DE3406171A1 - METHOD FOR COMPRESSING A METAL OR CERAMIC BODY - Google Patents

Description

Method for compacting a metallic or ceramic body

The present invention relates to the field of compaction of bodies and, more particularly, to a Improved process with which metallic or ceramic bodies are produced with the least possible distortion can be.

The methodology associated with the production of metallic high-density objects by compression is known from the prior art. Examples of the prior art dealing with this methodology are U.S. Patents 3,356,496 and 3,689,259. Before discussing these two references, a brief discussion will illustrate the two main techniques currently in use to compact either a loose powder or a pre-pressed metal powder compact. These two techniques are commonly referred to as "hot isostatic pressing" and "powder forging". The process of hot isostatic pressing ("HIP process") consists of placing loose metal powder or a pre-pressed molding in a metal can or hollow mold, then evacuating the can, sealing the can to prevent any gases from re-entering, and the can to be placed in a suitable pressure vessel. The pressure vessel has internal heating elements to raise the temperature of the powdered material to a suitable compression temperature. Internal temperatures of 1000 to 2100 ^° C. are usually used, depending on the material that is being processed. Same-

as the temperature inside the HIP vessel rises, the internal pressure is slowly increased and maintained in a range of 103.4 to 206.8 MPa (15,000 to 30,000 psi), which in turn depends on the Material that is being processed. Under the joint influence of temperature and isostatic pressure, the powder is compressed to the theoretical bulk density of the material.

A HIP can hold more than one can during a given cycle; this results in the Ability to compact a wide variety of powdered metal parts per cycle. Additionally is by the action of the isostatic pressure the compression more or less uniformly over the entire part treated with the hot isostatic pressing process. By applying a suitable design With the metal sleeve it is possible to make cuts for transverse holes or slots in the compacted object to train. However, the throughput time of a batch is low, as it often takes 8 hours or more a single cycle are required. In addition, at the end of the cycle, the metal cans that hold the object surrounded by powder-form metal, either mechanically or chemically removed.

The second known method of compacting powdered metal is the technique known as "powder forging" ("Powder Forging; PF") is called. The powder forging process comprises the following process steps:

a) cold pressing of loose metal powder at room temperature in a closed mold Pressures in the range of 10 to 50 TSI to a suitable geometry (often referred to as a "preform"),

to then subject it to the forging process. At this stage the preform is friable and can have a porosity of 20 to 30%; their stability is attributed to the mechanical interlocking of the pulverized particles.

b) Sintering the preform (i.e. the preform is raised Temperature at atmospheric pressure) under a protective gas atmosphere. The sintering process causes a welding together of the mechanically interlocked powdered particles in the solid state.

c) reheating the preform to a suitable one

Forging temperature (depending on the alloy). Alternatively, this reheating step can be incorporated into the sintering step, d) forging the preform in a closed mold to the final shape. The mold is typically maintained at a temperature of 148-316 ⁰ C (300 to 600 ⁰ F).

The forge step makes the porosity disappear, that includes the part from the pre-forming step and gives that treated by the PF process Part the final shape.

The advantages of powder forging are the high process speed (up to 1 000 parts per hour), the possibility of the part in the final design produce mechanical properties that are essentially similar to those of conventionally forged products are equivalent and high material utilization. However, there are also a number of disadvantages, such as the non-uniformity in density due to the cooling of the preform when in contact with the relative cold press form and the fact that it is not possible to make incisions, what is with the HIP technology is possible.

To come back to the above mentioned patents: These documents apparently disclose a combination of the isothermal and isostatic conditions of hot isostatic pressing and the possibility of with the HIP process to form incisions, with the continuous production at high Throughput speed and low cost normally associated with powder forging. U.S. Patent 3,356,496 teaches the use of an outer ceramic molded vessel as the first heat barrier use. In addition, this outer ceramic mold causes an almost even distribution of the Pressure on the powdery material when it is deformed.

U.S. Patent No. 3,689,259 teaches the use of granulated refractory materials. This publication intends to improve upon the aforementioned US Pat. No. 3,356,496 in respect of a faster heating of the fine-grained material and faster heating of the pre-pressed molding.

