Note: Descriptions are shown in the official language in which they were submitted.
BACl~GROUND OF TIIE INVF.NTION
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Ihis invention in-volves the casting o:E alloys
and particularly is it useful in the cas-ting of alloyed
parts or articles whicll must be of a high degree of
uniformity in alloy composition and cast to precise
dimensions to reduce or eliminate the necessity for any
significant amount of finish machining. It is particularly
useful in systems in which the size of the charge provided
for each mold is precisely the volume of alloy necessary
to cast tne finished part or parts. Such systems include
ones using a melting unit capable of discharging molten
metal through a controlled opening and certain directional
solidification "DS" casting processes and single crystal
processes. Examples of the type of parts or which this
particular system is useful are in the casting of alloyed
; turbine blades, wheels for superchargers and/or turbochargers.
Because of the high centrifugal speeds of these products,
it is essential that the parts all be of uniform composition,
shape, size and weight.
It has been conventional practice to prepare a
master alloy charge for remelt casting of precise parts such
as turbine blades by melting the various elements which form
the composition of the alloy and then casting them in a pipe
or similar mold. After the cast alloy has cooled and solidi-
fied, it is removed from the pipe. Frequently, the removal
of the alloy from the pipe is a very difficult, slow and
unsatisfactory procedure. Further, the cast product produced
from the pipe is not uniform in cross section and, therefore,
- must be machined by either turning or grinding to render it
uniform in cross section and to render it absolutely straight.
This has been necessary also to give it a proper external
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1 finish whereby throughout its length the charge was o-f
uniform characteristics. Machining is also necessary to
remove all slag and scale which, if not removed, would
modi-fy the composition and thus the resulting material would
not have a true net chemical composition by weight percent.
This procedure is expensive, time consuming and, unless great
care is taken, lacks the desired uniformity for accurately
charging the mold in the final casting procedure.
BRIEF DESCRIPTION OF THE INVENTION
This invention eliminates the necessity for the
use o-f a mold in preparing the alloy charge for the subsequent
casting operation. Instead of the conventional mold, a tube
or tubular shell of one of the elements or of an alloy
of elements which are to be part of the composition of the
final alloy to be cast is used as the mold. The composition
of the alloying material which is poured into this tube
represents the composition of the final alloy minus the
materials contained in the tube. The result is a rod-like
casting of the alloy with the tube forming the exterior
shell and also providing a part of the composition of the
final alloy as it will be used in the casting of the article
for which it is intended.
The resulting rod-like casting is then severed
into one or more segments of a predetermined precise length,
each one being of the exact amount necessary to cast one
of the articles. In doing this, at least one end of each
segment is rendered precisely perpendicular to the axis of
the cast charge. This then becomes the unit charge which
- is placed in the melting and/or pouring crucible or tundish
over the gate of the mold for the final article where, under
controlled conditions, the charge is melted in such a manner
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1 that both the inncr or corc portion and the exterior tube
are melted and the elements of both the core and the tube
become intermixed and blended and, thus, uniformly alloyed
before the charge flows into the mold. Thus, throughout
the process, nothing is used except the elements whicll form
the composition of the final alloy and the only mold involved
in preparing the charge is an integral part of the composi-
tion of the casting alloy.
BRIFF DESCRIPTION OF THF, DRAWINGS
.. . . . . _
Fig. 1 is a sectional elevational end view of one
of the tubes in which the charge is cast with the gate and
plug installed;
Fig. 2 is a sectional view of the tube taken along
the plane II-II of Fig. l;
Fig. 3 is a plan view of the tube illustrated in
Fig. l;
Fig. 4 is a side elevational view of a device for
pouring a plurality of the charges;
Fig. 5 is a plan view of the tundish used in filling
the device illustrated in Fig. 4;
Fig. 6 is a schematic sectional view of a modified
support for the tubes during pouring of the charge;
Fig. 7 is a sectional view (cross-hatching omitted
for clarity) of a typical unit charge made by use of this
invention; and
Fig. 8 is a schematic sectional view of a -typical
device used in a remelt, unit-charge or certain directional
solidification or single crystal casting systems for casting
~ the final product from the charge illustrated in Fig. 7.
DESCRIPTION OF THE INVENTION
.
