US20080302503A1

US20080302503A1 - Method for Adaptively Controlling Processes for the Production of Cast Iron

Info

Publication number: US20080302503A1
Application number: US12/096,640
Authority: US
Inventors: Manfred Fengler
Original assignee: Daimler AG
Current assignee: Mercedes Benz Group AG
Priority date: 2005-12-08
Filing date: 2006-12-06
Publication date: 2008-12-11
Also published as: WO2007065651A1; DE102005058532A1; DE102005058532B4; EP1957219B8; EP1957219A1; EP1957219B1; DE502006007242D1

Abstract

The aim of the invention is to be able to produce directly cast GGV and GGG melts in a single-stage process, simultaneously determine the physical and mechanical parameters such as the strength index and the pipe index by means of a thermal analysis and a mathematical evaluation model, continuously compare the process data to the target data with the aid of the process control computer, optimally determine the amounts to be added, and introduce the determined amount into the melt.

Description

The invention concerns a process for the adaptive control of the process of manufacturing cast iron, in particular GJV and GJS, and for computing the amounts of additives for the melt, in particular the iron melt, into which an alloy or alloying compound is to be introduced, which contains as treatment agents at least magnesium and an additional metal as well as a nucleating agent.
It is already known (DE19916234C2), to use a filled wire (wire injection) for treatment of melts, in particular of iron or steel by means of wire injections. The filled wire is comprised of an outer metal sheath and a filler material, wherein the filler material includes at least a first powder or granular treatment agent and a second treatment agent. In order to produce the filled wire, in which an even distribution of the treatments agents is to be ensured over the length of the filled wire in every case, and a separation is to be reliably prevented, it is provided in accordance with the invention, that the second treatment agent is provided in the form of at least one massive internal wire of a solid material. In one illustrative embodiment, the sheath is comprised of steel. The sheath could however also be comprised of other materials, in particular copper or aluminum, and thus could also be comprised of the material of the melt to be treated. The first or second treatment agent and/or the sheathing may comprise calcium, lead, sulfur, tellurium, boron, carbon, chrome, manganese, silicon, niobium, titanium, vanadium, iron or zirconium and/or alloys of these elements and/or compounds with other elements. In the known processes, two stage treatment methods and thus very long process times are required to make the corrections associated therewith, since the treatment of the metal melt, referred to in the following as the melt, is basically prepared in advance and the treatment of the melt occurs in the transport vessel and then with the aid of the wire injection in the casting oven. Further, there are high losses in efficiency in the automated standard equipment. Further, corrections are necessary in this two-step very long manufacturing process, and thus also the temperature losses and the expenditure of treatment agents is very high.
The invention is concerned with the task of providing a directly castable GJV- and GJS-melt in a single stage process and for this to optimally adjust the physical parameters and the pipe index of the cast parts within the predetermined process limitations, wherein the condition of the iron is continuously evaluated and the exact amounts of additive are automatically calculated, in order to introduce the computed amount into the melt.
The task is solved in accordance with the invention by (1) the following processes steps:
1.1 First the weight of the total melt and the amount of the base iron to be added are determined,
1.2 Thereafter the condition of the melt is determined with the aid of thermal and chemical analysis and the expected physical, mechanical properties, the strength index and pipe index are computed,
1.3 Subsequently the amount of the forming agents, the treatment agents, the seed or nucleus forming agents, the alloying agents, the decoking agents and the coating agents to be introduced into the melt are computed,
1.4 The forming or activation agents, together with the upper and the lower separating materials, are introduced into the melt, between the melt of a casting oven and the still untreated, to be introduced melt, at least in a runner or sprue or ingate of the casting oven or in the form of a wire injection.
Thereby an optimization of the physical characteristics of the cast part and a clear and significant reduction in tendency towards shrinkage is achieved. The process times and the process costs are thereby significantly reduced. The optimal determination of the treatment agents leads also to a very high utilization of the magnesium in the iron.
For this it is advantageous that (2) after each filling of the oven a thermal analysis of the melt is carried out during the casting, and the therefrom resulting process data serve for determining the forming agents which can be made available for the immediately subsequent oven filling.
It is also advantageous, that (3) the total weight of the melt in a cast oven (1) and/or in a transport vessel is determined and the melt is analyzed with the aid of a thermal measurement procedure.
It is also advantageous, that (4) during and/or after the casting process the instantaneous or actual process data are compared with the target data or with target data stored in a memory or computer and continuously are adapted or readjusted and thereafter the forming agents are determined.
For this it is advantageous, that (5) in the determination of the process data at least the physical, mechanical and chemical characteristic values and/or the determination of the characteristic value the strength index and the shrinkage index or pipe index occur with the aid of the determination of individual cooling temperature curves of the melt.
It is advantageous, that the thermal analysis occurs in one or more separate and closed off or compartmentalized crucibles of the measuring station and in the case of multiple crucibles each crucible can contain a different type of material such as for example nucleating material.
Further it is advantageous, that (8) during the determination of the process data, the melt to be cast into a form and the addition of the new melt in the cast oven occurs continuously. Thereby the overall processing time can be reduced.
