JP6454166B2 - Manufacturing method of glass blank for magnetic disk, manufacturing method of glass substrate for magnetic disk, and cutting blade member - Google Patents

Description

  The present invention relates to a method for manufacturing a magnetic disk glass blank having a pair of main surfaces, a method for manufacturing a magnetic disk glass substrate, and a cutting blade member.

  Today, a personal computer, a notebook personal computer, a DVD (Digital Versatile Disc) recording device, or the like has a built-in hard disk device for data recording. In particular, in a hard disk device used in a portable computer such as a notebook personal computer, a magnetic disk having a magnetic layer provided on a substrate is used, and a magnetic head slightly lifted above the surface of the magnetic disk ( Magnetic recording information is recorded on or read from the magnetic layer by a DFH (Dynamic Flying Height) head. As the substrate of this magnetic disk, a glass substrate is preferably used because it has a property that it is less likely to undergo plastic deformation than a metal substrate or the like.

  In order to manufacture a glass substrate for a magnetic disk, for example, a glass blank is prepared by sandwiching a glass gob obtained by cutting a molten glass stream into a predetermined length between a pair of press surfaces. The shape is processed into a shape, and grinding and polishing are performed as necessary. By the way, it is preferable that the surface roughness of the main surface of the magnetic disk glass substrate is extremely small in order to reduce the flying distance of the magnetic head in a magnetic disk having a magnetic layer formed on the main surface. For this reason, it is desirable that the main surface of the glass substrate for magnetic disks has small surface irregularities. In the method for producing a glass substrate for a magnetic disk described above, when the molten glass flow is cut by the cutting blade, the cutting blade member and the tip of the molten glass flow come into contact with each other and the tip of the molten glass flow is locally cooled. As a result, defects such as shear marks occur near the surface of the glass blank. This shear mark can be removed by grinding or polishing, but it is necessary to grind and polish with a machining allowance larger than the machining allowance of grinding and polishing to make the surface unevenness the target range. This has been a factor in reducing the production efficiency of glass substrates.

  By the way, it is known that the shear mark generation position is deepened and the size of the shear mark is increased by increasing the time during which the blade as a cutting blade contacts the molten glass. For this reason, the molten glass cutting device for shortening the time which the blade | blade which is a cutting blade contacts with molten glass is known (patent document 1). In the said apparatus, it is supposed that the time which the blade which is a cutting blade contacts with molten glass can be made into 50-70 milliseconds.

JP 09-227130 A

  The shear mark is formed inside the glass substrate in an arc shape, for example, but this shape is not located at a certain depth direction from the glass main surface, but the depth direction position changes. Yes. For this reason, hereinafter, the depth of the shear mark refers to the distance from the main glass surface to the deepest position of the shear mark. In the molten glass cutting apparatus described above, it has been found that the depth of the shear mark does not always exist within a certain range and varies. For this reason, in mass production, the machining allowance for grinding and polishing cannot always be made constant, and the production efficiency of the glass substrate for magnetic disks is still lowered.

  Accordingly, the present invention provides a method for manufacturing a glass blank for a magnetic disk, a method for manufacturing a glass substrate for a magnetic disk, and a cutting blade member capable of reducing the depth of the shea mark and suppressing variations in the depth of the shea mark. The purpose is to do.

One aspect of the present invention is a method for producing a glass blank for a magnetic disk having a pair of main surfaces used for a glass substrate for a magnetic disk. The manufacturing method is
A process of cutting the molten glass flow with a pair of cutting blades provided in a pair of cutting blade members, and forming a glass gob by the cutting,
Processing to form a glass blank by press molding sandwiching the glass gob between a pair of press surfaces,
The pair of cutting blades are provided on the upstream side and the downstream side of the molten glass flow so as to cut the molten glass flow,
Each of the cutting blade members cuts the molten glass flow by passing through the flow channel region of the molten glass flow in one direction, and when cutting the molten glass flow, the tip of the molten glass flow is Of the pair of cutting blade members, the time of contact with the upstream cutting blade located on the upstream side of the molten glass flow is 40 milliseconds or less.
Moreover, the other one aspect | mode of this invention is also a manufacturing method of the glass blank for magnetic discs which has a pair of main surface used for the glass substrate for magnetic discs. The manufacturing method is
Cutting the molten glass flow with a pair of cutting blades provided in a pair of cutting blade members, and forming a glass gob by the cutting;
Processing to form a glass blank by press molding sandwiching the glass gob between a pair of press surfaces,
Each of the cutting blade members cuts the molten glass flow by passing through the flow channel region of the molten glass flow in one direction when the pair of cutting blades intersect to form the glass gob, and the molten glass When cutting the glass flow, the time during which the tip of the molten glass flow contacts the upstream cutting blade member located upstream of the molten glass flow among the pair of cutting blade members is 40 milliseconds or less. .

