JPH0752023A - Abrasion method - Google Patents

Abstract

PURPOSE:To polish extremely effectively an abrasion target having a complicated shape including small recessed parts grooves, etc., for example, recessed parts or even including the insides of grooves of a bracket for straightening teeth, etc. CONSTITUTION:Fluid which is formed by mixing at least spherical glass beads and granular abrasives having grain sizes smaller than those of the spherical beads in liquid medium is moved relatively to an abrasion target while bringing the liquid into contact with the abrasion target.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention particularly relates to a polishing method for polishing the inside of minute grooves or recesses formed in an object to be polished.

[0002]

2. Description of the Related Art A barrel polishing method has been conventionally known as a method for polishing an object to be polished having a complicated shape. The barrel polishing method is a method in which polishing particles, water, and an object to be polished are put in a container, and the object to be polished is polished by rotating, vibrating or planetary moving the container. There are many types of materials for polishing particles such as ceramics, polymers or composite materials of both, natural products such as walnut shells and corn seeds, and various shapes such as irregular shape, spherical shape, rhombus, triangular pyramid, etc. It has been proposed and used properly according to the purpose (for example, Japanese Patent Application Laid-Open No. 1-177965).
177967). According to the conventional barrel polishing method, it is possible to efficiently polish the surface of a complicated shape such as a relatively large gear, a metal watch band, jewelry and a ring pedestal, and a camera part.

By the way, like some dental instruments,
In the case where the surface has fine recesses or grooves of 1 mm or less, it may be desired to polish the inside of the recesses or grooves. For example, an orthodontic bracket has a complicated overall shape and is formed with thin, long and long grooves having a groove width of about 480 μm, a depth of about 700 to 900 μm, and a length of about 3 mm (actual opening flat 2- 139617). Even if it is attempted to polish the inside of the groove of the orthodontic bracket by the conventional barrel polishing method, the abrasive particles commercially available for barrel polishing have a particle diameter of 1 mm or more in general, and therefore the particle diameter is not changed. Even if it is used, the inside of these minute grooves cannot be polished.

Therefore, if the orthodontic bracket is barrel-polished using commercially available abrasive particles having a particle size of 0.5 mm or less, which are not for ordinary barrel polishing,
Although the polishing particles can enter the grooves or dents, the abrasive particles that have entered will instantly be clogged in the grooves or dents, and the grooves or dents cannot be polished.

Therefore, the particle size is further reduced to 50 μm.
When the following general abrasives are used as the abrasive particles, the abrasives will not be clogged in the grooves and dents, but this time, when trying to polish the recesses and grooves sufficiently, the protrusions are excessively worn. However, there arises a problem that the dimensional accuracy is significantly deteriorated. Further, since the abrasive particles generally have an irregular shape, a large scratch is made on the surface of the object to be polished, so that there is a problem that a good polished surface cannot be obtained.

As described above, it was not possible to satisfactorily polish the inside of minute recesses and grooves simply by reducing the abrasive particles in the conventional barrel polishing method.

As a method further improving the barrel polishing method as described above, there is a method disclosed in JP-A-1-177965. In this method, an object to be polished such as glass is barrel-polished with a mixture of a spherical synthetic resin, an abrasive and water.

However, according to this polishing method, a synthetic resin and an abrasive having a small particle size are used for polishing glass and the like, and although a relatively flat surface and recesses can be polished, this can be used as it is for polishing a complex shaped part. There was a problem to apply. The reason is that the polishing speed is extremely slow, and the spherical synthetic resin is clogged in a groove having an extremely narrow width in a short time, so that the inner surface of the groove cannot be polished cleanly. It is considered that the reason why the spherical synthetic resin is clogged in the groove is that the spherical synthetic resin itself has a low hardness and thus wears quickly and the shape becomes irregular. Further, the reason that the polishing speed is slow is considered to be that the specific gravity of the spherical synthetic resin is smaller than that of the ceramics and the spherical synthetic resin is lifted to lower the polishing ability.

