JP2015112685A - Low melting and low shrinkable vitrified grindstone - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a low melting and low shrinkable vitrified grindstone which prepares a low melting vitrified bond rich in melting fluidity at a low temperature, satisfactorily secures abrasive grain retention property with a proper grind stone binding force, has little grind stone abrasion amount, has little shrinkage amount after calcination and has high machinability of a large finish ratio.SOLUTION: A low melting and low shrinkable vitrified grindstone is prepared by using vitrified bond which contains borosilicate glass by 91 to 97 mol% of the whole vitrified grindstone, and contains zinc carbonate molten and thermally decomposed to produce gas by calcination at 800°C or less as reaction sintering agent and metal fluoride such as lithium fluoride as melting agent. The reaction sintering agent is molten and is foamed by low temperature calcination and can uniformly disperse fine air bubbles, the melting agent made of metal fluoride improves melting fluidity, therefore a melting component is efficiently actuated and abrasive grains efficiently adhere even when being calcined at a low temperature of 800°C or less and, as the result, the low melting vitrified grindstone is turned to have low shrinkability.

Description

  The present invention relates to a low-melting / low-shrinking vitrified grinding stone having a reduced amount of thermal shrinkage during firing for a grinding stone using a low-melting vitrified bond that can be melted at a relatively low temperature.

  In general, for ultra-finishing of precision machine parts, vitrified grinding stones that hold abrasive grains using vitrified bonds as inorganic binders are applied, and these vitrified grinding stones are bonded with synthetic resin binders. Compared to the elastic grindstone, the shape is not deformed during use, and work grinding such as finishing of the corner portion can be performed with high accuracy.

  In order to securely hold the abrasive grains, it is necessary for such a vitrified grindstone to make the vitrified bond once a liquid phase and then cool it to a solid phase in the firing step. Usually, a siliceous raw material is used as a main raw material. The vitrified bond used is fired at a high temperature of 900 ° C. to 1200 ° C. or higher.

  Vitrified bond is finally cured as silicate glass and retains abrasive grains. For example, when performing high-temperature firing at 1200 ° C. or higher, such a high-melting siliceous bond, A small amount of flux may be added in order to promote molten vitrification as efficiently as possible.

  When added to the main raw material to be fired, the flux promotes the formation of a liquid phase by a chemical reaction or the like. For example, in a low-melting vitrified bond that can be baked at 750 ° C. or lower using composite abrasive grains of super (hard) abrasive grains and soft abrasive grains, the dissolution and diffusion of the bond proceeds as a flux that melts at a low temperature. Therefore, chloride (zinc chloride) is used (Patent Document 1).

  Further, it is known that a high-melting silicate glass phase is blended with a low-melting sodium borate glass phase together with a flux such as metal fluoride (Patent Document 2).

  In addition, in a CBN grinding wheel which is apparently non-porous (bond matrix type) and has discontinuous pores, the vitrified binder contains fine independent pores to facilitate dressing and improve the abrasive support force. Therefore, it is known to use hBN (hexagonal boron nitride), fluorite (CaF2) or calcium carbonate (CaCO3) as a foaming agent (Patent Document 3).

JP 2006-130635 A JP 2009-248207 A JP 2012-66365 A

By the way, a composite abrasive using soft abrasive grains such as cerium oxide (CeO ₂ ) and barium sulfate (BaSO 4) as described in Patent Document 1 described above and super (hard) abrasive grains (CBN, SD) in combination. In a vitrified bond grindstone using grains, soft abrasive grains containing many rare earth metal oxides as impurities are chemically and thermally unstable, and therefore usually withstand firing temperatures of 900 ° C. or higher. I can't.

Therefore, it is necessary to set the firing temperature to 800 ° C. or less so that such soft abrasive grains are not affected by thermal and chemical effects during firing. Borosilicate system (SiO2) with a large amount of melting components such as boric acid (B2O3), alkali metal oxide (R2O), alkaline earth metal oxide (RO), etc. so as to increase the power _{2 -B 2 O 3 -R 2 O} -RO) glass is used.

  In addition, low-melting vitrified bonds that have increased fluidity during low-temperature firing by increasing the amount of components such as borosilicate are large in thermal expansion and thermal shrinkage. It is not easy to produce a low-melting vitrified grindstone with low shrinkage and stable quality. This causes a problem with respect to the stability of the structure in the grindstone or between the grindstones, homogeneous quality, and quality without microcracks.