One embodiment of the present invention is also a method for producing a glass blank for a magnetic disk having a pair of main surfaces used for a glass substrate for a magnetic disk. The manufacturing method is
A process of cutting the molten glass flow with a pair of cutting blades provided in a pair of cutting blade members, and forming a glass gob by the cutting,
Processing to form a glass blank by press molding sandwiching the glass gob between a pair of press surfaces,
Each of the cutting blade members cuts the molten glass flow by passing through the flow channel region of the molten glass flow in one direction when the pair of cutting blades intersect to create the glass gob,
When the pair of cutting blades are referred to as the pair of front end cutting blades, a rear end cutting blade is provided at each rear end of the pair of cutting blade members, and the molten glass flow is obtained by intersecting the front end cutting blades. In addition to cutting the molten glass flow, the molten glass flow is also cut by moving the trailing edge cutting blade to intersect each other in the flow channel region of the molten glass flow.
Moreover, the other one aspect | mode of this invention is also a manufacturing method of the glass blank for magnetic discs which has a pair of main surface used for the glass substrate for magnetic discs. The manufacturing method is
Cutting the molten glass flow with a pair of cutting blades provided in a pair of cutting blade members, and forming a glass gob by the cutting;
Processing to form a glass blank by press molding sandwiching the glass gob between a pair of press surfaces,
Each of the cutting blade members is one of linear movement paths passing through the flow channel region of the molten glass flow when viewed from the upstream side of the molten glass flow when the pair of cutting blades intersect to form the glass gob. The molten glass stream is cut by moving along the direction and passing through the flow channel region of the molten glass stream in one direction.

When cutting the molten glass flow, the time during which the tip of the molten glass flow is in contact with the upstream cutting blade member located on the upstream side of the molten glass flow among the pair of cutting blade members is 40 milliseconds or less. It is preferable that
Further, each of the cutting blade members preferably moves along one direction of an arcuate movement path passing through the flow path region as viewed from the upstream side of the molten glass flow to cut the molten glass flow.
It is also preferable that each of the cutting blade members moves along one direction of a linear movement path passing through the flow channel region when viewed from the upstream side of the molten glass flow to cut the molten glass flow.
Each of the cutting blade members rotates in one direction along an annular movement path passing through the flow channel region when viewed from the upstream side of the molten glass flow, and the cutting blade member is on the annular movement path. It is also preferable to rotate so as to cross each other in the flow path region.
At this time, the annular movement paths in each of the cutting blade members are the same path, and the rotation directions of the cutting blade member in the annular movement path are opposite to each other when viewed from the upstream side of the molten glass flow. It is preferable. Alternatively, the annular movement paths in each of the cutting blade members are different from each other, and the rotation directions of the cutting blade member in the annular movement path are opposite to each other when viewed from the upstream side of the molten glass flow. Is also preferable. Alternatively, the annular movement paths in each of the cutting blade members are different from each other, and the rotation directions of the cutting blade member in the annular movement path are the same directions as viewed from the upstream side of the molten glass flow. Is also preferable.

  When the pair of cutting blades are referred to as the pair of front end cutting blades, a rear end cutting blade is provided at each rear end of the pair of cutting blade members, and the molten glass flow is obtained by intersecting the front end cutting blades. In addition to cutting for cutting, it is preferable to perform cutting for cutting the molten glass flow by moving the trailing edge cutting blade so as to intersect each other in the flow channel region of the molten glass flow.

  It is preferable that the molten glass flow is cut using the pair of front end cutting blades and the pair of rear end cutting waves alternately.

  Alternatively, after the rear end of the cutting blade member passes through the flow channel region through which the molten glass flow flows, the cutting blade member is positioned at a position before the cutting blade intersects, avoiding the flow channel region of the molten glass flow. It is also preferable to move.

  In the process which shape | molds the said glass blank, it is preferable to shape | mold the said glass blank by pinching the said glass gob with a pair of said press surface from the both sides of the said glass gob.

  Yet another embodiment of the present invention is a method for producing a glass substrate for a magnetic disk. The said manufacturing method includes the process which processes the said glass blank produced with the manufacturing method of the said glass blank for magnetic discs. The processing for machining includes a grinding process for the main surface of the glass blank and a polishing process for polishing the main surface of the glass blank after grinding.

Yet another embodiment of the present invention is a cutting blade member. The cutting blade member includes a cutting blade for cutting the molten glass flow to form a glass gob by crossing each other in a flow path region of the molten glass flow. The cutting blade member has the cutting blade at each of a front end and a rear end in a moving direction in which the cutting blade member moves due to the intersection of the cutting blade members.
The said cutting blade is arrange | positioned at the upstream and downstream of a molten glass flow, for example. The said cutting blade is arrange | positioned on both sides of the said molten glass flow, for example.

  According to the above-described method for manufacturing a magnetic disk glass blank, a method for manufacturing a magnetic disk glass substrate, and a cutting blade member, it is possible to reduce the depth of the shear mark and suppress variations in the depth of the shear mark.

It is a figure which shows an example of the cutting | disconnection of the molten glass flow of this embodiment. It is the figure which looked at the cutting | disconnection of the molten glass flow shown in FIG. 1 from upper direction. (A) And (b) is a figure explaining the movement of the cutting blade member used by this embodiment. It is a figure which shows the contact time (m second) of the upstream cutting blade member used for this embodiment, and the front-end | tip part of a molten glass flow, the average value of the depth of a shea mark, and the range of dispersion | variation. (A)-(d) is a figure explaining the example of a movement of a downstream cutting blade member and an upstream cutting blade member. (A)-(c) is a figure explaining the example of the movement path | route of a cutting blade member. It is a figure explaining an example of the shape of the cutting blade used by this embodiment.

  Hereinafter, the manufacturing method of the glass blank for magnetic disks of this invention, the manufacturing method of the glass substrate for magnetic disks, and a cutting blade member are demonstrated in detail.

