WO2017217321A1

WO2017217321A1 - Glass rolling body

Info

Publication number: WO2017217321A1
Application number: PCT/JP2017/021378
Authority: WO
Inventors: 田中　敦; 浩佑川本
Original assignee: 日本電気硝子株式会社
Priority date: 2016-06-14
Filing date: 2017-06-08
Publication date: 2017-12-21
Also published as: JPWO2017217321A1; JP6959584B2

Abstract

This glass rolling body is characterized by having a diameter dimensional tolerance of within 0.5%, and by having on the surface a compression stress layer formed through ion-exchange.

Description

Glass rolling element

The glass rolling element of the present invention relates to, for example, a spherical glass rolling element positioned between an inner ring and an outer ring of a bearing, and particularly relates to a glass rolling element made of chemically strengthened glass that is lightweight, high in strength, and excellent in manufacturing cost.

Stainless steel is widely used for rolling elements incorporated in bearing devices. Stainless steel rolling elements are advantageous in that they are easy to process and can be mass-produced at low cost. On the other hand, since the rolling element made of stainless steel has conductivity, it has a demerit that it cannot be used for applications requiring insulation (for example, a rolling element incorporated in a bearing device of a fan motor).

JP 2009-190959 A

Non-oxide ceramics such as silicon nitride are assumed as rolling elements that can be used for applications requiring insulation, but non-oxide ceramics are expensive and difficult to process into a spherical shape (patents) Reference 1).

Therefore, the present invention has been made in view of the above circumstances, and its technical problem is to create a rolling element that can be manufactured at low cost and has high workability and insulation.

As a result of various studies, the present inventor has found that the above technical problem can be solved by adopting a glass rolling element and subjecting the glass rolling element to ion exchange treatment, and proposes the present invention. Is. That is, the glass rolling element of the present invention is characterized by having a dimensional tolerance within 0.5% and having a compressive stress layer by ion exchange on the surface. Here, the “diameter dimensional tolerance” is a dimensional tolerance with respect to the average diameter, and can be measured by, for example, a known micrometer.

Glass is an insulating material, and has good moldability and workability. Therefore, the glass rolling element can be processed easily and inexpensively so that the dimensional tolerance of the diameter is within 0.5%. However, since glass is a brittle material, when it is used for a rolling element incorporated in a bearing device or the like, it may be damaged under severe conditions such as high-speed rotation, high friction, and high load. Then, the glass rolling element of this invention has the compressive-stress layer by ion exchange on the surface. That is, the glass rolling element of the present invention is characterized by being chemically strengthened glass. Thereby, since mechanical strength improves, even if it uses on severe conditions, sufficient lifetime can be ensured.

In addition, the glass rolling element of the present invention preferably has a polished surface. If it does in this way, it will become easy to reduce the dimensional tolerance of the diameter of a glass rolling element.

The glass rolling element of the present invention preferably has a chemically etched surface. In this way, polishing scratches and the like on the surface when processing into a spherical shape can be reduced or eliminated. As a result, even when used under severe conditions, the glass rolling element is difficult to break.

The glass rolling element of the present invention preferably has a surface roughness Ra of 3 nm or less. If it does in this way, even when it uses it on severe conditions, it will become difficult to break a glass rolling element. Here, the “surface roughness Ra” can be measured by a method based on JIS B0601: 2001 with the glass rolling element fixed with a jig or the like.

The glass rolling element of the present invention preferably has a compressive stress value CS of the compressive stress layer of 300 MPa or more and a stress depth DOL of 30 μm or more.

“CS” and “DOL” are measured as follows. A glass plate having the same composition and the same heat history as the glass rolling element is prepared. Next, the glass plate is subjected to ion exchange treatment under the same conditions as the glass rolling element to obtain a glass plate having the same surface composition profile as the glass rolling element. The surface composition profile can be measured by using a standardless quantitative analysis of the ZAF method by SEM-EDX (for example, S4300-SE manufactured by Hitachi High-Technologies, EX-250 manufactured by Horiba, Ltd.). In addition, about the glass which is the same composition, a heat history can be arrange | equalized by making the density measured by the well-known Archimedes method or the heavy liquid method the same. Subsequently, the cross section of the glass plate was observed with a surface stress meter (for example, FSM-6000 manufactured by Orihara Seisakusho Co., Ltd.), and the compressive stress value CSp of the surface stress layer of the glass plate was determined from the number of observed interference fringes and their spacing. The stress depth DOLp is calculated. Finally, the obtained CSp is evaluated as CS of the glass rolling element, and DOLp is evaluated as DOL of the glass rolling element.