In addition, the CBN grinding wheel described in Patent Document 3 holds a superabrasive grain called CBN (cubic boron nitride) abrasive grain with a low-shrinkage silicate-based bond that can be fired at a high temperature of 900 ° C. or higher. Since it does not contain components that are susceptible to thermal and chemical effects during firing, such as soft abrasive grains, it is not necessary to fire at low temperatures, and the calcium carbonate described in this document increases melt fluidity at low temperatures. There is no effect.
On the other hand, it is not easy to reliably obtain a vitrified grindstone with sufficient bonding between the low-melting vitrified bond and the abrasive grains and having a small shrinkage after firing.

  Therefore, an object of the present invention is to solve the above-described problems in the prior art and to obtain a low-melting vitrified bond rich in melt fluidity at a low temperature, thereby sufficiently securing abrasive grain retention with an appropriate grindstone bonding force. Moreover, the grinding wheel wear amount is small and the shrinkage amount after firing is small, that is, the finish ratio is high and the machinability is low-melting and low-shrinking vitrified grindstone.

  In order to solve the above-mentioned problems, in the present invention, a vitrified containing a reactive sintering agent comprising a carbonate which is melted by firing at a temperature of less than 800 ° C. and pyrolyzed to produce a gas, and a flux comprising a metal fluoride. This is a low-melting and low-shrinking vitrified grinding wheel formed by bonding abrasive grains with a bond.

  The low-melting and low-shrinking vitrified grinding wheel of the present invention configured as described above has a reactive sintering agent made of carbonate among the vitrified bond components of 800 ° C. or less, particularly at a relatively low temperature stage of the firing process. A solid reaction occurs in which it becomes a fine solid (glass) component and melts and diffuses. At that time, the amount of the liquid phase increases, and the microbubbles of the gas generated from the reaction sintering agent are evenly dispersed in the vitrified bond to further increase the amount of the liquid phase.

In addition, a flux made of a metal fluoride such as lithium fluoride (LiF) has a melting point higher than that of carbonate or hydrogencarbonate, and within a predetermined firing temperature range of 800 ° C. or lower, a relatively high temperature in the firing step. In the state, it becomes a medium solvent (mineralizer) and improves fluidity. That is, the metal fluoride increases the liquid phase amount of the vitrified bond component at a relatively high temperature stage within a predetermined firing temperature range of 800 ° C. or lower, which is raised from room temperature, and increases the fluidity to increase the fluidity or liquid. Acts as a phase generator.
At this time, the pores and pores formed at the initial stage of firing disappear, so that the bond is densified and the fluidity is enhanced, the adhesive strength with the abrasive grains is increased, and the strength of the grindstone is increased.

  Since metal fluorides such as lithium fluoride can replace part of the oxygen bond related to the three-dimensional network structure of silicon atoms in the glass component usually contained in the vitrified bond with a fluorine bond, The liquidity is expected to increase.

  Specific examples of the reaction sintering agent described above include carbonates or bicarbonates such as zinc carbonate (ZnCO3: melting temperature of about 300 ° C.), magnesium carbonate (MgCO3: melting temperature of 350 ° C.), or a mixture of both of them. Can be mentioned.

Such carbonate is liquefied at a relatively low firing temperature, for example, about 300 to 600 ° C. during firing, and is thermally decomposed to generate a gas such as carbon dioxide (CO ₂ ). Such a low-melting carbonate is thermally decomposed during firing, and therefore does not function as a soft abrasive grain after firing.

  In particular, as a composition of vitrified bond, borosilicate glass is contained in 91 to 97 mol% of the entire vitrified, zinc carbonate is contained in 1 to 4 mol% as a reactive sintering agent, and lithium fluoride is contained in 2 to 5 mol% as a flux. In addition, preferable results are obtained by using a low-melting / low-shrinking vitrified grindstone that employs a low-shrinking vitrified bond with a softening temperature of 770 ° C. or lower.