(Magnetic disk glass substrate)
First, the glass substrate for magnetic disks will be described. The glass substrate for a magnetic disk is an annular glass substrate in which a circular center hole concentric with the outer periphery is cut out from a disk-shaped glass plate. A magnetic disk is formed by forming an annular magnetic layer (recording area) on both surfaces of a magnetic disk glass substrate.

  A magnetic disk glass blank (hereinafter simply referred to as a glass blank), which is a base plate of a magnetic disk glass substrate, is a disk-shaped glass plate produced by press molding, which will be described later, before the center hole is cut out. It is a form.

  As a material for the glass blank, aluminosilicate glass, soda lime glass, borosilicate glass, or the like can be used. In particular, aluminosilicate glass can be suitably used in that it can be chemically strengthened and a glass substrate for a magnetic disk excellent in the flatness of the main surface and the strength of the substrate can be produced.

(Method for producing glass substrate for magnetic disk)
Next, a flow of a method for manufacturing a magnetic disk glass substrate will be described. In the method for producing a glass blank for a magnetic disk according to this embodiment, first, a molten glass stream is cut with a pair of cutting blades, a glass gob is formed by the cutting, and the glass gob is dropped. The pair of cutting blades are provided, for example, on the upstream side and the downstream side of the molten glass flow so as to cut the molten glass flow. Then, a glass blank is shape | molded by carrying out press molding by pinching | interposing a glass gob with a pair of press surface. Next, the glass blank is machined. The machining process includes an annular shape (ring shape) machining process, an end face polishing process, a main surface grinding process, and a main surface polishing process. Specifically, the produced glass blank is processed into an annular shape (ring shape). Thereby, a glass substrate is obtained. Further, shape processing is performed on the glass substrate. Next, end-face polishing is performed on the circular glass substrate that has been processed into a shape. Grinding is performed on the glass substrate that has been subjected to end face polishing. Next, the main surface of the glass substrate is polished. The glass substrate for magnetic disks is obtained through the above processing. Hereinafter, each process will be described in detail. Note that grinding may not be performed. Further, the order of the processes described above may be changed as appropriate.

(A) Press molding process First, a press molding process is demonstrated. The press molding process includes a cutting process and a press process. FIG. 1 is a diagram showing an example of cutting a molten glass flow. FIG. 2 is a view of the cutting of the molten glass flow shown in FIG. 1 as viewed from above, and FIGS. 3A and 3B are views for explaining the movement of the cutting blade member.

(A-1) Cutting process As shown in FIG. 1, when a predetermined amount of molten glass flows out from the outlet 12 at the lower part of the molten glass outflow pipe 10 and the molten glass flows out, the tip of the molten glass flow 20 Is cut by a cutter 30 to create a molten glass lump 21 (see FIG. 3A), and the molten glass lump 21 is dropped.

(A-2) Press treatment A pair of moving molds 90A and 90B (see FIG. 1) are moved to both sides in a direction (for example, horizontal direction) intersecting the falling direction of the molten glass block 21 shown in FIG. By bringing them close to each other, a lump of molten glass that is falling is sandwiched between press molding surfaces 91A and 91B of a pair of molds, and pressed to form a glass blank (hereinafter referred to as a horizontal press system). After pressing for a predetermined time, the molds 90A and 90B are opened and the glass blank is taken out. At the time of pressing, the temperature of press molding of the pair of molds 90A and 90B is made uniform. In addition, in the example shown in FIG. 1, although the molten glass lump 21 is pressed by a horizontal press system, you may press by a vertical press system other than a horizontal press system. In the vertical press method, the falling molten glass lump 21 is received by the press molding surface of one of the pair of molds, and then the other mold is pressed from above the molten glass lump. This is a system in which the molten glass lump 21 is sandwiched between two molding surfaces by moving toward the press molding surface of the metal mold, thereby pressing the molten glass lump 21.
In both the horizontal press method and the vertical press method, it is preferable that the press forming surface of the mold to be used is a flat surface without wedge-shaped or uneven projections. For example, the area of the press molding surface of the mold, which is a flat surface, is obtained by dividing the volume (cm ³ ) of the molten glass lump 21 made by cutting by the plate thickness (cm) of a glass blank produced by press molding. It is preferably larger than the area conversion value (cm ² ), and the area (cm ² ) of the press-molded surface is preferably 1.2 to 5 times the area conversion value (cm ² ). By doing in this way, when the molten glass lump 21 is sandwiched between the press forming surfaces of a pair of molds and crushed, the molten glass is caught in the protrusions and molded into a rugged shape. Can be prevented. Also, the mold may be provided with a wall that forms a step with respect to the press molding surface so as to surround the outer periphery of the press molding surface, but the tip of the molten glass that is spread out is on the wall that forms the step. Walls are provided so that they do not touch. In addition, although such a level | step difference may be provided by the role which determines the plate | board thickness of a glass blank, even when plate | board thickness is determined by methods and members other than a level | step difference, it is made not to contact molten glass to them. This is very important. If the molten glass lump is uniformly spread in all directions without causing such a catch and the tip of the molten glass does not contact the wall, it is formed into a disk shape. In such a case, the end portion (end surface) of the molten glass lump after spreading becomes a surface (free curved surface) that is cooled and solidified without touching another solid such as a mold. Here, the protrusion is a scale much larger than the surface roughness, and is a level that can be easily recognized visually. The surface roughness of the press-molded surface is preferably an arithmetic average roughness Ra obtained by measuring with a stylus type roughness meter, and is preferably 0.1 to 2.0 μm, and more preferably 0.5 to 1.5 μm. Is more preferable.

