FR2631862A1 - COOLED PISTON TRANSFER DEVICE, METAL FUSION COMPOSITION ON HIGH PRESSURE VERTICAL MOLDING PRESS - Google Patents

Abstract

The invention relates to a device for transferring a molten metal composition to a vertical molding press. This device consists of an upper module in which a mold 7 can be placed, and of a lower module comprising a feed device and a cooled piston 4 moving vertically to ensure the delivery of the metal in the mold. The piston 4 comprises a privileged cooling zone 18 located at the periphery of its front wall 16, this piston being able to slide with a predetermined clearance inside the supply device containing the metal to be forced.

Description

263 1862

  Cooled piston transfer device, of a molten metal composition on a high pressure die press

  The invention relates to a transfer device under strong pressure.

  of a molten metal composition, this system having

  a piston provided with a cooling system.

  The known pressure casting apparatus have for the most part a molten metal injection system arranged so

  to vertically inject the molten metal into molds.

  They generally consist of two modules: an upper module at which the mold and the demolding device can be installed; - A lower module whose main elements are the injection cylinder, the injection piston and the feed device. In the present text, the term "feeding device" means

  device at which the melt composition is introduced

pick.

  The main difficulty of the molding method under heavy pressure

  This is to prevent the molten metal from cooling too much during its transfer into the mold. Indeed the cooled metal increases its viscosity, which seriously affects the maintenance of pressure during the pressing operation and

  corollary to the quality of molded parts.

  It is known from the state of the art, many devices of

die casting.

  The most sophisticated ones are equipped with feeding devices aimed at

  to reduce the transfer time by acting on the power supply mode.

  tation of the molten metal composition.

  The patent FR 2,446,145 relates to a vertical die casting machine in which the fusion is done directly within the machine through an electromagnetic coil. The metal is introduced while it is solid by a mechanical arm. The melting chamber is arranged coaxially under an injection cylinder to reduce the time between the melting of the metal and its

injection into the mold.

  EP 164 301 describes a molding apparatus for its part

  vertical pressure comprising two modules. The lower module

  The piston and the injection cylinder are rotatably mounted on an axle so that the melt composition can be poured directly into the injection cylinder and, by a simple angular movement, quickly returned to the injection cylinder.

  module in order to undergo the pressing operation within the

  laughter of the mold. The feeding device therefore comprises the

injection cylinder itself.

  These devices make it possible to reduce the time and the transfer distance of the molten metal but inevitably generate a risk of thermal shock at the point where the molten metal falls. The duration of

  the life of the parts on which the molten metal is poured (ie

  mainly say the piston and the walls of the injection chamber

  tion), is considerably reduced.

  To avoid this excessive heating of the piston and the walls of the injection chamber, various cooling devices of the

piston were developed.

  During the pressing operation, the piston drives back rapidly

  the metal in the mold to ensure a good filling

of it.

  As we have just explained, the introduction of molten material into the injection chamber has the effect of causing significant heating, on the one hand of the front wall of the injection piston serving as a base for the chamber of injection. injection, secondly

walls of the room.

  One of the other problems inherent in die-casting will therefore be to control the temperatures of the injection chamber and the

  piston during loading and during the pressing operation.

  The different expansions of the injection piston and the walls of the injection chamber, due to structural characteristics, cause the increase of the space existing between these two parts, space in which the liquid metal penetrates more or less during casting or during injection. This flow has the effect of considerably increasing the friction between these two parts and slowing the speed of the piston in the cylindrical bore of the injection chamber and necessarily exerting a detrimental influence on the quality of the castings and on the life of the equipment especially when the penetration of the metal leads to seizure tending to jam the two moving parts. 263 18i62 It is known in the state of the art various processes of cooling the injection piston to limit the

  differences in the expansion of the piston and the injection chamber.

  French Patent No. 2,416,754 describes a device for cooling the injection piston using a cooling water circuit inside the piston connected to a water distribution network and coupled to a water flow control system. European Patent EP 116 906 discloses an injection piston provided with a more elaborate internal cooling system consisting of a pipe delimited by the inner walls of the piston and by a mouthpiece provided with a feed tube of the

cooling liquid.

  These devices allow uniform cooling of the entire front wall of the piston. They have the main disadvantage of inducing excessive cooling of the front wall, which has the effect of causing partial solidification of the metal which comes into contact with it. This semi-solidified metal is transformed into crusts which disturb the pressing operation and cause a variation of the filling time of the mold.

  which affects the quality of the molded parts.

  The technical problem to be solved by the invention is complex. The transfer time of the molten metal must be fast to ensure a good filling of the mold and a good quality of the molded parts. However, the metal to be molded must not possess

  too high a temperature in order to avoid the problems of

  tion and metallurgy explained earlier that affect the life of the press and the metallurgical quality of the parts.

molded.