The glass rolling element of the present invention preferably contains, as a glass composition, 45 to 75% of SiO ₂ , 10 to 30% of Al ₂ O _{3 and} 5 to 25% of Na ₂ O in terms of mass%. If it does in this way, since ion exchange performance improves, the mechanical strength of a glass rolling element can be raised.

Further, the glass rolling element of the present invention preferably has a liquidus viscosity of 10 ^4.0 dPa · s or more. Here, “liquidus viscosity” refers to the viscosity of the glass at the liquidus temperature. “Liquid phase temperature” means that after passing through a standard sieve 30 mesh (a sieve opening of 500 μm), glass powder remaining in a 50 mesh (a sieve opening of 300 μm) is placed in a platinum boat and kept in a temperature gradient furnace for 24 hours. Refers to the temperature at which crystals precipitate. If it does in this way, it will become easy to form a glass rolling element with high dimensional accuracy.

The glass rolling element of this invention has the compressive-stress layer by ion exchange on the surface. As a method for forming a compressive stress layer by ion exchange, a method in which a glass rolling element is immersed in an ion exchange solution and alkali ions having a large ion radius are introduced into the surface of the glass rolling element is preferable. In particular, in KNO ₃ molten salt It is preferable to ion-exchange K ions and the Na component in the glass rolling element to form a compressive stress layer on the surface of the glass rolling element. Thereby, the mechanical strength of a glass rolling element can be raised in a short time.

In the glass rolling element of the present invention, the dimensional tolerance of the diameter is within 0.5%, preferably within 0.1%, within 0.05%, within 0.02%, within 0.01%, particularly preferably within 0.1%. It is within 005%. The dimensional tolerance of the diameter is preferably within 10 μm, within 5 μm, within 3 μm, within 2 μm, within 1 μm, within 0.5 μm, and particularly within 0.1 μm. If the dimensional tolerance of the diameter is too large, the driving operation or the like becomes unstable, making it difficult to use as a rolling element.

In the glass rolling element of the present invention, the surface is preferably a polished surface. In this way, the dimensional tolerance of the diameter can be reduced. The polishing step is preferably performed before the ion exchange treatment and after the ion exchange treatment. This makes it possible to produce a glass rolling element with high mechanical strength and dimensional accuracy. The polishing treatment is preferably performed while rotating the glass rolling element. This facilitates reducing the dimensional tolerance of the diameter.

In the glass rolling element of the present invention, the surface is preferably a chemically etched surface. In this way, since the surface scratches are reduced or disappear, the glass rolling element is difficult to break under severe conditions such as high speed rotation, high friction, and high load. The chemical etching treatment is preferably performed while rotating or swinging the glass rolling element. In this way, an undue increase in the dimensional tolerance of the diameter can be prevented. The chemical etching process is preferably performed before the ion exchange process. Further, it is preferable to use a hydrofluoric acid-containing aqueous solution as the chemical etching solution.

In the glass rolling element of the present invention, the surface roughness Ra of the surface is preferably 3 nm or less, 1 nm or less, 0.5 nm or less, 0.4 nm or less, 0.3 nm or less, particularly 0.2 nm or less. If the surface roughness Ra is too large, the glass rolling element is easily damaged under severe conditions such as high-speed rotation, high friction, and high load.

The glass rolling element of the present invention preferably contains, as a glass composition, 45 to 75% of SiO ₂ , 10 to 30% of Al ₂ O _{3 and} 5 to 25% of Na ₂ O in terms of mass%. The reason for limiting the content range of each component as described above will be described below. In addition, in description of the containing range of each component, the following% display points out the mass%.

SiO ₂ is a component that forms a glass network, and its content is preferably 45 to 75%, 45 to 70%, 45 to 65%, 45 to 63%, particularly 48 to 61%. When the content of SiO ₂ is too large, meltability, moldability, thermal expansion coefficient is liable to lower. On the other hand, if the content of SiO ₂ is too small, it becomes difficult to vitrify and the thermal expansion coefficient becomes unreasonably high, so that the thermal shock resistance tends to decrease.