(B) Annular shape processing After the press forming process, the formed glass blank is made into an annular (ring shape) glass substrate of a predetermined size by a method such as a known core drill or scribe.

(C) Shape processing processing Next, the shape processing processing will be described. The shape processing treatment includes chamfering processing (chamfering processing of the outer peripheral side end surface and the inner end surface) to the end portion of the glass substrate after the annular shape processing processing. The chamfering is performed with a diamond grindstone or the like on the outer peripheral side end face and the inner end face of the glass substrate after the circular shape processing. A glass substrate having a predetermined shape is generated by this shape processing. The chamfering inclination angle is, for example, 40 to 50 degrees with respect to the main surface, and is preferably about 45 degrees.

(D) End Surface Polishing Process Next, the end surface polishing process will be described. In the end surface polishing, mirror finishing is performed by brush polishing on the inner end surface and the outer peripheral side end surface of the glass substrate. At this time, an abrasive slurry containing fine particles such as cerium oxide as free abrasive grains is used. By polishing the end surface, removing contamination such as contamination and scratches on the end surface of the glass substrate will prevent the occurrence of thermal asperity failure and cause corrosion such as sodium and potassium. The occurrence of ion precipitation can be prevented.

(E) Grinding process In the grinding process, grinding is performed on the main surface of the glass substrate using a double-sided grinding apparatus having a planetary gear mechanism. Specifically, the main surface on both sides of the glass substrate is ground while holding the glass substrate in the holding hole provided in the holding member of the double-side grinding apparatus on the outer peripheral side end surface of the glass substrate. Grinding may be performed using loose abrasive grains or may be performed using fixed abrasive grains.

(F) Polishing treatment Next, the main surface of the ground glass substrate is polished. For polishing, the main surface is mirror-polished by removing scratches and distortions remaining on the main surface of the glass, or adjusting fine surface irregularities (micro-waveness, roughness). In the polishing process, the glass substrate is polished using a double-side polishing apparatus while applying a polishing slurry containing loose abrasive grains. By carrying out the polishing treatment, the roughness (Ra) of the main surface is reduced and the micro-waveness of the main surface is reduced. In this way, the polished glass substrate is cleaned to become a magnetic disk glass substrate. The polishing process may include two polishing processes, a first polishing and a second polishing performed after the first polishing, in order to perform the polishing more precisely. There may be three or more polishing treatments. In this case, the first polishing removes scratches and distortions remaining on the glass main surface or adjusts minute surface irregularities. In the second and subsequent polishing, the glass main surface is mirror-polished to further reduce the surface unevenness. The first polishing may not be performed depending on circumstances.
Note that a chemical strengthening process may be performed between the grinding process and the polishing process or between the plurality of polishing processes.

(Cutting of molten glass flow)
FIG. 1 is a diagram showing an example of cutting a molten glass flow in the method for producing a magnetic disk glass blank of the present embodiment. In the method for manufacturing a magnetic disk glass blank according to this embodiment, as described above, a molten glass flow is cut with a pair of cutting blades, a glass gob is formed by the cutting, and the glass gob is dropped. Thereafter, the falling glass gob is sandwiched between a pair of press surfaces to perform press molding, thereby forming a glass blank. At this time, a pair of cutting blades are arrange | positioned in the position of the upstream and downstream of a molten glass flow, for example. Moreover, a pair of cutting blade is arrange | positioned so that a molten glass flow may be pinched | interposed, for example. Further, the pair of cutting blades are disposed to face each other, for example. The pair of cutting blade members including the pair of cutting blades are cut by crossing each other in the flow path region of the molten glass flow.
When cutting this molten glass flow, the time during which the tip of the molten glass flow contacts the upstream cutting blade member located on the upstream side of the molten glass flow among the pair of cutting blade members is 40 milliseconds or less. Moreover, a pair of cutting blade member used for the cutting | disconnection of a molten glass flow is provided in the front end of a pair of cutting blade member with a width | variety in the moving direction of a pair of cutting blade member. Further, each of the cutting blade members has a rear end that passes through the flow channel region of the molten glass flow when the pair of cutting blades intersect to obtain a glass gob. That is, each of the cutting blade members cuts the molten glass flow by passing through the flow path region of the molten glass flow in one direction. The one direction may be a direction along a straight line or a direction along a curved line such as an arc shape or an elliptical arc shape. When one direction is a direction along a curve, for example, each of the cutting blade members is along one direction of a moving path such as an arc shape or an elliptic arc shape passing through the flow path region when viewed from the upstream side of the molten glass flow. Move to cut the molten glass stream. The movement route may be a circular route. This point will be described in detail below.

  In cutting the molten glass flow, a molten glass lump that is an object of press molding is produced. Specifically, the molten glass is suspended from the outlet 12 at the lower part of the molten glass outflow pipe 10 to create a molten glass flow 20, and the tip of the molten glass flow 20 that continuously flows out downward in the vertical direction is provided. The molten glass lump 21 is formed by cutting. In addition, in order to cut | disconnect the front-end | tip part of the molten glass flow 20 as the molten glass lump 21, a pair of cutting blade member is used. Further, the viscosity of the molten glass is not particularly limited as long as it is suitable for cutting of the tip portion or press molding, but is usually controlled to a constant value within a range of 500 dPa · sec to 1050 dPa · sec. It is preferable.

