EP1146978A1

EP1146978A1 - Method and device for the production of castings

Info

Publication number: EP1146978A1
Application number: EP00993169A
Authority: EP
Inventors: Christian Boehnke; Uwe Kühn
Original assignee: Ing Walter Hengst GmbH and Co KG
Current assignee: Ing Walter Hengst GmbH and Co KG
Priority date: 1999-11-24
Filing date: 2000-11-21
Publication date: 2001-10-24
Also published as: KR20010101651A; DE19956478A1; TW533104B; WO2001038023A1; JP2003514670A; DE19956478C2; BR0007680A

Abstract

The invention relates to a device and method for the production of castings, whereby the material is placed in a chamber with moveable walls under pressure, then, subsequently forced from the chamber and, finally, injected into a mould. The injector unit comprises a chamber with two moveable walls, which are optionally displaceable, either together in one direction, or counter to each other, in such a way that the inner volume of the chamber is optionally either adjustable and/or displaceable. Said unit may be controlled, such that the volume thereof corresponds as accurately as possible to the volume of material contained in the chamber.

Description

"Method and device for producing castings"

The invention relates to a method and to an apparatus for producing castings according to the preamble of claim 1 and claim 4, respectively.

Generic methods and devices are known from DE 43 10 755 A1 and DE 198 29 336 A1. The chambers each have a single piston, by means of which the material is injected into the casting mold. The chamber according to DE 43 10 755 A1 is evacuated at a comparatively high cost before it is filled with the material in order to avoid the penetration of an undesirable atmosphere.

From WO 98/33610, non-generic methods and devices are known, according to which semi-rigid, rod-shaped blanks are either forged or injected into a mold by means of a device not described in detail. From DE 35 00 561 A1 it is known to supply the material to be injected into the mold instead of with a piston device by means of a screw and also to build up the desired injection pressure by means of this screw.

It is also known to cast metal in a process similar to the injection molding process, magnesium being used here, for example. Since magnesium is a highly reactive material, the devices used for casting magnesium require complex measures in order to prevent the ambient air from entering the magnesium melt. For example, it is known to operate the casting device under protective gas in the area of the injection device in order to prevent the penetration of external ambient air and thus of oxygen when, for example, the casting mold is opened and air can get into the system.

The invention has for its object to improve a generic method in such a way that this enables the processing of material with simple means excluding the external ambient atmosphere. Furthermore, the invention is based on the object of specifying a suitable device for this.

This task is accomplished by a process with the characteristics of

Claim 1 and a device with the features of claim 4 solved.

In other words, the invention proposes to provide a shape-changing chamber from which the plasticized material can be injected directly into the casting mold or initially conveyed further indirectly and then injected into the casting mold from a separate injection unit. This variability in the shape of the chamber and the interior space that can be changed thereby, in particular the variable interior volume, makes it possible to to minimize the injection process, to the extent that material is conveyed out of the chamber or injected into the mold and consequently the filling volume of the chamber decreases.

In this way, a free chamber volume, which is not filled by the material and into which air could thus enter, is always kept to a minimum or avoided entirely, so that the penetration of the external atmosphere into the chamber can be avoided or considerably minimized. In this way, surrounding or evacuating the chamber or the entire injection unit with protective gas can either be avoided or the requirements for encapsulation of the chamber or the injection unit can be considerably reduced, so that the device, despite the movable chamber walls, simplifies the overall structure in a cost-effective manner become and can be designed cheaper.

In particular, it can be provided in a simple manner to use the variability of the chamber walls to build up the injection pressure, so that through this

Combination of functions, the device can be designed to be comparatively simple and inexpensive.

In terms of process engineering, there is the advantage that the injection pressure can be built up in the chamber when this is completed by the material supply due to the movement of the chamber wall. Elaborate check valves can be avoided and the pressure build-up within the chamber can be controlled much more precisely than using such check valves. B. the mobility of the

If the chamber wall is used to open and close the inlet opening at the same time, the inlet opening and the area of the material supply in front of it are decoupled from the actual injection process, so that pressure can build up in the chamber without backflow into the area of the material. supply can take place. The injection pressure curve can therefore be controlled precisely.

Poorly calculable reflux quantities that escape through a check valve until it is completely closed are excluded. The feed unit in the area of the material feed is not involved in the pressure build-up of the injection process and can accordingly be of a simpler design and easier to control, since it only has to feed the material into the chamber and accordingly essentially only monitors the feed pressure and possibly the temperature must become.

