JPH01130908A - Manufacture of ceramics ball - Google Patents

Abstract

PURPOSE:To shorten the time of grinding work and obtain a highly spherical ball by a method wherein the ball is formed by employing the kneaded substance of ceramic powder, is added with a composition consisting of the principal constituent of thermoplastic organic polymeric compound as binding agent, and the green ball is worked to obtain a true sphere, thereafter, is degreaed and sintered. CONSTITUTION:A ball, formed by adding ceramic powder with organic thermoplastic polymeric compound and plasticizer or lubricant, if necessary, is prominent in wet grinding workability and degreasing property while the degreased and sintered ball shows a high-degree sphere, therefore, the good-quality ceramic ball may be obtained with the short time of grinding work. The organic thermoplastic polymeric compound, such as polyethylene or polystyrene, provides a molded form with a strength and toughness and, further, is provided with water- proofing property, therefore, the grinding and grinding properties thereof are excellent whereby chipping and peeling may be prevented. Further, molding property upon molding or degreasing property upon degreasing may be improved by adding plasticizer, lubricant and the like.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method and improvement for manufacturing ceramic balls.

[Prior Art] Ceramic balls used in ball bearings and the like are required to have highly accurate sphericity.

Known methods for manufacturing balls include powder pressing, cold isostatic pressing, and injection molding. Furthermore, in order to obtain a molded ball with high sphericity, the present inventor created a ball in which a mixture of hot extruded inorganic powder and a thermoplastic binder is sandwiched between a pair of spherical molds while it is still flexible. We considered the molding method and filed an application (Japanese Patent Application No. 61-224018,
No. 62-055420).

After sintering, the balls formed by each of the above-mentioned methods were subjected to highly accurate pearl processing to be finished to a predetermined size using a ball grinder. Sintered ceramic balls are extremely hard, and therefore polishing of the ceramic balls requires an extremely long time, which increases the manufacturing cost of the ceramic balls.

Therefore, various methods have been tried to shorten the polishing time after sintering. First, there are powder pressing and cold isostatic pressing as methods for forming balls, but these methods have problems such as band-like protrusions on the compact or poor dimensional accuracy of the compact. Therefore, in order to improve dimensional accuracy, we attempted green processing in which the green material was polished before firing, but many of the materials were destroyed by the pressure applied during polishing. In order to increase the strength of the ball to withstand pressure, we also tried calcining it and then polishing it. However, the method of calcining and polishing increases the number of steps, making it complicated, and the total time required for polishing is not significantly shortened, rather increasing the cost.

Next, injection molding was considered.

Although the injection molding method yields a ball with high dimensional accuracy, it is difficult to remove the gate portion, and the gate portion tends to become flat after removal, making it difficult to improve the sphericity of that portion. As mentioned earlier, the method for forming ceramic balls is to mold a mixture of ceramic powder and a thermoplastic organic binder into a flexible mixture between a pair of hemispherical molds, resulting in a highly spherical form. Although he was able to get the ball, the sphericity was still insufficient.

Therefore, the inventor of the present application focused on polishing such a molded ball with a green ball before degreasing to further improve the sphericity after sintering.

[Problem to be solved by the invention 1 Ceramic molded products are generally processed using lathes, milling machines, etc. for degreasing and green processing before firing, but the green molded bodies of balls are polished to improve their sphericity. No processing is performed. In other words, pearl machining of sintered balls is similar to machining of steel bearing balls.
A known method is to sandwich a large number of balls between two processing plates and apply pressure to rotate and polish the upper and lower plates at different rotation speeds.
If you try to apply this method directly to green balls, it will not work. In general, green balls have low strength, so they cannot withstand the pressure of the vertically rotating polisher and are easily destroyed.Also, as the polishing continues, the polishing powder adheres to the polisher, degrading the polishing ability. This is because the green ball is likely to be thermally deformed due to the accumulation of frictional heat during polishing, making it impractical. By dripping abrasive grains and water onto the polishing disk, it is possible to maintain the polishing ability of the polishing disk and prevent the balls from heating up. However, green balls generally do not have very high water resistance, and during wet polishing in the above method, ceramic The force that binds the particles decreases and the green balls tend to collapse.

The object of the present invention is to perform green polishing on a molded ball, to perform the polishing smoothly without chipping or collapsing, and to improve the sphericity after sintering by green polishing. It is an object of the present invention to provide a method for manufacturing a ceramic ball that is not only significantly improved over those that do not, but also shortens the polishing time after sintering.

[Means for Solving the Problems] In order to achieve the above object, the inventor has conducted extensive research and has found that
A ball is formed using a mixture of ceramic powder and a composition mainly composed of a thermoplastic organic polymer compound added as a binder, and the green ball is pearl-processed using a wet ball polishing machine, then degreased and baked. It has been found that by bonding, a ceramic ball with high sphericity can be obtained.

As mentioned above, molded balls made using conventional powder presses do not have sufficient strength to withstand the pressure applied by a polishing machine, and
Many of the binders commonly used in molding and the like are water-soluble, such as polyvinyl alcohol and methyl cellulose, and these binders tend to dissolve during wet polishing, making it easy for the ball to break.

Therefore, we researched various binders that can withstand pressure, do not dissolve in water, give balls sufficient strength, and can be easily removed by degreasing before firing. We have found that compositions based on molecular compounds are most suitable.

