EP0718059B1 - Oxide remover - Google Patents

Abstract

To produce shaped components from thixotropic metal bolts in horizontal die casting machines, the oxide skin round the metal bolt is wholly scraped clear before the thixotropic metal alloy is passed into the hollow zone (68) of the mould (70), and the oxide is collected in a container (40). In scraping, removal of oxide-free and homogenous thixotropic metal alloy is minimised by taking into account the asymmetrical mechanical and thermal characteristics of the thixotropic metal bolt in relation to its longitudinal axis. Also claimed is a horizontal die casting machine.

Description

The present invention relates to a method for producing molded parts from thixotropic Metal bolts in horizontal die casting machines, the inclusions of the thixotropic Oxide skin surrounding metal bolts in the alloy structure of the molding can be avoided. The invention further relates to one specifically for carrying out the method according to the invention designed die casting machine.

The process for the production of molded parts from thixotropic, i.e. partially solid / partially liquid, Metal bolts are called thixoforms. All bolts come as metal bolts from a metal that can be converted into a thixotropic state. In particular can the metal bolts made of aluminum, magnesium or zinc and the alloys of these metals consist.

The thixoforming of thixotropic metal alloys is known per se. With this procedure the thixotropic properties of partially liquid or partially solid metal alloys are used. In the following text, for the partially solid / partially liquid, i.e. thixotropic, state of Metal alloy also in this context is the equivalent expression of the semi-solid Condition used. The thixotropic behavior of a metal alloy means that a suitably prepared metal behaves unloaded like a solid, under However, shear stress reduces its viscosity to such an extent that it is similar to a Metal smelt behaves. This involves heating the alloy into the solidification interval between liquidus and solidus temperature required. The temperature should be set that, for example, a structure fraction of 20 to 80% by weight is melted, the However, the rest remains in solid form.

With thixoforming, partially solid / partially liquid metal is used in a modified die casting machine processed into molded parts. The die casting machines used for thixoforming differ from die casting machines for die casting metal melts by, for example, a longer casting chamber for receiving the thixotropic metal pin and a larger piston stroke required thereby, and for example a mechanically reinforced design of the thixotropic metal alloy leading parts of the die casting machine due to the higher pressure load on these parts during thixoforming.

Thixoforming is usually done with a horizontal die casting machine. At these machines have the casting chamber that receives the thixotropic metal bolt, horizontal and is at right angles to the parting plane of the mold, i.e. to the front surface of the Mold with the pouring opening, arranged. When thixoforming becomes a thixotropic Metal bolts placed in such a horizontal casting chamber of a die casting machine and by pressurizing with a casting piston at high speed and under high pressure in a steel, in particular hot work steel, existing Mold introduced, i.e. introduced into the mold cavity of the mold or shot, the thixotropic metal alloy solidifies in this.

That which forms during the solidification of the thixotropic metal alloy in the casting mold Cast structure essentially determines the properties of the molded parts. The microstructure is characterized by the phases, such as mixed crystal and eutectic phases, the Cast grain, such as globulites and dendrites, segregations as well as structural defects such as porosity (Gas pores, micro voids) and impurities such as oxides.

The metal bolts used for the thixoforming of partially solid alloys have a process-related nature fine grain on the - if during the pretreatment of the thixotropic Metal bolts, i.e. during the heating of the metal bolts and their transport into the Die casting machine, no coarsening occurs - again in the alloy structure of the Find molded parts. A fine grain generally improves the material properties, increases the homogeneity of the alloy structure and helps to avoid structural defects in the molded part. The thixoforming of partially solid alloys shows in comparison to the die casting of Metal melting also has other significant advantages. This includes significant energy savings as well as shorter production times, because firstly the thixotropic metal bolts in the Compared to the die casting of metal melts prior to thixoforming less high and therefore less long to heat up and secondly in the mold cooled faster, i.e. be returned to a solid state, resulting in a reduction contributes to the coarsening of the grain. The energy saving mainly results from that a large part of the heat of fusion as well as the total superheat, i.e. the the Metal alloy additionally supplied heat to achieve a temperature increase above the melting point to ensure the molten state of the metal alloy, and the energy for keeping the melt warm is eliminated. Another advantage is also the better dimensional accuracy due to lower shrinkage and the manufacturing to consider shaped parts close to the final dimensions, which reduces the machining steps and alloy material is saved. In addition, the processing temperature is around 100 ° C lower the change in temperature of the individual components of the Die casting machine smaller, which increases the tool life. The opposite the die casting of molten metal, lower processing temperature for thixoforming also allows the processing of alloys with a low iron content, since no alloying the tools happen by melting. In addition, thixoforming allows one better mold filling with fewer air pockets.

Cover bodies made of, for example, aluminum, magnesium or zinc, or their alloys in contact with their surrounding atmosphere with a natural oxide skin, whose thickness is usually well below a micrometer. During the heating process a metal bolt for converting the same into a thixotropic state, for example is this usually already existing oxide layer on the circumference of the metal bolt, the so-called oxide skin, reinforced. The thickness of those formed during the heating process Oxide skin depends on the heating time required, the atmosphere surrounding the stud, and the alloy composition of the bolt in question. The thickness of the during The oxide skin formed in the heating process is typically 0.1 to for aluminum bolts 10 µm. Especially with metal alloys in the molten or thixotropic state impurities, such as alkali and alkaline earth metals, deposit.

In the case of molded parts, the oxides formed during the heating process are usually found, i.e. Parts or particles of the oxide skin formed during the heating up again. The in the Thixotropic metal alloy existing oxidic particles form in the molded part, for example oxidic inclusions or lead to the formation of pores in the alloy structure. In addition can oxides and other non-metallic inclusions in the oxide skin in the molded part Create structural separation points. Consequently, the surface of the Thixotropic metal stud existing oxide skin, the alloy quality of the molded part and hence its mechanical properties. Especially for workpieces subject to high mechanical loads oxide inclusions are therefore undesirable or even prevent their use as mechanically strong components.

A major problem in thixoforming of thixotropic metal alloys therefore resides in the Oxide formation during pretreatment, such as the heating process or Transport, the metal bolt through the atmosphere surrounding it. The thickness of the formed Oxide skin can be removed by special measures during the pretreatment of the metal bolts, such as by using an inert gas atmosphere surrounding the metal bolt reduced, but not entirely avoided. They are also for reduction the thickness of the oxide skin to be taken, in particular when manufacturing in industrial scale, complex and expensive.

In view of these difficulties in thixoforming, the inventor has a task made the structural defects occurring due to oxide inclusions in the molded part inexpensively minimize and thus provide a method for thixoforming which inclusions of components of the oxide skin in the molded parts avoided.

According to the invention, this is achieved in that the one surrounding the thixotropic metal bolt Oxide skin before the thixotropic metal alloy is inserted into the mold cavity Mold completely stripped from the thixotropic metal bolt and in one container is collected, the co-stripping of oxide-free, homogeneously thixotropic metal alloy, by taking into account the asymmetrical with respect to the longitudinal axis of the metal bolt thermal and mechanical properties of the thixotropic metal bolt is minimized.

Consequently, the molded parts produced using the method according to the invention have no or only a small and subcritical for the intended use of the molded parts Amount of oxide inclusions.

Expediently, that for carrying out the method according to the invention is for the Production of the molded part required the amount of a metal alloy in the form of a bolt. The Metal studs are cylindrical and usually have a round or oval cross section on, but can also be polygonal cross-section. The diameter of the metal bolt is for example 50 to 180 mm, suitably 75 to 150 mm and preferred 100 to 150 mm. The length of the metal bolts is, for example, 80 to 500 mm.

Suitable metal alloys for the process according to the invention are all commercially available metal alloys which can be converted into a thixotropic state. The method according to the invention is particularly suitable for processing alloys made of aluminum, magnesium or zinc. In particular, cast aluminum and wrought aluminum alloys are preferred. The method according to the invention is advantageously also suitable for processing particle-reinforced aluminum alloys which contain, for example, homogeneously distributed SiC or Al ₂ O ₃ particles. The method according to the invention is very particularly suitable for aluminum alloys which have a pronounced solidification interval, such as AlSi7Mg.