An additional translational, axial mobility in the conveyor unit, as is known in the case of rotary-driven screw conveyors for building up particularly high pressures or for faster injection processes, can be dispensed with, so that simplifications in the design area and with regard to the process control can be achieved.

The method according to the invention and the device designed accordingly are suitable, for example, for processing magnesium, but this invention can also be used advantageously for processing other materials, in particular if such materials are to be processed in a manner sealed from the external atmosphere. It can be metals, plastics or other materials, these already being supplied to the device in liquid or at least partially liquefied form, or the device can have its own plasticizing unit which is connected upstream of the injection unit and into which solid, e.g. B. granular, input material is entered.

The above-mentioned design simplification and also a simplification of the process sequence due to the mobility of the

Chamber walls for controlling the inlet and outlet openings the chamber, ie in order to determine the opening and closing times of these openings, can be achieved, for example, by looking at the inlet and outlet of the chamber in the direction of movement of the movable chamber walls, so that movement of the chamber walls can be used to control whether the Inlet or outlet or both openings should be opened or closed at the same time. Such a closure also further excludes the possibility of allowing the ambient atmosphere to enter the chamber, since not only that

Chamber content that is accessible for such an atmosphere is minimized, but the chamber can be closed properly.

In a comparatively simple manner, the one provided for this purpose can be used

Device have a tubular chamber, two opposite walls of this tube, for example the two end walls, being formed by the movable walls, these walls then being able to be driven together in the same direction or in opposite directions, in each case either at the same speed or at different speeds, to set the desired conditions inside the chamber.

The tube can advantageously be designed as a cylinder with a round cross section, so that a comparatively simple reliable sealing of the movable walls with respect to the tube wall can be achieved.

It can advantageously be provided in the conveyor unit to use a plurality of intermeshing screws, which can be driven in the same or in opposite directions. In this way, a more uniform, defined pressure can be built up and self-cleaning or forced delivery can be achieved. A screw can have different external geometries along its length in order to be able to process the material in correspondingly different ways during the material transport, for. B. to homogenize, mix, incorporate additives, shear or knead.

Further conveying units can be connected upstream of the chamber, which, if necessary, can be configured as mixing, conveying and heating units similarly to the above-mentioned heated screw. Through this several conveyor units can be different

Materials are introduced into the chamber: for example different materials or the same material with different temperatures. Through targeted distribution of the different materials within the chamber, workpieces can be produced that have zones of different properties, e.g. B. fiber or particle-reinforced zones in the area of threads or abrasively stressed areas, or zones with a sandwich-like structure of the workpiece can result.

A separate control of each individual conveying unit or conveying and heating unit advantageously enables the desired dosages to be changed flexibly. However, the opening and closing of these openings can also be controlled by arranging and designing the inlet or outlet openings opening into the chamber and depending on the movement of the movable walls, so that either a basically fixed dosage ratio can be set or the dosage ratio can be influenced by a different control of the wall movements or in that the openings z. B. are variable by sliders.

Several chambers can advantageously connect to the same mold. As a result, the aforementioned production of

Workpieces with zones with different properties possible due to different injected materials. Each of the chambers can either be designed to supply a single material or, as mentioned, several different materials.

In particular, an additional feed unit for admixing z. B. granular or powdery particles or fibers. As granular or powdery particles such. B. SiC, Al ₂ O ₃ - or carbon particles can be provided. The particles or fibers can be added by adding them directly and unmixed to the chamber. However, the addition advantageously takes place in that the basic material of the material is also supplied in this additional feed unit, for. B. plastic or light metal, but enriched with particles or fibers, so that the desired distribution of particles or fibers can be achieved and at the same time the desired composite material of the base material can be ensured in the workpiece to be produced. In particular, it can be provided that the particles or fibers are homogeneously mixed with the base material at an external point before entering the chamber and possibly even before entering the feed unit, for. B. by inductive or mechanical stirring.

For the purposes of the present invention, “several”, for example based on the number of screws, conveyor units or chambers used, always means “at least two”. In addition to the screw conveyor units mentioned, other types of conveyor units can also be used.

An embodiment of the invention is explained in more detail with reference to the drawings. The show

1 to 4 in a purely schematic representation a section through the injection unit and through the adjacent bartender assemblies of a casting machine in different stages of a casting process.

In Fig. 1, 1 generally designates a device for the production of castings from scatterable, for. B. granular, raw material is used. In particular, it can be provided to process magnesium granules in a process similar to die casting or injection molding.