Any molding method may be used to mold the mixture of thermoplastic organic binder and ceramic powder into a ball shape.
Injection molding is useful because it is versatile and highly productive. Also preferred is a molding method in which the material is sandwiched between a pair of hemispherical molds while it is still flexible.

By polishing the balls formed by these methods using a wet polishing machine that circulates water and abrasive grains, green balls with high pearl quality can be obtained in a short time and efficiently.

[Effect] Figure 1 shows an overview of the wet green polishing machine.

The green ball l before being degreased and fired is sandwiched between an upper polishing plate 2 and a lower polishing plate 3. Green ball 1 is placed between the upper and lower polishers.
Fill it in layers so that the balls do not stick to each other. The upper polishing plate 2 and the lower polishing plate 3 rotate at different rotation speeds,
In addition, the ball is pressurized by the weight of the upper board. A mixture 4 of abrasive grains and water is supplied to the polishing disk through a hose, discharged from the periphery of the lower polishing disk, and circulated. Such wet polishing prevents the polishing disk from clogging and heat generation, and polishes efficiently. In order to carry out such a wet polishing process, it is first important that the ball has sufficient strength to withstand the pressing force and that it has water resistance.

If the binder is not water-resistant, the green balls are likely to chip or break during wet polishing. Thermoplastic organic polymer compounds such as polyethylene and polystyrene not only provide strength and toughness to molded products, but also have water resistance, so they have good grinding and polishing properties and prevent chipping, peeling, etc.

Furthermore, by adding a plasticizer, a lubricant, etc. to a thermoplastic organic polymer compound such as polystyrene or polyethylene, the moldability during molding and the degreasing performance during degreasing can be improved. The amount of the thermoplastic organic polymer compound added varies depending on the type of ceramic, but is preferably in the range of 15 to 45 parts by weight per 100 parts by weight of ceramic powder such as zirconia or silicon nitride. If it is less than 15 parts by weight, it will be difficult to obtain sufficient strength for the molded ball to be used in wet green polishing, and if it is more than 45 parts by weight, degreasing properties will be poor and firing shrinkage will be large, resulting in a decrease in dimensional accuracy.

In this way, ceramic balls formed using a kneaded mixture of ceramic powder with a thermoplastic organic polymer compound and, if necessary, a plasticizer and a lubricant, have excellent wet polishing processability and degreasing properties. The bonded balls have high sphericity, and high-quality ceramic balls can be obtained with a short polishing time.

[Example] Next, the manufacturing method of the present invention will be specifically explained based on the drawings.

Silicon nitride (Si3N4) powder with an average particle size of 1.0 100
20 parts by weight of polystyrene, 1 part by weight of polyethylene
0 parts by weight, 5 parts by weight of dioctyl phthalate as a plasticizer, and a lubricant were added, and kneaded at 140'O using a pressure kneader. This kneaded product was kneaded and extruded using a hot cylinder, and while the kneaded product was still flexible, it was sandwiched between a pair of hemispherical molds to form balls.

The diameter of this molded ball is 13.3φ and the average sphericity is approximately 1.
It was 00 ru. 250 of these green balls were put into the wet ball polishing machine shown in Fig. 1, and the upper board 80r, p.
, m, lower board 4Or, p.

Wet green processing was performed for 1 hour at a pressure of 25 kg.

No balls were broken during wet green processing, and the sphericity after green processing was approximately 1107p and the ball diameter was 12.8φ. When this was degreased and sintered, the average sphere diameter was 9.9φ.
A good ceramic ball with an average sphericity of 15 gm was obtained. This sintered ball is finished polished to a sphericity of 2 to 3 J.
The time required for polishing the Lm ceramic balls was 6 hours.

On the other hand, the sphericity of a ball that was degreased and sintered without green processing was 12,071 m, and it took 48 hours to polish this ball to 2 to 3 pm.

Therefore, when green processing is performed, the polishing time is 7 hours in total, including 1 hour of wet green processing time and 6 hours of polishing time after sintering. On the other hand, the polishing time for the sintered ball without green processing was 48 hours, and the green processing according to the present invention reduced the polishing time to about 1/7.

[Effect of the invention] Sintered ceramic balls with high sphericity can be obtained by molding using a composition mainly consisting of a thermoplastic organic polymer compound as a ceramic binder and performing green processing using a wet ball grinder. . Therefore, the polishing time after sintering is significantly shortened, and the total of the polishing time required for green processing and the polishing time after sintering is approximately 1/7 of the conventional polishing time after sintering without green processing. Therefore, manufacturing costs are reduced.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of green processing of a ceramic ball formed by the manufacturing method of the present invention using a wet polishing machine. In addition, 1 in the figure is a ceramic ball during green processing, 2
3 is a polished upper plate, 4 is a mixture of water and rust preventive abrasive grains.

Claims (1)

[Claims] 1) A ball is formed using a kneaded mixture of ceramic powder with a composition mainly composed of a thermoplastic organic polymer compound added as a binder, and the ball is pearl-processed using a wet ball polishing machine. A method for producing a ceramic ball, characterized in that the ball is then degreased and sintered. 2) The method for manufacturing a ceramic ball according to claim 1, wherein the method for molding the ball is an injection molding method. 3) The ceramic ball according to claim 1, wherein the ball is formed by sandwiching a hot extruded kneaded material between a pair of hemispherical molds while it is still flexible. Production method.