While the US patents mentioned may bring advances over the state of the art, they still remain significant problems related to the use of a layer of ceramic material in which the preform is located the compression is introduced. More specifically, it has been found that the use of crushed and ground Ceramic materials or carbides cause a significantly inconsistent pressure distribution from the top End of the batch (surface adjacent to the moving, pressure-exerting part) to the lower end of the batch (Surface adjacent to the fixed bed of the press). This inconsistency in the pressure distribution can be shown very well if a pre-pressed

ter round cylinder made of a powdery material is compressed. After compaction in a layer of crushed and ground or molten ceramic Material to almost 100% of the bulk density was found to be the surface of the prepressed Cylinder, which was located immediately next to the movable ram, was smaller in diameter than the surface closest to the immovable foot of the press. Making a cut by the compressed cylinder along its diameter and examining the cut surface showed that it was shaped like a trapezoid. The phenomenon described above was observed in all of the compacted molded parts observed when crushed and ground or molten granular ceramic material as Compaction medium was used.

The solution to the problems associated with such distortion and lack of dimensional stability related have been extensively studied, especially when the solution is also aimed at mass production must be applicable. The present invention makes a solution available that is also suitable for mass production is applicable.

The present invention is directed to a method for densifying metallic or ceramic materials Body comprising the following procedural steps:

a) Forming a shaped body from powdered metal or ceramic material. Preferably one of these

like shaping step carried out by pressing, as is per se from the prior art
is known;

b) sintering the shaped body in order to increase its density;

c) the next step is a hot layer of generally spherical ceramic particles produced, the graphite or a similar lubricant was added and in which the molded body is embedded. This layer, preferably made of a refractory material such as aluminum oxide (Al-O-.) And optionally a lubricant produced by initially heating the aluminum oxide particles (and lubricant compound, if present) in a fluidized bed or by other equivalent means. Since the sintered Molded body often cools down, it can then be additionally heated and placed in the hot fluidized bed be introduced. Additional spherical ceramic particles (and possibly a lubricant compound) are then added to cover the molding. Alternating layers hotter Ceramic particles and hot moldings are also within the scope of this invention.

d) Compression of the shaped body in the fluidized bed under high pressure in order to thereby compress the body and to bring it into the desired shape.

By applying the methodology of the present invention, structurally significant improvements can be made Moldings are produced which have minimal distortion.

The new features that are characteristic both of their organizational process and of the procedure are held, together with other objects and advantages essential to the invention, better understood from the following description, taken in conjunction with the accompanying drawings can be seen in which, for example, a present

tig preferred embodiment of the invention is shown. It is expressly assumed, however, that the drawings are for the purposes of illustration and description only and are not intended as a definition of the limits of the invention.
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Figure 1

Figure 3 is a flow diagram showing the method steps of the present invention.

Figure 2

is the plan view of a cut that the
Figure 10 shows densification step of the present invention.

Figure 3

Figure 11 shows a plan view of a compacted molding contained in a layer of aluminum oxide particles of non-spherical shape has been condensed.

Figure 4

shows a plan view of a compacted molded part, which is in a layer of spherical
Alumina particles have been compacted.

Figure 5

shows a plan view of a compacted molded part, which is in a layer of spherical,
with graphite coated aluminum oxide particles has been densified.

Reference is first made to FIG. Therein a flow diagram is shown showing the process steps of the present invention. As can be seen from number 10, a preform is first made

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made of metal, for example in the shape of a wrench. While a preferred embodiment contemplates the use of a metallic preform made from powdered steel particles, other metals and ceramic materials such as alumina, silica and the like are also within the scope of the invention. A preform typically has a density of 85% of the theoretical value. After the powder has been shaped into a preform, it is then sintered to increase its strength. In a preferred embodiment, temperatures in the range from 1093 to 1260 ^° C. (2000 to 2300 ^° F) over a period of approximately 2 to 30 minutes in a protective gas atmosphere are required for sintering the metal (steel) preform. In a preferred embodiment, nitrogen-based gas is used as the protective, non-oxidizing, inert atmosphere. Following the sintering process, illustrated by numeral 12, the sintered preforms can be stored for later processing. If this is the case, the preform is then, as shown at 14, to about 1065 ⁰ C (195o F ⁰⁾ were heated in a protective gas atmosphere.

The densification process illustrated by numeral 16 takes place after the hot coated Preform has been introduced into an embedding of ceramic particles, as described in more detail below is discussed. In order to achieve a desired high production rate, alternating layers can be hotter Ceramic particles and hot coated preforms can be used. To the speed of production To increase further, compaction can be carried out immediately after sintering, as long as the preform has not yet been able to cool down.

