WO2013046005A1

WO2013046005A1 - Method for verifying and improving the quality of a metal alloy during the solidification process and device suited to implement said method

Info

Publication number: WO2013046005A1
Application number: PCT/IB2012/001910
Authority: WO
Inventors: Adrian UDROIU; Mauro DE LISSANDRI
Original assignee: Tekom S.R.L.
Priority date: 2011-09-29
Filing date: 2012-09-28
Publication date: 2013-04-04
Also published as: ITVI20110258A1

Abstract

The invention is a method for verifying and improving the quality of a metal alloy during the solidification process, including, in the given order, the operations of: placing the metal alloy in the liquid state inside a crucible; providing a first constant electrical quantity, selected between electrical current and electrical voltage, between a first pair of electrodes immersed in said metal alloy during the solidification stage; measuring the values of a second electrical quantity, selected between electrical voltage and electrical current, for a plurality of instants during the solidification stage, by means of a second pair of electrodes immersed in the metal alloy; calculating, for each instant, the electrical resistance of the metal alloy obtained from the ratio between the first constant electrical quantity and each one of the values of the second electrical quantity; defining a real curve of the electrical resistance variation in the metal alloy during the solidification stage on a Cartesian graph where temperature and/or time values are indicated on the x-axis and electrical resistance values are indicated on the y-axis; comparing the real curve with reference values related to the resistance variation obtained from a plurality of statistical measurements on samples of the metal alloy whose defectiveness level is known, in such a way as to identify any dissimilarities of the real curve with respect to said reference values; including additives in the metal alloy in order to reduce the dissimilarities between the real curve and the reference values.

Description

METHOD FOR VERIFYING AND IMPROVING THE QUALITY OF A METAL ALLOY DURING THE SOLIDIFICATION PROCESS AND DEVICE SUITED TO IMPLEMENT SAID METHOD.

DESCRIPTION

The invention concerns a method for verifying and improving the quality of a metal alloy during its solidification process, in such a way as to make it possible to plan suitable interventions and reduce the risk of faults being present inside the metallic structure of the same alloy.

The invention also concerns a piece of equipment for verifying and improving the quality of a metal alloy comprising a device for measuring the electrical resistance of a metal alloy during its solidification process and a processing device containing a specific software suited to process the input data received, in such a way as to carry out the verification and improvement steps included in said method that is the subject of the invention.

It is known that in the industry, in general, pure metals are not used but, rather, metal alloys are used whose mechanical properties are better than those of the so-called pure metals.

In particular, every metal alloy is a combination of atoms, ions and molecules of different components, among which there are the already mentioned pure metals.

For example, steel is made of iron and carbon, while brass is made of copper and zinc. In even greater detail, said components can be divided into solvent and solute, wherein the solvent is present in the alloy in a quantity exceeding the quantity of solute.

It is also known that during the solidification process of every metal alloy, since the various components have different melting temperatures, the alloy passes through the so-called "biphasic zone", where solidification takes place with the nucleation of crystals usually followed by their growth in the remaining liquid, ending up with the solidification of all components.

To disadvantage, chemical and physical events can take place in that critical zone that determine the development of faults within the structure of the metal alloy once it has solidified, thus worsening its mechanical properties and increasing the risk of breakage.

The entry in and exit from the so-called biphasic zone during the solidification process of an alloy vary not only according to what components make up the metal alloy but also according to the percentage content of the same in the alloy.

For example, an alloy constituted by a component A that makes up 60% of it and by a second component B that makes up 40% of it has thresholds of entry and exit in/from the biphasic zone that are different from those of an alloy constituted by 40% of the same component A and 60% of the same component B, as can be seen in the diagram shown in Figure 1.

Furthermore, in the case of multi-component alloys, like for example cast iron, not only homogeneous compounds, in this case austenite, are formed in the metal matrix during the solidification process, but separate, non-mixable phases, like graphite, are produced.

This, moreover, determines a higher complexity of the phases that are generated during said solidification process of the metal alloy, which consequently increases the risk of formation of faults inside the metallic structure of the same alloy once it has solidified.

