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Патент USA US2121969

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Jung-28,1938. ‘
_ A, w, LMRD " '
wFiled Sept. 5, 1936 _
' ?r. Mail/m‘
Patented June 28, 1938
Alfred W. Laird, Chicago, 111., assignor toWest;
er'n Electric Company, Incorporated, New ,York, '
N. Y. a corporation of New York
ApplicationSepteinber '5, 1936, Serial No. 99,549
6 Claims. ' (01. 22-188)
' " The fused magnesium oxide is ground suiiié
‘This ‘invention relates to molds, and more ‘par
tlcularly to molds for casting high melting point
'ciently ?neto pass through a 10 mesh screen -
>before mixing. The hydrated calcium oxide
‘Certain articles made of_ palladium and other
5 expensive metals and 1alloys of the platinum
group are cast into shape'or machined from spe
cial billets to conserve material. Scrap produced
in machining operations is carefully meltedinto
billets and reused. Production of accurate and
I 10 uncontaminated castings and ‘billets from these
,metals has been hampered by lack of an en-v
tirely suitable casting mold. Generally used mold
' materials, such as plaster of -Paris, do not with
stand the high temperatures required tol-melt
15 the platinum group metals. ‘ Freshly burned. lime
has been usedqfor this purpose but due to its
tendency to combine with moisture and carbon
dioxide in the ‘air, special and costly processes
are required for the manufacture ‘and use of 7
molds made from this material.
An object of this invention is to provide an
functions as a binder in the mixture and the
exact proportion required is determined by the ,6
particle size distribution of the magnesium oxide
as measured by a ‘screen analysis. A ‘satisfac
tory mixture includes 25%‘ calcium, oxide and
75% magnesium oxide which in, an analysis is ,
retained 23% on a 20 mesh screen, 47% on a 10
40 mesh screen, 14% on a 60 .'mesh screen, with
the remainder of 16% passing through the 60
mesh screen. Another successful mixture com
prises 30% calcium oxide and 70% magnesium. c‘
oxide which will analyze with 35% retained 011' lb
a 20 mesh screen, 25% on a 40 mesh screen, 15%
on a 60 mesh screen, and 25% passing through
the 60 mesh screen.
- The necessity for ahigher proportion of binder
‘for the latter mixture is apparently due to an 20
an increase in total particle surface of the mag- ,
improved, serviceable and 'inexpensivemold for nesium oxide. It is desirable to‘coat the mag
nesium oxide particles completely and to avoid an
. casting high melting point materials.
of binder which tends to weaken the struc
~,In accordance with one embodiment of the ' excess
u invention there is provided a mold comprising ture in service. Consequently, further variations 25
. fused magnesium oxide and hydrated calcium in particle size distribution will require accom
oxide, thoroughly mixed and pressed in dry
form under high pressure into a body having a
modating adjustments in ingredient proportions.
For a very fine magnesium oxide a 50-50 mix
‘ ture may be indicated and, similarly, for a coarser‘
cavity for the metal to be cast.
A complete understanding of the invention material the quantity of binder may be reduced 00
may be had from the following detailed descrip
The two mixtures described above in which
‘ tion, taken in conjunction with the appended
25% or 30% of binder are-used give the best
drawing, infwhich
results and the particle size distribution of the
Fig. 1 is a plan view of a casting mold embody
magnesium oxide in either of these mixtures 35
“ ing the invention, and ‘be-maintained consistently by duplication
Fig. 2 is an elevation, partly in section, of the can
and control of the grinding operation.
After the ingredients have been combined,v the.
_ mold
. Theshown
mold in
l0 Fig.
l. in. the drawing is suitable
for casting billets.‘ , It has a disk-shaped body
40 ll withgtapered sides if to facilitate manufac
ture. A recess or cavity if in ‘the top vsurface
of the body is vformed with sloping sides I‘ or
other contour desired for the completed billet.
