KR19980026984A - Synthetic Method - Google Patents

Abstract

The present invention relates to a metal matrix composite prepared by assembling a preform of porous reinforcement material having an array of separator plates in a die of a pressure vessel and ejecting the molten metal matrix material. When the molten metal matrix material is introduced into the die and already evacuated by pressure, the ejection is assisted. Reintroduction of the gas during initial heating prior to melting enhances the method of heating up.

Description

Synthetic Method

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for producing a synthetic material, and more particularly, to a method for producing a material in which a porous pre-form is mixed with a matrix material by a spraying method.

British Patent Application No. 2 247 636 describes a number of methods used to make metal matrix composite materials and the use of very large dieblocks to withstand the pressure applied to pressurize molten metal to eject the preform. Its advantages are described.

British Patent Application No. 2 247 636 describes how a die comprising a porous preform of matrix material and reinforcing material is placed in a pressure vessel. The pressure vessel is vacuumed while the matrix material and the die are heated to a temperature above the melting point of the matrix material. The molten matrix material is then pressurized to allow the molten matrix material to exit the preform.

Applicants have a number of ways to improve and develop the methods described above.

Venting the molten matrix material into the porous preform of the reinforcing material in accordance with the present invention, and positioning the plurality of separator elements to form a plurality of cavities that form the final product dimension in the die; Provided is a method for filling a porous reinforcing material comprising a particle material whose particle size distribution is selected and controlled such that a majority of the particles can be close to or at one of two different sizes. The relative proportions of particles at each size are determined to position the die in the pressure vessel along with the amount of matrix material, and to bring the matrix material and die at a temperature above the melting point of the matrix material positioned to or in contact with the porous reinforcement material. Heating, and the molten matrix material And pressurizing the pressure vessel, thereby solidifying the matrix materials to the material to be ejected.

Conventionally, the matrix material is initially located in a crucible located in a pressure vessel such that the crucible and the die and its components are heated together to a temperature above the melting point of the matrix material when melting is transferred from the crucible to the die.

Preferably the matrix material is initially in the die but separates from the porous reinforcement material, thereby heating the die and the porous reinforcement material and the matrix material are heated to a temperature above the melting point of the matrix material ejecting the porous material.

In the device according to the invention, the separator element is formed of a thin plate formed between a plurality of disc shaped cavities filled with a porous reinforcing material.

In another form according to the invention, the separator elements are arranged in pairs, one element of each pair comprising a cavity filled with a porous reinforcing material and forming all of the desired shapes, while one side of the article is porous with matrix material. Formed upon ejection of the reinforcing material, each pair of second elements includes a thin plate positioned adjacent to the one element forming one side of the formed article.

The separator element may comprise graphite, ceramic (ie alumina) or metal, provided that the metal is capable of withstanding the temperature at which the die is exposed. Applicants have found that a thin separator substrate of stainless steel makes very good supply of molten aluminum into the interior region of the cavity containing the reinforcing material. The separator element must be able to withstand the exposure of the liquid to the matrix material. The resistance of the separator element to liquid metal can be improved by coating. The coating has deforming properties, for example as supplied by boron nitride or oxide layers.

Applicants have also found that it is possible to manufacture dies from metals such as stainless steel with very thin walls in order to use the device of this type. Then, after the cooling and ejection to solidify the matrix is completed, the die can be easily peeled off from the contents. Due to the low cost and high thermal conductivity, the use of softer steel than stainless steel is preferred in practical places. By introducing air (which may be atmospheric pressure) of nitrogen or other gas which does not contain hydrogen into the pressure vessel, the thermal diffusion of the preform is increased with a continuous decrease in the heating time. Heating can be performed by using a resistive element. However, it is preferable to use high frequency heating. The above point is that since the high frequency can bypass the heat transfer, the die has the advantage of having an optional heat transfer around the wall to promote directional solidification of the matrix material during the cooling step. An additional advantage of the high frequency heating is that the isothermal state can be kept controllable during ejection. It is also possible to preheat the preform outside of the pressure vessel and to transfer them into the pressure vessel.

