JP2006188735A - Rotor with excellent creep characteristic - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lightweight rotor having high creep strength and capable of being easily machined. <P>SOLUTION: This rotor can be obtained by impregnating, under pressure, a molten aluminum alloy containing ≥2% copper into a preform composed of aluminum borate whiskers or potassium titanate whiskers and then machining the resultant parts. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a rotating body made of an aluminum alloy matrix composite material that is lightweight, has good creep characteristics, and is easy to machine, and a method for manufacturing the same.

  The rotating body is preferably lightweight from the viewpoint of power energy, and preferably has a low specific gravity. At present, aluminum alloys are used for rotors of turbo molecular pumps and rotors of motors. However, the creep strength of aluminum alloys suddenly decreases from 150 ° C or higher. For example, A2618, which is a kind of aluminum alloy, has a higher creep strength, but it cannot be said to have a sufficient creep strength at 200 ° C. or higher, and its thermal expansion and elongation are large. Insufficient.

  On the other hand, the titanium alloy has sufficient creep properties even at 200 ° C. or higher, but its specific gravity is about 1.7 times larger than that of the aluminum alloy, so it cannot be said that it is a suitable material for a rotating body. Titanium alloys are not easy to machine. For example, in the case of a turbo molecular pump rotor, machining that cuts hundreds of blades or more by machining accounts for a large amount of cost, so it is not a suitable material.

  In view of the above-described conventional problems, an object of the present invention is to provide a rotating body made of a material that is lightweight, easy to machine, has high creep strength, and has low elongation.

  The present invention has focused on using an aluminum-based composite material in order to solve the above problems. Aluminum-based composite materials are preferable because they have high tensile strength at high temperatures, high creep strength, and low elongation.

  Next, in order to facilitate machining, which is another object of the present invention, the reinforcing material is selected from carbon, aluminum borate, and potassium titanate. In general, silicon carbide and alumina, which are well known, have high hardness, and therefore machining becomes extremely difficult when an aluminum-based composite material is used.

  Furthermore, among carbon, aluminum borate, and potassium titanate in the reinforcing material, if carbon is used, only the fiber direction shows an abnormally large strength, but the other direction can only be expected to have a strength below the aluminum matrix. In addition, carbon particles originally have little meaning as a reinforcing material and have been found to be ineffective in improving the creep strength, so they are limited to those of aluminum borate or potassium titanate.

  In the problem of the shape of the reinforcing material, the volume ratio still affects the machining characteristics, so it is necessary to make it 30% or less at the maximum. Therefore, since it is difficult to reduce the volume ratio to 30% or less in the reinforcing material preform in the particle shape, a whisker shape was selected in order to achieve the object of the present invention.

  When a preform is formed using aluminum borate whisker, potassium titanate whisker, or a mixture thereof as a reinforcing material, it is difficult to form at a volume ratio of 5% or less, and there is little improvement in creep strength. I can't hope. Therefore, the volume ratio of the reinforcing material is set to 5 to 30%.

  In addition, the aluminum alloy used as the matrix is selected, but the reinforcing material is an aluminum borate or potassium titanate whisker, so if magnesium is included as a component of the alloy, a reaction occurs between the reinforcing material and the matrix. This is not preferable because a very hard and brittle reaction product is formed. In addition, since the strength of the matrix is dominant in the whisker reinforced aluminum, an alloy containing 2% or more of copper is adopted.

  As described above, a reinforcing material and a matrix material are selected, and a composite material as a desired rotating body material can be obtained by a high pressure casting impregnation solidification method. Hereinafter, the production method will be described in more detail. First, a predetermined amount of whiskers are weighed, and an organic binder and, if necessary, an inorganic binder are added thereto and suspended in water to form a slurry. The organic binder used at this time is a water-soluble polymer such as polyvinyl alcohol, methylcellulose, or starch. As the inorganic binder, silica sol, alumina sol or the like can be used. Next, this slurry is filtered or pressure-molded, dried and solidified to obtain a preform.