The alloy of the metal bolts required for the method according to the invention contains, for example homogeneously distributed, primarily solidified solid particles that degenerate from individual ones Dentrites exist. The proportion of solidified primarily solidified expediently 40% by weight or more. For example, to achieve good thixotropic behavior in the case of aluminum alloys, the alpha mixed crystal is in a globulistic form in order to to achieve an even flow of melt and solid.

The degenerate dentrites generally generally have a globulistic shape, which ensures a uniform, homogeneous flow of melt and solid without segregation can be reached. The creation of a structure with globulistic dentrites among other things through a continuous casting process, combined with an intensive electromagnetic Stir also during the solidification phase. This leads to melting and Breaking off dentrite arms that mold near the solidus temperature and that form globulistic structures.

The metal bolt required for the method according to the invention is previously used for thixoforming to a temperature above the solidus temperature and below the liquidus temperature, i.e. heated to a partially solid, thixotropic state.

The metal bolts are usually heated in a separate oven. The heating the furnace can be fueled, such as gas or oil, or electric Energy, such as resistance heating or inductive energy input, happen. For the method according to the invention, the heating of the metal bolt is carried out in an induction furnace preferred.

The heating of the metal bolts is of great importance because the bolt condition, i.e. its partial strength, usually only in a small temperature range, Long heating times, for example the formation of a thick oxide skin or possible grain coarsening because of, must be avoided and to achieve a homogeneous end product the temperature distribution in the thixotropic metal bolt, the so-called Thixo blank, should be as homogeneous as possible. That is why the transfer of the Metal bolt into the thixotropic state, i.e. heating the bolt to the desired one Alloy portion is melted, preferably by a controlled with sensors Oven temperature.

To heat the metal bolts, they can be placed directly in an oven or the Metal bolts can preferably be placed in a container, for example in a metallic container made of stainless steel, or a crucible made of clay graphite or clay SiC. During the heating process, the metal bolts can change in relation to their longitudinal axis vertical or horizontal position.

To heat a metal bolt in a horizontal position, it is located, for example, in a container. The metal bolt converted to the thixotropic state can then be in the same Containers by means of, for example, a gripper in the casting chamber of the horizontal die casting machine transferred and further processing to produce a shaped body be fed. In this case, the metal bolt remains during the heating process and transport to the casting chamber in the same container.

If the metal bolt is directly converted to its thixotropic state, i.e. without a metal receptacle is placed in this container and placed in the oven preferably in a position vertical with respect to its longitudinal axis.

In the semi-solid state, the thixotropic alloy, the so-called thixotropic alloy pulp, contains the reverse developed dentritic, primary solid particles in a surrounding Liquid metal matrix. The percentage of primary solid dentritic particles will expediently chosen such that the thixotropic metal bolt during the heating process, the transport into the casting chamber and in the casting chamber itself no noticeable Undergoes deformation and no noticeable loss of material due to dripping, for example of melt takes place. The thixotropic alloy slurry preferably contains a proportion primary solid particles from 40 to 80 wt .-%.

The thixo blank is then by means of the feed rate of a casting piston caused pressurization through the through opening of a preferably annular Body, the so-called oxide wiper, in which the oxide skin of the Stripped Thixo blanks according to the invention and collected in a container. The Thixotropic metal alloy prepared in this way is then passed through the pouring opening of the casting mold introduced into the mold cavity. The mold itself usually consists of one fixed and a movable mold half, each mold half corresponding to a mold recess has and the mold recesses of the two mold halves together form the mold cavity of the mold. The mold cavity can during the the inventive method are under ambient pressure or it can be evacuated.

When heating the metal bolt and transforming it into a thixo blank becomes one essentially uniform over the entire circumference of the thixotropic metal bolt thick oxide skin formed. In thixoforming with a horizontal casting chamber, the Metal bolts positioned horizontally. The diameter of the metal bolt depends on the process usually smaller than the diameter of the casting chamber cavity. Since the Casting chamber cavity usually has a round or oval cross section the thixotropic metal bolt located horizontally in the casting chamber cavity compared with only a small area of its surface, i.e. the thixotropic metal bolt has, for example on its underside, only a small mechanical and thermal contact with the Casting chamber wall.

Because the casting chamber is at a lower temperature than the thixotropic metal bolt is more due to direct thermal contact on the underside of the metal bolt Heat is dissipated from the thixotropic metal bolt to the casting chamber than the rest Scope of the metal bolt, which has no direct mechanical and thermal contact to the Has casting chamber wall and in which the heat transfer to the casting chamber wall only by convection or heat radiation. Depending on the duration while of the metal bolt in the casting chamber, its mechanical properties, i.e. in particular its partial strength or the viscosity, with respect to the bolt cross-section become inhomogeneous. If the temperature of the metal bolt is initially in the temperature range, which allows the thixotropic state, there is also the risk that the contact surfaces of the metal bolt below the temperature required for the thixotropic state falls and this part of the metal bolt is difficult to process.

Because the metal bolt cools down faster and faster due to the process than the rest of the metal bolt, is the semi-solid content or the viscosity in the bearing surface The close area of the thixotropic metal bolt is usually smaller than in the remaining outer surfaces near area. At least the viscosity of the metal alloy is in the contact surface close range of the thixotropic metal bolt higher than in the rest of the thixotropic metal bolt. However, the semi-solid content inside the thixo blank shows no noticeable variation on. This semi-solid component corresponds essentially to that of the outer surface Area of the thixo blank, the surface of which has no direct mechanical and thermal Has contact with the casting chamber. Therefore, the optimal stripping of the Oxide skin according to the present invention, the consideration of the longitudinal axis of the metal bolt asymmetrical thermal and mechanical properties of the oxide skin and the area close to the oxide skin of the thixotropic metal alloy. Under optimal In the present text, stripping is understood to mean stripping the oxide skin in which none essential part of the thixotropic alloy that can be used for thixoforming becomes. In principle, of course, a large concentric outer area of the thixotropic Metal pin are stripped so that only the core area of the thixo blank in the Mold cavity of the mold is introduced. In addition to the oxide skin, it would also much thixotropic metal taken from the molding production. Even if this is the thixoform process removed thixotropic material for recycling is the Balance of such a procedure with regard to energy consumption and process costs, particularly uninteresting in industrial molded part production.

Since the inhomogeneous properties of the thixotropic metal bolt - - depending on the pretreatment and deposition time in the casting chamber - not necessarily limited to the oxide skin, is in a preferred embodiment of the inventive method the area of the thixotropic metal bolt in the casting chamber close to the bearing surface originating part of the metal alloy with that caused by the stronger cooling stripped less liquid portion during the stripping of the oxide skin.

In a preferred embodiment of the method according to the invention, the thixotropic metal alloy by means of one arranged between the casting chamber and the casting mold annular body, the so-called oxide wiper, performed, the oxide skin of the thixotropic metal bolt fluid mechanically through a recessed in the oxide wiper concentric, annular opening, the so-called oxide wiper opening, with one asymmetrical with respect to the concentric central axis of the oxide wiper opening Opening cross-section passed into a ring-shaped container, the so-called oxide collection ring becomes.

The ring-shaped body does not necessarily have to be a separate component of the die casting machine designate, i.e. the annular body can also be designed accordingly Part of the wall of the die casting machine surrounding the thixotropic metal alloy in the area between the casting chamber and the mold cavity of the mold.

The oxide wiper can, for example, be a toroidal structure made of a toroidal one Oxide collection ring, which is an annular ring directed against its concentric central axis Has oxide wiper opening.

Since the thickness of the oxide skin of the thixotropic metal bolt is essentially over its circumference is constant, is also the stripped amount of oxide over the entire circumference of the oxide scraper preferably the same so that the cross section of the oxide collection ring with respect its central axis is advantageously axially symmetrical. The cross-sectional shape of the Oxide collector ring is immaterial for the method according to the invention and can be any one Shape, i.e. one enclosed by an essentially closed curve Surface with an opening directed against the concentric central axis of the oxide collecting ring, accept. On the other hand, it is essential to the invention that even with one over the whole Stud circumference constant stripped amount of oxide, i.e. one all over the cylindrical Surface area of the thixotropic alloy pulp stripped layer more constant Layer thickness, the concentric, annular oxide wiper opening one with respect to it concentric central axis has an asymmetrical opening cross section, the opening cross section especially in the lower part of the horizontal ring-shaped oxide scraper is larger than, for example, the upper part. For example the higher viscosity of the metal alloy or oxide skin flowing past, which consists of the area of the thixotropic metal bolt in the casting chamber near the contact surface comes, taken into account.

