JP2013091130A - Grinding abrasive grain collecting device, grinding liquid control system, method of manufacturing glass substrate, and method of collecting grinding abrasive grain - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a grinding abrasive grain collecting device even in damage to a screw and a bowl, excellent in control accuracy, and having high collecting efficiency.SOLUTION: The grinding abrasive grain collecting device separates a concentrated liquid including grinding abrasive grains from slurry including the grinding abrasive grains. The grinding abrasive grain collecting device includes: a bowl which holds the slurry; a screw conveyor for scraping out the concentrated liquid from the bowl; a driving means for driving the bowl and the screw conveyor to rotate; and a control means for controlling the driving means. The control means controls a difference between the rotating speed of the bowl and the rotating speed of the screw conveyor based on a driving current value of the driving means which drives the bowl or the screw conveyor to rotate.

Description

  The present invention relates to a polishing abrasive recovery device, a polishing liquid management system, a glass substrate manufacturing method, and a polishing abrasive recovery method.

  It is desired that the surfaces of glass substrates, semiconductor wafers, and films formed thereon used in magnetic disk recording devices and the like be highly flat. Usually, a method of polishing (CMP or the like) using a polishing liquid containing polishing abrasive grains is employed for flattening a glass substrate or a semiconductor wafer. At this time, abrasive grains such as cerium oxide, aluminum oxide, and silicon oxide (colloidal silica) are used as the abrasive grains. Further, a pH adjuster, a surfactant and other additives are added to the polishing liquid.

  Wastewater collected after the polishing process for glass substrates and semiconductor wafers includes polishing debris such as a polishing object, a polishing pad, and abrasive grains. These polishing scraps cause scratches on the surface of the object to be polished, and the polishing rate decreases due to a decrease in the concentration of polishing abrasive grains. Therefore, waste water cannot be reused as it is after these polishing steps. Therefore, for the purpose of reusing wastewater after the polishing process, treatment such as removal of impurities and concentration of abrasive grains is performed, and abrasive grains are collected and a polishing liquid containing abrasive grains of a predetermined composition is prepared. Research to readjust is underway.

  Specifically, in Patent Document 1, the specific gravity and flow rate of the slurry before and after being charged into the polishing abrasive recovery device are detected, and the polishing abrasive recovery rate by the polishing abrasive recovery device is calculated based on the detection result. A technique for controlling the rotational speed of the abrasive recovery device so that the result becomes a predetermined value is disclosed.

Japanese Patent No. 3408879

  However, in the method of Patent Document 1, depending on the conditions of the slurry to be charged, the load on the screw and bowl of the abrasive abrasive recovery device becomes high, which contributes to early failure. Further, there is a problem that the control accuracy with respect to the slurry charging conditions (for example, the specific gravity of the slurry) is lowered.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a polishing abrasive recovery device that has a low load on the screw or bowl of the polishing abrasive recovery device, has high control accuracy, and a high recovery rate of polishing abrasive particles.

According to the present invention,
A polishing abrasive recovery device for separating a concentrated liquid containing abrasive grains from a slurry containing abrasive grains,
The abrasive abrasive recovery device
A bowl holding the slurry;
A screw conveyor for scooping out the concentrate from the bowl;
Drive means for rotationally driving the bowl and the screw conveyor;
Control means for controlling the drive means;
Have
The control means, based on the drive current value of the drive means for rotationally driving the bowl or the screw conveyor, the difference between the rotation speed of the bowl and the rotation speed of the screw conveyor (hereinafter referred to as the rotation speed). (Also called the difference).
An abrasive recovery device is provided.

  The present invention has the following effects.

  It is possible to provide a polishing abrasive recovery device with little damage to the screw or bowl of the polishing abrasive recovery device, high control accuracy, and high polishing abrasive recovery rate.

FIG. 1 is a schematic configuration diagram of an example of a polishing abrasive recovery device according to the present invention. FIG. 2 is an example of a flowchart of a polishing abrasive grain recovery method according to the present invention. FIG. 3 is a schematic diagram showing an example of a polishing liquid management system according to the present invention.

