JP2023120062A - vitrified grinding wheel - Google Patents

Abstract

To provide a vitrified grindstone having abrasive grains bonded together with a vitreous, vitrified bond free of boron, the vitrified grindstone having sufficiently high strength and less prone to degradation in grinding performance.SOLUTION: In a vitrified grindstone, a vitreous, vitrified bond 14 is free of boron, except for inevitable impurities. A boundary product BL between the vitreous, vitrified bond 14 and alumina abrasive grains 12 has a thickness T smaller than 6.5 μm. The vitrified grindstone has a three-point bending strength of more than 15 MPa to 45 MPa or less. This allows for firing at a temperature lower than or equal to 1000°C, while suppressing the growth of the boundary product BL between the vitreous, vitrified bond 14 and the alumina abrasive grains 12, leading to improved grindstone strength.SELECTED DRAWING: Figure 5

Description

TECHNICAL FIELD The present invention relates to a vitrified grindstone in which abrasive grains are bonded by a vitreous vitrified bond.

A vitrified grindstone is known in which alumina abrasive grains produced using a sol-gel method are bonded with a vitreous vitrified bond. For example, the vitrified grindstone described in Patent Document 1 is one of them.

When microcrystalline alumina abrasive grains prepared by the sol-gel method are fired at a high temperature of 1000° C. or higher, there is a concern that the abrasive grains will deteriorate and the grinding performance will decrease. Therefore, a sintering temperature of 1000° C. or less is essential when sintering the vitrified grindstone. For this reason, conventionally, the glassy vitrified bond contains a large amount of modifying components such as boron, alkali metals, alkaline earth metals, etc. to lower the melting point of the vitreous vitrified bond, and the firing temperature is 1000 ° C. or less. It enables firing of vitrified grinding wheels.

JP 2003-181764 A

By the way, the vitrified grindstone using alumina abrasive grains prepared by the sol-gel method is fired at a firing temperature of 1000° C. or less. In some cases, the strength of the grindstone was not sufficient, and the lack of strength reduced the grinding performance.

The present invention has been made against the background of the above circumstances, and its object is to provide a vitrified grindstone in which abrasive grains are bonded by vitreous vitreous bonds that do not contain boron, in which sufficient strength can be obtained, An object of the present invention is to provide a vitrified grindstone that suppresses deterioration of grinding performance.

The inventors of the present invention conducted various studies against the background of the above circumstances, and found that vitreous vitrified bonds containing modifier elements such as alkali metals, alkaline earth elements, and bismuth, but containing no boron, were found to be alumina abrasive grains. An interface product (reaction layer) was found due to the reaction with the vitrified grindstone, and it was presumed that the presence of the interface product became the starting point of fracture and caused the lack of strength of the vitrified grindstone. By adjusting the composition ratio between the glass-forming component (main component) constituting the skeleton of the vitreous vitrified bond and the modifying component, it is possible to perform firing at a firing temperature of 1000° C. or less while maintaining the vitreous content. It was found that the reaction between the vitrified bond and the abrasive grains can be suppressed, and the strength of the grindstone can be improved more than before. The present invention has been made based on such findings.

That is, the gist of the first invention is (a) a vitrified grindstone in which alumina abrasive grains prepared using a sol-gel method are bonded with a vitreous vitrified bond that does not contain boron except for unavoidable impurities. (b) the thickness of the boundary product between the alumina abrasive grain and the vitreous vitrified bond in the vitreous vitrified bond is less than 6.5 μm; The three-point bending strength is in the range of greater than 15 MPa and less than or equal to 45 MPa.

The gist of the second invention is that in the first invention, the vitreous vitrified bond is an oxide R ₂ O of an alkali metal element R, an oxide R'O of an alkaline earth metal element R', and bismuth oxide. and the glass-forming component of silica and alumina constituting the vitreous skeleton (=glass-modifying component/glass-forming component) is 0.2 or more and 0.4 in terms of molar ratio. It is composed within the range below.

The gist of the third invention is that in the second invention, the alkali metal element R is any one of Li, Na, and K, and the alkaline earth metal element R' is any one of Ca, Mg, and Ba. There is something to be said.

The gist of the fourth invention is that in any one of the first to third inventions, the thickness of the boundary product between the alumina abrasive grain and the vitreous vitrified bond is the SEM- It is the thickness of the K element high density layer in which the K (potassium) element is formed in layers on the surface of the abrasive grain in the element mapping image of the K (potassium) element in the vitreous vitrified bond by EDS.