  As shown in FIG. 1, a cutter 30 is disposed below the outlet 12 of the molten glass outlet pipe 10. The cutting device (cutting device) 30 includes a downstream cutting blade member 40, an upstream cutting blade member 50, and a drive unit 44. The downstream cutting blade member 40 is located on the downstream side of the upstream cutting blade member 50 in the direction of the flow of the molten glass flow 20. The upstream cutting blade member 50 is located on the upstream side in the flow direction of the molten glass flow 20 compared to the downstream cutting blade member 40.

For example, as shown in FIG. 1, the downstream cutting blade member 40 and the upstream cutting blade member 50 are opposed to each other on both sides in the horizontal direction with the molten glass flow 20 interposed therebetween. This arrangement position is referred to as a reference position.
The downstream-side cutting blade member 40 has a top surface 41T directed toward the center side of the molten glass flow 20 and directed in a direction opposite to the flow direction of the molten glass flow 20, and a tip on one side (a side close to the molten glass flow 20). Front end cutting blade 41A inclined downward from the tip of the molten glass flow 20 and away from the center of the molten glass flow 20, and the tip of the other side (the tip far from the molten glass flow 20) ) And a rear end cutting blade 41B inclined downward in the direction approaching the center of the molten glass flow 20.
The upstream-side cutting blade member 50 has a lower end 51U that faces the center of the molten glass flow 20, faces the flow direction of the molten glass flow 20, and a tip on one side (a tip closer to the molten glass flow 20). From the front end cutting blade 51A inclined in the upward direction (upstream direction of the molten glass flow 20) and away from the center of the molten glass flow 20, and from the tip on the other side (tip on the side far from the molten glass flow 20) And a rear end cutting blade 51B that is inclined in a direction approaching the center of the molten glass flow 20.
The downstream cutting blade member 40 and the upstream cutting blade member 50 are arranged such that the upper surface 41T of the downstream cutting blade member 40 and the lower surface 51U of the upstream cutting blade member 50 are at substantially the same height. The

  The downstream cutting blade member 40 moves in a direction crossing the central axis D of the molten glass flow 20. The upstream cutting blade member 50 moves in a direction crossing the central axis D of the molten glass flow 20. The downstream-side cutting blade member 40 and the upstream-side cutting blade member 50 move in a direction approaching each other. The downstream cutting blade member 40 and the upstream cutting blade member 50 are connected at one end of rod-shaped support members 42 and 52, and the other ends of the support members 42 and 52 are connected to the drive unit 44. Yes. The drive unit 44 moves the support members 42 and 52 in a direction crossing the central axis D. Accordingly, the downstream cutting blade member 40 and the upstream cutting blade member 50 move so as to approach each other. Specifically, the drive unit 44 moves the upstream cutting blade 50 in the horizontal direction and across the central axis D of the molten glass flow 20, and moves the downstream cutting blade 50 to the center of the molten glass flow 20. Move in a direction across axis D. Here, the time of contact with the upstream cutting blade member 50 positioned on the upstream side of the molten glass flow 20 is 40 msec or less so that the molten glass flow 20 of the downstream cutting blade 40 and the upstream cutting blade 50 is in contact with the upstream cutting blade member 50. The moving speed and the moving timing in the direction crossing the central axis D are controlled. That is, the drive unit 44 moves the downstream cutting blade member 40 and the upstream cutting blade member 50 so that the time for contacting the upstream cutting blade member 50 located on the upstream side of the molten glass flow 20 is 40 milliseconds or less. To drive. In the present embodiment, the downstream cutting blade member 40 and the upstream cutting blade member 50 are moved along one direction of the linear movement path, that is, one direction along the straight line, but a curve such as a circle or an ellipse is used. You may move in the direction along.

  Here, the downstream-side cutting blade member 40 and the upstream-side cutting blade member 50 include the rear ends of these members by driving the downstream-side cutting blade member 40 and the upstream-side cutting blade member 50 by the drive unit 44, as shown in FIG. As shown in (b), it passes through the flow channel region of the molten glass flow 20. Here, the passage of the cutting blade means that the rear ends of the downstream cutting blade member 40 and the upstream cutting blade member 50 in the moving direction pass through the flow path region. The state shown in FIG. 3B is a state after a predetermined time has elapsed from the state shown in FIG. That is, the downstream cutting blade member 40 and the upstream cutting blade member 50 have a width in the moving direction of the pair of cutting blade members, and the front ends of the downstream cutting blade member 40 and the upstream cutting blade member 50 in the moving direction. Are provided with front end cutting blades 41A and 51A, and rear end cutting blades 41B and 51B are provided at the rear end in the moving direction. When the downstream cutting blade member 40 and the upstream cutting blade member 50 intersect to obtain the glass gob 21, in addition to the respective front ends of the downstream cutting blade member 40 and the upstream cutting blade member 50, the rear end, that is, The rear end cutting blades 41 </ b> B and 51 </ b> B also pass through the flow channel region of the molten glass flow 20. The rear end in the present embodiment refers to a portion that passes through the flow channel region of the molten glass flow 20 when the downstream cutting blade member 40 and the upstream cutting blade member 50 intersect.