  It is therefore necessary to cool the metal but it is also necessary not to cool it too much, while ensuring a good transfer into the mold which implies that no seizure must

  occur between the piston and the injection chamber.

  The present invention relates to a device for transferring under pressure a molten metal composition provided with a piston to

  privileged peripheral cooling zone which makes it possible

  during the very short time of the transfer of the molten metal composition, to hold the autoconstruction of a seal while avoiding problems relating to the thermal expansion of the piston

  and galling on the walls of the injection chamber.

  The object of the invention is to provide a seal between the piston and the wall of the injection chamber, so as to avoid

  any flow of molten material while excluding the possibility of

  excessive cooling of the front part of the pis-

  your tone, in order to overcome the disadvantages mentioned in the introduction.

  This molding apparatus can be used to mold materials

  with a melting point above 400 ° C, that is the

  metals and alloys. In this description, the denomination

  The term "metallic composition" should be understood to include metals and alloys, especially metal matrix composite alloys. The working pressures generated by the

piston range from 200 to 800 bars.

  The molten metal composition transfer device according to the invention consists of an upper module, made according to a method known from the state of the art and in which the mold can be placed and a lower module comprising a

  feeding device and a piston.

  The piston has a preferred cooling zone located

  located on the periphery of its front wall, this sliding piston

  predetermined clearance within the feed device

  containing the metal composition to be reprocessed.

  More specifically, the front wall of this piston is provided with a peripheral chamfer forming with the front wall an acute angle less than 45 'and preferably between 25 and' and delimiting with the wall of the injection chamber a frustoconical cavity. The piston is also provided with an internal cooling circuit comprising a peripheral groove dug in the front wall of the piston, this groove making it possible to transform the peripheral chamfer mentioned above into a zone

privileged cooling.

  Another feature of the invention lies in the fact that the front wall of the piston has a thickness which is at least twice as great in its central part as in its part.

  peripheral. The central part is thus much less

die than the peripheral part.

  According to a preferred embodiment of the invention the front wall of the piston is coated with a heat shield. This shield consists of a layer of a material having, on the one hand, a

  sufficiently low coefficient of thermal conductivity

  that is to say less than that of the piston head, and secondly a hardness greater than that of the piston head. The materials preferably used are carbides and nitrides such as chromium carbide or tungsten carbide, of the type marketed by Union Carbide under the UCAR trademark.

  The piston ring is also wholly or partly

  fitted with thermal protection to improve the sliding between the piston and the wall of the chamber and also having an anti-wear role. According to another preferred aspect of the invention, the zone of

  cooling is in connection with a cooling circuit

  In a first stage, corresponding to the period preceding the introduction of the melt-molding material, the flow rate of the coolant is low so as not to excessively cool the piston, while avoiding the risks of spraying; - in a second time during which the molten casting material is introduced, the flow is strong to ensure a good

  cooling of the privileged peripheral zone of the piston.

  This increase in the flow rate accelerates the formation of the tight seal in the frustoconical cavity, while avoiding the

  coolant to go into the vapor phase.

  The molten metal supply device may be any system described in the prior art, such as the device described in patent EP 164 301. In this patent the molten metal is introduced directly into the injection cylinder. However,

  according to a preferred variant which makes it possible to accelerate

  According to the invention, this feed system consists of a bottomless container which can slide horizontally and in a sealed manner on a heating floor of a

  loading position to a molding position and vice versa.

  versa. When the container is in the molding position, it constitutes

  kills the upper part of the injection chamber.

  The invention is hereinafter more specifically described with reference to the

  attached drawings as a non-limiting

  tative: Figure 1 shows, in frontal section, the lower module of

26'31 62

  the molding apparatus according to the invention equipped with the feeding system

  preferential treatment; Figure 2 shows a sectional view of the piston of Figure 1; Figure 3 shows an end view of the piston head of Figure 1; Figure 4 shows a side view of the head of a piston

  constructed according to a preferred variant.

  The die casting apparatus described below is made of 5% chromium alloy steel, commonly used in the treated state.

in the making of mussels.

  According to Figure 1, the upper module made according to a known method is not shown. Only the mold 7 is here figured in

fine mixed lines.

  The press body 9 is constituted, on the one hand, of a frame 1 sur-

  mounted with an asbestos seal 34 and equipped with a heating floor 2 and in which is arranged along a vertical axis an injection cylinder 3 and secondly, a bottomless container 5 slidable on the floor 2 in a horizontal motion so as to

  to be placed coaxially with the injection cylinder 3.

  The bottomless container is shown in the molding position, while the loading position is shown in outline.

mixed purposes.

  The piston 4 slides vertically in the injection cylinder and

  is here represented in the low position.

