JPS5949146B2 - Grinding wheel and its manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a ceramic grinding wheel and a method for manufacturing the same.

Traditional ceramic grinding wheel manufacturing methods have used clay and abrasive grains of various sizes and shapes for many years.

This invention relates to a special binder composition and process for manufacturing a grinding wheel for use in the final polishing of steel balls for ball bearings.

When grinding spheres, a very dense, vertical grinding wheel containing a vitrified bond is used.

The spheres to be ground flow through a groove on the working support plate, while the grinding wheel is operated above the support plate in such a way that the spheres engage with the flat side of the wheel.

Spherical grinding wheels operated in this manner are bonded with a vitrified binder or a vitreous binder that inherently has some degree of porosity, the porosity being reduced by increasing the vitreous binder content of the grinding mixture. Although it is reduced as much as possible during the firing process, it is necessary to reshape the wheel after firing to make it suitable for ball bearing grinding.

Conventional grinding process involves grinding grains, a binder that binds the grains,
It consists of stomata.

Grinding wheels typically contain 40-60% by volume abrasive.

Sufficient binder is added to create a hardness of the wheel suitable for the particular grinding purpose.

That is, the more binder or vitreous material added to the grinding wheel mixture, the harder the wheel will be after firing.

In the manufacturing process of ball bearings, grinding wheels that are extremely hard and wear resistant are desired.

This hardness is achieved by increasing the vitreous binder phase in the grinding wheel at the expense of porosity, resulting in
A typical vitrified grinding wheel for ball bearings contains about 1/2 abrasive and 1/2 binder, and has a porosity in the range of 5% or less.

In a firing process when 50% by weight binder is in the mixture, the grinding wheel will shrink by 10% during a conventional firing process.

Also, when such a large amount of binder is present, in order to properly bind the grains during firing of the grinder, the binder component is fired at a high temperature that makes the binder somewhat less viscous. must be done.

When the relatively large amount of the binder component is in this somewhat fluid state, the shape integrity of the cold-pressed grinding wheel is not well maintained and the final shape of the fired wheel is rounded at the edges. It is somewhat warped and has some depressions and deformations to accommodate any surface.

Additionally, the bottom of at least some of conventional ball grinding wheels is susceptible to refractory debris or furnace sand from the firing vat.

For this reason, in order to produce a ball grinding wheel of the desired size with a flat surface and the dimensional tolerances required for ball bearing manufacturing, conventional vitreous or vitrified bonded wheels are used. G) must be reshaped after firing.

That is, all the excess material added to compensate for 10% shrinkage, warpage, etc. must be scraped off.

Considering that such wheels are hard and dense ceramics, reshaping or grinding or cutting operations on conventional vitrified or glass-bonded wheels can be very difficult, time-consuming, and costly. You can see that this is a process that requires a lot of effort.

Due to the natural variations in raw materials for glass binders, the degree of shrinkage cannot be predicted with certainty.

Therefore, sometimes the grinding wheel becomes smaller or larger in size, resulting in rejection or excessive reshaping.
Is required.

Variations in shrinkage also have a negative effect on the grinding action, so if the expected shrinkage does not occur during firing, the wheel will work softer and will not satisfy the user.

An example of a vitrified binder for grinding wheels containing alumina and grains is U.S. Pat. No. 1,910,031 (
230 May 1933, Mi II gan).

Another example of a vitrified bond for an abrasive wheel is U.S. Pat. No. 2,475,565 (Houchins, July 5, 1949).

Although this patent suggests a binder for diamond and grains, the particular structure of which is not particularly useful in ball bearing grinding processes, it does indicate the use of bentonite and ball clay together as a binder for grinding wheels. It is interesting that

Prior art patents relating to alumina-containing products include U.S. Patent No. 1,572,730 (February 9, 1926, Lock
e et al.), U.S. Patent No. 2,290,107 (July 14, 1942, Luks), U.S. Patent No. 2,360,8
No. 41 (October 1944, 248. Baumann
Jr. et al.) etc.

All of these patents show various embodiments of the use of manganese oxide as a fluxing agent or sintering aid for ceramic binders in the presence of alumina.

U.S. Patent No. 3,089,764 (May 14, 1963)
Abrasive compositions useful for barrel firing are disclosed in Smith Gorman (Japan).

