Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C1/00—Making non-ferrous alloys
  • C22C1/10—Alloys containing non-metals
  • C22C1/1036—Alloys containing non-metals starting from a melt
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C26/00—Coating not provided for in groups C23C2/00 - C23C24/00
  • C23C26/02—Coating not provided for in groups C23C2/00 - C23C24/00 applying molten material to the substrate

Definitions

• the present invention relates to the production of composite metal parts comprising a contact coating intended to resist abrasion.
• Such mechanical parts known as “wearing parts” are known, which are superficially reinforced by the addition of a material having improved characteristics in terms of resistance to wear by abrasion.
• the present invention relates more particularly to hard reloads using a structure of grains of high hardness bonded together by a metal alloy which is commonly referred to as the metallic matrix.
• the grains of high hardness can advantageously be grains based on tungsten carbide.
• a first known technique for producing an abrasion-resistant coating is hard hardfacing by welding.
• rigid rods or flexible rods are used, one end of which is applied to the surface to be recharged and is subjected to an electric arc or to an oxyacetylene flame.
• the rod includes a tungsten carbide powder embedded in an alloy based on nickel or other suitable metals.
• Such hard surfacing obtained with tungsten carbide rods has drawbacks, however: in particular, the welding processes result in depositing the surfacing in the form of successive beads, juxtaposed side by side one after the other . It is understood that the realization of a relatively large area using such a technique is tedious, and requires a certain dexterity and a certain habit on the part of the operator. On the other hand, the waves inherent in such a material deposition process, reproducing the shape of the successive beads, cause thickness irregularities of up to several millimeters.
• Document FR-A-814 171 describes a process for producing a shaped part by sintering in the liquid phase, in which a mixture of carbide chips and molten metal powder is introduced into a carbon mold. The shaped part is melted under pressure. Such a process causes, during the fusion, a significant dimensional shrinkage.
• a more advanced technique for producing a layer of abrasion-resistant material is described in document FR-A-1 398 732. It is an infiltration technique, in which a hollow mold is used "n carbon or ceramic material having a desired shape; a metal substrate is placed in the hollow of the mold, opposite the mold molding walls; filling with grains of tungsten carbide or equivalent the hollow interior space between the substrate and the mold molding walls, vibrating the assembly to pack the grains; grains or pellets of metal or of alloy binder are placed above the grains of carbide; the assembly is heated to a temperature above the melting temperature of the alloy and below the melting temperature of the core and the mold.
• the rise in temperature melts the alloy or binder metal, which infiltrates the space filled with tungsten carbide grains, and ensures the welding with the metal substrate. It is then left to cool and can be removed from the mold.
• This infiltration technique is quite suitable for rooms in which a convex substrate is of relatively small dimensions, and of relatively compact shape, the abrasion-resistant layer being relatively massive. The technique is also suitable when the substrate is concave.
• the abrasion-resistant coating tends to break under the action of impacts, and that in particular this coating does not allow subsequent re-machining after infiltration.
• the weld between the thickness of the abrasion-resistant material and the metal substrate is of poor quality.
• this technique of infiltration on a metal substrate does not allow the production of a part that is mechanically strong enough to constitute a needle for a needle valve used in hydroelectric plants. Indeed, during the closing of the needle on its seat, the anti-abrasion coating of the needle tends to burst under the effect of shocks and mechanical stresses occurring at this closing time.
• the problem proposed by the present invention is to ensure satisfactory mechanical resistance to an abrasion-resistant coating based on infiltrated tungsten carbide grains covering a substrate of a different nature, the assembly constituting a composite part.
• Such a composite part must have qualities of mechanical resistance at the surface sufficient to withstand shocks, and to allow possible re-machining of its abrasion-resistant coating surface without cracking or falling apart.
• the idea which is the basis of the present invention is that the defects observed in mechanical strength of the abrasion-resistant coatings based on tungsten carbide grains produced by infiltration on a substrate would result from differential expansions occurring during infiltration.
• the entire substrate and the surface reloading of tungsten carbide grains must be brought to a temperature sufficient for the melting of the alloy or binder metal which must infiltrate into space. filled with tungsten carbide grains and which must ensure the weld with the substrate.