  The bottomless container 5 delimits a cylindrical space which

  the upper part of the injection chamber 6, the lower part of this chamber being delimited by the injection cylinder 3. The internal diameter of the bottomless container 5 is the

  same as that of the injection cylinder 3.

  The walls of the bottomless container 5 are thermally insulated and anti-adhesion treated. This bottomless container 5 is further provided with

  an internal preheating system 8.

  The bottomless container slides by a horizontal movement to

  variable speed on the heating floor 2 also thermally insulated

  and treated anti-adhesion. The sole 2 is provided with a means

heating 33.

  According to this preferred structure of the supply system, the hearth 2 is only heated on a part, approximately corresponding to the zone in contact with the container when the latter is in the loading position. This position is represented in lines

mixed purposes.

  The thermal insulation and anti-adhesion treatment of the walls of the bottomless container 5 and the surface of the heating floor 2 are made by adding a layer of rectified tungsten carbide, followed by a graphite smoothing. The carbides and nitrides preferentially employed are chromium carbide,

  tungsten carbide, bromine nitride and tungsten nitride

  Stene. The sealing of the container 5 without sliding bottom on the heating floor 2 is obtained by metal-metal contact of the isolated areas

  on the floor 2 and on the walls of the container 5.

  The injection cylinder 3 has a position coaxial with the container when the latter is in the molding position. The inner surface of this cylinder is also coated with a thermal protection and treated anti-adhesion in the same way as the heating sole 3 and

  the walls of the bottomless container 5.

  The inside of the press corps, ie the injection chamber

  tion 6 delimited on the one hand by the injection cylinder 3 on the other hand by the inner walls of the container 5 is entirely graphited.

  The graphiting operation of the chamber is regularly performed.

  killed by a graphite floss. The surface of the sole is also

  permanently graphited thanks to a graphite tank.

  According to FIG. 2, the injection piston 4 according to the invention is

  consisting of a rod 10, a body 11 and a head 12.

  The piston rod 10 comprises in its end a body 13 provided with a shoulder 14. The body 11 is screwed into the body 13

  from the piston to an abutment position defined by

  14. The seal between the piston body 11 and the body of the

  the rod 13 is made by means of an O-ring 15.

  At the upper end of the body 11 of the piston is fixed the head 12 of the piston. The piston head has on the outer face of its front wall 16 a peripheral chamfer 17 forming a

  acute angle of 25 'with the normal to this face. The boundary wall

  tale 16 is hollowed on its inner face with a peripheral groove

  19. The chamfer 17 and the groove 19 define an area

  preferred cooling device 18.

  The rod 10 of the piston comprises a coaxial channel 20 in which is

  disposed a central tube 21 of annular section for the food

  cooling liquid. The diameter of the tube 21 is sufficiently smaller than the diameter of the coaxial channel of the piston so as to provide an annular slot 28 between the inner wall

  of the piston rod and the outer wall of the tube 21.

  This tube 21 is provided at its end with a lateral opening 22

  of diameter equal to the diameter of the inner section of the tube 21.

  An elongate 23 bears against the inner central part of the piston head 12 and has, on the one hand, an opening 24 of the same diameter as the opening 22 and, on the other hand, a spiral rib with a trapezoidal section so that the openings 22 and 24 are facing each other. All internal parts of the piston is held in place by means of the body of the rod 13 which is screwed

in the piston body 11.

  The walls of the body 11 of the piston and the elongate 23 define a helicoidal chamber 26. This chamber is extended by another annular chamber 27 defined by the peripheral groove 19 formed in the inner wall of the piston head and is also communication with the annular slot 28 defined by the walls of

  the rod 10 of the piston and the tube 21.

  According to FIG. 3, the chamfer 17 and the plate 29 form the

  front wall 16 of the head 12 of the piston. The plate 29 is coated

  kills a heat shield 32 over its entire surface. The chamfer 17 has hollow surfaces 30 covered with a thermal protection of the same nature as the coating of the plate and

  ensure continuity with the coating of the shell.

  The number of staves that has the chamfer 17 is four

  but this number may vary from four to eight.

  Referring to Figure 4, the head 12 of the piston constructed according to a preferred embodiment of the invention comprises a shell 31 which is provided with a partial thermal protection arranged in spirals with large pitch and having continuity

  partial with the thermal coating 32 of the plate.

  Description of the operating mode of the molding apparatus

  under pressure according to the invention is carried out with reference to

the set of figures.

  Before starting the molding operation, a molding composition is, for example, waiting in a so-called holding oven that allows it to be kept at a given temperature, generally

around 650'C.

  The bottomless container 5 is placed in the loading position (in

  fine lines in Figure 1). An automatic ladle allows the

  container in the waiting position by a predetermined volume

  completed the melt composition.

  The ladle allows the removal of the volume of metal in the container, possibly through a gas shield to avoid the

formation of oxides.

