JP4785185B2 - Inner hole processing method of hollow brittle material - Google Patents

Description

  The present invention relates to a novel method for processing an inner hole of a hollow brittle material using a drill for processing a hollow brittle material having a predetermined configuration, and particularly used for manufacturing a core tube and a lamp used in the semiconductor industry. Of hollow brittle material that is effectively applied to process the inner diameter of a quartz glass cylindrical body that is a base material for manufacturing a silica glass tube and a silica glass tube that is a base material of an optical fiber. It relates to a processing method.

  A quartz glass cylinder used as a base material for manufacturing a quartz glass tube used as a base material for an optical fiber and a quartz glass tube used for manufacturing a core tube and a lamp used in the semiconductor industry Although it is processed into various dimensions depending on the application, if it is made from a base material for each dimension, it takes time and labor in productivity, leading to a large cost increase.

  For this reason, in general, a primary base material of quartz glass having a certain size is first prepared, and then an inner wall and an outer wall are processed into the respective dimensions to prepare a secondary glass quartz glass cylindrical body. The material is stretched to produce the final product. The difference in wall thickness variation in the final product is a deviation of the circle center of the average inner diameter from the circle center of the average outer diameter, and is required to be 1.0 mm or less, so accuracy of 1.0 mm or less is also required for the base material. .

  For example, a non-porous primary base material produced by the VAD method or the direct method is drilled with a hot carbon drill drilling device or the like according to the center of the circle of the base material, or a soot base material by the OVD method. After making the material, pull out the mandrel, make it transparent glass and make a transparent primary base material, then polish it with a precision honing machine to make a quartz glass cylinder that is the secondary base material, but the primary base material When drilling holes with a hot carbon drill, especially when drilling holes in a base material exceeding 1 m, the straightness of the core drill is excellent due to non-uniform melting of the tip of the core drill and deflection of the core of the core drill. Difficult to open holes.

  In the case of the OVD method, when the soot base material is made transparent glass in a hollow state, the inner surface is made transparent with a non-uniform inner diameter. When grinding and polishing with a precision honing apparatus from these states, it takes a very long time just to adjust the inner diameter, and the productivity deteriorates.

  In order to eliminate these problems, a secondary crack is generated in the boundary region due to the impact of the rotating cam against the inner wall of the hole, and the hollow brittle material in which the hole is formed is prevented from further reducing the strength. There has been disclosed a method and drill for minimizing damage to a brittle material and accurately guiding a drill to drill a deep hole in the hollow brittle material (Patent Document 1).

  As shown in FIG. 5, in the conventional drill 10 for processing a hollow brittle material, the number of the grindstone chips 14 provided on the head disk body 12 of the drill head portion is set in order to process the inner wall to a specified dimension. Although eight holes were drilled, the gap between the center of the average inner diameter and the center of the average inner diameter with respect to the center of the circle of the average outer diameter can be expanded to 1.0 mm or less without leaving cracks on the inner wall. A quartz glass cylinder with high accuracy was obtained.

  However, when the number of grindstone chips 14 is set to 8 and the hole-growing grinding is performed by +5 mm or more from the inner diameter before processing, the straightness during grinding decreases, and the average inner diameter with respect to the circle center of the average outer diameter after processing. The deviation of the center of the circle became 1.0 mm or more, and the hole expansion process had to be performed again. That is, the processed inner diameter has been processed so as to be bent with respect to the longitudinal direction of the base material.

  Also, due to mechanical shearing and impact stress that the grinding part of the grindstone tip of the drill head part acts on the inner wall of the hole, the inner wall of the hole is greatly damaged and deep cracks occur, which cannot be removed by other steps Cracks remained at such a depth that the holes had to be re-extracted.

  In order to prevent these problems, it is possible to finish to the desired inner diameter by repeating the grinding process of less than +5 mm from the inner diameter before processing several times, especially when performing hole expansion grinding of +5 mm or more from the inner diameter before processing. It takes a lot of time and effort, and the cost increases. Although it is possible to increase the number of steps of the grinding tool (drill crown) as in Patent Document 1, the structure of the grinding tool becomes complicated, and the difference in level difference between the steps must be taken into consideration. First and foremost.

  As a result of intensive studies on the conventional problems, the present inventors have found that the cause of the problems is as follows.

