CA1115553A - Method and apparatus for predicting metallographic structure - Google Patents
Method and apparatus for predicting metallographic structureInfo
- Publication number
- CA1115553A CA1115553A CA363,367A CA363367A CA1115553A CA 1115553 A CA1115553 A CA 1115553A CA 363367 A CA363367 A CA 363367A CA 1115553 A CA1115553 A CA 1115553A
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Abstract
METHOD AND APPARATUS FOR PRE-DICTING METALLOGRAPHIC STRUCTURE
ABSTRACT OF THE DISCLOSURE
A metallographic structure such as nodularity in castings to be made from molten metal is predicted by causing one part of the sample to rapidly solidify at a first rate and a second part of the sample to solidify at a slower rate. The temperature of at least said one part of the sample is measured during solidification.
After solidification of the one part of the sample, the heat conduc-tivity of the sample is used to predict the metallographic structure of the sample.
ABSTRACT OF THE DISCLOSURE
A metallographic structure such as nodularity in castings to be made from molten metal is predicted by causing one part of the sample to rapidly solidify at a first rate and a second part of the sample to solidify at a slower rate. The temperature of at least said one part of the sample is measured during solidification.
After solidification of the one part of the sample, the heat conduc-tivity of the sample is used to predict the metallographic structure of the sample.
Description
- ~15SS~
~` -1 Background The present invention relates generally to a process for rapidly predicting a metallographic structure, such as the degree of nodularity, of castings to be made from molten metal before cast-ing and apparatus for performing the same.
It is known that the composltion of molten metal may be estimated by recording the liquidus and eutectic temperatures using ~--known cooling curves. Such method provides information such as a change in phase, carbon equivalent, etc. It is also known to deter-L0 mine the thermal conductivity of solid bodies by measuring the heat flow through such body ~hen subjected to a thermal gradient.
~_ It has been observed that in grey cast iron in the solid state, the thermal conductivity is substantially influenced by the graphitic structure and that a nodular cast iron, for instance, has a lower conductivity than a lamellar or equivalent composition.
When pouring cast iron, it is important that analysis be carried out very quickly and before casting. If one waits too long ~
before completing a pour of a nodular cast iron, a large percentage ~ ~.
of the magnesium which is present in the molten metal will dissipate 0 or will otherwise be lost and there is a likelihood of making an unsatisfactory cast.
The industry has long sought a simple, rapid and effective way of accurately predicting the degree of nodularity of a cast iron before casting of the sa~e. One method proposed heretofore is dis-closed iri U.S. Patent 3,670,558 wherein the properties of a nodular ~~~~~
cast iron are evaluated by way of a comparative study of conventional cooling curves and a set or family of curve segments. Tlle method ~ .
proposed by said patent has not proven to be acceptable.
Thus, at tile present time, the degree of nodularity of a ) cast iron can only be determined with precision if the sample is ' - :
c~h.rJ :~ .
~ ~ ~5~
1 cooled and evaluated by ultrasonic or metallographic analysis, and the like.
The main object of the present invention i8 to cope with said problem by proposing a new process and apparatus making it pos- ::
sible to predict in a simple, rapid and effective manner the degree of nodularity of the cast iron casting while the iron is still molten and while it is still possible to change the composition of the r----molten metal or it is possible to scrap the molten metal.
Summary of the Invention The process of the presen~ invention is directed to pre-dicting a metallographic structure of a casting which will result from use of a molten metal and comprises the steps of obtaining a sample of the molten metal; causing one part of the sample to solid-ify at a first rate and a second part of the sample to solidify at a slower rate; ascertaining a parameter of heat conductivity, and using the heat conductivity parameter of the sample after solidifi- ,~
cation of the first part to determine the metallographic structure which would result from use of the molten metal.
Apparatus for accomplishing the method described above in-cludes a small crucible into which a sample of molten metal is poured and within which the sample cools. The crucible in one embodiment has two temperature sensing devices at spaced locations correspond-ing to the first and second parts of the sample. In the preferred embodiment of the crucible, there is only one temperature sensin~
device. A means is associated with each of the types of crucibles to cause one part of the sample to solidify at a faster rate.