- In the; ?rst operation in the manufacture of
mixture, without additions, is pressed into a mold.
of the desired size and shape. This operation 40 Y
is conveniently performed in a cavity die on a
conventional hydraulic or mechanical press.
Substantial forming pressures are required and
values around'8000 pounds per Square inch are
45 the mold fused magnesium oxide ground to a satisfactory. The tapered sides‘of the mold fa- 4|
prescribed particle size and powdered hydrated - cilitate its removal; from. the die after pressing.
The molds can be manufactured conveniently
calcium oxide are mixed inthe proper propor
tions ina tumbling barrel or by other suitable and economically. As the material is not subject
to air contamination the mixture is prepared and
' , means to coat the calcium powder on’ the mag
pressedinto molds invquantities suitable for most 00 _ '
so’nesium particles.
eiilcient manufacture and the completed‘ molds
- supplied in the form of fine powder, can be used . can be carried in storage until needed without
satisfactorily and fused magnesium oxide hav . deterioration.
Before use the ‘mold is. heated graduallyto a
ing suitable characteristics is available commer- '
of approximately. 150ml". in an oven I‘
u'cially as "Periclase”.
. ~
. Commercial hydrated ‘calcium oxide, which‘ is
2,121,909 -
_or with a‘ torch to eliminate contained moisture
and condition the mold for service. Gradual
and it is to be understood that the invention is
limited only by the scope of the appended claims.
I‘ ; application of the heat prevents spalling due to
What is claimed is:
face of ‘the mold.
Elimination of’moisture from
1. A mold forcasting high melting point ma
spontaneous generation of steam under the sur
terialsnconsisting of from 50% to 85% fused mag
the .mold changes the original ingredient propor
nesium oxide and respectively from 50% to 15%
tions'. ' A mold made from 75-25 mixture and
calcium oxide.
2. A casting mold for high melting point ma
oxide and 20% calcium oxide and a mold pressed ,terials consisting of approximately 75% fused
heated contains approximately 80%‘ magnesium
10 from the 70-30 mixture will contain approximatei magnesium oxide‘ and approximately 25% cal
iv 75% magnesium oxide and 25% calcium oxide , cium oxide.
3. A casting mold for high melting point ma
when ready for use.
The form of mold shown in the attached draw-
ing is particularly suitable for melting palladium
or‘ platinum scrap.‘ The scrap is placed in the
terials consisting of approximately 80% fused
magnesium oxide and 20% calcium oxide. ’
4. A mixture for casting molds suitable for high 15
cavity in the top of the hot mold and melted to temperature metals, consisting of from 50% to
form ‘the billet with a torch or in a furnace.‘ 85% fused magnesium oxide and respectively from
‘when a torch is used the ?ame is played over 50% to 15% hydrated calcium oxide.
5. {i method of making a casting mold for high
the mold‘ surface periodically during the melting
20 to prevent wide discrepancies between the metal melting point materials which comprises tum 20
bling a mixture consisting of from 50% to 85%
. and mold temperatures.
ground fused magnesium oxide and the remain;
After‘ the metal is cooled the mold can be re
moved readily ,from the billet by breaking it with der hydrated calcium oxide to coat the calcium
' - a hammen'. The mold material is embrittled by. e oxide on the ground magnesium oxide particles,
the melting operation and does not adhere to the - and pressing the tumbled mixture into the form
billet which avoids’ contamination of the cast
of a mold.
' 6. A method of making a casting mold for high
The open'cavity . in
~ the mold face can
- be formed
melting point materials which comprises- prepar
ing a mixture consisting of from 50% to 85%
can be provided by joining two cooperating mold 7, ground fused magnesium oxide and the remain
’ to any desired contour and a fully enclosed cavity
portions having a. gate for the introduction 'of
der calcium hydroxide; pressing the mixture into
- ‘Other .modi?cations and adaptations of the
a shaped mass,.and heating the shaped mass to
convert the calcium hydroxide to calcium oxide.
methods and article described above are feasible
molten metal.
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