  The larger the number of grinding wheel tips, the smaller the grinding load during grinding, which is advantageous for hollow brittle materials such as glass to be ground. However, the smaller the grinding load, the smaller the grinding stone bond part (abrasive bonding part). Wear is relatively slow, diamond grains and other abrasive grains are removed, and the timing at which new next abrasive grains come out is also delayed, so the so-called dressing effect is reduced and the abrasive surface of the grindstone tip Also clogging will occur, conversely the grinding ability will fall.

  This phenomenon becomes more conspicuous as the inner diameter of a hollow brittle material with a long length, that is, with a long overall length, is reduced. The grinding ability of the grinding wheel tip is reduced, but the force that rotates the grinding wheel tip when the ability is not reduced. In addition, since the grindstone tip is pushed in by the pushing force, in an unprocessed state where the inner diameter is not uniform, the drill head is bent in that direction due to resistance at the inner wall portion where the grinding stone tip is large and the grinding resistance is large.

  Also, in some cases, the grinding ability of the grinding wheel tip is reduced, and the inner wall of the hole is greatly damaged by the mechanical shear and impact stress that the grinding part of the grinding wheel tip of the drill head part acts on the inner wall of the hole, resulting in a deep crack Occurs and deep cracks remain.

Therefore, as a result of further intensive studies, the present inventors have obtained the knowledge that a good grinding result can be obtained by reducing the number of grindstone tips and setting a predetermined grinding condition for grinding.
Japanese Patent Laid-Open No. 08-174538

  The present invention has been made in view of the above-described conventional problems. When grinding an inner hole before processing a hollow brittle material, the grinding ability and straightness of grinding can be improved even if the object to be ground is relatively long. An object of the present invention is to provide a hollow brittle material inner hole machining method that is excellent and does not damage the object to be ground.

An inner hole machining method for a hollow brittle material according to the present invention comprises a drill rod that rotates about a longitudinal axis, and a drill head provided at a front end of the drill rod, wherein the drill head is a head disk. A hollow having a head drill body provided with two or more and four or less head grindstone tips provided at equal intervals on the outer peripheral surface of the body, and the width of the head grindstone chip is 4 mm or more and 10 mm or less An inner hole machining method for performing hole expansion grinding with an inner diameter of an inner circumferential surface of a hollow brittle material before machining of a hollow brittle material using a drill for brittle material machining, wherein the inner diameter of the hollow brittle material is +5 mm or more . the contact area with the bore to restrict the 5 mm ² or more 80 mm ² or less, the deviation of the circle center of the average inner diameter for the circle center of the average outer diameter of the hollow brittle material which is grinding is processed such that 1.0mm or less It is characterized by.

  The drill head further includes an intermediate drill body having a plurality of intermediate grindstone tips provided at equal intervals on the outer peripheral surface of the intermediate disk body and having a diameter larger than that of the head drill body, It is preferable that the outer diameter difference between the drill body and the intermediate drill body is 1 mm or less. A plurality of the intermediate drill bodies are installed, and the outer diameter of the rear end side intermediate drill body positioned on the rear end side of the drill rod is gradually larger than the outer diameter of the front end side intermediate drill body positioned on the front end side of the drill rod. It is also possible to configure so that the diameter of each intermediate drill body is 1 mm or less. It is preferable that the number of the head grindstone chips is 2 or more and 4 or less. Moreover, it is preferable that the abrasive grains of the head grindstone chip are diamond abrasive grains or CBN abrasive grains.

When the contact area of the head grindstone tip with respect to the inner hole of the hollow brittle material is set to 5 mm ² or more and 80 mm ² or less, the wear of the abrasive bonding portion of the head grindstone chip is relatively fast, and the abrasive grains are removed and new. The timing at which the next abrasive comes out also becomes faster, and the grinding ability is maintained by the dressing effect. Moreover, even if the hollow brittle material has an uneven inner diameter, the grinding ability of the head grindstone tip is maintained, so that the grinding is performed with good straightness. Further, the mechanical shear and impact stress acting on the inner wall of the hollow brittle material are also relatively weakened by the grinding portion by the drill head, and the inner wall of the hollow brittle material is not greatly damaged, and a deep crack does not occur. This is particularly effective when a deep hole is opened in a hollow brittle material.

  In addition, although the effect of this invention is achieved even if it does not install an intermediate drill body, if desired, one or several intermediate drill bodies can be provided. The number of intermediate grindstone tips provided in the intermediate drill body is not particularly limited, but for example, 6 to 9 can be installed as in the case of the conventional structure.