According to the vitrified grindstone of the first invention, the vitreous vitrified bond containing no boron except for unavoidable impurities has (c) the thickness of the boundary product between the alumina abrasive grain and the vitreous vitrified bond is smaller than 6.5 μm, and (d) the three-point bending strength of the vitrified grindstone is in the range of more than 15 MPa and 45 MPa or less. As a result, it is possible to suppress the growth of boundary products between the vitreous vitrified bond and the alumina abrasive grains while enabling firing at a firing temperature of 1000° C. or lower, thereby improving the strength of the grindstone.

According to the vitrified grindstone of the second invention, the vitreous vitrified bond is an oxide R ₂ O of an alkali metal element R, an oxide R'O of an alkaline earth metal element R', and a glass of a modifying element of bismuth oxide. The molar ratio of the modifying component to the glass-forming components of silica and alumina that serve as the vitreous skeleton component (=glass-modifying component/glass-forming component) is in the range of 0.2 or more and less than 0.4. configured within. As a result, the vitreous vitrified bond is melted at a firing temperature of 1000° C. or less, and the growth of boundary products between the vitrified bond and the alumina abrasive grains is suppressed in the molten state.

According to the vitrified grindstone of the third invention, the oxide R ₂ O of the alkali metal element R is any one of Li, Na, and K, and the oxide R'O of the alkaline earth metal element R' is Since it is one of Ca, Mg, and Ba, the vitreous vitrified bond becomes a molten state at a firing temperature of 1000° C. or less, and the growth of the boundary product between the molten vitrified bond and the alumina abrasive grains is suppressed. be done.

According to the vitrified grindstone of the fourth invention, the thickness of the boundary product between the alumina abrasive grains and the vitreous vitrified bond is the thickness of the K (potassium) element in the vitreous vitrified bond by SEM-EDS. It is the thickness of the K (potassium) element high-density layer in which the K (potassium) element is formed in layers on the surface of the abrasive grain in the elemental mapping image. This has the advantage that the thickness of the boundary product can be grasped as the thickness of the K element high density layer.

It is a figure which expands and shows the structure of the vitrified grindstone of one Example of this invention. It is a figure explaining the manufacturing process of the vitrified grindstone of FIG. Regarding multiple types of test pieces of the vitrified grinding wheel conducted by the present inventors, the composition ratio of the test piece, the composition ratio (= glass modifying component / glass forming component), the three-point bending strength of the test piece, and the vitrified bond and the abrasive 4 is a chart showing the thickness of boundary products between grains. 4 is a scanning electron micrograph (SEM photograph) showing the structure of a comparative example product among the test pieces of FIG. 3. FIG. FIG. 4 is a diagram showing a copy of a scanning electron micrograph (SEM-EDS photograph) using an energy dispersive X-ray spectrometer (EDS), showing the structure of a comparative example product among the test pieces of FIG. 3;

An embodiment of the present invention will now be described in detail with reference to the drawings. In the following examples, the drawings are intended to explain the essential parts related to the invention, and the dimensions, shapes, etc. are not necessarily drawn accurately.

A vitrified grindstone 10 of one embodiment of the present invention, as shown in FIG. . The alumina abrasive grains 12 are abrasive grains obtained by mixing alumina abrasive grains prepared using a sol-gel method and fused alumina abrasive grains.

The vitrified bond 14 is composed of a total component of an oxide R ₂ O of an alkali metal element R, an oxide R′O of an alkaline earth metal element R′, and bismuth oxide, and silica and alumina serving as a vitreous skeleton component. It is The vitrified bond 14 is formulated so that the vitrified bond 14 is intentionally free of boron. Therefore, the vitrified bond 14 does not contain boron except for inevitable impurities. Unavoidable impurities are impurities that are unavoidably generated due to slight impurities contained in the raw materials used, and are 1 wt% or less, preferably 0.5 wt% or less, more preferably 0.1 wt% or less. .

FIG. 2 is a process drawing explaining the manufacturing process of the vitrified grindstone 10. As shown in FIG. In FIG. 2, in the raw material mixing step P1, the raw materials of the vitrified grindstone 10 are weighed at a preset ratio and mixed. For example, 50 parts by volume of alumina abrasive grains prepared by the sol-gel method with a predetermined particle size (for example, about #60), 20 parts by volume of the raw material of the vitrified bond 14, and 6 parts of a binder (adhesive amount) such as dextrin. A volume is weighed and provided. The raw materials of the vitrified bond 14 are an oxide R ₂ O of an alkali metal element R, an oxide R′O of an alkaline earth metal element R′, a glass modifying component of bismuth oxide, and a vitreous skeleton (main) component. The composition ratio (= glass modifying component/glass forming component) of silica and alumina, which are glass forming components, is blended so that the molar ratio is in the range of 0.2 to 0.4. The alkali metal element R contained in the vitrified bond 14 is an oxide of Li, Na or K, and the alkaline earth metal element R' is an oxide of Ca, Mg or Ba.

