U.S. patent application number 11/912861 was filed with the patent office on 2009-07-02 for method for predicting and preventing shrinkage cavity of iron casting.
This patent application is currently assigned to KIMURA CHUZOSHO CO., LTD.. Invention is credited to Ilgoo Kang, Toshitake Kanno, Kimio Kubo, Toshihiko Murakami.
Application Number | 20090165982 11/912861 |
Document ID | / |
Family ID | 37307644 |
Filed Date | 2009-07-02 |
United States Patent
Application |
20090165982 |
Kind Code |
A1 |
Kanno; Toshitake ; et
al. |
July 2, 2009 |
Method for Predicting and Preventing Shrinkage Cavity of Iron
Casting
Abstract
A method for predicting and preventing occurrence of shrinkage
cavity in an iron casting of any of various shapes or in each part
of an iron casting precisely prior to casting. The shape of an iron
casting is approximated entirely or partially to a rectangular
parallelepiped or a cube, to the sum of the two long sides is
divided by the short side to determine a shape coefficient, and
occurrence of shrinkage cavity is predicted by determining whether
the value exceeds a predetermined value (determination coefficient)
or not.
Inventors: |
Kanno; Toshitake; (Shizuoka,
JP) ; Kang; Ilgoo; (Shizuoka, JP) ; Murakami;
Toshihiko; (Osaka, JP) ; Kubo; Kimio;
(Tochigi, JP) |
Correspondence
Address: |
THOMPSON COBURN LLP
ONE US BANK PLAZA, SUITE 3500
ST LOUIS
MO
63101
US
|
Assignee: |
KIMURA CHUZOSHO CO., LTD.
Shizuoka
JP
QUALICA INC.
Tokyo
JP
EKK JAPAN INC.
Tochigi
JP
|
Family ID: |
37307644 |
Appl. No.: |
11/912861 |
Filed: |
April 26, 2005 |
PCT Filed: |
April 26, 2005 |
PCT NO: |
PCT/JP2005/007886 |
371 Date: |
December 30, 2008 |
Current U.S.
Class: |
164/76.1 |
Current CPC
Class: |
B22D 46/00 20130101;
B22C 9/088 20130101 |
Class at
Publication: |
164/76.1 |
International
Class: |
B22D 46/00 20060101
B22D046/00 |
Claims
1. A method for predicting shrinkage cavity in an iron casting, the
method comprising: determining a shape coefficient which is a value
obtained by dividing a sum of two long sides by a remaining short
side from a shape of a casting product; and confirming whether the
shape coefficient is not more than 8 or not to predict occurrence
of the shrinkage cavity.
2. A method for predicting shrinkage cavity in an iron casting, the
method comprising: determining a shape coefficient of each of
closed elliptical loops in a solidification distribution chart
obtained from a temperature distribution or a solidification time
distribution in a solidification of a casting product; and
confirming whether or not the shape coefficient is 8 or more to
predict occurrence of the shrinkage cavity in each of the closed
elliptical loops.
3. The method for predicting shrinkage cavity according to claim 2,
wherein the size of the elliptical loop is measured on a screen
using the solidification distribution chart obtained from the
temperature distribution or the solidification time distribution
due to a solidification simulation, thereby to calculate the shape
coefficient.
4. The method for predicting shrinkage cavity according to claim 2,
wherein the shape coefficient is calculated from the number in X, Y
and Z directions of elements constituting the elliptical loops
divided by mesh cutting by use of the solidification distribution
chart obtained from the temperature distribution or the
solidification time distribution due to a solidification
simulation.
5. A method for predicting shrinkage cavity in an iron casting, the
method comprising: dividing a product using a chiller or a feeder
head or using the chiller and the feeder head together when the
shape coefficient is more than 8 to set the shape coefficient to 8
or less.
6. The method for predicting and preventing shrinkage cavity
according to, claim 1 wherein the shape coefficient of whether the
shrinkage cavity occurs or not is determined by a component of the
casting, a property of a mold and a cast position.
7. The method for predicting and preventing shrinkage cavity
according to claim 2 wherein the shape coefficient of whether the
shrinkage cavity occurs or not is determined by a component of the
casting, a property of a mold and a cast position.
8. The method for predicting and preventing shrinkage cavity
according to claim 3 wherein the shape coefficient of whether the
shrinkage cavity occurs or not is determined by a component of the
casting, a property of a mold and a cast position.
9. The method for predicting and preventing shrinkage cavity
according to claim 4 wherein the shape coefficient of whether the
shrinkage cavity occurs or not is determined by a component of the
casting, a property of a mold and a cast position.
10. The method for predicting and preventing shrinkage cavity
according to claim 5 wherein the shape coefficient of whether the
shrinkage cavity occurs or not is determined by a component of the
casting, a property of a mold and a cast position.
