JP2021020263A - Vitrified super finishing grinding wheel - Google Patents

Abstract

To produce a structure having a weak degree of coupling of abrasive grains by devising a structure regulator to be added, and thereby achieve both improvement of sharpness and improvement of abrasion resistance of a vitrified super finishing grinding wheel.SOLUTION: A vitrified super finishing grinding wheel obtained by coupling hard abrasive grains 2 with an average particle size of 20 μm or less with a vitrified bond 6 contains spherical silica gels 4 that are obtained by aggregating and coupling an infinite number of superfine silicas with a nano-millimeter size and have an average particle size of 30-100 μm at a volume ratio of 3-20% based on the grinding wheel, and the spherical silica gels 4 are dispersed in the structure of the grinding wheel.SELECTED DRAWING: Figure 4

Description

The present invention relates to a vitrified super-finishing grindstone for polishing or grinding in which diamond abrasive grains or cubic boron nitride (CBN) abrasive grains, which are called super-abrasive grains, are fired and bonded using a vitrified bond as a binder. ..

The above-mentioned Vitrified super-finishing grindstone is often used for finishing the raceway groove (track surface) of a bearing that requires a smooth surface because it can perform super-finishing with high accuracy and high efficiency.

The vitrified grindstone has excellent sharpness. Its sharpness is that it has a porous structure, which is a characteristic of this grindstone.

The pores (cavities in the tissue) of the vitrified grindstone usually occupy 30-65% of the grindstone volume. Due to its high porosity, when the work material is machined, an edge effect can be expected due to the abrasive grains existing around the pores, and it is possible to increase the actual machined surface pressure, thereby exhibiting good sharpness.

In addition, since the pores act to promote the discharge of chips (polishing chips) generated during processing, it is possible to maintain stable sharpness.

Superfinishing is the surface of the target part of the work (workpiece) while applying relative vibration with an amplitude of 1 to 5 mm and a frequency of about 5 to 30 Hz to the grindstone using a grindstone with fine-grained abrasive grains. It is a processing method to finish the mirror surface.

It is a low-pressure and low-speed machining compared to general machining, and a force is applied to the abrasive grains from various directions due to the relative vibration with the workpiece. In this situation, the rough surface (unevenness) of the workpiece before processing causes the abrasive grains to crush and fall off, thereby maintaining sharp sharpness at all times. Therefore, the grindstone used for super-finishing requires a structure in which the degree of bonding of abrasive grains is weak.

In order to realize a structure having a weak binding degree, an artificial pore-forming agent or a tissue-adjusting agent having a porous structure is added to maintain an appropriate working hardness.

There are two types of pore-forming agents, one that burns out in the firing process of the grindstone and the other that does not need to be burned. The former pore-forming agents include starches such as corn and potato, coconut shell activated carbon, graphite, naphthalene, peach flour, and wood chips, but these have a non-constant particle size and shape, and stabilize the quality of the grindstone. It lacks stability in planning.

In addition, there are styrene-based, acrylic-based, or phenol-based resins as pore-forming agents having the same shape and particle size, but these are combustion devices that process toxic gas because they generate toxic gas during combustion. It is necessary to prepare separately, and the manufacturing cost of the grindstone is high.

On the other hand, as a pore-forming agent that does not need to be burned, there is an inorganic hollow balloon. As the hollow balloon, the following Patent Document 1 describes a shirasu balloon, an alumina-based balloon, and a coal ash balloon, but these are weak in strength and difficult to handle.

The artificially created pores help facilitate the discharge of chips, but depending on the size of the work and the processing conditions, chips may accumulate in the pores and cause welding.

On the other hand, as the structure adjusting agent, various fillers (fillers) such as silicon carbide (GC: green carbonite) abrasive grains, alumina (WA: white random) abrasive grains, mullite, and salt are used.

Depending on the type of filler and the amount added, the grindstone will work both softly and hardly, but if it is too hard, the sharpness will be extremely reduced, and if it is too soft, the sharpness will be improved, but the bearing capacity of the abrasive grains will be improved. Is greatly reduced and the amount of wear of the grindstone is increased.

Special Fair 6-24700 Gazette

In super-finishing, the polished surface of the grindstone is often brought into surface contact with the work, and when the chips carved from the work are vitrified grindstones, they tend to clog the pores that are characteristic of the grindstone. There is.

As the clogged chips grow, clogging occurs, which induces welding and covers the edge that acts as the cutting edge of the abrasive grains on the polished surface, so that the sharpness of the grindstone is extremely reduced.

Further, since the welded portion is raised, a high pressure is partially applied, the structure of the grindstone is destroyed, the amount of wear of the grindstone is significantly increased, and the roughness of the finished surface is deteriorated.