It is also advantageous therein, that (9) the determined process data from the analysis of the melt, continuously supported by the computer, are compared with the target data, adapted and used for determination of the amounts of forming agents to be subsequently added.
It is of particular significance for the present invention, that (10) for forming the separation layer between the melts in the casting or die-casting oven and the still untreated melt to be influenced at least in one down-sprue or runner first the nucleating or seed agents involved in the process and lastly the process-neutral separating or insulating materials are added in.
Thereby it is possible to produce a directly castable GJV- or as the case may be GJS-melt in a casting oven. The process can be very rapidly carried out since the process steps which had until now been necessary can be dispensed with. By the advantageous selection and the type and manner of the input of the alloying components into the melt a high process reliability in the achievement of the physical characteristics and the shrinkage behavior of the cast parts is achieved. Further, a controlled reaction leads to a reduced consumption of alloying components. The treatment agent produces very small amounts of slag so that the removal of slag or scum need occur only periodically at extended time intervals. As a result of the high reproducibility of the desired instantaneous process data one is now in a position, as already mentioned, of economically providing a directly castable GJV- or also GJS-melt in a one step work process in a casting oven.
For this it is advantageous, that (11) the forming agents form a multilayer sandwich such as a three layer sandwich or four layer sandwich, that the lower-most separating layer contains at least a seed or crystal nucleating agent based on FeSi, subsequently at least one treatment agent such as metal and Mg, and then as the upper-most layer at least one cover material not influencing the process of the melt. Thereby a premature reaction of the forming agent with the melt is avoided, the process time is reduced and among other things also a more even or consistent process of the formation of the melt in the casting oven is achieved.
It is also advantageous, that (12) the upper-most layer is the cover or insulating material, which is comprised of finely divided steel such as steel granules or steel grit.
A further possibility according to a further development of the invention is that (13) the treatment agent is an alloy, which contains approximately 10% to 50% Mg and at least one additional alloying component such as Cu, Ni, Sn or a lanthanoid such as cerium and is introduced into the melt. By an advantageous composition in the treatment agent of Mg and the supplemental metal, a high utilization is achieved resulting in a smaller consumption of the treatment agent.
It is further advantageous, that (14) the alloy contains 15% to 30% Mg and beyond this at least Cu or another metal. By introduction of the separating material for example in the area of the inlet sprue of the die-casting oven a separating layer is formed to the iron level and the iron to be filled and thus a premature reaction and a burning off is prevented, so that among other things also the desired process parameter is reliably achieved and a high process reproducibility with a simultaneously large incorporation or utilization of the Mg of up to 95% is ensured.
It is also advantageous for this, that (15) the treatment agent is an alloy, which contains approximately 20% Mg and 80% Cu and is introduced into the melt.
According to a preferred embodiment of the inventive solution it is finally envisioned, that (16) the alloying is carried out substantially with the exclusion of oxygen from the atmosphere in the die-casting oven, wherein the treatment and the control of the seeding or nucleating condition and/or the modification of the alloying components occur within the die-casting oven.
Of particular significance for the present invention is that (17) as the outer most layer or as the cover material a steel granulate or as the case may be steel grit is provided, which forms a separation layer during the injection of the melt, wherein a multilayer sandwich is pushed in during the introduction of the base iron into the crucible and the forming of the iron is initiated only therein. The lower separating layer and the upper layer prevent a reaction during casting in, wherein as the upper most layer or as the cover layer a liner of steel granulate or as the case may be steel grit is provided.
In association with the inventive development and arrangement it is of advantage, that (18) the treatment material formed of at least of metal and Mg is provided in the form of grains or grit onto the inoculum or as the case may be separating layer. Thereby, as already described, very small amounts of scum are produced. Further, by the metallurgical separation the treatment of the melt by the employment of alloying components such as Cu and by the inoculation of foreign seeds, a controlled reaction in the casting oven is accomplished. Cu is present as a former of perlite in the iron, its proportion in the treatment amount can however in advantageous manner be adjusted depending upon the base content in the iron.
It is further advantageous, that (19) prior to introduction of the forming agents such as seed agents, treatment agents, alloying agents, cover or as the case may be separating or insulating materials, the weight of the melt in the casting oven and in the transport vessel is determined, that is, the instantaneous process data are determined among other things via the thermal analysis and therewith the amount of the base iron to be influenced is determined and the analysis of the melt is undertaken.
Besides this it is advantageous, that (20) with regard to the total melt the treatment means contain 0.03% to 0.09% Mg or 0.005% to 0.03% Mg.
In the production of the base material GJV a narrow process window 0.005% to 0.03% is advantageous, and for the base material GJS the larger window of 0.03% to 0.09%.
By the inventive process and the advantageous introduction of the forming agent or medium into the melt an automation of the treatment, the introduction of the foreign seeds, and the alloying is possible, so that by reduction of the duration of the process high efficiency of the automated processing equipment is achieved. The work process can be very rapidly carried out, since the process steps which had until now been necessary can be dispensed with. Also advantageous is the very high utilization of the Mg, which lies between 80% and 95%.
Further advantages and details of the invention are set forth in the patent claims and explained in the description and in the drawings.