Densification is accomplished by exposing the embedded coated preform to high temperature and pressure. For metal (steel) parts, temperatures in the range of about 1093 ⁰ C (2000 ⁰ F) and off-axis pressures of about 551.6 MPa (40 TSI) are used. Crimping at pressures from 137.9 to

827.4 MPa (10 to 60 tons), depending on the material, is also in the range of these Invention. The coated preform is now solidified and, as shown under item 18, can be separated with the ceramic particles easily separable from the preform and reused can. If necessary, any particles adhering to the preform can be removed; the end product can be further machined.

As stated above, a problem associated with the use of a conventional ceramic sheet has been that the final product was disadvantageously distorted. A microscopic examination of such crushed ones and ground or melted granulated ceramic materials gives a very irregular shape, many individual particles having a / either rectangular or triangular cross-section. However, significantly less distortion is achieved when using the generally spherical ceramic Particles of the present invention, especially in combination with a lubricant, are used.

Upon further investigation it was found that by using a layer of spherical ceramic Particles, preferably alumina, without a lubricant have some, albeit very small, distortion stayed behind. Although the use of such a layer for the production of parts with in ver-35

immediately led to the prior art of better dimensional stability, there remains the need to improve this dimensional stability. The present invention addresses this problem by adding a specific lubricant to the layer of spherical ceramic material in an amount of about 1 to 2% by weight of the spherical ceramic particles. In a preferred embodiment, carbon was mixed in in the form of graphite with a particle diameter of less than 0.045 mm (325 mesh); it adhered to the ceramic particles much like a coating. The addition of graphite leads to a lubricant effect between the ceramic particles and facilitates solidification. Other similar temperature stable, generally non-reactive lubricants such as MoS ₂ , iron mica, and the like, are also within the scope of this invention.

In a preferred embodiment, the lubricant is mixed with the alumina particles prior to the formation of the hot coat layer. Mixing can be carried out in a V-mixer or a drum mixer or in other conventional systems, to ensure that the lubricant and ceramic particles are intimately mixed.

The selection of the ceramic material for the layer is also important for another reason which is described in Compaction process lies. If a particulate material is selected that has a tendency to sinter in the Compaction temperature shows, the pressure applied is both for the compaction of the pre-compressed powdery Metal as well as for the solidification of the ceramic medium. For example, requires

the use of silicon oxide at a compression temperature of about 1093 ⁰ C (200O ⁰ F) a higher pressure, to achieve solidification, compared to the use of alumina at the same temperature. The use of zirconia, silica or mullite at temperatures above 926 ⁰ C (1700 ⁰ F) leads to higher pressures solidification because these ceramic materials (F 1700 ⁰⁾ begin to sinter even at temperatures above 926 ° C.

To overcome the problem of sintering and the resulting higher pressures required with some ceramic materials, spherical aluminum oxide is used as the preferred densification medium up to temperatures of 1204 ^° C (2200 ^° F).

In addition, spherical aluminum oxide has good flow properties, shows good heat transport and only to a very small extent does the particles stick to one another during the densification process. An additional advantage of the spherical shape is the greatly reduced sticking of the particles after the compression process. Preferably, the spherical particles of the present invention range in size from 0.15 to 0.10 mm (100 to
140 mesh).

Referring to Figure 2, the compression step will now be explained in more detail. In a preferred embodiment The preform 20 is completely converted into a layer of generally spherical alumina particles 22 embedded, which were coated with graphite as a lubricant and which in a for Compaction suitable mold 24 had been introduced. The foot of the press 26 forms the lower part, while a hydraulic ram 28 the upper part

of the press and is used to apply pressure to the particles 22 and preform 20. The coated The preform 20 made of metal powder is very quickly under a high, non-axial pressure of the punch 28 compressed into the mold 24. The die 28 has no defined dimensions (such as the dimensions of a Wrench), and there will be only a negligibly small lateral deviation of the preform 20 observed. Accordingly, compression takes place almost exclusively in the direction of travel of the ram 28.

As discussed above, the use of non-spherical particles results in non-uniformity Pressure distribution after the compression process. A top view of a cylinder 30a, cut open along one of its diameters, would have the shape of a trapezoid, as shown in Figure 3, and would come close to 100% full density.