When the contact area of the head grindstone tip with respect to the inner hole of the hollow brittle material exceeds 80 mm ² , if the inner diameter of the hollow brittle material is not uniform, the grinding ability of the head grindstone tip is not maintained, and the straightness of the drill head If the contact area is less than 5 mm ² , there is a disadvantage that the grinding ability is lowered.

  The width of the head grindstone tip is preferably 4 mm or more and 10 mm or less. When the width of the head grindstone chip is less than 4 mm, the head grindstone chip is chipped. On the other hand, when the width of the head grindstone tip exceeds 10 mm, the grinding resistance increases, and the grinding ability is lowered.

    In particular, when drilling with a diameter of +5 mm or more from the inner diameter before processing, the deviation of the circle center of the average inner diameter from the circle center of the average outer diameter is precisely 1.0 mm or less without leaving a crack in the inner wall. And a quartz glass cylinder with good dimensional accuracy can be obtained.

  The above-mentioned average outer diameter is obtained by measuring the outer diameter of the base material with a laser-type outer diameter measuring device at intervals of 4 to 360 points at intervals of 50 to 100 mm with respect to a predetermined length of the base material. The average inner diameter is 4 to 360 points at intervals of 50 to 100 mm in the same manner as described above, and the thickness of the tube is measured with a laser type wall thickness measuring instrument. It is a value obtained by measuring the thickness, obtaining the inner diameter on the circumference by calculation with the outer diameter, and averaging them. Further, the deviation of the center of the circle is based on the surface center of the average outer diameter and average inner diameter of the end face of the base material, with respect to the axis extending perpendicularly to the longitudinal direction of the pipe from the circle center of the outer diameter surface and inner diameter surface. This is a deviation.

  According to the inner diameter processing method of the hollow brittle material of the present invention, when grinding the inner hole before processing the hollow brittle material, even if the object to be ground is relatively long, it has excellent grinding ability and straightness of grinding, and It has a remarkable effect that inner diameter machining without damage to the object to be ground can be realized.

  Further, according to the inner diameter machining method of the hollow brittle material of the present invention, even when the hole grinding is performed by +5 mm or more from the inner diameter before machining as described above, the hollow brittle material is accurately ground without damaging the hollow brittle material. There is an advantage that you can. Moreover, since the number of tips of the grindstone of the hollow brittle material processing drill to be used can be reduced, there is an advantage that the cost can be reduced.

  Embodiments of the present invention will be described below with reference to the accompanying drawings. However, the illustrated examples are merely illustrative, and various modifications other than the illustrated examples are possible without departing from the technical idea of the present invention. Needless to say.

  FIG. 1 is a schematic longitudinal sectional view showing one embodiment of a drill for processing a hollow brittle material used in the method of the present invention, and FIG. 2 is an enlarged sectional view of a head grindstone chip. FIG. 3 is a schematic plan sectional view taken along line II of FIG. 1, and FIG. 4 is a schematic plan sectional view showing another embodiment of a drill for processing a brittle brittle material used in the method of the present invention.

  1-3, the code | symbol 20 shows the drill for hollow brittle material processing used for the method of this invention. The hollow brittle material processing drill 20 is used for expanding and grinding an inner hole of a hollow brittle material before processing to a predetermined inner dimensional accuracy.

  The hollow brittle material processing drill 20 includes a drill rod 22 that rotates about a longitudinal axis Z, and a drill head 24 provided at the front end of the drill rod 22. The drill head 24 has a head disc 26 provided on the tip side thereof, and an intermediate disc connected to the head disc 26 and having a diameter larger than that of the head disc 26. 28. A plurality of head grindstone tips 30 are installed at equal intervals on the outer peripheral surface on the front end side of the head disc body 26 to form a head drill body 31. A plurality of intermediate grindstone tips 32 are installed at equal intervals on the outer peripheral surface of the intermediate disc body 28 to form an intermediate drill body 33.

  In the example of FIG. 1, the case where one intermediate drill body 33 is installed is shown. However, even when the intermediate drill body 33 is not installed, the effect of the present invention can be achieved. A plurality of intermediate drill bodies 33 can also be installed. In the case where a plurality of intermediate drill bodies 33 are installed, the intermediate drill body located on the rear end side of the drill rod 22 is gradually increased in diameter from the intermediate drill body located on the front end side of the drill rod 22. To do. As the abrasive grains of the head grindstone chip 30 and the intermediate grindstone chip 32, diamond abrasive grains or CBN abrasive grains are preferably used. Reference numeral 34 denotes a hollow brittle material in which the inner hole 36 is opened.