[Abrasive abrasive recovery device]
First, the abrasive grain collection device according to the present invention will be described. The polishing abrasive grain recovery device of the present invention can concentrate and regenerate slurry containing polishing abrasive grains after the polishing process (for example, used polishing liquid, dressing water, washing water, waste water, etc.). The abrasive grain recovery device according to the present invention may be referred to as a centrifugal separator including a centrifugal settling machine and a centrifugal dehydrator depending on the material to be input, application, and process. Centrifugal sedimentators are usually classified as separation plate type, cylindrical type, and decanter type, and centrifugal dehydrators are sometimes classified as batch type or continuous type. In the present embodiment, a decanter type centrifugal settling machine having stable and long-time separation / concentration performance is used, but the present invention is not limited to this, and it is applicable to all types of the above-described abrasive grain collection devices. Can be applied.

  In FIG. 1, the schematic block diagram of an example of the abrasive grain collection | recovery apparatus which concerns on this invention is shown. The abrasive abrasive recovery device 1 mainly continuously discharges the bowl 2 rotating at high speed and the concentrated liquid (the slurry containing the abrasive abrasive is processed by the recovery method according to the present invention and the abrasive abrasive is concentrated). And a screw conveyor 3. Further, the polishing abrasive grain collection device 1 includes a dam plate (weir plate) 4 on one end wall portion of the bowl 2, and an input pipe 5 for introducing the slurry after the polishing process into the polishing abrasive grain recovery device 1; Have

  The bowl 2 includes a straight barrel-like straight portion 6 and a tapered cone portion 7 following the straight portion 6, and has a screw conveyor 3 therein. The dam plate 4 is installed on the end wall portion of the bowl 2 on the straight portion side, and forms a first tip opening 8 of the straight portion 6. The dam plate 4 is normally oriented perpendicular to the rotation axis of the bowl 2. The input pipe 5 is inserted and disposed in the second tip opening 9 of the cone portion 7, and a slurry including abrasive grains 10 and the like is supplied into the polishing abrasive collection apparatus 1 through the input pipe 5.

  The abrasive grain recovery device 1 is connected to a driving means such as a motor (not shown), and the bowl 2 and the screw conveyor 3 are independently rotated. Usually, the driving means for driving the bowl 2 is called a main drive, and the driving means for driving the screw conveyor 3 is called a back drive. Further, the polishing abrasive grain recovery device 1 has a control means 11. The control means 11 includes an arithmetic processing unit (not shown) made of, for example, a CPU and a recording medium (not shown) made of, for example, a hard disk. The CPU of the control unit 11 controls the operation of the drive unit in accordance with a program or the like recorded on the hard disk of the control unit 11, for example.

  The concentration rate of the slurry is greatly affected by the flow rate ratio between the first tip opening 8 side of the straight portion 6 and the second tip opening 9 side of the cone portion 7. Therefore, by changing the height of the dam plate 4, the liquid level in the abrasive grain collecting device 1 can be adjusted and the concentration rate can be changed. In the present embodiment, the height of the dam plate 4 is set to a constant length of about 100 mm.

[Abrasive grain recovery method]
Next, a polishing abrasive grain collection method using the abrasive grain collection device according to the present invention will be described with reference to the drawings. Specifically, a method for controlling the rotation speed of the bowl 2 and the screw conveyor 3 by the above-described control means will be described in detail. FIG. 2 shows an example of a flowchart of the polishing abrasive grain recovery method according to the present invention.

  When the bowl 2 and the screw conveyor 3 are rotated in order to concentrate and separate the abrasive grains from the slurry containing the abrasive grains, the loaded slurry (in this embodiment, used polishing containing cerium oxide as the abrasive grains). Part of the liquid (dressing water, washing water, drainage, etc.) (such as cerium oxide) is deposited on the inner wall of the bowl 2 of the abrasive grain collection device 1. In addition, normally, the rotation direction of the bowl 2 and the rotation direction of the screw conveyor 3 are the same direction, and this invention is not limited to the rotation direction. By collecting the abrasive grains 10 (cerium oxide, etc.) deposited on the inner wall of the bowl 2 with the screw conveyor 3 having a different rotational speed with respect to the rotational speed of the bowl 2, the concentrated liquid in which the abrasive grains are concentrated is recovered. it can. At this time, since the accumulated abrasive grains 10 become resistance of the rotating bowl 2 and the screw conveyor 3, a load is generated on the bowl 2 and the screw conveyor 3.