Referring to Figure 4, it can be seen that the same precompressed rectangular cylinder 30 is of equal diameter in the upper and lower part and a slightly larger diameter in the middle of the height, when compacted in a matrix of uncoated spherical alumina particles. why the large diameter that occurred in the middle of the height is not known. However, the difference became so significantly reduced in diameter that this is a significant improvement over the prior art the technology is. To compensate for this slight distortion, minor changes in the format of the Preform made before the compaction step or the Moldings are machined. Additionally

the use of spherical particles also greatly reduces the bonding of the particles to the preform during the compaction process. The spherical ceramic particles 22 thus have three important functions:

(1) transfer the compaction pressure to the preform 20,

(2) To serve as a semi-liquid mold that defines the format the preform is maintained during the compaction process and

(3) the heat loss in the preform 20 during the
Delay transfer and compaction.

To continue a distortion in the molded body, with the use of spherical alumina particles is connected, to compensate and largely, if not completely, the machine A lubricant can prevent machining and / or redesigning of the preform, as mentioned above to be used.

Referring to Figure 5, yet another rectangular cylinder 30b is shown. In this embodiment the spherical alumina particles were coated with graphite. How to recognize can, the cylinder 30b kept its original shape, i.e. the diameter remained completely uniform from the top of the body to the bottom. So by using a lubricant completely eliminating the need to further machine and / or redesign the preform.

From the description of the present invention will become it will be apparent to those skilled in the art that other embodiments clearly within the scope of the present

finding lie. For example, the preform 20 can be a wrench or similar item.

In addition, other generally spherical particles such as silica, ZrO ₂ and similar ceramic oxides can be used for the bed. It is therefore not intended to limit this invention to the specific embodiments disclosed herein.

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Claims (11)

VON KREISLER SCHÖNWALD EISHOLD FtIES ^ FROM KREISLER KELLER SELTING WERNER PATENT LAWYERS Dr.-Ing. by Kreisler 11973 Metal Alloys, Inc. Dr.-Ing. K. W. Eishold 11981 Signal Hill, California, U.S.A. Dr.-Ing.K. Schönwald Dr. J. F. Fues Dipl.-Chem. Alek von Kreisler Dipl.-Chem. Carola Keller Dipl.-Ing. G. Selling Dr. H.-K. Werner DEICHMANNHAUS AT THE MAIN RAILWAY STATION D-5000 KDLN 1 AvK / m 02/20/1984 Claims A method for compacting a metallic or ceramic body, comprising the following method steps: a) Production of a molding from powdered metal or Ceramics, b) sintering said molding to increase its strength, c) providing the body with a layer of heated, generally spherical ceramic particles and d) compacting the coated molding in said heated layer of generally spherical shape, with a coated ceramic particle under high pressure, in order to thereby produce said molding on a desired, to bring compressed format. 2. A method for compacting a metallic or ceramic body according to claim 1, characterized in that said Shaped body is formed by pressing powdered metal. 3. A method for compressing a metallic or ceramic body according to claim 1, characterized in that the in general spherical ceramic particles are alumina. TtWon: (0221) 13 1041 T.l.xj 868 2307 dopo d Ttlagrammi Oompol.nl Cologne 4. A method for compressing a metallic or ceramic body according to claims 1 to 3, characterized characterized in that said generally spherical ceramic particles have a particle size of less than 0.1 mm (140 mesh). 5. A method for compressing a metallic or ceramic body according to claims 1 to 4, characterized characterized in that said generally spherical ceramic particles have a thermally stable, generally non-reactive lubricants. 6. A method for compacting a metallic or ceramic body according to claim 5, characterized in that that said lubricant is graphite. 7. A method for compacting a metallic body, comprising the following method steps: a) Production of a molding from powdery
Metal, b) sintering said molding to its density
to increase c) Providing the molding with a layer of heated, generally spherical ceramic particles with a coating of a
thermally stable, generally non-reactive lubricants have been coated, d) heating said coated one Moldings to a predetermined temperature and e) pressing said molding in said heated layer of generally spherical ceramic coated with a coating
Particles under high pressure, in order to thereby produce the mentioned molding in a desired, dense format
to condense. 8. A method for compressing a metallic body according to claim 7, characterized in that the generally spherical ceramic particles mentioned are aluminum oxide. 9. A method for compressing a metallic body according to claim 7, characterized in that the Process steps (b) and (d) are carried out in a protective gas atmosphere. 10. A method for compressing a metallic body according to claim 8, characterized in that the said generally spherical alumina particles having a size in the range from 0.15 to 0.10 mm (100 to 140 mesh). 11. A method for compressing a metallic body according to claims 7 to 10, characterized in that that said lubricant is graphite.