This composition is a granular alumina and silica binder composition with 120-220 Mess alumina.

French Patent No. 2,151,509 shows a ball bearing grinding wheel consisting of a ceramic binder with beta alumina and finely divided silicon carbide to fill the pores.

Although not related to the abrasive wheel technology, the applicant of this invention has previously sold, at least in the United States, a barrel-finished abrasive product comprising an alumina abrasive grid bonded with a ceramic binder composition.

Its composition is somewhat similar to the ceramic binder for alumina grinding wheels which is the subject of this invention.

This barrel finish abrasive composition contains ball clay, bentonite, crystalline filler, manganese dioxide, and about 10% by weight lOO Meush alumina abrasive grid.

This invention relates to the use of compositions that are particularly useful for finish polishing steel ball bearings.

In other words, we designed the grinding action of the grinding wheel to be hard and soft according to the pre-determined grinding standards required for a specific steel ball grinding action, and we developed a crystalline ceramic bonding agent for manufacturing the ceramic bonded grinding wheel. is the relative addition of abrasive to a given weight of binder composition (wt%
) has been found to be able to be prescribed by changing.

This binder can be used to create grinding wheel mixtures that are used within a certain pressure range during the cold pressing process.

It has been found that the grinding action of a wheel manufactured for this purpose can be predicted if its porosity, that is, its casting density and modulus of elasticity are known.

Porosity can be controlled and the modulus of the wheel can be varied to obtain a defined grinding action by varying the relative loading of grains for a particular weight of binder composition containing crystalline filler.

The porosity can be further adjusted by varying the compaction pressure to obtain a specific modulus at a given abrasive content.

The elastic modulus decreases as the grain addition rate increases relative to the weight of the binder in the grinding mixture, and the sintered density decreases. Porosity was found to be directly proportional to elastic modulus.

As the volume of the pores in the wheel increases, the grinding action of the wheel becomes softer.

If the relative weight percentage of grains to binder weight is reversed,
The opposite is true.

It is therefore possible to determine the relative loading of a given abrasive grid to the weight of the particular binder composition shown herein, which will produce a grinding wheel with a given porosity, modulus, and desired abrasive action. can get.

The wheel is usually fired, but there is little need to reshape it after firing.

Not only does the resulting spherical grinding wheel have predictable grinding properties when in use, but the binder matures without becoming so fluid that it dents, warps, or shrinks during firing.

If the stone is fired without such undesirable occurrences, the shape of the unfired, cold-pressed stone will remain intact during firing and there will be little need for reshaping.

Therefore, the manufacturing process of conventional spherical grinding wheels can be omitted.

In the grinding wheel industry, the following is known.

That is, as the elastic modulus increases, the grinding action becomes harder and the wheel becomes stronger, but at the same time the cutting rate decreases.

Conversely, by decreasing the elastic modulus, it is possible to produce a cutting wheel that is faster, more flexible, but less durable.

If the composition to be cold-pressed can be blended to a density within the range enclosed in Figure 1, a stone having an elastic modulus as specified, appropriate durability, and relative hardness or softness after firing can be prepared at any time. It becomes possible to manufacture.

Therefore, any type of steel ball bearing finishing grinding wheel can be manufactured.

Also, as shown in FIG. 3, when used, it is possible to change the durability and cutting speed by changing the grain size.

For example, for a fused milled alumina grid with an average particle size of 173 microns (US standard size 00), as the percentage of abrasive to binder weight in the grinder increases, the modulus increases for an average particle size of 63 microns (240 grit). decreases more rapidly than

In comparison, when a fused powder sand alumina grid with an average particle size of 63 microns (240 grid, compliant with U.S. Trade Standards C8-371-65) is added to a given amount of binder, the slope curve is slower. .

A similar relationship between abrasive loading percentage and binder weight holds true when using silicon carbide of any grid size.

However, the slope of the curve showing the decrease in elastic modulus is somewhat steeper than that for alumina particles of corresponding size.

Aluminum oxide and grains are preferred over silicon carbide and grains because of their compatibility with the ceramic binder of this invention.

This explains the difference in the effect of silicon oxide particles and aluminum oxide particles on the elastic modulus, as described above.