For super-finishing, shortening of machining time and further improvement of finished surface roughness are required, and a vitrified grindstone capable of high-efficiency and high-precision machining using finer-grained abrasive grains that can meet these demands. Is desired.

For high efficiency and high precision machining, it is necessary to further improve the sharpness and wear resistance of the grindstone. However, as described above, it is not easy to further improve the sharpness and wear resistance of the vitrified grindstone.

The present invention creates a structure with a weak bond of abrasive grains by devising a structure adjusting agent to be added, thereby achieving both improvement in sharpness and wear resistance of a vitrified superfinishing grindstone while suppressing an increase in manufacturing cost and the like. The challenge is to let them do it.

In order to solve the above problems, in the present invention, it is a vitrified superfinishing grindstone in which hard abrasive grains having an average particle size of 20 μm or less are bonded with a vitrified bond (binder).
Vitrified containing 3 to 20% of spherical silica gel with an average particle size of 30 to 100 μm, in which innumerable nanomillimeter-sized ultrafine silicas are aggregated and bonded, in the volume ratio of the grindstone, and the spherical silica gel is dispersed in the structure of the grindstone. Provides a super-finishing grindstone.

This vitrified super-finishing grindstone uses diamond abrasive grains or cubic boron nitride abrasive grains as the hard abrasive grains. Further, as the binder, vitrified bond, one that melts at 650 to 750 ° C. is used.

The vitrified superfinishing grindstone may be one in which small-sized natural pores generated in the structure are impregnated with wax.

In this vitrified superfinishing grindstone, the hard abrasive grains and the vitrified bond are wet-mixed to disperse the hard abrasive grains in the vitrified bond, and then a predetermined amount of spherical silica gel having an average particle size of 30 to 100 μm is added. , Wet mixing was continued to form a slurry in which hard abrasive grains, vitrified bond, spherical silica gel and water were mixed, and the slurry was poured into a molding die and dried and solidified without applying molding pressure to obtain the obtained slurry. The molded product can be produced by a method of firing at a temperature of 650 to 750 ° C.

The present invention also provides a method for producing the above-mentioned vitrified superfinishing grindstone.

The vitrified superfinishing grindstone of the present invention employs spherical silica gel having an average particle size of 30 to 100 μm as a structure adjusting agent.

Spherical silica gel having a bulk density (bulk specific gravity) of, for example, 0.5 g / cm ³ obtained by gelling the nanomillimeter-sized ultrafine silica gel has pore cavities of 60 to 65% by volume. Fragile.

The spherical silica gel is relatively brittle, and when the spherical silica gel that appears on the surface (polished surface) of the grindstone after polishing is pressed against the work, it is damaged by the unevenness of the work surface, and the scratches are the starting point for large crushing. It collapses.

As a result, cavities appear on the surface of the grindstone, the edges of the grindstone are promoted to protrude, and the sharpness can be improved.

In addition, chips will be discharged through the cavities that appear on the surface of the grindstone, making it possible to maintain stable sharpness without welding.

On the other hand, the spherical silica gel that is not exposed on the polished surface retains its original shape, and no useless cavity is formed in the structure of the grindstone. Therefore, the wear resistance does not decrease, and a good grindstone structure is stably maintained.

Spherical silica gel is an inorganic substance, and it is not necessary to provide environmental protection equipment or the like required when using an organic pore-forming agent, and it is possible to suppress an increase in cost.

Further, according to the method for producing a vitrified superfinishing grindstone of the present invention, the spherical silica gel is mixed with other materials by a wet mixing method, and the obtained mud is poured into a molding die without applying molding pressure. Since it is dried and solidified, spherical silica gel mixed with other materials can be dispersed in the structure of the grindstone in its original form.

As already mentioned, spherical silica gel is relatively brittle, so if a method of mixing with other materials by a dry mixing method and applying a stronger molding pressure is adopted, it will be destroyed by the pressure and molding pressure applied during mixing, and the structure will be adjusted. The role as an agent is lost.

According to the manufacturing method of the present invention, since wet mixing and molding without applying molding pressure are performed, excessive pressure is not applied to the spherical silica gel in the manufacturing process of the grindstone.

Therefore, the added spherical silica gel retains its original shape until it is destroyed by the work, and it is possible to obtain a vitrified super-finishing grindstone that achieves the purpose of improving sharpness and improving wear resistance by suppressing welding by the action of the spherical silica gel. become.

