JPH0624700B2 - Vitrified grindstone - Google Patents

Description

TECHNICAL FIELD The present invention relates to a vitrified grindstone in which abrasives are bonded by vitrified bonds, and particularly to a vitrified grindstone using superabrasive grains as an abrasive.

[Prior Art and Problems] Some vitrified grindstones contain an organic pore-forming agent to form pores. However, this type of vitrified grindstone has problems that the pore-forming agent is removed during firing, the holding force of the abrasive is reduced, and the shrinkage of the grindstone is large.

Therefore, there is a vitrified whetstone that uses perlite made of natural glassy rock as a pore-forming agent and has the function of a binder as a binder to enhance the holding force of the abrasive material. Kosho 37-746
issue). However, in this vitrified grindstone, since pearlite softens and melts during firing, the binding function is fulfilled, so that the grindstone is inevitably shrunk and the desired shape cannot be maintained. In addition, it was difficult to control the grindstone structure (porosity, abrasive material ratio, etc.), which was a problem in product management.

Further, in these conventional vitrified grindstones (those using organic or pearlite as a pore-forming agent), it is inevitable that the grinding shrinkage of the grindstone due to burnout or softening and melting is unavoidable. It was impossible to obtain a grindstone with porosity.

By the way, a vitrified grindstone (particularly, one having a high porosity) has an advantage that dressing is easy. However, the superabrasive grains (diamonds or CBs) that are often used as abrasives in these vitrified grindstones.
In the case of applying N), from the viewpoint of economical mass productivity, the concentration is reduced by mixing an inorganic filler (for example, an alumina-based component, a silicon carbide-based component). However, in this case, depending on the grinding conditions, the filler wears out and wears, which hinders the grinding, so that sharpening is frequently required and the above advantages of vitrified cannot be fully utilized.

In view of the above technical background, an object of the present invention is to provide a vitrified grindstone that maintains pores of an arbitrary porosity without lowering the holding force of the abrasive, has very little dimensional shrinkage during firing, and simplifies dressing. To do.

[Means for Solving Problems] The inventors of the present invention have conducted various studies on a vitrified grindstone to change the porosity by adopting superabrasive grains as an abrasive, and as a result, the vitrified grindstone contains a specific substance. However, the result is extremely excellent as a vitrified grindstone, so it is proposed here.

In the vitrified grindstone of the present invention, the abrasive material is superabrasive grains,
It contains an inorganic hollow substance that is easily destroyed by the frictional force with the work material, and the softening point of the hollow substance is higher than the intrinsic firing temperature of the vitrified bond for superabrasive grains,
It is characterized in that it has pores other than those caused by the hollow substance at least in the binder phase, and has a porosity of at least 30% or more.

Here, the pores in the binder phase refer to pores in which the boundary wall forming the pores is composed only of the binder. The pores other than those caused by the hollow substance do not exclude the voids generated between the abrasive grains, the hollow substance, and the binder.

[Preferred Embodiment] The inorganic hollow substance contained in the vitrified grindstone of the present invention has a softening point of 50 ° C. or more, more preferably 100 ° C. or higher than the intrinsic firing temperature of the vitrified bond for superabrasive grains.
It is preferable that the temperature is higher than ℃. This is to prevent the deformation of the grindstone due to the softening or abnormal expansion of the inorganic hollow material during firing. Here, the intrinsic firing temperature of the vitrified bond for superabrasive grains is lower than the intrinsic firing temperature of the vitrified bond when general abrasive grains are used as an abrasive, and is generally 650 to 1000 ° C.
More preferably, the firing temperature is in the range of 700 to 950 ° C. If it exceeds the upper limit, superabrasive grains will deteriorate, and if it is less than the lower limit, strength development will be impaired. More specifically, it is adopted according to the type of vitrified used.

Examples of the inorganic hollow substance are as follows (the temperature in the parentheses is the softening point):-Glass balloon (1000 ° C) -Shirasu balloon (900 ° C) -Carbon balloon (900 ° C)- Alumina balloon (1500 ° C) -Coal ash balloon (1300 ° C) The diameter and wall thickness of the inorganic hollow material must be such that they are not easily broken during grinding and hinder the self-generated effect. In terms of Vickers average hardness Hv, Hv30
It is preferably about 0 to 1000.

The coefficient of thermal expansion of an inorganic hollow material is that of a vitrified bond (for example, 4 to 6 × 10 ⁻⁶ /
C.) is preferably about the same. A coal ash balloon is suitable because its thermal expansion coefficient is close to that of superabrasive grains and vitrified bonds.

The grain size of the superabrasive grains used in the present invention is from 60 mesh (average particle size 220 μm) to 800 mesh (average particle size 20 μm)
Those in the range are preferred.

From the viewpoint of suppressing firing shrinkage as much as possible, it is preferable that the particle size of the inorganic hollow material is about 1/2 to 2 times the average particle size of the superabrasive particles, and more preferably substantially the same.

By the way, in the grinding stone,
Abrasive holding power is reduced. Therefore, there is a natural limit to the proportion of hollow spheres that can be blended to obtain a grindstone with high porosity.