  Usually, the load on the bowl 2 and the screw conveyor 3 depends on the supply flow rate (supply speed) of the slurry to be charged, the concentration of abrasive grains in the slurry, the difference in rotational speed between the bowl and the screw conveyor, and the like.

  In the present invention, as shown in FIG. 2, if the load generated in the main drive is within a predetermined value range, the process is continued (S20), and the generated main drive load is within a predetermined value range. If it is outside, the control means controls the drive means, and changes the rotation speed of the bowl 2 and the screw conveyor 3 so that the load of the main drive falls within a predetermined value range (S30). The user can control the flow rate of the slurry to be charged. Therefore, when the concentration of the abrasive grains in the slurry to be charged is constant or the concentration of the abrasive grains is low, the load of the main drive generated in the bowl 2 is a predetermined value in terms of the drive current value of the main drive. You may control so that it may become.

  The control of the drive means by the control means can be configured to change the rotational speed of both the bowl 2 and the screw conveyor 3 to control the difference between the rotational speed of the bowl and the rotational speed of the screw conveyor. In addition, the configuration may be such that the difference between the rotation speed of the bowl and the rotation speed of the screw conveyor is controlled by rotating the bowl 2 at a constant rotation speed and changing the rotation speed of the screw conveyor 3. Further, the screw conveyor 3 may be rotated at a constant rotational speed, and the rotational speed of the bowl 2 may be changed to control the difference between the rotational speed of the bowl and the rotational speed of the screw conveyor. In the present embodiment, the difference between the rotation speed of the bowl 2 and the rotation speed of the screw conveyor 3 is controlled by rotating the bowl 2 at a constant rotation speed and changing the rotation speed of the screw conveyor 3. However, the present invention is not limited in this respect.

  For example, when the bowl 2 is rotationally driven at a constant rotational speed, if slurry exists in the abrasive grain collecting apparatus 1, this slurry becomes a load, and the drive current value increases. Therefore, the generated load can be approximated by a drive current value for driving the bowl 2 or the screw conveyor 3 to rotate at a predetermined rotational speed, for example. At this time, since the generated load is proportional to the bowl 2 and the screw conveyor 3, it can be approximated to the driving current value of either the bowl 2 or the screw conveyor 3, that is, the bowl 2 or the screw conveyor. The load generated based on any one of the drive current values of 3 may be evaluated to control the drive means.

  In the embodiment, as described above, the bowl 2 is rotated at a constant rotation speed, and the rotation speed of the screw conveyor 3 is changed. Therefore, the current value for rotating the bowl 2 at a predetermined rotational speed was measured, and this value was approximated to the load on the bowl 2 (that is, the abrasive abrasive recovery device 1). Specifically, the difference in rotational speed between the bowl 2 and the screw conveyor 3 was controlled so that the drive current value for rotating the bowl 2 at a predetermined rotational speed was within a predetermined value range.

  In the present embodiment, a polishing abrasive recovery device having a rated current value of 12A for the bowl 2 of the polishing abrasive recovery device 1 is used. In this case, the generated load is greater than the drive current value of the bowl 2 when the atmosphere is only present inside the abrasive grain recovery device 1 in terms of the drive current value of the bowl 2, and is 11.4 A or less (that is, It is preferably 95% or less of the rated current value of the abrasive grain recovery device 1. When the load generated in the bowl 2 (that is, the abrasive grain collecting device 1) exceeds 11.4 A in terms of the driving current value of the bowl 2, the abrasive grains 10 are excessively deposited inside the abrasive grain collecting device. It becomes a state. Therefore, it is necessary to clean the polishing abrasive recovery device and remove the polishing abrasive 10 inside. That is, the time loss required for cleaning and the loss of the polishing abrasive grains 10 are generated, so that the abrasive grain recovery efficiency is deteriorated. Moreover, the cost for washing away the abrasive grains 10 inside the abrasive grain recovery device is also required. Further, if the load on the bowl 2 and the screw conveyor 3 continues to be high, the screw conveyor 3 (and other components) may fail. That is, in the present invention, since the load generated in the polishing abrasive grain collection device 1 is controlled to be within a predetermined range, stable operation of the polishing abrasive grain collection device 1 can be realized. The generated load is more preferably in the range of 9.0 A to 11.3 A (that is, 75% to 94% of the rated current value of the abrasive grain recovery device 1) in terms of the drive current value of the bowl 2. 9.6A to 11.2A (that is, 80% to 93% of the rated current value of the abrasive grain recovery device 1) is more preferable.