There is shown:

FIG. 1A casting oven with a multilayer sandwich in the down-sprue, the transport vessel with base iron,

FIG. 2 A process overview with measurement or sensing and evaluation station for calculating the forming materials, industrial dispensing equipment for providing the amount and for its addition into the down-sprue.

In FIG. 1 a casting oven is shown schematically with the essential functional sites, which could also take the form of an die-casting oven 1. The die-casting oven 1 includes among other things a down-sprue 2, a drain 9 as well as a crucible 8, in which the iron melt, referred to in the following as the melt 3, is maintained at the required casting temperature with the aid of the inductor 10.
With the inventive process described in greater detail in the following a reliable process for the manufacture of directly castable GJV-GGV- and GJS-GGG-melts are possible.
A recently developed material is a cast iron with vermicular graphite, which will be referred to in the following with the abbreviation GJV or GGV. In this material the graphite is present not as a lamella nor as a sphere, but rather as knots or as the case may be as worms. The mechanical characteristics of this material lies between that of the cast iron with lamellar graphite and that of cast iron with spherical graphite. Its manufacture is however difficult and requires treatment of the melt with narrow tolerances. That the cast iron exhibiting vermicular graphite as compared to conventional cast iron or gray iron (GG) exhibits a significantly higher strength. Its characteristics allow, for example, a higher pressure in cylinder blocks. At the same time the GGV-casting offers the possibility for reduction in weight, so that it can also be employed in other areas as cast parts for engine construction.
In accordance with the inventive process (FIG. 1) there occurs first the determination of the actual process data of the melt 3,11 in the casting oven during the casting-out, the computation of the forming medium, and subsequently the filling in of the individual materials as multilayer sandwich 4.1 in the down-sprue 2, wherein the lower and upper separating layers of the multilayer sandwich 4.1 prevent a premature reaction and a burning off of a treatment medium 5 between the melt 3 in the crucible 8 and the iron 11 to be filled in from the transport vessel 12. The forming material 5 and the cover material 6 is characterized or indicated in FIG. 1 as separating layer. Thereafter there occurs the filling-in of the base iron 11 out of the transport vessel 12.
As can be understood from the Figure, the forming materials 4.1 form, as explained above, the three layer sandwich. In place of the three layer sandwich also a multilayer sandwich can be employed, wherein the further layers can be for example additional alloying agents which beneficially influence the melt process. The lower-most layer of the forming materials 4.1 exhibit a separating layer 4. This separating layer 4 serves simultaneously as adjusting lever for adjusting the seed budget of the iron in the casting oven 1. The separating layer 4 provides an inoculum medium and is comprised in advantageous manner of an alloy based on FeSi or another material.
The treatment medium 5 can be comprised of an alloy, which contains approximately 10% to 50% Mg or 15% to 30% Mg or 10% to 25% Mg or beyond this at least Cu or in the place of Cu Ni, Sn or ?? and also other metal, wherein in a later to be explained process step the alloy is introduced or rinsed into the melt 3.
It is also advantageous, when the treatment medium 5, which is introduced into the melt 3, is an alloy, which contains approximately 20% Mg and 80% Cu or another metal approximately in the same proportion.
It is further advantageous, that the treatment medium 5 comprised for example of metal-Mg, CuMg, NiMg, or SnMg or the like is introduced in a predetermined granulation to the separating layer 4. Prior to input of the forming medium 5 the weight of the oven as well as the amount of base iron 11 to be supplied is determined and an analysis of the melt 3 is undertaken.
The third layer is the cover medium 6 which does not influence the process of the melt, which can be comprised of fine particles of steel, for example steel grit or steel granules. These three layers form the multilayer sandwich 4.1 with the separating layer 4 and the cover medium 6.
The untreated base iron 11, with the aid of the transport vessel or as the case may be casting vessel 12, is introduced at the required speed into the down-sprue 2 which contains the forming medium 4, 5 as well as cover medium 6, and there meets on the multilayer sandwich 4.1, so that there, with the exclusion of oxygen from the atmosphere, it is rinsed or pushed as a sandwich into the crucible 8 and does not react until there.
