the same abrasive grains as those contained in the evaluation target grindstone,
(3) For the grindstone standard sample whose porosity is known, the capacitance is measured in an atmosphere where the humidity is higher than 25% and lower than 30%, and the dielectric constant is calculated from the capacitance,
(4) By repeating the step (3) for a plurality of grindstone standard samples having different porosities, a database showing the correlation between the porosity and the dielectric constant of the grindstone standard samples is constructed,
(5) For the evaluation target grindstone, the capacitance is measured in an atmosphere where the humidity is higher than 25% and lower than 30%, and the dielectric constant is calculated from the capacitance.
(6) The method described above, wherein the porosity of the evaluation target grindstone is evaluated by comparing the dielectric constant of the evaluation target grindstone with the dielectric constant of a standard grindstone sample in the database.   A grindstone to be evaluated includes a plurality of types of abrasive grains, and a plurality of types of grindstone standard samples are selected as a grindstone standard sample, and the plurality of types of grindstone standard samples include one or more types of abrasive grains contained in the evaluation target grindstone. The method of claim 1, comprising each.   The method according to claim 1 or 2, wherein the grinding stone to be evaluated is a porous sintered body containing continuous pores.   The method according to any one of claims 1 to 3, wherein the grindstone to be evaluated is a vitrified superabrasive grindstone.