Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
104~285
Background of the Invention
The present invention relates to a composite metal
article containing additive agents and1method of adding same to
molten metal. More particularly, the invention relates to a
composite metal article for adding relatively volatile metallic
agents to molten ferrous material as it is being cast.
The addition of alloying and treating agents into
molten metal, such as steel, is well known in the art. The
addition of such agents in wire~like form is also known and has
been described in U. S. Patent No. 3,634,o75 issued January 11,
1972, to J. C. Hoff, and in the October 28, 1971, issue of "Iron
Age." Thus, the use of wire-like structures for adding alloying
and treating agents to molten metal provides an advantageous
means of providing a final desired casting under excellent
controlled conditions.
However, certain problems have been encountered where
the agent to be added is relatively volatile because of the
tendency of the material to be discharged or released prematurely
~hen fed into a ferrous melt. For example, where such treating
agents are carried in a sheathed wire, materials such as
magnesium melt at a temperature below the melting point of a
ferrous melt, and thus become discharged or released before the
wire is melted and absorbed into the molten bath.
Efforts have been made to provide a solution to the
problem, and United States Patent 3,056,190 issued October 2,
1962 to D. S. Chisholm, et al discloses a method of combining
magnesium with silicon to form magnesium silicide and carry
the same within a ferrous metal envelope. However, even in
th~æ ~orm, the magnesium tends to become dxscharged or released
30 prematurely. In United States Patent 3,741,753 issued ~une 26,
1973 to H. ~alz, et al,~ a method is taught for adding manganese
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104~iZ85
to molten steel under vacuum conditions where the manganese is relatively
volatile and presents a problem. In accordance with that patent, the
manganese is first alloyed so as to reduce its volatility before being used.
Thus, it is seen that both of these patents require an additional alloying
step in preparing the material for use as an additive to molten metal.
Summary of the Invention
In accordance with one aspect of the invention there is provided a
method of adding a relatively volatile metallic agent to molten ferrous metal
comprising the steps of continuously feeding a composite wire-like structure
containing said agent at a controlled rate sufficient to provide a desired
amount of said agent within the molten ferrous metal, said composite wire-
like structure comprising an inner core containing said relatively volatile
metallic agent, an outer sheath of ferrous metal substantially concentrically
disposed to said core, and a particulate insulating material having a melting
or subliming point generally at least about equal to the melting point of
said outer sheath disposed between said core and said sheath, said insulating
material providing a heat barrier sufficient to protect said inner core from
delivery prior to the melting of said outer sheath of ferrous metal.
In accordance with another aspect of the invention there is provided
a composite wire-like structure for adding relatively volatile metallic agents
to a molten metal, comprising an inner core of relatively volatile metallic
agent, an outer sheath of non-volatile metal having a melting capability at
the temperature of said molten metal, and a particulate insulating material
with a melting or subliming point generally at least about equal to the melt-
ing point of said outer sheath disposed between said sheath and said core in
surrounding relation to said core, said insulating material providing a heat
barrier sufficient to protect said core from delivery prior to the melting of
said outer sheath.
As used herein, the term "relatively volatile" is intended to
embrace substances that exert a substantial vapor pressure at the temperature
of the molten metal to which the agent is to be added. The outer sheath will
generally be of a metal similar in melting point to the molten metal being
2 -
lO~Z~5
treated, and advantageously will be of a similar composition. In other words,
the outer sheath will generally not materially affect the composition of the
molten metal, but it will be understood that non-volatile alloying agents or
other additives could be included in the outer sheath, if desired. The insu-
lating material may be any material capable of retaining the core material
below its boiling point or the point at which the vapor pressure becomes
excessive prior to the melting of the sheath material. Preferably, the core
material is also kept below its melting point. In this way, delivery of the
core material will occur simultaneously with the melting of the sheath
material.
The insulating material should also be a substance which is compat-
ible with the molten melt desired, i.e., it should not add any unwanted
materials. Thus, a preferred form of insulating material is a particulate
substance of either an agent desired to be added, or of a composition sub-
stantially similar to the melt, or a combination of both. The invention has
been particularly valuable in adding alloying or treating agents to molten
ferrous metal, where the temperature of the melt will be of the order of
around 2600F. or higher, and where a number of the desired additives are
volatile.
