The invention relates to a method for producing molded bodies from a silicon alloy, comprising the production of plates and the water jet cutting of the plates to form a plurality of molded bodies. The thus obtained molded bodies contain in particular additional inoculant additives and are used in particular as inoculant for metal casting.
Inoculating a molten metal is understood to be the addition of solid substances in the form of an inoculant, in particular with the aim of influencing the solidified casting with regard to its metallurgical structure and, thus, its mechanical and thermal properties during the transition from the molten metal into the casting.
Cast iron is an iron-carbon alloy which is frequently utilized for producing castings. Cast iron is obtained by mixing the desired constituents in the liquid state at a temperature between 1260 and 1450° C. prior to the casting, whereupon the mixture is cast into a casting mold and solidified in the desired shape by cooling the cast iron.
One of the constituents of cast iron besides iron is carbon. Cast iron is an iron-carbon alloy with a carbon content higher than 2.06 wt %. When it cools down, the carbon in the cast iron can take on multiple physico-chemical structures. The carbon forms differently shaped graphite phases within the alloy. EN 1560 differentiates between four types of cast iron, depending on the graphite geometry:
The abbreviation GJS stands for G=cast iron, J=iron, S=spherical. If carbon is associated with iron and forms iron carbide Fe3C (also called cementite), the resulting cast iron is referred to as white cast iron. White cast iron has the property of being hard and brittle, which is undesirable for many applications.
When carbon occurs in the form of graphite, the resulting cast iron is called gray cast iron or spheroidal graphite cast iron. Both types of cast iron, namely white cast iron and gray cast iron (as well as transitional or intermediate forms of these such as, e.g., graphite), have special properties, are softer and can be processed. It is therefore desirable to influence the cooling process in such a way that carbon develops in the form of graphite in the cooled melt.
In order to obtain castings with good mechanical and/or thermal properties, it is advantageous to obtain a cast iron that contains a maximum of carbon in the form of graphite and to limit the formation of the precipitation-hardening iron carbides as much as possible. In the absence of inoculants, however, carbon has a tendency to order iron in such a way that iron carbide is created. It is therefore necessary to treat the molten cast iron with an inoculant in the liquid state before it solidifies in order to modify the association parameters of carbon and to obtain the desired structure. For this purpose, the liquid cast iron is subjected to an inoculation treatment, the aim of which is to introduce graphitizing components or graphitization carriers into the cast iron, which are also referred to generally as nuclei and which, when the cast iron cools in the casting mold, encourage the appearance of graphite and reduce the tendency to form iron carbide.
In general, the constituents of an inoculant for obtaining gray cast iron therefore consist of elements that promote the formation of graphite and the decomposition of iron carbide or prevent the formation during the solidification of the cast iron. Depending on the required properties, it may additionally be desirable to not only repress the formation of iron carbide (cementite) by the inoculant in favor of lamellar graphite (=gray cast iron) or nodular graphite (=spheroidal graphite), but also to deliberately form vermicular graphite. Each of the possible graphite forms can be promoted by a special inoculation treatment of the cast iron by means of specific components.
Thus, the formation of nodular graphite (GJS) can be encouraged, for example, by adding a sufficient quantity of magnesium to the cast iron so that the carbon can grow in such a way that round particles (spheroids or nodules) are formed. These nodular graphite components are generally added to the cast iron in the form of a special alloy (nodular graphite alloy). Consequently, the nodular graphite alloy makes it possible to influence the shape of the graphite nodules, while the inoculant product increases the number of these nodules and is intended to homogenize the graphitic structures.
Another type of treatment is the addition of desulphurization products or products that allow specific treatment of some defects in the cast iron, depending on the initial composition of the liquid cast iron bath, such as micro-shrinkages and pinholes, in order to avoid such defects occurring during cooling. A suitable compound for this is, e.g., calcium carbide.
As regards bismuth, it is known that the latter accelerates the decanting of magnesium into cast iron and that, as a result, it loses more active magnesium which is used to convert lamellar graphite into nodular graphite.