To disadvantage, up to date neither techniques nor devices are known that make it possible to determine the complex chemical events that take place during the solidification process of a metal alloy, so as to be able to predict and avoid the formation of faults on the metal matrix of the same alloy.

The present invention aims to overcome the drawbacks listed above.

In particular, the invention has the purpose to define and develop a method and a piece of equipment for verifying and improving the quality of a metal alloy that make it possible to provide information on its tendency to generate faults during the solidification of the same metal alloy.

Consequently, it is the object of the present invention to define and develop a method and a piece of equipment that make it possible to determine how and to what extent to intervene on the metal alloy during its solidification process. Again, it is the object of the present invention to define and develop a method and a piece of equipment that make it possible to determine the chemical composition of the metal alloy during the entire solidification stage of the same alloy and, in the case where the chemical composition of said metal alloy deviates from the reference values, make it possible to identify the types and quantities of additives suited to improve its quality.

It is a further object of the invention to define and develop a method and a piece of equipment that make it possible to identify and predict the final mechanical characteristics of the solidified metal alloy.

It is another, yet not the least object of the invention to define and develop a method and a piece of equipment that make it possible to predict the shrinkage effects of the metal alloy during the solidification stage and, in the case where said possible shrinkage effects are identified, make it possible to indicate the type of operations to be carried out in order to improve the quality of the metal alloy.

The objects described above are achieved by the method of the invention having the characteristics illustrated in the first independent claim.

The invention includes also the quality verification and improvement equipment described in claim 8, which makes it possible to carry out the operations belonging to the method of the invention.

Further characteristics of the method and of the equipment that are the subjects of the invention are described in the dependent claims.

The objects and advantages described above will be highlighted in greater detail in the description of a preferred embodiment of the invention that is provided as an indicative, non-limiting example, with reference to the enclosed drawings, wherein:

- Figure 1 shows a typical phase diagram of a generic metal alloy made up of two components A and B;

- Figure 2 shows the Cartesian graph of the real curve related to the electrical resistance variation of a specific metal alloy during the solidification process;

- Figure 3 shows the Cartesian graph of the first derivative related to the real curve shown in Figure 2;

- Figure 4 shows a schematic view of a first embodiment of the equipment of the invention;

- Figure 5 shows a schematic view of a second embodiment of the equipment of the invention.

The method of the invention for verifying and improving the quality of a metal alloy during the solidification process is based on the concept that the value of the electrical resistance of a given metal alloy is directly related to the chemical composition of the same alloy and to its solidification stage.

Therefore, by interpreting the values corresponding to the electrical resistance variation of a particular metal alloy during the entire solidification process and, successively, comparing them with the values corresponding to the electrical resistance variation of the same metal alloy ideally with no faults, or whose level of defectiveness is statistically known, it is possible to achieve the objects of the invention as mentioned above.

In particular, the applicant has discovered that by measuring the electrical resistance of a metal alloy during the solidification process at short time intervals or continuously it is possible to determine the progress of the latter and, consequently, to intervene to the correct extent and in due time to avoid the formation of faults and improve the quality of the same alloy.

In particular, the method of the invention includes a first operation that consists in placing a given quantity of metal alloy in the liquid state inside a crucible, where its solidification process will take place.

According to the invention, at this point a first constant electrical quantity, selected between electrical current or electrical voltage, is provided between a first pair of electrodes immersed in the metal alloy, so that it is possible to measure simultaneously the values of a second electrical quantity, selected between electrical voltage and electrical current, present in said alloy by means of a second pair of electrodes also immersed in the alloy during its solidification.

According to the preferred embodiment of the method of the invention, the first electrical quantity is electrical current, while the second electrical quantity is electrical voltage.

Again, preferably but not necessarily, the measurement of said electrical voltage values is carried out continuously during the solidification process. However, it cannot be excluded that said measurement can be carried out at specific time instants according to regular intervals.

The measurement of the electrical voltage values makes it possible to calculate, preferably during the same solidification process, the electrical resistance corresponding to each of them.

As is known, obviously, the values of the electrical resistance are obtained from the ratio between the electrical voltage values measured and the electrical current value provided.