  In the drill 20 for processing a hollow brittle material shown in FIG. 1, as shown in FIG. 3, two head grindstone tips 30 are provided on the outer peripheral surface of the head disc body 26 at equal intervals. . This head grindstone chip 30 should just be installed 2 or more and 4 or less. In FIG. 4, the structural example of the drill 21 for hollow brittle material processing which provided the four head grindstone tips 30 in the head disc body 26 was shown.

Moreover, the width | variety d of the head grindstone chip | tip 30 can use suitably 4 mm or more and 10 mm or less. Even if the number of head grindstone tips 30 is four or less, does the straightness during grinding worsen if the contact area where the head grindstone tip 30 contacts the hollow brittle material 34 exceeds 80 mm ² ? Alternatively, since cracks occur in the hollow brittle material 34, the width d of the head grindstone chip 30 needs to be 4 mm or more and 10 mm or less, and the contact area of the head grindstone chip 30 needs to be 80 mm ² or less.

The upper surface of the head grindstone tip 30 may be a horizontal plane, but as shown in FIG. 2, the upper surface is inclined downward at a predetermined inclination angle α toward the center of the head drill body 31. The inclination angle α is preferably 5 degrees or more and 70 degrees or less. When the inclination angle α is less than 5 degrees, when the grinding of the inner hole 36 of the hollow brittle material 34 to be ground is finished, the head grindstone tip 30 is cracked when it is removed from the inner hole 36 of the hollow brittle material 34. May occur. Moreover, when this inclination | tilt angle (alpha) exceeds 70 degree | times , load will be applied to the head grindstone chip | tip 30, and the problem that the head grindstone chip | tip 30 may be missing may arise.

The hollow brittle material inner hole machining method of the present invention includes the above-described hollow brittle material machining drill 21, that is, a drill rod 22 that rotates about a longitudinal axis, and a drill head 24 provided at the front end of the drill rod 22. And the drill head has a head drill body 31 having a plurality of head grindstone tips 30 provided at equal intervals on the outer peripheral surface of the head disk body 26, and the head An inner hole processing method in which the inner diameter of the inner peripheral surface of the inner hole 36 of the hollow brittle material 34 is expanded and ground by a predetermined dimension using the hollow brittle material processing drill 21 having a width of the grindstone tip 30 of 4 mm to 10 mm. The contact area of the head grindstone tip 30 with respect to the inner hole 36 of the hollow brittle material 34 is regulated to 5 mm ² or more and 80 mm ² or less, and is centered on the circle of the average outer diameter of the ground hollow brittle material 34. versus The average inner diameter is processed so that the deviation of the center of the circle is 1.0 mm or less.

  The drill head 24 includes a plurality of intermediate grindstone tips 32 provided at equal intervals on the outer peripheral surface of the intermediate disc body 28 and has an intermediate drill body 33 having a diameter larger than that of the head drill body 31. It is preferable that the outer diameter difference between the head drill body 31 and the intermediate drill body 33 is 1 mm or less. Further, a plurality of the intermediate drill bodies 33 are installed, and a rear end side intermediate drill body positioned on the rear end side of the drill rod 22 with respect to the outer diameter of the front end side intermediate drill body positioned on the front end side of the drill rod 22. It is also possible to configure such that the outer diameter of each is gradually increased and the difference in outer diameter from each intermediate drill body is 1 mm or less. Furthermore, it is preferable that 2 or more and 4 or less of the head grindstone tips 32 are installed. The abrasive grains of the head grindstone tip 26 and the intermediate grindstone chip 32 are preferably diamond abrasive grains or CBN abrasive grains.