Description
TECHNICAL FIELD
[0001] The present invention relates to a method for predicting and
preventing shrinkage cavity of an iron casting.
BACKGROUND ART
[0002] Various types of methods for predicting shrinkage cavity
have been posed for many years. Typical examples thereof include an
evaluating method proposed by Tivolinov of Russia and an evaluating
method proposed by Niiyama. The former uses modulus which is a
value obtained by dividing the volume of a casting by the surface
area thereof. The latter uses a value obtained by dividing a
temperature gradient G by the square root R of a cooling rate.
[0003] However, these methods for predicting shrinkage cavity can
be effective for cast steel, nonferrous metal or the like having no
expansion caused by the generation of graphite. However, the
methods are not necessarily effective for cast iron caused by the
generation of graphite.
[0004] Therefore, Yoshida et al. has proposed Patent Document 1 as
a method for determining occurrence of shrinkage cavity of
spheroidal graphite cast iron. This method measures eutectic
crystal solidification times of the inside and surface of the
casting, and determines whether the shrinkage cavity exists or not
from the overlapping degree of the eutectic crystal solidification
times, i.e., the Massey degree. Patent Document 2 proposes a method
for obtaining a solid phase rate from the number of grains and
graphite diameter of graphite and using the solid phase rate for
determining the shrinkage cavity.
[0005] The determining methods proposed by Yoshida et al. are
useful to some extent for determining the tendency of the shrinkage
cavity of the spheroidal graphite cast iron. However, it is
difficult to predict the shrinkage cavity using such methods. This
is because the shrinkage cavity occurs in a larger iron casting in
these methods, which disagrees with the fact discovered by the
present inventors that no correlation exists between the shrinkage
cavity and the size of the product when the mold strength is
sufficiently high.
[0006] A "hot spot method" using a solidification simulation has
been usually employed as the method for predicting shrinkage
cavity. This method focuses on easy occurrence of shrinkage cavity
in a non-solidified metal part since molten iron cannot be
resupplied to the non-solidified metal part when an island of
molten iron broken from the other, i.e., loops (referred to as "hot
spot" in an island of the non-solidified metal surrounded by a
metal having solidified circumference) having a closed temperature
constant-temperature line or solidification line are formed in the
casting in a solidification process. Since the cast steel and
nonferrous metal having no expansion caused by the crystallization
of graphite has an extremely high probability that the shrinkage
cavity occurs in the "hot spot" part, the "hot spot method" has
been widely used as a high-precision determining method. However,
when the "hot spot" is formed in the cast iron having expansion
caused by the crystallization of graphite, this part does not
necessarily become the shrinkage cavity.
[0007] Patent Document 1: Japanese Patent Application Laid-Open No.
10-296385
[0008] Patent Document 2: Japanese Patent Application Laid-Open No.
05-96343
DISCLOSURE OF INVENTION
Problem to be Solved by the Invention
[0009] As the methods for preventing shrinkage cavity, a feeder
head and a chiller etc. are used. As for the feeder head ordinary
used is a method for calculating a modulus of a product and
erecting a feeder head having a larger modulus than the modulus of
the product. Therefore, there is a problem that the size of the
feeder head is almost the same as that of the product, and the
yield becomes extremely worse. Cast iron hardly causes occurrence
of shrinkage cavity as compared with cast steel. For this reason,
when the amount of the feeder head is lessened, the shrinkage
cavity occurs, and after all, the shrinkage cavity occurs in many
cases if the same feeder head as that of the cast steel is not
erected. For the method for preventing shrinkage cavity using the
chiller, the place of the shrinkage cavity can be moved by
constructing the chiller, but the shrinkage cavity cannot be lost.
This is because the cast iron has the complicated occurrence
mechanism of the shrinkage cavity and the mechanism is not
sufficiently resolved.
[0010] Various types of methods for predicting shrinkage cavity
have been proposed as described in the prior art. However, the
method for predicting shrinkage cavity, which is appropriate to the
property of cast iron and has high accuracy, has not been
established at present. Also, a method for preventing shrinkage
cavity, which is efficiently appropriate to the property of cast
iron, has not been proposed even if the method can predict the
shrinkage cavity.
[0011] It is an object of the present invention to provide means
for precisely predicting existence or nonexistence of occurrence of
shrinkage cavity in a casting of any of various shapes or in each
part of the casting, and capable of performing a suitable casting
method and changing a product shape for the casting predicted to
cause the occurrence of the shrinkage cavity or each part of the
casting so that a sound casting can be obtained.