Thus, in this embodiment, each rear end of the downstream cutting blade member 40 and the upstream cutting blade member 50 passes through the flow path region of the molten glass flow 20, so that the molten glass flow 20 is cut. Thereafter, it is possible to pass through the flow channel region of the molten glass flow 20 while maintaining or accelerating the moving speed. The downstream cutting blade member 40 and the upstream cutting blade member 50 break the glass by cooling and solidifying the portion of the molten glass that contacts the downstream cutting blade member 40 and the upstream cutting blade member 50 moving in this way. The molten glass stream 20 is cut as follows. Even in conventional cutting, cutting is performed by cooling and solidifying a portion of the molten glass to be cut. At this time, in the conventional cutting, even if the moving speed of the cutting blade member when the cutting blade member is in contact with the molten glass flow is high, after the cutting of the molten glass flow, the upstream cutting blade member and the tip of the molten glass flow Since the downstream cutting blade member and the upstream cutting blade member stop moving and start moving in the reverse direction and return to the original reference position, the tip of the molten glass flow is cut upstream. The time for contacting the upper surface of the blade member is long. For this reason, the degree of cooling and solidification of the molten glass flow differs between the cut surface of the molten glass flow when the cutting blade starts contact with the molten glass flow and the cut surface of the molten glass flow immediately before the contact is finished. The depth of the shear mark is likely to vary. In this regard, in the present embodiment, the upstream cutting blade member 50 and the downstream cutting blade member 40 pass through the flow channel region of the molten glass flow 20 in one direction while maintaining the moving speed constant, and thus the molten glass flow 20 The time during which the front end of the contact portion contacts the upper surface of the upstream cutting blade member 50 is short. For this reason, variations in the depth of the shear mark are unlikely to occur. Moreover, in this embodiment, since the contact time with the molten glass flow 20 of the upstream cutting blade member 50 becomes short, the thermal degradation of the upstream cutting blade member 50 is suppressed, and the upstream cutting blade member 50 and the downstream side are suppressed. Since the time for rubbing when the cutting blade member 40 intersects is shortened, the lifetimes of the upstream cutting blade member 50 and the downstream cutting blade member 40 are improved.
Thus, the inventors have found that the variation in the depth of the shear mark is affected by the cutting method of the molten glass flow 20, and shortens the time during which the tip of the molten glass flow 20 contacts the upstream cutting blade member 50. I found it important to do.

  FIG. 4 shows the contact time (msec) between the upstream cutting blade member 50 and the tip of the molten glass flow 20, the average value of the depth of the shear mark, and the range of variation (of the depth of the shear mark of 100 glass substrates, It is a figure which shows the range defined by the deepest position and the shallowest position. The depth of the shear mark was determined from the machining allowance of grinding and polishing performed until the shear mark disappeared visually by the above-described grinding and polishing. As can be seen from FIG. 4, the variation in the depth of the shear mark decreases rapidly with a contact time of 40 milliseconds. In order to reduce the variation in the depth of the shear mark, the contact time needs to be 40 milliseconds or less. Preferably, the contact time is 15 msec or less. It can also be seen that the depth of the shear mark is reduced by shortening the contact time.

  In the present embodiment, rear end cutting blades 41B and 51B are provided at the rear ends of the downstream cutting blade member 40 and the upstream cutting blade member 50, as shown in FIG. That is, the downstream cutting blade member 40 and the upstream cutting blade member 50 are respectively connected to the downstream cutting blade member 40 and the upstream cutting blade member 50 due to the intersection of the downstream cutting blade member 40 and the upstream cutting blade member 50. Has a cutting blade at each of the front end and the rear end in the moving direction. Therefore, as shown in FIG. 3B, after the upstream cutting blade member 50 and the downstream cutting blade member 40 intersect and pass through the flow channel region of the molten glass flow 20, the rear end cutting blades 41B and 51B It is also preferred that the molten glass stream 20 is cut by moving the two so as to face each other and cross each other in the flow channel region of the molten glass stream 20 and the glass gob obtained by this cutting is dropped. In particular, it is preferable to cut the molten glass flow 20 by using the front end cutting blades 41A and 51A and the rear end cutting blades 41B and 51B alternately in order to cut the molten glass flow 20 efficiently.

  Further, as shown in FIG. 3B, after the downstream end of the downstream cutting blade member 40 and the rear end of the upstream cutting blade member 50 pass through the flow channel region through which the molten glass flow 20 flows, the downstream cutting blade As shown in FIGS. 5A to 5D, the member 40 and the upstream-side cutting blade member 50 are moved to a position before the front-end cutting blades 41A and 51A intersect, avoiding the flow channel region of the molten glass flow 20. A moving form is also preferable. FIGS. 5A to 5D are diagrams illustrating an example of movement of the downstream cutting blade member 40 and the upstream cutting blade member 50. FIG. The state shown in FIG. 5B is obtained by the movement of the crossing of the arrow shown in FIG. 5A, and the movement of the arrow shown in FIG. 5B (the movement in the direction orthogonal to the moving direction of the crossing) 5 (c), the movement of the crossing of the arrows shown in FIG. 5 (c) results in the state shown in FIG. 5 (d), and the movement of the arrows shown in FIG. The state shown in FIG. 5A is restored by the movement in the orthogonal direction. Thus, the molten glass flow 20 is efficiently cut using the front end cutting blades 41A and 51A by moving to the position before the front end cutting blades 41A and 51A crossing the flow path region of the molten glass flow 20. can do. Also in this case, the molten glass flow of the downstream cutting blade 40 and the upstream cutting blade 50 is such that the time of contact with the upstream cutting blade member 50 located on the upstream side of the molten glass flow 20 is 40 milliseconds or less. The moving speed and the moving timing in the direction crossing the 20 central axis D are controlled. The rear ends of the downstream cutting blade member 40 and the upstream cutting blade member 50 used for cutting the molten glass flow 20 pass through the flow path region of the molten glass flow 20. For this reason, time for the front-end | tip part of the molten glass flow 20 to contact the upstream cutting blade member 40 can be shortened. For this reason, the depth of the shear mark becomes shallow, and the variation in the depth of the shear mark becomes small. In the example shown in FIGS. 5A to 5D, the downstream cutting blade member 40 and the upstream cutting blade member 50 move in one direction along a straight line, but in one direction along a curve such as a circle or an ellipse. You can also move to.