FIG. 2 shows that the modulus of the present invention wheel varies with both firing density and porosity.

That is, as the elastic modulus shown by the solid line increases, the fired density increases, and the porosity decreases as shown by the broken line.

The three properties of the wheel, modulus of elasticity, density and porosity, vary in a certain manner.

For certain compositions within the scope of this invention, the modulus and/or porosity (% by volume) can be predicted from a cold pressed green grinder as shown in FIG.

Within the conventional cold pressing pressure range, the amount of abrasive grid added to the weight of the binder of this invention determines the firing density, so it is possible to produce a soft grinding wheel for fast cutting or for slow cutting. It is also possible to freely manufacture hard grinding wheels.

To control the properties of a steel ball bearing finishing wheel for any given forming pressure, four components in the wheel forming mixture can be varied to control the malleability of the sintered product. do.

(1) clay as a binder with added bentonite, (2) fluxing agent of manganese dioxide and soda or soda ash, (3) e-fine alumina crystal additive, and (4)
The abrasive material has four grains.

In formulating the binder for the grinding wheel of this invention, we will start with ordinary vitrified bonded clay.

This clay contains alumina, silica, and
and various low melting point oxides to provide not only the firing binder but also some formability during processing into green iron.

That is, the grains are sufficiently compressed to provide good green strength during the pressing process.

The variety of clay is not limited, but a conventional clay for the binder, so-called ball clay, must be selected.

Mississippi ball clay is preferred from the standpoint of convenience and economy.

In formulating the wheel, we start with an amount of clay corresponding to about 20% by weight of the final mixture, and preferably about 1% bentonite.

These provide compressibility to the final mixture, which may be cold pressed or hot pressed.

Although bentonite concomitantly serves to lower the melting point of the clay binder mixture, the binder composition may be made without the addition of bentonite.

If bentonite is added, it is used at no more than 4-5% by weight of the final mixture.

This is because clay causes large shrinkage during firing.

The ball clay content of the complete mixture is between 10 and 10 of the final mixture.
It can vary between 30% by weight.

Below 10%, the result is a mixture with poor compressibility and low binder content, and above 30%, some of the alumina filler added to the binder loses its effectiveness and the quality of the sintered product decreases. It won't be the best.

The second basic component contained in the mixture is a manganese compound,
Preferably it is manganese dioxide, which acts as a suitable flux for the clay during firing.

This flux controls the density of the product during firing, and the degree of density is related to the amount of flux added to the mixture and the firing temperature.

For example, if manganese is not present, 1600 to 1
A hard and dense grindstone can be obtained only when fired at a temperature of about 6500C.

If 5% manganese dioxide is added, the firing temperature can be significantly lowered.

Preferably 7% m-manganese oxide is added.

This is the amount that burns best in a standard Orton cone 12 furnace.

When fired in cone 12, manganese dioxide contents of less than 5% will result in a soft product, but mixtures fired at elevated temperatures above the preferred range will result in optimum wheel density.

When the manganese content of the mixture exceeds about 9% and is fired in cone 12, bulges and depressions occur in the product.

For firing temperatures within the conventional ceramic stone firing range of 10 to 16 Orton cones, manganese dioxide is preferably added in the range of 6 to 8% by weight of the final mixture.

The amount of manganese dioxide required is related to the specific calcination temperature desired for the product, increasing the amount of manganese if a lower calcination temperature is used, and decreasing the amount of manganese if a higher calcination temperature is used. .

When MnO2 acts as a ceramic flux, it becomes fluid at a temperature lower than that of the Al120s SiO acid component of the clay binder, and the resulting viscous glass pulls the stone mass due to surface tension, achieving a predetermined density. The elastic modulus can be obtained.

The tension or controlled contraction of the binder surrounding the abrasive particles reduces the porosity created by the pressing operation, resulting in a denser product.

Further, during firing, Mn 02 loses oxygen and becomes Mn2O3, and finally becomes Mn3O4.

This free oxygen plays the role of ring-forming the remaining carbon of the ball clay, and also completely oxidizes the glass forming body such as SiO□.

Soda is added separately as a component of the filler described below.