The first step in practicing this invention is
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1 to select the desired alloy. That is, to select an alloy
which will produce an end product of the desired character-
istics. While this invention can be practiced with a wide
range of alloys, it is particularly suitable for iron or
nickel alloys, that is, alloys in which either iron or
nickel is the most abundant element.
If the selected alloy is an iron alloy, the tube
or shell 10 will be iron or an alloy of iron. If the alloy
is a nickel alloy, the tube will be nickel or an alloy of
nickel. Normally the tube will be a commercially available,
seamless tube. The use of rolled, crimped or lock-seamed
tubing is also acceptable. ~elded tubing produced by resis-
tance welding or by a rnethod which introduces only a very
minor quantity of welding alloy can also be used. Normally
such commercial tubing is manufactured from an alloy. In
selecting the tubing, the precise alloy must be known. It
is important to this invention that the tubing be of uniform
composition, of uniform wall thickness, not only cross sec-
tionally but throughout its length. The tubing must be free
of impurities. Since economic factors must be considered,
the price of the tubing must be taken into account. If tubing
of an alloy compatible with the aIloy to be used in the final
product is less expensive than a single element tube, all
; other factors being considered, it will be used and the balance
of the material used in preparing the final alloy will be
adjusted accordingly.
The tube having been selected, the next step is to
fill the tube with the balance of the alloy. This is done
by melting the remaining alloy materials and pouring them
into the tube to form a core. In preparing the alloy for the
core, the type and amount of each element present in the
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l form of the tube are deducted from the formula of elements
incorporated in the composition of the alloy which is poured
to form the core. For example, if tlle tube is 100% nickel,
the quantity of nickel represented by the tube is deducted
from the quantity of nickel which will be incorporated in
the alloy used to pour the core. If the tube is an alloy
such as nickel-chrome, the quantity of nickel and the quantity
of chromium are both calculated by weight and deducted from
the quantities of the same elements incorporated in the core
alloy. The same is done in the case of a tube of iron or
iron alloy.
While tubes of iron and nickel have been described,
it will be recognized that tubes of other elements such as
chromium or made of alloys of known composition with high
lS ratios of the primary element could be selected. The selec-
tion of the tube is governed not only by the type of final
alloy to be created but also by economics. For example,
tubes of chromium and other materials are frequently far more
expensive than tubes of nickel or iron. Availability is also
a factor in determining the selection.
The diameter and wall thickness of the tubing may
be varied within a limited range depending upon availability
and cost. Thick wall tubing, however, is frequently not
useable either because of cost or because it would introduce
into the final alloy an amount of one element in excess of
the formula specifications. On the other hand, the tubing
wall thickness must be sufficient to permit the core to be
poured and without the heat of the molten core either melting
through the tube wall or softened to a point which will
result in the tube's loss of geometric integrity. Experience
has indicated that with either nickel or iron based tubing,
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1 a wall thickness of 0.065 lnch thickness performs satisfac-
torily.
Having selected the particular alloy composition
and the type of tubing to be used, a plurality of the tubes
of a suitable length SUC]l as 40 inches are placed in a pour-
ing rack 20 (Figs. 4 and 6). The pouring rack is a conven-
tional structure long used in the metal casting field. It
can incorporate a number of different designs. Thus, the
construction about to be described is merely exemplary. The
pouring rack 20 consists of a frame having vertical corner
members 21 and side members 22 or bands joined together to
form a preferably square basket-like structure, closed at
the bottom by a base 23. The top 24 of the rack is flared
out to provide a seat for a tundish.
To prepare the individual tubes 10 for placement
within the rack, each tube is sealed at its lower end by
a chill plug 30 and at its upper end by a pouring nozzle 31
having a -funnel-like gate 32. Both the plug and the pouring
nozzle have a portion of a suitable diameter to be inserted
in the ends of the tube 10. This portion of the chill plug
has a sufficiently close fit to the tube to prevent leakage
of molten metal. In the case of the pouring nozzle, a sleeve
33 of fibrous paper especially made for foundry casting
operation is placed between the nozzle and the inside wall
of the tube. Both the nozzle and the chill plug are normally
made of a ceramic material specifically designed for metal
casting operations. Prior to insertion of the chill plugs
and pouring nozzles, the tubes are inspected for cleanliness
and, if necessary, cleaned to remove all foreign matter.
