ES2423326T3 - Procedure for manufacturing pressure casting parts - Google Patents

Abstract

Procedure for manufacturing pressure casting parts from an aluminum alloy, in which the aluminum alloy passes through a machine with a housing (31) with a working space (34) enclosed by an inner housing envelope (32) and a tree with fins that rotates around a longitudinal axis (x) in the inner shell envelope (32) and moves with translation back and forth along the longitudinal axis (x), in which at one end of the shell ( 31) A fluid aluminum alloy is supplied to the workspace (34) and at the other end of the housing (31) it is removed from the workspace (34) as a semi-solid aluminum alloy with a predetermined percentage of solid, transferred to the interior of a filling chamber (12) of a pressure-decorated machine (10) and by means of a piston (20) is pushed into a casting mold, in which the percentage of solid aluminum alloy in space working (34) it is adjusted to the percentage of solid determined by means of cooling and precise heating of the work space (34), characterized in that the aluminum alloy is subjected to high shear forces in a mixing and kneading machine (30) with a helical shaft (36) interrupted in the perimeter direction forming individual kneading fins (38) with axial through openings (40) between kneading fins (38) and with kneading bolts (42) fixed in the inner housing wrap (32), which enter the space of work (34) and hook into axial pass openings (40).

Description

Procedure for manufacturing pressure casting parts

The invention relates to a process for manufacturing pressure casting parts from an aluminum alloy according to the preamble of claim 1.

Pressure casting parts made from aluminum alloys are increasingly used among others in the automobile industry due to the increasing weight required. For technical reasons of casting, for example in the case of knots for Space Frame structures (space mesh) with conventional pressure casting procedures, as a general rule, it cannot remain below a wall thickness of the casting piece of approximately 2 mm The filling of the die casting mold with semi-solid metal castings by means of the application of thixocasting or rheocasting leads to a better filling of the mold and as a consequence to a possible further reduction of the wall thickness of the casting piece to approximately 1 mm. However, as the wall thickness decreases, the diminished capacity to receive forces becomes increasingly a limiting factor. This disadvantage could be overcome in itself by adding nanoparticles to an aluminum alloy matrix. However, a suitable process for the economical manufacture of aluminum alloys reinforced with nanoscopic scale particles and their preparation to form semi-solid metal smelters for pressure casting is lacking.

In a process disclosed in US 2003/0201088 A1, a cylindrical tube in which a pressure rod is coaxially arranged is fed with a metal foundry in a fluid state. In this sense the outer diameter of the pressure rod is smaller than the inner diameter of the cylindrical tube, so that the fluid metal flows in the intermediate space between the cylindrical tube and the pressure rod. The pressure rod is provided for the realization of an axial movement back and forth and a rotation around its longitudinal axis. A valve that surrounds the pressure rod and can be moved by sliding on the inner wall of the cylindrical tube overcoming a friction resistance divides the cylindrical tube into an upper and a lower chamber. Depending on the direction of axial displacement of the pressure stem, the valve opens or closes and enables

or blocks the flow of metal between the upper and lower chamber. In the case of a forward movement of the pressure rod the valve remains closed and the metal in the lower chamber of the cylindrical tube is pushed through an exhaust opening into the filling chamber of a pressure casting machine. The temperature profile of the metal foundry in the cylindrical tube is controlled by means of heating elements so that a semi-solid cast with a certain percentage of solid material is adjusted. Flaps leave radially from the surface of the pressure rod. The fins serve on the one hand for the coaxial support of the pressure rod in the cylindrical tube, with the fins resting on the inner wall of the cylindrical tube. On the other hand, the fins, by rotating the pressure rod around its longitudinal axis, lead to a stirring of the metal smelting in order to distribute the temperature evenly in the metal.

The invention is based on the objective of achieving a process of the type mentioned at the beginning with which a semi-solid aluminum alloy casting can be prepared continuously and economically and further treated to form pressure casting parts. A further object of the invention is to achieve a process for the manufacture of pressure casting parts from an aluminum alloy reinforced with nanoparticles, with which a semi-solid aluminum alloy casting can be prepared continuously and economically the action of shear forces typical of the process with a high fine dispersion of nanoparticles and further treated to form pressure casting parts.

To the solution according to the invention of the first objective leads a process with the characteristics of claim 1. In this regard the high shear forces existing in the semi-solidified phase state in the kneading process cause a continuous crushing of dendrite branches which form, which leads to increased ductility of the pressure casting parts. The high compression forces also lead to a higher heat transmission, which finally allows a more precise adjustment of the percentage of solid in the aluminum alloy.