Al ₂ O ₃ is a component that increases ion exchange performance, strain point, and Young's modulus. However, when the content of Al ₂ O ₃ is too large, devitrification crystal glass becomes easy to precipitate, hardly molded into a desired shape. Further, the meltability and the coefficient of thermal expansion are likely to decrease. Therefore, the preferred upper limit range of Al ₂ O ₃ is 30% or less, 28% or less, 24% or less, 23% or less, 22% or less, 21.5% or less, particularly 21% or less. 10% or more, 12% or more, 13% or more, 15% or more, 17% or more, particularly 18% or more.

Na ₂ O is an ion exchange component and a component that improves meltability and moldability. It is also a component that improves devitrification resistance. However, when the content of Na ₂ O is too large, the thermal expansion coefficient becomes unreasonably high, so that the thermal shock resistance tends to decrease. Further, the balance of the glass composition may be lost, and the devitrification resistance may be reduced. Therefore, the content of Na ₂ O is preferably 5 to 25%, 10 to 25%, 11 to 22%, 12 to 20%, 13 to 19%, particularly 14 to 18%.

In addition to the above components, for example, the following components may be introduced.

P ₂ O ₅ is a component that enhances the ion exchange performance, and particularly a component that increases the stress depth DOL. As described above, increasing the amount of Al ₂ O ₃ is effective for improving the ion exchange performance. However, if the content of Al ₂ O ₃ is too large, the devitrification resistance tends to decrease. Therefore, there is a limit to the increase in Al ₂ O ₃ . However, when P ₂ O ₅ is introduced, even if the amount of Al ₂ O ₃ is increased, it becomes difficult for the glass to devitrify, so that the allowable amount of introduction of Al ₂ O ₃ can be increased. As a result, ion exchange performance can be dramatically improved. On the other hand, if too much amount of P ₂ O _5, glass or phase separation, the water resistance and the devitrification resistance tends to decrease. Based on the above points, the preferable upper limit range of P ₂ O ₅ is 10% or less, 9% or less, 8% or less, 7% or less, particularly 6% or less, and the preferable lower limit range is 0.1% or more. 0.5% or more, 1% or more, 2% or more, 3% or more, particularly 4% or more.

B ₂ O ₃ is a component that lowers the liquidus temperature, high-temperature viscosity, and density, and is a component that increases the ion exchange performance, particularly the compressive stress value CS. There is a risk that burns will occur or water resistance, liquid phase viscosity, and stress depth DOL will decrease. Therefore, the content of B ₂ O ₃ is preferably 0 to 6%, 0 to 4%, 0 to 3%, 0 to 2%, particularly 0 to less than 1%.

Li ₂ O is an ion exchange component and a component that lowers the high-temperature viscosity to improve the meltability and moldability. Furthermore, it is a component that increases the Young's modulus. However, when the content of Li 2 _O is too large, and decreases the liquidus viscosity, it tends glass devitrified. Further, the low-temperature viscosity is excessively lowered, and stress relaxation is likely to occur during the ion exchange treatment, and the compressive stress value CS may be lowered. Therefore, the content of Li ₂ O is preferably 0 to 10%, 0 to 8%, 0 to 5%, 0 to less than 3%, 0 to 2%, 0 to less than 1%, 0 to 0.1%. Less than, in particular, 0 to less than 0.01%.

K ₂ O is a component that promotes ion exchange, and is a component that has a high effect of increasing the stress depth DOL, particularly among alkali metal oxides. Further, it is a component that lowers the high-temperature viscosity to increase meltability and moldability, and improve devitrification resistance. However, if the content of K ₂ O is too large, the thermal expansion coefficient becomes unreasonably high, the thermal shock resistance is lowered, and it is difficult to match the thermal expansion coefficient with the surrounding materials. Furthermore, there is a possibility that the strain point is excessively lowered, the balance of the glass composition is lost, and the devitrification resistance is reduced. The preferable upper limit range of K ₂ O is 10% or less, 9% or less, 8% or less, 7% or less, particularly 6% or less, and the preferable lower limit range is 0% or more, 0.5% or more, 1% or more. 2% or more, 3% or more, particularly 4% or more.