  Next, this molded body is heated to about 600 to 900 ° C., and on the other hand, the aluminum alloy is dissolved. On the other hand, after the high-pressure casting mold is heated to about 200 to 300 ° C. and the heated compact is placed in the mold, molten aluminum alloy is poured into the mold and approximately 30 inside the mold with a hydraulic plunger. Impregnation by applying pressure of ~ 200MPa to solidify. Thereafter, the composite material portion is cut out from the solidified material to obtain a rotating body material.

  The composite material obtained as described above is machined by using a lathe, a milling machine, a machining center, etc., for example, a turbo molecular pump rotor, a motor rotor, a screw compressor screw, a screw compressor scroll, a mechanical vacuum. The problem of the present invention was solved by processing into the shape of the rotor of the pump and other rotating bodies.

Since the composite material of the present invention uses aluminum borate whisker and / or potassium titanate whisker as a reinforcing material, the tool used for machining can be processed with a normal tool and has a fairly complicated shape. However, it can be done in the same processing time as a normal aluminum material, so an increase in cost due to processing costs can be avoided.

The rotating body made of the composite material obtained by the present invention is useful as a rotating body because of its high creep strength. In particular, rotating bodies such as pumps that keep the inside of semiconductor, liquid crystal, and solar cell manufacturing equipment in a vacuum are used at high temperatures. Creep characteristics are very important physical properties. The material of JIS-A2618 used in the past has a creep strength of 195 Mpa at 205 ° C. for 100 hours, whereas the product of the present invention is over 280 Mpa under the same conditions. It has become. This creep strength is unattainable with any other aluminum alloy. In addition, the elongation at 200 ° C. of JIS-A2618 is 24%, whereas that of the product of the present invention is 0.5% or less, so that it is very useful as a rotating body at high temperatures.

Furthermore, since the specific gravity of the present invention is 2.75 to 3.0 and about 65% of titanium, energy consumption as a rotating body is small. As a further effect of the invention, the thermal expansion coefficient of A2618 is 22 to 23 × 10 ⁻⁶ 1 / K, whereas that of the present invention is 14 to 20 × 10 ⁻⁶ 1 / K. Since the clearance of the outermost periphery of the rotating body with respect to the cylinder can be reduced by design, a highly efficient device can be made.

  The reinforcing material used in the present invention is a whisker having a diameter of 1 μm or less and a length of about 20 μm. Specifically, as an aluminum borate whisker, Alborex manufactured by Shikoku Kasei Kogyo Co., Ltd. An acid potash whisker or the like is preferable. If these are in contact with molten aluminum not containing magnesium within 1 minute, no harmful reaction occurs.

As the aluminum used in the present invention, for example, wrought materials include A2025, A2219 and A4000 in A2000 series, and AC1A, AC2A, AC2B, AC4B, ADC10, ADC12, etc. are suitable in casting alloys. From the viewpoint of mechanical strength and ease of machining, A2025, A2219, AC1A, and the like are more preferable.

In the present invention, whisker preforms are prepared, but the manufacturing methods are not limited because they are diverse. A predetermined amount of whisker is added to and suspended in the polyvinyl alcohol solution, and silica sol is added so as to be 1% by weight with respect to the amount of whisker. This suspension (slurry) is filtered, filtered and pressurized to a predetermined volume, and the filter cake is taken out and dried at 100 ° C. Thereafter, it is kept at 800 ° C. for 1 to 3 hours in air to obtain a desired preform.

The preform thus obtained was preheated to 750 to 800 ° C. in the air, while a molten aluminum was prepared at 700 to 850 ° C., and the mold shown in FIG. ) Is previously maintained at 200 to 300 ° C. First of all, a preheated preform (4) is placed, and immediately after that, molten aluminum (5) is poured and pressurized onto the pressure punch (2) with a hydraulic plunger (3). At this time, a pressure of 30 to 200 MPa is applied for 2 to 20 minutes to solidify the aluminum.