  As described above, the load generated in the bowl 2 depends on the supply flow rate (supply speed) of the slurry to be added, the concentration of the abrasive grains in the slurry, and the difference in the rotation speed between the bowl and the screw conveyor. When the difference in rotational speed between the bowl 2 and the screw conveyor 3 is made constant, the load generated in the bowl 2 increases as the supply flow rate of the slurry to be introduced and the concentration of abrasive grains in the slurry increase. In the conventional abrasive recovery device, if the abrasive abrasive concentration in the slurry is 2%, for example, and the supply flow rate of the slurry to be added is 25 L / min or more, the load on the screw conveyor 3 exceeds the rated current value and becomes high. Too much (overload), it was necessary to reduce the supply flow rate of the slurry to be added. However, in the present invention, the difference between the rotational speed of the bowl 2 and the rotational speed of the screw conveyor 3 is also obtained under the condition that the concentration of the abrasive grains in the slurry is 2% and the supplied flow rate of the slurry is 25 L / min or more. By controlling this, the load on the screw conveyor 3 can be reduced. As a result, since the polishing abrasive recovery device can be operated continuously and stably, productivity of polishing abrasive recovery can be increased as compared with the conventional method. At this time, since the difference between the rotational speed of the screw conveyor 3 and the rotational speed of the bowl 2 becomes large, the abrasive grains 10 are sufficiently scraped out from the bowl 2 by the screw conveyor 3 even if the abrasive grains in the slurry are high in concentration. And a high recovery rate of abrasive grains can be realized. Furthermore, in the method of the present invention, the load of the screw conveyor 3 is reduced even when the concentration of the abrasive grains in the slurry is as high as 5% and the supply flow rate of the slurry to be added is 25 L / min, and A high polishing abrasive grain recovery rate can be realized (see Examples described later).

  On the other hand, even when the load generated in the bowl 2 is low, that is, when the concentration of the abrasive grains in the slurry to be charged is as low as 1% or less, for example, the load generated in the bowl 2 is Is controlled so as to be within a predetermined value range in terms of the drive current value. In this embodiment, more specifically, the difference between the rotational speed of the screw conveyor 3 and the rotational speed of the bowl 2 is controlled so as to increase the load generated in the bowl 2. That is, in the embodiment in which the bowl 2 is set to a constant rotation speed, the rotation speed of the screw conveyor 3 is decreased. Thereby, the abrasive grains 10 deposited in the bowl 2 can be made a certain amount or more, and the concentration rate can be increased even in a low concentration slurry.

[Polishing liquid management system]
Next, a polishing liquid management system having the abrasive grain recovery device 1 of the present invention will be described with reference to the drawings. FIG. 3 is a schematic diagram showing an example of a polishing liquid management system according to the present invention.

  The polishing liquid management system 100 includes the abrasive grain collection device 1, the coarse particle separation device 150, the component adjustment tank 160, and other tanks as necessary. Examples of other tanks include a slurry tank 120, a discharge water tank 130, a dispersion tank, and a water tank 140.

  By using the polishing liquid management system 100 of the present invention, for example, a slurry (for example, used polishing liquid, dressing water, cleaning water, waste water) from the polishing apparatus 110 when a glass substrate for a magnetic recording medium is manufactured. Etc.) can be circulated through the slurry tank and the water tank provided in the polishing apparatus, respectively.

  The polishing apparatus 110 is not particularly limited as long as it can polish the glass using polishing abrasive grains. For example, glass such as a glass substrate for magnetic recording media, glass for optical parts, glass for photomask, glass for liquid crystal display, etc. A glass polishing apparatus can be used.

  The abrasive grains contained in the polishing liquid include, for example, cerium oxide particles, silica particles, alumina particles, zirconia particles, zircon particles, silicon carbide particles, boron carbide particles, diamond particles, manganese oxide particles, titania particles, and oxidation. One or more kinds of particles selected from iron particles can be used.

  Polishing abrasive grains used in the polishing apparatus are stored in the slurry tank 120 and circulate repeatedly between the polishing apparatus and the slurry tank.