The preferred upper limit range of Li ₂ O + Na ₂ O + K ₂ O is 30% or less, 25% or less, particularly 22% or less, and the preferred lower limit range is 8% or more, 10% or more, 13% or more, particularly 15% or more. is there. If the content of Li ₂ O + Na ₂ O + K ₂ O is too large, the devitrification resistance is lowered, the thermal expansion coefficient is unduly high, the thermal shock resistance is lowered, and the thermal expansion coefficient matches with the surrounding materials. It becomes difficult to do. On the other _hand, when the content of _{Li 2 O + Na 2 O +} K 2 O is too small, the ion exchange performance and meltability is liable to decrease. “Li ₂ O + Na ₂ O + K ₂ O” is the total amount of Li ₂ O, Na ₂ O and K ₂ O.

The molar ratio K ₂ O / Na ₂ O is preferably 0 to 1, 0 to 0.8, 0.05 to 0.7, 0.1 to 0.5, 0.15 to 0.4, 0.15. To 0.3, in particular 0.15 to 0.25. In this way, the compressive stress value CS and the stress depth DOL are likely to increase in a short time. “K ₂ O / Na ₂ O” is a value obtained by dividing the content of K ₂ O by the content of Na ₂ O.

The content of MgO + CaO + SrO + BaO is preferably 0 to 15%, 0 to 9%, 0 to 6%, particularly 0 to 5%. When there is too much content of MgO + CaO + SrO + BaO, a density and a thermal expansion coefficient will become unreasonably high, or devitrification resistance and ion exchange performance will fall easily. “MgO + CaO + SrO + BaO” is the total amount of MgO, CaO, SrO and BaO.

MgO and CaO are components that lower high-temperature viscosity to increase meltability and moldability, and increase strain point and Young's modulus. Among alkaline earth metal oxides, MgO and CaO are highly effective in increasing ion exchange performance. It is an ingredient. However, when the contents of MgO and CaO increase, the density and thermal expansion coefficient increase and the glass tends to devitrify. Therefore, the content of MgO is preferably 10% or less, 8% or less, 6% or less, 5% or less, particularly 4% or less. The content of CaO is preferably 8% or less, 6% or less, 4% or less, 2% or less, particularly less than 1%.

SrO and BaO are components that lower the high-temperature viscosity, increase the meltability and moldability, and increase the strain point and Young's modulus. However, when the contents of SrO and BaO increase, the density and thermal expansion coefficient increase, and the ion exchange performance tends to decrease. Therefore, the content of SrO is preferably 3% or less, 2% or less, 1% or less, 0.5% or less, and particularly less than 0.1%. The content of BaO is preferably 3% or less, 2% or less, 1% or less, 0.5% or less, particularly less than 0.1%.

The mass ratio (MgO + CaO + SrO + BaO) / (Li ₂ O + Na ₂ O + K ₂ O) is preferably 0.5 or less, 0.4 or less, particularly 0.3 or less, in order to increase the devitrification resistance. “(MgO + CaO + SrO + BaO) / (Li ₂ O + Na ₂ O + K ₂ O)” is a value obtained by dividing the total amount of MgO, CaO, SrO and BaO by the total amount of Li ₂ O, Na ₂ O and K ₂ O. .

ZnO is a component that enhances ion exchange performance. Moreover, it is a component which reduces high temperature viscosity, without reducing low temperature viscosity. However, when ZnO is increased in the presence of P ₂ O ₅ , the glass is likely to undergo phase separation or devitrification. Therefore, the ZnO content is preferably 8% or less, 4% or less, 1% or less, 0.1% or less, and particularly 0.01% or less.

ZrO ₂ is a component that increases ion exchange performance, Young's modulus, and strain point, and is a component that decreases high temperature viscosity. However, when the content of ZrO ₂ increases, the devitrification resistance tends to be lowered. Therefore, the content of ZrO ₂ is preferably 0 to 10%, 0 to 5%, 0 to 3%, 0 to less than 1%, 0 to 0.4%, particularly 0 to less than 0.1%.

TiO ₂ is a component that enhances ion exchange performance and is a component that reduces high temperature viscosity. However, when the content of TiO ₂ increases, the glass is likely to be colored or devitrified. In particular, the transmittance tends to fluctuate due to the melting atmosphere and the raw material impurities. Therefore, the content of TiO ₂ is preferably 0 to 4%, 0 to less than 1%, 0 to less than 0.1%, particularly 0 to less than 0.01%.

SnO ₂ is a component that increases the ion exchange performance, particularly the compressive stress value CS. However, when the content of SnO ₂ increases, devitrification due to SnO ₂ occurs or glass tends to be colored. Therefore, the SnO ₂ content is preferably 0 to 3%, 0.01 to 2%, 0.05 to 1%, and particularly 0.1 to 0.5%.