It is an object of the present invention to provide app~- ;
ratus and method which will facilitate predicting in a simple, rapid and reliable manner the degree of nodularity or other metallographic structure which will be present in a casting made from a particular batch of cast iron.
~.
s~
In accordance with a broad aspect, the invention relates to apparatus for use in determining a metallographic structure of molten metal, comprising:
(a~ a crucible having a cavity therein, ' ;~
(b) means for causing a first part of a sample in said cavity to cool at a faster rate than a second part of the sample, and temperature sensing means associated with said first part for measuring the temperature of a sample in said first part, and including a crucible with first and second contiguous parts of said ca~ity with a smallex transverse dimension for said first part so that the ratio of surface area to vol~me of the second cavity part is smaller than ~ -~
that of said first cavity part.
.
- 2a -~7,.
~S5~
1 Other objects will appear hereinafter.
For the purpose of illustrating the invention, there is shown in the drawings a form which is presently preferred; it being understood, however, that this invention is not limited to the pre-cise arrangements and instrumentalities shown.
Figure 1 is a sectional view through a first type of crucible usable in practicing the method of the present invention.
Figure 2 is a sectional view through another type of crucible usable when practicing the method of the present i-nvention.
Figure 3 is a graph showing two cooling curves showing temperature plotted against time.
Figure 4 is a graph showing a cooling curve wherein tem-perature is plotted against time using a single thermocouple.
- Figure S is a sectional view through another crucible.
Figure 6 is a graph of temperature after 3 minutes versus temperature to cool through a 100C zone containing the solidus arrest of the sample.
Figure 7 is a graph plotting ~T versus nodularity.
Referring to the drawings in detail, wilerein like numerals indicate like elements, there is shown in Figure 1 a first form of apparatus for use in practicing the method of the present invention.
Thus, there is shown a crucible designated generally as 10, the di-ameter of the upper part 12 being much greate} than the diameter of the lower part 13. As used herein, the word crucible is intended to include sample cups, molds used for I~-MOLD processes, and the like.
A crucible 10 constructed in this manner makes it possible to cool a sample of molten metal at two different rates. Thus, the lower portion 14 of a sample in the crucible 10 will cool more rapidly than the upper portion 15 of the sample in crucible 10 because the ratio of surface area to volume of the upper portion is smaller - than that of the lower portion.
~ - 3 -55~ i 1 In Figure 2, there is illustrated a second iorm of appa-ratus for use in practicing the method of the present invention. In F-gure 2, there is shown a crucible 10' of constant diameter. The lower portion 13' of the crucible 10' is placed in a jacket 18 of heat insulating material. As a result of the Jacket 18, the portion of the sample in the upper portion 19 of the crucible 10' will solid-ify at a faster rate as compared with the rate of solidification of the sample in the lower portion of the crucible 10'.
! Although the crucibles 10 and 10' are slightly different in construction as to their contour, the principle utilized in the method of the present invention is the same. In order to prevent ^
the formation of shrinkage cavities in the sample, it is preferable to design the crucibles in such a way that the portion having the fastest rate of solidification is in the lower portion of the cru-cible. Hence, the following description with respect Figure 3 will only make reference to crucible 10 shown in Figure 1.
Figure 3 represents the solidification curve 11 of portion 14 of a sample of grey cast iron at a first rate of cooling. The -temperature of the sample in portion 14 is sensed by a thermal sens-ing element such as a thermocouple 22. The thermocouple 22 is, in a preferred embodiment, ~enerally perpendicular to the center line or axis of the crucible 10. It will be seen from the curve 11 that ; a change in cooling rate ~t point 23 is recorded and corresponds to the liquidus temperature. There is also a more pronounced tempera-ture cha~ge at point 24 corresponding to the solidous temperature.