The opening cross section which is asymmetrical with respect to the concentric central axis (m) is preferred depending on the asymmetrical with respect to this concentric central axis (m) Viscosity properties of the thixotropic metal alloy selected such that a radially uniformly thick layer of the oxide skin and the region close to the oxide skin thixotropic metal alloy is stripped.

Accordingly, the stripping of a radially uniformly thick layer of aluminum oxide and thixotropic metal alloy with an essentially the circumference of the thixo bolt, i.e. the surface area of the thixotropic alloy pulp, different viscosity through an annular oxide wiper opening with a viscosity selected, different opening cross-section achieved. In particular, the opening cross section in the lower part of the ring-shaped oxide scraper chosen to be larger higher viscosity of the thixotropic originating from the area close to the contact surface Metal alloy and the oxide skin to be taken into account.

For particularly sensitive molded parts, the higher viscosity of the contact surface can already be close range originating thixotropic metal alloy the alloy quality affect. Therefore, in a further preferred method, this part of the stripped thixotropic metal alloy together with the oxide skin, i.e. instead of stripping a radially uniformly thick layer of aluminum oxide and thixotropic metal alloy, becomes thicker in the lower part of the oxide wiper compared to the upper part Stripped off layer of thixotropic metal alloy. Because with this procedure in the lower Part of the oxide scraper is fed more material into the oxide collection ring, the corresponding part of the oxide collecting ring has a larger cross-section, whereby the Oxide collector ring loses its axial symmetry.

The term “lower part” or “upper part” of the oxide collecting ring means in the present case Text always the corresponding part with respect to a horizontal plane through the concentric Understand the center axis of the oxide wiper.

With very fast mold filling, turbulent flow conditions can occur during the thixoforming process occur, which leads to gas inclusions (air, release agents or lubricants) in the Molding can lead, which may result in a subsequent heat treatment of the molded part because of the different coefficients of thermal expansion between the metal alloy and the gas inclusions is often impossible. Such gas inclusions lead to pores in the cast structure. This pore formation can be caused by evacuation of the mold cavity the mold and / or by slower mold filling including ventilation of the Mold cavity can be reduced. A slower mold filling, i.e. the filling of the Cavity has the aim of avoiding turbulence in the metal alloy, which is a special control of the pressurization of the metal bolt Feeding speed of the casting piston conditional. Essential for the inventive The method is that the stripping of the oxide skin during the entire process of the Thixoform process happens continuously, so that the amount of material stripped per unit of time is proportional to the feed rate of the thixotropic metal bolt.

The pressurization of the casting piston to fill the mold cavity of the mold during the thixoforming process, it is therefore preferred that turbulence in the thixotropic metal alloy and thus the formation of gas and oxide inclusions in Molding should be avoided if possible, i.e. the pressure on the casting piston happens preferably such that there is a laminar flow of the thixotropic metal alloy with the surrounding oxide skin. The one on the thixo blank through the casting piston The pressure exerted is, for example, between 200 and 1500 bar, expediently between 500 to 1000 bar. The resulting flow velocity of the thixotropic Alloy slurry is, for example, 0.2 to 3 m / s, expediently 0.3 to 2 m / s.

During the solidification of the molded part, high pressures improve the feeding behavior, i.e. to ensure complete filling of the mold cavity Mold, and to reduce shrink porosity, i.e. to avoid education from so-called micropipes. While cooling the thixotropic metal alloy in the density of the mold increases until the solidification point is reached. A high one Void risk arises in the course of solidification shrinkage, during which it goes to training can come from voids in the structure of the molded part. Because of the solidification shrinkage Volume deficit caused is between 4% and 7.1%. The after the Solidification upon further cooling down to permanent shrinkage to room temperature is compensated with the help of the so-called shrinkage in the manufacture of the molds.

The molded parts produced according to the invention typically have a porosity of less than 1% by volume and an oxide content between, for example, 0 and 3% by weight, prefers 0 to 1% by weight. The method according to the invention thus allows production of safety components through thixoforming, with the required high elongation properties for example through the interaction of low iron alloys (<0.15 % By weight of Fe), rapid solidification and the avoidance of oxide inclusions will.

The invention further relates to a horizontal die casting machine for the production of molded parts made of thixotropic metal bolts, with inclusions of the thixotropic metal bolts surrounding oxide skin in the alloy structure of the molding can be avoided, and the horizontal die casting machine a horizontal casting chamber with a cylindrical one Casting chamber cavity for receiving a thixotropic metal bolt, a shield with a shield opening and a mold with a sprue opening and a mold cavity contains.

This is achieved according to the invention in that between the casting chamber and the casting mold an oxide scraper is arranged, the oxide scraper being an annular body with a horizontal, concentric central axis as well as an outside and Inner surface represents, and the cross section perpendicular to the concentric central axis through the inner surface of the oxide wiper defines the passage cross section of the oxide wiper, the oxide scraper contains an annular recess, the oxide collection ring, which is connected to the through the inner surface and the side of the oxide scraper on the casting chamber and the mold side defined through opening of the oxide wiper via a concentric, annular Oxide wiper opening is connected, the oxide wiper opening with respect to the concentric central axis of the oxide wiper an asymmetrical opening cross-section having.

The oxide scraper according to the invention acts as a peeling tool during the filling process of the mold cavity of the mold, the oxide skin present on the pin circumference scrapes in the thixotropic state of the metal bolt and this in the oxide collecting ring of the oxide scraper. The oxide scraper is therefore conveniently located immediately before the shaping tool, i.e. the mold.

With horizontal die casting machines, the pin receiver, i.e. the casting chamber, in which the semi-rigid metal bolt is placed horizontally. The casting chamber provides essentially a cylindrical one, delimited by the casting chamber wall Body with a cavity, the so-called casting chamber cavity, wherein the to Inserting the thixotropic metal pin provided area of the casting chamber, i.e. the the Side of the casting chamber facing away from the mold, for example half-shell-shaped is closed, while the side of the casting chamber facing the casting mold is cylindrical and the resulting cavity is, for example, round, oval or polygonal Has cross section.

The diameter of the casting chamber suitably corresponds to 102 to 120%, preferably 103 to 115% and particularly preferably 103 to 110% of the diameter of the metal bolt, so that the thixotropic metal bolt after insertion into the casting chamber in the essential only on its underside a mechanical and thermal contact with the Has casting chamber.

The mold consists, for example, of a fixed and a movable mold half, whereby each mold half has a mold recess and the mold recesses of the two mold halves together form the mold cavity of the mold. The ones to introduce the thixotropic metal alloy into the mold cavity due to the casting opening expediently has a cross section which is optimized with respect to the mold filling on, which is usually different from the cross section of the casting chamber cavity, wherein the pouring opening expediently has a smaller cross section than the cross section the mold-side casting chamber opening. Due to the different cross sections of the different flow zones (pouring chamber, shield opening, pouring mold cavity) the thixotropic metal alloy exercises the latter along the individual areas of the flow zones different forces on the surrounding walls, so that, for example axially on the walls of the various components of the horizontal die casting machine power transmission is different. To accommodate part of this axial, i.e. in the direction of flow of the thixotropic metal alloy in the direction of the mold acting forces, is usually between the casting chamber and the mold a sign with a sign opening.

Prior to thixoforming, the metal bolts are made in accordance with the through the mold cavity defined material requirements cut and in an oven, preferably one Induction furnace converted to the thixotropic state, the substantially cylindrical Metal bolts during the heating process, for example in a half-shell, cylindrical containers are stored horizontally. After that, the semi-solid Metal bolts using a manipulator or manually in the horizontal casting chamber transferred. To prevent the metal bolt from solidifying, the thixotropic Metal bolts relatively quickly, i.e. for example within one minute of the other at the longest Processing to be fed. The casting chamber is usually made - from cost and Energy saving reasons not heated, i.e. the metal bolt cools, especially its contact surfaces on the wall of the casting chamber.