  For example, the water used for cleaning the glass substrate or the like is stored in the water tank 140 and supplied through the water nozzle.

  The drainage water tank 130 is a tank for storing slurry (for example, used polishing liquid, dressing water, washing water, drainage, etc.), and is normally stirred to prevent precipitation and aggregation. The slurry in the discharge water tank 130 is conveyed regularly or continuously to the polishing abrasive grain recovery device 1 of the present invention, and the concentrated liquid containing the abrasive grains concentrated by the above-described polishing abrasive grain recovery method, , Separated. Thereafter, the concentrated liquid is conveyed to the coarse particle separator 150. The separation liquid is usually discarded, but may be returned to the water tank 140 and reused.

  FIG. 3 shows an example in which the concentrated liquid from the abrasive grain collection device 1 of the present invention is conveyed to the coarse particle separation device 150. However, the concentrated liquid from the abrasive grain recovery device 1 of the present invention may be transported to a coarse particle separator 150 after being transported to a dispersion tank (not shown). In this case, in the dispersing tank, a dispersing agent and water are added regularly or continuously, and redispersion processing is performed. The dispersion tank is usually stirred in order to prevent precipitation and aggregation. The dispersant is not particularly limited, and for example, oxycarboxylic acid, polyacrylic acid, or a salt thereof can be used.

  The concentrated liquid or the re-dispersed concentrated liquid is transferred to a centrifugal separator such as the coarse particle separator 150, where coarse particles (for example, particles having a particle size larger than 5 μm) are removed and conveyed to the component adjustment tank 160. Is done. Usually, the coarse particles separated here are discarded.

  In the component adjustment tank 160, component adjustment such as concentration adjustment and pH adjustment is performed, and a dispersant is added as necessary. At this time, the component adjustment tank 160 is usually stirred to prevent precipitation and aggregation. The polishing liquid regenerated by adjusting the concentration of the concentrated liquid is returned to the slurry tank 120 and used again for polishing.

  If necessary, a filter may be installed at any place in the polishing liquid management system.

[Method for producing glass substrate for magnetic recording medium]
The polishing liquid management system can be applied to various polishing apparatuses by using the polishing abrasive recovery apparatus 1 of the present invention to recover and correct the polishing abrasive as a polishing liquid. Specifically, as described above, the polishing apparatus can be used in a polishing apparatus for polishing glass such as a glass substrate for magnetic recording media, glass for optical parts, glass for photomask, glass for liquid crystal display.

  Here, the case where the polishing liquid management system of the present invention is applied to a method of manufacturing a glass substrate for a magnetic recording medium will be described.

An example of the method for producing a glass substrate for a magnetic recording medium of the present invention is as follows:
(1) A shape imparting step of chamfering the inner peripheral side surface and the outer peripheral side surface after processing the glass base substrate into a disk shape having a circular hole in the central portion;
(2) An outer peripheral end surface polishing step for polishing the outer peripheral end surface of the glass substrate,
(3) The inner peripheral end face of the glass substrate is polished. Inner peripheral edge polishing process,
(4) a main surface polishing step for polishing the upper and lower main surfaces of the glass substrate;
(5) A cleaning step of precisely cleaning and drying the glass substrate to obtain a glass substrate for a magnetic recording medium,
It is manufactured by such processes. Although this invention is not limited to the said method, the slurry containing the abrasive grain (for example, used in the outer peripheral end surface grinding | polishing process of (2), the inner peripheral end surface grinding | polishing process of (3), and the main plane grinding | polishing process of (4) (for example) By applying the used polishing liquid, dressing water, cleaning water, drainage, etc.) to the polishing liquid management system of the present invention, the abrasive grains can be efficiently recovered. Examples of the abrasive grains include one selected from cerium oxide particles, silica particles, alumina particles, zirconia particles, zircon particles, silicon carbide particles, boron carbide particles, diamond particles, manganese oxide particles, titania particles, and iron oxide particles. The above particles can be used.

  Note that (2) the outer peripheral end face polishing step and (3) the inner peripheral end face polishing step may be performed first. In addition, at least one of the end surface polishing steps (2) and (3) before and after the end surface polishing step, a main plane lapping (for example, loose abrasive lapping, fixed abrasive lapping, etc.) may be performed. Glass substrate cleaning (inter-process cleaning) and glass substrate surface etching (inter-process etching) may be performed. Note that the main plane lapping here is polishing of the main plane in a broad sense.