Also, in order to increase the transverse rupture strength, it is necessary to sinter by applying sufficient pressure to bond the particles in close contact.
Therefore, in order to obtain a grindstone having a certain degree of hardness, the ratio occupied by the particle gaps is naturally limited.

However, since the vitrified grindstone of the present invention requires pores in the binder phase in addition to pores caused by the hollow spheres and particle gaps, it is possible to obtain a grindstone having both high porosity and durability. It became possible.

In the vitrified grindstone of the present invention, the porosity of the grindstone itself, which is not due to the inorganic hollow substance, is preferably at least 2
0%, more preferably 20-35%. The inorganic hollow substance is contained in the raw material composition in an amount of at least 10% (volume%, the same applies hereinafter), and may be contained up to 45 to 55%.

Therefore, the porosity of the whole grindstone can be adjusted according to the application by adjusting the addition amount of the hollow substance, and it is possible to obtain a grindstone having a porosity of at least greater than 30% and up to about 70%. Particularly preferred porosity is 45-55%
Is. If the porosity of the whole grindstone is 30% or less, sharpening is considerably required and the grinding performance is insufficient.

The vitrified grindstone of the present invention is suitable for grinding highly precise parts. In addition to general ferrous materials (cast iron, steel, etc.), non-ferrous materials such as aluminum, plastics, etc., new materials that are difficult to machine, such as ceramics and FRM, are also targeted as work materials.

For reference, a schematic diagram of the grindstone of the present invention is shown in FIG. In the figure, 1 is a superabrasive grain, 2 is a vitrified bond, 3 is a pore other than that caused by an inorganic hollow substance, and 4 is an inorganic hollow substance.

[Advantages of the Invention] The vitrified grindstone of the present invention has the following various effects because it has the above-described configuration.

Since inorganic hollow substances also function as pore-forming agents,
The porosity can be easily adjusted by adjusting the content.

Since the inorganic hollow substance remains in the grindstone without being removed even after firing, the decrease in the holding force of the abrasive and thus the strength of the grindstone is extremely small.

Since the inorganic hollow substance has a softening point higher than the intrinsic firing temperature of the vitrified bond for superabrasive grains, it does not soften during firing, and therefore firing shrinkage can be suppressed as much as possible. Therefore, the grindstone structure can be maintained as expected and product management is easy. Speaking of porosity, the porosity derived from the inorganic hollow substance is added to the porosity of the grindstone itself, so that the porosity can be made high and at least 30%.
A larger grindstone of up to about 70% can be obtained (up to about 40% for conventional organic pore-forming agents).

In addition, since the inorganic hollow substance does not soften, it is possible to obtain a grindstone with an arbitrary porosity even by hot pressing or the like.

Since the inorganic hollow substance functions as a pore-forming agent and also as an inorganic filler, it is possible to change the degree of concentration of the grindstone without adding an inorganic filler separately. Therefore, it is convenient when superabrasive grains are used as the abrasive as in the present invention.

In addition, since the partition walls of the inorganic hollow material are easily broken during grinding, almost no burning occurs and no grinding failure occurs. Therefore, good self-reliance can be exhibited without sharpening, which is convenient from the viewpoint of grinding efficiency.

Since pores other than those caused by the hollow substance are present in the binder phase, it is possible to obtain a grindstone having both high bending strength (durability) and high porosity (dressing property).

[Examples] Hereinafter, the present invention will be described based on Examples. Example 1
3 (CBN abrasive grains: concentration 100) ・ CBN abrasive grains (# 80/100) 25 parts by volume ・ Inorganic hollow substance (151-165 μm) 27 〃 ・ Vitrified bond 18 〃 ・ Glue 6 〃 Grindstone component And the inorganic hollow substance shown in Table 1 was used to obtain a grindstone having a porosity of about 55% (Vitrified bond is in accordance with JP-B-52-27394). As Comparative Examples 1 and 2, those in which an organic pore-forming agent or perlite (which is softened and melted by firing) was used instead of the inorganic hollow substance were used.

Each compound of the examples and comparative examples was press-molded into a prismatic shape and fired at 950 ° C. for 5 hours to obtain a grindstone. The results of the firing shrinkage are also shown in Table 1.

As is clear from this table, the grinding stones of Examples 1 to 3 have less firing shrinkage than the grinding stones of Comparative Examples 1 and 2.
This is particularly noticeable when coal ash balloons and alumina balloons are used (Examples 1 and 3).

In addition, for the compounding example according to Example 1, press molding,
Baking at 900 ℃ for 5 hours, outer diameter: 305, thickness: 1
5, Create a grindstone with a hole diameter of 76.2 (mm), perform surface grinding, grinding performance, namely (a) grindstone wear size, (b)
The grinding ratio and (c) power consumption were examined. The results are shown in FIGS.