Thereafter curve 11 shows ~n inflection at a temperature TX instead of continuing to cool e~rollenti~lly along the line 25 as would be the case in an ordinary solidification curve in the case of a homo-geneous cooling of the s;l(nple.
5~
1 In the present case, the inflection of the curve 11 at point X is caused by the thermal reflection during the eutectic solidification of the upper portion 15 of the sample cooling at a second and lower rate as compared with the rate of cooling of the portion 14. The temperature T~ is the temperature at the point of inflection X on the curve 11. The temperature TX is a first param-. eter which is directly related to the thermal conductivity of the molten metal. The change in cooling rate results from the tempera~
ture of the eutectic level stretch of line 16 remaining practically constant around 1150C.
Curve 11 and line 25 delimit an area A which is also di-rectly related to the thermal conductivity of the sample. That is, the area A represents the thermal influence of the eutectic of por-- tion 15 of the sample on portion 14 o~ the sample. It has been noted that the thermal conductivity is related to the metallographic structure of a metal. A reading of temperature TX which relates to the point of inflection in the curve 11 and/or the evaluation of the area A, are related to the metallographic structure of the metal sample being analyzed.
The two parameters mentioned above can also be checked when the solidification curve 16 of the sample is recorded at the same ,,; . -.~ .
time on a single graph along with curve 11. To obtain the solidifi-cation curve 16, a temperature sensor such as a second thermocouple 27 is provided in the crucible 10 at a location which is associated with portion 15 of the sample. Thus, the thermocouples 22 and 27 are at substantially different locations but each is associated with one portion of the s~mple. At any given time, the differellce in temperature between the two curves 11 and 16 varies with the conduc-tivity of the metal sample and consequently with its degree of nodu-larity. Ilereinafter, such temperature difference will be referred to as ~ T'.
5~
1 It has been ascertained that TX is influenced by the eutec-tic temperature of portion 15 and a number of other factors including thermal conductivity, pouring temperature, the manner of pouring. It is desired to determine the thermal conductivity of the sample. It is thus desirable to eliminate the influence of the other parameters.
If the thermocouple 22 is at about the eutectic temperature of por-............... tion 14, cooling rate is not influenced to any significant extent by thermal conductivity since thermal gradiants are relatively low.
This makes possible the determination of a parameter "normal cooling rate" which is a rate without substantial influences of thermal con-ductivity. In this example, this rate is defined as the rate ol cooling across the 100C range between 1160C to 1060. It is fur-ther convenient to use a temperature which is related ~ TX such as ~ the temperature of the iron sample exactly 3 minutes after start of pouring. Other periods of time could be used or other techniques could be used to establish "normal cooling rate" such as a first derivative of tl1e cooling curve at a point where thermal conductivity plays a minOr role such as a point near the eutectic temperature.
Furthermore, other parameters derived from the cooling curve can be used in place of TX such as the time required to reach a prescribed temperature which is suitably lower tllan the eutectic, or the first 1 derivative of the cooling curve at a certain time or temperature, can be satisfactorily related to thermal conductivity.
Another embodiment of this invent1on is to use crucib]e 10 without thermocouple 27, namely crucible 30, In Figure 4, there is shown a cooling curve of time versus temperature obtained from a sample of cast iron cooled in crucib1e 30. In Figurc 4, the dcsiglla-tion "X" indicates the time to cool tilrough the 100~C range from 1160 C to 1060 C.
~55~
, Crucible 30 is similar to crucible 10 but only contains a single alumel-chromeI thermocouple 32 within lower portion 34. Crucible 30 has a larger portion 36 coextensive with partion 34. Typical dimensions for portion 34 are diameter of 18.5 mm;
height 29 mm; and thermocouple 32 spaced from the bottom of portion 34 by 6 mm. Typical dimensions for portion 36 are diameter of 50 mm and a height of 46 mm. For the reasons described above, that part of the sample in portion 34 will cool at a faster rate than the part of the sample in portion 36. A crucible as disclosed in U.S. Patent 4,056,407 can be modified to have the features of crucible 30.