  The polishing step may be only primary polishing, primary polishing and secondary polishing may be performed, or tertiary polishing may be performed after secondary polishing.

  In the present invention, the glass substrate for a magnetic recording medium may be amorphous glass, crystallized glass, or tempered glass (for example, chemically tempered glass) having a tempered layer (compressive stress layer) on the surface layer of the glass substrate. As an example, when high mechanical strength is required for a glass substrate for magnetic recording media, a strengthening step (for example, a chemical strengthening step) for forming a reinforcing layer on the surface layer of the glass substrate is performed. The strengthening step may be performed either before the first polishing step, after the last polishing step, or between each polishing step. The glass substrate of the glass substrate of the present invention is produced by a method such as a float method, a fusion method, a redraw method, or a press molding method, but the present invention is not limited in this respect.

  A magnetic disk can be manufactured by laminating layers such as an underlayer, a magnetic layer, a protective layer, and a lubricating layer on the glass substrate for a magnetic recording medium obtained by the above method. A conventional method or the like can be appropriately used as a method for laminating each layer. The size of the magnetic disk is not particularly limited. For example, 0.85 inch type magnetic disk (inner diameter 6 mm, outer diameter 21.6 mm, plate thickness 0.381 mm), 1.0 inch type magnetic disk (inner diameter 7 mm, outer Diameter 27.4 mm, plate thickness 0.381 mm), 1.8 inch type magnetic disk (inner diameter 12 mm, outer diameter 48 mm, plate thickness 0.508 mm), 2.5 inch type magnetic disk (inner diameter 20 mm, outer diameter 65 mm, plate) Magnetic disks of various sizes, such as 0.635 mm and 0.8 mm thick, can be manufactured.

[First Embodiment]
Next, an embodiment in which the effects of the abrasive grain collection device and the abrasive grain collection method of the present invention have been confirmed will be described.

  Table 1 shows the implementation conditions in the embodiment in which the effects of the abrasive grain collection device and the abrasive grain collection method of the present invention were confirmed.

図１の研磨砥粒回収装置に、研磨砥粒として酸化セリウムを所定の濃度で含有するスラリ（表１参照）を、所定の供給流量（表１参照）で投入し、ボウル及びスクリューコンベアを回転駆動させることで、研磨砥粒（酸化セリウム）を濃縮して回収した。この時、ボウルの回転速度を一定にし、スクリューコンベアの回転速度を変更して、スクリューコンベアとボウルの回転速度の差（差速と呼ぶこともある。）を制御した。例１〜例５においては、ボウル（メインドライブ）の負荷が、ボウルの駆動電流値換算で、表１に示す範囲となるように、回転速度の差を制御した。例６〜例８においては、回転速度の差が１５ｒｐｍになるようマニュアルで制御し、ボウルの駆動電流値を測定した。

A slurry containing cerium oxide as a polishing abrasive at a predetermined concentration (see Table 1) is put into the polishing abrasive collection device of FIG. 1 at a predetermined supply flow rate (see Table 1), and the bowl and screw conveyor are rotated. By driving, the abrasive grains (cerium oxide) were concentrated and recovered. At this time, the rotation speed of the bowl was kept constant, the rotation speed of the screw conveyor was changed, and the difference between the rotation speeds of the screw conveyor and the bowl (sometimes referred to as differential speed) was controlled. In Examples 1 to 5, the difference in rotational speed was controlled so that the load of the bowl (main drive) was in the range shown in Table 1 in terms of the bowl drive current value. In Examples 6 to 8, manual control was performed so that the difference in rotational speed was 15 rpm, and the drive current value of the bowl was measured.

The rotational speed difference R1 (rpm) in the above is defined by the following equation (1) using the rotational speed R _s (rpm) of the screw conveyor and the rotational speed R _b (rpm) of the bowl. .

R1 = | R _s −R _b | / 10 Formula (1)
[Evaluation]
The evaluation of the first embodiment is based on the concentration of polishing abrasive grains (cerium oxide) in the collected concentrated liquid (solution in which cerium oxide as polishing abrasive grains is concentrated) and the recovery rate of polishing abrasive grains (cerium oxide). And went on.