5A to 5D, the movement paths of the downstream cutting blade member 40 and the upstream cutting blade member 50 for cutting repeatedly performed by the downstream cutting blade member 40 and the upstream cutting blade member 50 will be described. However, it is not limited to such a movement route, and may be a movement route as shown in FIGS. 6A to 6C are diagrams illustrating examples of movement paths of the downstream cutting blade member 40 and the upstream cutting blade member 50. FIG.
In the example shown in FIG. 6A, each of the downstream cutting blade member 40 and the upstream cutting blade member 50 is an annular arc path or an elliptic arc path that passes through the flow channel region of the molten glass flow 20. In this example, the downstream cutting blade member 40 and the upstream cutting blade member 50 are rotated in one direction along the moving path, and rotate so as to intersect each other in the flow path region on the annular moving path 100. In this example, the annular movement paths 100 in each of the downstream cutting blade member 40 and the upstream cutting blade member 50 are the same paths as viewed from the upstream side (or downstream side) of the molten glass flow, and the downstream cutting blade member 40 and the upstream cutting blade member 50 are rotated in opposite directions in the annular movement path 100. The annular moving path 100 of the downstream cutting blade member 40 and the upstream cutting blade member 50 repeatedly circulates on this path, thereby repeatedly cutting the molten glass flow 20.
In the example shown in FIG. 6B, an annular moving path that is an example of an arcuate path or an elliptical arcuate path that passes the downstream cutting blade member 40 and the upstream cutting blade member 50 through the flow channel region of the molten glass flow 20. This is an example in which the downstream cutting blade member 40 and the upstream cutting blade member 50 are rotated so as to intersect with each other in the flow path regions on the annular movement paths 102 and 104. In this example, the annular movement paths 102 and 104 in the downstream cutting blade member 40 and the upstream cutting blade member 50 are paths different from each other when viewed from the upstream side (or downstream side) of the molten glass flow. The rotation directions of the blade member 40 and the upstream cutting blade member 50 in the annular movement paths 102 and 104 are opposite to each other. The annular moving path 100 of the downstream cutting blade member 40 and the upstream cutting blade member 50 repeatedly circulates on this path, thereby repeatedly cutting the molten glass flow 20.
In the example shown in FIG. 6C, an annular moving path that is an example of an arcuate path or an elliptical arcuate path that passes the downstream cutting blade member 40 and the upstream cutting blade member 50 through the flow channel region of the molten glass flow 20. This is an example in which the downstream cutting blade member 40 and the upstream cutting blade member 50 are rotated in one direction along the lines 106 and 108 so as to intersect with each other in the flow path regions on the annular movement paths 102 and 104. In this example, the annular moving paths in each of the downstream cutting blade member 40 and the upstream cutting blade member 50 are paths that are different from each other when viewed from the upstream side (or downstream side) of the molten glass flow. In addition, the rotation directions of the upstream-side cutting blade member 50 in the annular movement paths 106 and 108 are the same as each other. The annular moving path 100 of the downstream cutting blade member 40 and the upstream cutting blade member 50 repeatedly circulates on this path, thereby repeatedly cutting the molten glass flow 20.
In this case, the cutting blades of the downstream cutting blade member 40 and the upstream cutting blade member 50 are preferably blades having a shape as shown in FIG. FIG. 7 is a diagram illustrating an example of the shape of the cutting blade. FIG. 7 is a view of the downstream cutting blade member 40 and the upstream cutting blade member 50 as viewed from the upstream side of the molten glass flow 20. The cutting edges of the cutting blades of the downstream cutting blade member 40 and the upstream cutting blade member 50 are inclined with respect to the moving direction. For this reason, the cutting blade of the downstream cutting blade member 40 and the cutting blade of the upstream cutting blade member 50 are in contact with the molten glass flow 20 in an V shape at an angle θ. As shown in FIG. 6C, when the downstream cutting blade member 40 and the upstream cutting blade member 50 approach the flow path region of the molten glass flow 20, the cutting blade and the upstream cutting blade of the downstream cutting blade member 40. The cutting blade of the member 50 approaches the flow path region of the molten glass flow 20 and starts cutting as shown in FIG. Furthermore, the downstream-side cutting blade member 40 and the upstream-side cutting blade member 50 advance from the flow path region of the molten glass flow 20 downward in FIG. 7 by rotation along the annular movement path, and the molten glass flow 20 The process proceeds in a direction away from the flow path area, and thus passes through the flow path area in one direction.
The downstream cutting blade member 40 and the upstream cutting blade member 50 that rotate along such various movement paths also pass in one direction with respect to the flow channel region of the molten glass flow 20, so that the tip of the molten glass flow 20 The time for which the part contacts the upstream cutting blade member 40 can be shortened. For this reason, the depth of the shear mark becomes shallow, and the variation in the depth of the shear mark becomes small.