The multilayer sandwich 4.1 thus forms the barrier between the iron level 8.1 and the iron to be added by means of the transport vessel 12, the separating layers preventing a premature reaction of the treatment medium 5 and bringing about finally a very good incorporation of the Mg of up to 95%. Therewith, as already explained, a directly castable GGV- or GGG-melt into the casting oven 1 is made possible by a one-step process.
The computation of the amount to be added occurs in the following process steps:
After the designated forming materials and the cover material 4.1 are introduced into the down-sprue 2, the base iron 11 presses or rinses the multilayer sandwich 4.1 into the crucible 8, so that in the inside of the oven with the help of the Mg the treatment of the iron takes place. Now with the aid of the special inoculum or seed material based on FeSi, the seed budget, and the possible alloy medium, the chemical end analysis can be adjusted.
According to FIG. 2, during the casting process the required actual process data of the melt 2 are determined in the casting oven 1, and by the comparison to the target data the automatic determination for the addition amount of forming materials 4.1 occurs. The necessary process data include at least the determination of the strength index and the shrinkage index, which can be determined using the individual cooling temperature curves of the melt 3.
From at least one silo or also from two or three or more small silos 14, 15, 16 or of a dosing or metering device 13 the forming 4, 5 and cover materials 6 as determined by a computer 17, as described above, are provided and introduced in the required amount into the down-sprue 2, in which, as already mentioned, the multilayer sandwich 4.1 is formed.
In the silo 14 there is for example the seed material such as for example a material based on FeSi, in the second silo 15 the treatment material 5 (Mg+metal) and in the third silo 16 the cover material 6. The forming of the iron can however also occur with the aid of a wire injection.
The inventive process for an adaptive process control for production of cast iron, in particular of GJV and GJS and for computation of the addition amounts or as the case may be treatment medium in the iron melt can also occur with utilization of wire injection in a casting oven.
The casting off of the melt 3 via the drain 9 occurs continuously during the measurement process. With the assistance of measurement devices 17 the thermal analysis is carried out into closed crucibles, the weight of the melt, the cast temperature, the various other parameters are determined and a chemical analysis of the melt 3 is undertaken. The determination of the strength index and the shrinkage index for GJV can occur with the aid of the following described thermal analysis:
For the mechanical characteristics of the cast components the microstructure is of decisive importance. This cast microstructure is determined during crystallization depending upon the chemical composition, the speed of cooling and the seed budget.
The parameter is the degree of saturation or as the case may be the carbon equivalent. This determines the position of the cast alloy in the FeSi diagram. These parameters are influenced by ancillary elements. Further important values include the elements that directly influence the microstructure and in particular these are the perlite formers.
The rate of cooling is influenced by a variety of factors, and namely:
a) the relationship of volume to surface area of the cast part,
b) the thermophysical characteristics of the core- and mold materials,
c) the thermal transition of the cast body to the mold and the thermal content of the melt.
The determination of the strength and the shrinkage index for GJV by means of thermal analysis is explained in the following:
The difference of the specific volume of solid to liquid is the cause for the development of volume defects. The size of the volume deficit is primarily dependent upon the respective casting material. The eutectic solidification brings about an expansion of the separated graphite against the shrinkage of the austenite. This means, that depending upon the chemical composition, the cooling conditions and the seed content the “self feeding” is improved. So that the “self feeding” is effective, and endogenous jacket forming solidification must occur. The start of the solidification is influenced by the chemical composition, the seed content and the cooling speed.