A plurality of the tubes equipped with the chill
plugs and the pouring nozzles are seated in the pouring rack
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1 20 and are separated from each other and held in position
by narrow strips 25 of a paper based material of the same
type as that used to surround the pouring nozzle. These
paper strips are wrapped back and forth between the tubes
to hold each tube spaced from every other tube (Fig. 6).
These strips, preferably, are 3 inches wide and 1/8 to 1/4
inch thick. The strips 25 are mounted in at least two and
preferably three vertically spaced locations.
The tubes 10, with the strips 25 in place, are held
together by spacer bars 26 and 27 which space them from the
sides and ends of the pouring rack. Thus, the tubes are
firmly held and positively spaced. It is important that
the tubes be Eirmly held in a vertical position during the
actual pouring.
The tubes 10 having been locked into the pouring
frame 20, a tundish 40 is placed on the top of the frame
and secured by suitable clamps 41 and 41a ~Fig. 5). The
; tundish is a basin with a plurality of holes 42 in its
bottom wall. The holes 42 are arranged in a pattern to
align with the gates 32 of the pouring nozzles inserted in
the tops of the tubes 10, one hole 42 being provided for
each of the tubes. Normally, tundishes of this type are
of a ceramic material and are a conventional product long
used in the metal casting field.
The alloy composition from which the core is to be
poured is melted and is then poured through the tundish to
fill alI of the tubes in the pouring rack 20. In this
pouring operation, it is important that the temperature of
the metal, as it enters the tubes be controlled within a
relatively narrow range because it is essential that the
metal of the core bond to the surrounding tubes eliminate
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l all voids or separation lines between the tube and core. It
is preferable that actual fusing occur at the boundary
between the core and the tube whereby there is a certain
degree of melting and fusing of the inner wall surface of
the tube with the core material. At the same time, it is
important that the heat of the core ma-terial not be suffi-
cient to either melt through the walls of the tube or to
soften the tube to the extent it starts to warp or distort,
i.e., lose its geometric integrity because this will cause
the tube to collapse. Therefore, accurate temperature
control in a narrow range is essential to successfully
pour the core and produce a satis-factory product. In general,
it has been found that maintaining the temperature within
a range of 25F. plus or minus of a predetermined melt
temperature for the core alloy will prevent overheating
of the tube yet result in the desired Eusing at the bound-
ary. This~ however, will vary from alloy to alloy because
o-f the characteristics of the alloy.
After the core has been poured, the tubes and core
are allowed to cool permitting the poured metal to solidify.
While the melting of the core alloy and its pouring
into the tubes can be done under normal atmospheric condi-
tions, this invention is particularly concerned with the
making of charges for casting highly specialized parts of
sensitive alloys which must be done under controlled condi-
tions such as under a vacuum or at least under a neutral
atmosphere. In either case, the melting of a core alloy
and the pouring of the core and the cooling of the tubes
after the core has been poured is carried on in a suitable
pressure vessel which is either evacuated or charged with
a neutral gas such as argon or nitrogen. This is essential
1 to maintain metallurgical cleanliness oE the composition
and eliminate scaling which would have to be removed
mechanically because it upsets the net composition of the
alloy.
After the tubes have been poured and cooled, they
-form a master charge. No mold is used, the tubes 10
serving as the confining mold for the core and the exterior
shell of the master charge. Thus, the problem of recovering
the cast alloy material from the conventional mold is elimin-
ated along with the step of machining the master charge to
produce a rod-like unit of uni-form cross section and free
from surface contamination resulting Erom incorporation oE
material from the inside wall of the mold. Further, the
conventional molds used for this purpose have a relatively
thick wall and, thus, occupy a substantial area within
the pressure vessel. This is most important because these
vessels are limited in size and unnecessary use of potential
production space within them is expensive. This invention
permits a substantially larger charge to be melted and poured
in each batch than is possible using conventional molds. The
next step is to cut the master charge into segments of a
precise weight. Each segment becomes a unit charge 50 to be
used in making single or multiple castings (Fig. 7). Each
unit charge 50 must have at least one end which is square,
that is, the plane of the end is perpendicular to the axis of
the charge. The number of segments obtained from each tube
will depend upon the size of the cross section of the unit
charge and the weight o-f the final part to be cast.