Figure 6 is a graph wherein the temperature of the sample as read by the thermocouple 32 at the end of 3 minutes is plotted against time in seconds for the sample to cool from 1160C to 1060C. The graph of Figure 6 has been experimentally determined to define the time temperature relationship o~
suitable nodular iron when poured into a speci~ic arucible.
From Figure ~, the temperature is 938C and the time "X" is 50 seconds. When these parameters are applied to Figure 6, ~ T is 4C.
The operator will have been previously supplied with a graph of ~ T versus nodularity as shown in Figure 7. The graph of Figure 7 has been established for typical nodular iron when poured into crucible 30. Changes in crucible design will require a new graph utilizing the principles disclosed herein. As shown in Figure 7, the graph is preferably designated with zones such as green, yellow and red. When a T falls in the green zone, one is certain that the iron has sufficient nodularity. If a~ T falls in the yellow zon~ on the graph shown in Figure 7, the iron may be satis~actory but is questionable and further examination is necessary.
~ ' s~ ~
If the~T falls in the red zone on the graph shown in Figuxe 7, the iron is certain to have insufficient nodularity. ~;
When analyzing a specimen of cast iron, it is recommended that the cooling time starting with the casting of the sample and endiny with solidification of portions 14 or 34 should not be less than l-l/2 minutes in order to prevent the formation of carbides. Furthermore, the total duration of the analysis should be no longer than S minutes in arder for the method to produce economic advantages. With these goals in mind, the dimensions of the crucible lO are preferably chosen to meet these goals. Thus, the crucible 10 is preferably made from foundry sand with a resinous material binder, and with the inner diameter of the crucible lower part 13 being between about 18.5 mm and the inner diameter of part 12 is about 50 mm.
If a single temperature sensing element is used in that portion of the crucible which cools the fastest,~ is obtained from a graph as shown in Figures 4 and 6. If the crucible has dual thermal couples as shown in Figure l, ~T' is obtained off the graph shown in Figure 3. Then, the~T' is used with a graph attained experimentally, such as a graph in Figure 7, to ascertain nodularity.
Thus, the present invention comprehends obtaining a parameter of heat conductivity such as a~T after pouring a sample into a crucible and thereaftar using the parameter to predict whether or not the nodularity of castings to be made from the entire ladle will be satisfactory whereby pouring can commence~ If the nodularity is unsatisfactory, correc~ions may be made before the molten metal is poured or the entire ladle i5 pigged, thereby saving the molds and other operating C05tS. Nodularity can change with time. ~ence, it may be desirable to use the present invention to check nodularity iS3 after all castings have been p~ured to confirm the quality of the last poured castings.
5S5~3 1 When the present invention is used as part of an IN-MOLD
process, a variety of variations are possible. For example, the main mold cavity could correspond to portion 36 of crucible 30 and portion 34 of the crucible 30 could be a small auxiliary cavity and arranged to cool at a faster rate. The casting resulting from the auxili-ary cavity would be removed along with the sprue. --- An electronic microprocessor or desk calculator may be in-terfaced with a digital pyrometer for use as computer analysis con-trol equipment with red, yellow and green lights comparable to the ~ones of Figure 7. The present invention will drastically reduce quality control problems and eliminate tile cast of casting of molten metal with insufficient nodularity.
The present invention may be embodied in otller specific forms without departing from the spirit or essential attributes ;
thereof and, accordingly, reference should be made to the appended :~
claims, rather than to the foregoing specification as indicating ~
the scope of the invention. ~ ~ ;
,Y~
-E~
_ g _
~` -1 Background The present invention relates generally to a process for rapidly predicting a metallographic structure, such as the degree of nodularity, of castings to be made from molten metal before cast-ing and apparatus for performing the same.
It is known that the composltion of molten metal may be estimated by recording the liquidus and eutectic temperatures using ~--known cooling curves. Such method provides information such as a change in phase, carbon equivalent, etc. It is also known to deter-L0 mine the thermal conductivity of solid bodies by measuring the heat flow through such body ~hen subjected to a thermal gradient.