  Only the composite material is cut out from the casting that has been solidified. The composite material is cut using a lathe, machining center, or the like with a blade or tool similar to that using JIS-A2618 of an aluminum alloy to obtain a desired rotating body.

  Hereinafter, the present invention will be described more specifically with reference to examples.

  To 10 liters of 5% polyvinyl alcohol solution, 2770 g of aluminum borate whisker was added, suspended by stirring, 90 ml of 30 wt% silica sol was added, and then transferred to a filter with an inner diameter of 20 cm and filtered under reduced pressure. Since the filter cake had a height of 25 cm, it was further pressurized and compressed to a height of 20 cm, and placed in a dryer at 100 ° C. to obtain a cylindrical preform (4) having a diameter of 20 cm and a height of 20 cm. . The volume ratio of this product was 15%. This was kept at 800 ° C. in air. On the other hand, the molten aluminum of A2219 composition was held at 750 ° C. In addition, after placing the preform (1) in a mold for high pressure casting (1) having an inner diameter of 30 cm and a height of 39 cm which has been heated to 250 ° C., the A2219 melt ( Simultaneously with completion of pouring of 5), the hydraulic plunger (3) was operated to apply pressure to the molten metal (5) via the pressure punch (2). After maintaining the pressure at 70 MPa for 8 minutes, the completely solidified casting was taken out and cooled, and only the composite material portion was cut out to obtain the material of the rotating body of the present invention. Thereafter, various test pieces were cut out from the obtained material of the rotating body and the Young's modulus was measured after a tensile test at room temperature, and the values shown in Table 1 were obtained. Further, when the creep strength was measured at 205 ° C. for 100 hours and 1000 hours, the values shown in Table 1 were obtained. In addition, the results of measurement of specific gravity, elongation and coefficient of thermal expansion are also shown.

  When a composite material similar to the above was processed into a rotor of a turbo molecular pump, it could be cut sufficiently with a normal high-speed steel tool.

  As a comparative example, various physical property values of JIS-A2618 are also shown in Table-1.

  The rotating body made of the whisker-reinforced composite material according to the present invention is excellent in creep strength, small in elongation and light in weight, and has a low coefficient of thermal expansion. Therefore, the rotating body is not only an efficient rotating body but also suitable as a long-life rotating body. is there.

Schematic cross-sectional explanatory drawing showing an example of the high-pressure casting apparatus of the present invention

Explanation of symbols

1 Mold 2 Punch 3 Hydraulic plunger 4 Whisker preform 5 Molten aluminum

Claims (6)

A rotating body made of a composite material made of a matrix material made of a reinforcing material made of either one or two of aluminum borate whisker or potassium titanate whisker and an aluminum alloy (hereinafter referred to as aluminum). The rotating body made of the whisker-reinforced aluminum material according to claim 1, wherein the volume ratio of the reinforcing material whisker is 5 to 30%. A rotating body made of the whisker reinforced aluminum material according to claim 1 or 2, wherein a creep strength is 250 MPa or more at 205 ° C for 100 hours. The rotating body made of a whisker-reinforced aluminum material according to claim 1, 2 or 3, wherein the aluminum material of the matrix is an alloy having a magnesium content of 0.3% or less and a copper content of 2% or more. The rotating body is a turbo molecular pump rotor, a motor rotor, a screw compressor screw, a scroll compressor scroll, a mechanical vacuum pump rotor, or other rotating body. Using a material consisting of either one or two of aluminum borate whisker or potassium titanate whisker, using organic or inorganic or both binders, a preform is made and preheated so that the volume ratio is 5 to 30%. 6. A manufacturing method for obtaining a rotating body according to claim 5, wherein the rotating body according to claim 5 is installed in a pressurizing mold, and a composite material is prepared by impregnating and solidifying molten aluminum with high pressure casting.

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