In particular, an injection unit 2 is shown. The

Injection unit 2 is supplied with the plasticized, that is to say flowable, material by a plasticizing unit 3. The plasticizing unit 3 is provided with a screw which, on the one hand, heats the primary material by friction. In addition, the plasticizing unit 3 is heated to allow further heating of the primary material, and finally the screw also conveys the heated and flowable material through an inlet 4 into the injection unit 2.

The plasticizing unit 3 thus initially represents a conveyor unit. Since granular starting material is used, the plasticizing unit 3 not only serves to transport this material, but also to soften or plasticize it. When using already liquid or pulpy primary material, the plasticizing unit 3, on the other hand, can be designed exclusively as a conveying unit, possibly with an additional mixing or homogenizing function, but without the task of softening or plasticizing the material.

The material is then injected from the injection unit 2 through an outlet 5 into a casting mold 6 which is also only indicated schematically. The casting mold 6 can be cooled in order to enable rapid solidification and thus rapid removal of the casting from the casting mold 6. The injection unit 2 has a chamber 7 which can be filled or emptied through the inlet 4 and the outlet 5. The walls of chamber 7 are formed on the one hand by a cylindrical tube 8 and on the other hand by two movable walls 9 and 10, so that a cylindrical chamber 7 with movable end walls is created overall.

The movable walls 9 and 10 can also be used as pistons

9 and 10 are referred to in analogy to the conditions in internal combustion engines, pumps or compressors and are accordingly actuating rods with which the pistons 9 and

10 can be moved, referred to as connecting rods 11 and 12. These connecting rods 11 and 12 can be firmly connected to the pistons 9 and 10, e.g. B. if they are only moved axially and are moved back and forth hydraulically, for example.

However, there may also be an articulated connection of the connecting rods 11 and 12 to the pistons 9 and 10, e.g. B. if the connecting rods 11 and 12 are mechanically driven by means of cranks, cams or the like and should be deflected from their axially aligned arrangements shown in FIG. 1 and angled relative to the walls or pistons 9 and 10.

Fig. 1 shows the beginning of a filling process for the chamber 7: From the plasticizing unit 3, the screw conveys the material that has become fluid into the inlet 4. Due to the correspondingly raised position of the upper piston 9 and the correspondingly lowered position of the lower piston 10, the inlet is 4 open to the chamber 7 so that the material can get into the chamber 7. First - as indicated by the vertical arrow - only the piston 9 is further raised with the aid of the connecting rod 11 in order to increase the volume of the chamber 7 so that it can hold an increasing amount of material. During this filling process, the lower piston 10, supported by the connecting rod 12, remains in a position in which it closes the outlet 5. Fig. 2 shows the beginning of the casting process: The lower piston 10 is pulled down by the connecting rod 12 and releases the outlet 5. The upper piston 9 is moved in the same direction, so that material already flows through the outlet 5 into the mold 6 due to the pressure prevailing within the chamber 7. Due to the filling pressure prevailing in the chamber 7, this also applies when the two pistons 9 and 10 are moved at the same speed, ie the chamber 7 with the same volume is only displaced. By moving the upper piston 9 faster than the lower piston 10, but in the same direction, the chamber volume can be reduced and thus the pressure within the chamber 7 can be increased or the pressure which initially drops due to the material outlet can be maintained in favor of a faster casting process ,

The movement of the pistons 9 and 10 can advantageously be controlled during this phase so that the pressure in the chamber 7 does not exceed the filling pressure, that is to say the pressure in the region of the plasticizing unit 3, so that a backflow of the material from the chamber 7 through the inlet 4 is avoided without having to provide check valves or the like.

Fig. 3 shows a second phase of the casting process, in which the upper piston 9 closes the inlet 4. Now the relative speed between the lower piston 10 and the upper piston 9 can be increased, so that pressures can be built up inside the chamber 7 which are higher than the pressure inside the plasticizing unit 3. For this purpose, the lower piston 10 can be stopped completely or even in opposite directions can be moved towards the upper piston, or the speed of the upper piston 9 can be increased. Because the inlet 4 is closed, a backflow of the material from the chamber 7 into the plasticizing unit 3 is excluded. In Fig. 3 it is also shown that the screw of the plasticizing unit 3 is withdrawn from the inlet 4, so that it can initially convey material to the inlet 4 solely on account of its rotary movement and later translationally in order to refill the chamber 7 in addition to this rotary conveying movement can be moved in the direction of the inlet 4 in order to enable the chamber 7 to be filled particularly quickly. However, for reasons of a simplified construction, it can also be provided that the screw is driven exclusively in rotation, since it is not involved in the pressure build-up in the chamber 7 during the casting process anyway.