For example, it is well known to add magnesium to cast iron or steel
in order to provide modular treatement thereof. However, magnesium has a boil-
ing point of about 2025F. Accordingly, additions of magnesium have been some-
what troublesome in the area now under discussion. Similarly, zinc has a
rather low boiling point and where it is desired to add zinc to a molten
metal, volatility problems are likely to occur. In addition, certain casting
processes are carried out in a vacuum, and in such a case metals such as
aluminum and manganese are also sufficiently volatile to cause problems. Thus,
these and any other materials, which may be sufficiently volatile to cause a
problem, may be advantageously added by using the present invention.
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t
104~S
Brief Description of the Drawings
A preferred form of the invention is illustrated in
the accompanying drawings forming a part of this description,
in which:
Figure 1 is an isometric view partly in section of a
composite wire-like structure fabricated in accordance with the
invention; and
~ igure 2 is a sectional view of the structure shown
ln ~igure 1 taken substantially in the plane of line 2-2 of
~igure 1.
~ hile only the preferred form of the invention is
shown, it should be understood that various changes or modifi-
cations may be made within the scope of the claims attached
hereto without departing from the spirit of the invention.
Detailed Description of the Preferred Embodiment
Referring now more particularly to the drawings, there
is shown in ~igure 1 a composite wire-like structure 11 comprising
an inner core 12 of relatively volatile agent, an outer sheath
13 of relatively non-volatile metal, and an insulating material
14 disposed bet~een said sheath and said core in surrounding
relation to the core.
Preferably, the structure is used for adding an agent
to molten ferrous metal comprising the step of continuously
feeding the wire-like structure at a controlled rate sufficient
to provide a desired amount of agent in the molten ferrous metal.
In the preferred form, the tubular sheath 13 is also generally
composed of ferrous metal with or without an alloying agent,
and the insulating material 14 is preferably composed of
particulate ferrous material such as iron or steel.
B30 rhe ~ire-like treating agent is used to add alloying
agents or treating materials or both by any of the available
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processes for adding wire-like treating agents to molten metal.
~or a more detailed description of such process, the citations
given a~ove may be consulted.
In order to better illustrate the in~ention, the
~ollo~ing examples of composite articles are g~ven, and it
should ~e understood that these examples are gi~en for illus-
trative purposes and are not to be construed as limiting the
invention. In the examples, the ~ire core 12 has a diameter of
.125 inch and the tubular sheath 13 has a nominal diameter of
.375 inch and a wall thickness of O.15 inch.
Example 1.
In this example, the protective ~lanket consists o~
powdered iron, the sheath is steel, and the core is magnesium.
The protective blanket is particularly suitable due to its
high specific heat C0.11 ~tu~lb. degree ~ and relatively slow
thermal conductivity.
The following parameters setting forth the composition
~ r~
more clearly ~5 given in Table I belo-~:
Table I
~OLUME~100 Ft. C%~ DENSITYWEIGHT (%~
Sheath408.89 cc C 18.8~ x 7.82 a 3~197.5 gms. C 33.3
~e Powder1~521.67 cc C 70.1~ x 3.92 = 5~964.9 gms ( 62.2
Mg Core241.32 cc ( 11.1~ x 1.80 = 434.4 gms. ( 4.5
Total2~171.88 cc (100.0~ x 4.42 = 9~596.8 gms. (100.0
~xample 2.
In this example~ the protecti~e blanket consists of a
blend of lron powder and graphite, while the sheath is steel and
t~e core is magnesium. It is well known that carbon suppresses
30 the reaction of magnesium vapor, and is therefore included to
~o~zf~s
control the degree of the reaction. ~t will also be appreciated
that the addition of carbon can be tolerated in certain desired
ferrous allo~s by starting with a melt capable of utilizing such
addition, Moreover, the amount of carbon added by this example
is rather small The physical parameters given in Table II
below have been established for the article of this example:
Table II
~LU~E~100 Ft. {~ DENSITY ~EIGHT C~i
Shea~h408.89 cc C 18.8~ x 7.82 =3,197.5 gms. ( 37.92
~e Po~der1,141.25 cc C 52.52 x 3.92 =4,473.7 gms. ( 53.0
Graphite (C~ 380.42 cc ( 17.62 x 0.8~ = 338.6 gms. ( 4.0~
~g, Core241.32 cc ( 11.12 x 1.80 =434.4 gms. C 5.12
Total2,171.88 cc (100.02 x 3.89 =8,444.2 gms. (100.0
~xample 3
In this example, the protective blanket consists of
po~dered magnesium and coke. This is a commercial product
produced by the American Cast Iron Pipe Company of Birmingham,
Alabama, and contains magnesium and carbon. The product, which
is foundry coke filled with approximately 45~ by weight ~ith
magnesium, provides a timed release of magnesium vapor in addition
to the magnesium contained in the solid core. In Table III
below, the physical parameters of this exa~ple are given;
Table III
~OLU~100 ~t. C~2 D~N~ITY ~ErGHT C~2
Sheath 408,89 cc C 18.82 x 7,82 = 3,197,5 gms. C 65.5
~ag-Coke Powder 1,521.67 cc ( 70,12 x 0.82 = 1,247.8 gms. C 25.6~
Mg Core 241,32 cc C 11.1~ x 1.80 = 434.4 gms. C 8.92
. . . . . . .