The inoculation can be carried out once or multiple times and at different times during the production of the cast iron.
Many known inoculants comprise a ferrosilicon base alloy such as, e.g., FeSi60, FeSi65 or FeSi75 containing iron with a silicon proportion of 40, 65 or 75 wt % in addition to other metals, compounds or elements such as those mentioned above as alloying constituents, wherein the chemistry or the selection of the inoculant additives and the ratio thereof is/are adjusted in accordance with the striven-for properties of the inoculant.
It is also possible to add multiple inoculants in the form of alloys having different compositions or ferrosilicon alloys in lumpy form to molten iron in order to produce the desired doping.
To date, the known process has been to add inoculants as granular material, as a cast molded body, as powders in a cored wire, as fragments or as a pressed part obtained from a powdery or granular material and a binding agent.
The object of the present invention is to provide a new production route for molded bodies in the form of an alloy which is simple, allows lumpy production with a low volume or weight tolerance, minimizes rejects during production and avoids the formation of dusts and the use of binding agents. Furthermore, it must be guaranteed that the molded body can be gripped by a robot arm.
The molded bodies should have a lumpy form, wherein similar molds weigh approximately the same and thus allow the addition as inoculant additives in portions in a defined quantity. It should also be possible to assemble the suitable quantity of inoculant additives by assembling the quantity, with the aid of a modular system, from different numbers of and/or different sizes of molded bodies, approximately comparable to a set of suitable weights for a scale.
An additional object of the invention is to increase the molded body yield of the pre-alloy.
The invention is defined by the subject-matter of the independent claims; advantageous embodiments are the subject-matter of the subclaims or are described below.
The invention relates to a method for producing molded bodies, comprising the production of a plate, e.g., by casting a melt in the form of plates, and the water jet cutting of the plates to form molded bodies of defined volume, wherein the plates are cut into the molded bodies by water jet cutting, utilizing an abrasive agent.
The top surfaces and the bottom surface of the molded bodies are defined by the upper side of the plate, and the side faces of the molded bodies are at least defined in part by the water jet cutting.
Suitable methods for producing plates are
The plates have two plane-parallel surfaces. Otherwise, the plate can in principle be expanded as desired. In terms of handleability and stability, plates of, e.g., 10 to 40 cm in width and 20 to 60 cm in height are very suitable. The thickness should not exceed 8 cm because of the better cutting ability and should not be less than 10 mm because of the ease of handling, plate thicknesses of 16 mm to 50 mm are preferred. 3 to 12 molded bodies per row are preferably produced from the plates by water jet cutting.
The plates predominantly comprise silicon alloys, i.e., the plates are greater than 50 wt %, in particular greater than 80 wt %, or even greater than 90 wt %:
Then, the aforementioned combinations of metals each make up at least 50 wt %, preferably at least 80 wt % and, in particular, 90 wt % of the plate.
Plates or molded bodies made from the following silicon alloys are particularly suitable:
Further possible additional ingredients of the above plates are, e.g., manganese, barium, cerium, lanthanum, bismuth, zirconium, antimony, strontium or additional elements or a combination thereof, or the following metals: aluminum, calcium, iron, magnesium, titanium and/or chromium if they have not yet been listed above in each case.
The molded bodies are the inoculant. Essential constituents of the inoculant are silicon, calcium, manganese and aluminum and, optionally, the following metals: barium, cerium and lanthanum, bismuth, titanium, zirconium, antimony, strontium or additional elements or a combination thereof.
The composition of the plate corresponds to the composition of the inoculant or the molded body. The molded body is used as an inoculant.
The inoculant contains in particular at least the following constituents as inoculant additives:
The above details refer to 100 wt %=total of all metals (including semimetals such as Si) calculated as an element. Carbon or oxygen is, e.g., not included.
A typical inoculant consists, e.g., of the following main constituents (total=100 wt %.)
When the elements or metals or additional elements are talked about here, this includes compounds which contain these metals or elements. The use of metals or alloys is preferred.