A method disclosed in Japanese Patent Laid-Open No. 4-329946 has been proposed as a method for polishing a dental instrument, particularly an article having a complicated shape having small irregularities or narrow grooves such as an orthodontic bracket. There is. JP-A-4-3299
In the method disclosed in Japanese Patent Publication No. 46, a mixture of spherical ceramics having a particle size of 30 to 400 μm, an abrasive having a particle size of 20 μm or less, and a liquid, and fine grooves or recesses formed by ceramics or a composite material containing ceramics are provided. The dental instrument is put into a container and the container is moved to polish the dental instrument.

In this case, the spherical ceramic material is
It is disclosed that zirconia, silica, alumina, silicon carbide, silicon nitride and the like can be used, and as the abrasive, general abrasives such as alumina, zirconia, silicon carbide, silicon nitride, cerium oxide and diamond can be used. . Spherical ceramics have high hardness, little wear, can maintain a constant shape, and have relatively good fluidity even when mixed with an abrasive. Therefore, it is less likely that spherical ceramics, which are polishing particles, will be clogged in recesses such as narrow grooves. Further, according to this method, the spherical ceramics enter the narrow grooves or recesses of the object to be polished and rub against the abrasive, so that the inner surface of the narrow grooves or the small recessed portion can be ground. Further, since the spherical ceramics are spherical, the surface of the object to be polished is not scratched, and the deterioration of the dimensional accuracy due to the abrasion of the convex portions can be minimized.

[0011]

By the way, in the method disclosed in Japanese Patent Laid-Open No. 4-329946 described above, a portion where spherical ceramics are hard to contact, such as a recessed portion, has a significantly slower polishing speed than other portions. There is a problem. In particular, when polishing a concave portion of a material having high hardness such as ceramics, the polishing time becomes very long and the polishing cost becomes high. Therefore, it is necessary to use a highly efficient polishing machine such as a centrifugal barrel polishing machine for barrel polishing ceramics and the like. Since this centrifugal barrel polisher applies centrifugal force to flow the contents of the polishing container, the polishing efficiency is higher than that of a conventional barrel polisher.

However, since the amount of frictional heat generated by the flow of the contents is large, there is a problem that the temperature in the polishing tank rises when the polishing time is prolonged. Generally, the inner surface of the polishing tank is lined with urethane rubber or the like, and when the temperature exceeds 50 ° C., the urethane rubber lining is severely worn, which is a problem.
Further, since the polishing tank is a sealed container, the internal pressure of the polishing tank rises when the temperature rises to 50 ° C. or more, and the lid may fly and the contents may be blown out, which is extremely dangerous. For this reason, when the centrifugal barrel polisher is operated for a long time, it is necessary to suspend the polishing from time to time to cool the polishing tank. In the case of commonly used polishing particles, the continuous operation time of the centrifugal barrel polishing machine is about 30 minutes, and the rest time for cooling is about 2 hours. In other words, when polishing with a centrifugal barrel polisher for a long time, the time required for polishing becomes 3 to 5 times longer than the operating time. Of course, since other barrel polishers have a long polishing time, the polishing also requires a long time.

The spherical ceramics used for polishing is a sintered body obtained by forming a ceramic raw material powder into a spherical shape by some method and sintering it. Therefore, fine irregularities of crystal particles are always present on the surface of the spherical ceramic. Further, ceramics generally have a specific gravity of 3.0 to
Since it is relatively large at 6.1, the flow resistance in the liquid is relatively large. As described above, it is difficult to reduce the frictional resistance generated on the surface of the spherical ceramic during flow due to the shape distortion, the fine irregularities on the surface, and the relatively large specific gravity. Therefore, the temperature of the polishing tank rises sharply due to the frictional heat of polishing, and the continuous operating time of the polishing machine cannot be extended.

The present invention has been made in view of the above-mentioned conventional problems, and an object of the present invention is to grind an object to be ground having minute grooves or recesses at a high grinding speed and also to perform friction. An object of the present invention is to provide a polishing method capable of continuously operating the polishing machine for a long time because the temperature of the polishing tank is not increased by heat.