In Fig. 4 it is shown after the casting process that the lower piston 10 completely up to the upper end of the

Tube 8 is raised, so that a remaining in the injection unit 2 pouring residue laterally from the injection unit 2 through a corresponding recess 14, which is provided in a machine plate 15, can be ejected. For this purpose, the upper piston 9 is pulled up as far as possible in accordance with the arrow indicated on the piston 9 in order to enable a correspondingly wide ejection opening for the chamber 7.

Following this ejection position shown in FIG. 4, the upper piston 9 is moved as close as possible to the lower piston 10, so that the chamber contents 7 are minimized or brought to zero, so that accordingly no air from the external atmosphere between the two pistons 9 and 10 can get. The two pistons are then moved down together and brought into the position shown in FIG. 1, in which a new working cycle of the injection unit 2 can then begin.

Alternatively, it can be provided the recess 14 and an adjoining receiving space for the pouring residue can be ejected through the recess 14 to seal against the external atmosphere, for example in the form of a closed container which receives the pouring residues and only has to be emptied in comparatively larger periods of time, or it can be provided to the recess 14 by a protective gas from the external atmosphere to have the shielded area connected, so that even if the two pistons 9 and 10 cannot be moved against one another down into the tube 8, the penetration of the outside atmosphere into the chamber 7 is avoided.

Compared to the initially described procedure, in which the pistons 9 and 10 are moved down as close to each other as possible in order to create a minimal or no longer existing chamber cavity, these alternatives are more complex, but they nevertheless enable the injection unit to be designed in a considerably simple manner 2, as if it had to be completely shielded from the outside atmosphere.

Claims

claims:

1. A process for producing castings from a flowable or scatterable primary material which is first heated and at least partially plasticized, and the at least partially plasticized material is pressurized in a chamber, then conveyed out of the chamber and finally into one Injection mold is injected, the material being pressurized in a chamber with movable walls, and wherein the volume of the interior of the chamber is changed by the movements of the walls such that the volume of the chamber during the supply of material through the Inlet into the chamber is enlarged and reduced during the casting process, characterized in that this volume is as close as possible to that in the chamber

(7) contained volume of the material, such that the contents of the chamber (7) is set to approximately zero when there is no melt in the chamber (7), as before filling the chamber (7) or after the injection process ,

2. The method according to claim 1, characterized in that the walls (9, 10) at the inlet (4) and the outlet (5) are moved past such that by the movement of the walls (9, 10) the opening and closing times of the inlet (4) and the outlet (5) can be controlled.

3. The method according to claim 1 or 2, characterized in that the material is fed to the chamber (7) by means of a conveyor unit having a screw, the screw being driven exclusively by rotation becomes.

4. Device for producing castings from a flowable or scatterable primary material, with an injection unit, from which the at least partially liquefied material can be injected into a mold, the injection unit having an inlet opening for supplying the material and an outlet opening leading to the mold, wherein the injection unit has a chamber with a movable wall which is movable, such that the interior of the chamber is variable in volume, characterized in that the chamber (7) of the injection unit (2) has two movable walls (9, 10), which can either be moved jointly in one direction or can be moved in opposite directions to one another, such that the interior of the chamber (7) can optionally be changed in volume and / or is displaceable, the interior of the chamber (7) being able to be reduced to approximately zero.

5. The device according to claim 4, characterized in that the inlet (4) and the outlet (5) in the direction of movement of the movable walls (9, 10) are arranged spaced one behind the other.

6. The device according to claim 4 or 5, characterized in that the movable walls (9, 10) as two opposite pistons of an otherwise tubular

Chamber (7) are formed.

7. The device according to claim 6, characterized in that the interior of the chamber (7) has a round cross-section.

8. Device according to one of claims 4 to 7, characterized in that the injection unit (2) is a plasticizing unit (3) serving for at least partial liquefaction of the primary material upstream.

9. The device according to claim 8, characterized in that the plasticizing unit (3) is designed as a heated screw-melting unit.

10. The device according to claim 9, characterized in that the plasticizing unit (3) has two intermeshing screws.

11. The device according to claim 9 or 10, characterized in that the screw can only be driven in rotation.

12. The device according to one of claims 4 to 11, characterized in that the chamber (7) upstream of two or more conveyor units which are connected to the chamber (7).

13. Device according to one of claims 4 to 12, characterized in that several chambers connect to a casting mold.