FR2641795A1 - MANUFACTURE OF PARTS IN COMPOSITE MATERIAL - Google Patents

Abstract

The invention concerns an apparatus for the preparation of composite metallic or organic materials by centrifugation, a moulding method implementing the said apparatus, the composite materials obtained and the parts constituted by these materials. The apparatus according to the invention comprises a module (5) having an axis of revolution (6) and is provided with means enabling it to rotate about its axis, a device (7) for feeding a liquid matrix material and a device (8) for feeding a reinforcing element. It is characterised in that the device (8) opens into the flow zone (10) of the device (7). The apparatus of the invention allows the local reinforcing at will of one or more characteristics of a part having an axial symmetry of revolution.

Description

The present invention relates to a method of manufacturing materials

  metallic or organic composites by centrifugation, a device for its implementation, the composite materials obtained and

  the pieces made up of these materials.

  The manufacture of metal parts of revolution by centrifugation is well known. The process consists in introducing the

  metallic material in a mold that is rotated.

  This process has also been applied to a mixture consisting of a metal alloy in the liquid state and a reinforcing agent, for example graphite, a ceramic, etc., and parts have been obtained.

made of reinforced metal alloy.

  However, this method has at least two disadvantages. On the one hand, the distribution of the reinforcing agent in the fabricated part is badly maltreated. It depends essentially on the difference in density between the matrix material and the reinforcing agent. Depending on the significance of this difference, the distribution of the

  reinforcement will be more or less homogeneous.

  On the other hand, some products which are capable of constituting good reinforcing agents can not form a stable mixture with the liquid metal matrix material for a sufficiently long time: the reinforcing agent separates from the metal matrix material before the It could not be put in the mold. Such

  is the case for mixtures cuprous alloys - graphite powder.

  The wettability of graphite in liquid copper alloys is very low, even when the graphite particles are coated with nickel or copper. If the graphite powder is mixed with a liquid cuprous alloy, the powder separates after a very short time, less than 2 seconds. It is therefore not possible, by projecting such a mixture into a rotating mold, to orient the

  distribution of the reinforcing agent in the metal part.

  The present inventors then developed a process for the preparation of composite materials by centrifugation, which does not present

  not the disadvantages mentioned above.

  The subject of the present invention is a process for the preparation of

  composite, metallic or organic materials.

  It also relates to the composite materials obtained.

  Finally, another object of the present invention is constituted by

  parts made of composite material.

  The process for preparing composite materials comprising a metal or organic matrix and reinforcing elements according to the invention comprises casting, in a rotating mold, the matrix material in the liquid state and at least one reinforcing agent. It is characterized in that the metal or organic matrix material and the reinforcing agent (s) are fed separately

in the mold.

  Preferably, the incorporation of the reinforcing element to the matrix material is carried out immediately before the introduction.

in the mold.

  By proceeding in this way, it is possible to incorporate reinforcing agents in a matrix which are in the form of particles or short fibers whose wettability is very low in the matrix material. The time elapsing between the moment the reinforcing member is mixed with the matrix material and the hardening of the material in the mold is sufficiently short that the reinforcing member can not dissociate from the matrix material.

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  By adapting the various parameters of the casting, it is possible to obtain pieces of material having zones of revolution.

  reinforced, or pieces of material reinforced uniformly.

  These can not be obtained by conventional centrifugation when the reinforcing element does not have sufficient wettability or its density is significantly different.

from that of the matrix.

  For example, one can choose the casting time of the material of

  matrix and the casting time of the reinforcing element.

  In a variant of the process of the present invention, the addition of the reinforcing agent can be delayed with respect to the beginning of the casting of the matrix material in the case where one only wants to reinforce the interior of the room . It is thus possible to avoid trapping a part of the reinforcing elements on the outside of the parts, trapping which tends to occur due to the solidification

  almost instantaneous outer skin area.

  By sufficiently delaying the casting of the reinforcing element with respect to the beginning of the casting of the matrix material, we will obtain

  a zone of reinforced revolution closer to the bore.

  Furthermore, it is preferable that the casting of the reinforcing element terminates before or at the same time as the casting of the matrix material, to avoid the presence of free reinforcement elements in the bore of the piece of composite material obtained. In addition, the choice of temperatures makes it possible to influence the content of reinforcing element of the zones to be reinforced. Thus, a lower mold temperature, i.e. a higher cooling rate, provides faster solidification near the mold wall, thereby reducing the risk of separation> reinforcement - material of matrix in the case of reinforcing elements having a low wettability in the

matrix material.

  Moreover, the temperature of the matrix material plays a part on the one hand, in terms of the rate of solidification and, on the other hand, in the ease or not of incorporation of the reinforcing elements.

in this matrix.

  The temperature of the reinforcing elements can also play a role in the ease of incorporation of these elements of

reinforcement in the matrix.