~_ It has been observed that in grey cast iron in the solid state, the thermal conductivity is substantially influenced by the graphitic structure and that a nodular cast iron, for instance, has a lower conductivity than a lamellar or equivalent composition.
When pouring cast iron, it is important that analysis be carried out very quickly and before casting. If one waits too long ~
before completing a pour of a nodular cast iron, a large percentage ~ ~.
of the magnesium which is present in the molten metal will dissipate 0 or will otherwise be lost and there is a likelihood of making an unsatisfactory cast.
The industry has long sought a simple, rapid and effective way of accurately predicting the degree of nodularity of a cast iron before casting of the sa~e. One method proposed heretofore is dis-closed iri U.S. Patent 3,670,558 wherein the properties of a nodular ~~~~~
cast iron are evaluated by way of a comparative study of conventional cooling curves and a set or family of curve segments. Tlle method ~ .
proposed by said patent has not proven to be acceptable.
Thus, at tile present time, the degree of nodularity of a ) cast iron can only be determined with precision if the sample is ' - :
c~h.rJ :~ .
~ ~ ~5~
1 cooled and evaluated by ultrasonic or metallographic analysis, and the like.
The main object of the present invention i8 to cope with said problem by proposing a new process and apparatus making it pos- ::
sible to predict in a simple, rapid and effective manner the degree of nodularity of the cast iron casting while the iron is still molten and while it is still possible to change the composition of the r----molten metal or it is possible to scrap the molten metal.
Summary of the Invention The process of the presen~ invention is directed to pre-dicting a metallographic structure of a casting which will result from use of a molten metal and comprises the steps of obtaining a sample of the molten metal; causing one part of the sample to solid-ify at a first rate and a second part of the sample to solidify at a slower rate; ascertaining a parameter of heat conductivity, and using the heat conductivity parameter of the sample after solidifi- ,~
cation of the first part to determine the metallographic structure which would result from use of the molten metal.
Apparatus for accomplishing the method described above in-cludes a small crucible into which a sample of molten metal is poured and within which the sample cools. The crucible in one embodiment has two temperature sensing devices at spaced locations correspond-ing to the first and second parts of the sample. In the preferred embodiment of the crucible, there is only one temperature sensin~
device. A means is associated with each of the types of crucibles to cause one part of the sample to solidify at a faster rate.
It is an object of the present invention to provide app~- ;
ratus and method which will facilitate predicting in a simple, rapid and reliable manner the degree of nodularity or other metallographic structure which will be present in a casting made from a particular batch of cast iron.
~.
s~
In accordance with a broad aspect, the invention relates to apparatus for use in determining a metallographic structure of molten metal, comprising:
(a~ a crucible having a cavity therein, ' ;~
(b) means for causing a first part of a sample in said cavity to cool at a faster rate than a second part of the sample, and temperature sensing means associated with said first part for measuring the temperature of a sample in said first part, and including a crucible with first and second contiguous parts of said ca~ity with a smallex transverse dimension for said first part so that the ratio of surface area to vol~me of the second cavity part is smaller than ~ -~
that of said first cavity part.
.
- 2a -~7,.
~S5~
1 Other objects will appear hereinafter.
For the purpose of illustrating the invention, there is shown in the drawings a form which is presently preferred; it being understood, however, that this invention is not limited to the pre-cise arrangements and instrumentalities shown.
Figure 1 is a sectional view through a first type of crucible usable in practicing the method of the present invention.
Figure 2 is a sectional view through another type of crucible usable when practicing the method of the present i-nvention.
Figure 3 is a graph showing two cooling curves showing temperature plotted against time.
Figure 4 is a graph showing a cooling curve wherein tem-perature is plotted against time using a single thermocouple.
- Figure S is a sectional view through another crucible.
Figure 6 is a graph of temperature after 3 minutes versus temperature to cool through a 100C zone containing the solidus arrest of the sample.
Figure 7 is a graph plotting ~T versus nodularity.