Total 2,171.88 cc C100.02 x 2.25 = 4,879,7 gms. Clob~
The thermal protection afforded by the blanket 14 is
determined b~ the ther~al conductivity and particle size of the
blanket material. ~04~Z85
Thus, it is seen that the preferred insulating material is a partic-
ulate form of one or more of the substances to be added and has a melting or
subliming point (temperature) at least about equal to the melting point of
the outer metallic sheath. Thus, as illustrated in the preceding examples,
iron has a melting point substantially equal to the melting point of the steel
sheath while graphite and coke sublime well above the melting point of the
sheath. These particles may vary from small powder form to large granular
form. Since correspondingly smaller particles present a greater number of
non-homogeneous heat transfer surfaces, and'therefore reduced thermal conduc-
tivity, the protection provided by any of the above blanket compositions may
be varied by an appropriate change in the size of the particles incorporated
in the blanket. It has been determined that a wire having the aforementioned
dimensions in a composition as described in Example 1 will melt in a 2500F.
bath at a rate of approximately 6 to 7 inches per second. For these condi-
tions, the iron powder protective blanket of Example 1 comprising particles
lE2 prD r~' d ~s
ILP between 40 and 140 mesh ro~i~L~ adequate thermal protection to prevent pre-
mature melting and vaporization of the magnesium core. In the event that it
is found desirable to increase the thermal protection provided by the 40 to
140 mesh particles, smaller particles could be used. In this way, a slower
feed rate could be used.
For large castings that may require wire feed rates about 6 to 7
inch per second melting rate provide4 t~e instant wire, two or more wires may
be fed simultaneously into the molten metal bath. Alternatively, the wire
may be heated to increase the melting rate. In general, any suitable heating
method may be used such as passing the wire through a heated zone or utilizing
resistance heating of the sheath.
If resistance heating of the sheath is desired, the blanket and/or
the core should be electrically isolated to prevent resistant heating of
these components. For this purpose,
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electrically non-conductive materials may be selected ~or the
blanket or electrically conductive materials may be processed
such as by coating to render them non-conductive. Also a non-
conductive coating could be provided on the inner surface of
the sheath or on the outer surface of the core.
~ rom the above examples, it is seen that the wire-
like structure made according to the invention is suitable for
use in any of the methods cited above, and may be utilized either
with or without additional heating. It is also seen that the
composite wire-like structure is capable of protecting the inner
core of volatile material from premature release in a reliable
manner .
A further benefit is provided by the present invention
by virtue of the fact that as the ~ire is melted, the granular
or particulate blanket material is absorbed into the molten
stream. This absor~tion reduces the temperature of the stream
at a small zone contiguous to the end of the wire where the
inner core is ~eing deli~ered. This reduced temperature zone
permitS cores such as magnesium to be absorbed into the stream
in a less volatile manner since the severity of the magnesium
reaction 1~ temperature dependent.
In addition, the use of an outer core of a material
having a melting point similar to that of the molten metal
~eing treated causes the delivery and reactions such as the
magnesium reaction to occur while ~elow the surface of the molten
material This further reduces the severity of the reaction.
From the foregoing description, it is seen that an
improved composite metal article containing additive agents
a~e provided for use in a method of adding alloying or treating
3Q agents to molten metal, It is also seen that an article is
provided ~hlch is particularly advantageous for adding volatile
additives such as magnesium to molten ferrous metal and the like.