Advantages when two or more head grindstone tips 32 are installed are as follows.
(1) For example, when eight head grindstone tips 32 having a width of 4 mm are provided and the inner diameter of the hollow brittle material inner diameter is set to 50 mm, the head grindstone tip is controlled by the rate of contact area with the inner hole of the hollow brittle material. Since the inner diameter of the primary base material can be cut only to about +5 mm (contact area is 80 mm ² ), the inner diameter of the primary base material before processing is limited to 45 mm or more. In addition, the primary base material must be made with an inner diameter of 45 mm or more before processing the primary base material, resulting in poor productivity. If 2 to 4 head grindstone tips 32 are used, even if the inner diameter difference is as wide as 1 mm to several tens of mm, it is possible to cope with the grinding, even if the inner diameter of the primary base material before processing is about 40 mm. Processing is possible and productivity is improved because there is no need to precisely control the inner diameter.
(2) Further, as shown in Example 2, in the material vitrified by the OVD method, the head grindstone tip 32 is increased even if the difference between the large inner diameter portion and the small inner diameter portion of the material is large. If there is a configuration in which two or more and four or less are installed, the difference in inner diameter that can be expanded is 1 mm to several tens of mm, so that grinding can be performed with almost no limitation. For example, if the head grindstone tips 32 are eight, the inner diameter difference of the primary base material can only cope up to about 5 mm, but if the head grindstone tips 32 are two or more and four or less, the inner diameter exceeds 5 mm. Even if there is a difference or bending of the inner diameter, it can be handled.
(3) If the number of head grindstone chips 32 is 2 or more and 4 or less, the number of chips can be reduced, and the cost can be reduced accordingly.
(4) If the number of head grindstone chips 32 is 2 or more and 4 or less, the number of chips is small, so that the coolant flowing for grinding can easily flow from the gap, and the cooling effect increases accordingly.

  Examples of the present invention will be specifically described below, but it is needless to say that these examples are illustrative and should not be construed in a limited manner.

Example 1
Using the same apparatus as the drill for processing hollow brittle materials shown in FIGS. 1 to 3, silicon tetrachloride is vaporized by VAD method, flame-hydrolyzed in an oxyhydrogen flame, and silica glass is rotated on a rotating quartz glass rod. A porous soot body was prepared by depositing fine particles. This porous soot body was put into an electric furnace, heated and dehydrated with He gas at 1100 ° C., and then transparent vitrified at 1600 ° C. in a He gas atmosphere to obtain a cylindrical quartz glass ingot.

  Cut both ends of the cylindrical quartz glass ingot, accurately grind the outer periphery to a predetermined dimension with a cylindrical grinding machine equipped with diamond abrasive grains, measure the dimensions with a laser outer diameter measuring machine, Asked. A cylindrical primary base material having an inner diameter of about 30 mm and a length of about 3 m was manufactured in accordance with the center of the circle using a hot carbon drilling device. The inner diameter was in a transparent state, but when the dimensions of the obtained primary base material were measured with a laser outer diameter measuring device and a wall thickness measuring device at intervals of 50 mm, a portion 2 m in length from the opening start portion. The deviation of the average inner diameter circle center from the average outer diameter circle center was 2.0 mm at the maximum.

The cylindrical primary base material is cut at both ends, and the grinding diameter of the head disk 26 is set to 38 mm in order to reduce the inner diameter from 30 mm to 40 mm, and the head grindstone tip of # 100 metal bond diamond with a width of 10 mm. 2 is arranged with an inclination angle α of 50 degrees, and is ground by a hollow brittle material processing drill 20 in which the grinding outer diameter of the intermediate disk 28 is set to 40 mm, and a secondary mother having an inner diameter of 40 mm and a length of 3 m. Made the material. The grinding conditions were such that the contact area of the head grindstone tip with respect to the inner hole of the hollow brittle material was 80 mm ² , the head rotation speed was 900 rpm, the feed rate was 15 mm / min, and coolant water as a grinding fluid was flowed at a pressure of 0.2 MPa. Continued.

  When the dimensions of the obtained secondary base material were measured with a laser outer diameter measuring device and a wall thickness measuring device at intervals of 50 mm, the length was 3 m, the average inner diameter was 40 mm, the average inner diameter difference was 0.02 mm, and a perfect circle The degree of deviation was 0.05 mm at the maximum, the deviation from the circle center of the average outer diameter was 0.1 mm at the maximum, and the deviation of the circle center of the average inner diameter from the circle center of the average outer diameter was at most 0.1 mm.