The inoculant is typically added in quantities of 0.05 to 0.8 wt %, in particular 0.08 to 0.3 wt % of the molten metal/molten cast iron, based on the molten metal/molten cast iron.
The inoculants are used during metal casting production, in particular for producing cast iron, and are added to the melt, in particular:
The use for gray cast iron is preferred.
In order to produce the molded body, the procedure is usually that a melt (a) to (e) is first produced. The melt usually has a temperature of 1350 to 1700° C. The inoculant additives or molded bodies are mixed into the melt, e.g., by pouring the melt into a ladle and the inoculant additives are added by being stirred or poured in, in order to obtain a mixed melt. The mixed melt has, e.g., a temperature of 1300 to 1550° C.
Plates are cast from the mixed melt, wherein the corresponding molds, usually cast-iron molds which represent the negative shape of the plate, have upright cavities for the respective plates, are in particular arranged perpendicular with respect to the primary plane of the plate and have a size of, e.g., 10 to 40 cm in width, 20 to 60 cm in height, in particular 22.5 cm. The plates have, e.g., a thickness of 10 to 80 mm, in particular they are plates of different thicknesses from 10 mm to 80 mm, in particular from 16 mm to 50 mm. For example, 6 plates of different thicknesses are produced in one casting run. The plates preferably stand upright in order to be sufficiently compressed by the metallostatic pressure. This makes it easier to produce plates of uniform thickness and homogeneity. The plates are poured directly out of the ladle or via a pouring basin having multiple holes, e.g., 3 holes per row. It is advantageous if the plates cool down slowly.
The cast-iron mold is preferably constructed from steel plates ST37 or from gray cast iron GG25, which are finished and assembled in such a way that a cast-iron mold forms multiple plate-shaped cavities. The coatings are characterized by the fact that they build up a protective layer that is heat-resistant up to 1400° C. on the surface of the cast-iron mold and, consequently, protects the cast-iron molds. For example, water-based zirconium silicate coatings are used. A commercial product suitable for this is, e.g., the Solitech WP 601 coating made by ASK Chemicals GmbH, Hilden.
The cast-iron mold is opened after the plates have cooled down by folding back the front side wall (transverse side wall) together with the partitions downwards. A hinge is provided for this purpose at the bottom of the front side wall. The plates can now be extracted. Multiple cast-iron molds (cast basket strainers) are welded on a traveling pallet. The traveling pallet is used to move the cast basket strainers together with the plates and for stacking and storing. The cast basket strainers are preferably only opened when the plates are fed to the next processing step. This is the water jet cutting.
The material removal during water jet cutting is based on the high pressure caused by the jet on the surface of the workpiece. The water jet, which contains an abrasive agent, detaches microscopic particles near the surface. No expansions of the workpiece therefore occur due to heat or processing forces. The water flowing off transversely from the point of action also causes shearing forces which likewise contribute to the material removal. The water jet cutting can be performed with multiple cutting heads at the same time.
In order to generate an abrasive water jet from the pure water jet, an abrasive agent is added in the cutting head, in an additional mixing chamber. Garnet or olivine sand, sometimes also corundum or metal silicides, is/are mostly used as the abrasive agent. The high jet speed creates a negative pressure in the cutting head, as a result of which the abrasive agent is sucked into the mixing chamber and mixed with the water. The mixture is focused and accelerated through the abrasive nozzle. The jet diameter is roughly 0.2 mm larger than during pure water cutting. It was found that the cutting ability increases with the hardness of the abrasive agent utilized.
During water jet cutting, the plate is separated by a high-pressure water jet with the addition of abrasive agent such as sharp-edged cutting sand. This jet generates, e.g., a pressure of, e.g., 4500 to 6000 bar on the workpiece surface and reaches exit speeds of, e.g., up to 1000 m/s. The cutting product barely warms up.