Means for Solving the Problem
[0012] The present inventors investigated the existence or
nonexistence of occurrence of shrinkage cavity and carried out
various types of experiments such as solidification simulation and
measurement of temperature for various casting products having
different sizes, materials or shapes to resolve that the shrinkage
cavity occurs in the casting product having what type of shape. The
means will be illustrated using an example of a block of a
rectangular parallelepiped. The present inventors have discovered
that the occurrence of the shrinkage cavity is prevented regardless
of the size of the casting when a value (herein, referred to as
"shape coefficient") obtained by dividing the sum of two long sides
of the rectangular parallelepiped by the length of a remaining
short side is not more than a certain numerical value. The present
inventors have discovered that the certain numerical value herein
is about 8 in ordinary spheroidal graphite cast iron which contains
no elements promoting the shrinkage cavity such as Cr and Mo, and
also that the value changes as Cr or Mo increases.
[0013] The present inventors have also discovered that when the
casting product has a shape which is not the rectangular
parallelepiped block, the shape may be approximately considered to
be the rectangular parallelepiped. For example, in the case of the
spherical product, the shape may be considered as a cube with one
side to which a sphere is inscribed being equal to the diameter of
the sphere, and in the case of a product having a cylindrical
shape, the shape may be considered as a rectangular parallelepiped
of which two long sides are equal to the diameter of a circle. The
shape may be considered as a rectangular parallelepiped obtained by
developing the cylinder in the case of a doughnut-shaped cylinder
having a hole therein. The present inventors have discovered that a
product of a combination of various shapes may be considered by
dividing the parts of the product.
[0014] As described above, the existence or nonexistence of the
shrinkage cavity can be determined from only the shape of the
product. Also, the present inventors have discovered that the
occurrence of the shrinkage cavity can be predicted in each of
closed elliptical loops as follows. Solidification analysis or the
like is performed to obtain a shape coefficient of each of the
closed elliptical loops in a solidification distribution chart
obtained from a temperature distribution or a solidification time
distribution in the solidification of the casting product, followed
by determining whether the value is not more than 8.
[0015] The use of such a method can determine whether or not
shrinkage cavity occurs in "hot spot" which is an island of molten
iron broken from the other, i.e., loops having a closed temperature
constant-temperature line or solidification line in the casting in
the solidification process. Naturally, the shape coefficient may be
determined as an elliptical sphere. However, the shape coefficient
may be determined by approximating an elliptical sphere having a
closed Rugby ball shape to the rectangular parallelepiped.
[0016] A method for determining the shape coefficient of each of
the closed elliptical loops in the solidification simulation using
a computer is as follows.
[0017] As one method, there is a method for measuring the size of
an arbitrary elliptical loop on a screen by operation of a mouse or
the like using a solidification distribution chart obtained from a
temperature distribution or solidification time distribution due to
solidification simulation to obtain a shape coefficient.
[0018] As the other method, there is used a method for specifying
an arbitrary elliptical pool to determine a shape coefficient. For
example, the whole solidification time is divided to a plurality of
times, and the elliptical loop in arbitrary time of them is
specified. This elliptical loop is composed by elements in the mesh
cutting. It is determined how many elements exist in X, Y and Z
directions of this mesh to determine a shape coefficient of the
elliptical loop.
[0019] Examples of the other methods include a method for
processing data of extracted arbitrary elliptical loop in another
place to evaluate the shape and to calculate a shape
coefficient.
[0020] Thus, many means can be considered as the method for
determining a shape coefficient of an elliptical loop using a
computer.
[0021] Of course, the industrial greatest worth of the present
invention is that the shrinkage cavity can be predicted. The other
worth thereof is that a method for preventing the shrinkage cavity
is proposed. That is, the present inventors have discovered that
occurrence of the shrinkage cavity is prevented by dividing a
product so that a shape coefficient is set to not more than 8 using
a chiller or a feeder head, or both the chiller and the feeder
head.
[0022] The example of the rectangular parallelepiped will be
illustrated. When a plate of 800.times.400.times.80 mm is used as
an example, it is turned out that a shape coefficient of the plate
is (800+400)/80=15 and the shrinkage cavity occurs when the shape
coefficient is 8 or more. When the plate is divided into four by
the chiller, the shape coefficient is (400+200)/80=7.5, and the
shrinkage cavity does not occur when the shape coefficient is 8 or
less. The phenomenon as the description could be observed even in
the actual product test. As for the chiller available is a method
for constructing a chiller directly brought into contact with
molten iron. However, since one loop of blocked solidification need
only to be divided into four, a method for constructing the chiller
which is not directly brought into contact with the molten iron has
also no problem. When the construction area of the chiller is
excessively increased, and the closed solidification loop is not
divided into four, the shrinkage cavity naturally occurs. It is,
therefore, necessary to pay attention to the shrinkage cavity. When
the feeder head is used, the feeder heads are constructed at four
places of the above plate, and the closed solidification loop may
be divided into four.