Since the cylindrical thixotropic metal bolt expediently has a smaller cross section than the cylindrical or semi-cylindrical casting chamber, this lies only on the small area of the casting chamber wall, which - due to the good thermal Contact of these contact surfaces, i.e. through direct heat conduction - an inhomogeneous Temperature distribution in the thixotropic metal bolt arises. Is the thixotropic metal bolt on several small areas of the casting chamber wall distributed over the pin circumference , the metal bolt also has - due to its own weight the lower contact surfaces have better thermal contact, so that more Heat is released from the metal bolt downwards as upwards. This cools it down Metal studs with respect to its circumference on its lower contact surface in the casting chamber most strongly. As a result, the axial symmetry of the thermal and mechanical bolt state with respect to the concentric longitudinal axis of the metal bolt lost, for example, the viscosity or the liquid content of the thixotropic alloy becomes asymmetrical with respect to the concentric longitudinal axis of the metal bolt.

During the heating process of the thixotropic metal bolt and its transport into the The casting chamber becomes the mostly naturally existing oxide skin, the higher bolt temperature in the partially solid state and therefore because of the more reactive bolt surface, essential reinforced. The introduction of parts or particles of the oxide skin into the mold cavity Mold usually leads to strong structural defects in the molded part or to the formation of pores, whereby the alloy quality of the molded part can be severely impaired. With the Die casting machine according to the invention can now on the circumference of the thixotropic metal bolt existing oxide skin by means of a between the casting chamber and the mold arranged oxide wipers are completely removed. As little as possible for the Thixotropic metal alloy that can be used with the thixoforming process is what the Consideration of the asymmetrical with respect to the concentric longitudinal axis of the metal bolt thermal and mechanical properties of the thixotropic metal bolt.

According to the invention, the oxide scraper is an annular body, which has a inside concentric, annular, for example toroidal, recess, the so-called Has oxide collection ring. The inner part or that which represents the through opening Part of the oxide scraper, i.e. through the inner surface and the two end faces of this Body limited interior space, has a concentric central axis perpendicular to the end faces - The concentric central axis of the oxide scraper - which is expedient with the concentric longitudinal axis of the casting chamber cavity and in particular with the concentric central axis of the gate opening coincides. The cross section of the through opening perpendicular to the concentric central axis of the oxide wiper, the so-called Passage cross section, preferably corresponds to the cross section of the mold-side casting chamber opening, i.e. the opening of the cylindrical casting chamber facing the casting mold.

The end face of the oxide scraper on the casting chamber is usually located directly on the mold-side casting chamber opening. The form-side end face of the oxide scraper is located preferably located directly on the outer edge of the pouring opening leading into the interior of the mold, i.e. the form-side termination of the oxide wiper lies directly on the oxide wiper-side On the front of the mold or on the fixed mold half.

The oxide wiper opening provides an annular recess in the inner surface of the oxide wiper It is preferably formed by a recess on the form of the oxide wiper, i.e. it is located on the end face of the mold or on that of the casting chamber opposite side of the oxide scraper. This creates between the mold end the inner surface and the oxide wiper-side front of the mold a cylindrical shell Distance so that the through this opening between the interior, i.e. of the Through opening of the oxide scraper, and the oxide collection ring created space that so-called oxide wiper opening, is hollow cylindrical. The through a longitudinal section cut through the concentric central axis of the oxide scraper from the hollow cylinder The area represents the opening cross section of the oxide wiper opening.

For fluid mechanics reasons, the through opening of the oxide scraper expand conically towards the end face of the oxide scraper. The wall the conical extension closes with the horizontal part of the inner surface of the oxide wiper an acute angle of, for example, 2 to 30 °, preferably between 5 and 15 ° and in particular between 5 and 10 °, the angle information in the present text are always related to a full circle of 360 °.

The oxide scraper according to the invention, the casting chamber and the mold are made expediently made of thermally and mechanically highly resilient material, for example made of steel, in particular hot-work steel (DIN X 38 CrMoV51), made of ceramic materials or from a surface exposed to the thixotropic metal alloy a ceramic coated steel. Preferably there are at least the thixotropic metal alloy leading components of the die casting machine and in particular the oxide scraper made of hot-work steel.

The oxide stripper-side front of the mold has fluid-mechanical reasons preferably has a conically tapered gate opening, i.e. mostly through the fixed mold half of the casting mold, which has a casting opening on the oxide wiper side Opening a greatly increasing opening angle, i.e. only slightly from one Right angle deviating opening angle of, for example, 80 to 87 °.

At the front end of the gate, i.e. where the essentially parallel to Frontal concentric thixotropic metal alloy of the pouring opening against the wall of the mold cavity of the movable mold half, for example bounces, a front recess can also be created in this area of the mold be the part of the oxide skin of the thixo blank facing the mold can record.

In a preferred embodiment of the die casting machine according to the invention the oxide scraper in the shield opening, the length of the annular oxide scraper suitably the thickness of the sign, i.e. corresponds to the length of the shield opening. Since the thixotropic alloy is usually applied to all of them during the thixoforming process leading parts of the die casting machine high forces in the flow direction of the thixotropic Occur metal alloy and the oxide wiper, for example, on its mold-side face, due to the oxide wiper opening and the oxide collecting ring, a thinner one The oxide wiper has wall thickness than at its end surface on the casting chamber side expediently on other means to the forces acting on him towards the mold to catch up. This can be done, for example, by means of an end face on the casting chamber side of the oxide scraper molded stop rib happen that is such that it engages in a groove-shaped recess of the shield and thus parallel to the concentric Center axis of the oxide wiper absorbs forces acting in the direction of the mold. The Groove-shaped recess and the molded stop rib are preferred radially symmetrical, i.e. their cross section perpendicular to the concentric central axis the oxide scraper is preferably annular.

However, the oxide collection ring does not necessarily have to be a separate component of the die casting machine be educated; i.e. the annular body can also be designed accordingly Part of the wall of the die casting machine surrounding the thixotropic metal alloy in the area between the casting chamber and the mold cavity of the mold or a corresponding Designate the molded end of the casting chamber on the mold side. Is preferred however, the formation of the oxide scraper as a separately manufactured and between the mold and the casting chamber insertable part.

If the oxide scraper is designed as a separate part of the die casting machine, it becomes conveniently positioned between the casting chamber and the mold. With that, the caused by the pressurization of the thixo bolt in the casting chamber Transfer forces in the axial direction to the oxide wiper. To the oxide scraper mechanically not to burden excessively, are therefore preferred means for collecting this Forces are provided on the shield. This can be done, for example, by a molded or on the shield fixed casting chamber wall bracket and a casting chamber guide, for example Rib formed or fixed on the outer periphery of the casting chamber. The casting chamber wall bracket and the casting chamber guide are preferred ring-shaped, i.e. their cross section perpendicular to the concentric central axis of the The oxide scraper is preferably circular.

The training necessary for an optimal stripping of the oxide skin with respect to the Central axis of the oxide wiper asymmetrical opening cross-section and the necessary optimal shape and the required capacity of the oxide collecting ring depend on the thickness of the oxide skin surrounding the thixotropic metal bolt and the Size (length, diameter) of the metal bolt. The thickness of the oxide skin depends largely from the alloy composition and the history of the metal bolt from. The exact dimensions of the opening cross-section and the optimal shape and the capacity of the oxide collector ring must therefore be for those to be manufactured Moldings are calculated in advance or determined by preliminary tests.

It preferably points through the concentric central axis with respect to a horizontal plane of the oxide scraper lower part of the oxide scraper opening, at least in a partial area of that, i.e. in a segment of the hollow cylindrical oxide wiper opening, a larger one Opening cross-section on than in the upper part. Up to this segment the hollow cylindrical oxide wiper opening, the opening cross section may be constant or itself enlarge continuously or gradually towards the bottom. The opening cross section in the bottom lying segment of the hollow cylindrical oxide wiper opening with a larger opening cross section can also be constant or continuous or step-like from above enlarge down. The segment relates to the hollow cylindrical oxide wiper opening with a larger opening cross-section essentially the area of the oxide wiper opening, in which the part of the oxide skin originating from the area close to the contact surface and the thixotropic metal alloy flows through the segment of the hollow cylindrical Oxide wiper opening with larger opening cross-section included central angle is - based on a full circle with 360 ° - preferably between 30 and 70 ° and in particular between 50 and 65 °.