  This invention is a low-bonding abrasive grain bonded by vitrified bond containing a predetermined reactive sintering agent that is melted by firing at a low temperature below a predetermined temperature and is thermally decomposed to generate a gas and a flux composed of a metal fluoride. Because it is a low melting shrinkable vitrified grinding stone, the reactive sintering agent melts by low-temperature firing and foams to uniformly disperse fine bubbles, and the flux made of metal fluoride improves the melt fluidity and is dense. There is an advantage in that the abrasive grains are efficiently bonded by the reduced-melting vitrified bond to form a low-melting / low-shrinking vitrified grindstone having a low shrinkage rate.

  In addition, because of the relatively dense vitrified bond used to bond the abrasive grains, the retention of the abrasive grains is sufficiently secured, resulting in a high-cutting grindstone with low grinding wheel wear and high efficiency and a high finish ratio. There is an advantage that a low-melting and low-shrinking vitrified grindstone can be obtained by using a composite abrasive grain to obtain a highly accurate finished surface.

Explanatory drawing which shows the result of the melt test of the vitrified bond used for the Example Explanatory drawing which shows the result of the melt test of the vitrified bond used for the comparative example Explanatory drawing of melting test of JISR2204

  The low-melting / low-shrinking vitrified grinding wheel according to the embodiment of the present invention includes a reactive sintering agent made of carbonate and a flux made of metal fluoride that are melted by firing below 800 ° C. and thermally decomposed to generate gas. This is a low-melting / low-shrinking vitrified grindstone formed by bonding abrasive grains with vitrified bonds.

The abrasive grains and vitrified bond used in the low-melting / low-shrinking vitrified grindstone of the embodiment contain the following components (1) and (2).
(1) Abrasive Grain This invention is intended for a grindstone using a low-melting vitrified that can be fired even at a low temperature of 800 ° C. or lower so that soft abrasive grains and the like are not chemically modified by firing, and cerium oxide (CeO 2 melting point). 1950 ° C.), barium sulfate (BaSO 4 melting point 1345 ° C.), calcium carbonate (CaCO ₃ melting point 825 ° C.) and sodium carbonate (NaCO ₃ melting point 851 ° C.) can be blended.

Such soft abrasive grains have no cutting action, reduce the damage of bond erosion caused by chips generated from hard abrasive grains CBN, SD, and improve the grinding wheel finishing performance. It has the characteristic that it is hard to be crushed.
Furthermore, you may mix | blend the composite abrasive grain which mix | blended the hard abrasive grain or the cemented carbide grain as needed.
Examples of superabrasive grains include cubic boron nitride (CBN) and artificial diamond (SD). Examples of general hard abrasive grains include aluminum oxide (alumina) -based abrasive grains and silicon carbide-based abrasive grains.

(2) Vitrified bond The vitrified bond used in the present invention may be any component that can be fired at 800 ° C. or lower in a state where a predetermined flux composed of a metal fluoride is blended, and it is used even if it is not a particularly limited glass component. it can.

As a preferable component in terms of a large amount of molten component, it is preferable to use a vitrified bond containing borosilicate glass as a main component, for example, 90 mol% or more, more preferably 91 to 97 mol%.
Further, as a melting component, required amounts of boric acid (B ₂ O ₃ ), alkali metal oxide (R ₂ O), and alkaline earth metal oxide (RO) are added as necessary.
Examples of the alkali metal oxide (R ₂ O) include K ₂ O and Na ₂ O, and examples of the alkaline earth metal oxide (RO) include MgO, CaO, SrO and BaO. It is done.

  The reactive sintering agent used in the present invention contains, as an essential component, a carbonate that melts and diffuses by firing at 800 ° C. or lower and is thermally decomposed to generate carbon dioxide (carbon dioxide gas).

The carbonates, as a melting point of 800 ° C. or less, zinc carbonate (ZnCo ₃ melting point of about 300 ° C.), magnesium carbonate (MgCO ₃ mp 350 ° C.), and the like lithium carbonate _(Li 2 CO ₃ mp 618 ° C.) .

The hydrogen carbonate has the same properties as the above carbonate, and is liquefied at a low firing temperature and thermally decomposed to release carbon dioxide (CO ₂ ) and water to become a carbonate. So it can be used together with carbonate.

Examples of the hydrogen carbonate include sodium hydrogen carbonate (NaHCO ₃ melting point 270 ° C.), potassium hydrogen carbonate (KHCO ₃ melting point 292 ° C.), ammonium hydrogen carbonate (NH ₄ HCO ₃ melting point 106 ° C.), and the like.