As a fining _{_{_{_{agent, As 2 O 3, Sb 2}}}} O 3, CeO 2, F, may contain _SO 3, Cl one or two or more selected from the group of. However, from environmental considerations, it is preferred that no added _As 2 _{O 3} and _Sb 2 _{O 3,} the content of _As 2 _{O 3} and _Sb 2 _{O 3} content _of each less than 0.1%, particularly less than 0.01% Is preferred. The CeO ₂ content is preferably less than 0.1%, particularly preferably less than 0.01%, in order to increase the transmittance. The content of F is preferably less than 0.1%, particularly preferably less than 0.01%, in order to suppress stress relaxation due to a decrease in low-temperature viscosity.

Transition metal oxides such as CoO and NiO are components that color glass. Therefore, the content of the transition metal oxide is preferably 0.5% or less, 0.1% or less, particularly 0.05% or less.

Rare earth oxides such as Nb ₂ O ₅ and La ₂ O ₃ are components that increase the Young's modulus. However, when the content of the rare earth oxide increases, the raw material cost increases, and the devitrification resistance tends to decrease. Therefore, the rare earth oxide content is preferably 3% or less, 2% or less, less than 1%, 0.5% or less, particularly 0.1% or less.

The contents of PbO and Bi ₂ O ₃ are each preferably less than 0.1% in consideration of the environment.

The glass rolling element of the present invention has a compressive stress layer by ion exchange on the surface. The compressive stress value CS of the compressive stress layer is preferably 300 MPa or more, 600 MPa or more, 800 MPa or more, 900 MPa or more, 1000 MPa or more, particularly 1100 MPa or more. The larger the compressive stress value CS, the higher the mechanical strength of the glass rolling element. However, if the compressive stress value CS is too large, the tensile stress inherent in the glass rolling element may become extremely high. Therefore, the compressive stress value CS of the compressive stress layer is preferably 2500 MPa or less. Note that the compression stress value CS can be increased by shortening the ion exchange time or lowering the ion exchange temperature.

The stress depth DOL is preferably 30 μm or more, 40 μm or more, 50 μm or more, 60 μm or more, particularly 70 μm or more. The greater the stress depth DOL, the more difficult the glass rolling element breaks even if the surface of the glass rolling element is deeply damaged due to wear or foreign matter during high-speed rotation. On the other hand, if the stress depth DOL is too large, the tensile stress inherent in the glass rolling element may become extremely high. Therefore, the stress depth DOL is preferably 500 μm or less, 300 μm or less, 200 μm or less, particularly 150 μm or less. Note that the stress depth DOL can be increased by increasing the ion exchange time or increasing the ion exchange temperature.

In the glass rolling element of the present invention, the internal tensile stress value CT is preferably 200 MPa or less, 150 MPa or less, 100 MPa or less, particularly 50 MPa or less. The “internal tensile stress value CT” refers to a value calculated by the following mathematical formula 1. The smaller the internal tensile stress value CT, the harder the glass rolling element is damaged by internal defects. However, when the internal tensile stress value CT becomes extremely small, the compressive stress value CS and the stress depth DOL decrease, and the glass The mechanical strength of the rolling element is reduced. Therefore, the internal tensile stress value CT is preferably 1 MPa or more, 2 MPa or more, 3 MPa or more, 5 MPa or more, 10 MPa or more, particularly 15 MPa or more.

[Equation 1]
CT = CS × DOL / (t−2 × DOL)
t: Diameter (plate thickness)
CT: Internal tensile stress value CS: Compressive stress value DOL: Stress depth

The thermal expansion coefficient in the temperature range of 30 to 380 ° C. is preferably 70 × 10 ⁻⁷ to 110 × 10 ⁻⁷ / ° C., 75 × 10 ⁻⁷ to 110 × 10 ⁻⁷ / ° C., 80 × 10 ⁻⁷ to 110 × 10 ⁻⁷ / ° C., particularly 85 × 10 ⁻⁷ to 110 × 10 ⁻⁷ / ° C. If the coefficient of thermal expansion is regulated as described above, even if the surrounding metal member expands due to heat generated during high-speed rotation, it can be driven properly. Here, the “thermal expansion coefficient” is an average value measured with a dilatometer in a temperature range of 30 to 380 ° C.