Approximately 1.5% by weight of the final grinding mixture weight is soda ash.
Acts as an additional flux to make the binder more fluid.

If soda is present in the selected filler component of the binder, no additional addition is necessary if the final mixture contains approximately 1.5-1.6% soda.

The vitreous ceramic binder formed by the action of MnO□ and soda provides strong adhesion to the Al2O3 abrasive particles.

It is well known that the surface must be wetted in order for glue or adhesive to adhere to the surface, but this adhesive glass is formed at a relatively low temperature by the action of a fluxing agent and has a certain degree of surface tension. This allows the abrasive particles to be tightly bonded without wetting the abrasive surface as in the case of glue.

The viscous vitreous binder is also a strong solvent of Al2O3, so the surface of the abrasive is dissolved by the liquid glass,
Ensures adhesion or wetting of abrasive material with glass.

Manganese oxide is soft manganese ore (Pyrolusite)
, Hausmannite, Manganite, Rhodochrosite
odochr-os ite), Rhophyroxene Rh
odon ite) or smooth rock (Rp
Mn 02-Ad, such as
203-SiO□ can be used in any form of bound minerals or chemicals.

Pyrosite is suitable for use as it is abundant and the cheapest.

Soda can be added if desired in the form of sodium carbonate, which loses CO□ to form soda, or is used as a component of the binder mixture as shown below.

The third basic component of the grinding wheel of this invention is crystalline alumina in the form of dust collector particles and/or Bayer process alumina form.

Such crystalline alumina exhibits certain abrasive properties when calcined wheels are used.

This crystalline alumina is initially added to the mixture of this invention as part of the binder.

This component also imparts some of the abrasive action of aluminum oxide to sphere grinding, while imparting hardness, durability, and long wear resistance to the essentially crystalline binder.

It is believed that this fine particle size alumina uniformly dispersed in the binder makes the product superior to conventional spherical grinding wheels.

100 microns may include any particle size, but
Fine aluminum oxide of any crystalline form is used, mostly with grain sizes below 50 microns, but with an average grain size of 7.
~12 microns.

The alumina filler accounts for 15-60% by weight of the final dry mixture.

Some fused alumina products have soda impurities in them, and when this material is crushed, the soda causes the formation of beta alumina crystals, which are softer than alpha alumina and are therefore selective in dust collectors. It has a tendency to be separated into two parts.

Beta alumina, which is relatively soft, is easily ground to a fine particle size and collected in the dust collector of the grinding system.

When dust collector particles are used as filler,
Sufficient soda is present in the filler.

If Bayer's alumina is used, the soda content must be sufficient to give the mixture the proper soda content.

The fourth added component of this mixture is acacia grains.

This serves two purposes; one is that the relatively large abrasive particles increase the grinding rate of the ball bearing;
Second, relatively large grids of fused milled aluminum oxide are produced by sintering the compositions of this invention with a binder to control the porosity and thereby control the modulus of elasticity.

As mentioned above, the grinding speed of the wheel is determined by the degree of porosity and elastic modulus.

The cutting rate and grinding efficiency are directly related to the addition ratio (wt%) of abrasive particles to the combined cutting weight in the grinding wheel.

As the weight percent of abrasive particles relative to the weight of binder increases, the porosity also increases.

A volumetric binder mixture containing fine alumina dust collector particulates and/or Bayer's alumina shrinks during firing to form a dense spherical grinding wheel, whereas the already pre-shrunk large particle size abrasive Since the material particles do not shrink when the binder shrinks, pores are formed.

Due to this, the shrinkage of pre-shrinked abrasive grid components and mixed compositions containing alumina-containing ball clay, manganese oxide-soda flux and dust collector and/or Bayer's alumina filler are unique. , it can be explained that the abrasive particles act to reduce the elastic modulus by decreasing the density of the ball abrasive wheel and increasing the porosity.

A range of relatively large size abrasive particle loadings (percentage) is evident in FIGS. 1 and 3.

Such alumina abrasive particles account for approximately 10% of the weight of the binder.
It is desirable that the range is from 50% to 50%.

This 50% upper limit is determined relative to the total weight of the binder mixture containing dust collector and/or bayer alumina included in the binder weight.

Abrasive particles of 50% by weight of the total weight of each component appears to be the upper limit for this product.