  In addition, the density | concentration of the cerium oxide in a slurry and the collect | recovered concentrate was measured with the moisture meter (Moisture analyzer MX-50; made by A & D Company, Limited).

The recovery rate R2 of cerium oxide was defined by the following formula (2) using the recovered cerium oxide weight W _{out ce} and the input cerium oxide weight W _{in ce} .

R2 = W _{out ce} / W _{in ce} equation (2)
Here, the recovered cerium oxide weight W _{out ce} (or W _{in ce} ) can be calculated by the following method. Here, only the method of calculating the recovered cerium oxide weight W _{out ce} will be described, but the input cerium oxide weight W _{in ce} can also be calculated by the same method.

The recovered cerium oxide concentration is (outside cerium oxide concentration in the recovered concentrate) C _{out ce} , the discharged cerium oxide solution flow rate is V _{out ce,} and the volume of water and cerium oxide in the discharged cerium oxide solution is V _w , respectively. And V _Ce and the specific gravity of cerium oxide is SG _Ce , the following formulas (3) and (4) hold.

W _{out ce} = (V _Ce × SG _Ce ) / (V _w + V _Ce × SG _Ce ) Formula (3)
V _{out ce} = V _w + V _Ce formula (4)
By substituting Equation (4) into Equation (3), the volume V _Ce of cerium oxide in the discharged cerium oxide solution is expressed by Equation (5) below.

V _Ce = (W _{out ce} × V _{out ce} ) / (SG _Ce − (SG _Ce −1) W _{out ce} ) Equation (5)
That is, the discharged cerium oxide weight W _{out ce} is calculated by the following formula (6) obtained by multiplying the formula (5) by the specific gravity of cerium oxide.

W _{out ce} = SG _Ce (W _{out ce} × V _{out ce} ) / (SG _Ce − (SG _Ce −1) W _{out ce} ) (6)
Table 1 also shows the concentration of cerium oxide in the collected concentrated liquid and the recovery rate of cerium oxide in each example.

  As is clear from Table 1, in the methods of Examples 1 to 5, the rotational speed of the bowl and screw conveyor is optimally controlled by the load of the abrasive grain recovery device, so cerium oxide in the slurry that has been charged. The concentrated cerium oxide concentration of the collected concentrate was higher than the concentration (concentration rate was high). Further, even when the concentration of cerium oxide is a high concentration of 2% by mass or more and the supply flow rate is a high supply flow rate of 25 L / min, the rated current value of the abrasive abrasive recovery device is exceeded (specifically, It was found that the continuous operation can be stably performed without the bowl drive current value exceeding 12 A). That is, it is not necessary to clean and remove the slurry that has accumulated excessively in the abrasive abrasive recovery device, and the recovery rate of abrasive abrasives (cerium oxide) can be maintained as high as 80% or more. It was confirmed that the productivity of polishing abrasive grain collection was increased by using the apparatus and the recovery method. Further, according to the result of the present embodiment, even when the abrasive grain concentration in the slurry to be charged is changed during the process, the rotation speed of the bowl and the above-mentioned are based on the driving current value of the bowl (or screw conveyor). It was found that a high abrasive recovery rate can be realized by controlling the difference from the rotational speed of the screw conveyor.

[Second Embodiment]
Next, an embodiment that demonstrates the effect of controlling the difference in rotational speed between the screw conveyor and the bowl to be small when the concentration of abrasive grains in the slurry to be charged is low will be described.

  When the concentration of the abrasive grains in the slurry to be added is as low as 1% or less, for example, the load generated in the bowl may be lower than a predetermined value. In this case, control is performed to reduce the difference in rotational speed between the screw conveyor and the bowl so that the load generated in the bowl increases.

  As in the first embodiment, the slurry having the cerium oxide concentration shown in Table 2 is introduced into the polishing abrasive grain recovery device of FIG. 1 at the supply flow rate shown in Table 2, and the bowl (main drive) and screw conveyor (back drive) ) Was rotationally driven to concentrate and collect the abrasive grains. As in the first embodiment, the rotational speed of the bowl was kept constant, the rotational speed of the screw conveyor was changed, and the difference in rotational speed was controlled.

