FR2541151A1 - PROCESS FOR CONSOLIDATING A METAL OR CERAMIC MASS - Google Patents

Abstract

THE INVENTION CONCERNS A PROCESS FOR CONSOLIDATION OF A METAL OR CERAMIC MASS, CHARACTERIZED IN THAT IT INCLUDES THE SUCCESSIVE PHASES CONSISTING OF: A. FORMING A MANUFACTURED ARTICLE FROM A METAL OR A POWDERED CERAMIC; B. FRITTING THE MANUFACTURED ARTICLE SO AS TO INCREASE ITS MECHANICAL STRENGTH; C. PROVIDE A BED OF SENSITIVELY SPHEROIDAL CERAMIC PARTICLES HEATED 22; AND D. COMPACT THE MANUFACTURED ARTICLE IN THE HEATED BED OF SENSITIVELY SPHEROIDAL CERAMIC PARTICLES UNDER HIGH PRESSURE TO THUS CONSOLIDATE THE MANUFACTURED ARTICLE AND GIVE IT A DENSE DESIRED SHAPE.

Description

"Process for consolidating a metallic or ceramic mass"

  invention relates to the consolidation of

  masses or bodies and more particularly a perfected process

  designed to produce metallic masses or

  ramic with minimal distortion.

  The methodology associated with the production of high density metal objects by consolidation is known in the art. Examples of prior art documents which envisage such a methodology are US patents.

  Nos. 3,356,496 and 3,689,259 Before discussing these documents

  The following is a brief discussion illustrating

  the two methodologies currently used to denounce

  sify either a loose powder or a tablet of powder

  these two techniques are usually

  called hot isostatic forging and forging of

  The isostatic hot stamping process consists of

  to place free metal powder or a pre-compressed tablet

  molded into a box or mold, then to evacuate the atmosphere.

  box, to seal the box to prevent any

  subsequent gas inlet, and to place the box in a

  appropriate clave The autoclave has heating elements

  internal fages to raise the temperature of the material

  powder to an appropriate consolidation temperature

  The internal temperatures of 1000 to 21000 C are typically

  used, depending on the material being treated Simultaneously with the increase in the internal temperature of the autoclave

  isostatic hot stamping, the internal pressure is slow-

  increased and maintained at a value between

2 2

  1000 kg / cm and about 2000 kg / cm, again depending on the

  treated material Under the combined effects of temperature and isostatic pressure, the powder is densified up to

  the theoretical mass density of the material.

  A hot isostatic die-back autoclave may be

  If more than one canister is used during a given cycle, it is possible to densify several powdered metal articles per cycle. In addition, using isostatic pressure, the densification is more or less uniform at the same time.

  within the article subjected to hot isostatic stamping.

  Using appropriate box shapes, it is possible to

  However, the duration of the charging cycle is long and often amounts to 8 hours or more for one cycle. Moreover, at the end of the cycle, the boxes surrounding the powdered metal article must be

  removed either by machining or chemically.

  The second conventional method for densifying a metal in

  powder is a technique called powder forging.

  powder forging process comprises the steps of: (a) cold compacting a loose metal powder to

  ambient temperature in a matrix closed under pres-

  between 1400 and 7000 kg / cm 2 to give it an appropriate geometry (often called a preform), for subsequent shaping; at this point the preform is friable and

  can have a porosity of 20 to 30%, its resistance

  coming from mechanical attachment of powder particles;

  (b) sinter the preform <that is, submit the pre-

  forms at a high temperature at atmospheric pressure) under a protective atmosphere; sintering causes the "welding" into a block of powder particles mechanically hooked together; (c) reheating the preform to a suitable forging temperature (alloy function); alternatively, this reheating step may be incorporated in the sintering step; (d) forging the preform into a closed matrix for him

  give its definitive form The matrix is typically

  held at a temperature of between 150 and 320 ° C.

  The forging step eliminates the inherent porosity of the preform and gives the piece subjected to the forging of powder

its final form.

  Advantages of powder forging include:

  processing speed (up to 1000 pieces per hour),

  It is possible to obtain a clean shape, mechanical properties substantially equivalent to those of conventionally forged products and an increased material yield. However, there are a number of disadvantages including the non-uniformity of the density due to the cooling of the product.

  the preform when it comes into contact with the matrix

  latively cold, and the impossibility of forming

  that can be achieved in the isostatic matrix

hot.