In order to manufacture a sintered wheel with an elastic modulus of approximately 110 or more, the remaining 50% by weight must be made of clay, manganese, soda,
and an alumina-containing binder in an alumina dust collector and/or a bayer.

If the fine filler component in the binder increases to 60% of the weight of the grinding wheel, the relatively large size of the abrasive particles in the grinding wheel can be reduced to zero; It is difficult to press mixtures containing
Furthermore, this is not a desirable mixture because the finished wheel will be too hard and will grind very slowly.

Since such hard, dense grindstones can withstand very high pressures, the composition of this mixture is extremely useful when such grinders are suitable for use.

Each has a diameter of 60.96 crIl (24 inches), 91.
44 cm (36 inches), thickness 7.62 crfL
(3 inches).

10, 16cTL (4 inches), center hole diameter 30.4
8crrL (12 inches), 45.72CrIL (
Two grinding wheels of different sizes (18 inches) were invented by Otsu for ball grinding.

Ranging from hard to soft with the following compositions: *38A is a very pure fused alumina abrasive with concentrated beta alumina particles, which are used in alumina grinding operations. Collected with a dust collector (sold by Two Tone Company).

This dust collector particulate is generally in a weak form (5 hap
e) and is highly variable from 2 to 50 microns, with some particles reaching 100 microns, but the average particle size is about 7 to 12 microns.

The alumina dust collector particulates of this application are of this material or commercially available equivalents.

※※E67 is a conventional Bayer method alumina.

The grain size of this crystalline alumina is 2 to 15 microns, with an average grain size of 7 microns.

※※※E1 is a "regular" fused alumina grid sold by Two-Tone Company obtained from molten bauxite in an arc furnace.

After the dry mixing was completed, 6% by weight water was added to complete the mixing.

This mixture yields 140.62 kg/c of unfired grinding wheel.
Cold pressed wt.

After drying in air, it was calcined in an Orton cone 12.

Typical data for the above-mentioned wheel are as follows.

Typical chemical values (wt%) for this wheel are: Al2O379% 8102 13% Mn 304 6.4% Other oxides 16% 38A, such as when Bayer's alumina is used as filler. When soda ash is added in place of soda in the DCF, a typical calcining wheel has the following composition.

Ball clay 20 (wt%) Bentonite] (〃) Mn02 7 (tt) Bayer method A#20a 40.5 (tt) Soda ash l, (tt) Melting 7
'Lyif average grain 3° (7) A ball bearing grinding wheel with 10% by weight addition of 100 mesh alumina abrasive with particle diameter 173 micron melt grinding is superior to a conventional grinding wheel containing the same abrasive grid of the same size and content. It lasted 4 times longer.

However, the grinding wheel of this invention cut at half the speed of the commercially available grinding wheel.

This lack of cutting speed can be easily reversed by increasing the content of abrasive particles in the wheel relative to binder weight in order to lower the elastic modulus and increase the porosity.

The composition of this invention is mixed and then 77.5ky/c
rtt to 15 skg/ff1(1/2 to 1) ton/1n2), ground and dried using conventional grinding wheel manufacturing processes.

Pressures of 31-310 kg/i (2/10-2 t/i♂) are used.

If a hot press device is used, it should be used at a pressure of no more than 500 lb/1n2, which is compatible with the strength of the mold.

The firing process for these compositions is similar to that for firing conventional spherical grindstone compositions.

The preferred process is to use a tunnel furnace, and the usual process is to fire in an Orton cone of about 12 mm, and the oven is placed in sand on a suitable vat.

The wheel described here shrinks linearly by 5 to 9%, but the overall shape of the wheel is maintained, and no matter how much the binder melts or becomes limbs during firing, there will be no obvious melting or depression, bubbles, or There are no foxtails or anything like that.

It should be noted that scratches, chips, spots, scratches, etc. on the surface of the unfired grindstone will clearly appear on the fired grindstone.

After firing, the wheel retains its cylindrical shape and has a flat surface, making it necessary to adjust the length and size of the pre-made wheel for grinding certain steel spheres (used in traditional ball bearing grinding processes). can do.

In addition to virtually eliminating the expense of the reshaping operations required in the prior art, the present invention reduces process time, allowing a stone to meet customer specifications to be provided in a very short period of time.