The solution of the second objective according to the invention leads to nanoparticles being mixed with the aluminum alloy in the mixing and kneading machine for the manufacture of pressure-casting parts with nanoparticles and by high shear forces they are finely dispersed in the aluminum alloy, in which at one end of the housing a fluid aluminum alloy and nanoparticles are supplied to the workspace and at the other end of the housing, the semi-solid aluminum alloy with a percentage of solid is extracted from the workspace predetermined and with nanoparticles dispersed finely in the aluminum alloy. In this regard, the high shear forces existing in the semi-solidified phase state in the kneading process cause, in addition to the crushing of dendrite branches that form and the greater ductility achieved with it, a fine dispersion of the nanoparticles that is necessary for its resistance increase action.

Conveniently the inner shell wrap is surrounded by an outer shell wrap forming an intermediate space preferably in the form of a hollow cylinder and for cooling and heating the work space, hot and / or hot gases are conducted through the intermediate space. Through the intermediate space, preferably air, preferably pressurized air, and for heating, hot gases, preferably combustion gases, are conducted for cooling.

The gases are conducted through the intermediate space preferably in countercurrent with respect to the direction of transport of the aluminum alloy.

The solid percentage of the aluminum alloy is preferably adjusted to 40 to 80%, in particular more than 50%.

In a preferred embodiment of the process according to the invention, the semi-solid aluminum alloy is extracted from the work space as a semi-solid metal bar. The semi-solid metal bar that comes out continuously is divided into semi-solid metal portions and the semi-solid metal portions are transferred into the filling chamber of the pressure casting machine.

The percentage by weight of the nanoparticles in the alloy is preferably between about 0.1 and 10%. Suitable inexpensive nanoparticles are preferably composed of pyrogenic silicic acid, such as Aerosil®. However, other nanoparticles, such as known carbon nanotubes (carbon nanotubes, CNT), as well as additional nanoscopic scale particles, for example manufactured according to the known Aerosil® process, from metal and semimetal oxides, can also be used. such as aluminum oxide (Al2O3), titanium dioxide (TiO2), zirconium oxide (ZrO2), antimony oxide (III), chromium oxide (III), iron oxide (III), germanium oxide (IV) ), vanadium oxide (V) or tungsten oxide (VI).

Advantages, features and additional details of the invention are deduced from the following description of preferred embodiments as well as by drawing, which only serves for explanation and should not be construed as limiting. The drawing schematically shows in

1 shows a longitudinal section through a pressure casting machine with a mixing and kneading machine attached;

Figure 2 a longitudinal section through a part of a mixing and kneading machine;

Figure 3 a cross section through the mixing and kneading machine of Figure 1;

Figure 4 characteristic elongation and shear flow fields in a product mass, triggered by a kneading fin that passes in front of a kneading bolt;

Figure 5 the continuous manufacture of semi-solid raw material for pressure casting with an arrangement according to Figure 1.

An installation shown in Figure 1 for pressure casting of pressure casting parts optionally reinforced with nanoparticles from an aluminum alloy has a pressure casting machine 10 and a mixing and kneading machine 30 placed before the casting machine. under pressure 10.

The pressure casting machine 10 reproduced only partially in the drawing is a common machine in the market for conventional pressure casting of aluminum alloys and has, among others, a filling chamber 12 connected with a fixed side 18 of a casting mold , with an opening 16 to receive the metal to be pushed by means of a piston 20 out of the filling chamber 12 and into a hollow mold space 14 of the casting mold.

The mixing and kneading machine 30 is shown in detail in Figures 2 and 3. The basic construction of such a mixing and kneading machine is known for example from document CH-A-278 575. The mixing and kneading machine 30 It has a housing 31 with a working space 34 enclosed by an inner housing envelope 32, in which a helical shaft 36 is arranged, which rotates around an longitudinal axis in the inner housing envelope 32 and moves with translation forward and backward on the longitudinal axis x. The helical shaft 36 is interrupted in the perimetral direction forming individual kneading fins 38. In this way axial through openings 40 originate between the individual kneading fins 38. From the inner side of the inner shell envelope 32 kneading bolts are introduced. 42 in the working space 34. The kneading bolts of the housing side 42 engage in the axial through openings 40 of the kneading fins 38 arranged on the helical or main shaft 36. An actuation shaft 44 arranged concentrically with respect to the Helical shaft 36 is driven from the front side outwardly from the inner housing envelope 32 and connected with a drive unit not shown in the drawing for performing a rotational movement of the helical shaft 36. In the drawing, a drawing is also not shown. device that acts together with the helical shaft 36 for carrying out the movement with translation ón of the helical tree 36.

The cylindrical inner shell wrap 32 of the mixing and kneading machine 30 delimiting the working space 34 is surrounded by a cylindrical outer shell wrap 46. The inner shell wrap 32 and the outer shell wrap 46 form a double wrap already in this respect they enclose an intermediate space 48 in the form of a hollow cylinder.