• the metal substrate expands appreciably, while the grains of tungsten carbide which form a compact stack expand very little, roll on each other and can thus follow the expansion of the mold and the substrate.
• the substrate tends to contract, while the very compact stacking of tungsten carbide grains contracts very little. This results in significant mechanical stresses at the interface between the substrate and the layer of abrasion-resistant material which covers it.
• the tungsten carbide grains no longer have the possibility of rolling over one another, since they are bonded by the alloy or binder metal, so that the abrasion-resistant coating can no longer be shrink by a coefficient similar to that of the substrate.
• abrasion-resistant parts obtained by infiltration appear advantageous, because the abrasion-resistant surface thus obtained by infiltration exhibits remarkable properties of abrasion resistance.
• infiltration makes it possible to produce abrasion-resistant surfaces having particularly regular and smooth shapes, promoting the efficiency of the parts thus produced.
• a valve needle for a hydroelectric plant such a needle must have a very regular conical surface allowing efficient sealing.
• the surfaces Being a kneader tooth or a paving stone of a kneader cylinder, the surfaces must also be very regular, so as not to impede the flow of the fluid to be kneaded.
• the object of the present invention is therefore to produce parts whose abrasion-resistant coating is obtained by infiltration of alloy into a stack of tungsten carbide grains, these parts having, after production, markedly improved qualities of mechanical resistance to impact resistance. , avoiding separation between the substrate and its abrasion-resistant layer.
• such parts with abrasion-resistant coating can be obtained at low cost, in particular when the parts are large dimensions, lowering costs being obtained in particular by reducing the risk of waste.
• Another advantage of the invention is that it becomes possible to produce relays or abrasion-resistant coatings on substrates which are themselves liable to not withstand temperatures as high as that necessary for melting the alloy or binder metal during infiltration. It is thus possible to design a part made of composite material in which the substrate can be non-metallic, associated with a layer of abrasion-resistant material based on infiltrated tungsten carbide grains.
• the present invention provides a new process for producing a composite part with an abrasion-resistant coating, the part comprising at least one substrate covered with a layer of anti-abrasion material based on carbide grains.
• tungsten the method comprising the following steps: a) providing a substrate whose shape and surface condition are suitable for receiving by bonding coating elements made of abrasion-resistant material based on tungsten carbide grains, b) producing, by infiltration of a binder alloy into a stack of tungsten carbide grains, one or more coating elements made of abrasion-resistant material, comprising an internal face shaped to adapt to the surface of the substrate, and comprising an external face shaped to constitute the abrasion-resistant face of the composite part to be produced, c) joining the covering element or elements in anti-material material by bonding abrasion on the substrate, by applying said coating elements on the substrate with the interposition of an appropriate layer of adhesive.
• the substrate can be made of steel.
• the glue used for bonding can be an epoxy glue.
• the epoxy adhesive is of a single-component or poly-component type which can be polymerized under heat.
• the bonding step then comprises a step of heating to an appropriate temperature for the duration of polymerization of the adhesive.
• an alloy infiltration technique is used in a stack of tungsten carbide grains.
• the mold used is advantageously a mold for molding walls in foundry sand bound by resins. A difficulty is then encountered because the mold comprises walls whose surface is relatively large relative to the volume of the abrasion-resistant layer to be produced, since this layer generally does not have to have a very large thickness relative to its surface.
• the difficulty then appears by the fact that the resin used to bind the sand of the mold tends to be consumed during infiltration, and impairs the production of a good quality abrasion-resistant layer.
• the amount of resin will be less than 6% by weight of the amount of foundry sand.
• FIG. 1 shows atically dried in perspective a mold according to the invention for producing a coating member in abrasion-resistant material in the form of a cylindrical sector intended to cover a cylindrical substrate;
• FIGs 2 to 5 schematically illustrate the different steps of the process for producing a coating element in antiabra ⁇ sion material in a mold of Figure 1 shown in section;
• FIG. 6 shows the abrasion-resistant coating element thus obtained
• FIG. 7 and 8 illustrate the steps of forming the substrate intended to receive the abrasion-resistant coating elements
• FIG. 9 illustrates the step of assembling the abrasion-resistant coating elements on the substrate of Figure .8;
• FIG. 10 is a longitudinal section along the axis I-I of Figure 9;
• FIG. 11 illustrates the stage of production by infiltration of a conical abrasion-resistant coating element, in a mold shown in chopped off ;
• - Figure 12 illustrates the step of assembling the conical element of Figure 11 on a substrate which is itself conical, for producing a valve needle for a hydroelectric plant
• - Figure 13 illustrates, in longitudinal section, the structure of a valve needle according to the present invention
• FIGS. 10 and 13 to 14 illustrate the internal structure of the composite parts with abrasion-resistant coating obtained by a method according to the present invention.