The thermal analysis is a method for checking the quality of the melt. It is based on the plotting of the time-temperature curve during the solidification of the melt and the evaluation of prominent points which occur during crystallization. Upon dropping below the liquid temperature the crystal formation begins and austenite dendrites grow in the melt. By the growth of the dendrites, heat is released. A tilt point occurs in the curve. In the further cooling, the eutectic equilibrium temperature is dropped below. Below this temperature, seeds of materials capable of growth begin to form in the melt. During the following grain growth heat is released, which can lead back to a higher temperature of the melt (recalescence).
The cooling curve thus always shows the interaction between heat removal and heat development and therewith the course of the crystallization.
By the thermal analysis the following characteristic values are determined:
a) Carbon content, Sc, CE-value,
b) Tendency towards stable or metastable solidification,
c) Estimation of microstructures of GJS,
d) Estimation of seed population of GJL.
Determination of the data results for the solidity or strength index.
From the preceding computation of the cast parts the mechanical properties are determined. The data results for the shrinkage index are determined as follows:
Over the expected range of the volume deficit defect the size of the defect surface area is determined by means of X-ray or control sections.
Via the mathematical model of the evaluation of the cooling curve of the melt in the crucibles 14, 15, 16 of the measurement station 17, the parameters are determined with a high correlation of the process data to the result data. The mathematical association of these parts results in solidity and shrinkage index.
The determination of the solidity or strength index and the shrinkage index for GJV by means of the thermal analysis occurs according to the following process protocol (FIGS. 1 and 2):
1. Casting the melt 3 in a mold 19 and thereby extraction of the melt 3 out of the drain 9 and filling in one or more small crucibles 14 through 16 of the measurement station 17,
2. Undertaking thermal analysis with the aid of the measurement device 17,
3. Transmitting the determined data to the databank of the process controlling computer of the measurement station 17,
3. Evaluation of the actual process data,
4. Computing the strength and the shrinkage index, comparing with the intended process data, computing the amount of alloying and forming material 4.1 to be added,
5. Preparing the forming material 4.1 by means of the dispensing device 13,
6. Transporting the transport vessel 12 to the casting oven 1,
7. Filling the forming material 4.1 or as the case may be the three or the four plies into the sprue 2,
8. Filling the base iron 11 from the transport vessel 12 into the sprue 2 of the casting oven 1, rinsing the forming medium 4.1 into the melt 3 according to FIG. 2,
9. Repeating step 1 and subsequent.
The determination of the strength index and the shrinkage index for GJV or as the case may be GGV, GGG melts by means of the thermal analysis occurs for each filling with base iron 11 in the same manner as described, so that a very precise determination of the amount or as the case may be the adaptation of the forming medium 4.1 for subsequent charges or as the case may be melts is possible taking into consideration the target data.
Each crucible 14 through 16 of the measurement station 17 can, as described above, contain a different material in interest or as the case may be seed or inoculum material.
A determined value or as the case may be process data are, as already described, conveyed to the databank or as the case may be the process controlling computer 17 and evaluated and are available for the selection or as the case may be the determining of the amount of the forming material 4.1.
Later there occurs a continuous comparison of the process data with the predetermined target data, so that the process can be continuously adapted or conformed or as the case may be optimized (learning system).
As already mentioned, from the two determined temperature-cooling curves of the melt 3 in the crucibles 14 through 16 of the measurement station 17, the solidity index and the shrinkage index are determined. For this, the process data are determined via a mathematically optimal model and compared with the resulting data.
On the basis of the determined parameters now an automatic computation and a weighing out of the individual forming medium 4.1 or as the case may be the automatic determination of the alloying components is possible, which are contained in the multilayer sandwich 4.1. Thereafter there occurs the automatic addition of the forming medium at least as a three-layer sandwich 4.1 into the sprue 2. This occurs taking into consideration the oven or as the case may be transport vessel-content, so that an optimal forming of the melt 3 in the casting oven 1 is possible.