Referring to the drawings in detail, wilerein like numerals indicate like elements, there is shown in Figure 1 a first form of apparatus for use in practicing the method of the present invention.
Thus, there is shown a crucible designated generally as 10, the di-ameter of the upper part 12 being much greate} than the diameter of the lower part 13. As used herein, the word crucible is intended to include sample cups, molds used for I~-MOLD processes, and the like.
A crucible 10 constructed in this manner makes it possible to cool a sample of molten metal at two different rates. Thus, the lower portion 14 of a sample in the crucible 10 will cool more rapidly than the upper portion 15 of the sample in crucible 10 because the ratio of surface area to volume of the upper portion is smaller - than that of the lower portion.
~ - 3 -55~ i 1 In Figure 2, there is illustrated a second iorm of appa-ratus for use in practicing the method of the present invention. In F-gure 2, there is shown a crucible 10' of constant diameter. The lower portion 13' of the crucible 10' is placed in a jacket 18 of heat insulating material. As a result of the Jacket 18, the portion of the sample in the upper portion 19 of the crucible 10' will solid-ify at a faster rate as compared with the rate of solidification of the sample in the lower portion of the crucible 10'.
! Although the crucibles 10 and 10' are slightly different in construction as to their contour, the principle utilized in the method of the present invention is the same. In order to prevent ^
the formation of shrinkage cavities in the sample, it is preferable to design the crucibles in such a way that the portion having the fastest rate of solidification is in the lower portion of the cru-cible. Hence, the following description with respect Figure 3 will only make reference to crucible 10 shown in Figure 1.
Figure 3 represents the solidification curve 11 of portion 14 of a sample of grey cast iron at a first rate of cooling. The -temperature of the sample in portion 14 is sensed by a thermal sens-ing element such as a thermocouple 22. The thermocouple 22 is, in a preferred embodiment, ~enerally perpendicular to the center line or axis of the crucible 10. It will be seen from the curve 11 that ; a change in cooling rate ~t point 23 is recorded and corresponds to the liquidus temperature. There is also a more pronounced tempera-ture cha~ge at point 24 corresponding to the solidous temperature.
Thereafter curve 11 shows ~n inflection at a temperature TX instead of continuing to cool e~rollenti~lly along the line 25 as would be the case in an ordinary solidification curve in the case of a homo-geneous cooling of the s;l(nple.
5~
1 In the present case, the inflection of the curve 11 at point X is caused by the thermal reflection during the eutectic solidification of the upper portion 15 of the sample cooling at a second and lower rate as compared with the rate of cooling of the portion 14. The temperature T~ is the temperature at the point of inflection X on the curve 11. The temperature TX is a first param-. eter which is directly related to the thermal conductivity of the molten metal. The change in cooling rate results from the tempera~
ture of the eutectic level stretch of line 16 remaining practically constant around 1150C.
Curve 11 and line 25 delimit an area A which is also di-rectly related to the thermal conductivity of the sample. That is, the area A represents the thermal influence of the eutectic of por-- tion 15 of the sample on portion 14 o~ the sample. It has been noted that the thermal conductivity is related to the metallographic structure of a metal. A reading of temperature TX which relates to the point of inflection in the curve 11 and/or the evaluation of the area A, are related to the metallographic structure of the metal sample being analyzed.
The two parameters mentioned above can also be checked when the solidification curve 16 of the sample is recorded at the same ,,; . -.~ .
time on a single graph along with curve 11. To obtain the solidifi-cation curve 16, a temperature sensor such as a second thermocouple 27 is provided in the crucible 10 at a location which is associated with portion 15 of the sample. Thus, the thermocouples 22 and 27 are at substantially different locations but each is associated with one portion of the s~mple. At any given time, the differellce in temperature between the two curves 11 and 16 varies with the conduc-tivity of the metal sample and consequently with its degree of nodu-larity. Ilereinafter, such temperature difference will be referred to as ~ T'.