Normally the cutting is done with an abrasive wheel.
In the use of this type of wheel, it is important that the
boundary between the core and the inner face of the tube have
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1 no gaps or spaces ln which any of the abrasive material
from the cutoff wheel can become lodged and, thus 3 ultimately
become embedded in the final casting made from the unit charge.
A typical unit charge 50 is illustrated in Pig. 7.
The exterior of the charge is formed by the tube which forms
a shell 51. The interior o-f the unit charge is occupied by
the core 52. At the boundary between the shell or tube and
the core is a thin fusion zone 53 formed by the fusing or
a thin layer of the inside surface Gf the tube with the
adjacent material of the core. This zone of fused material
eliminates any vo:ids in which foreign materials can become
deposited during the cutting or subsequent handling o-f the
unit charge 50. Each unit charge 50 has at least one
square end and a precisely calibrated weight based upon
the final weight of the part for which the unit charge is
to be used. Since both the exterior tube or shell 51 and
the core 52 form part of the alloy of the -final casting,
the entire unit charge will be used. Since the use of
the tube as a mold eliminates machining or other surfacing
dressing and size truing, cost both in labor and materials
is significantly reduced. This is significant since many
of the alloys used in the type of products to which this
invention is particularly addressed are very expensive.
The final step is to use unit charges 50 to pour
the final product. For this purpose a mold 60 is provided
with a mold cavity 61 and a pouring gate 62 (~ig. 8). A
crucible or tundish 63 is placed over the mold. The bottom
of the crucible has a pouring opening 64 which is aligned
with the gate 62 of the mold. The crucible is selected to
have an internal opening which will receive without signi-
ficant side gap, a unit charge 50 of the exact predetermined
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1 size and -weight necessary to produce the cast part, 'i'he
crucible is surrounded by an induction heating coil 65. The
induction coil does not extend to the bottom oE the crucible.
Because oE this, the bottom end of the unit charge 50 is the
last portion of the charge to melt. Thus, the upper portion
of the unit charge 50 including the core 52 and the surround-
ing shell 51, that is the tube, are both melted and form a
pool of molten alloy metal within the crucible. This permits
the element or elements or the tube and those o-f the core to
blend so that the melted content of the crucible becomes an
alloy consisting of both the tube and the core as the alloy
was originally -formulated. Sufficient time occurs during
the heating to permit thorough intermixing and blending of
the elements because the lower end of the unit charge 50
remains solid providing a plug or dam preventing the molten
charge above it from flowing into the mold cavity 61. Pinally
the plug melts and the entire charge flows into the mold
cavity. Because it is important that the lower end of
the unit charge form a dam or plug preventing discharge of
the remaining molten portion of the unit charge from enter-
ing the mold until all the rest of the unit charge has been
melted, it is essential that the end of the unit charge 50
seating against the bottom 66 of the crucible be flat and
perpendicular to the axis of the unit charge so there will
be no gap through which the molten metal can prematurely
escape into the mold cavity 61. The weight of the unit
charge having been calibrated to the weight of the product
to be formed in the mold cavity 61, the entire unit charge
is used in filling the mold cavity. Thus, the entire unit
charge flows into the mold, fills the mold cavity 61 and
provides a short sprue extending up into the gate 62.
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1 ~XAMPLE I
An alloy of the following composition was selected:
Percentage
PP~
Max. ~in.(Max.)
Carbon 0.16 0.14
Silicon 0.55 0 35
Manganese 0.40 0 25
Sulfur 70*
Aluminu]n 3.9 3.7
Boron 0.7 0 3
Chromium 16.0 14 5
Iron 11.5 10.0
Magnesium 60*
Molybdenum 5-5 4-7
Nickel Balance
Phosphorus 0.015*
Titanium 2.1 1.9
Nitrogen so*
Oxygen 20*
Lead 10*
Silver 5*
Bismuth 0.5
Selenium 3
Tellurium .5
Thallium 5
~; *content to be as low as possible
Twenty-five, 100% nickel, seamless tubes of 1 1/4
iDches diameter, 40 inches~long and having a wall thickness
o-f 0.065 inches were selected. The weight of the complete
chargé was 339 lbs. The collective weight of the tubes was
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74 lbs. Thereore, the weight o:E the charge poured to form
the core was 265 lbs. The weight of the tubes was deducted
from the~weight o-f the nickel used to formulate the alloy
to be poured as the core. The~tubes were inspected for for-
eign substances~ and, where necessary, cleaned. Each was
equlpped~with a chill plug on one end and a pouring gate on
: the other end;. The tubes were then placed vertically in a
pour~lng rac;k~and a tundlsh mounted on the top of the rack.