If the separator element is made of metal and high frequency heating at an appropriate frequency is used, the separator element enhances heat transfer to the center of the preform and the heating time can be reduced. It is preferred that the separator element have a higher thermal diffusivity than the preform which produces a better heating of the core, ie the interior of the die. Separator elements in the form of very high thermal conductivity thin plates preferably have flanged portions at the edges to enhance the heat transfer path from the die wall to the next adjacent separator.

When microwaves are used, the metal presence of the die and its contents can be avoided, and of course microwave heating may not be applied to any continuous heating or melting of the metal matrix material upon ejection. However, enhanced internal heating using microwaves can be achieved by using a suitable ceramic separator, such as zirconium oxide or zirconium oxide coated ceramic.

According to a preferred feature of the invention, the particle size is controlled,

(A) The volumetric friction in the product of the reinforcing material meets certain requirements, in particular to match the specific coefficient of thermal expansion,

(B) the capillary size in the gap between the particles in the preform allows for ejection at an appropriate pressure and time;

(C) the minimum particle size is larger than the Kapitze radius,

(D) The maximum particle size is smaller than the threshold in order to avoid the whole particle since the whole particle exhibits a defect (ie cracking occurs). This drawback can repair the mechanical properties of the product and adversely affect the metal layer. The presence of total particles may be undesirable in thin sections where the physical properties of the synthetic article are too uniform.

The present invention includes ejecting a molten matrix material into a porous preform of a reinforcing material, positioning the preform on a die, covering the preform with a mesh held between the perforated lead and the preform firmly fixed in the die, Placing a solid metal matrix material on top of the perforated leads in the top of the, and heating the die to melt the metal matrix material through the perforated leads distributed by the mesh and eject the preform. It provides a method of another feature.

It is preferred that the die be positioned before vacuuming first and the metal matrix material is melted and then heated in a continuously pressurized pressure vessel.

1 is a schematic cross-sectional view according to the present invention.

2 is a schematic cross-sectional view of a modified device.

3 is a schematic enlarged cross sectional view of the device portion shown in FIG. 2;

4 is a cross-sectional view taken along line 4-4 of FIG.

* Description of the symbols for the main parts of the drawings *

1: pressure vessel 2: base plate

3: Port 5: Chamber

8: Valve 9: Die

10: heater 13: hole

17: molten metal matrix material 22, 23: separator element

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following is described in accordance with the accompanying drawings and embodiments of specific structures of apparatus and methods for practicing the invention.

In FIG. 1, the apparatus for producing a reinforced composite of a metal matrix comprises a pressure vessel 1 having a base plate 2. The port 3 connects the pressure vessel 1 to a pressure accumulator or a vacuum pump (not shown) via a two-way valve 4. The chamber 5 is mounted in the pressure vessel 1. The port 6 in communication with the interior of the pressure vessel 1 is at the base of the chamber 5. Near the top of the chamber 5 there is a vent 7 which passes through the base 2 of the pressure vessel 1 and comprises a valve 8. Inside the chamber 5 is a die 9 surrounded by a heater 10. Also on the die 9 is an open crucible 11 surrounded by a heater 12. A hole 13 at the bottom of the crucible 11 is in communication with a small hole 14 at the top of the chamber 5. The hole 13 of the crucible 11 is closed by a plug 15 which can be withdrawn when required by a suitable mechanism (not shown).

In the device shown in FIG. 1, the die 9 has a thin-walled cylindrical steel conduit with a perforated lead 21 positioned on top of an open mesh member which is press fit inside the cylindrical part of the die 9. Include. The lid 21 and the open mesh member are thus used to press up and down to densify the contents of the die 9 and also to allow penetration into the die, where the metal matrix material 17 is carried from the crucible 11. When the molten metal matrix material 17 is distributed. The lid 21 also prevents the contents of the die 9 from floating upward when molten metal matrix material is introduced into the die 9.