  Another factor influencing the distribution of the reinforcing element is the difference between the density of the matrix material and that of the reinforcing element. The higher the density of the reinforcing element relative to that of the matrix material,

  the more this element will tend to be on the periphery of the room.

  In the opposite case, the reinforcing element is with a

  higher concentration around the bore.

  In addition, a higher rotational speed of the mold accentuates

the effect of O to other factors.

  The type and thickness of poteyage play an important role in

  level of solidification speed of the piece.

  Thus, an insulating and thick poteyage will cause a slow solidification of the part, thus facilitating the reinforcement of its periphery (this is used in the case of reinforcing elements whose

  density is greater than that of the matrix).

  One of the essential advantages of the method of the invention resides in the fact that it makes it possible to locally reinforce one or more characteristics of a piece of matrix material having an axial symmetry of revolution. It suffices for this purpose to choose the reinforcement element or elements appropriate to the desired characteristic and the conditions of implementation of the process capable of permitting the

  strengthening of the hedged area.

  The method according to the invention makes it possible to reinforce two zones of a piece diem with the aid of different reinforcement elements. The mode of implementation depends in this case on the difference that exists between the density of each of the reinforcing elements. If their density is very close, the reinforcing element for the outer zone of the workpiece is first introduced, and then the reinforcement element for the internal zone of the workpiece. If the reinforcing element of the outer zone has a density substantially greater than that of the inner zone, the two reinforcing elements may be mixed before being incorporated into the matrix material in the liquid state. When casting by centrifugation, the settling of the reinforcing elements will cause the desired distribution within the room. In this case it is advisable to choose the temperatures so that the solidification is slow enough to allow the heavier elements to come

stand outside.

  The process according to the invention can be implemented for almost all metal alloys, among which mention may be made of copper-based alloys (for example bronze, copper,

  cupro-aluminum, brass) and aluminum alloys.

  It can also be used for organic materials such as, for example, parts made of PVC, epoxy resin, polyester or methacrylate, loaded with silicon carbide particles, in order to

  to give the periphery properties of high resistance to wear.

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  The reinforcing elements may be in the form of particles or short fibers. For example, it is possible to use

  graphite particles, silicon carbide, chromium carbide.

  To improve the wettability of the particles or short graphite fibers when they are intended to reinforce copper alloys and aluminum alloys, it is advantageous to coat them with a layer of nickel or copper, for example, of which thickness can

vary between 1 and 50 Fm.

  The present invention will be described in more detail with reference to the accompanying drawings and the examples given below as

illustrative and not limiting.

  In the drawings, Figures 1, 2 and 3 each represent a

  axial sectional view of a revolution piece made of composite material.

  Figures 4 and 5 each represent a diagram of a device

  for the implementation of the invention.

  In FIGS. 1 to 3, (1) represents the axis of revolution of the part, (2) represents the part, (3) the reinforced part, (4) represents

the bore of the piece.

  Figure 4 shows a mold (5) rotating about a vertical axis (6). The matrix material is introduced into the mold by

  through a chute (7) which enters the mold in (9).

  The reinforcing elements are introduced via a chute (8). This chute (8) opens into the zone (10) of the end portion of the chute (7) so that the mixture of the matrix material and the element of. reinforcement can be done

before introduction into the mold.

  When the mixture in the liquid state is introduced into the mold (5) driven in a rotational movement about the axis (6), it falls on 7. the bottom of the mold and the centrifugal forces due to the rotation of the mold distribute it on the vertical walls of the mold. To facilitate the placement of the material on the walls of the mold, it may be preferable to use a chute (7) whose end portion is located inside the mold (and not at the entrance of the mold) and curved so that the flow of material is directed towards the wall of the mold. When the reinforcing elements are incorporated in the matrix material in the zone (10), the turbulences which form in this zone (10) are sufficient to form a mixture between the

  matrix material and reinforcing elements.

  FIG. 5 represents another device allowing the implementation of the method according to the invention. In this figure, the elements equivalent to those of Figure 4 bear the same references. In this variant, the mold rotates about a horizontal axis. During the introduction of the matrix material (or matrix material mixture + reinforcement element), it falls on the wall of the

  mold on which it is distributed by the centrifugal forces.

  It goes without saying that the invention is not limited to one or the other

of these embodiments.

  The axis of rotation of the mold may be oblique. The feed chute is not necessarily parallel to the axis of rotation of the mold or coaxial. However, it is imperative that, in the feed device of the mold, the feed chute of the reinforcing element opens into an area near the end of the feed chute of the matrix material, thereby creating a zone mixing in the immediate vicinity of the mold inlet. Throughout the text, the term "ugoulotte" should be understood in a broad sense, that is to say, it includes analogous devices such as a

  casting, a feed pipe, a funnel, etc.