It is a perspective view which shows the appearance of an example of the Vitrified superfinishing grindstone of this invention. It is a perspective view which shows the appearance of another example of the Vitrified superfinishing grindstone of this invention. It is a perspective view which shows the appearance of still another example of the Vitrified superfinishing grindstone of this invention. It is a figure which shows the schematic structure of the structure of the vitrified superfinishing grindstone of this invention. It is a micrograph which shows the appearance of the spherical silica gel. It is a micrograph which magnified the surface of spherical silica gel 30,000 times. It is a micrograph which shows the state which the spherical silica gel is buried in the structure of a grindstone. It is a micrograph which shows the state that the spherical silica gel in the structure appears on the polished surface of the grindstone and a part of the spherical silica gel is crushed. It is explanatory drawing of the super finish processing method of the raceway surface of the inner ring of a ball bearing by a vitrified super finish grindstone. It is explanatory drawing of the super finish processing method of the roller end face of a conical roller bearing and a cylindrical roller bearing by a vitrified super finish grindstone.

Hereinafter, embodiments of the vitrified superfinishing grindstone of the present invention will be described with reference to FIGS. 1 to 8 of the attached drawings.

An example of the vitrified superfinishing grindstone of the present invention is shown in FIGS. 1 to 3. The vitrified super-finishing grindstone 1 (hereinafter, simply referred to as a grindstone) in FIG. 1 is a grindstone with R used for super-finishing the raceway grooves of the inner ring and the outer ring of a ball bearing.

Further, the grindstone 1 in FIG. 2 is a grindstone with a concave radius used for super-finishing the inner ring raceway surface and the outer ring raceway surface of a conical roller bearing and a cylindrical roller bearing.

The grindstone 1 in FIG. 3 is a grindstone for surface polishing used for super-finishing the end faces of cylindrical rollers and conical roller bearings of cylindrical roller bearings and conical roller bearings.

These grindstones 1 represent only one form. There are various shapes such as a grindstone formed into a cylindrical shape, a grindstone with a shaft, and a grindstone for flat surface polishing.

9 and 10 show an example of a super finish processing method using a super finish grindstone. FIG. 9 shows a method of processing a raceway groove of an inner ring of a ball bearing (details of this method will be described later) using the grindstone 1 with R shown in FIG.

Further, FIG. 10 shows a method of processing the end face of the roller 13 of the conical roller bearing / cylindrical roller bearing using the grindstone 1 for surface polishing shown in FIG. This processing is performed by rotating the grindstone 1 and 13.

Note that these processing methods are only examples. There are a wide variety of processing methods using a super-finishing whetstone.

If necessary, any of the grindstones is used by performing additional processing to match the polished surface with the required surface roughness of the surface to be polished.

The illustrated grindstones are all vitrified super-finishing grindstones in which hard abrasive grains are bonded with a vitrified bond as a binder.

The schematic structure of the structure of these grindstones is shown in FIG. In the figure, 2 is hard abrasive grains, 3 is small-sized natural pores generated inside the structure, 4 is spherical silica gel dispersed in the structure, and 6 is a vitrified bond as a binder.

The hard abrasive grains 2 are covered with the vitrified bond 6 and bonded by the vitrified bond 6 which is melted and solidified, and the spherical silica gel 4 is scattered in the structure.

The spherical silica gel 4 is obtained by aggregating innumerable ultrafine silica particles having a nanomillimeter size (for example, about 6 nm), and has an average particle size of 30 to 100 μm. The spherical silica gel 4 is contained in the structure of the grindstone at a volume ratio of 3 to 20% of the grindstone.

An enlarged photograph of the appearance of the spherical silica gel 4 is shown in FIG. The spherical silica gel 4 in the photograph has a particle size of approximately 60 μm. FIG. 6 shows an SEM (scanning electron microscope) photograph in which the surface of the spherical silica gel 4 is magnified 30,000 times. 5 in FIG. 6 is ultrafine silica.

FIG. 7 is an SEM photograph showing a state in which the spherical silica gel 4 is buried in the structure of the grindstone 1, and FIG. 8 shows a part of the spherical silica gel 4 due to the contact of the spherical silica gel 4 with the work by superfinishing. It is an SEM photograph which shows the state which was crushed.

The hard abrasive grains 2 are diamond abrasive grains or cubic boron nitride abrasive grains. As the hard abrasive grains 2, those having an average particle size of 20 μm or less, preferably about 2 to 10 μm are used.

Further, as the vitrified bond 6, one that melts at 650 to 750 ° C. is used.

The vitrified bond 6 has, for example, a composition in which SiO ₂ , Al ₂ O ₃ , B ₂ O ₃ , R ₂ O, RO, and TiO ₂ are mixed.

The grindstone 1 may be one in which wax (carnauba wax) is impregnated in the natural pores 3 formed in the structure.