  As mentioned above, although the manufacturing method of the glass blank for magnetic discs of this invention, the manufacturing method of the glass substrate for magnetic discs, and the cutting blade member were demonstrated in detail, this invention is not limited to the said embodiment and Example, this invention. Of course, various improvements and changes may be made without departing from the spirit of the present invention.

DESCRIPTION OF SYMBOLS 10 Molten glass outflow pipe 12 Outlet 20 Molten glass flow 21 Molten glass lump 30 Cutting device 40 Downstream side cutting blade member 41A, 51A Front end cutting blade 41B, 51B Rear end cutting blade 41T Upper surface 42, 52 Support member 44 Drive part 50 Upstream Side cutting blade member 51U Lower surface 90A, 90B Mold 91A, 91B Press molding surface 100, 102, 104, 106, 108 Annular movement path

Claims (9)

A method for producing a glass blank for a magnetic disk having a pair of main surfaces used for a glass substrate for a magnetic disk,
A process of cutting the molten glass flow with a pair of cutting blades provided in a pair of cutting blade members, and forming a glass gob by the cutting,
Processing to form a glass blank by press molding sandwiching the glass gob between a pair of press surfaces,
The pair of cutting blades are provided on the upstream side and the downstream side of the molten glass flow so as to cut the molten glass flow,
Each of the cutting blade members cuts the molten glass flow by passing through the flow channel region of the molten glass flow in one direction, and when cutting the molten glass flow, the tip of the molten glass flow is The method of manufacturing a glass blank for a magnetic disk, wherein a time of contact with an upstream cutting blade located upstream of the molten glass flow among the pair of cutting blade members is 40 milliseconds or less. A method for producing a glass blank for a magnetic disk having a pair of main surfaces used for a glass substrate for a magnetic disk,
A process of cutting the molten glass flow with a pair of cutting blades provided in a pair of cutting blade members, and forming a glass gob by the cutting,
Processing to form a glass blank by press molding sandwiching the glass gob between a pair of press surfaces,
Each of the cutting blade members cuts the molten glass flow by passing through the flow channel region of the molten glass flow in one direction when the pair of cutting blades intersect to form the glass gob, and the molten glass When cutting the flow, the time for the tip of the molten glass flow to contact the upstream cutting blade member located on the upstream side of the molten glass flow among the pair of cutting blade members is 40 milliseconds or less . A method for producing a glass blank for a magnetic disk.   A method for producing a glass blank for a magnetic disk having a pair of main surfaces used for a glass substrate for a magnetic disk,
  A process of cutting the molten glass flow with a pair of cutting blades provided in a pair of cutting blade members, and forming a glass gob by the cutting,
  Processing to form a glass blank by press molding sandwiching the glass gob between a pair of press surfaces,
  Each of the cutting blade members cuts the molten glass flow by passing through the flow channel region of the molten glass flow in one direction when the pair of cutting blades intersect to create the glass gob,
  When the pair of cutting blades are referred to as the pair of front end cutting blades, a rear end cutting blade is provided at each rear end of the pair of cutting blade members, and the molten glass flow is obtained by intersecting the front end cutting blades. A glass blank for a magnetic disk, wherein the molten glass stream is also cut by moving the trailing edge cutting blade to cross each other in the flow path region of the molten glass stream. Production method.   A method for producing a glass blank for a magnetic disk having a pair of main surfaces used for a glass substrate for a magnetic disk,
  A process of cutting the molten glass flow with a pair of cutting blades provided in a pair of cutting blade members, and forming a glass gob by the cutting,
  Processing to form a glass blank by press molding sandwiching the glass gob between a pair of press surfaces,
  Each of the cutting blade members is one of linear movement paths passing through the flow channel region of the molten glass flow when viewed from the upstream side of the molten glass flow when the pair of cutting blades intersect to form the glass gob. A method for producing a glass blank for a magnetic disk, wherein the molten glass flow is cut by moving along a direction and passing through a flow path region of the molten glass flow in one direction. Each of the said cutting blade member moves along one direction of the cyclic | annular movement path | route which passes along the said flow-path area | region seeing from the upstream of the said molten glass flow, and cut | disconnects the said molten glass flow. A method for producing a glass blank for magnetic disk according to claim 1 . Each of the said cutting blade member moves along one direction of the linear movement path | route which passes along the said flow-path area | region seeing from the upstream of the said molten glass flow, and cut | disconnects a molten glass flow . The manufacturing method of the glass blank for magnetic discs of any one of Claims 1 . When the pair of cutting blades are referred to as the pair of front end cutting blades, a rear end cutting blade is provided at each rear end of the pair of cutting blade members, and the molten glass flow is obtained by intersecting the front end cutting blades. in addition to cutting the also performs the cutting of the molten glass flow by intersecting each other at the passage region of the molten glass flow by moving the rear end cutting blade, according to claim 1, claim 2, claim 5, And the manufacturing method of the glass blank for magnetic discs of any one of Claim 6 . The glass blank produced by the production method of a glass blank for a magnetic disk according to any one of claims 1-7 wherein the process of machining,
The process for machining includes a grinding process for the main surface of the glass blank and a polishing process for polishing the main surface of the glass blank after grinding. A cutting blade member comprising a cutting blade for cutting the molten glass flow to make a glass gob by crossing each other in the flow channel region of the molten glass flow,
The cutting blade member has the cutting blade at each of a front end and a rear end in a moving direction in which the cutting blade member moves to intersect the cutting blade member.

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