The strain point is preferably 520 ° C. or higher, 550 ° C. or higher, 560 ° C. or higher, particularly 570 ° C. or higher. The higher the strain point, the better the heat resistance. In addition, when the strain point is high, stress relaxation is less likely to occur during the ion exchange process, and thus it is easy to ensure a high compressive stress value CS.

The temperature corresponding to the high temperature viscosity of 10 ^2.5 dPa · s is preferably 1650 ° C. or lower, 1600 ° C. or lower, 1580 ° C. or lower, 1550 ° C. or lower, 1540 ° C. or lower, especially 1530 ° C. or lower. The lower the temperature corresponding to the high temperature viscosity of 10 ^2.5 dPa · s, the more the glass can be melted at a lower temperature. Therefore, as the temperature corresponding to the high temperature viscosity of 10 ^2.5 dPa · s is lower, the burden on the glass production equipment such as the melting kiln is reduced, and the bubble quality of the glass rolling element can be improved.

Liquid phase temperature is preferably 1200 ° C. or lower, 1150 ° C. or lower, 1130 ° C. or lower, 1110 ° C. or lower, 1090 ° C. or lower, particularly 1070 ° C. or lower. If the liquidus temperature is too high, it becomes difficult to form a spherical shape.

Liquidus viscosity, preferably of ¹⁰ 4.0 dPa · s or ^{more, 10} 4.3 dPa · s or ^{more, 10} 4.5 dPa · s or ^{more, 10} 5.0 dPa · s or more, particularly ¹⁰ 5.4 dPa · s or more. If the liquid phase viscosity is too low, it becomes difficult to form a spherical shape. If the liquid phase temperature is 1200 ° C. or lower and the liquid phase viscosity is 10 ^4.0 dPa · s or higher, it can be formed into a spherical shape by a marble molding method or the like.

In the glass rolling element of the present invention, the diameter is preferably 100 mm or less, 80 mm or less, 50 mm or less, particularly 30 mm or less, and preferably 1 mm or more, 2 mm or more, 4 mm or more, particularly 5 mm or more. If it does in this way, it will become suitable for a rolling element built in a bearing device etc.

The glass rolling element of the present invention can be produced, for example, as follows. First, a glass batch prepared to have a desired glass composition is put into a continuous melting furnace, heated and melted at 1500 to 1600 ° C. to obtain a molten glass, and then a molding apparatus through a clarification container and a stirring container. The product is then formed into a spherical shape and slowly cooled. Next, polishing is performed while rotating the surface of the obtained glass rolling element to reduce the dimensional tolerance of the diameter. Subsequently, the glass rolling element is immersed in an ion exchange solution to form a compressive stress layer on the surface.

Various molding methods can be adopted as the molding method. Among them, it is preferable to adopt a marble forming method and a droplet forming method. It is also preferable to adopt a pressing method. If it does in this way, it will become easy to form a glass rolling element with high dimensional accuracy. As a result, the dimensional tolerance of the diameter of the glass rolling element can be reduced even with a small amount of surface polishing.

In order to increase the mechanical strength before the ion exchange treatment, a step of chemically etching the surface of the glass rolling element may be provided. The chemical etching is preferably performed while rotating or swinging the glass rolling element. In this way, since the etching depth of the surface layer of the glass rolling element is made uniform, the dimensional tolerance of the diameter can be reduced.

The ion exchange treatment can be performed, for example, by immersing the glass rolling element in a molten potassium nitrate at 360 to 550 ° C. for 1 to 100 hours. From the viewpoint of production efficiency, it is preferable that a plurality of glass rolling elements are subjected to ion exchange treatment at the same time. In that case, a metal jig having a mesh width smaller than the diameter of the glass rolling elements, etc. so that the glass rolling elements do not contact each other More preferably, the plurality of glass rolling elements are arranged at equal intervals, and the ion exchange treatment is performed in a state where the jig is laminated.

The ion exchange treatment is preferably performed while rotating or swinging the glass rolling element. In this way, since the glass composition of the surface layer of the glass rolling element is made uniform, the dimensional tolerance of the diameter can be reduced.

The ion exchange process may be performed a plurality of times. When the ion exchange treatment is performed a plurality of times, the distribution curve of the K ion concentration in the depth direction can be bent, and the tensile stress accumulated inside is increased while increasing the compressive stress value CS and the stress depth DOL of the compressive stress layer. The total amount of stress can be reduced.