In a particularly preferred embodiment of the oxide scraper according to the invention points in a longitudinal section of the vertical through the concentric central axis Oxide scrapers with respect to a horizontal plane through the concentric central axis upper part of the oxide wiper opening a distance of 0.5 to 4 mm, in particular 1 to 3 mm, between the mold-side end of the inner surface of the oxide scraper and the mold-side End face of the oxide wiper, or the oxide wiper-side front of the mold, on.

In a further preferred embodiment of the oxide scraper according to the invention points in a longitudinal section of the vertical through the concentric central axis Oxide scrapers with respect to a horizontal plane through the concentric central axis lower part of the oxide wiper opening a distance of 1 to 10 mm, in particular 3 to 6 mm, between the mold-side end of the inner surface of the oxide scraper and the mold-side End face of the oxide wiper.

With an oxide wiper opening on the end face of the oxide wiper on the mold side the asymmetrical opening cross section required according to the invention can also be made through a corresponding recess on the oxide wiper-side front of the mold, through a so-called recess. The recess is preferably located with respect to the horizontal plane through the concentric central axis of the oxide wiper lower part of the oxide wiper opening and is arranged such that the opening cross section in this lower part of the oxide wiper opening, i.e. one segment the hollow cylindrical oxide wiper opening is enlarged.

The necessary for the uniform stripping of the oxide skin according to the invention with respect the concentric central axis of the oxide wiper asymmetrical opening cross-section can accordingly also by a with respect to the concentric central axis of the oxide wiper axially symmetrical oxide wiper opening with a recess according to the invention on the oxide scraper side of the mold can be reached. A corresponding recess on the oxide wiper-side front of the mold, however, can also additionally an oxide wiper opening with an already with respect to the concentric central axis of the Oxide scraper asymmetrical opening cross section and thus the opening cross section enlarge in this sub-area of the oxide wiper opening or for better Introduction of the oxide skin into the corresponding part of the oxide collection ring to serve.

The configuration of the recess on the oxide wiper-side front side of the casting mold can have any shape and, in particular, can have a cylindrical shape, cylindrical shape being used to describe a spatial shape caused by the displacement of an area delimited by any closed curve. The term cylindrical shape also includes, in particular, cuboid, cylinder segment or hollow cylindrical segment configurations of the recess. Further preferred forms of the recess are barrel or truncated pyramid. The spatial dimensions of the cutout are preferably selected such that the cutout enlarges the opening cross section of the oxide wiper opening in the area in which the oxide skin originating from the contact surface is scraped off. Preferred configurations of the recess have a maximum height of 10 to 40 mm, in particular 10 to 20 mm, and a maximum width of 20 to 80 mm, in particular 20 to 50 mm, and in the direction through the concentric central axis of the oxide scraper the concentric central axis to a maximum depth of 2 to 20 mm and in particular from 2 to 8 mm. The cutout more preferably has a volume of 0.4 to 64 cm ³ .

To be essentially constant over the entire scope of the thixotropic metal alloy To strip off thick oxide skin, an oxide collecting ring is concerned with the concentric Central axis of the oxide wiper axially symmetrical cross section preferred. The shape of the Oxide collection ring is immaterial. The oxide collection ring can be, for example Toroidal recess in the ring-shaped oxide wiper with a ring-shaped oxide wiper opening represent, the toroidal recess, for example by rotation a surface enclosed by any closed curve with a counter the axis of rotation directed around the concentric central axis of the oxide wiper can arise. The concentric central axis of the toroidal recess thus falls preferably together with the concentric central axis of the oxide wiper. The cross section the oxide collecting ring can in particular be rectangular, circular or elliptical. For The ring-shaped process control which concerns the stripping of the oxide skin can be improved Oxide collection ring can also be divided into individual areas by partitions.

The capacity of the oxide collection ring, i.e. the volume of the toroidal recess, is expediently chosen such that it is at least the one to be stripped Material volume of oxide skin and any thixotropic metal alloy to be stripped corresponds. The capacity of the oxide collecting ring is preferably between 1 and 10 % By volume and in particular from 3 to 6% by volume of the thixotropic metal bolt, i.e. the in the Casting chamber imported thixo blank.

Since the thixotropic metal alloy, e.g. the material to be stripped, a certain pressure for fluid mechanical reasons is necessary so that the material to be stripped due to, for example, its viscosity and cohesion should be able to flow through the oxide wiper opening to achieve a continuous, even stripping of the thixotropic alloy slurry - - at least in the area of the oxide wiper opening - prevailing pressure at a given oxide wiper opening remain constant. The pressure in the thixotropic alloy pulp is often with the oxide skin surrounding it during the thixoform process, however, not, or at least not constant enough.

In a preferred embodiment of the horizontal die casting machine according to the invention the oxide collection ring therefore consists of several annular cavities, the so-called oxide collection ring chambers, i.e. instead of just a single toroidal recess in the ring-shaped oxide wiper, there are several toroidal recesses, wherein the toroidal recesses with each other by an annular Oxide wiper opening are connected. The capacity of each Oxide manifold chambers versus using a single toroidal recess be chosen accordingly smaller. All oxide collecting ring chambers are particularly preferred an oxide scraper form-side recesses of the corresponding Oxide scraper.

The oxide collecting ring chambers are very particularly preferred with regard to their shape and the oxide scraper openings relating to the individual oxide collecting ring chambers are designed in such a way that they are related to each, during the thixoforming process in the thixotropic Alloy resulting pressure, or according to the pressurization of the thixo blank, an optimal stripping of the oxide skin and the area close to the oxide skin Allow thixotropic metal alloy.

The oxide collecting ring particularly preferably has 1 to 5 and in particular 1 to 3 oxide collecting ring chambers and a corresponding number of oxide wiper openings. This corresponds to every oxide collection ring chamber and the optimal opening cross-section for filling this chamber the corresponding oxide wiper opening of a printing phase of the thixoforming process, each pressure phase is selected such that the filling resistance of the during the respective process phase of the molded part to be filled with the corresponding mold cavity cross section can be overcome.

Different printing phases are usually required for thixoforming. Happens first for example a first mold filling with a relatively low pressure. For complete Mold filling in the edge areas of the mold cavity must be followed by the pressure for example, be increased. The phase with the highest pressure takes place prevention of micro voids or pores - during the solidification phase of the molded part, taking place in this last phase no longer flows into the metal forming the molded part and therefore also none Oxide skin must be stripped. In this last phase, i.e. the solidification phase can if necessary, add thixotropic metal; is the amount of flowing metal Usually, however, so small that they no longer enter the mold cavity forming the molded part arrives and is therefore irrelevant for the molded part properties. Because the pressurization according to the filling resistance to be overcome during the thixoforming process is increased continuously or gradually, expediently show the inner, ring-shaped oxide wiper openings have a larger average opening cross section than that outer oxide wiper openings.

In order to achieve a better alloy quality of the molded part, that from the contact surfaces close area, close to the oxide skin, thixotropic metal alloy with higher Viscosity are stripped off together with the oxide skin. For this, an oxide collecting ring with a larger capacity in this area. In another The preferred embodiment of the oxide collecting ring thus has a horizontal one Plane through the concentric central axis of the oxide scraper, lower part of the oxide collecting ring, at least in a partial area thereof, a larger cross section than in the upper one Part, i.e. the oxide collection ring points with respect to the concentric central axis of the oxide scraper an asymmetry. Preferably, one shows through the concentric central axis of the Oxide scraper vertical longitudinal section in the with respect to a horizontal Plane through the concentric central axis lower half of the oxide scraper one to one triple and in particular a 1.1 to 1.8 times larger longitudinal sectional area of the oxide collecting ring than in the top half of the oxide wiper.

The horizontal die casting machine according to the invention is suitable in principle for thixoforming all metal alloys that can be converted into a thixotropic state and have an oxide skin or during pretreatment, such as during heating up, form an oxide skin. The horizontal die casting machine according to the invention is preferred for thixoforming of aluminum, magnesium or zinc alloys used. The horizontal die casting machine according to the invention is particularly preferably suitable for thixoforming of aluminum die casting alloys, especially for AlSi, AlSiMg, AlSiCu, AlMg, AlCuTi and AlCuZnMg alloys.