[0015]

In order to solve the above-mentioned problems, a polishing method according to the present invention comprises: (Structure 1) At least spherical glass beads in a liquid medium and a particle size smaller than that of the spherical glass beads. A structure characterized by polishing a polishing object by bringing a fluid containing a mixture of granular polishing materials into contact with the polishing object and moving them relatively to each other, and (configuration 2) at least a liquid medium Put an object to be polished in a container containing a fluid containing spherical glass beads and a particulate abrasive having a particle size smaller than that of the spherical glass beads, and move the container or stir the fluid. By polishing the object to be polished, and as an aspect of this configuration 1 or 2, (configuration 3) in the polishing method of configuration 1 or 2, The particle size of the beads is 30 to 400 μm, and the particle size of the granular abrasive is 20 μm or less. As a mode of this structure 3, (configuration 4) any one of configurations 1 to 3 In the polishing method, the composition ratio of the granular abrasive material to the spherical glass beads is 1 to 50% in volume ratio, and as an aspect of any one of Configurations 1 to 4, (Configuration 5) In the polishing method of any one of 1 to 4, the spherical glass beads have a specific gravity of 3 or less, and further, in any one of the configurations 1 to 5, (configuration 6) In the polishing method according to any one of 5 above, the object to be polished is formed of ceramics or a composite material containing ceramics, and has a width of 450 to 600 μm and a depth of Has a groove or a recess having a size of 700 to 1300 μm, and as an aspect of any one of Configurations 1 to 6, (Configuration 7) In the polishing method according to any one of Configurations 1 to 6, The object to be polished is a bracket for orthodontics.

[0016]

According to the above-mentioned constitution 1, while the liquid medium is mixed with at least the spherical glass beads and the granular abrasive having a particle diameter smaller than that of the spherical glass beads, the fluid is brought into contact with the object to be polished. By making these relatively move, it becomes possible to extremely efficiently polish the inside of the recess or groove of the object to be polished having a complicated shape having minute recesses or grooves.

This is considered to be due to the following reason. That is, first, since the spherical glass beads are spherical, have a smooth surface, and have an appropriate specific gravity, it is possible to easily impart the property of actively moving even when they enter the inside of the recess or groove of the object to be polished. . On the other hand, its own polishing ability is inevitably low. On the other hand, abrasives have excellent polishing ability, but especially those with a particle size that is small enough to fit in the minute recesses or grooves of the object to be polished, the movement of the abrasive alone in the recesses or grooves becomes very slow. It has such a surface shape and specific gravity that it will end up. However, as described above, if the two are properly mixed, the property that the spherical glass beads can actively move in the recess or groove and the polishing ability of the polishing material complement each other's weaknesses and are effective together. It is thought that the inside of minute recesses and grooves can be efficiently polished by utilizing this feature. Moreover, since the spherical glass beads have a very smooth surface, heat generation due to friction with the object to be polished can be suppressed to an extremely small level.

According to the constitution 2, the conventional barrel polishing technique is applied to obtain the same action as the constitution 1 by a relatively simple method.

Further, according to the constitutions 3 to 5, the constitution 6 or 7 which has been very difficult to polish by the conventional barrel polishing.
It has become possible to polish the inside of a minute recess or groove of an object to be polished as described above very efficiently.

[0020]

EXAMPLE A polishing method according to an example of the present invention will be described in detail below.

In the polishing method according to one embodiment of the present invention, the object to be polished is, for example, an orthodontic bracket,
It is formed of ceramics or a composite material containing ceramics and has a groove or a recess having a width of 450 to 600 μm and a depth of 700 to 1300 μm. It is used when polishing.

The construction of this embodiment is such that a mixture of spherical glass beads, an abrasive and a liquid and an object to be polished are put in a container and the container is moved, or the contents of the container are stirred and mixed. It is a method of polishing and is a method based on the barrel polishing method.

Here, the polishing efficiency in barrel polishing is
It is said that it depends on the difference in relative flow velocity between the polishing particles and the object to be polished (part). That is, it is considered that the larger the difference in flow velocity between the polishing particles and the object to be polished, the higher the speed at which the particles to be polished move on the surface of the object to be polished, so that the polishing efficiency is improved. Particularly, in the case of a part having a complicated shape, the flow speed of the object to be polished (part) is lower than the flow speed of the abrasive particles. Therefore, it is considered effective to increase the flow velocity on the abrasive particle side in order to increase the relative velocity difference. As a result of the comparative study, in order to increase the flow rate,
It has been found effective to use abrasive particles having a low specific gravity, a spherical shape and a smooth surface.