When the ion exchange treatment is performed twice, a heat treatment step may be provided between the ion exchange treatments. In this way, the K ion concentration distribution curve in the depth direction can be bent by the same potassium nitrate molten salt. Furthermore, the time for the first ion exchange treatment can be shortened.

After the ion exchange treatment, a polishing step for polishing the surface of the glass rolling element may be provided in order to reduce the dimensional tolerance of the diameter.

The present invention will be described based on examples. However, the present invention is not limited to the following examples. The following examples are merely illustrative.

Table 1 shows the glass composition and characteristics of Examples (Nos. 1 to 5) of the present invention.

Each sample shown in Table 1 was produced as follows. First, the glass raw material was prepared so that it might become the glass composition in a table | surface, and it melted at 1580 degreeC for 8 hours using the platinum container. Thereafter, the molten glass was poured out on the carbon plate and formed into a plate shape to obtain a glass plate. Separately, molten glass was formed into a spherical shape by a marble molding method, and then the surface was polished while rotating to obtain glass rolling elements having the dimensions shown in the table. The glass plate and the glass rolling element are annealed under the same heat treatment conditions, and the thermal history is the same. Various characteristics were evaluated about each glass plate and glass rolling element.

The density is a value measured by the well-known Archimedes method.

The strain point Ps and the annealing point Ta are values measured by the method of ASTM C336.

The softening point Ts is a value measured by the method of ASTM C338.

Temperature corresponding to a viscosity ^{^{10 4.0 dPa · s, 10 3.0}} dPa · s, 10 2.5 dPa · s of the glass, a value measured by a platinum ball pulling method.

The thermal expansion coefficient is an average value measured with a dilatometer in a temperature range of 30 to 380 ° C.

The liquid phase temperature TL passes through a standard sieve 30 mesh (a sieve opening of 500 μm), and the glass powder remaining in a 50 mesh (a sieve opening of 300 μm) is put in a platinum boat and kept in a temperature gradient furnace for 24 hours to obtain a crystal. It is the value which measured the temperature which deposits.

Liquid phase viscosity log ηTL indicates the viscosity of each glass at the liquidus temperature.

Subsequently, after both surfaces of each glass plate were optically polished, ion exchange treatment was performed. The ion exchange treatment was performed by immersing each glass plate in a molten potassium nitrate at 440 ° C. for 6 hours. Similarly, the ion exchange treatment was performed while rotating each glass rolling element. After the ion exchange treatment, the surface of each glass plate is washed, and the compressive stress value and stress of the compressive stress layer are determined from the number of interference fringes observed using a surface stress meter (FSM-6000 manufactured by Orihara Seisakusho Co., Ltd.). Depth was calculated. In the calculation, the refractive index of each glass plate was 1.52, and the optical elastic constant was 28 [(nm / cm) / MPa]. Since the glass composition, thermal history, and ion exchange conditions of the glass plate and the glass rolling element are the same, the compression stress value of the glass plate is the compression stress value CS of the glass rolling element, and the stress depth of the glass plate is the stress of the glass rolling element. The stress depth was DOL.

In addition, although the glass composition of the surface layer of a glass rolling element changes microscopically before and after an ion exchange process, when it sees as the whole glass rolling element, the fluctuation | variation of a glass composition is very small.

The diameter and its dimensional tolerance are values measured using a micrometer for each glass rolling element.

As can be seen from Table 1, sample no. Nos. 1 to 5 are considered to be suitable as rolling elements incorporated in a bearing device or the like because the dimensional tolerance of the diameter is good and the compressive stress value CS and the stress depth DOL of the compressive stress layer are large.

Claims

A glass rolling element characterized by having a dimensional tolerance of a diameter within 0.5% and having a compressive stress layer by ion exchange on the surface.
The glass rolling element according to claim 1, wherein the surface is a polished surface.
The glass rolling element according to claim 1, wherein the surface is a chemically etched surface.
The glass rolling element according to any one of claims 1 to 3, wherein the surface roughness Ra of the surface is 3 nm or less.
5. The glass rolling element according to claim 1, wherein the compression stress value CS of the compression stress layer is 300 MPa or more and the stress depth DOL is 30 μm or more.
The glass composition according to any one of claims 1 to 5, wherein the glass composition contains SiO 2 45 to 75%, Al 2 O 3 10 to 30%, and Na 2 O 5 to 25% by mass. Glass rolling element.
7. The glass rolling element according to claim 1, wherein the liquid phase viscosity is 10 4.0 dPa · s or more.