The horizontal die casting machine according to the invention thus allows optimal removal the oxide skin surrounding the thixo blank shortly before the mold filling and enables thus the production of molded parts without inclusions of parts of the oxide skin. Also allowed the horizontal die casting machine according to the invention minimizes material loss of thixotropic metal alloy usable for thixoforming.

The present invention is further explained by way of example with reference to FIGS. 1 to 5.

Figure 1 shows a partial view of a vertical through the concentric central axis of a horizontal die casting machine running longitudinal section.

Figure 2 shows a view vertically through the concentric central axis of an inventive Oxide scraper running longitudinal section, the one shown in Figure 2a Oxide scraper one axially symmetrical to the concentric central axis of the oxide scraper Has oxide collection ring and the oxide scraper shown in Figure 2b with respect the concentric central axis shows asymmetrical oxide collection ring.

Figure 3 shows a vertical longitudinal section through the concentric central axis of one at the solid mold half of a mold abutting oxide wiper and one at right angles to concentric central axis lying cross section (section along A-A) through the oxide wiper side Front of the mold.

Figure 4 shows a vertical longitudinal section through the concentric central axis of one at the solid mold half of a mold attached to the oxide scraper, the oxide collecting ring three Has oxide collecting ring chambers and three associated oxide wiper openings.

Figure 5 shows a diagram of the thixotropic process during the thixoforming process Metal alloy setting pressure p as a function of time t.

Figure 1 shows an example of a partial view of a vertical through the concentric central axis a horizontal die-casting machine running longitudinal section, the oxide wiper side Part of the horizontal casting chamber 10, the oxide wipers 30, the shield 20 as well as the mold 70 can be seen. The oxide scraper 30 lies within the shield opening 24, i.e. between the casting chamber 10 and the mold 70.

The casting chamber 10 has a casting chamber cavity 11 which is cylindrical Casting chamber wall 12 is encased and the inclusion of a - not shown - -thixotropic Metal pin is used. The casting chamber cavity 11 essentially represents one cylindrical body delimited by the casting chamber wall 12. Die However, the casting chamber 10 is only in the region of the mold-side casting chamber opening 13 from a closed cylindrical casing, the casting chamber wall 12, surrounded and has a semi-cylindrical half-shell on the side facing away from the mold 70 - -Not marked - on, which serves to introduce the thixotropic metal bolt. Of the Casting chamber cavity 11 caused by the cylindrical casting chamber wall 12 has, for example, a round, oval or polygonal cross section. In the field of Casting chamber opening 13 on the mold side, the casting chamber 10 thus has a hollow cylindrical shape Shape up. The diameter of the casting chamber cavity 11 preferably corresponds 103 to 115% of the diameter of the thixotropic metal bolt, so that the metal bolt after insertion into the casting chamber 10 only on its underside a mechanical and has thermal contact with the casting chamber wall 12.

On the side of the casting chamber 10 facing away from the mold 70 there is a - - not shown - Pouring piston introduced, which during thixoforming with the thixotropic alloy high pressure in the mold cavity 68 of the mold 70. During the die casting process the thixotropic metal bolt is initially inserted into the hollow cylindrical part of the casting chamber 10 transported, at least after the impact of the metal bolt on the oxide wiper-side front 46 of the mold 70 Thixotropic metal stud or thixo blank loses its original shape and for example the entire casting chamber cavity in the area of the mold-side casting chamber opening 13 11 fills out.

The mold 70 shown in Figure 1 consists of a fixed mold half 50 and a movable Mold half 60, each mold half 50, 60 having a mold recess 54, 66 has, and the mold recesses 54, 66 of the two mold halves 50, 60 together form the mold cavity 68 of the mold 70. The one for introducing the thixotropic metal alloy in the mold cavity 68 of the mold 70 conditional opening 52 points expediently has a cross section which is optimized with respect to the mold filling and which is opposite the cross section of the mold-side casting chamber opening 13 is made smaller.

The oxide stripper-side front side 46 of the mold 70 shown in FIG. 1 has fluid-mechanical reasons a conically tapering part 56 of the Gate 52 open, i.e. the leading through the fixed mold half 50 of the mold 70 The pouring opening 52 has a part on the oxide wiper-side part 56 of the pouring opening 52 greatly increasing opening angle, i.e. one that deviates only slightly from a right angle Opening angle, on.

At the front end of the gate 52, i.e. where the essentially parallel to concentric central axis m of the pouring opening 52 extending thixotropic metal alloy collides head-on with the wall of the mold cavity 66 of the movable mold half 60 in addition, a front-side recess 64 is shown, which faces the mold 70 front part of the oxide skin of the thixo blank.

The oxide scraper 30 represents an annular body which has a concentric, annular, for example toroidal, recess, the so-called oxide collecting ring 40 having. The inner part of the oxide scraper 30, i.e. the through the inner surface 36 and the two end faces 37, 38 of this body limited interior space, i.e. the through opening 31 of the oxide scraper 30, has a concentric central axis perpendicular to the end faces 37, 38 - The concentric central axis m of the oxide wiper 30 - on that with the concentric Longitudinal axis of the casting chamber cavity 11 and with the concentric central axis the gate 52 coincides. The cross section of the through opening 31 is perpendicular to the concentric central axis m of the oxide wiper 30, the so-called passage cross section, corresponds to the cross section of the mold-side casting chamber opening 13, i.e. the the Opening of the cylindrical casting chamber 10 facing the mold.

The end face 38 of the oxide wiper 30 on the casting chamber is located directly on the Mold-side casting chamber opening 13. The mold-side end face 37 of the oxide wiper is located directly on the outer edge of the gate opening leading into the interior of the mold 70 52 or at its conical pouring opening 56, i.e. the form end 37 of the oxide wiper 30 lies directly on the oxide wiper-side front 46 of the casting mold or on the fixed mold half 50.

The oxide wiper opening 42 provides an annular recess in the inner surface 36 of the Oxide scraper 30. It is through a recess on the form of the oxide scraper 30 formed, i.e. it is located on the mold-side end face 37 or on that of the casting chamber 10 facing away from the oxide scraper 30. This creates between the mold side End of the inner surface 36 and the oxide wiper-side front side 46 of the mold 70 a cylinder jacket-shaped distance, so that through this opening between the through opening 31 of the oxide scraper 30 and the oxide collecting ring 40, i.e. the oxide wiper opening 42 is hollow cylindrical. The through a longitudinal section through the concentric central axis m of the oxide scraper 30 cut from the hollow cylinder The area represents the opening cross section of the oxide wiper opening 42 shown through opening 31 of the oxide wiper 30 widens conically against the Form-side end face 37 of the oxide scraper 30, with a conical extension 34 is created. In the lower part of the fixed mold half 50 shown in Fig. 1 is on the oxide scraper-side front 46 also a recess 44 drawn, the opening cross-section enlarged at the corresponding point of the oxide wiper opening 42.

To accommodate the axial, i.e. in the direction of flow of the thixotropic metal alloy The forces acting on the mold 70 are between the casting chamber 10 and the Mold 70 a shield 20 with a shield opening 24. The oxide wiper 30 is located in the shield opening 24, the length of the annular oxide scraper 30 the thickness of the Shield 20, i.e. corresponds to the length of the shield opening 24. Because during the thixoforming process usually on all parts 12, 30, 70 of the thixotropic alloy Die casting machine high forces occur in the flow direction of the thixotropic metal alloy and the oxide wiper 30 on its mold-side end face 37, due to the oxide wiper opening 42 and the oxide collecting ring 40, has a thinner wall thickness than at of its end surface 38 on the casting chamber side, the oxide scraper 30 has one on the casting chamber side Stinfläche 38 molded stop rib 32, which is such that it engages in a groove-shaped recess 22 of the shield 20 and thus part of the parallel to the concentric central axis m of the oxide scraper 30 acting in the direction of the mold 70 Absorbs forces. The groove-shaped recess 22 and the integrally formed stop rib 32 are radially symmetrical, i.e. their cross section perpendicular to the concentric central axis m of the oxide scraper 30 is annular.