[0023] The shape coefficient of whether the shrinkage cavity occurs
or not is naturally changed when containing elements such as Cr and
Mo for promoting the shrinkage cavity, or conversely, according to
the amount of C preventing the shrinkage cavity. Also, the shape
coefficient is changed depending on, for example, the strength
(correctly, the strength of a mold at a high temperature) of the
mold, and the rigidity of a mold frame. The value of the shape
coefficient for determining the shrinkage cavity is preferably
determined by considering these conditions. However, in the case of
an organic self-hardening mold generally used, the experiment of
the present inventors shows that the shape coefficient of about 8
needs only to be used. Even in flake graphite cast iron, the
existence or nonexistence of the shrinkage cavity can be determined
by the shape coefficient to construct a measure so as to prevent
the shrinkage cavity from occurring.
[0024] To summarize the description, a first aspect of the present
invention provides a method for predicting shrinkage cavity in an
iron casting, the method comprising: determining a shape
coefficient which is a value obtained by dividing a sum of two long
sides by a remaining short side from a shape of a casting product;
and confirming whether or not the shape coefficient is 8 or more to
predict occurrence of the shrinkage cavity.
[0025] A second aspect of the present invention provides a method
for predicting shrinkage cavity in an iron casting, the method
comprising: determining a shape coefficient of each of closed
elliptical loops in a solidification distribution chart obtained
from a temperature distribution or a solidification time
distribution in a solidification of a casting product; and
confirming whether or not the shape coefficient is 8 or more to
predict occurrence of the shrinkage cavity in each of the closed
elliptical loops.
[0026] A third aspect of the present invention provides the method
for predicting shrinkage cavity according to the second aspect,
wherein the size of the elliptical loop is measured on a screen
using the solidification distribution chart obtained from the
temperature distribution or the solidification time distribution
due to a solidification simulation, thereby to calculate the shape
coefficient.
[0027] A fourth aspect of the present invention provides the method
for predicting shrinkage cavity according to the second aspect,
wherein the shape coefficient is calculated from the number in X, Y
and Z directions of elements constituting the elliptical loops
divided by mesh cutting by use of the solidification distribution
chart obtained from the temperature distribution or the
solidification time distribution due to a solidification
simulation.
[0028] A fifth aspect of the present invention provides a method
for predicting shrinkage cavity in an iron casting, the method
comprising: dividing a product using a chiller or a feeder head or
using the chiller and the feeder head together when a shape
coefficient is more than 8 to set the shape coefficient to 8 or
less.
[0029] A sixth aspect of the present invention provides the method
for predicting and preventing shrinkage cavity according to any of
the first to fifth aspects, wherein the shape coefficient of
whether the shrinkage cavity occurs or not is determined by
components of the casting, a property of a mold and a cast
position.
Effect of the Invention
[0030] The present invention founds a new concept of a shape
coefficient, and can use the shape coefficient to simply predict
occurrence of the shrinkage cavity with extremely high accuracy.
Even when the casting components, the type of the mold, the cast
position and the like are different, the occurrence of the
shrinkage cavity can be predicted by the shape coefficient.
Furthermore, when the occurrence of the shrinkage cavity is
predicted, the occurrence of the shrinkage cavity can be logically
prevented by using effectively the chiller or the feeder head.
Therefore, the present invention has effects such as the reduction
of defective fraction in the iron casting, the improvement in yield
and the shortening of delivery time, and can produce spheroidal
graphite cast iron efficiently at low cost.
BRIEF DESCRIPTION OF DRAWINGS
[0031] FIGS. 1A, 1B, 1C, 1D, 1E, 1F and 1G describe the shape
approximation of a casting product.
[0032] FIG. 2 is a graph showing the relationship between a shape
coefficient of a rectangular parallelepiped and shrinkage
cavity.
[0033] FIG. 3 is a graph showing the relationship between a shape
coefficient of a disc-shaped object and shrinkage cavity.
[0034] FIG. 4 is a graph showing the relationship between a shape
coefficient of a cylindrical body and shrinkage cavity.
[0035] FIG. 5 is a graph showing the relationship between shape
coefficients of rectangular parallelepipeds in different cast
positions and shrinkage cavity.
[0036] FIG. 6 is a graph showing the relationship between shape
coefficients of rectangular parallelepipeds of different molten
iron components and shrinkage cavity.
[0037] FIG. 7 is a graph showing the relationship between shape
coefficients of rectangular parallelepipeds and shrinkage cavity in
a case of using different molds.
[0038] FIG. 8 shows an example predicting shrinkage cavity in a
computer simulation.
[0039] FIG. 9 shows an example of a section in which elliptical
loops exist.
[0040] FIG. 10 shows a dialog for measuring a width (w), a length
(l) and a thickness (t.sub.MS).
[0041] FIG. 11 shows an example of a section in which elliptical
loops exist.
[0042] FIG. 12 shows an example of elliptical loops of a
solidification distribution chart.
[0043] FIG. 13 shows an example of a cube circumscribed to
elliptical loops.