Garnet or olivine sand, for example, is used as an abrasive agent. The abrasive agent preferably meets the following specification (in each case independently of one another):
It is surprising that something which itself has a hardness of around 9.5 according to Mohs can be effectively cut by garnet sand in the water jet. The water pressure is in particular 4500-6500 bar. Surprisingly, the hydrogen evolution during water jet cutting is very low. The water jet cutting machine can be, e.g., a STM 2020 PremiumCut)(2×TAC-12°.
The molded bodies are preferably cut conically so that truncated cones or truncated pyramids are produced, but the base (top and bottom surface) can be almost any shape; the main point is that side surfaces run together conically. In particular, the bevel cut for forming the conical shape is approximately from 2° to 15° and, in particular, 6° to 12°. Due to the conical shape, the molded bodies remain in the plate. The possibility of swiveling the cutting head (3-D processing) means that even complicated shapes can be cut in the space by means of a cutting vector control. According to an embodiment, the cutting line has a thickness of 1.5 mm.
A water jet cutting machine consists of various components that can be combined in different ways. Usually, components include: storage, high-pressure piping, CNC-controlled guide machine, pressure intensifier, oil tank, oil pump, electric motor, valve and nozzle.
The machine frame, which is mostly erected from tubular steel of different formats, carries the individual axes of the machine. The standard design for water jet cutting is the so-called portal design as a flat bed. In the case of portal machines, the two guide axes travel in a so-called gantry network and are consequently coupled via the CNC control (two axes behave like a single axle). In addition to the portal, there is also the design variant as a support arm, in which the crossbeam is only guided on one side.
The residual energy of the water jet that remains after the cutting work has been performed can be dissipated in various ways. A water tank which acts as a “jet catcher” is preferably deployed. The water tank should usually have a sufficient water column of, e.g., more than 600 mm so that the residual energy of the water jet can be converted into heat.
According to an embodiment, high-pressure pumps that utilize a hydraulic unit are used in water jet cutting.
The cutting water mixed with abrasives is removed from the jet catcher, and the recyclable materials can be returned to the electric low-shaft furnace. It is also possible to recondition the abrasives. This is done either continuously through disposal or manually at intervals. The continuous disposal consists either of a scraper conveyor which removes the cutting agent residues from the jet destroyer, or of a water circulation which separates the residues from the jet destroyer. The water from the jet destroyer is then filtered and fed back into the cutting basin.
Water jet cutting systems are consistently equipped with CNC controls. In addition to the simplest designs that only allow a plotter control, higher-quality machines have controls which can both interpolate all axes and perform an adaptive feed rate reduction depending on the cutting process. In addition to a CAD interface, there is often also a CAM connection.
In a water jet machine having a flat-bed design, an arm moves over the portal surface with the plates positioned thereon so that the plates that have already been trimmed can be removed before the arm is retracted and new plates are positioned thereon. Since the plates have a standard dimension, they can easily be positioned, for example against a stop that fixes two sides that are at right angles to one another. Then the cutting heads can already cut the newly positioned plates when they move back. The plates are preferably positioned on the other side of the cutting areas in the water bed.
According to an embodiment, the cutting head travels along a wavy line on the way out and a wavy line on the way back so that the waves supplement one another to form circles or rectangles, with the result that the time-consuming cutting into the material is minimized.
Due to the conical shape, the molded bodies can be deposited particularly well in that the plate is rotated while a storage plate, which may already have corresponding indentations, is positioned on the plate. According to another variant, a bed of nails is arranged under the plate, which is raised so that the molded bodies are pushed out of the plate and a receiving device slides in laterally between the molded bodies, wherein the molded bodies are held in the receiving device thanks to their conical shape.
To allow the molded bodies to be gripped by robots, it is expedient to pack them in an orderly manner, for example in a box in which one cardboard box is inserted for each layer of molded bodies, which is punched out as an intermediate layer and fixes the molded bodies to prevent lateral displacement. The punching is preferably the size of the smaller end surface, so that the latter encompasses the upper molding body relatively far down, but cannot slide over the next molding body having the larger end surface at the top.