• these parts comprise a substrate 1 covered at least in part by a layer of antiabra ⁇ ion material 2 which is secured to it by an intermediate layer 3 of glue.
• Smelter mixers include a cylindrical tubular enclosure, several meters long, with a diameter of around 60 centimeters, intended to contain a carbon paste to be kneaded by kneader teeth. Some teeth are mounted fixed on the wall of the enclosure and protrude towards the inside of the enclosure, other teeth are mounted on a rotor rotating axially in the enclosure.
• the mixer teeth are for example as shown in longitudinal section in FIGS. 14 and 15.
• FIGS. 1 to 6 one of the coating elements made of abrasion-resistant material which will be used to cover the internal surface of the cylindrical enclosure is produced by infiltration of a binder alloy in a stack of tungsten carbide grains of mixer.
• a hollow mold 4 is prepared, comprising an interior recess 5 delimited by molding walls having the shape of the surface element made of abrasion-resistant material to be produced. This mold is shown empty in section in FIG. 2.
• FIG. 3 we introduce into the recess 5 of the mold 4 particles 6 of hard material such as molten tungsten carbide, vibrating the assembly, so that the surface particles come to bear against the mold walls as much as possible and are joined to each other.
• a sufficient quantity of an appropriate alloy 7 is prepared in suitable form, to ensure a subsequent distribution of the alloy during its subsequent melting phase.
• the alloy 7 is a brazing alloy capable of wetting the particles of hard material and of melting at a temperature below the melting temperature of the particles of hard material 6 and of the mold 4.
• FIG. 5 the assembly is heated of the mold 4 and its content up to a temperature above the melting temperature of the alloy 7 and below the melting temperature of the hard material particles 6 and of the mold 4.
• This temperature is maintained for a sufficient time to ensuring the infiltration of the molten alloy 7 into the space filled with particles of hard material 6. It is then allowed to cool, and it is removed from the mold, in order to obtain the element 8 of coating in abrasion-resistant material shown in FIG. 6.
• FIGS. 7 and 8 the substrate intended to receive the coating elements made of abrasion-resistant material is prepared.
• FIG. 7 we start from a rectangular sheet 9.
• this rectangular sheet 9 is bent to give it a semi-cylindrical shape of appropriate diameter so that, after affixing of the elements of coating in antiabra ⁇ ion material, the internal diameter of the assembly is in accordance with the diameter of the mixer tube to be produced.
• the assembly and the attachment of the abrasion-resistant coating elements such as the element 8 are carried out on the substrate 1 such as the curved sheet metal. This attachment is effected by gluing, by applying the said abrasion-resistant coating elements 8 on the substrate 1 of curved sheet 9 with the interposition of an appropriate layer of adhesive.
• FIG. 10 is a longitudinal section along the axis I-I in FIG. 9, the assembly thus obtained, showing the abrasion-resistant layer 2, the substrate 1 or sheet 9 and the intermediate layer of glue 3.
• the adhesive 3 used is an epoxy adhesive, preferably of a single-component or poly-component type which can be polymerized hot.
• the assembly and bonding step shown on FIG. 9 comprises a step of heating to an appropriate temperature during the polymerization time of the glue 3.
• the mechanical resistance thus obtained from all of the abrasion-resistant elements bonded to the sheet 9 is sufficient so that the abrasion-resistant surface can be subsequently equalized during a subsequent machining step.
• the mold 4 used can be made of different materials.
• a graphite mold 4 previously machined to form the recess 5.
• a more advantageous solution consists in using a mold 4 comprising molding walls made of foundry sand bound by resins.
• the hollow 5 is then produced by immersing a model in the mold 4 before setting the resin, and removing the model after setting the resin, according to a traditional technique in molding for the casting of metals.