  The method of the invention is advantageously used for the manufacture of metallic or organic parts having an axial symmetry of revolution having zones of revolution in which certain properties are reinforced. These parts with axial symmetry of revolution can be parts usable as such (bearings, rings, etc. ..). These pieces can also be a material in which will be cut parts that will not be "revolution". We can thus envisage the manufacture of

  chopsticks, rails having a reinforced area.

  A particularly interesting application is the manufacture of bearings self-lubricating locally. The metal matrix of such

  Bearings is a copper alloy or an aluminum alloy.

  The reinforcing element used is graphite in the form of particles having an average size of 5 to 500 m, optionally coated with a layer of nickel or copper of a thickness of the order

from 1 to 10 m.

  The manufacture of a self-lubricating bearing can be carried out

  using a device as shown in Figures 4 or 5.

  The volume of graphite powder, coated or uncoated, is a function of the thickness and graphite concentration of the zone

  self-lubricating desired in the bearing.

  The flow of the graphite powder is carried out by the trough 8,

  pouring the matrix material through the chute 7.

  In order to avoid trapping graphite particles on the outside of the pieces due to the instantaneous solidification of the outer skin zone, the arrival of the powder in the powder / alloy mixing zone (10) becomes little moment after the start of the

casting the matrix material.

  It is desirable that the casting of powder terminates before or, at the latest, at the same time as the casting of the matrix material, for

  avoid the presence of loose powder in the bore.

  Due to the difference in density between the matrix material and the powder, the latter settles immediately inside the room, this settling being greatly amplified by the centrifugal acceleration within the centrifuged piece (= 20 to 200 g). In order to prevent the powder from being rejected by the bore outside the workpiece (especially in the case of the copper-based die), it is necessary to water the mold very strongly in order to very rapidly advance the solidification front towards the inside the room, allowing it to catch the particles and trap them in the material of

solidified matrix.

  The parts thus produced have, as shown in the diagram of FIG. 1, a high proportion of graphite in the bore, the

thus making self-lubricating.

  In the case of bronze matrix pieces (type UE 12 for example), the presence of porosities within the graphite zone plays the role of a lubrication pocket and dust coming from the running-in period. Indeed, during this period, graphite particles and bronze can tear from the room and then become lodged in these pores, which avoids wear abrasion of the opposing part. However, this presence of porosities can be reduced by adding, in the coated graphite powder, aluminum powder, phosphorus, copper phosphide, zinc or calcium. The percentage, very low, will depend on the number of porosities that the type of use of the bearing will allow. The addition of this powder to the coated graphite powder will be done very

  neat to avoid any heterogeneity of composition.

  The method according to the invention makes it possible to obtain parts of revolution whose length can vary from 2 to 7000 mm and the diameter

outside of 30 to 7000 mm.

  The process according to the invention can also be used for shaping reinforced organic matrix pieces. It is thus possible to produce parts whose periphery can be reinforced, for example by particles of silicon carbide (SiC) to make it particularly resistant to abrasion, or also by

  graphite particles to make the exterior self-lubricating.

  Other types of pairs of organic materials / reinforcing elements can thus be achieved when it is possible to perform, in the mixing zone (10), the matrix / reinforcing elements mixture.

Claims (12)

  A method of preparing composite materials comprising a metal or organic matrix and at least one reinforcing element, comprising casting, in a rotating mold, the matrix material & the liquid state and the reinforcing agent (s), characterized in that the matrix material and the reinforcing agent (s) are   brought separately to the entrance of the mule.   2. Method according to claim 1, characterized in that the matrix material in the liquid state and the reinforcing agent (s) are mixed immediately before introduction into the mold.   3. Method according to any one of claims 1 and 2,   characterized in that a reinforcing agent is incorporated into the matrix material after the start of the casting of the matrix material only.   4. Method according to any one of claims 1 and 2,   characterized in that two different reinforcing agents are   successively incorporated into the matrix material during casting.   5. Method according to any one of claims 1 to 4,   characterized in that the amount of reinforcing agent mixed with the matrix material in the liquid state is adjusted upon introduction into the mold according to the desired volume for the reinforced zone and   the content of reinforcing element.   6. Device enabling the implementation of a method according to   any one of claims 1 to 5, comprising a mold (5) to   axis of revolution (6) provided with means allowing it to rotate about its axis and means for supplying matrix material and reinforcing elements, characterized in that said supply means are distinct, but have a common zone at   near the inlet (9) of the mold.   7. Device according to claim 6, characterized in that the supply means are chutes, the chute (7) bringing the reinforcement element opening into the flow zone (10) of   the chute (8) bringing the matrix material to the liquid state.   8. Device according to claim 7, characterized in that the end of the chute (7) releasing the material is located at   the inside of the mold (5), and curved towards the wall of the mold.   9. Xaterials obtained by the process according to any one of Claims 1 to 5.   10. Parts made of a material according to claim 9.   11. Parts according to claim 10, characterized in that   have an axial symmetry of revolution.   12. Self-lubricating bearing obtained by the process according to one of the Claims 1 to 5.