The rack along with a crucible containing the materials for
;~ 30 the core alloy were placed in a pressur~e chamber which was
~ then evacuated. The core materials were melted, allowed to
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1 blend and when the core alloy's temperature had been adjusted
to the correct range, the molten alloy was poured into tundish
from which it flowed into and filled all the tubes. During
pouring, care was taken to avoid heating the tubes to a temp-
erature which would result in melting through the tube wall or
softening the tube wall to the extent it started to lose its
geometric integrity. Howevery the temperature was maintained
high enough to assure some surface melting of the inner face
of the tube resulting in a boundary area between the tube and
core in which the elements of the tube and core became fused.
After the resulting tube-core castings had cooled,
they were removed. The product was a master charge each
cross-sectional portion of which contained the precise alloy
composition of the product to be cast from segments of the
master charge. The chill plug and the pouring gates were
removed and one end of the :Eilled portion of the tube was
cut square.~ The tube was then cut into segments each of a
precise, predetermined weight. Each segment constituted a
unit charge ready for casting a part which would become the
final product
EXAMPLE II
` An alloy of the same composition as Example I was
selected. ~lowever, seamless steel tubes of 1 1/4 inches
2~5 diameter, 40 inches long a~d having a wall thickness 0.035
inches were selected. The weight of the complete charge
was to be 341 lbs. The collective weight of the tubes was
36 lbs. Therefore, the weight of the charge poured to form
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the core was 36 1bs. The weight of the iron and carbon in
the tubes was deducted from the weight of these elements
; used to formulate the alIoy~to be poured as the core. The
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1 tubes were inspected -for foreign substances and, where neces-
sary, cleaned. ~ach was equipped with a chill plug on one
end and a pouring gate on the other end. The ~ubes were then
placed vertically in a pouring rack and a tundish mounted on
the top of the rack. The rack along with a crucible contain-
ing the materials for the core alloy were placed in a pressure
chamber which was then evacuated. The core materials were
melted, allowed to blend and when the core alloy's temperature
had been adjusted to the correct range, the molten alloy
was poured into tundish from which it flowed into and
-filled all the tubes. During pouring, care was taken to
avoid heating the tubes to a temperature which would result
in melting through the tube wall or softening the tube wall
to the extent it started to lose its geometric integrity.
However, the temperature was maintained high enough to assure
some surface melting of the inner face of the tube resulting
in a boundary area between the tube and the core in which the
elements of the tube and core became fused.
After the resulting tube-core castings had cooled,
they were removed.~ The~product was a master charge each
cross-sectional portion of which contained the precise
aIloy~composition of the product to be cast from segments ~
of the master charge. The chill plug and the pouring gates
were removed and one end of the filled portion of the tube
was cut square. The tube was then cut into segments each of
a precise, predetermined weight. Each segment constituted
a unit charge ready for casting a part which would become
the final product.
30~ The particular alloys to which this invention is
applled are not part of the invention. The formulation of
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1 the alloys, their mechanical and chemical characteristics
are known to or within the skill of the trained metallurgist.
Thus, their melting temperatures and the temperatures at
which the tubes will soften or melt are known and need not
be set out here. Further, because the invention is applica-
ble to a wide range of alloy materials, unit weights melting
points and shrinkage characteristics will also vary in a
substantial range. These are characteristics either known
to metallurgists or reasonably readily available from
existing sources.
It will be understood that the length, diameter
and wall thickness of the tubes as well as their alloy
composition can vary through a substantial range. Also
; the number of tubes included in a single pouring can vary
depending upon the quantity of alloy to be produced and
the capacity of the equipment available for its production.
; Havlng described my invention, and a preferred
~; procedure for practicing it, it will be understood that
modification thereof can be made without departing from its
;~ 20 principles. Such modlficatlons are to be considered to be
included in the hereinafter appended claims, unless their
language expressly states otherwise.
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