However, first, although it is possible to increase the flow velocity for abrasive particles having a spherical shape and a smooth surface,
On the contrary, the polishing ability of the particles themselves decreases. Also, the smaller the specific gravity of the abrasive particles, the faster the flow velocity,
On the contrary, the pressure at which the abrasive particles come into contact with the surface of the object to be polished decreases, and the polishing rate may decrease.

As a result of investigating which of these contradictory effects governs the polishing rate, the side of the reduction of the polishing ability of the polishing particles themselves is compensated by adding an abrasive of 20 μm or less to the polishing solution. It was found that increasing the fluidity of the particles is effective in improving the polishing rate, and that the frictional heat generated by the flow of the abrasive particles can be reduced by using the abrasive particles with good fluidity. . The present embodiment is based on the results of this examination.

In the polishing method according to this embodiment,
The spherical glass beads serve to rub the fine abrasive particles on the surface of the object to be polished. In order to polish the surface of a narrow groove or a recess, the particles of the spherical glass beads need to enter the recess, and it is desirable that the size of the glass bead is as small as possible in order to polish the details.

Here, the size of the glass beads is 400 μm.
If it exceeds m, frictional heat increases, so the upper limit of the size of the glass beads is limited to 400 μm.

Further, in order to prevent the glass beads from being clogged in the groove or the like, it is necessary to use as small particles as possible in addition to the spherical particles. Especially for polishing a deep and long groove such as an orthodontic bracket, 200μ
It is desirable to use spherical glass beads of m or less.
However, if the diameter of the spherical glass beads is 30 μm or less, the fluidity of the glass beads decreases, so the lower limit of the diameter of the glass beads is limited to 30 μm. Further, in order to prevent the beads in the narrow grooves or recesses from being clogged, it is necessary that the spherical glass beads do not change their shape due to abrasion.

Next, the spherical glass beads used in this polishing method will be described.

The spherical glass beads are produced by lowering the powdered glass in a high temperature furnace having a glass softening temperature or higher and then cooling it. Since the amorphous glass powder softens in the furnace and becomes spherical due to the surface tension, glass beads that are very close to a true sphere can be obtained at an extremely low cost. The spherical glass beads obtained by such a method have a smooth surface so that they can be used as a spherical lens.

Moreover, the specific gravity of glass is relatively small, such as 2-3, except for special ones such as optical glass. In particular, quartz glass is as small as 2.2, and even the most common soda-lime glass is about 2.5. Since spherical glass beads having a small specific gravity and a smooth surface have a small bead weight, it is possible to reduce the pressure exerted between the beads when flowing. In this case, when the specific gravity of the glass beads exceeds 3, the amount of frictional heat generated also increases, so the specific gravity of the glass beads is limited to 3 or less. There are polymer beads as beads with a smaller specific gravity, but due to their low hardness, the beads are subject to severe wear, and their shapes change, resulting in clogging of grooves and the like, which is not suitable for polishing complex shaped products. . On the contrary,
The Mohs hardness of the glass beads is as large as 6.5 to 7, and the abrasion of the beads and the change of the shape due to the polishing hardly cause any problem.

Further, as the abrasive, general abrasives such as alumina, zirconia, silicon carbide, silicon nitride, cerium oxide and diamond can be used. The average particle size of the abrasive is preferably 20 μm or less. This is because if it exceeds 20 μm, the polished surface becomes rough and the polishing effect is not fully exhibited. If it is 20 μm or less, the abrasive is crushed during polishing and becomes finer, so that a clean polished surface can be obtained. It is preferably 0.2 to 10 μm.

When the amount of the abrasive added is small, the polishing rate is slow, and when it is too large, the spherical glass beads are likely to be clogged in the narrow groove or recess. The upper limit of the amount added varies depending on the type and particle size of the abrasive, but is about 50% of the volume of the spherical glass beads. If it exceeds 50%, the apparent viscosity of the polishing liquid increases, the movement of the spherical glass beads becomes poor, and the polishing speed decreases, which is not preferable. If it is less than 1%,
It is not preferable because the amount of the abrasive is small and the polishing speed is low.

The method of moving the container is not particularly limited, but it is preferable to use a barrel polisher. This method is a method in which an object to be polished and polishing particles are put in a container, and the container is wet (water is often used) or dry and rotation, vibration or planetary motion is applied to the container. By rotating or planetary motion of the container, the spherical glass beads flow, the abrasive particles are forcibly rubbed by the spherical glass beads on the surface of the object to be polished (part), and the surface is polished. In addition to the barrel grinder, a method of moving the container with a general mixer may be used. Further, polishing can also be performed by fixing the container and mixing the contents with a rotary feather or the like.