Compared to conventional production, according to which the molded bodies are cast individually in the cast-iron molds and then mechanically broken along the casting connections, the method according to the invention has far fewer rejects. The rejects are usually melted or pulverized again and sold as granular material. According to the conventional method, all the molded bodies were weighed and those outside the target weight range were eliminated.
According to the new method, the tolerance is less than 5 wt %, based on the basic weight of the molding body, so that it is possible to dispense with the process of weighing each molding body for quality control.
Compared to existing techniques, the yield is significantly higher because no individual shapes are cast, but rather only plates. The plates can be cast at a significantly higher flow rate and a lower temperature. For conventional production, following which the molded bodies are in each case already in the desired shape as a result of casting or of compressing dusts with binding agents in a mold, there is no need at all for subsequent shaping.
This significantly increases the yield during casting compared with casting of the molded bodies themselves. A low temperature reduces the wear and tear on the cast-iron molds for the shapes. Due to higher yields, the method lowers the furnace production times, which is sensible from an energy point of view.
Cutting the molded bodies from plates results in a significantly higher exposed contact surface of the molded bodies without a casting skin for the cast melt than existing pressed parts or cast molded bodies in the current prior art. This makes it easier to distribute the inoculant metals of the molded body in the molten metal.
The invention is further explained by the following figures, without being restricted thereto, wherein:
The cast basket strainers 2 are each folded-out in
When the longitudinal walls 5 are erected vertically again, opposite longitudinal walls 5 are each fixed vertically by means of a quick-release connector 11. To this end, the quick-release connector 11 is folded down and engages in a snap-in hook 12 on the opposite longitudinal wall 5. The partitions 8 and the plate walls 10 can now be slid in.
The partitions 8 each bridge opposing longitudinal walls 5 of the cast basket strainer 2, are built into the cast basket strainer 2 in the transverse direction such that they can be extracted upwardly or laterally, and embody the plane-parallel side surfaces of the respective plate. The plate wall 10 defines the end of the plate on the narrow longitudinal side. The plate wall 10 runs parallel to the longitudinal axis of the traveling plate 3 in each case. A cluster 13 for producing the respective plate is embodied between two opposing partitions 8 and two opposing plate walls 10. The partitions 8 are selected to be different in terms of thickness depending on the thickness of the plates to be cast, e.g., 10 mm to 30 mm.
Each cast basket strainer 2 has two longitudinal walls 5. All of the longitudinal walls 5 are foldable. After opening one or the second longitudinal wall 5, the partition 8 can be removed. The partition 8 can be pulled laterally or upwards. The partitions 8 can be removed by hand or robot operation. To this end, eyelets 9 are provided in the partition 8, with which said partition is easier to handle. After removing the partition 8, the plate can be removed.
The casting pallets 1 can also be utilized as a store for the plates, because they are stackable. The cast pallets 1 can be conveyed by means of a forklift or a crane.
Each cast basket strainer 2 can have, e.g., 2 to 5 cavities 13. The plates each have a cast basket strainer 2 of approximately the same width (from one plate wall 10 to the opposite plate wall 10) and heights/lengths (from the upper edge of the partition 8 to the lower one), but plates of different thicknesses are preferably produced in a cast basket strainer 2 at the same time. The height resulting from the vertical alignment of the cavities 13 results in each case in a metallostatic pressure which has a positive effect during casting. The casting process is also faster as a result.
The different casting components such as the longitudinal wall 5, partition 9, plate wall 10 can each be exchanged/replaced with one another. The casting components are fabricated, e.g., from GJS. All casting components can be finished.
It is possible to pour into the cavities via casting basins 14 or directly from the casting ladle into the plate slot opening. A casting basin 14 is shown in
Number | Date | Country | Kind |
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10 2019 116 828.7 | Jun 2019 | DE | national |
10 2019 131 210.8 | Nov 2019 | DE | national |
Filing Document | Filing Date | Country | Kind |
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PCT/DE2020/100525 | 6/19/2020 | WO |