  Referring now again to the above-mentioned patents, these documents teach what appears to be a combination of isothermal and isostatic conditions that make it possible in hot isostatic die-casting and powder forging to form clearances, with high velocity and continuous production at low cost

  normally associated with the forging of powders In the

  No. 3,356,496, the use of an outer container

  molded ceramic is considered the first barrier

  In addition, when it is deformed, this container

  molded ceramic outer surface causes a

  uniformly uniform pressure on the powder material.

  U.S. Patent No. 3,689,259 teaches the use of

  This document is considered to be a refinement of the previous US Pat. No. 3,356,496.

  due to a faster heating of the grains and a heat

  fage faster of the pre-stamped part.

  Although US Pat. Nos. 3,356,496 and 3,689,259 may

  represent progress in the field of technology, problems

  important is the use of a ceramic bed in which a preform is placed before consolidation. More precisely, it has been found that the use of crushed and ground ceramics or carbides results in a distribution of the substantially non-uniform pressure of the top of the load (the surface against the moving die member) towards the bottom of the load (the surface against the die table)

  fixed) This nonuniformity of the distribution of pressure.

  is easily demonstrated when consolidating a cy-

  pre-stamped circular straight liner of a powder material.

  After consolidation in a bed of ceramic material con-

  broken and crushed or melted down to a mass density of

  almost 100%, it was determined that the surface of the cylinder

  The closest pre-coined die to the moving die was smaller in diameter than the nearest surface of the fixed table.

  along a diameter indicated that it was in the form of a

  The above phenomenon has been observed in all

  consolidated sheets when the consolidation medium used was a crushed and crushed granular ceramic matrix

or melted.

  The solution to the problems associated with such distortion

  sion and such defects in dimensional stability

  This form of solution has proved elusive, especially when this solution must also be applied to mass production. The present invention proposes a solution which is

  adaptable to mass production.

  For this purpose, the present invention relates to a method for

  to consolidate metallic or ceramic masses,

  characterized in that it comprises the steps of:

  (a) to form a manufactured article from a ceramics

  or metal powder; preferably this forming step is carried out by compacting, as is well known in the art;

  (b) sinter the manufactured article so as to increase

ter its mechanical strength;

  (c) in the next step, embedding the article

  manufactured in a hot bed of ceramic particles sensi-

  spheroids, in which graphite has been added

  or a similar lubricant; this bed, preferably in one

  refractory material such as alumina (A 1203), possibly

  supplemented with a lubricant, is obtained by initially heating the alumina particles (and the lubricating compound if present) in a fluidized bed, or by any other equivalent means; in addition, because it sometimes appears that the sintered manufactured article is cooled, the article may be subsequently warmed up and placed in the hot bed; additional spheroidal ceramic particles (and optionally the lubricating compound) are then added

  to cover the article; layers can be provided

  coated with hot particles and hot manufactured articles without departing from the scope of the invention; and (d) compacting the manufactured article in the hot bed under high pressure to thereby consolidate the article and

  give a dense character in the desired configuration.

  Thanks to the process of the present invention, it is possible

  to keep manufactured articles of structure substantially

  improved, with minimal distortion.

  The new features that seem to

  of the present invention, both as regards its organization and implementation, as well as other objects and advantages thereof, will be better understood in the

  reading the following description of an embodiment

  preferred embodiment of the invention, given by way of nonlimiting

  FIG. 1 is a block diagram of the process steps of the present invention;

  FIG. 2 is a broken plan view illustrating the

  consolidation step of the present invention;

  FIG. 3 is a plan view of a manufactured article.

  consolidated rein which has been consolidated in a bed of non-spheroidal alumina particles;

  FIG. 4 is a plan view of an article manufac-

  consolidated solid which has been consolidated in a bed of spheroidal alumina particles; and

  FIG. 5 is a plan view of a manufactured article.

  Consolidated re consolidated in a bed of spheroidal alumina particles coated with graphite. Firstly with reference to Figure 1 is shown a block diagram illustrating the steps of the method of the present invention. As indicated by the reference number, a manufactured article or metal preform is all

  first realized, which has the shape of a key (tool).