It cannot be excluded, however, that in an alternative embodiment of the method of the invention the first constant electrical quantity is a constant electrical voltage while the second electrical quantity measured is the electrical current that flows through the metal alloy.

In turn, these resistance values are used to define a real curve 100 of the variation in the same electrical resistance during the entire solidification process of the metal alloy.

In particular, according to the preferred embodiment of the method of the invention, said real curve 100 is defined on a Cartesian graph 101 having temperature values on the x-axis and electrical resistance values on the y-axis, as shown in Figure 2.

An alternative embodiment of the method of the invention may require that said Cartesian graph is defined indicating on the x-axis, instead of the temperature values, the value of the time necessary for the solidification of the metal alloy. Again, a different embodiment of the invention may require the definition of a Cartesian graph in three dimensions, where the quantities indicated on the three axes are respectively the electrical resistance of the metal alloy that is solidifying, the temperature value and the solidification time.

Going back to the preferred embodiment of the invention described, preferably but not necessarily, said real curve 100 is defined progressively during the solidification process, as the data are measured and calculated.

It cannot be excluded, however, that said real curve 100 is defined on said graph 101 following the conclusion of the solidification process of the alloy being analysed.

According to the method of the invention, once said real curve 100 has been defined, it must be interpreted.

Generally, said interpretation requires that said real curve 100 is compared with reference values related to the variation in the electrical resistance obtained from a plurality of statistical measurements on samples of the same metal alloy being analysed, the defectiveness level of which is known. Said statistical measurements are obviously carried out before implementation of the method of the invention.

In particular, according to the preferred embodiment of the method of the invention, the interpretation consists, as first thing, in obtaining from said statistical measurements and defining on the same graph 101 an ideal curve 102 of the variation in the electrical resistance of the metal alloy being analysed, with no faults.

More precisely, the ideal curve 102 is defined using those statistical measurements related to samples of the specific allow being analysed, with no faults.

Thus, once the real curve 100 has been superimposed to the ideal curve 102, the interpretation consists in identifying the dissimilarities between them.

In particular, as can be seen again in Figure 2, the positive peaks 103 of the electrical resistance values identified along the two curves 100 and 102 are compared.

In fact, said peaks 103 assume an important meaning during the solidification process of a metal alloy, as they indicate the various moments at which the changes of state of the alloy take place.

Preferably but not necessarily, the comparison step requires that the first derivatives 104 of said two curves 100 and 102 are compared, so as to compare the speed of variation in the electrical resistance of the metal alloy being analysed with the speed of variation in the resistance of the ideal alloy, as shown in Figure 3.

According to an alternative embodiment of the method of the invention, said statistical measurements referring to samples of the specific metal alloy being analysed, whose level of defectiveness is known, are used to determine a statistical regression equation.

In particular, according to the method of the invention, said positive peaks 103 of the real curve 100 are determined and the electrical resistance values related to said peaks 103 are used as variables of said regression equation. The result of the equation indicates, at a statistical level, the dissimilarity of the real curve 100 with respect to a metal alloy of the same type with no faults. Said result, therefore, indicates the level of defectiveness of the metal alloy of which the real curve 100 has been defined.

Independently of whether the ideal curve 102 is compared with the real curve 100, according to the preferred embodiment of the method of the invention, or the resistance values related to the positive peaks 103 are used as variables in a regression equation, according to the alternative embodiment, the results obtained make it possible to understand how and when it is possible to intervene during the solidification process of the metal alloy to improve its quality.

Said interventions, in fact, represent the final operation of the method of the invention and require that specific additives are introduced in the alloy during the solidification stage in order to reduce said dissimilarities between the two curves 100 and 102 being compared or between the real curve 100 and the statistical data, so that the characteristics of the alloy being analysed become more similar to those of the ideal metal alloy without faults.

As already explained, the invention includes also the equipment 1 , shown in Figures 4 and 5, comprising a device 11 for measuring the electrical resistance of a metal alloy L during the solidification process and a processing device 12 in which a specific software has been loaded that is suited to process the input electrical current and electrical voltage values, so as to carry out the verification and improvement operations belonging to said method of the invention.