In the grindstone of the present invention, hard abrasive grains and vitrified bond are wet-mixed to disperse the hard abrasive grains in the vitrified bond, then a predetermined amount of spherical silica gel having an average particle size of 30 to 100 μm is added, and wet mixing is continued. A mixture of hard abrasive grains, vitrified bond, spherical silica gel, and water is formed to form a slurry, which is poured into a molding die and dried and solidified without applying molding pressure. The obtained molded product is 650- It can be produced by a method of firing at a temperature of 750 ° C.

When the firing temperature of the molded product exceeds 750 ° C., the spherical silica gel added during the firing of the molded product melts and hardens firmly, and the destruction due to contact with the work is less likely to occur, and the effect of adding the spherical silica gel diminishes.

On the other hand, the obtained grindstone is preferably one that can withstand as high a temperature as possible in consideration of heat resistance during use, so it is preferable to set the lower limit of the firing temperature to about 650 ° C.

Therefore, the firing temperature is set to 650 to 750 ° C., and the vitrified bond used as the binder is one that melts at a temperature within that range.

In the grindstone 1 of the present invention to which the spherical silica gel 4 is added, as the polished surface wears, the spherical silica gel 4 buried in the structure appears on the polished surface and comes into contact with the work, which can be seen from FIG. As described above, a part of the spherical silica gel 4 is crushed and large pores 7 opened to the outside are formed on the polished surface.

The edges of the hard abrasive grains 2 existing around the pores 7 are exposed and easily come into contact with the work, and the edge becomes a cutting edge to be expected to have an edge effect of cutting the work, and the actual machined surface pressure can be reduced. It is also possible to increase the number, and good sharpness is exhibited.

Further, since the pores 7 promote the discharge of chips, stable sharpness is maintained. Further, unlike the air pores in the structure of the conventional grindstone created by adding an artificial pore agent, even if a part of the spherical silica gel 4 is crushed, as can be seen from FIG. 7, the uncrushed part is in the structure. Remain. Therefore, the grindstone does not become too soft, and a large decrease in the abrasive grain bearing capacity due to the excessive softness is suppressed, and an increase in the amount of wear of the grindstone is suppressed.

Further, unlike the pore-forming agents having a non-constant particle size and shape that have been conventionally used, the spherical silica gel 4 has a stable particle size and shape, which makes it easier to stabilize the quality of the grindstone.

Furthermore, no toxic gas is generated during firing, and the manufacturing cost does not increase due to the treatment of toxic gas.

In order to evaluate the performance of the grindstone of the present invention, a grindstone 1 for an evaluation test was prepared. As the prototype grindstone, CBN abrasive grains having an average particle size of 5 μm (grain size 2500 mesh) were used as hard abrasive grains.

The binder, vitrified bond, has the composition shown in Table 1 that can be fired at a low melting point of 650 to 750 ° C. because the added spherical silica gel is sintered and becomes difficult to crush when the firing temperature is in the high temperature range. Using.

In order to cover the degree of binding from soft to hard, a grindstone in which the content of the binder (vitrified bond) was changed as shown in Table 2 was prepared.

The grindstone contained spherical silica gel that also served as a tissue regulator and a pore-forming agent. The spherical silica gel used here is manufactured by Fuji Silysia Chemical Ltd., and innumerable silica gels having an average particle size of 6 nm are aggregated and bonded to form a spherical mass.

As the spherical silica gel, those having an average particle size of φ30 μm, φ60 μm, and φ100 μm were used. These spherical silica gels have a bulk density of 0.5 g / cm ³ and a pore volume of 0.70 to 0.85 ml / g.

10% and 20% by mass ratio of this spherical silica gel was added to the hard abrasive grains. See Table 2 for the volume ratio content of the entire grindstone. The addition was carried out by adopting a wet mixing method.

Spherical silica gel is brittle and vulnerable to pressure, so it is necessary to mix it so that it does not break. It is also important to uniformly cover the surface of the hard abrasive grains with a vitrified bond in order to stably hold the hard abrasive grains having a small average particle size. From these two points of view, dry mixing was considered unsuitable, and a wet mixing method was adopted in which water was added and the materials were kneaded.

Wet mixing was performed according to the following procedure. First, put hard abrasive grains (CBN abrasive grains) in a container, add 50% of powder paste consisting of 4% wheat flour and 4% rice flour, and water, and stir for 1 minute with a stirrer to surface the hard abrasive grains. Was covered with glue.

Next, the binder having the composition shown in Table 1 is weighed by weight at 35 to 50% of the amount of abrasive grains, put into the container, 10% of the paste is added, and the mixture is further stirred for 1 minute to have a viscosity of 400. A slurry of ± 100 mPa · s was obtained. Here, after confirming the viscosity, stirring was further performed for 5 minutes.