  Although the present embodiment uses a

  metal preform consisting of steel particles in

  other metallic and ceramic materials, such as alumina, silica and the like, are within the scope of

  The theoretical density of a preform is approximately

  85% After the powder has been brought into a

  preformed ration, it is then sintered to increase

  its mechanical strength In the pre-

  the sintering of the metal (steel) preform

  temperatures between about 1100 and 12500 C

  lasting about 2 to 30 minutes under a

  In the present preferred embodiment, such a protective, non-oxidizing and inert atmosphere is nitrogen-based. Subsequently to sintering, indicated at 12, the sintered preforms can be stored for further processing. If so, as indicated at 14, the preform is subsequently reheated to about 1050 ° C

under protective atmosphere.

  The consolidation process, indicated at 16, takes place after the hot and coated preform has been placed in a bed of ceramic particles, as described below.

  in detail In order to obtain the high production rates

  alternated layers of hot ceramic particles

  hot and coated preforms and preforms can be used

  In addition, in order to speed up manufacturing, the consolidation

  The sintering can take place as long as the preform has not been allowed to cool. The consolidation takes place by subjecting the coated and embedded preform to

  high temperature and pressure For metal objects

  (steel), temperatures of the order of 11000 C and uniaxial pressures of about 5500 kg / cm are used Compaction at pressures of 1400 to 8400 kg / cm 2, depending on the material, also as part of the

  The coated preform was then densified

  and may be separated, as indicated in 18,

  ceramics separating easily from the preform and

  If necessary, any particles adhering to the preform may be removed, and the finished product may

still be machined.

  As mentioned above, one of the problems associated with using a conventional ceramic bed was the fact that

  the finished product was distorted A mid-term review

  croscopically such granular ceramic materials con-

  broken and crushed or melted indicates a quite irregular shape, many individual particles having a

  cross-sectional aspect either rectangular or triangular

  However, using ceramic particles

  substantially spherical components of the present invention, particularly

  when combined with a lubricant, one obtains

  holds a substantially lower distortion.

  More particularly, it has been determined that by using a bed of spheroidal ceramic particles, preferably alumina, without lubricant, some minimal distortion remains although the use of such a bed allowed

  to obtain articles of superior dimensional stability

  compared to the prior art, the need to improve

  Such dimensional stability has remained

  This invention solves this problem by incorporating a lubricant

  Specifically, in an amount of about 1 to 2%, by weight, based on the spheroidal ceramic particles,

  in the spheroidal ceramic bed In the form of

  preferred embodiment, carbon in the form of graphite having a particle size of less than 0.044 mm sieve

  is mixed with the ceramic particles and adheres to

  these are quite like a coating The addition of graphite acts as a lubricant between the ceramic particles and promotes the consolidation of other lubricants.

  analogous, thermally stable and substantially

  reagents, such as molybdenum disulfide, mica and

  analogous, are also within the scope of the invention.

  In the present preferred embodiment, the lubricant is

  The mixture can be blended with the alumina particles before forming the hot bed. The blending can be carried out in a V-shaped or double cone mixer, or in another conventional system, so as to ensure an intimate mixing of the lubricant and the lubricants.

ceramic particles.

  The choice of the ceramic material of the bed is also

  important for another reason in the process of conso-

  lidation If particles with a tendency to sinter at the consolidation temperature are selected, the pressure applied will be absorbed both to achieve the

  densification of the pre-filled powdered metal and to achieve

  For example, if one uses silica with a temperature of consolidation of about

  1100 WC, a higher pressure will be needed to achieve

  densification in comparison with the use of

  at the same temperature The use of zinc oxide

  conium, silica or mullite at temperatures higher than

  at 900 ° C also imposes densification pressures

  because these ceramics themselves start

  hundred to sinter at temperatures exceeding 900 WC.

  To avoid sintering and the need for pressure

  resulting from certain ceramics

  alumina is the preferred

  temperatures up to 1200 WC In addition the spheroidal alumina

  dale has good casting, trans-

  The additional advantage of the spheroidal form is that the particle adhesion is quite reduced after consolidation. Preferably, the spheroidal particles of the present invention have a high degree of self-adhesion during consolidation.

  size between sieves of 0.149 mm and 0.105 mm.

  The consolidation step is more fully illustrated in FIG. 2. In the preferred embodiment, the preform 20 has been completely buried in a bed of substantially spheroidal alumina particles 22 which have

  have been coated with a graphite lubricant, and who have

  The table 26 of the matrix constitutes the bottom, while a hydraulic stamping cylinder 28 defines the top and is used.

  to exert pressure on the particles 22 and the pre-

  The coated metal powder preform 20 is rapidly compressed under a high uniaxial pressure by the action of the jack 28 in the die 24. The die 24 has no defined shape (such as the shape of a tool-key, and there appears a negligible lateral creep of the preform

  As a result, consolidation takes place almost exclusively.

  in the direction of movement of the cylinder 28.