Regarding the device 11 for measuring the electrical resistance, this is used to obtain the data (the electrical current and voltage values and consequently the electrical resistance values) necessary for comparing the characteristics of the same metal alloy L being analysed with those of the same alloy ideally without faults.

In particular, the measuring device 11 comprises a crucible 2 suited to contain a given quantity of metal alloy L in the liquid state to be analysed.

Preferably, said crucible 2, in the preferred embodiment of the invention, is of the disposable type and is made of sand.

Furthermore, the measuring device 11 comprises a first pair of electrodes 3, each one of which has a first end 31 inserted in the empty space defined inside said crucible 2 so that it can come into contact with the metal alloy L in the solidification stage.

The second end 32 of the electrodes belonging to the first pair 3 is connected to a current generator 4 that, as explained above, has the function of providing a constant electrical current to the metal alloy L.

The measuring device 11 comprises a second pair of electrodes 5, each one of which, similarly to those belonging to the first pair of electrodes 3, has a first end 51 inserted in the empty space defined inside the crucible 2 so that it can come into contact with the metal alloy L.

The second end 52 of the two electrodes of the second pair 5 is connected to a voltage measuring device 6, so as to measure the electrical voltage present in the metal alloy L during said solidification process.

Preferably but not necessarily, the electrical current generator 4 and the electrical voltage measuring device 6 belong to a milliohmmeter 8.

In the case where the Cartesian graph of the real curve 100 is determined by calculating the ratio between the resistance value and the value of the solidification temperature of the metal alloy L, the measuring device 11 , as shown in Figure 4, also comprises, inside the crucible 2, a temperature sensor 9, preferably a thermocouple 91.

Said sensor 9 is capable of determining the variation in the temperature of the metal alloy L during its solidification stage.

Obviously, in the case where said graph is defined by the variation in the electrical resistance over time, the presence of said temperature sensor 9 is not necessary, as shown in Figure 5.

Regarding, instead, the processing device 12, this comprises an input/output system 7 capable of exchanging the data concerning the first electrical quantity provided, the second electrical quantity measured and if necessary the measured temperature with the measuring device 11.

Consequently, the processing device 12 is capable of calculating the variation in the electrical resistance during the solidification process and of defining the graph 101 of the real curve 100, shown in Figure 2, so as to be able to carry out the successive comparison and interpretation operations belonging to the method of the invention.

The above clearly shows that the method and the device of the invention achieve all the set objects.

In particular, the invention achieves the object to define and implement a method and a piece of equipment for verifying and improving the quality of a metal alloy that make it possible to provide information on its tendency to generate faults during the solidification of the same metal alloy.

Consequently, the invention also achieves the further object to define and develop a method and a piece of equipment that make it possible to determine how and to what extent to intervene in the metal alloy during its solidification process.

The invention also achieves the further object to define and develop a method and a piece of equipment that make it possible to determine the chemical composition of the metal alloy during the entire solidification stage of the same alloy and, in the case where the chemical composition of said metal alloy deviates from the reference data, make it possible to identify the types and quantities of additives suited to improve its quality.

The invention also achieves the further object to define and implement a method and a piece of equipment that make it possible to identify and predict the final mechanical characteristics of the solidified metal alloy.

The invention also achieves the further, and not the least, object to define and implement a method and a piece of equipment that make it possible to predict the shrinkage effects of the metal alloy during the solidification stage and, where said possible shrinkage effects are identified, to indicate the type of operations to be carried out to improve the quality of the metal alloy.

Upon implementation, the method and the equipment that are the subjects of the invention may undergo changes that, though not illustrated or described herein, shall nonetheless be covered by the present patent, provided that they come within the scope of the claims that follow.

Where technical features mentioned in any claim are followed by reference signs, those reference signs have been included for the sole purpose of increasing the intelligibility of the claims and accordingly such reference signs do not have any limiting effect on the protection of each element identified by way of example by such reference signs.