Moreover, as for the mixture ratio in the case of using carbonate (ZnCO ₃ ) and bicarbonate (NaHCO ₃ ) together, it is desirable to use NaHCO ₃ corresponding to 10 to 30% of the amount of ZnCO ₃ . This is because when NaHCO ₃ is less than 10%, the amount of generated bubbles and the dispersing action are small, and the effect of expanding the liquid phase region due to the liquid phase of the low melting component is small. Moreover, when NaHCO ₃ is mixed in a large amount exceeding 30%, active large and small bubbles are generated, and uniform dispersion of microbubbles is not realized. In this case, a uniform melt fluidity of the bond matrix cannot be obtained, and the firing shrinkage difference in the grindstone causes defects such as uneven hardness and cracks.
Incidentally, the large pores generated at 300 to 600 ° C. in the early stage of firing do not disappear at 700 to 800 ° C. in the later stage of firing, and the bond matrix does not become dense, so the grinding stone firing shrinkage after cooling increases.

In addition, hydrates and hydroxides of metal oxides such as hydrous magnesium hydroxide (talc) are also melted by firing at 800 ° C. or less and thermally decomposed to generate gas components (H ₂ O water vapor). As such, it can be added together with the carbonates of this invention.

  The flux composed of a metal fluoride used in the present invention does not melt on the low temperature side before firing at a relatively high temperature among firing temperatures of 800 ° C. or lower, that is, lower than the melting point of the above-mentioned reactive sintering agent. On the low temperature side, the other components in the bond are melted by solid reaction, and the liquid phase is increased to densify the bond.

  Examples of the metal fluoride include lithium fluoride (melting point 848 ° C.), potassium fluoride (melting point 860 ° C.), sodium fluoride (melting point 993 ° C.), calcium fluoride (melting point 1402 ° C.), and the like. As is clear from the examples described later, particularly preferable results were obtained using lithium fluoride.

  By the way, increasing the liquid phase amount of the bond that melts during firing using borosilicate glass increases the bond strength between the abrasive grains and the bond, but on the other hand, the shrinkage amount of the grinding stone firing increases, which is inappropriate. It becomes a grindstone with a hard bond.

  However, in the present invention, the liquid phase having fine pores is increased by the reactive sintering agent to the initial stage of firing at a relatively low temperature of, for example, 300 to 600 ° C., and then fired at a relatively high temperature of, for example, 700 to 800 ° C. By using metal fluoride as a flux in the later stage, the liquid phase having no pores can be increased to eliminate the pores and pores in the initial stage, and the bond can be densified to suppress the volume shrinkage after firing.

In this invention, the carbonate such as ZnCO ₃ is sufficiently effective to increase the amount of liquid phase by adding 1 to 4 mol%, preferably 1.5 to 4 mol% as the compounding ratio of the bond component. This is preferable. Moreover, it is preferable to mix | blend 2-5 mol% of metal fluorides, such as LiF, in order to fully exhibit the effect | action of increasing a liquid phase amount and improving fluidity | liquidity.

  When the amount of carbonate and metal fluoride is less than the above predetermined range, the amount of the molten liquid phase of vitrified bond decreases, and the adhesiveness with the abrasive grains decreases, which is not preferable. Moreover, when a large amount exceeding the predetermined range is blended, the shrinkage rate is increased, which is not preferable.

  Although the abrasive grain used for this invention is not specifically limited, The soft abrasive grain which needs to be baked at low temperature can be included. For example, soft abrasive grains that have a chemical cutting action due to embrittlement due to chemical reactions such as oxidation on steel and other work materials, and that do not have physical machinability, and general hard abrasive grains or carbide Composite abrasive grains mixed with abrasive grains can be employed.

  Thus, in this invention, it is possible to employ composite abrasive grains containing soft abrasive grains as abrasive grains. For example, soft abrasive grains composed of cerium oxide, barium sulfate or zirconium oxide, and alumina or silicon carbide. It is preferable to employ composite abrasive grains made of hard abrasive grains or cubic boron nitride abrasive grains or superhard abrasive grains made of diamond.