5~
1 It has been ascertained that TX is influenced by the eutec-tic temperature of portion 15 and a number of other factors including thermal conductivity, pouring temperature, the manner of pouring. It is desired to determine the thermal conductivity of the sample. It is thus desirable to eliminate the influence of the other parameters.
If the thermocouple 22 is at about the eutectic temperature of por-............... tion 14, cooling rate is not influenced to any significant extent by thermal conductivity since thermal gradiants are relatively low.
This makes possible the determination of a parameter "normal cooling rate" which is a rate without substantial influences of thermal con-ductivity. In this example, this rate is defined as the rate ol cooling across the 100C range between 1160C to 1060. It is fur-ther convenient to use a temperature which is related ~ TX such as ~ the temperature of the iron sample exactly 3 minutes after start of pouring. Other periods of time could be used or other techniques could be used to establish "normal cooling rate" such as a first derivative of tl1e cooling curve at a point where thermal conductivity plays a minOr role such as a point near the eutectic temperature.
Furthermore, other parameters derived from the cooling curve can be used in place of TX such as the time required to reach a prescribed temperature which is suitably lower tllan the eutectic, or the first 1 derivative of the cooling curve at a certain time or temperature, can be satisfactorily related to thermal conductivity.
Another embodiment of this invent1on is to use crucib]e 10 without thermocouple 27, namely crucible 30, In Figure 4, there is shown a cooling curve of time versus temperature obtained from a sample of cast iron cooled in crucib1e 30. In Figurc 4, the dcsiglla-tion "X" indicates the time to cool tilrough the 100~C range from 1160 C to 1060 C.
~55~
, Crucible 30 is similar to crucible 10 but only contains a single alumel-chromeI thermocouple 32 within lower portion 34. Crucible 30 has a larger portion 36 coextensive with partion 34. Typical dimensions for portion 34 are diameter of 18.5 mm;
height 29 mm; and thermocouple 32 spaced from the bottom of portion 34 by 6 mm. Typical dimensions for portion 36 are diameter of 50 mm and a height of 46 mm. For the reasons described above, that part of the sample in portion 34 will cool at a faster rate than the part of the sample in portion 36. A crucible as disclosed in U.S. Patent 4,056,407 can be modified to have the features of crucible 30.
Figure 6 is a graph wherein the temperature of the sample as read by the thermocouple 32 at the end of 3 minutes is plotted against time in seconds for the sample to cool from 1160C to 1060C. The graph of Figure 6 has been experimentally determined to define the time temperature relationship o~
suitable nodular iron when poured into a speci~ic arucible.
From Figure ~, the temperature is 938C and the time "X" is 50 seconds. When these parameters are applied to Figure 6, ~ T is 4C.
The operator will have been previously supplied with a graph of ~ T versus nodularity as shown in Figure 7. The graph of Figure 7 has been established for typical nodular iron when poured into crucible 30. Changes in crucible design will require a new graph utilizing the principles disclosed herein. As shown in Figure 7, the graph is preferably designated with zones such as green, yellow and red. When a T falls in the green zone, one is certain that the iron has sufficient nodularity. If a~ T falls in the yellow zon~ on the graph shown in Figure 7, the iron may be satis~actory but is questionable and further examination is necessary.
~ ' s~ ~
If the~T falls in the red zone on the graph shown in Figuxe 7, the iron is certain to have insufficient nodularity. ~;
When analyzing a specimen of cast iron, it is recommended that the cooling time starting with the casting of the sample and endiny with solidification of portions 14 or 34 should not be less than l-l/2 minutes in order to prevent the formation of carbides. Furthermore, the total duration of the analysis should be no longer than S minutes in arder for the method to produce economic advantages. With these goals in mind, the dimensions of the crucible lO are preferably chosen to meet these goals. Thus, the crucible 10 is preferably made from foundry sand with a resinous material binder, and with the inner diameter of the crucible lower part 13 being between about 18.5 mm and the inner diameter of part 12 is about 50 mm.