In Comparative Example 3, mullite (inorganic filler) was used instead of the coal ash balloon, and the grinding conditions are as follows: Wheel peripheral speed 1600 m / min Table feed speed 20 m / min Depth of cut 10 μm / Pass Work material SKH51 Work material size Length 300 × width 10 (mm) With the grindstone of Comparative Example 3, burn was generated when the grinding was not performed (Fig. 4). On the other hand, the grindstone of Example 1 can be used without sharpening. Further, the grindstone of Example 1 has small grindstone wear size and power consumption, a high grinding ratio, and excellent grinding performance, as compared with the grindstone of Comparative Example 3 that is dressed. Figures to 4).

Example 4 (diamond abrasive grains) Next, diamond abrasive grains (# 80/10) were used as superabrasive grains.
No. 0) was used, and the others were molded and fired in the same manner as in the above-described CBN abrasive grain example to obtain an abrasive grain having a porosity of about 55%. The result of the firing shrinkage is shown in Table 2 (it should be noted that, as a comparative example, the one in which the organic pore forming agent was mixed with the diamond abrasive grains was used).

Even in this example, it was confirmed that the firing shrinkage was smaller than that in the comparative example. That is, the inorganic hollow substance was effective in diamond abrasive grains as in CBN.

Example 5 (CBN abrasive grains: concentration 150) -CBN abrasive grains (# 170/200) 37.5 parts by volume-Coal ash balloon 14.5 〃-Vitrified bond 18 〃-Glue 6 〃 Grindstone components were mixed in the above proportions, A grindstone having a porosity of about 44% is formed by molding and firing in the same manner as in Examples 1 to 3 (however, the grindstone dimensions are outer diameter: 15, thickness: 10, hole diameter: 6 (m
m). ), The inner surface was ground and the grinding performance was investigated. The results are shown in FIGS.

As Comparative Example 5, a mullite (inorganic filler) blend was used instead of the coal ash balloon, and the grinding conditions are as follows: Machine Toyo Kogaku internal grinding machine (T-111) Grinding wheel peripheral speed 1700m / Min Work 〃 50m / min Stroke amount 2mm Cutting speed Coarse grinding φ20 μm / sec Precision grinding φ 5 μm / sec Cutting allowance φ 0.2 mm Sparfout 5 stroke Work material SUJ2 (HRC62) φ50 × 10 × φ20 Coolant Noritake Cool SA-02 Dress Conditions Dresser single stone 1/2 ct (octahedron) Notch φ4 (μm / pass) Dress feed lead 0.07 mm / rev of wheel With the dressing under the above conditions, the grindstone of Example 5 has a substantially flat surface (0.3 The grindstone of Comparative Example 5 has a swell (about 1 μm).
Was generated (FIGS. 8 (a) and (b)), and it was confirmed that the grindstone of Example 5 was very excellent in dressing property.

In addition, the grindstone of Example 5 showed excellent results in terms of grindstone wear size, grinding ratio, and power consumption as compared with the grindstone of Comparative Example 5 (FIGS. 5 to 7).

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a vitrified grindstone of the present invention, and FIGS. 2 to 4 are graphs comparing grinding performance of the grindstone of Example 1 and the grindstone of Comparative Example 3, and FIG. Grinding wear size, FIG. 3 shows grinding ratio, FIG. 4 relates to power consumption, and FIGS. 5 to 7 are graphs comparing grinding performance of the grindstone of Example 5 and the grindstone of Comparative Example 5. Fig. 5 shows grinding wear dimensions, Fig. 6 shows grinding ratio, Fig. 7 relates to power consumption, and Fig. 8 shows a cross-sectional shape of the grindstone grinding surface after dressing (magnification × 5000). ), (A) relates to Example 5, (b) relates to Comparative Example 5, and FIG. 9 is a schematic view showing another vitrified grindstone of the present invention. DESCRIPTION OF SYMBOLS 1 ... Super abrasive grain, 2 ... Vitrified bond, 3 ... Pores other than a hollow substance, 4 ... Inorganic hollow substance.

 ─────────────────────────────────────────────────── ─── Continuation of front page (56) Reference JP-A-59-107859 (JP, A) JP-A-57-178667 (JP, A) JP-A-57-21270 (JP, A) JP-B-38- 23594 (JP, B1)

Claims (5)

[Claims] 1. A vitrified grindstone in which an abrasive material is superabrasive grains and contains an inorganic hollow substance that is easily broken by a frictional force with a work material, wherein the softening point of the hollow substance is the above A vitrified grindstone having a porosity higher than at least 30%, which is higher than the intrinsic firing temperature of the vitrified bond for abrasive grains and has pores other than those caused by the hollow substance in at least the binder phase. 2. The vitrified grindstone according to claim 1, wherein a difference between the softening point and the intrinsic firing temperature is at least 50 ° C. or more. 3. The intrinsic firing temperature is 650 ° C. or higher and 1000.
Claim 1 or 2 within the range of ℃ or less
The vitrified whetstone described in the item. 4. The vitrified grindstone according to any one of claims 1 to 3, wherein the hollow substance is at least one of shirasu balloon, alumina balloon and coal ash balloon. 5. The vitrified grindstone according to any one of claims 1 to 3, wherein the hollow substance is at least one of a glass balloon and a carbon balloon.