At the end of the housing 31 near the driving side of the helical shaft 36 a feed opening 50 is provided for the supply of a fluid aluminum alloy and optionally nanoparticles in the working space 34. Although only the drawing is shown a feed opening 50, for the aluminum alloy and for the nanoparticles, two separate feed openings may be provided. In principle, it is also possible to add the nanoparticles of the fluid aluminum alloy already before the metal is fed into the kneading and mixing machine 30. At the end of the inner casing shell 32 away from the driving side of the helical shaft 36 it is provided an exhaust opening 52 for the extraction of the semi-solid aluminum alloy with optionally dispersed nanoparticles therein.

Intake openings 54, 56 for the introduction of cold or hot gases into the intermediate space 48 are provided at the end of the housing 31 away from the driving side of the helical shaft 36. Correspondingly, in the end of the housing 31 near the driving side of the helical shaft 36, outlet openings 58, 60 are provided for the exit of the gases from the intermediate space 48. To guarantee a maximum through-gas flow and distributed uniformly over the perimeter of the Inner shell casing 32 from the intake openings 54, 56 to the outlet openings 58, 60 and thereby a uniform heat evacuation from the work space 34 or a uniform heat input to the work space 34, are openings of intake and exhaust 54, 56 or 58, 60 evenly distributed around the perimeter of the outer shell housing 46 according to Figure 3.

Figure 4 shows in a schematic representation characteristic elongation and shear flow fields in a mass of product P, as they appear in a mixing and kneading machine 30 configured according to the state of the art by a kneading fin 38 passing in front of it. of a kneading bolt 42. The direction of rotation of kneading fin 38 is schematically indicated by a curved arrow A, while the translational movement of kneading fin 38 is indicated by a double arrow B. By the movement of rotation of the kneading fin 38 its tip divides the mass of product P, as indicated by the arrows C, D. Between the kneading bolt 42 and the main surface 39 directed to the kneading bolt 42, of the kneading fin 38 and kneading fin 38 that passes in front of it there is an interstitium 41, the width of which varies by rotation and the translational movement of the helical shaft 36. In this interstitium 41, For a shear operation in the product mass P, which is indicated by the arrows E. Both in front and behind the kneading bolt 42 relaxes and redirects the mass of product P, as indicated by the rotation arrows F , G. As already detailed at the beginning, for each shear cycle, by means of the sinusoidal axial movement of the respective kneading fin 38 in a line a maximum approach of the kneading fin 38 and the kneading bolt 42 and with this means a maximum shear rate in the product mass P.

In the following, the operation mode of the installation for pressure casting of pressure castings optionally reinforced with nanoparticles from an aluminum alloy is explained in more detail by way of example.

An aluminum alloy foundry maintained slightly above the melting temperature of the alloy is supplied alone or together with nanoparticles in dosed form to the working space 34 through the feed opening 50. By crushing the alloy of semi-solidified aluminum with nanoparticles between kneading fins 38 and kneading bolts 42 high shear forces are applied that lead to crushing dendrite branches and cause fine dispersion of existing nanoparticles in the form of agglomerates. An efficient mixing, which homogenizes, is obtained from the superposition of the longitudinal and radial mixing effect. By regulating the gas flow of hot and cold gases through the intermediate space 48 between the inner shell wrap 32 and the outer shell wrap 46, the percentage of solid of the aluminum alloy in the working space 34 is adjusted. such that it is in the desired range during the extraction of the metal through the exhaust opening 52.

The adjustment of the desired solid percentage of the aluminum alloy is produced by measuring the change in the viscosity of the metal smelting in the kneading and mixing machine 30. The viscosity increases as the percentage of solid in the alloy increases. semi-solid aluminum can be detected, for example, by measuring the resistance to rotation in the drive shaft 44 of the helical shaft 36. By determining the resistance to rotation for defined percentages of solid, corresponding theoretical values can be established, to which they are regulated Actual values measured by controlling the through flow of hot and cold gases through the intermediate space 48 between the inner and outer shell wrap 32, 46.

The aluminum alloy having the desired solid percentage and optionally containing finely dispersed nanoparticles is provided through the feed opening 16 to the filling chamber 12 of the pressure casting machine 10 and is pushed from this periodically by means of the piston 20 in known manner outside the filling chamber 12 inside the hollow mold space 14 of the casting mold.

Next, Figure 5 describes in more detail by way of example the continuous manufacture of semi-solid raw material in the form of a rod for pressure casting of pressure casting pieces optionally reinforced with nanoparticles from an aluminum alloy. The operation mode explained above is preserved by means of figures 1 and 2.