REFERENCE NUMBER LIST

- 1. Casting Oven, Die-Casting Oven
- 2. Sprue
- 3. Melt
- 4. Separating Layer, FeSi (Inoculum)
- 4.1 Buffer Zone, Buffer Material, Treatment Medium (Three Layer Sandwich also Forming Material)
- 5. Treatment Medium, Alloying or as the case may be Inoculum Medium
- 6. Cover Medium
- 8. Crucible
- 8.1 Iron Level
- 9. Drain
- 10. Heating Inductor
- 11. Base Iron, Untreated Melt
- 12. Transport Vessel, Casting Vessel
- 13. Dosing Device
- 14. Silo
- 15. Silo
- 16. Silo
- 17. Computer
- 18. Measurement Device
- 19. Mold

Claims

1. A process for adaptive control of the alloy composition of cast parts in casting ovens, in particular of GJV and GJS, by computing the additive amounts and addition of forming medium and base iron in the melt (3) of the cast oven (1), including the steps:

1.1 determining the amount of the melt (3) in the casting oven (1) and the amount of base iron (11) to be added

1.2 computing the expected physical and mechanical properties, solidity index as well as shrinkage index of the melt (3) with an aid of thermal and chemical analysis,

1.3 computing the amount of forming medium to be introduced into the melt (3) necessary for the desired physical and mechanic properties,

1.4 introducing the forming medium in the sprue (2) of the casting oven (1), and

1.5 pouring in the base iron through the sprue (2), wherein

the forming medium contains:

treatment medium of Mg or an alloy, which contains 10% to 50% Mg and at least one additional alloying component such as Cu, Ni, Sn or a lanthanoid such as cerium,

inoculating or seed medium based on FeSi,

alloying medium,

carbonizing medium, and

cover material of particulate steel, and

the forming medium forms is in the form of a multilayer sandwich (4.1), which as the lower most layer contains at least the seed or inoculum material (4), beyond this at least the treatment medium (5), and as the upper most layer at least the cover material (6).

2. A process according to claim 1, wherein after each casting or pouring of the casting oven the process data determined for the respective melt for determination of the forming medium (4.1) for the melt introduced immediately subsequently into the casting oven is made available.

3. A process according to claim 1, wherein the process is applied to a melt in a transport vessel (12).

4. A process according to claim 1, wherein during and/or after the casting the actual process data are compared with target data or with target data stored in a computer and continuously adapted and thereafter the forming medium (4.1) is determined.

5. A process according to claim 1, wherein the determination of the physical, mechanical and chemical and/or the determination of the parameters such as solidity index and shrinkage index occur with the aid of the determination of individual cooling temperature curves of the melt (3).

6. A process according to claim 1, wherein during the determination of the process data the melt (3) be cast into the mold (19) and the addition of new melt (11) into the casting oven (1) occurs continuously.

7. A medium for influencing the process according to claim 1, wherein the cover material (6) is a divided steel such as steel granules or steel grit.

8. A medium for influencing the process according to claim 1, wherein the treatment medium (5) is a Mg—Cu alloy with 15% to 30% Mg.

9. A process according to claim 1, wherein the treatment medium (5) is an alloy, which contains approximately 20% Mg and 80% Cu is introduced into the melt (3).

10. A process according to claim 1, wherein the treatment medium (5) is introduced substantially under exclusion of oxygen from the atmosphere in the casting oven (1), wherein the treatment and the control of the nucleating addition and/or the modification of the alloy and components occur within the die cast oven (1).

11. A process according to claim 1, wherein a granulated steel or as the case may be a steel grit is provided as cover medium (6), which forms a separating layer during the casting in of the melt (11).

12. A process according to claim 1, wherein the treatment medium (5) is supplied in granular form to the nucleating medium (4).

13. A medium for influencing the process according to claim 1, wherein the total melt following addition of the treatment medium (5) contains 0.03% to 0.09% Mg or 0.005% to 0.03% Mg.