Next, in the mixing step P2, the raw materials prepared in the raw material preparation step P1 are stirred and mixed using a mixer. Next, in the molding step P3, the grindstone raw material mixed in the mixing step P2 is filled in the molding die and press-molded into the vitrified grindstone 10 shape. Then, the press-molded product molded in the molding step P3 is fired at a firing temperature of 1000° C. or less. This firing burns off the binder and melts the raw material of the vitrified bond 14, so that the vitrified grindstone 10 having the porous grindstone structure shown in FIG. 1, for example, is obtained.

Experimental example 1 and experimental example 2 conducted by the present inventors will be described below.

(Experimental example 1)
The inventors prepared the amount of vitrified bond 14 (glass amount), the alumina abrasive grains prepared by the sol-gel method, and the binder (paste amount) so that the amount of glass was 20% by volume with respect to the entire grindstone. and the _composition ratio ( = total component / bone component), 11 types of test pieces each prepared so that the molar ratio is within the range of 0.2 to 0.43, 5 points each using the same manufacturing process as in FIG. 3-point bending strength was measured under the following 3-point bending test conditions. In addition, the fracture surface of each test piece after the three-point bending test was observed using SEM-EDS, and the boundary product or interface product or reaction layer at the interface between the alumina abrasive grain 12 and the vitreous vitrified bond 14 ) was measured.

(3-point bending test conditions)
・Test piece: length 20 mm x width 80 mm x thickness 15 mm
・ Effective speed of the head of the three-point bending strength measuring device: 1 mm / min
・Measured value: Measured at n = 5, and the average value was taken as the 3-point bending strength.

(Conditions for measuring thickness of interfacial product)
・ Among the elemental mapping images obtained using SEM-EDS, the maximum thickness of the layer in which the K element is concentrated on the surface of the alumina abrasive grain 12 in the vitrified bond 14 in the elemental mapping image of the K element is defined as the boundary product BL was set to T.

FIG. 3 shows the glass composition ratio (mol%), the glass composition ratio (mol%), the three-point bending strength (MPa), and the thickness T (μm) of the boundary product BL for each of the 11 types of test pieces. there is In FIG. 3, comparative examples 1-2 and 4-6 among the test pieces are an oxide R ₂ O of an alkali metal element R, an oxide R'O of an alkaline earth metal element R', and a modifying element of bismuth oxide. and the glass-forming components of silica and alumina serving as the vitreous framework component (=glass-modifying component/glass-forming component) in molar ratio is 0.40 or more, and the three-point bending is The strength was 15 MPa or less, and the thickness of the boundary product was 6.5 μm or more. On the other hand, in Examples 1-5 and 7, the composition ratio (=glass-modifying component/glass-forming component) was 2.0 or more and less than 0.40 in terms of molar ratio, and the three-point bending strength was 17. .2 to 28.2 MPa, and the thickness T of the boundary product BL was 3.3 μm or not detected.

FIG. 4 shows an SEM photograph of Comparative Example Product 4, and FIG. 5 shows K (potassium) obtained using SEM-EDS (scanning electron microscope using an energy dispersive X-ray spectrometer) of the same portion. Fig. 3 shows an elemental mapping image of an element; FIG. 5 is a copy of the elemental mapping image of the K (potassium) element, because a monochrome photograph of the element mapping image would be black and the whole would be unclear. In FIG. 5, a region where the K element is concentrated in layers in the vitrified bond 14 on the surface of the alumina abrasive grain 12 was observed. This layered region is the boundary product BL.

(Experimental example 2)
Next, the inventors prepared the grinding wheels shown below, and conducted surface grinding tests under the grinding conditions shown below.
(grinding wheel)
Abrasive grains: Mixed abrasive grains of sol-gel method alumina grains and fused alumina grains Grindstone specific gravity: 2.12
Abrasive grain ratio volume (vol%): 44.1
Bond rate volume (vol%): 14.8
Vitrified bond composition: same as Example product 1 in FIG. 3 (grinding test conditions)
・Grinding method: Wet surface reciprocating grinding ・Whetstone peripheral speed: 26.7 m/s (1600 m/min)
・Table speed: 0.33m/s (20m/min)
・Total depth of cut: 4.5 mm
・Grinding oil: Water-soluble grinding oil ・Work material: SUJ-2 quenching (HRc60)

According to the grinding test of Experimental Example 2, suitable grinding performance was obtained with a grinding ratio of 113, a surface roughness of 1.24 μm, and a maximum power value of 1.75 kW.