5 The aluminum alloy having the desired solid percentage and optionally containing finely dispersed nanoparticles is pushed out continuously through the exhaust opening 52 in the form of a semi-solid metal bar 70. From the bar semi-solid metal 70, for example with a jointly operated blade, semisolid metal portions 72 are cut off. The semi-solid metal portions 72 correspond

10 usually in each case the amount of metal necessary for the manufacture of an individual pressure casting part and are transferred for each stroke individually into the filling chamber 12 of the pressure casting machine 10 and pushed from it periodically by means of the piston 20 in a known manner outside the filling chamber 12 inside the hollow mold space 14 of the casting mold.

15 Usually the semi-solid metal bar 70 leaves the mixing and kneading machine 30 in the direction of the longitudinal axis x of the helical shaft 36 in the horizontal direction, however, another exit direction, for example vertical, is also conceivable. The cross section of the metal bar 70 follows the cross section of the exhaust opening 52 and is usually circular. The semi-solid metal portions 72 can for example be grasped with tweezers and transferred into the filling chamber 12 of the pressure casting machine 10.

Claims (10)

one.

Procedure for the manufacture of pressure casting parts from an aluminum alloy, in which the aluminum alloy passes through a machine with a housing (31) with a working space (34) enclosed by an inner housing envelope ( 32) and a tree with fins that in the inner shell wrap (32) rotates around a longitudinal axis (x) and moves with translation back and forth on the longitudinal axis (x), where at one end a fluid aluminum alloy is supplied to the working space (34) from the housing (31) and at the other end of the housing (31) it is extracted from the working space (34) as a semi-solid aluminum alloy with a percentage of solid By default, it is transferred into a filling chamber (12) of a pressure casting machine (10) and by means of a piston (20) it is pushed into a casting mold, in which the percentage of solid of the aluminum alloy in the working space Garlic (34) adjusts to the predetermined solid percentage by cooling and precisely heating the work space (34), characterized in that the aluminum alloy is subjected to high shear forces in a mixing and kneading machine (30) with a helical shaft (36) interrupted in the perimeter direction forming individual kneading fins (38) with axial through openings (40) between the kneading fins (38) and with kneading bolts (42) fixed on the inner shell envelope (32), that enter the workspace (34) and engage in axial through openings (40).

2.

Method according to claim 1, characterized in that the inner shell wrap (32) is surrounded by an outer shell wrap (46) forming an intermediate space (48) preferably in the form of a hollow cylinder and for cooling and heating the work space (34) cold and / or hot gases are conducted through the intermediate space (48).

3.

Method according to claim 2, characterized in that through the intermediate space (48), air, preferably pressurized air, and for heating, hot gases, preferably combustion gases, are conducted for cooling.

Four.

Method according to claim 2 or 3, characterized in that the gases are conducted through the intermediate space (48) in countercurrent with respect to the direction of transport of the aluminum alloy.

5.

Method according to one of claims 1 to 4, characterized in that for adjusting a desired solid percentage, the viscosity of the aluminum alloy in the working space (34) is measured and adjusted to a predetermined value by cooling and precise heating. of the workspace (34).

6.

Method according to one of claims 1 to 5, characterized in that the percentage of solid of the aluminum alloy is adjusted to 40 to 80%, preferably more than 50%.

7.

Method according to one of claims 1 to 6, characterized in that the semi-solid aluminum alloy is extracted from the work space (34) as a semi-solid metal bar (70), the semi-solid metal bar

(70) is divided into semi-solid metal portions (72) and the semi-solid metal portions (72) are transferred into the filling chamber (12) of the pressure casting machine (10). 8. Method according to one of claims 1 to 7, characterized in that nanoparticles are mixed with the aluminum alloy in the mixing and kneading machine (30) for the manufacture of pressure-casting parts reinforced with nanoparticles and by high shear forces dispersed finely in the aluminum alloy, in which at one end of the housing (31) a fluid aluminum alloy and nanoparticles are supplied to the workspace (34) and at the other end of the housing (31) extract from the workspace (34) as a semi-solid aluminum alloy with a predetermined percentage of solid and with nanoparticles finely dispersed in the aluminum alloy.

9.

Method according to claim 8, characterized in that the volume percentage of the nanoparticles in the alloy amounts to 0.1 to 10%.

10.

Method according to claim 9, characterized in that as nanoparticles pyrogenic silicic acid, carbon nanotubes (carbon nanotubes, CNT) are used, as well as other nanoscopic scale particles from metal and semimetal oxides, such as aluminum oxide (Al2O3 ), titanium dioxide (TiO2), zirconium oxide (ZrO2), antimony oxide (III), chromium oxide (III), iron oxide (III), germanium oxide (IV), vanadium oxide (V) or tungsten oxide (VI).