In the polishing method of this embodiment, water, alcohol or the like can be used as the liquid added together with the spherical glass beads and the polishing material, but it is not particularly limited.
As a rough guide, the volume of spherical glass beads is 0.5-
If it is about 3 times, polishing can be preferably performed.

Hereinafter, examples of actual polishing by the method of this embodiment (polishing examples) and examples of polishing by the conventional barrel polishing method (comparative examples) will be given.

(Polishing Example 1) An orthodontic bracket made of partially stabilized zirconia was polished under the following conditions.

In a 1 liter urethane container, spherical glass beads (soda lime glass) (specific gravity 2.5, particle size 10
0-200 μm) and 650 g (bulk volume 0.5 liter) and 50 g of alumina powder having an average particle size of 1 μm are added, and water containing 10% of a commercially available barrel polishing additive solution is added to adjust the volume of the mixture. It was 0.8 liter. The above orthodontic bracket was put in this barrel polishing container, and this container was mounted on a centrifugal barrel polishing machine. In order to prevent boiling of the polishing liquid, barrel polishing was performed by intermittent operation, the bracket was taken out of the container every 10 hours during operation, and the inner surface roughness of the groove was examined by the following method. The cross section of the groove was observed with a scanning electron microscope to measure the size of the surface irregularities. The unevenness of the groove surface is Rmax (JIS 0601)
The polishing time of 30 hours was required to smooth the surface to 1 μm or less. In the intermittent operation, the time during which continuous operation was possible was 4.5 hours, and the down time for cooling was 1 hour. Therefore, the total polishing time is 36.
It was 7 hours.

In this polishing example, 3 after the start of polishing.
When the temperature in the polishing container was measured and plotted every 0 minutes, a temperature curve as shown by the curve A in FIG. 1 was obtained. As is clear from the curve A, the temperature inside the container reaches 39 ° C. after 4.5 hours from the start of polishing.

COMPARATIVE EXAMPLE 1 Zirconia beads (partially stabilized zirconia) were placed in a 1 liter urethane polishing container.
(Specific gravity 6.0, particle size 100-200 μm) 1850 g (bulk volume 0.5 liter) and alumina powder 50 g having an average particle size 1 μm were added, and water containing 10% of a commercially available barrel polishing additive solution was added. In addition, the volume of the mixture was set to about 0.8 liter. The above-mentioned ceramic bracket was put in this barrel polishing container, and this container was mounted on a centrifugal barrel polishing machine. In order to prevent boiling of the polishing liquid, barrel polishing was performed by intermittent operation, the bracket was taken out of the container every 10 hours during operation, and the inner surface roughness of the groove was examined by the same method. In order to smooth the unevenness of the groove surface to Rmax of 1 μm or less, a polishing time of 50 hours was required as an operation time. In the intermittent operation, the time during which continuous operation was possible was 1.5 hours, and the downtime for cooling was 1 hour. Therefore, the total polishing time was 83.5 hours. More than twice the time as in Example 1 was required.

In this comparative example, the temperature in the polishing container was measured and plotted every 30 minutes after the start of polishing in the same manner as in Polishing Example 1. As a result, a temperature curve as shown by curve B in FIG. 1 was obtained. Was obtained. As is clear from the curve B, the temperature in the container reached 39 ° C. as early as 1.5 hours after the start of polishing, and it was found that the temperature rise was more severe as compared with the polishing example 1 using spherical glass beads.

(Abrasion Example 2) Spherical glass beads (soda lime glass) (specific gravity 2.
5, Alumina powder 1 having a particle size of 100 to 200 μm) of 1300 g (bulk volume 1.0 liter) and an average particle size of 1 μm
Add 00 grams and add 10% of commercially available barrel polishing additive.
The added water was added to bring the volume of the mixture to 1.6 liters. An orthodontic bracket was placed in this container and the container was moved by a shaker mixer. Polishing time of 60 hours in continuous operation was required to smooth the unevenness of the groove surface of the bracket to 1 μm or less in Rmax.