[0044] FIG. 14 shows a dialog for automatically calculating a shape
coefficient.
[0045] FIG. 15 shows a method for constructing a chiller to prevent
shrinkage cavity.
[0046] FIG. 16 shows a method for constructing a feeder head to
prevent shrinkage cavity.
[0047] FIG. 17 shows an example using a mistake chiller.
[0048] FIG. 18 shows an example using a correct chiller.
[0049] FIG. 19 is a flow chart of a method for predicting and
preventing shrinkage cavity in an iron casting product.
BEST MODE FOR CARRYING OUT THE INVENTION
[0050] The above and other objects, aspects and advantages of the
present invention will make apparent, to those skilled in the art
with reference to the following detailed description in which the
preferred specific examples suitable to the principle of the
present invention are shown as embodiments and the accompanying
drawings. As a matter of course, the present invention, which is
described in the following detailed description, is not limited to
the embodiments shown in the accompanying drawings.
[0051] Hereinafter, the present invention will be described in
detail based on specific examples.
[0052] The present invention fundamentally uses a shape coefficient
(F) determined as a value obtained by dividing the sum of two long
sides by a remaining short side. As most understandable examples,
in a case of a block having a casting shape of a rectangular
parallelepiped, a value obtained by dividing the sum of a width (W)
and length (L) of the block by a thickness (T.sub.MS: the shortest
side of three sides) is a shape coefficient. The shape of a block
having a shape other than the rectangular parallelepiped may be
approximately considered to be the rectangular parallelepiped.
[0053] FIG. 1 shows examples in the case of determining a shape
coefficient of each of castings having various shapes.
[0054] FIG. 1(a) shows a cube, and all of a width (W), length (L)
and height (T.sub.MS) become a length of one side of the cube.
FIGS. 1(b) and 1(c) respectively show the case where a plate of a
rectangular parallelepiped is horizontally placed and the case
where the plate of the rectangular parallelepiped is vertically
placed, with the width (W), the length (L) and the height
(T.sub.MS) being taken. FIG. 1(d) shows a disc having a height of
less than a diameter. As for the shape of the disc, the diameter of
the disc is considered to be the width (W) and the length (L), and
the height (wall thickness) is considered to be T.sub.MS to
determine a shape coefficient. As shown in FIG. 1(e), in the case
of a cylinder having a height of not less than a diameter, the
diameter of the cylinder is considered to be the width (W) and the
height (T.sub.MS), and the height of the cylinder is considered to
be the length (L). In the case of a doughnut-shaped tube shown in
FIG. 1(f), a tube is developed to form a rectangular
parallelepiped, and a shape coefficient is determined by
respectively considering the height of the tube, the length of the
circumference and the thickness of the tube to be the width (W),
the length (L) and T.sub.MS.
[0055] In FIG. 1(g) where the cylinder, the plate of the
rectangular parallelepiped and the tube are combined, a cylindrical
part, a plate part of a rectangular parallelepiped and a tubular
part are respectively considered to be a cylinder, a plate and a
tube. A shape coefficient of each of the parts may be determined by
the above method, and it may be determined whether or not shrinkage
cavity occurs in each of the parts. Also, a measure for preventing
the shrinkage cavity to be described later may be performed for
each of the parts.
[0056] FIGS. 2, 3 and 4 show experimental results obtained by
measuring the relationship between a shape coefficient
((L+W)/T.sub.MS) and an area rate of shrinkage cavity in test
pieces having different shapes and sizes. An ordinary ductile iron
casting (FCD600) is used for the material of the test pieces, and a
furan self-hardening mold is used for a mold. In the experiment,
the dimensions (width, length, thickness and diameter) of the test
piece are changed as shown in Table of each of FIG. 2 to 4 to
produce some test pieces shown by numbers A, B and C, and to
measure the relationship between the shape coefficient and the area
rate of the shrinkage cavity for each of the test pieces.
[0057] FIG. 2 shows a plate test piece of a rectangular
parallelepiped, FIG. 3 shows a test piece of a disc shape, and FIG.
4 shows a test piece of a tubular shape. FIGS. 2, 3 and 4 show that
the shrinkage cavity occurs when the shape coefficient
((L+W)/T.sub.MS) is more than 8 and the shrinkage cavity does not
occur when the shape coefficient is not more than 8. That is, FIGS.
2, 3 and 4 show that the occurrence of the shrinkage cavity can be
predicted by the shape coefficient in spite of the shape. Herein,
when the shape coefficient causing no occurrence of the shrinkage
cavity is referred to as determination coefficient, FIGS. 2, 3 and
4 show that the determination coefficient is 8.