Within die 9 is a stacked array of separator elements, shown at 22 and 23. The array extends continuously from the bottom of the die 9 to the lid 21, but only three pairs of separator elements are shown for simplicity.

Each separator element 22 is in the form of a thin plate of stainless steel. It cooperates with the double side shaped separator element 23 and is made of stainless steel to form a plurality of disc shaped cavities 24. Other shapes can easily be provided by the appropriate shape of separator element 23.

The cavity 24 is filled with a preform of reinforcing material, for example compact silicon carbide particles.

The preform is prepared from a mixture of high purity (Green) 240 grade and 600 grade silicon carbide. It is important to achieve particle size distribution for two average size values that minimize the presence of fines and to minimize the number of particles having a size smaller than the copy radius as described above. It is also important to avoid the presence of full sized particles. The mixture comprising 60 to 70 volume percent 240 grade particles and 40 to 30 volume percent 600 grade particles provides a maximum packed volume friction of silicon carbide substantially close to 70 percent. If the maximum value is required in the product, it is possible to choose a mixture that is biased towards coarser friction, ie 70 percent 240 grade with 600 volume of 30 volume percent. This point changes only very slowly with the change in particle friction since the packing density is near the maximum value of the first range described above. In contrast, the permeability of the mixture is altered at a rapid ratio over this range, and the fundamental increase in permeability can be released by defining packing friction spaced from the absolute maximum volume friction without significant loss of volume friction.

In order to produce composites that allow lower volume friction, the above-mentioned requirements for avoiding particle size distribution, in particular the presence of fines, are relievable. For this application, it may be appropriate to use an unclassified grade of material, such as a soft material.

Additional densification of the preforms is preferred, for example achieved by additional pre-pressing using cold isoformation. Some of the corrosion strength of the preforms can be improved by using binders (ie, cytonic colloidal silica binders) or partial pre-sintering. Pre-sintering is useful for increasing volume friction while maintaining permeability. However, it is important that any pre-sintering be carefully controlled to avoid loss of proper porosity. Ideally the effect of pre-sintering is all the fine pores that exist between the remaining particles and those that remain accessible but of a reduced size. This ideal point can be approached by using a deeply controlled microwave of the pre-sintering step.

Preferred packing densities can be achieved by slip injection of the silicon carbide mixture, by freeze injection or by sedimentation of the fluid, and warm molding of the compound with silicon carbide can be used. Application of vibrations (ie, ultrasonic vibrations) can improve packing density. In practice, ultrasonic vibrations can be applied well during ejection to support the ejection method.

When the prepared die 9 and its contents are located in the chamber 5 for ejection, for example with molten aluminum matrix material 17 from the crucible 11, the vent valve 8 of the vent 7. ) Is closed and set to connect the vacuum pump pressure vessel (1). When the pressure vessel 1 and the chamber 5 are vacuumed, the port 6 is closed. The heaters 10 and 12 are turned on and the die together with the preform 24 and the crucible 11 are raised to a temperature above the melting of the matrix material 17 of the crucible 11. In the case of aluminum, the die 9 and its contents are preheated to about 700 ° C. and the aluminum matrix material 17 is preheated to about 730 ° C. The plug 15 resists so that the molten matrix material 17 can only pass into the die 9 under the influence of gravity. Then, the valve 4 is reversed to pressurize the pressure vessel 1, causing the matrix material 17 to eject the preform 24. Finally, the valve 8 and the port 6 are open so that gas flows from the interior of the pressure vessel 1 past the die 9 to cool the pressure vessel 1 and solidify the mixture therein. do. The cooling geometry which affects the shrinkage of the preform 24 ejected during solidification is supplied by the liquid remaining from the supply. This effect is enhanced by providing insulation (not shown) around the sidewalls of the die 9.