(Comparative Example 2) Zirconia beads (specific gravity 6.0, particle size 100 to 20) were placed in a 2-liter nylon container.
0 μm) to 3700 g (bulk volume 1.0 liter) and 100 g of alumina powder having an average particle size of 1 μm, and water containing 10% of a commercially available barrel polishing additive liquid was added,
The volume of the mixture was 1.6 liters. An orthodontic bracket was placed in this container and the container was moved by a shaker mixer. Rmax on the groove surface of the bracket
The polishing time of 140 hours was required in continuous operation in order to smooth to 1 μm or less.

(Polishing Example 3) Spherical glass beads (specific gravity 2.5, particle size 100 to 2) were placed in a 1 liter glass polishing container.
00 μm) and 650 g (bulk volume 0.5 liter) and alumina powder having an average particle size of 1 μm 50 g, water containing 10% of a commercially available barrel polishing additive solution was added, and the volume of the mixture was 0.8 liter. And A ceramic bracket was placed in this container, and the mixture was mixed at a rotation speed of 1000 rpm. Rma on the groove surface of the bracket
Polishing for 40 hours in continuous operation was required for smoothing to 1 μm or less in x. In addition, in order to perform continuous operation,
The outer surface of the glass container was cooled with water.

COMPARATIVE EXAMPLE 3 Zirconia beads (specific gravity 6.0, particle size 100 to 2) were placed in a 1 liter glass polishing container.
00 μm) 1850 g (bulk volume 0.5 liter)
And 50 g of an alumina powder having an average particle diameter of 1 μm were added, and water containing 10% of a commercially available additive liquid for barrel polishing was added to make the volume of the mixture 0.8 liter. A ceramic bracket was placed in this container, and the mixture was mixed with urethane blades at 1,000 rpm. In order to smooth the unevenness of the groove surface of the bracket to 1 μm or less in Rmax, polishing for 85 hours was required in continuous operation. The outer surface of the glass container was water-cooled for continuous operation.

In the above-mentioned embodiment, while at least the spherical glass beads and the granular abrasive having a particle diameter smaller than that of the spherical glass beads are mixed in the liquid medium, the fluid is brought into contact with the object to be polished. As a method of moving these relatively, the example of applying the method of barrel polishing in which a fluid and an object to be polished are put in a container and the container is moved is described. It is also possible to use a method in which the material is moved in the body or a fluid is sprayed on the object to be polished.

[0047]

As described in detail above, in the polishing method according to the present invention, a fluidized medium is formed by mixing at least spherical glass beads and a granular abrasive having a particle size smaller than that of the spherical glass beads. By making them move relative to each other while bringing the body into contact with the object to be polished,
The object to be polished having a complicated shape having minute recesses or grooves, for example, the inside of recesses or grooves of an orthodontic bracket or the like, can be polished extremely efficiently.

[Brief description of drawings]

FIG. 1 is a diagram showing a temperature rise curve in a polishing container in polishing example 1 and comparative example 1.

Claims (7)

[Claims] 1. A fluid comprising at least spherical glass beads and a granular abrasive having a particle size smaller than that of the spherical glass beads mixed in a liquid medium is brought into contact with an object to be polished and relatively moved. A polishing method characterized by polishing an object to be polished by performing the polishing. 2. An object to be polished is put in a container containing a fluid containing at least a spherical glass bead and a granular abrasive having a particle size smaller than that of the spherical glass bead in a liquid medium. A polishing method comprising polishing an object to be polished by moving the object or stirring the fluid. 3. The polishing method according to claim 1, wherein the spherical glass beads have a particle size of 30 to 400 μm, and the granular abrasive has a particle size of 20 μm or less. . 4. The polishing method according to claim 1, wherein the composition ratio of the granular abrasive to the spherical glass beads is 1 to 50% by volume. 5. The polishing method according to claim 1, wherein the spherical glass beads have a specific gravity of 3 or less. 6. The polishing method according to claim 1, wherein the object to be polished is formed of ceramics or a composite material containing ceramics, and has a width of 450.
The polishing method is characterized by having a groove or a recess having a size of ˜600 μm and a depth of 700 to 1300 μm. 7. The polishing method according to any one of claims 1 to 6, wherein the object to be polished is an orthodontic bracket.