[0058] The present inventors also investigated whether or not there
is the difference in the shape coefficients causing no occurrence
of the shrinkage cavity depending on a cast position, i.e., how to
place a casting, i.e., the determination coefficients. FIG. 5 shows
experimental results of the relationship between the shape
coefficient ((L+W/T.sub.MS) and the area rate of the shrinkage
cavity when the same casting (a plate of a rectangular
parallelepiped as the test piece) is vertically and horizontally
placed. The test piece is an ordinary ductile iron casting
(FCD600).
[0059] As shown in FIG. 5, when the shape coefficient is 8 or less,
the shrinkage cavity does not occur in the test piece (number D1 of
Table) horizontally placed. However, when the shape coefficient is
6 or less, the shrinkage cavity does not occur in the test piece
(number D2 of Table) vertically placed. Therefore, the
determination coefficient is 8 in the test piece horizontally
placed, and the determination coefficient is 6 in the test piece
vertically placed.
[0060] The reason why the difference in the determination
coefficients appears according to the cast position is believed to
be based on the influence of gravity. That is, it is turned that
the shape coefficient (determination coefficient) causing no
occurrence of the shrinkage cavity changes even in the casting
having the same component and size. Therefore, a shape coefficient
value for determining the shrinkage cavity is preferably determined
by considering these conditions.
[0061] Next, the present inventors also investigated whether or not
there is the difference in the shape coefficients causing no
occurrence of the shrinkage cavity when a ductile casting contains
elements promoting the occurrence of the shrinkage cavity. Mo is a
well-known element promoting the occurrence of the shrinkage
cavity.
[0062] FIG. 6 shows experimental results of the relationship
between the shape coefficient and the area rate of the shrinkage
cavity for three test pieces (numbers E1, E2 and E3 of Table)
having different contents of Mo.
[0063] The experiment results show that the shrinkage cavity does
not occur in the ordinary ductile casting which does not contain Mo
when the shape coefficient is not more than 8. The experiment
results also show that the shrinkage cavity does not occur at the
shape coefficient of not more than 6 when the ductile casting
contains Mo of 0.3% by weight and at the shape coefficient of not
more than 3 when the ductile casting contains Mo of 0.6% by weight.
That is, it is clear that the inclusion of the elements promoting
the occurrence of the shrinkage cavity changes the shape
coefficient (determining coefficient) causing no occurrence of the
shrinkage cavity. The value of the shape coefficient for
determining the shrinkage cavity is preferably determined by
considering these conditions.
[0064] The present inventors also investigated whether there is the
difference in the shape coefficients causing no occurrence of the
shrinkage cavity, i.e., the determination coefficients when the
type of the mold is different. FIG. 7 shows the relationship
between the shape coefficient and the area rate of the shrinkage
cavity when the type of the mold is different (the numbers F1, F2,
F3 and F4 of Table).
[0065] A plate of a rectangular parallelepiped is used as the test
piece in FIG. 7, and the shrinkage cavity does not occur when the
shape coefficient is not more than 2 in a CO.sub.2 type mold
believed to have no high temperature strength. Next, the shrinkage
cavity does not occur when the shape coefficient is not more than 6
in a greensand type mold having a low high temperature strength,
when the shape coefficient is not more than 8 in a furan type mold
having a sand strength of 10 kgf/cm.sup.2 at a normal temperature,
and when the shape coefficient is not more than 10 in a furan type
mold having a sand strength of 30 kgf/cm.sup.2 at a normal
temperature. That is, FIG. 7 shows that the shape coefficient
(determination coefficient) causing no occurrence of the shrinkage
cavity is different according to the type of the mold. The value of
the shape coefficient for determining the shrinkage cavity is
preferably determined by considering these conditions.
[0066] FIG. 8 shows an example predicting shrinkage cavity using a
solidification simulation due to a computer.
[0067] In the solidification simulation, a solidification
distribution chart is obtained from a temperature distribution or a
solidification time distribution. A shape coefficient (f) can be
calculated by respectively measuring dimensions of a width (w),
length (l) and thickness (t.sub.MS) from closed elliptical loops.
As the elliptical loops, the innermost loop need not to be
necessarily used, and the loops are preferably used to a last
solidification part from a last half solidification part (the
elliptical loop used in the following description means the loops
to the last solidification part from the last half solidification
part).
[0068] In the example shown in FIG. 8, the shape coefficient (F)
determined from the shape of the test piece is (200+200)/100=4, and
the shape coefficient (f) determined from the elliptical loop due
to the solidification simulation is also (60+60)/30=4. This result
shows that the shape coefficient (f) determined from the elliptical
loop of the solidification distribution chart obtained from the
solidification simulation is a value approximated to the shape
coefficient (F) determined from the shape of the test piece. That
is, the shrinkage cavity can be predicted based on the shape
coefficient from the solidification distribution chart by the
solidification simulation due to the computer. When the product
shape is particularly complicated, the shrinkage cavity is
effectively predicted based on such a solidification simulation.