The firing temperature of the low-melting / low-shrinking vitrified grinding wheel in the present invention is determined by considering the use of composite abrasive grains of soft abrasive grains and super (hard) abrasive grains. The maximum firing temperature that does not deteriorate is set to 800 ° C. or lower. In the case of using abrasive grains containing 20% or more of soft abrasive grains such as CeO ₂ , the more preferable maximum firing temperature is 650 ° C. to 780 ° C., more preferably 720 ° C. to 770 ° C. .

The composition A shown in Table 1 below is a preferred blending composition (%) of a vitrified bond containing ZnCO 3 and LiF used in the present invention (hereinafter, the vitrified bond is simply abbreviated as a bond), and this average composition B The compound composition of this bond was used in each example described later.
Similarly, composition C in Table 2 shows a range that may vary as a comparative example, and the blend composition of this average value composition D was used in each example described later.

The total of boric acid (B ₂ O ₃ ), alkali metal (R ₂ O), and alkaline earth metal (RO), which are flux components, is slightly larger in C in Table 2 than in A in Table 1. However, it is almost the same value. Further, in the comparative example, titanium oxide (TiO2) was added at 2.5 to 6 mol% in terms of bond compounding ratio for improving strength or thermal stability by low-temperature firing at less than 800 ° C.

  Here, in order to investigate the melting state in the firing step of the bonds used in the examples and comparative examples, the melting characteristics of the bonds were examined as follows, and the results are shown in FIGS.

[Melting properties of bond]
(A) Bond wettability A cylindrical molded bond test body 1 or 2 having a constant density of 10 mm in diameter and 10 mm in height with the bond composition of Example (composition B) and Comparative Example (composition C). This was prepared and melted by holding it at a firing temperature of 770 ° C. for 4 hours with respect to the examples, and by melting at a firing temperature of 750 ° C. for 3 hours for the comparative example. FIG. 1 schematically illustrates the observation result of the molten state of the example, and FIG. 2 schematically illustrates the observation result of the molten state of the comparative example.

  As is clear from the results shown in FIGS. 1 and 2, the evaluation test bond molded body 1 (composition B) in the example of FIG. 1 expands in the horizontal direction and is in a completely expanded wet state 1 ′. On the other hand, it can be seen that the evaluation molded bond molded body 2 (composition D) of the comparative example of FIG. 2 is in an incomplete adhesion wet state 2 ′. That is, it can be seen that the bond molded body for evaluation test 1 of the example is easy to bond to the abrasive grain surface and has a large amount of adhesion. Reference numerals 3 and 4 in FIGS. 1 and 2 are ceramic cradles provided separately.

(B) Melting temperature As shown in FIG. 3, in order to investigate the melting temperature of the bond, a test cone 5 made of a triangular pyramid shaped body was prepared using the bond of Example or Comparative Example according to JISR2204, and separately. In the state of being fixed upright on the ceramic cradle 6 provided and heated at a temperature rising rate of 125 ° C./hour, the tip of the test cone 5 is in contact with the cradle 5 ′ (see FIG. 3) The temperature was measured.
The measured melting temperature was 652 ° C. for the bond having the composition used in the example (Table 1B) and 655 ° C. for the bond having the composition used in the comparative example (Table 2D).

[Production of grinding wheels of Examples 1 to 6 and Comparative Examples 1 to 6]
The vitrified grindstone of the example and the comparative example was manufactured by the following steps.
First, the abrasive grains used were composite abrasive grains of approximately 80% CBN (hard) abrasive grains and approximately 20% CeO ₂ soft abrasive grains in the volume ratio shown in Table 3. In super (hard) abrasive grains CBN, Examples 1 to 3 and Comparative Examples 1 to 3 have an abrasive particle diameter of 4 to 8 μm (2500 mesh), and Examples 4 to 6 and Comparative Examples 4 to 6 are 2 to 2. A particle size of 4 μm (4000 mesh) was used. The soft abrasive grain CeO ₂ has a primary particle diameter of 0.5 μm.

  The binder used in the examples has the composition of B in Table 1, and the comparative example has the composition of D in Table 2. Moreover, the binder ratio with respect to 1.0 part by weight of unit abrasive grains was 0.4 parts by weight in Examples 1 and 4 and Comparative Examples 1 and 4, and 0.5 parts by weight in Examples 2 and 5 and Comparative Examples 2 and 5. Parts, Examples 3 and 6 and Comparative Examples 3 and 6 were 0.6 parts by weight, and the content of the grinding stone with a large amount of binder, for example, 1.0 part by weight of unit abrasive grains, the binder ratio was 0.4. ˜0.6 parts by weight.