The slurry was then poured into a mold. The formwork was placed on a water-permeable base with a filter cloth laid on it.

Then, the slurry in the mold was dried in a low temperature environment of 40 ° C. for 3 to 4 days. Then, the mold was removed and dried in a low temperature environment of 40 ° C. for another 3 to 4 days to obtain a molded product from which water had been removed.

Next, the dried molded product was placed in a furnace and calcined at a temperature of 550 ° C. to burn off the contained paste. In addition, following the temporary firing, the temperature inside the furnace is raised to the firing temperature at a heating rate of 60 ° C. per hour, and holding firing is performed at a temperature with a lower limit of 700 ° C. and an upper limit of 750 ° C. for 3 to 4 hours to complete the firing. Obtained a product whetstone. Table 2 shows the structure and physical properties of the grindstone thus obtained.

The physical characteristics of the prototype grindstone are expressed in RL hardness. The RL hardness was measured by pressing a steel ball having a diameter of 3.175 mm against a grindstone with a reference load of 29.4 N and a test load of 196 n using a Rockwell superficial hardness tester.

In the No. 12 grindstone in Table 2, as an artificial pore-forming agent, a φ100 μm acrylic resin (copolymer of a methacrylic acid ester) that creates an air pore portion instead of the spherical silica gel is substantially used as the spherical silica gel of Example 6 having a diameter of 100 μm. It is a porous grindstone manufactured by adding the same amount by a wet mixing method and molding without applying a molding pressure.

This No. 12 porous grindstone is used as a reference product (listed in Table 2) to see the difference in performance due to the difference in manufacturing method from the porous grindstone obtained by dry mixing and press molding. Got ready.

No. 1 of the comparative example in Table 2 is a special porous grindstone obtained by performing dry mixing and press molding. The grindstone of Comparative Example 1 is a grindstone proposed in Japanese Patent Application Laid-Open No. 01-2870, and has a large particle size of organic particles having a particle size of 20 to 50 times the abrasive particle size and a particle size of 1. A porous structure is created by blending 5 to 10 times smaller particle size organic particles and using these organic particles.

No. 2 of the comparative example in Table 2 is a grindstone formed only with hard abrasive grains and a binder without containing a pore forming agent or a structure adjusting agent. Further, in Comparative Example No. 3 of Table 2, 2500 mesh of GC (green carbonite) fine abrasive grains as a structure adjusting agent was applied to a grindstone whose amount of binder was similar to that of Comparative Example 2, and spherical silica gel of Example 7 was used. It is added in a smaller amount than the simple amount of silica gel.

[Performance evaluation test]
A performance evaluation test was conducted using a grindstone having the composition shown in Table 2. In the evaluation test, the grindstone of the example uses CBN abrasive grains that are effective for steel processing as hard abrasive grains, so the bearing steel SUJ2 (hardness: HRC), which is the most frequently used for super-finishing among bearings. ≈60) Finishing of the raceway surface of the inner ring of the ball bearing was performed.

The ball bearing of the work is the # 608 miniature bearing, which is the most mass-produced and requires processing efficiency and cost performance.

The test was carried out focusing on so-called two-step roughing, in which roughing and finishing are performed in order. The rough processing is a processing in which a significant difference is likely to occur.

As shown in FIG. 9, the inner ring 10 of the work is rotated at high speed, and the grindstone 1 inserted into the grindstone holder 11 is pressed against the raceway surface of the concave groove of the inner ring 10 by the air cylinder 12 to process the raceway surface of the inner ring. It swings at high speed to secure the shape and surface roughness in rough processing in a short time.

Roughing by the two-stage machining method requires high-speed machining within 5 seconds, a allowance of φ5 μm or more, and a machined surface roughness of about 0.025 to 0.05 μm Ra. Therefore, one second before the end of processing, the number of swings of the grindstone was reduced to 120 cpn to adjust the raceway surface to the required surface roughness.

In this processing, in order to improve cost performance, the amount of wear of the grindstone is required to be 2 μm or less, more preferably 1 μm or less per work.

Since the bearing manufacturer usually displays the allowance for the raceway surface of the inner ring by the diameter, it is also expressed by the diameter according to the custom. The same applies to the following. The actual replacement cost is half that value.

The grindstones in Table 2 used for the performance evaluation were finished in order of track width, straddle width, and grindstone length to 3 mm × 3 mm × 16 mm from the left, and this grindstone was waxed. The natural pores formed inside were impregnated with carnauba wax.