• the abrasion-resistant coating element 8 to be formed has a very large surface area in relation to its volume. This is due to the fact that the covering element is generally flat.
• the problem that can occur is that, during infiltration, the combustion of the resin binding the sand of the mold 4 produces gas emissions which tend to seep into the recess 5 filled with hard abrasion-resistant particles 6. These gas evolution can form deposits on the particles, and, if these deposits are in excess, they can harm the wetting of the particles by the binder alloy 7 during infiltration. This then results in a poor quality of mechanical strength of the abrasion-resistant element 8 thus produced.
• the quantity of resin present in the mold 4 is adjusted to be just sufficient to maintain the foundry sand until infiltration. In practice, the quantity of resin can be chosen less than 6 ° L in weight of the amount of mold foundry sand 4.
• a composite part shown in Figure 9, comprising a sheet metal substrate 1 9 of semi-cylindrical steel shape, with, on the inner surface of the half-cylinder , a layer of polymerized glue adhering to the half-cylinder and, adhering to the layer of polymerized glue and surmounting it, a paving of abrasion-resistant plates or covering elements 8 in the form of a cylinder sector with generally rectangular outline, the paving according to the curvature of the inner surface of the half-cylinder, the assembly forming a shielding plate for an aluminum mixer.
• the composite part obtained by the method of the invention comprises a steel substrate 1 having a generally convex shape.
• a layer of polymerized adhesive 3 On the exterior surface of the substrate, there is a layer of polymerized adhesive 3.
• a cap 2 Overlying said layer of glue 3, there is a cap 2 made of abrasion-resistant material.
• Figures 11 to 13 relate to the production of a needle valve needle used in hydroelectric plants.
• a needle is conical in shape, and comprises a conical substrate 1 of steel whose conical outer surface is covered with a conical cap 2 forming an element made of abrasion-resistant material.
• the substrate 1 and the cap 2 are produced separately.
• the cap 2 is itself produced by infiltration, as shown diagrammatically in FIG. 11, in a mold 4 comprising a removable core 40, the mold 4 forming the outer surface of the cap, the core 40 forming the inner surface of the conical cap.
• the cap 2 is adapted on the substrate 1. as shown in FIG. 12, with the interposition of a layer of glue, and the needle is obtained as shown in section in FIG. 13, presenting the cap 2 , the substrate 1 and the intermediate layer of adhesive 3.
• Figures 14 and 15 relate to the. production of an aluminum mixer knuckle.
• the part must advantageously have the shape shown in the figures. This part is formed according to a process similar to that described in relation to the previous figures, by separately producing the substrate 1 and the cap 2, the cap 2 being obtained by infiltration in a mold.
• the assembly of the substrate and the cap by gluing allows the intermediate adhesive 3 to act as a damper between the substrate 1 and the abrasion-resistant element 2. It increases considerably the apparent mechanical resistance of the abrasion-resistant coating thus produced, so that subsequent re-machining of its surface is made possible.
• the part has a significantly improved impact resistance compared to production techniques by overmolding infiltration.
• this technique according to the present invention avoids heating the substrate 1, so that one does not alter its external appearance.
• the heating of the substrate 1, when it is made of steel causes an alteration of its surface and requires re-machining.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Other Surface Treatments For Metallic Materials (AREA)
• Polishing Bodies And Polishing Tools (AREA)
• Mold Materials And Core Materials (AREA)
• Physical Vapour Deposition (AREA)
• Laminated Bodies (AREA)

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• 1991
  • 1991-09-16 FR FR9111578A patent/FR2681271A1/fr active Pending
• 1992
  • 1992-09-15 EP EP92920632A patent/EP0605585B1/de not_active Expired - Lifetime
  • 1992-09-15 CA CA002118603A patent/CA2118603A1/fr not_active Abandoned
  • 1992-09-15 AU AU26523/92A patent/AU662171B2/en not_active Expired - Fee Related
  • 1992-09-15 AT AT92920632T patent/ATE126547T1/de not_active IP Right Cessation
  • 1992-09-15 DE DE69204168T patent/DE69204168D1/de not_active Expired - Lifetime
  • 1992-09-15 WO PCT/FR1992/000865 patent/WO1993006255A1/fr active IP Right Grant

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