The ejection can be continued isothermally as long as required. A particular advantage of the silicon carbide / aluminum system is that it is a feature of the system that the wet angle of the silicon carbide / liquid aluminum is reduced in minutes. The smallest holes that do not initially eject continuously under the applied pressure are ejected continuously while maintaining pressure and temperature over the size of the time unit. In the above-described embodiment including the separator element and the array of preforms 24, the ejection time allowed before cooling of 5 minutes becomes appropriate.

2 shows a modification of the device of FIG. 1, which is a modified device that provides a number of advantages. Components which perform an action similar to that shown in FIG. 1 are indicated by the same reference numerals to distinguish the subscript a.

The die 9a includes a thin walled container having a rectangular box shape. The side wall of the die 9a is a thermally insulated portion 31. High frequency heating is provided via a coil 10a that is well connected with the stainless steel of the die 9a to provide fast heating rise.

The port 3a and the valve 4a are provided for vacuum and pressurization as in the apparatus of FIG. 1. Separate pipeline 32 and valve 33 are provided for the supply of cooling gas. The vent pipe 7a controlled by the valve 8a is provided from the perforated collection ring pipe 34. The cooling gas pipeline 32 and the integrated ring pipe 34 are positioned to guide the flow of the cooling gas over the non-insulated bottom wall of the die 9a.

The preform 35 of the porous reinforcing material is positioned and held in the die 9a by means of a perforated lead 21a that fits within the die 9a. An open mesh member 36 is positioned between the lid 21 and the preform 35 to distribute the molten metal matrix material 37 when leached through the perforations of the lid 21a. The mesh member also attaches silicon carbide powder located in the die 9a. The action of the lid 21 and the mesh member 36 may be combined in the form of a lead having a hole fine enough to attach a single component, ie, silicon carbide powder.

The metal matrix material 37 is initially positioned as shown when the solid block itself in the die 9a is on top of the perforated lid 21a. The gap between the block of matrix material 37 and the wall of the die is necessary to allow the release of gas from the preform during vacuum.

When the prepared die 9a and its contents are placed in the pressure vessel 1a, the pressure vessel 1a is first vacuumed and the heater 10a is turned on. When the metal matrix material 37 is melted, pressure is applied via the valve 42a. After the ejection is almost completed, the heater 10a is turned off and the cooling gas is supplied under pressure via the valve 33 and the pipeline 32. At the same time, the vent 73a is opened to the atmosphere via the valve 8a. The controlled flow of cooling gas provides good control of the directional solidification that occurs in the die.

The shape of FIG. 2 has an advantage over FIG. 1 in that the device is simpler, in particular only a simple RF heater is required and does not need to be controlled at high temperatures of the flow of molten metal matrix material. The capacity of the FIG. 1 device used for each drive can be controlled very close to the heating and cooling that can be performed and better controlled relative to temperature.

The apparatus of FIGS. 1 and 2 initially preforms the preforms of the pressure vessels 1, 1a with a gas pressure selected to increase the thermal diffusion of the preform material compared to thermal diffusion when the gas is evacuated and vacuumed. It operates in an improved form of heating. In this mode of operation, the pressure vessels 1, 1a are vacuumed before removing unwanted residual oxygen or water vapor. Once in vacuum, the gas enters the containers 1, 1a. This point is chosen when it is chosen to be non-reactive or oxidative and must have a sufficiently low moisture content. The gas may be the same as the gas used to pressurize the vessels 1, 1a, in which case a valve 4 is used which connects the vessels 1, 1a to the accumulator. Other gases may also be used.

When the pressure vessels 1, 1a are filled with gas at the required pressure (always ambient atmospheric pressure), the heater is turned on. Once the temperature of the preform core is sufficient, the gas is discharged and vacuumed by connecting the pressure vessels 1, 1a to the vacuum pump as before. The remainder of the method is then executed as described above.