In order to transmit axially acting forces from the casting chamber 10 to the oxide wiper 30 to reduce, a casting chamber wall bracket 16 is formed on the shield 20 or fixed. At a distance from the mold-side casting chamber opening 13, the The length of the casting chamber wall bracket 16 corresponds to the outer circumference of the casting chamber 10 a rib designed as a casting chamber guide 14 is formed or fixed. The casting chamber wall bracket 16 and the casting chamber guide 14 are annular trained, i.e. their cross section perpendicular to the concentric central axis m of the oxide wiper 30 is circular. The inside diameter of the annular casting chamber wall bracket 16 corresponds essentially to the outer diameter of the casting chamber wall 12, and the outer diameter of the casting chamber guide 14 is larger than the inner diameter the casting chamber wall bracket 16.

Figure 2a shows a view vertically through the concentric central axis m of an inventive Oxide scraper 30 extending longitudinal section, the oxide scraper 30th has an oxide collecting ring 40 which is axially symmetrical with respect to the concentric central axis m. The with respect to a horizontal plane through the concentric central axis m of the oxide wiper 30 lower part of the oxide wiper opening 42 has, at least in a partial area of that, i.e. in a segment of the hollow cylindrical oxide wiper opening 42, one larger opening cross-section than in the upper part. Up to this segment the hollow cylindrical oxide wiper opening 42, the opening cross section may be constant or increase continuously or gradually towards the bottom. The opening cross section in underlying segment of the hollow cylindrical oxide wiper opening 42 with a larger one Opening cross-section can also be constant or continuous or step-like enlarge from top to bottom. The segment relates to the hollow cylindrical oxide wiper opening 42 with a larger opening cross section essentially the area of Oxide scraper opening 42, in which the area coming from the contact surface Part of the oxide skin and the thixotropic metal alloy flows through.

The passage opening 31 widens to form a conical extension 34 against the mold-side end face 37 of the oxide scraper 30 and thereby allows a better one Introduction of the oxide skin and the oxide skin near thixotropic metal alloy in the Oxide collection ring.

The oxide collecting ring 40 shown in FIG. 2a is m with respect to the concentric central axis of the oxide scraper 30 axially symmetrical and is suitable for stripping one over the entire scope of the thixotropic metal alloy essentially constant thick oxide skin. The cross section of the oxide collecting ring shown in FIG. 2a shows particularly good properties with regard to the introduction of the oxide skin and regions close to the oxide skin thixotropic metal alloy.

Figure 2b shows a view of a vertical through the concentric central axis m of an inventive Oxide scraper 30 extending longitudinal section, the oxide scraper 30th has an oxide collecting ring 40 which is asymmetrical with respect to the concentric central axis m. Of the with respect to a horizontal plane through the concentric central axis m of the oxide wiper 30 lower part of the oxide collecting ring 40 has, at least in a partial area thereof, a larger cross-section than in the upper part, i.e. the oxide collection ring 40 shows with respect the concentric central axis m of the oxide wiper 30 has an asymmetry. Such a trained oxide collection ring 40 with an enlarged capacity in the lower part is particularly suitable for co-wiping the area close to the contact surface originating, close to the oxide skin, thixotropic metal alloy with respect to the interior the thixotropic metal alloy with higher viscosity.

The longitudinal section through the oxide wiper 30 shown in FIG. 2b again shows one suitable for the particularly good introduction of the material to be stripped Oxide collector ring 40. The oxide wiper opening 42 has the same shape as that of the in Figure 2a shown oxide scraper 30th

Figure 3 shows a vertical longitudinal section through the concentric central axis m one the fixed mold half 50 of a mold 70 adjacent oxide wiper 30 and one cross section perpendicular to the concentric central axis m (section along A-A) through the oxide wiper-side front 46 of the mold 70. The recess 44 is located preferably in the horizontal plane through the concentric central axis of the oxide scraper lower part of the oxide scraper opening 42 and is arranged such that the opening cross section in this lower part of the oxide wiper opening 42, i.e. a segment of the hollow cylindrical oxide scraper opening 42 is enlarged. The Recess 44 on the oxide wiper-side front 46 of the mold 70 is in addition to an oxide wiper opening 42 with a m already with respect to the concentric central axis of the oxide scraper 30 attached asymmetrical opening cross section and thus enlarged the opening cross section in this partial area of the oxide wiper opening 42 or serves for better introduction of the oxide skin into the corresponding part of the oxide collection ring 40.

The plan view shown in section A-A on the oxide wiper-side front side 46 of FIG The casting mold 70 or the fixed mold half 50 in particular shows a preferred embodiment the recess 44 and their position with respect to the oxide wiper opening 42 and Inlet opening 52. The recess 44 shown in FIG. 3 along the section A-A relates a segment of the oxide wiper opening 42, which has a central angle of approx. 65 ° includes.

FIG. 4 shows a vertical longitudinal section through the concentric central axis m one the fixed mold half 50 of a mold 70 adjacent oxide scraper 30, the oxide collecting ring 40 three oxide collection ring chambers 40a, 40b, 40c and three associated therewith Has oxide scraper openings 42a, 42b, 42c, the oxide collection ring chambers 40a, 40b, 40c in terms of their capacity and the oxide wiper openings 42a, 42b, 42c are designed with respect to their opening cross-section such that they pressure which arises in the thixotropic alloy during the thixoforming process p an optimal, i.e. a continuous and even over the entire scope of the stripping of the oxide skin and the oxide skin near thixotropic alloy pulp Allow range of thixotropic metal alloy.

The oxide collecting ring chambers 40a, 40b, 40c are one below the other through an oxide wiper opening 42a, 42b, 42c connected, i.e. an oxide wiper opening 42a for connecting the Through opening 31 of the oxide scraper 30 with the oxide collection ring chamber 40 a, one Oxide scraper opening 42b for connecting the oxide collection ring chamber 40a to the oxide collection ring chamber 40b and an oxide wiper opening 42c for connecting the oxide collection ring chamber 40b with the oxide collection ring chamber 40c. The oxide wiper openings 42a, 42b and 42c are selected in such a way that they continuously remove what is to be stripped Allow materials during the three phases of the thixoforming process. Hence the annular oxide wiper openings 42a, 42b, 42c show one from the inside to the outside decreasing mean opening cross-section, i.e. the average opening cross section of the Oxide wiper opening 42a is larger than the average opening cross section of the oxide wiper opening 42b and the average opening cross section of the oxide wiper opening 42b is larger than the average opening cross section of the oxide wiper opening 42c. With a medium opening cross-section is the opening cross section averaged over the ring-shaped oxide wiper opening Understood.

FIG. 5 schematically shows a diagram of the pressure p which arises during the thixoforming process in the thixotropic metal alloy as a function of time t. In a first phase of the thixoforming process up to process time t ₁ , that is to say during the passage of the thixotropic alloy slurry through the pouring opening and during the filling of the large-volume regions of the mold cavity 68 adjacent to the pouring opening 52, only a slight pressure p ₁ builds up in the alloy slurry, so that - in order to allow the material to be stripped to pass through the oxide wiper opening 42a - the latter must have a large opening cross section. In a second phase of the thixoforming process in the time interval between the process times t ₁ and t ₂ , ie during the mold filling of the small-volume regions of the mold cavity 68, or in the mold cavity regions with a small cross-section, in particular in the edge regions of the mold cavity 68, the pressure increases p ₂ in the thixotropic alloy pulp usually abruptly, or the pressurization of the thixo bolt must be increased accordingly. Corresponding to the higher pressure, in order to achieve a continuous and uniform wiping behavior, the opening cross section of the oxide wiping opening 42b must be smaller than 42a. In a third phase of the thixoforming process in the time interval between the process times t ₂ and t ₃ , the pressurization of the thixo bolt is increased further to a pressure p ₃ , for example to fill areas of the mold cavity 68 with a very small cross section, which is a factor for the third phase compared to the opening cross section for the second phase further reduced opening cross section of the oxide wiper opening 42c. Thereafter, the pressurization is usually increased further in order to prevent the formation of, for example, microholes or pores during the solidification phase of the molded part. During the third phase of the thixoforming process, however, no further thixotropic material forming the molded part flows into the mold cavity 68, so that during this phase the oxide skin or region close to the thixotropic alloy no longer has to be stripped off.