When the complicated shapes are combined, it is turned out that a
shape coefficient (f) of the elliptical loop occurring for each of
the shapes is determined and the shrinkage cavity may be predicted
from the shape coefficient (f) thus determined.
[0069] (1) One Example of Methods for Measuring Width (w), Length
(l) and Thickness (t.sub.MS) due to Solidification Simulation
[0070] There is shown an example of methods for measuring a width
(w), length (l) and thickness (t.sub.MS) required for calculating a
shape coefficient due to a solidification simulation in the present
invention.
[0071] In the solidification simulation, the solidification
distribution chart is obtained from the temperature distribution or
the solidification time distribution. First, as shown in FIG. 9, a
section in which the elliptical loop exists is displayed for
measuring the closed elliptical loop from the obtained distribution
chart. Next, the size of the elliptical loop is measured. The
dialogs of U, V and W shown in FIG. 10 in measuring the size are
used. If "Measurement in U direction" of this dialog is pushed on
the screen, for example, the loop of an XY section viewed from an X
direction is displayed. If "Measurement in V direction" is pushed,
for example, the loop of a YZ section viewed from a Y direction is
displayed. If "Measurement in W direction" is pushed, for example,
the loop of a ZX section viewed from a Z direction is displayed. In
the measurement of l, w and t.sub.MS of the elliptical loop, a
measurement starting position and a measurement end position are
specified on the screen using a mouse or the like. The measurement
in the thickness direction of the section displayed is performed by
changing the section to be displayed using the dialog of FIG. 10,
as shown in FIG. 11. At this time, the measurement in three
directions is required. However, since it is unknown which
direction is the width (w), the length (l) and the thickness
(t.sub.MS), the system automatically considers that the shortest
length is the thickness t.sub.MS from the measuring results of
three directions. The system considers and determines that the
others are the width (w) and the length (l). When the measurement
in three directions is completed, the shape coefficient is
calculated by clicking a "calculation" button. A calculated value
is displayed on a shape coefficient column of FIG. 10.
[0072] (2) One Example of Automatic Calculation of Shape
Coefficient Due to Solidification Simulation
[0073] There is shown an example of methods for automatically
calculating a shape coefficient due to simulation.
[0074] In the solidification simulation, a solidification
distribution chart is obtained from a temperature distribution or a
solidification time distribution. The total frame number (a value
for dividing how many times to the solidification end from the
solidification start) and the display frame number (a numerical
value for displaying an island (loop) of what position of times
divided to the solidification end from the solidification start)
are specified for obtaining (displaying) an arbitrary closed
elliptical loop from the solidification distribution chart.
Therefore, some islands shown in FIG. 12 are obtained. These
islands mean an isothermal distribution or an equal solidification
time distribution. These islands are composed by elements divided
by the mesh cutting for the solidification simulation. As shown in
FIG. 13, a rectangular parallelepiped circumscribed to this island
is calculated by counting the number of elements in each of X, Y
and Z directions. A width (w), a length (l) and a thickness
(t.sub.MS) are determined from the rectangular parallelepiped, and
the shape coefficient is automatically calculated.
[0075] Finally, the shape coefficient of each of islands can be
determined by clicking a calculation button shown in FIG. 14. For
example, it can be determined whether or not the shrinkage cavity
occurs in a portion by coloring blue to red for the shape
coefficient and viewing whether the shape coefficient is high or
low.
[0076] Of course, the present invention can predict the shrinkage
cavity. However, the present invention also proposes a method for
preventing the shrinkage cavity, and an example thereof is shown
below.
[0077] FIG. 15 shows a construction example of a chiller preventing
the occurrence of the shrinkage cavity.
[0078] Since the test piece is an ordinary ductile iron (FCD600),
and has a cast position horizontally placed, the determination
coefficient is 8. However, since the shape coefficient of the test
piece is (400+800)/80=15, exceeding 8 in the example of FIG. 15,
the shape causes the occurrence of the shrinkage cavity. The
chillers are constructed crosswise at the upper and lower sides of
the test piece, and the solidification distribution chart was
determined by the solidification simulation. An A-A' section and a
B-B' section in FIG. 15 show that the closed elliptical loop is
divided into four. That is, four rectangular parallelepipeds
divided by the chiller may be believed to solidify independently
and respectively. Therefore, since the shape coefficient of the
divided rectangular parallelepiped is (400+200)/80=7.5, that is,
above 8, the occurrence of the shrinkage cavity can be
prevented.
[0079] FIG. 16 shows one of construction examples of a feeder head
for preventing the occurrence of the shrinkage cavity.
[0080] Since the test piece having the same material and dimensions
as those of the case of FIG. 15 is used, the shape coefficient of
the test piece is 15, and the shape causes the original occurrence
of the shrinkage cavity. Four feeder heads having a diameter of 150
mm and a height of 225 mm were constructed on the test piece, and
the solidification distribution chart is determined by the
solidification simulation. An A-A' section of FIG. 16 shows that
the closed elliptical loop is divided into four. That is, even in
this case, four rectangular parallelepipeds divided by the feeder
head may be believed to solidify independently and respectively. A
shape coefficient (F) of the divided rectangular parallelepiped is
7.5, and the occurrence of the shrinkage cavity can be
prevented.