表２より明らかであるように、投入するスラリ中の研磨砥粒の濃度が低い場合においても、本発明の研磨砥粒回収装置及び回収方法を使用することで、高い濃縮率を実現することができた。また、研磨砥粒（酸化セリウム）の回収率も６５％以上とすることができた。

As is apparent from Table 2, even when the concentration of abrasive grains in the slurry to be added is low, a high concentration ratio can be realized by using the abrasive grain collection device and collection method of the present invention. did it. Moreover, the recovery rate of the abrasive grains (cerium oxide) could be 65% or more.

  Furthermore, when the concentration of abrasive grains in the slurry to be added is low, the difference in rotational speed is reduced to increase the amount of abrasive grains accumulated in the abrasive grain recovery device (converted to the bowl drive current value). Thus, it was found that a higher recovery rate can be realized by setting the value within a predetermined value range. Therefore, for example, when the concentration of the abrasive grains in the slurry to be charged is low, a higher recovery rate can be realized by setting the drive current value range of the drive means high.

  By using the abrasive grain recovery device and recovery method of the present invention, the rotational speed of the bowl and screw conveyor is controlled based on the drive current value of the bowl (or screw conveyor) of the abrasive grain recovery device. It was found that a high recovery rate of grains, high productivity of abrasive grain recovery, and stable continuous operation can be realized. More specifically, the rotation speed of the screw conveyor and the bowl is reduced so that the load of the abrasive grain collecting device is reduced (to a predetermined range) under the condition that the flow rate of the slurry is high and the abrasive grain concentration is high. Increase the difference. On the other hand, under the condition that the concentration of abrasive grains in the added slurry is low, the difference in rotational speed is reduced so as to increase the load of the abrasive grain recovery speed (to a predetermined range). Thereby, the damage to the screw or bowl of the abrasive grain recovery device is uniform and small, the control accuracy is high, and the abrasive grain recovery rate can be increased.

DESCRIPTION OF SYMBOLS 1 Abrasive grain collection | recovery apparatus 2 Bowl 3 Screw conveyor 4 Dam plate (weir plate)
5 Input tube 6 Straight portion 7 Cone portion 8 First tip opening 9 Second tip opening 10 Abrasive grain 11 Control means

Claims (6)

A polishing abrasive recovery device for separating a concentrated liquid containing abrasive grains from a slurry containing abrasive grains,
The abrasive abrasive recovery device
A bowl holding the slurry;
A screw conveyor for scooping out the concentrate from the bowl;
Drive means for rotationally driving the bowl and the screw conveyor;
Control means for controlling the drive means;
Have
The control means controls the difference between the rotational speed of the bowl and the rotational speed of the screw conveyor based on the drive current value of the driving means for rotationally driving the bowl or the screw conveyor. ,
Polishing abrasive collection device. The control means adjusts the difference between the rotational speed of the bowl and the rotational speed of the screw conveyor so that the driving current value of the driving means for rotationally driving the bowl or the screw conveyor is within a predetermined range. To control,
The abrasive grain recovery device according to claim 1. The control means controls the rotational speed of the screw conveyor so that the driving current value of the driving means for rotating the bowl at a constant rotational speed is in a predetermined range.
When the drive current value is larger than the predetermined range, the rotational speed of the screw conveyor is increased, and the drive current value is controlled to be within the predetermined range.
When the drive current value is smaller than the predetermined range, the rotational speed of the screw conveyor is lowered, and the drive current value is controlled to be within the predetermined range.
The abrasive grain collection device according to claim 1 or 2. Abrasive grain recovery device according to any one of claims 1 to 3,
A coarse particle separator,
An ingredient adjustment tank;
A polishing liquid management system containing abrasive grains. Polishing process,
Cleaning process,
A method for producing a glass substrate for a magnetic recording medium, comprising:
The polishing process uses the polishing liquid management system according to claim 4.
A method for producing a glass substrate for a magnetic recording medium. A bowl for holding a slurry containing abrasive grains;
A screw conveyor for scraping the concentrated liquid containing the abrasive grains from the bowl;
Drive means for rotationally driving the bowl and the screw conveyor;
Control means for controlling the drive means;
A polishing abrasive recovery method using an abrasive recovery device having
A polishing abrasive grain recovery method for controlling a difference between a rotation speed of the bowl and a rotation speed of the screw conveyor based on a drive current value of the driving means for rotationally driving the bowl or the screw conveyor.

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