(Example 2)
Using the same equipment as the hollow brittle material processing drill shown in Fig. 3, OVD vaporizes silicon tetrachloride, flame-hydrolyzes it in an oxyhydrogen flame, and deposits silica glass particles around the rotating mandrel A large porous soot body was prepared. Subsequently, the mandrel is pulled out, this hollow porous soot body is placed in an electric furnace, heated and dehydrated with He gas at 1100 ° C., and then transparently vitrified at 1600 ° C. in a He gas atmosphere, and has a cylindrical shape with an inner diameter of about 60 mm and a length of about 4 m. A primary matrix was produced. Since it was made into transparent glass without a mandrel, a cylindrical primary base material having a non-uniform inner diameter was manufactured. When the dimension measurement of the obtained primary base material was performed with a laser outer diameter measuring device and a wall thickness measuring device at intervals of 50 mm, the entire inner diameter difference was in a range of 6 mm.

The cylindrical primary base material is cut at both ends, and the grinding diameter of the head disk 26 is set to 68 mm in order to reduce the inner diameter from 60 mm to 70 mm, and the head grindstone tip of # 100 metal bond diamond with a width of 4 mm. 4 is arranged with an inclination angle α of 10 degrees, and the intermediate disk 28 is ground with a hollow brittle material drill 10B in which the grinding outer diameter is set to 70 mm. The secondary base material has an inner diameter of 70 mm and a length of 4 m. It was created. The grinding conditions were such that the contact area of the head grindstone tip with respect to the inner hole of the hollow brittle material was 64 mm ² , the rotational speed of the head was 600 rpm, the feed rate was 20 mm / min, and coolant water as a grinding fluid was flowed at a pressure of 0.2 MPa. Continued.

  When the dimensions of the obtained secondary base material were measured with a laser outer diameter measuring device and a wall thickness measuring device at intervals of 50 mm, the length was 4 m, the average inner diameter was 70 mm, the average inner diameter difference was 0.12 mm, and a perfect circle The degree was 0.1 mm at the maximum, the deviation from the circle center of the average outer diameter was 0.6 mm at the maximum, and the deviation of the circle center of the average inner diameter from the circle center of the average outer diameter was 0.7 mm at the maximum.

(Comparative Example 1)
The VAD method was used in the same manner as in Example 1, and silicon tetrachloride was vaporized, flame hydrolyzed in an oxyhydrogen flame, and silica glass fine particles were deposited on a rotating quartz glass rod to prepare a porous soot body. This porous soot body was put into an electric furnace, heated and dehydrated with He gas at 1100 ° C., and then transparent vitrified at 1600 ° C. in a He atmosphere to obtain a cylindrical quartz glass ingot. Cut both ends of the cylindrical quartz glass ingot, accurately grind the outer periphery to a predetermined dimension with a cylindrical grinding machine equipped with diamond abrasive grains, measure the dimensions with a laser outer diameter measuring machine, Asked. A cylindrical primary base material having an inner diameter of about 30 mm and a length of about 3 m was manufactured in accordance with the center of the circle using a hot carbon drilling device. The inner diameter was in a transparent state, but when the dimension measurement of the obtained primary base material was performed with a laser outer diameter measuring machine and a wall thickness measuring machine at intervals of 50 mm, a length of 2.5 m from the opening start portion. In the portion, the deviation of the circle center of the average inner diameter from the circle center of the average outer diameter was 1.9 mm at the maximum.

In order to cut both ends of this cylindrical primary base material, the grinding diameter of the head disk is set to 38 mm so that the inner diameter is 30 mm to 40 mm, and a # 100 metal bond diamond head grindstone chip with a width of 4 mm is used. Eight of them were arranged with an inclination angle α of 50 degrees, and ground with a drill for a hollow brittle material in which the outer diameter of the intermediate disk was set to 40 mm, thereby producing a secondary base material having an inner diameter of 40 mm and a length of 4 m. The grinding conditions were such that the contact area of the head grindstone tip with respect to the inner hole of the hollow brittle material was 128 mm ² , the head rotation speed was 900 rpm, the feed rate was 15 mm / min, and coolant water as a grinding fluid was flowed at a pressure of 0.2 MPa. Continued.

  The inner surface was processed without cracking, but when the dimensions of the obtained secondary base material were measured with a laser outer diameter measuring device and a wall thickness measuring device at intervals of 50 mm, the length from the opening start portion was long. In the portion of 2.5 m in length, the deviation of the average inner diameter circle center from the average outer diameter circle center was 1.5 mm at the maximum.

