Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22C—FOUNDRY MOULDING
  • B22C9/00—Moulds or cores; Moulding processes
  • B22C9/06—Permanent moulds for shaped castings
  • B22C9/061—Materials which make up the mould

Definitions

• the present invention relates to a mold for the casting of a liquid metal, of the type comprising a shaped surface corresponding to the surface of the product to be produced by casting and intended to come into contact with liquid metal. It applies in particular to installations for manufacturing pipes by casting. Molds are known for the production of cast iron pipes by casting. These molds have the general shape of a hollow cylinder around an axis of rotation and include an end corresponding to the plain end of the pipe as well as an end corresponding to the end-fitting of the pipe. The interior surface of the mold forms the exterior surface of the manufactured pipe. When making pipes, the mold is rotated about its axis, and a liquid metal is poured onto the interior surface of the mold. The metal is successively cast from the nesting end end to the plain end end.
• Known molds are made of low chromium alloy steel in order to withstand the temperature of the liquid steel. Due to the high temperature of the liquid metal and the temperature variation of the mold during the successive casting of several pipes, cracks appear on the interior surface of the mold. When pouring liquid metal enters these cracks. The metal in the cracks prevents the extraction of the pipe from the mold and leads to scratches on the outside of the mold. When the cracks exceed a predetermined size, the mold must be repaired by machining the interior surface or by filling cracks by welding. However, these operations modify the interior surface so that the pipes produced after repair may no longer meet the required tolerances. The lifespan of known molds is therefore limited.
• Known steel molds have another drawback. When the first pipes are cast, the steel mold is plastically deformed significantly. Consequently, the mold is manufactured with dimensions which take account of this initial deformation. In order to bring the mold to its desired dimensions, several pipes, for example six, are poured.
• the object of the present invention is to provide a mold for the casting of liquid metal which has a long service life while allowing the casting of parts with low tolerances.
• the invention relates to a mold of the aforementioned type, characterized in that it comprises a heat removal portion made of a material having a thermal conductivity greater than 150 W / mK.
• the invention comprises one or more of the following characteristics: - the material has a thermal conductivity greater than 300 W / mK; - the material has a thermal conductivity greater than 325 W / mK; the heat removal portion is of a copper-based alloy, in particular comprising more than 50% by weight of copper; the copper-based alloy comprises chromium, in particular between 0.25% and 2% by weight; - The alloy comprises zirconium, in particular between 0.05% and 0.25% by weight; - The heat removal portion forms at least part of an outer surface of the mold; - The heat removal portion forms at least part of the form surface; the heat removal portion extends continuously between the form surface and the exterior surface; - The mold comprises a coating forming at least a part of the form surface and extending from the form surface to the heat removal portion; the coating and the heat removal portion have coefficients of thermal expansion such that the thermal expansion of the coating is greater than the thermal expansion of the heat removal portion under the effect of the cast metal; - The coating is
• the invention further relates to a method of manufacturing an object by casting, of the type comprising the step of casting liquid metal into a mold, characterized in that the mold is a mold as defined above.
• the process according to the invention may include the following characteristics: - the metal is a cast iron, in particular gray cast iron or spheroidal graphite cast iron; and - the method is further characterized by a step of annealing the object produced by casting.
• FIG. 1 is a schematic view of a pipe manufacturing installation according to the invention
• Figure 2 is a detail view of the installation of Figure 1, showing the mold on a larger scale
• - Figure 3 is a partial sectional view of the mold according to the invention taken along line III-III of the Figure 2
• FIG. 4 represents a variant of the mold of FIG. 3.
• FIG. 1 is shown an installation for manufacturing cast iron pipes according to the invention, designated by the general reference 2.
• the installation 2 comprises a container 4, a pouring device 6, a pouring channel 8, a rotary mold
• the installation 2 is used to manufacture pipes 16.
• the container 4 is a crucible of refractory material containing liquid metal, for example cast iron.
• the pouring device 6 is a scale having a volume corresponding to the quantity of liquid metal necessary for a pipe 16. The scale can be tilted between a position for receiving liquid metal from the container and a position for pouring the liquid metal into the pouring channel 8.
• the pouring channel 8 is a channel which leads from the pouring device 6 to the mold 10. It comprises an inlet 20 located near the device 6 and an outlet 22 s extending into the mold 10. The channel 8 is inclined relative to the horizontal so that the outlet 22 is located lower than the inlet 20, thus allowing the liquid iron to flow by gravity.
• the rotary mold 10, also called “shell”, has a shape with symmetry of revolution, in the present example generally cylindrical, of axis XX, inclined relative to the horizontal so that it is parallel to the channel 8
• the mold 10 has an inner surface 24 of shape which is the negative surface of the pipe 16, as well as a cylindrical outer surface 26 (see Figure 2).
• the surface 26 does not come into contact with the liquid metal during casting.
• the mold 10 comprises a plain end end 28, turned towards the inlet 20, and a socket end end 30, which is turned away from the inlet 20.
• the plain end end 28 forms the plain end of the pipe 16, while the socket end 30 forms the socket end of the pipe 16.
• the mold 10 can be rotated about the axis XX by a drive device not shown. Furthermore, the mold 10 can be driven in translation along the axis XX between a position for the start of casting, in which the outlet 22 is opposite the end with socket end 30, and a position for the end of casting. , in which the outlet 22 is opposite the plain end 28.