3 and 4 show the die 9a in more detail, in particular a preferred apparatus for forming a number of rectangular articles.

A rectangular sheet-shaped silicon carbide preform is formed and positioned by an array of separator substrates 41. The two sides of the separator substrate 41 have flanges 42 (see FIG. 4) that maintain the desired separation of the plate 41 and transfer heat from the walls of the die 9a into the innermost contents forming the core. Equipped.

The contents of the die 9a are held by the lid 21a, and the intermediate open mesh 36 distributes the molten metal matrix 37 when filtered into the preform via the perforated lid 21a. do.

The gap between the inner surface of the wall of the die 9a and the flange 42 of the separator plate 41 is made as small as possible to increase heat transfer, which separates the plates 41 from each other after ejection and removal of the die 9a. something to do.

Silicon carbide preforms may be introduced into the spaces between the plates 41 by any of the methods described above with respect to FIG. 1. However, the particular shapes shown are easily seated using pre-prepared sheets of plastic molded from silicon carbide powder pressed together by the binder. The binder can be easily removed by heating before the blowing method.

In the device of FIGS. 3 and 4, the separator plate 41 is vertical as clearly shown from the horizontal shape of FIG. 1. The vertical stack is preferred to provide a better installation for the ejection of the molten metal matrix material upon ejection when directional solidification occurs.

Although it is possible for the graphite or ceramic separator plate 41 to be made of metal, they can provide better thermal conductivity because they are better to recover and reuse. The metal separator 41 appears to be effective in providing an improved jet path for the molten metal material.

However, the use of carefully selected thermally good alloys can be good, in which case the thermal conductivity may not be so good. For example, since it is particularly preferable to follow the mixture of the separator substrate 41 of the alloy, their coefficient of thermal expansion is smaller than the coefficient of thermal expansion of the metal matrix mixture above the melting point of the metal matrix material, but higher than below the melting point of the metal matrix material. . The effect then acts for the separator plate 41 to pressurize the mixture upon ejection and deflation after solidification to facilitate continuous separation.

In another method, a simple plate of zirconium is coated with colloidal graphite attached in a shape cut from the graphite sheet. The cuts form a folding back shape of the desired product and are filled (ie, doctor-blading) as a slurry of ceramic reinforcement particles. After drying, a number of preforms produced by the method are laminated and then ejected as described above. The holes are preferably made of dried slurry. They will be filled with metal upon ejection, but the metal can be drilled back more easily than through the ceramic reinforcement.

If graphite or ceramic separator 41 is used, it is preferred that the surface be coated with a release agent that readily prevents any tendency that the molten metal matrix material is more readily ejected into the graphite or ceramic separator.

The present invention is not limited to the above-described embodiment. For example, the preform shape in die 9 or 9a may be supported by the sheath material where a composite product shape is desired. Of course, the envelope material is hardly ejected. Fine silicon carbide particles are suitable for this purpose and are formed using salts. Water-soluble salt binders will readily remove the shell material after the product has been ejected and solidified.

The support mount of the die 9a is movable over the track among the multiple stations. At one or more stations, the high frequency heating coil in the hood can be lowered (and raised) onto the supported die 9a to preheat the die and its contents. At the other station the vacuum chamber and the associated device described with reference to FIG. 2 can be lowered (raised) to clamp into the vacuum sealing device as a support mount. In the apparatus comprising, for example, three stations, it is possible to effectively operate the plant operation. Thus, while the seated die is ejected at the central (vacuum chamber) station, the seated die is prepared and preheated at the external station to prepare for transfer to the center station as soon as the ejection of the preceding batch is completed.