Claims (23)

1. Process for the production of moulded parts from thixotropic metal bolts in horizontal die-casting machines, avoiding inclusions of the oxide skin surrounding the thixotropic metal bolt in the alloy structure of the moulded part, characterised in that the oxide skin surrounding the thixotropic metal bolt is stripped completely off the thixotropic metal bolt before the thixotropic metal alloy is introduced into the mould cavity (68) of the casting mould (70) and is collected in a container (40) the simultaneous stripping of oxide-free homogeneously thixotropic metal alloy being minimised by taking account of the thermal and mechanical properties of the thixotropic metal bolt asymmetrical with respect to the longitudinal axis of the metal bolt.
2. Process according to claim 1, characterised in that the part of the metal alloy originating from the region of the thixotropic metal bolt in the casting chamber (10) close to the bearing surfaces with the smaller liquid fraction as a result of the more intense cooling is also stripped off during the stripping of the oxide skin.
3. Process according to claim 1, characterised in that the thixotropic metal alloy is guided through an annular body arranged between the casting chamber (10) and the casting mould (70), i.e. the oxide stripper (30), the oxide skin of the thixotropic metal bold being led fluidically through a concentric annular opening formed in the oxide stripper (30), i.e. the oxide stripper opening (42), with an opening cross section asymmetrical with respect to the concentric centre axis (m) of the oxide stripper opening (42) into an annular container, i.e. the oxide collecting ring (40).
4. Process according to claim 3, characterised in that the opening cross section asymmetrical with respect to the concentric centre axis (m) is selected as a function of the viscosity properties of the thixotropic metal alloy asymmetrical with respect to this concentric centre axis (m) in such a manner that a layer of the oxide skin and of the region of the thixotropic metal alloy close to the oxide skin of radially uniform thickness is stripped off.
5. Process according to claim 3, characterised in that the part of the thixotropic metal alloy originating from the region of the metal bolt in the casting chamber (10) close to the bearing surfaces with a higher viscosity than the remainder of the thixotropic alloying slurry is also stripped off together with the oxide skin.
6. Process according to claim 1, characterised in that the oxide skin is stripped off continuously for the entire duration of the thixoforming process so that the quantity of material stripped off per unit of time is proportional to the rate of advance of the thixotropic metal bolt.
7. Horizontal die-casting machine for the production of moulded parts from thixotropic metal bolts, avoiding inclusions of the oxide skin surrounding the thixotropic metal bolt in the alloy structure of the moulded part, the horizontal die-casting machine comprising a horizontal casting chamber (10) with a cylindrical casting chamber cavity (11) for receiving a thixotropic metal bolt, a shield (20) with a shield opening (24) and a casting mould (70) with a filling hole (52) and a mould cavity (68), characterised in that an oxide stripper (30) is arranged between the casting chamber (10) and the casting mould (70), the oxide stripper (30) being an annular body with a horizontal concentric centre axis (m) and an outer surface and an inner surface (36) and the cross section through the inner surface (36) of the oxide stripper (30) perpendicular to the concentric centre axis (m) defining the through cross section of the oxide stripper (30), the oxide stripper (30) comprising an annular recess, i.e. the oxide collecting ring (40), which is connected via a concentric annular oxide stripper opening (42) to the through opening (31) of the oxide stripper (30) defined by the inner surface (36) and the end face (38) of the oxide stripper (30) at the casting chamber side and the end face (37) of the oxide stripper (30) at the mould side, the oxide stripper opening (42) having an opening cross section asymmetrical with respect to the concentric centre axis (m) of the oxide stripper (30).
8. Die-casting machine according to claim 7, characterised in that the concentric centre axis (m) of the oxide stripper (30) coincides with the concentric centre axis of the filling hole (52) of the casting mould (70) and the concentric longitudinal axis of the casting chamber cavity (11).
9. Die-casting machine according to claim 7, characterised in that the cross section of the though opening (31) corresponds to the cross section of the casting chamber opening (13) at the mould side.
10. Die-casting machine according to claim 7, characterised in that the annular oxide stripper opening (42) is formed by a recess on the oxide stripper (30) at the mould side.
11. Die-casting machine according to claim 7, characterised in that the lower part of the oxide stripper opening (42) with respect to a horizontal plane through the concentric centre axis (m) of the oxide stripper (30) has a larger opening cross section than in the upper part, at least in a partial region thereof.
12. Die-casting machine according to claim 7, characterised in that, in a longitudinal section of the oxide stripper (30) extending vertically through the concentric centre axis (m), the upper part of the oxide stripper opening (42) with respect to a horizontal plane through the concentric centre axis (m) displays a distance of 0.5 to 4 mm between the mould end of the inner surface (36) of the oxide stripper (30) and the end face (37) of the oxide stripper (30) at the mould side.
13. Die-casting machine according to claim 7, characterised in that, in a longitudinal section of the oxide stripper (30) extending vertically through the concentric centre axis (m), the lower part of the oxide stripper opening (42) with respect to a horizontal plane through the concentric centre axis (m) displays a distance of 1 to 10 mm between the mould end of the inner surface (36) of the oxide stripper (30) and the end face (37) of the oxide stripper (30) at the mould side.
14. Die-casting machine according to claim 10, characterised in that, in the case of an oxide stripper opening (42) situated on the end face (37) of the oxide stripper (30) at the mould side, a recess, i.e. the hollow (44), is provided on the front side (46) of the casting mould (70) at the oxide stripper side, the recess (44) being arranged in such a manner that the opening cross section is increased in the lower part of the oxide stripper opening (42) with respect to a horizontal plane through the concentric centre axis (m) of the oxide stripper (30), or a partial region thereof
15. Die-casting machine according to claim 14, characterised in that the hollow (44) is cylindrical, barrel-shaped or in the shape of a truncated pyramid.
16. Die-casting machine according to claim 14, characterised in that the hollow (44) has a maximum height of 10 to 40 mm and a maximum width of 20 to 80 mm in the vertical plane through the concentric centre axis (m) of the oxide stripper (30) and a maximum depth of 2 to 20 mm in the direction of the concentric centre axis (m).
17. Die-casting machine according to claim 7, characterised in that the capacity of the oxide collecting ring (40) is between 1 and 10 % by volume of the thixotropic metal bolt.
18. Die-casting machine according to claim 7, characterised in that the oxide collecting ring (40) consists of a plurality of annular cavities, i.e. the oxide collecting ring chambers (40a, 40b, 40c), with a common concentric centre axis (m) which corresponds to the concentric centre axis (m) of the oxide stripper (30), and the oxide collecting ring chambers (40a, 40b, 40c) are connected to one another and to respective annular oxide stripper openings (42a, 42b, 42c).
19. Die-casting machine according to claim 18, characterised in that the shape of the oxide collecting ring chambers (40a, 40b, 40c) and of the oxide stripper openings (42a, 42b, 42c) associated with the individual oxide collecting ring chambers (40a, 40b, 40c) is such that they allow for optimum stripping of the oxide skin and the region of the thixotropic metal alloy close to the oxide skin with respect to the respective pressure (p) produced in the thixotropic alloy during the thixoforming process.
20. Die-casting machine according to claim 19, characterised in that the oxide collecting ring (40) comprises 1 to 5 oxide collecting ring chambers (40a, 40b, 40c) and 1 to 5 annular oxide stripper openings (42a, 42b, 42c) connecting the latter.
21. Die-casting machine according to claim 7, characterised in that the lower part of the oxide collecting ring (40) with respect to a horizontal plane through the concentric centre axis (m) of the oxide stripper (30) has a larger cross section than in the upper part, at least in a partial region thereof
22. Die-casting machine according to claim 21, characterised in that a longitudinal section extending vertically through the concentric centre axis (m) of the oxide stripper (30) has a longitudinal sectional surface of the oxide collecting ring (40) one to three times larger in the lower half of the oxide stripper (30) with respect to a horizontal plane through the concentric centre axis (m) than in the upper half of the oxide stripper (30).
23. Die-casting machine according to claim 21, characterised in that a longitudinal section extending vertically through the concentric centre axis (m) of the oxide stripper (30) has a longitudinal sectional surface of the oxide collecting ring (40) 1.1 to 1.8 times larger in the lower half of the oxide stripper (30) with respect to a horizontal plane through the concentric centre axis (m) than in the upper half of the oxide stripper (30).

Images