The processing machine for super finishing uses the super finishing board SF-R-12S for No. 608 manufactured by Daisei Co., Ltd., and the inner ring is rotated at a peripheral speed of 400 m / min, the grindstone swing angle: 18 °, and the grindstone swing. The track surface was polished under the conditions of number: 1000 cpm and 120 cpm, grindstone pressing force: 1.8 MPa, processing time short time: 5 seconds (rough processing 4 seconds, finishing 1 second).

Roughing for 4 seconds was performed with a grindstone swing number of 1000 cpn, and finishing for 1 second was performed with a grindstone swing number of 120 cpn.

Further, for this processing, an oil-based super-finishing liquid (Yushiron Cut SF-36) manufactured by Yushiro Chemical Industry Co., Ltd. was used. The pre-processed surface roughness of the raceway surface of the inner ring was unified to 0.1 to 0.14 μmRa.

In addition, the number of inner rings processed is 20, the first 10 are discarded, and the total 10 inner ring allowances from the 11th to the 20th are measured, and the average value of the obtained values is obtained. It was.

Further, for the grindstone wear amount for evaluating the wear resistance, the total wear amount of the 20 grindstones was obtained, and the value obtained by dividing the total wear amount by 20 was taken as the wear amount per grindstone.

The processing conditions in this test are shown in Table 3, and the actual cutting results are shown in Tables 4 and 5, respectively. The measured values in Table 4 are the results of actual machining in which the pressing pressure of the grindstone on the inner ring (grindstone pressing force) is 1.8 MPa under the same high pressure conditions, and the measured values in Table 5 are the grindstone pressing force on the inner ring. It is the actual cutting result in the processing performed by changing in 4 steps.

The actual cutting results of the grindstones No. 1 to No. 11 of the examples will be considered. From the actual cutting results in Table 4, the No. 1 grindstone has excellent sharpness and can earn a margin, but the grindstone wear amount does not meet the requirement in the machining with the grindstone pressing force of 1.8 MPa. However, the amount of wear of the grindstone is smaller than that of the comparative example manufactured by adopting the dry mixing method, and it can be inferred that the effectiveness is fully exhibited in the region where the grindstone pressing force is low.

In addition, the No. 2 grindstone has a low content of binder (vitrified bond), but the surface of the hard abrasive grains is widely covered with the binder by using the wet mixing method, and the abrasive grains are supported by the vitrified bond. The force is increased, which results in a medium hardness, which results in a required allowance, good wear resistance (grindstone wear) and excellent machined surface roughness.

Further, the No. 3 grindstone also has a low content of the binder, but like the No. 2 grindstone, it has excellent sharpness, wear resistance, and machined surface roughness, and good results are obtained. There is.

From the result of the removal allowance, it can be seen that the sharpness of the No. 4 whetstone is close to that of the No. 3 whetstone. However, the amount of wear of the grindstone is slightly larger than that of the No. 3 grindstone, and the roughness of the machined surface is a little poor. It is considered that this is because the particle size of the spherical silica gel used was φ100 μm, which was larger than that of the No. 3 grindstone, and the grindstone hardness was lowered by that amount.

The No. 5 grindstone is made by using spherical silica gel having a diameter of 60 μm and adding a standard amount of a binder. This whetstone has a smaller removal allowance than the No. 3 whetstone, but has sufficient sharpness, and as a result, it has better results than the No. 3 whetstone in terms of wear resistance and machined surface roughness. Has been obtained.

The No. 6 grindstone uses the same spherical silica gel having a diameter of 100 μm as the No. 4 grindstone, and the addition ratio of the binder is larger than that of the No. 4 grindstone.

The wear resistance and machined surface roughness of this No. 6 whetstone are close to those of the No. 5 whetstone and are within the range of no problem, but the removal allowance is slightly smaller than that of the No. 5 whetstone. .. It is presumed that this is because the grindstone wear amount became smaller than that of the No. 4 grindstone by increasing the addition amount of the binder, but the grindstone hardness became larger than that of the No. 4 grindstone.

The No. 7 grindstone has a porosity smaller than that of the No. 2 grindstone, even though the amount of spherical silica gel having a diameter of 30 μm is almost doubled as compared with the No. 2 grindstone. This No. 7 whetstone is
The removal allowance is good, but the amount of whetstone wear is slightly larger than that of the No. 2 whetstone.

It can be considered that the No. 8 grindstone replaces the φ30 μm spherical silica gel used in the No. 7 grindstone with a φ60 μm spherical silica gel, and good values are obtained in terms of replacement allowance, grindstone wear amount, and machined surface roughness. Has been done.

Compared to the No. 3 grindstone, the No. 8 grindstone has almost twice the addition ratio of φ60 μm spherical silica gel, and as a result, chips are promoted to be discharged through many pores created by the spherical silica gel. The fact that welding is less likely to occur is also considered to be a factor that led to good results.