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Claims (21)

Discharging the molten matrix material into the porous preform of the reinforcing material and positioning the plurality of separator elements to form a plurality of cavities that form the final product dimensions in the die, and filling the cavity with the porous reinforcing material A method is provided wherein the porous reinforcement material comprises a particular material whose particle size distribution is selected and controlled such that a majority of the particles can be close to or at one of two different sizes, at each of the two sizes. The relative proportion of the particles is predetermined to position the die in the pressure vessel with the amount of matrix material and to heat the matrix material and the die to a temperature above the melting point of the matrix material positioned to be in contact with or in contact with the porous reinforcement material. The molten matrix material may be formed into a porous reinforcing material in the die. Pressurizing a pressure vessel to eject the synthetic material, characterized in that the matrix material is cooled and solidified. The method of claim 1 wherein the matrix material is initially located in a crucible located in a pressure vessel such that the crucible and the die and its contents are heated together to a temperature above the melting point of the matrix material when melting is transferred from the crucible to the die. Synthetic material production method characterized in that. The method of claim 1 or 2, wherein the separator element is in the form of a thin plate formed between a plurality of disk-shaped cavities filled with a porous reinforcing material. The article of claim 1, wherein the separator elements are arranged in pairs, each pair of first elements comprising a cavity filled with a porous reinforcing material and formed when ejecting the porous material with a matrix material. Forming a preferred shape of one side, wherein each pair of second elements comprises a thin plate positioned adjacent to the first element forming the other side of the product to be formed. 3. A method according to claim 1 or 2, wherein the separator element comprises a metal that is rigid and maintains its structure at the temperature at which the die is ejected. 6. The composite of claim 5, wherein the die comprises a metallic thin-walled container that remains solid and maintains its structure at the temperature at which the die will eject and can be easily removed after ejection and solidification are complete. Manufacturing method. The method of claim 1 or 2, wherein the separator element is made of graphite. 7. A method according to claim 6, wherein the die is heated by high frequency heating at a sufficiently low frequency of the separator element to internally heat the die contents. The method of claim 1, wherein the die is a nonmetal and the contents of the die are heated by microwave heating. 10. The method of claim 9, wherein the separator element is made of a ceramic, such as zirconia, which converts microwave radiation into heat. The method of claim 1 or 2, wherein the particle size distribution of the porous reinforcing material is controlled to minimize a plurality of particles having a size smaller than the Kapitze radius. The method according to claim 1 or 2, wherein the particle size distribution of the porous reinforcing material is controlled to minimize a plurality of particles having a size exceeding a predetermined maximum size. The method of claim 1 or 2, wherein the two particle sizes are 240 grade and 600 grade, respectively. The method of claim 13, wherein each of the two size particle mixtures provides a maximum volumetric friction of the specific reinforcement of the product that is finally ejected. The composite of claim 13, wherein each of the two size particle mixtures comprises an excess of larger particle size components compared to providing maximum volumetric friction of the specific reinforcement of the last ejected product. Manufacturing method. 14. The preparation of a synthetic material according to claim 13, wherein said two-size particle mixture is selected to provide a predetermined volumetric friction of a specific reinforcement in the last ejected product to match the required thermal expansion coefficient of the product. Way. Ejecting the molten matrix material into the porous preform of the reinforcing material, positioning the preform on the die, covering the preform with a rigidly fixed and perforated closure member in the die, the closure member being perforated within the top of the die. Placing a solid metal matrix material on the top and heating the die to blow the preform through the closed and perforated closing member of the metal matrix material. 18. The method of claim 17, wherein the die is positioned prior to vacuuming and before the metal matrix material is melted and then heated in a continuously pressurized pressure vessel. 19. A method according to claim 17 or 18, wherein the first evacuation and then the pressure vessel gas is reintroduced at an initial cycle while the matrix material is heated and again evacuated before reaching its melting point. 3. A method according to claim 1 or 2, wherein the first vacuum is applied and then the pressure vessel gas is drawn in at an initial cycle while the matrix material is heated and vacuumed again before reaching its melting point. 21. A product characterized by being produced by the method of any one of claims 1-20.