As described above, according to the vitrified grindstone 10 of this embodiment, the vitreous vitrified bond 14 that does not contain boron except for unavoidable impurities is the boundary between the alumina abrasive grain 12 and the vitreous vitrified bond 14. The thickness T of the product BL is less than 6.5 μm, and the three-point bending strength of the vitrified grindstone 10 is in the range of over 15 MPa and 45 MPa or less. As a result, it is possible to suppress the growth of the boundary product BL between the vitreous vitrified bond 14 and the alumina abrasive grain 12 while enabling firing at a firing temperature of 1000 ° C. or less, thereby improving the grindstone strength. can.

Further, according to the vitrified grindstone 10 of the present embodiment, the vitreous vitrified bond 14 is modified with an oxide R ₂ O of an alkali metal element R, an oxide R′O of an alkaline earth metal element R′, and a modified bismuth oxide. The molar ratio of the elemental glass-modifying component to the glass-forming component of silica and alumina serving as the vitreous framework component (=glass-modifying component/glass-forming component) is 0.2 or more and 0.4. It is composed within the range below. As a result, the vitreous vitrified bond 14 is melted at a firing temperature of 1000° C. or less, and the growth of boundary products between the vitrified bond 14 and the alumina abrasive grain 12 is suppressed in the molten state.

According to the vitrified grindstone 10 of this embodiment, the alkali metal element R of the glass modifying component contained in the vitrified bond 14 is any one of Li, Na, and K, and the alkaline earth metal element R′ is Ca, Mg. , Ba, the vitreous vitrified bond becomes molten at a firing temperature of 1000° C. or less, and the growth of the boundary product BL between the molten vitrified bond 14 and the alumina abrasive grain 12 is suppressed. be done.

According to the vitrified grindstone 10 of this embodiment, the thickness of the boundary product BL between the alumina abrasive grains 12 and the vitreous vitrified bond 14 is K (potassium) in the vitreous vitrified bond 14 by SEM-EDS. It is the thickness T of the K element high-density layer in which the K (potassium) element is formed in layers on the surface of the alumina abrasive grain 12 in the elemental mapping image of the element. Accordingly, there is an advantage that the thickness T of the boundary product BL can be grasped as the thickness T of the K element high-density layer.

Although one embodiment of the present invention has been described above with reference to the drawings, the present invention is also applicable to other aspects.

For example, in the above-described examples, mixed abrasive grains of sol-gel method alumina abrasive grains and fused alumina abrasive grains were used as vitrified abrasive grains, but even if only sol-gel method alumina abrasive grains It's okay.

Further, the fused alumina abrasive grains used in the above-described examples may be abrasive grains containing alumina as a main component.

It should be noted that what has been described above is merely an embodiment of the present invention, and various modifications can be made to the present invention without departing from the gist thereof.

10: Vitrified grindstone 12: Alumina abrasive grain 14: Vitrified bond BL: Interface boundary layer T: Thickness

Claims (4)

A vitrified grindstone in which alumina abrasive grains prepared using a sol-gel method are bonded by a vitreous vitrified bond that does not contain boron except for unavoidable impurities,
a thickness of an interface product between the alumina abrasive grain and the vitreous vitrified bond in the vitreous vitrified bond is less than 6.5 μm;
The three-point bending strength of the vitrified grindstone is in the range of over 15 MPa and 45 MPa or less.
A vitrified whetstone characterized by: The vitreous vitrified bond includes an oxide R ₂ O of an alkali metal element R, an oxide R′O of an alkaline earth metal R′, a glass modifying component of bismuth oxide, and silica and 1. A composition ratio of alumina to a glass-forming component (=glass-modifying component/glass-forming component) is within a range of 0.2 or more and less than 0.4 in terms of molar ratio. vitrified grinding wheel. The vitrified grindstone according to claim 2, wherein the alkali metal element R is Li, Na or K, and the alkaline earth metal R' is Ca, Mg or Ba. The thickness of the boundary product between the alumina abrasive grain and the vitreous vitrified bond is the thickness of the alumina abrasive grain in the element mapping image of the K (potassium) element in the vitreous vitrified bond by SEM-EDS. 4. The vitrified grindstone according to any one of claims 1 to 3, wherein the vitrified grindstone has a thickness of a K element high-density layer in which the K (potassium) element is formed in layers on the surface.

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