[0081] When the feeder head is generally constructed, it is
considered that the closed elliptical loop which is the last
solidification part must be confined in the feeder head. Therefore,
the feeder head larger than the product is often erected. However,
it is understood from the viewpoint of the shape coefficient that
even a small feeder head is sufficient as long as the closed
elliptical loop of the solidification distribution chart obtained
by the solidification simulation is divided and the shape
coefficient of each of the parts divided by the feeder head or the
shape coefficient of the divided elliptical loop is a value which
does not exceed the determination coefficient.
[0082] The chiller is generally used for preventing the shrinkage
cavity. However, many wrong usages, i.e., many usages promoting the
occurrence of the shrinkage cavity exist. In the present invention,
the right usage of the chiller, i.e., a method for logically
preventing the occurrence of the shrinkage cavity has been found by
focusing attention on the shape coefficient.
[0083] FIG. 17 shows an example of a wrong usage of the
chiller.
[0084] Since the shape coefficient (F) of the test piece is
(240+400)/80=8, the shape does not essentially cause the shrinkage
cavity. However, a method is often adopted in the casting spot,
which constructs feeder heads 10a and 10b at the upper and lower
sides of the test piece and prevents the shrinkage cavity. In the
method, the shrinkage cavity may increase by contrast. When the
solidification distribution chart is determined by the
solidification simulation in a state where the feeder heads 10a and
10b abut on the upper and lower sides, the shape coefficient (f) of
the closed elliptical loop is (72+170)/13=19 as shown in an A-A'
section and a B-B' section of FIG. 17, which shows that the
shrinkage cavity occurs in spite of constructing the feeder
head.
[0085] On the other hand, FIG. 18 shows the right usage of the
chiller.
[0086] The shape coefficient (F) of the test piece is
(100+400)/50=10, and the shape causes the occurrence of the
shrinkage cavity. The feeder heads 10a and 10b are attached to both
the sides of the test piece, and similarly, the solidification
distribution chart is determined by the solidification simulation.
As shown in the A-A' section and the B-B' section, the shape
coefficient (f) of the closed elliptical loop is (17+60)/13=6, and
the shrinkage cavity does not occur. Therefore, the sections show
that the shrinkage cavity can be prevented by the idea based on the
shape coefficient in constructing the chiller.
[0087] FIG. 19 collectively shows a flow chart of the method for
predicting and preventing the shrinkage cavity in the present
invention.
[0088] The method for predicting and preventing the shrinkage
cavity of the present invention includes the following steps (1) to
(6).
[0089] (1) The dimensions of two long sides (W, L) and remaining
short side (T.sub.MS) of the casting are measured. Alternatively,
two long sides (w, l) of the closed elliptical loop and remaining
short side (t.sub.MS) are calculated by the computer
simulation.
[0090] (2) The shape coefficient [F=(W+L)/T.sub.MS] is determined
from W, L and T.sub.MS. Alternatively, the shape coefficient
[f=(w+l)/t.sub.MS] is determined from w, l and t.sub.MS.
[0091] (3) When the shape coefficient (F or f) is smaller than the
determination coefficient (E, generally 8), the shrinkage cavity is
determined as "nonexistence".
[0092] (4) When the shape coefficient (F or f) is larger than the
determination coefficient, the shrinkage cavity is determined as
"existence".
[0093] (5) When the shrinkage cavity is determined as "existence",
the product is divided by the chiller or the feeder head.
[0094] (6) The shape coefficient (F or f) is made smaller than the
determination coefficient by repeating the processes (1) to
(5).
[0095] The present invention founds a new concept of a shape
coefficient, and can use the shape coefficient to simply predict
the occurrence of the shrinkage cavity with extremely high
accuracy. Even when the casting components, the type of the mold,
the cast position and the like are different, the occurrence of the
shrinkage cavity can be predicted by the shape coefficient.
Furthermore, when the occurrence of the shrinkage cavity is
predicted, the occurrence of the shrinkage cavity can be logically
prevented by using effectively the chiller or the feeder head.
Therefore, the present invention has effects such as the reduction
of defective fraction in the iron casting, the improvement in
extraction rate and the shortening of delivery time, and can
produce the spheroidal graphite cast iron efficiently at low
cost.
INDUSTRIAL APPLICATION
[0096] Since the present invention can predict whether or not the
shrinkage cavity is formed from the shape of the casting in the
iron casting before the cast, and can previously prevent the
shrinkage cavity, the present invention is useful in the iron
casting technique.
* * * * *