  As mentioned above, the use of non-spheroidal particles results in a nonuniform distribution of pressure, so that after consolidation, a plan view of a transversely cut cylinder would have the shape of a trapezoid, as illustrated in Figure 3, and its density

  would approach 100% of the maximum density.

  With reference to FIG. 4, it can be observed that the same right circular cylinder pre-stamped 30, when it is

  consolidated in a matrix of spheroidal alumina particles

  uncoated dales, with identical diameters at the top and

  at the bottom, its diameter being slightly larger at half height.

  It is not known why the diameter at half height was higher;

  however, the differences in diameter were so great

  This is a substantial improvement over the prior art. To compensate for this slight distortion, minor changes can be made.

  be brought to the shape of the preform before the consolidation

  tion, or the article can be machined. In addition, the use of

  of spheroidal particles also reduces significantly

  the self-adhesion of particles on the preform during consolidation. Thus the spheroidal ceramic particles 22 have

  three main functions: (1) they transfer the pres-

  consolidation of the preform 20; (2) they serve as semifluid mold so that the preform retains its shape during consolidation; and (3) they retard the heat losses in the preform during transfer and consolidation To further compensate for this distortion of the article associated with the use of spheroidal alumina, and

  to avoid most, if not all, of the

  swimming and / or fitness of the preform such as

  mentioned above, a lubricant can be used.

  Referring to Figure 5 is illustrated yet another right cylinder 30b In this embodiment, graphite

  has been deposited on the spheroidal aluminé As can be ob-

  server, the cylinder 30b has retained its original form, that is,

  that is to say that its diameter has remained substantially uniform from top to bottom Thus, thanks to the use of a lubricant, substantially any other machining step and / or

fitness of the preform.

  Note that if preferred embodiments of the invention have been described, other embodiments are within the reach of those skilled in the art without departing from the scope of the present invention. For example, the preform 20 may In addition, it is possible to use other substantially spheroidal particles such as silica, zirconium oxide and similar ceramic oxides for the bed. The invention is therefore not to be considered as limited to the described embodiments. 1 l

Claims (7)

  1 Method for consolidating a metallic mass or   ramique, characterized in that it comprises the successive phases   sives consisting of (a) forming a manufactured article from a powdered metal or ceramic;   (b) sinter the manufactured article in such a way as to to bring out its mechanical resistance;   (c) providing a bed of ceramic particles sensi-   heated spheroidal (22); and (d) compacting the article of manufacture in the heated bed of substantially spherical ceramic particles   under high pressure to consolidate the article manufac-   tured and give it a desired dense shape.   Process according to claim 1, characterized in that the manufactured article is formed by compacting a powdered metal. Process according to Claim 1 or 2, characterized in that the substantially spheroidal ceramic particles (22) are alumina.   Process according to any one of the claims   Previous, characterized in that the substantially spheroidal ceramic particles (22) have a particle size   between the sieves of 0.149 mm and 0.105 mm.   Process according to any one of the claims   preceding, characterized in that the ceramic particles   substantially spheroidal (22) were coated with a lubricant   thermally stable and substantially nonreactive.   Process according to claim 5, characterized in that that the lubricant is graphite.   7 Method for consolidating a metallic mass,   characterized in that it comprises the successive phases consisting of:   (a) to form a manufactured article from a powdered tal;   (b) sinter the manufactured article in such a way as to to bring out its mechanical resistance;   (c) providing a bed of ceramic particles sensi-   spheroidal heaters (22) which have been coated with a thermally stable and substantially nonreactive lubricant; (d) heating the coated article of manufacture to a predetermined temperature, (e) compacting the article of manufacture in the bed   heated with substantially spherical coated ceramic particles   roldales under high pressure to consolidate the article   manufactured and give it a desired dense shape.   Process according to Claim 7, characterized in that the substantially spheroidal ceramic particles <22) are made of alumina.   9 Process according to claim 7 or 8, characterized in that the phases (b) and (d) are implemented under protective atmosphere.   Process according to claim 8 or 9, characterized in that the substantially spherical alumina particles (22) have a particle size between the sieves of 0.149 mm and 0.105 mm.   Process according to any one of the claims   7 to 10, characterized in that the lubricant is or graphite.