Claims

1) Method for verifying and improving the quality of a metal alloy during the solidification process, characterized in that it comprises the following operations:

- placing said metal alloy in the liquid state inside a crucible;

- providing a first constant electrical quantity, selected between electrical current and electrical voltage, between a first pair of electrodes immersed in said metal alloy during said solidification stage;

- measuring the values of a second electrical quantity, selected between electrical voltage and electrical current, for a plurality of instants during said solidification stage, by means of a second pair of electrodes immersed in said metal alloy;

- calculating, for each one of said instants, the electrical resistance of said metal alloy obtained from the ratio between said first constant electrical quantity and each one of said values of said second electrical quantity;

- defining a real curve of the electrical resistance variation in said metal alloy during said solidification stage on a Cartesian graph where temperature and/or time values are indicated on the x-axis and electrical resistance values are indicated on the y-axis;

- comparing said real curve with reference values related to the resistance variation obtained from a plurality of statistical measurements on samples of said metal alloy whose defectiveness level is known, in such a way as to identify any dissimilarities between said real curve and said reference values;

- including additives in said metal alloy in order to reduce said dissimilarities of said real curve with respect to said reference values.

2) Method according to claim 1), characterized in that said reference values comprise an ideal curve of the resistance variation in said metal alloy with no faults and in that said comparison step includes the operations of:

- defining said ideal curve on said Cartesian graph;

- comparing said real curve with said ideal curve so as to identify said dissimilarities between said curves.

3) Method according to claim 2), characterized in that said comparison step includes the comparison of the first derivative of said real curve with the first derivative of said ideal curve, in such a way as to compare the speed of variation in the electrical resistance of said curves during said solidification stage.

4) Method according to claim 1), characterized in that said reference values comprise a statistical regression equation defined through said statistical measurements regarding samples of said metal alloy whose defectiveness level is known and in that said comparison step includes the operations of:

- determining the positive peaks of said real curve;

- using the electrical resistance values related to said positive peaks as variables of said regression equation so as to determine the level of defectiveness of said metal alloy during the solidification process.

5) Method according to any of the preceding claims, characterized in that said measurement of said values of said second electrical quantity is carried out continuously during said solidification of said metal alloy.

6) Method according to any of the preceding claims, characterized in that said first electrical quantity is electrical current and said second electrical quantity is electrical voltage.

7) Method according to any of the claims from 1) to 5), characterized in that said first electrical quantity is electrical voltage and said second electrical quantity is electrical current.

8) Equipment (1) for verifying and improving the quality of a metal alloy (L) during the solidification process, characterized in that it comprises:

- a device (11) for measuring the electrical resistance of said metal alloy (L) during the solidification process, of the type comprising a crucible (2) suited to contain said metal alloy (L) in the liquid state; a first pair of electrodes (3), each one of which has a first end (31) inserted in said crucible (2) so as to come into contact with said metal alloy (L), while the second end (32) is connected to a generator (4) of a first electrical quantity, selected between electrical current and electrical voltage, in such a way as to provide a constant value of said first electrical quantity to said metal alloy (L); and a second pair of electrodes (5), each one of which has a first end (51) inserted in said crucible (2) so as to come into contact with said metal alloy (L), while the second end (52) is connected to a device (6) for measuring a second electrical quantity, selected between electrical voltage and electrical current, in such a way as to measure said second electrical quantity present in said metal alloy (L) during said solidification stage;

- a processing device (12) comprising an input/output system (7) for connection and exchange of data related to said first electrical quantity and to said second electrical quantity with said measuring device (11), said processing device (12) being suited to process said data in order to define said real curve and compare it with said reference values following the method according to any of the claims from 1) to 7).

9) Equipment (1) according to claim 8), characterized in that said generator (4) of said first electrical quantity and said device (6) for measuring said second electrical quantity belong to a milliohmmeter (8).

10) Equipment (1) according to claim 8) or 9), characterized in that said crucible (2) is a disposable container made of sand, in whose walls said first and said second pair of electrodes (3, 5) are arranged.

11) Equipment according to any of the claims from 8) to 10), characterized in that said electrical resistance measuring device (11) comprises a temperature sensor (9) arranged inside said crucible (2).

12) Equipment according to claim 11), characterized in that said temperature sensor (9) is a thermocouple (91).