• the cooling device 12 is a sprinkler which is adapted to spray coolant, for example water, on the external surface 26 of the mold 10.
• this device 12 can be constituted by a system of water circulation in known manner.
• the extraction device 14 is suitable for axially extracting the poured pipe 16 from the mold 10.
• the devices 6, 12 and 14, the container 4 as well as the pouring channel 8 are known per se and are not described in more detail.
• the mold 10 according to the invention is entirely in
• CuCrZr which is a copper-based alloy.
• the alloy comprises more than 50% by weight of copper, preferably more than 60% by weight of copper, and in particular more than 75% by weight of copper.
• it is made of an alloy of copper, chromium and zirconium, in particular according to standard DIN 17666.
• a particularly suitable alloy comprises 1% by weight of chromium and 0.15% by weight of zirconium, the rest being unavoidable copper and impurities.
• This alloy has an average thermal conductivity at 220 ° C of 340 W / mK.
• the alloy can comprise between 0.25% and 2% by weight of chromium, and preferably between 0.5% and 1.5% by weight.
• the alloy can comprise between 0.05% and 0.25% by weight of zirconium, and preferably between 0.10% and 0.20% by weight.
• at least part of the material of the mold 10 has a thermal conductivity greater than 150 W / mK, in particular greater than 300 W / mK, and in particular greater than 325 W / mK.
• the liquid pig iron is poured from the device 6 into the channel 8, flows along the latter and is poured into the mold 10 at the plug end end 30. Successively, the mold 10 is brought to its position end of casting.
• the liquid iron found in the mold is pressed against the surface 24 by centrifugation, solidifies and forms the pipe 16. Thanks to the high thermal conductivity of the material of the mold 10, the temperature gradient between the inner surface 24 and the surface exterior 26 is weak. In other words, the heat provided by the liquid cast iron is quickly dissipated from the surface 24 towards the surface 26. Consequently, there is only a little thermal stress in the mold 10, which reduces or avoids the appearance of cracks. The mold 10 therefore has a long service life.
• the internal surface 24 reaches a temperature of 150 ° C.
• the external surface 26 reaches a temperature of 100 ° C.
• the temperature gradient is therefore 50 °.
• State-of-the-art steel molds lead, under similar conditions, to a temperature gradient of approximately 580 ° C.
• the heat is removed from the interior surface 24 quickly enough so that the latter does not reach the melting temperature (approximately 1083 ° C) of the mold material.
• the thermal conductivity of the material of the mold is chosen to be high enough to avoid melting of the mold at the level of the surface 24.
• the cast iron solidifies rapidly in the mold, with a solidification speed of between 1 , 20mm / s and 0.80 mm / s. Due to the rapid solidification, the carbon contained in the cast iron precipitates in the form of Fe 3 C (iron carbide) in an area in contact with the surface 24, while in an area distant from the surface 24, the carbon is found mainly in the form of graphite. Rapid solidification therefore leads to a large gradient of iron carbide - graphite in the pipe 16. During annealing, which transforms the iron carbide into graphite, the outside surface of the pipe 16 is heated faster than the inside surface of the pipe. this.
• the pipe 16 can be annealed at a low temperature or for a short time.
• the mold 10 according to the invention is therefore particularly suitable for the casting of objects in gray cast iron or in spheroidal graphite cast iron.
• the mold 10 quickly reaches its initial temperature.
• the mold 10 according to the invention also leads to small local deformations of the external surface of the pipe thanks to the rapid solidification.
• the pipe therefore has a better appearance.
• the plastic deformation of the mold 10 according to the invention is low. Even the first pipes produced thus meet the required dimensions and can be used. Thus, the installation has a significant yield.
• the mold 10 is a composite mold. It comprises an outer heat dissipation layer 40 which forms the outer surface 26 and an inner protective layer 42 which forms the inner surface 24 of form.
• the layer 40 is made of the same material as the mold 10 described above.
• the layer 42 is made of a material which has a hardness greater than the hardness of the layer 40. It is for example made of chromium or nickel, or an alloy based on these metals.
• the layer 42 protects the layer 40 against scratches generated during the extraction of the pipe 16.
• the coefficients of thermal expansion of the materials of the layers 40 and 42 are chosen so that the thermal expansion, due to heating.
• the inner layer 42 is greater than the expansion of the outer layer 40.
• the inner layer 42 is pressed against the outer layer 40, and does not come off from it.
• the mold which serves to dissipate the heat of the cast iron from the form surface is made of a material having a high thermal conductivity such as the copper-based alloy.
• the alloy of the mold 10 or of the heat removal portion is based on copper comprising small amounts of tellurium or small amounts of silver and phosphorus.
• the mold 10 comprises an inner thermal evacuation layer with high thermal conductivity which forms at least part of the inner surface 24 and an outer layer in a different material, such as chromium or nickel or chromium and nickel to increase the hardness or else chromium and zinc to avoid the formation of scale.
• a different material such as chromium or nickel or chromium and nickel to increase the hardness or else chromium and zinc to avoid the formation of scale.

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• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Molds, Cores, And Manufacturing Methods Thereof (AREA)
• Mold Materials And Core Materials (AREA)
• Heat Treatment Of Articles (AREA)
• Moulds For Moulding Plastics Or The Like (AREA)

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• 2004
  • 2004-04-01 FR FR0403444A patent/FR2868346B1/fr not_active Expired - Fee Related
• 2005
  • 2005-03-30 CN CN2005800102269A patent/CN101014433B/zh not_active Expired - Fee Related
  • 2005-03-30 EP EP05746797A patent/EP1732718A2/fr not_active Withdrawn
  • 2005-03-30 WO PCT/FR2005/000777 patent/WO2005097376A2/fr not_active Application Discontinuation
  • 2005-03-30 BR BRPI0508751-1A patent/BRPI0508751B1/pt not_active IP Right Cessation

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