It can be said that the No. 9 grindstone replaces the φ60 μm spherical silica gel used in the No. 8 grindstone with a φ100 μm spherical silica gel. This No. 9 whetstone has the same wear resistance and machined surface roughness as the No. 8 whetstone and is within the range of no problem, but the removal allowance is slightly lower than that of the No. 9 whetstone. ..

Both the No. 10 and No. 11 grindstones have a small amount of grindstone wear and excellent wear resistance, and the machined surface roughness has the best value in the examples, but the target is the removal allowance. It has not reached φ5 μm. However, since the amount of wear of the grindstone is small, it is presumed that the target allowance can be sufficiently cleared by increasing the processing pressure to 2 MPa or more.

The reference No. 12 grindstone does not contain spherical silica gel. By adding an acrylic resin of φ100 μm by the wet mixing method, the grindstone structure is almost the same as that of the No. 1 grindstone in the comparative example using the dry mixing method, and the No. 1 grindstone hardness RL45 in the comparative example. On the other hand, although the grindstone hardness is RL33, which is slightly softer, the abrasive grain bearing capacity is enhanced by the vitrified bond, and as a result, the sharpness and abrasion resistance comparable to those of the No. 4 grindstone are secured. ..

However, in this reference product No. 12 grindstone, the acrylic resin burns during firing to generate toxic gas. Therefore, gas processing equipment is required, and there is a drawback that the manufacturing cost is high.

The grindstone of the present application using an inorganic spherical silica gel that does not generate toxic gas as a tissue conditioner does not cause problems of environmental deterioration and increase in manufacturing cost.

The No. 1 grindstone in the comparative example has good sharpness and the removal allowance meets the requirements. The roughness of the machined surface is 0.05 μmRa or less, but the amount of wear of the grindstone is abnormally large. It is clear that it cannot withstand use in high pressure regions where the machining pressure is as high as 1.8 MPa.

The No. 2 grindstone of Comparative Example does not contain a tissue conditioner, and the pores in the tissue are only natural pores. It was reconfirmed that this grindstone has poor sharpness and wear resistance, and does not exhibit high performance in a structure having only natural pores.

The No. 3 grindstone of the comparative example is one in which GC abrasive grains are added as a structure adjusting agent without using an artificial pore forming agent. The sharpness is improved by the addition of the GC abrasive grains, but the amount of wear of the grindstone is large, and there is a problem in wear resistance.

In the old days, it was thought that the pore-forming agent that creates air pores in the structure of the grindstone was most effective at a size of 3 to 10 times the particle size of the abrasive grains, but with the aim of shortening the processing time. Recently, a method of applying high pressure to process at high speed has been adopted, and the lower and upper limits of the particle size of the effective pore-forming agent have changed to a large value, which is considered to be about 10 to 15 times the abrasive particle size. Has been done.

The prototype grindstone used in the evaluation test described above has an average particle size of 5 μm of the hard abrasive grains used. As for this prototype grindstone, the one using spherical silica gel having a particle size of φ60 μm shows better performance than the one using spherical silica gel having a particle size of φ100 μm, and “the particle size of the pore-forming agent considered to be effective” is shown. Test results consistent with the view that "the upper limit is about 15 times the abrasive particle size" have been obtained.

As the hard particles, those having an average particle size larger than the illustrated 5 μm may be used, and in that case, it is better to increase the particle size of the spherical silica gel, which leads to a better result. Therefore, the upper limit of the particle size of the spherical silica gel used in the present invention is set to 100 μm.

Further, as the average particle size of the hard particles is smaller, the roughness of the processed surface is improved, but on the contrary, the removal allowance is smaller. Therefore, it is preferable to set the lower limit value to about 2 μm. In this case, the particle size of the spherical silica gel The lower limit is φ20 μm.

However, the grindstone No. 7 of the examples in Table 4 does not satisfy the more preferable requirement for a grindstone wear amount of 1 μm, even though spherical silica gel having a particle size of φ30 μm is used. The No. 2 grindstone of the embodiment also barely meets the requirement for a grindstone wear amount of 1 μm.

For these reasons and the following reasons, the lower limit of the particle size of the spherical silica gel used was set to 30 μm.

The applicant has commercialized a vitrified grindstone for superfinishing having a pore size of 30 μm, 50 μm, 80 μm and 100 μm produced by using a resin pore-forming agent.

In commercializing the grindstone, products with air pore diameters of 10 μm and 20 μm were also prototyped and tested. As a result, the products having the particle size of the air pores of 10 μm and 20 μm were unpleasant.