  In this way, ultra-hard (hard) abrasive grains, soft abrasive grains, and vitrified bonds are blended, and the reactive sintering agents (zinc carbonate, lithium fluoride, titanium oxide) shown in Tables 1 and 2 are added to form a slurry. Were mixed by wet mixing. After completion of mixing, the mixture was adjusted to powder by giving an appropriate humidity.

  Subsequently, it was compression molded into the dimensions and shape of a predetermined sample grindstone, dried and fired. The firing temperature was kept at a maximum firing temperature of 770 ° C. for 4 hours in Examples 1 to 6, and kept at a maximum firing temperature of 720 ° C. for 3 hours in Comparative Examples 1 to 6.

The hardness and grindstone structure (volume ratio, concentration) of the obtained grindstone are also shown in Table 3. Incidentally, the concentration is the mass of the CBN abrasive grains contained in the unit volume of the abrasive grain layer, and the concentration 100 is the case where 880 mg (4.4 ct) is contained in 1 cm ³ .

  The grindstone hardness shown in Table 3 was measured using a Rockwell superficial hardness tester with a steel ball indenter of 3.175 mm, a standard load of 29.4 N, and a test load of 196 N.

  Next, for the grindstones of Examples 1 to 6 and Comparative Examples 1 to 6 prepared as described above, whether or not the expected low shrinkage effect is obtained by the following evaluation method for the shrinkage rate. The results are shown in Table 4.

[Shrinkage factor(%)]
(A) Sample for measuring shrinkage rate After quantifying the mixed powder adjusted for humidity with a square die, CIP (cold isotropic compression) molding is performed at a constant pressure to produce a square sample (30 × 60 mm), Baking after drying.

(B) Linear shrinkage rate α (%)
The linear shrinkage rate α (%) in Table 4 was determined by the following equation when the length L before firing the grindstone and the length L ′ after firing were calculated.
α (%) = (L−L ′) / L × 100

  As is apparent from the results in Table 4, Examples 1 to 3 using abrasive grains having a particle size of 2500 mesh have a linear shrinkage rate (%) of the grinding stone firing of about 10% smaller than Comparative Examples 1 to 3. In Examples 4 to 6 using abrasive grains having a particle size of 4000 mesh, the linear shrinkage rate (%) in the grinding stone firing was as small as about 15% compared to Comparative Examples 4 to 6.

  Further, in comparison with the melted state of the vitrified bond described above, Comparative Examples 1 to 6 are in an adhesion wet state (see FIG. 2), whereas in Examples 1 to 6, the extended wettability usually occurs when there are many melt components. Despite the state (see FIG. 1), the shrinkage rate (%) of the vitrified grindstone was small.

  That is, since the chemical composition of the bond is obtained by increasing the amount of the glass liquid phase in substantially the same manner as in Examples 1 to 6 and Comparative Examples 1 to 6, it is naturally expected that the grinding stone firing shrinkage amount is large. However, as shown in Table 4, Examples 1 to 6 had a low shrinkage rate.

  Next, in order to evaluate the high machinability of the grindstones of Examples and Comparative Examples, the following actual cutting tests were performed, and the results are shown in Table 5.

[Practical cutting test]
In the actual cutting test, superfinishing was performed with the ball bearing as a workpiece and the race surface of the inner ring as the work surface. The surface to be machined is also superfinished as a pre-processing, using a WA 1200 mesh (particle diameter: 9.5 μm · JIS R6001) vitrified bond grindstone, with a surface roughness of 0.18 to 0.20 μmRa (centerline average roughness). Processed).

The test grindstone was cut out from the raw stone into a square shape with a width of 5.5 mm and a thickness of 5.0 mm in the circumferential direction of the workpiece. After finishing, the grindstone pores were carefully treated with an organic treatment agent.
The surface speed of the grindstone with respect to the workpiece was 5 m / s for both roughing and finishing, the number of grindstone oscillations, rough 13.3 Hz, finishing 2.0 Hz, roughening processing time 8 s, and finishing 2 s. The processed oil was a sulfurized fat-based water-insoluble oil. The cutting amount, the grinding wheel wear amount, and the finished surface roughness were actually cut with a constant grinding wheel surface pressure of 1.0 MPa.