  The filled container 5 is driven by a horizontal sliding movement at variable speed on the heating floor 2. The molten composition is thus translated above the injection cylinder 3 in which the piston 4 is placed in the low position. The low position of the piston is such that the plate 29 thereof is in the same plane as the upper surface of the sole 2. The front wall 16 of the piston 4, that is to say the plate

  29 and the bevel 17 thus form the base of the injection chamber

tion 6.

  After having started the liquid supply system of

  cooling, it is brought under pressure by the tube 21.

  It then invades the annular chamber 27 through the connection formed by the openings 22 and 24. The small thickness of the wall of the piston head at the chamfer 17 creates a preferred cooling zone 18 on the periphery of the head of the piston. The coolant then circulates in the helical chamber 26 and then in the slot

  annular 28 which communicates with a pump not shown. -

  During the horizontal sliding of the bottomless container 5 on the heating floor 2 to the molding position, as soon as the opening of the container 5 reaches the edge of the injection cylinder 3, there is

  produces a very fast natural distribution of a predefined volume

  finished melt composition in the truncated conical cavity

  The contacting of the metal with the cooled zone then causes the local crystallization of the metal to be molded and the joint thus formed persists, for the duration of the process, by the chamfer 17 and the lower surface of the injection chamber 6. vertical transfer. During the stroke of the piston the frustoconical ring-shaped seal thus produced seals and resists pressure and

  therefore allows to maintain this pressure during solidification.

  Any unwanted flow is thus avoided at the level of the game between

  the piston and the feed system containing the refolding metal

  ler, and any risk of seizure between the piston and the container

bottomless is thus discarded.

Claims (12)

claims   1. Device for transferring a molten metal composition   on a vertical molding press, consisting of a superior module   in which can be placed a mold (7), and a lower module comprising a feeder and a piston   cooled (4) moving vertically to ensure failure   metal in the mold (7), characterized in that the piston   (4) has a coolant zone.privileged (18) locally   located on the periphery of its front wall (16), this piston being able to slide with a predetermined clearance inside the device   feed containing the metal to be reprocessed.   2. Device for transferring a molten metal composition on a vertical molding press according to claim 1 characterized in that the front wall (16) of the piston (4) has on its outer face a peripheral chamfer (17) and on its inner face an annular peripheral groove (19) delimiting an area   preferred cooling (18).   3. Device for transferring a molten metal composition on a vertical molding press according to claim 2 characterized in that the peripheral chamfer (17) forms with the front wall (16) of the piston an acute angle less than 45 'and   preferably between 25 'and 35'.   4. Device for transferring a molten metal composition   on a vertical molding press according to one of the claims   cations 1 to 3 characterized in that the thickness of the front wall (16) of the piston has a thickness which is at least twice   more important in its central part than in its peri-   pheric. 5. Device for transferring a molten metal composition   on a vertical molding press according to one of the claims 263 1862   cations 1 to 4 characterized in that the central plate (29) of the piston is covered with a thermal protection (32) having on the one hand a coefficient of thermal conductivity lower than that of the piston head and on the other hand a hardness greater than that of the piston head. 6. Device for transferring a molten metal composition   on a vertical molding press according to one of the claims   cations 1 to 5 characterized that the shell (31) of the piston is totally or partially covered with a thermal protection (32), of the same nature as the thermal protection of the plate (29) of the piston.   7. Device for transferring a molten metal composition   on a vertical molding press according to one of the claims   cations 5 and 6 characterized in that the thermal coating of the plate (29) and the shell (31) consists of a layer of   chromium carbide or tungsten carbide.   8. Device for transferring a molten metal composition   on a vertical molding press according to one of the claims   1 to 7 characterized in that the preferred cooling zone (18) is in connection with an internal circuit of   cooling whose flow is flexible and controlled.   9. Device for transferring a molten metal composition   on a vertical molding press according to one of the claims -   1 to 8, characterized in that the feed device   consists of a bottomless container (5) sliding horizontally   without play on a heated floor (2).   10. Device for transferring a molten metal composition on a vertical molding press according to claim 9   characterized in that the heating means (33) of the heated hearth   fante is located below the zone in contact with the liquid metal   when the bottomless container (5) is in the loading position.   11. Device for transferring a molten metal composition   on a vertical molding press according to one of the claims   cations 1 to 10, characterized in that the heating sole (2) and the   walls of the injection chamber (6) are protected by   thermal energy having on the one hand a coefficient of   thermal stability lower than that of the piston head and   on the other hand a hardness greater than that of the piston head.   12. Device for transferring a molten metal composition on a vertical molding press according to claim 10 characterized in that the heating floor (2) and the walls of the bottomless container (5) are coated with a carbide layer. of chrome or tungsten carbide.