This is because the ball bearing raceway surface is super-finished, and the size of chips generated under high-speed processing conditions such as this time is 1/10 to 1/5 of the abrasive grain size in width and abrasive grain in length. Two to four times the diameter is common. When such chips are generated, the cavities formed on the polished surface are clogged with chips, which tends to cause welding. It is considered that the reason why the products with the particle size of the air pores of 10 μm and 20 μm were not good was due to the welding.

Therefore, in the case of an invention product using hard abrasive grains having an average particle size of 20 μm or less, there is a high possibility that chips generated when the particle size of the spherical silica gel is 30 μm or less will be clogged in the cavity formed by crushing the spherical silica gel. ..

The cavities created on the polished surface by spherical silica gel are shallower than the air pores created by using a pore-forming agent such as resin. Therefore, there is a concern that chips are more likely to be clogged. The lower limit of the particle size of spherical silica gel was set to 30 μm with the aim of dispelling that concern.

In super-finishing, the allowance increases as the grindstone pressure increases. Along with this, the amount of wear of the grindstone increases, and the roughness of the machined surface tends to deteriorate. In addition, there is a pressure that increases sharply where there is a grindstone wear amount, which is called the grindstone critical pressure.

As can be seen from the results in Table 5, the grindstone in the comparative example in which the critical pressure of the grindstone uses the dry mixing method is low, and the grindstone pressure exceeds the critical point at the stage of 1.3 MPa, so that the grindstone reacts sensitively. The amount of whetstone wear is rapidly increasing.

The grindstone of the comparative example can be said to be a grindstone with low robustness (robustness) in which the machining performance varies depending on the surface roughness (roughness before machining) of the workpiece to be machined, the machining conditions, the rigidity of the machining machine, and the like.

On the other hand, as can be seen from Table 5, the grindstones of the examples in which spherical silica gel was added using the wet mixing method are less affected by the grindstone pressing force, and the removal allowance, grindstone wear amount, and processed surface are not affected by the grindstone pressing force. The roughness shows good values, and it can be seen that the grindstone is easy to use and has high robustness.

By adopting the wet mixing method, the coating of the hard abrasive grains with the binder was improved and the bearing capacity of the abrasive grains by the binder was enhanced, and the use of spherical silica gel as the pore forming agent was the height of the grindstone. It greatly contributes to performance improvement.

In the spherical silica gel, the portion under pressure is crushed by the unevenness of the machined surface of the work and the contact with the discharged chips, and a cavity comparable to the air hole of the conventional grindstone is generated on the polished surface of the grindstone. The edge of the hard abrasive grains appears at the position facing the cavity, and the edge effect that the edge bites into the work exerts good sharpness. Furthermore, the cavity generated on the polished surface improves the discharge of chips and allows for removal. Becomes larger.

Further, the portion where the spherical silica gel does not come into contact with the work remains without being crushed, and supports the abrasive grains and the binder. Therefore, the amount of wear of the grindstone is suppressed and the wear resistance is improved.

1 Vitrified super-finishing grindstone 2 Hard abrasive grains 3 Natural pores 4 Spherical silica gel 5 Ultra-fine silica 6 Vitrified bond 7 Pore 10 Inner ring 11 Grindstone holder 12 Air cylinder 13 Rollers

Claims (4)

A vitrified super-finishing whetstone in which hard abrasive grains with an average particle size of 20 μm or less are bonded with a vitrified bond.
Vitrified containing 3 to 20% of spherical silica gel with an average particle size of 30 to 100 μm in which innumerable nanomillimeter-sized ultrafine silicas are aggregated and bonded in terms of the volume ratio of the grindstone, and the spherical silica gel is dispersed in the structure of the grindstone. Super finishing whetstone. The vitrified superfinishing grindstone according to claim 1, wherein the hard abrasive grains are diamond abrasive grains or cubic boron nitride abrasive grains, and the vitrified bond has a melting temperature of 650 to 750 ° C. The vitrified superfinishing grindstone according to claim 1 or 2, wherein the natural pores generated in the structure are impregnated with carnauba wax. The method for producing a vitrified superfinishing grindstone according to claim 1, wherein hard abrasive grains and vitrified bond are wet-mixed to disperse the hard abrasive grains in the vitrified bond, and then spherical particles having an average particle size of 30 to 100 μm are dispersed. A predetermined amount of silica gel is added, and wet mixing is continued to form a slurry in which the hard abrasive grains, vitrified bond, spherical silica gel, and water are mixed, and the slurry is poured into a molding die without applying molding pressure. A method for producing a vitrified superfinishing abrasive, which is dried and solidified, and the obtained molded product is fired at a temperature of 650 to 750 ° C.