As is clear from the results of the actual cutting test shown in Table 5, the following excellent grinding wheel finishing performance was recognized for Examples 1 to 6 with respect to Comparative Examples 1 to 6.
(1) Cutting amount: The example had a high cutting amount of about 20% or more at 2000 mesh and about 10% at 4000 mesh compared to the comparative example.
(2) Grinding wheel wear amount: About 20% or more for the abrasive grains 2500 mesh of Examples 1 to 3 and Comparative Examples 1 to 3, and about 10 for the abrasive grains 4000 mesh of Examples 4 to 6 and Comparative Examples 4 to 6 A reduction effect of the grinding wheel wear amount of less than 1% was observed.
(3) Finish ratio: In the 2500 mesh abrasive grains of Examples 1 to 3 and Comparative Examples 1 to 3, an increase in the finish ratio of about 50% or more was recognized, and the abrasives of Examples 4 to 6 and Comparative Examples 4 to 6 With a grain of 4000 mesh, an increase in the finishing ratio of about 20% was recognized, and it was recognized that the economy was improved.

(4) Finished surface roughness: about 10% or more at 2000 mesh and less than about 5% at 4000 mesh, but an improvement effect was recognized.
5) Grinding wheel working surface: Since the abrasive grains are composite abrasive grains of soft abrasive grains and super (hard) abrasive grains, all of the grinding wheel working surfaces are particularly severely clogged, chipped (metal welded), or chipped. No damage was found.
(6) Stable grinding wheel quality and finishing performance: Bonded with zinc carbonate, bond liquid phase and gas generation by pyrolysis reaction sintering at low temperature side, and lithium fluoride ore on high temperature side Since there was an increase in the amount of the liquid phase due to the crystallization action, it was confirmed that it had a stable high machinability and a high finish ratio.

In addition, if the grindstone using the vitrified bond having an increased liquid phase amount as in the example causes microcracks during shrinkage, this becomes a factor of low shrinkage (low expansion) of the grindstone. There is a possibility.
However, the amount of grinding wheel wear was confirmed by the actual cutting test by vibration pressurization of the grinding wheel in super finishing, and the stability of the finishing characteristics was ensured, so that the grinding wheel strength and stability were excellent. You can see that Although detailed explanation is omitted, it is clear from the result of observing a SEM (scanning electron microscope) image (10,000 times) and conducting a three-point bending test that microcracks are not generated. It was.

1, 2 Bond molded body for evaluation test 3, 4, 6 6 Receiving base 5 Test cone

Claims (6)

  Low melting and low bonding by combining abrasive grains with a vitrified bond containing a reactive sintering agent consisting of carbonate that melts and pyrolyzes to produce gas when fired at 800 ° C or less and a flux consisting of metal fluoride Shrinkable vitrified grinding wheel.   The low-melting / low-shrinking vitrified grinding wheel according to claim 1, wherein the carbonate is zinc carbonate or magnesium carbonate or a carbonate using both.   The low melting and low shrinkage vitrified grindstone according to claim 1 or 2, wherein the metal fluoride is lithium fluoride.   The low-melting / low-shrinking vitrified grindstone according to any one of claims 1 to 3, wherein the abrasive grains are composite abrasive grains composed of soft abrasive grains and hard abrasive grains or superhard abrasive grains.   The composite abrasive grains are composed of soft abrasive grains made of cerium oxide, barium sulfate or zirconium oxide, and hard abrasive grains made of alumina or silicon carbide, cubic boron nitride abrasive grains or cemented carbide grains made of diamond. The low-melting / low-shrinking vitrified grindstone according to claim 4, which is an abrasive.   The vitrified bond contains 91 to 97 mol% of the borosilicate glass of the entire vitrified, 1 to 4 mol% of zinc carbonate as a reactive sintering agent, and 2 to 5 mol% of lithium fluoride as a flux, The low-melting / low-shrinking vitrified grinding wheel according to any one of claims 1 to 5, which is a vitrified bond having a softening temperature of 770 ° C or lower.

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