(Comparative Example 2)
Using the OVD method as in Example 2, silicon tetrachloride was vaporized, flame hydrolyzed in an oxyhydrogen flame, and silica glass fine particles were deposited around the rotating mandrel to create a large porous soot body. Subsequently, the mandrel is pulled out, this hollow porous soot body is placed in an electric furnace, heated and dehydrated with He gas at 1100 ° C., and then transparently vitrified at 1600 ° C. in a He atmosphere. A cylindrical primary having an inner diameter of about 60 mm and a length of about 4 m. A base material was manufactured. Since it was made into a transparent glass without a mandrel, a primary base material having a non-uniform inner diameter was produced. When the dimension measurement of the obtained primary base material was performed with a laser outer diameter measuring device and a wall thickness measuring device at intervals of 50 mm, the entire inner diameter difference was in a range of 6 mm.

In order to cut both ends of this cylindrical primary base material, the grinding diameter of the head disk body is set to 68 mm so that the inner diameter is changed from 60 mm to 70 mm, and a # 100 metal bond diamond head grindstone chip with a width of 15 mm is used. Four of them were arranged with an inclination angle α of 10 degrees, and ground with a drill for a hollow brittle material in which the outer diameter of the intermediate disk was set to 70 mm, thereby producing a secondary base material having an inner diameter of 70 mm and a length of 4 m. Grinding conditions were as follows: the contact area of the head grindstone tip with respect to the inner hole of the hollow brittle material was 240 mm ² , the head rotation speed was 600 rpm, the feed rate was 20 mm / min, and water as the grinding fluid was continuously supplied at a pressure of 0.2 MPa. It was. However, since a crack deeper than the inner wall grinding portion by the head tip portion occurred in the portion 1 m long from the opening start portion, grinding was stopped.

  As described above, it was confirmed that the secondary base materials obtained in Examples 1 and 2 could be accurately ground without being damaged as compared with the secondary base materials in Comparative Examples 1 and 2.

It is a schematic longitudinal cross-sectional view which shows one embodiment of the drill for hollow brittle material processing used for the method of this invention. It is an expanded sectional view of a head grindstone chip. It is a schematic plane sectional view seen from the II line of FIG. It is a schematic longitudinal cross-sectional view which shows another embodiment of the drill for hollow brittle material processing used for the method of this invention. It is a schematic plane sectional view showing an example of the conventional drill for hollow brittle material processing.

Explanation of symbols

  20, 21: Drill for processing brittle material used in the method of the present invention, 22: Drill rod, 24: Drill head, 26: Head disc body, 28: Intermediate disc body, 30: Head grindstone tip, 31: Head drill body, 32: intermediate grindstone tip, 33: intermediate drill body, 34: brittle material, 36: inner hole.

Claims (5)

A drill rod that rotates about a longitudinal axis and a drill head provided at the front end of the drill rod, the drill heads being provided at equal intervals on the outer peripheral surface of the head disk body Processing of a hollow brittle material using a drill for processing a hollow brittle material having a head drill body including two or more and four or less head grindstone tips, and the width of the head grindstone tip being 4 mm or greater and 10 mm or less. An inner hole machining method in which the inner diameter of the inner peripheral surface of the front inner hole is subjected to expansion grinding of +5 mm or more, and the contact area of the head grindstone tip with respect to the inner hole of the hollow brittle material is set to 5 mm ² or more and 80 mm ² or less. An inner hole machining method for a hollow brittle material, characterized in that processing is performed so that a deviation of a circle center of an average inner diameter with respect to a circle center of an average outer diameter of a hollow brittle material that has been regulated and ground is 1.0 mm or less.   The drill head further includes an intermediate drill body having a plurality of intermediate grindstone tips provided at equal intervals on the outer peripheral surface of the intermediate disk body and having a diameter larger than that of the head drill body, The processing method according to claim 1, wherein an outer diameter difference between the head drill body and the intermediate drill body is 1 mm or less.   A plurality of the intermediate drill bodies are installed, and the outer diameter of the rear end side intermediate drill body positioned on the rear end side of the drill rod is gradually larger than the outer diameter of the front end side intermediate drill body positioned on the front end side of the drill rod. The machining method according to claim 2, wherein the diameter of each intermediate drill body is set to be 1 mm or less. The upper surface of the head grindstone tip is inclined downward at a predetermined inclination angle α toward the center direction of the head drill body, and the inclination angle α is 5 degrees or more and 70 degrees or less. machining method of any one of 1-3. Processing method according to any one of claims 1-4, wherein the abrasive grains of the head grinding chips are diamond abrasive grains or CBN abrasive grains.

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