After the firing process is completed, the cracks, dimensions, and
The elastic modulus and density are examined.

Most grinders made by the process of this invention pass inspection and are usually ready for shipment without the need for any finishing operations.

Other compositions within the scope of this inventive concept may be used to meet customer needs.

A wheel with an elastic modulus of 110 to 170-180 was designed using fused and ground alumina and grains with an average particle size of 63 microns (240 grit) and an average particle size of 173 microns (100 grit), and with reference to Figure 1. Good morning.

Compositions with elastic modulus and density within the range specified by the 10-50% abrasive line and A curve, 8 curve exhibit acceptable linear shrinkage and do not require reshaping of the firing wheel. .

If the grinding wheel is not pressed at least to the minimum limit,
Unfired grindstones cannot be handled properly.

Curve A is 31 kg/i (2/ i 0 ton/i, 2
) shows the elastic modulus and porosity (density) of the sintered stone of the surface composition pressed.

Curve B represents the results obtained by applying a pressure of 3 i 0ky/ff1 (2 tons/1n2).

Applying too high a pressure will result in flaking, so
The range enclosed in the figure is the preferred range of the present invention.

In some cases, a light reshaping may be required to perfect the firing process, but usually this is rarely necessary and most wheels are used as-fired. can be done.

Specially shaped or thin stones are pressurized (but not fired).
After that, it can be made by cutting and forming, but since this invention usually does not require reshaping, a special shaped wheel can also be made at a very low cost.

Average particle size is 63 microns (240 grid), 122
micron (150 grid), 142 micron (120
Grains ranging from 173 microns (100 grits), 173 microns (100 grits), or 266 microns (80 grits) are used, depending on the ratio of grains added to the binder weight and during firing to control the elastic modulus. It affects only the relationship that controls the amount of linear contraction that occurs.

Silicon carbide and grains may be used in a range of 4-12% by weight.

Compared to this, in the case of alumina and grains, it is 15 to 47% by weight.
It is.

However, it is not preferred to use silicon carbide.

This is because the use of silicon carbide causes difficulties during firing which adversely affects the finished shape and requires reshaping of the finishing wheel.

In contrast, this does not occur with the alumina grid shown here.

[Brief explanation of drawings]

Figure 1 shows the relationship between the elastic modulus and compacted density of a cold-pressed unfired wheel obtained by firing it, and Figure 2 shows the relationship between the density, elastic modulus, and firing density of a fired wheel. Figure 3 is a diagram showing the relationship between the volume percentage of pores in the binder, and Figure 3 is a diagram showing the change in elastic modulus corresponding to a change in abrasive content with respect to binder weight, and the difference in effect when the abrasive grid size is different. It is.

Claims (1)

Claims: 1. 10 to 30% by weight of the dry mixture forming the grinding wheel, and 15 to 60% by weight of the mixture having a major diameter of less than about 44 microns. , crystalline alpha alumina filler in the binder and 0 to 50% by weight of the dry mixture of A403. s
ic and mixtures thereof, having an average particle size of 266 microns or finer, and wherein the binder and abrasive mixture contains at least 5-9% by weight of oxidized A hard, dense ceramic for finishing sesame ball bearings containing manganese. 2.5 to 9 of the final dry mixture containing manganese oxide.
A grinding mixture is prepared by mixing the ball clay and manganese oxide in an amount of 15% to 60% by weight of the final dry mixture and having an average particle size of 2 to 15 microns. fine-grained crystalline alumina filler is mixed into the manganese oxide and ball clay mixture, and granules with an average particle size of 266 microns or finer are added in an amount of 0 to 50% by weight of the final mixture to form the final product. 31-3 i okg to control sintered density
The resulting mixture is cold pressed at a pressure of /i (2/i 0-2 / 1n2) and then has a sintered density of about 2.80-3.25 g/cc and an elasticity of about 105-175 dynes/d. Orton cone 10 to produce a ceramic bonded grinding wheel with
16 to 16, and designed to meet steel ball bearing grinding specifications with respect to grain type and size, cutting rate, and finish, prior to use. A method of manufacturing a grinding wheel that requires no or almost no reshaping.