If a single temperature sensing element is used in that portion of the crucible which cools the fastest,~ is obtained from a graph as shown in Figures 4 and 6. If the crucible has dual thermal couples as shown in Figure l, ~T' is obtained off the graph shown in Figure 3. Then, the~T' is used with a graph attained experimentally, such as a graph in Figure 7, to ascertain nodularity.
Thus, the present invention comprehends obtaining a parameter of heat conductivity such as a~T after pouring a sample into a crucible and thereaftar using the parameter to predict whether or not the nodularity of castings to be made from the entire ladle will be satisfactory whereby pouring can commence~ If the nodularity is unsatisfactory, correc~ions may be made before the molten metal is poured or the entire ladle i5 pigged, thereby saving the molds and other operating C05tS. Nodularity can change with time. ~ence, it may be desirable to use the present invention to check nodularity iS3 after all castings have been p~ured to confirm the quality of the last poured castings.
5S5~3 1 When the present invention is used as part of an IN-MOLD
process, a variety of variations are possible. For example, the main mold cavity could correspond to portion 36 of crucible 30 and portion 34 of the crucible 30 could be a small auxiliary cavity and arranged to cool at a faster rate. The casting resulting from the auxili-ary cavity would be removed along with the sprue. --- An electronic microprocessor or desk calculator may be in-terfaced with a digital pyrometer for use as computer analysis con-trol equipment with red, yellow and green lights comparable to the ~ones of Figure 7. The present invention will drastically reduce quality control problems and eliminate tile cast of casting of molten metal with insufficient nodularity.
The present invention may be embodied in otller specific forms without departing from the spirit or essential attributes ;
thereof and, accordingly, reference should be made to the appended :~
claims, rather than to the foregoing specification as indicating ~
the scope of the invention. ~ ~ ;
,Y~
-E~
_ g _
Claims (4)
EXCLUSIVE PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS
FOLLOWS:
1. Apparatus for use in determining a metallographic structure of molten metal, comprising:
(a) a crucible having a cavity therein, (b) means for causing a first part of a sample in said cavity to cool at a faster rate than a second part of the sample, and temperature sensing means associated with said first part for measuring the temperature of a sample in said first part, and including a crucible with first and second contiguous parts of said cavity with a smaller transverse dimension for said first part so that the ratio of surface area to volume of the second cavity part is smaller than that of said first cavity part.
(a) a crucible having a cavity therein, (b) means for causing a first part of a sample in said cavity to cool at a faster rate than a second part of the sample, and temperature sensing means associated with said first part for measuring the temperature of a sample in said first part, and including a crucible with first and second contiguous parts of said cavity with a smaller transverse dimension for said first part so that the ratio of surface area to volume of the second cavity part is smaller than that of said first cavity part.
2. Apparatus in accordance with claim 1 wherein said first part is the lower end portion of said crucible.
3. Apparatus according to claim 1 wherein the first part of the sample is the only part of the cavity containing a temperature sensing means.
4. Apparatus in accordance with claim 3 wherein said crucible is a mold, said first cavity par. being an auxiliary cavity to the main mold cavity which is said second part.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA363,367A CA1115553A (en) | 1977-05-18 | 1980-10-27 | Method and apparatus for predicting metallographic structure |
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| FR7715402A FR2391473A1 (en) | 1977-05-18 | 1977-05-18 | METHOD AND DEVICE FOR DETERMINING THE METALLOGRAPHIC STRUCTURE OF METALS OR ALLOYS |
| FR7715402 | 1977-05-18 | ||
| CA303,295A CA1114196A (en) | 1977-05-18 | 1978-05-15 | Method and apparatus for predicting metallographic structure |
| CA363,367A CA1115553A (en) | 1977-05-18 | 1980-10-27 | Method and apparatus for predicting metallographic structure |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1115553A true CA1115553A (en) | 1982-01-05 |
Family
ID=27165659
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA363,367A Expired CA1115553A (en) | 1977-05-18 | 1980-10-27 | Method and apparatus for predicting metallographic structure |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1115553A (en) |
-
1980
- 1980-10-27 CA CA363,367A patent/CA1115553A/en not_active Expired
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