Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Process of Making Set Cast Pieces of Jewellery
This invention relates to a process having the features ~
recited in the prior art part of claim 1. ~ ~ -
DE-38 24 574 Al describes a lost-wax melting process of
making pieces of jewellery. In the process a master pattern
of the piece of jewellery is made first and is used to make
a master mold. To make the mold, the master pattern may be
placed into a flask and a molding composition, e.g., a two- `
component silicone-rubber mixture, may be poured into the
flaks and cured therein. The resulting body may then be
dissected into two halves and the master pattern may
then be taken. Alternatively the master pattern may be
placed between two blocks of thermoplastic material,
which are then heated under pressure until they are ~ ~
15 plastically deformed and hug the master pattern so ~`
that a faithful impression of the master pattern is
formed in the two blocks (DE-35 46 188 Al). Because the
resulting bipartite master molds usually consist of ~ `
elastomeric material, they are sometimes called rubber
molds. A pattern-making composition, particularly a
wax, is then charged into such a master mold by casting
or injection molding. When the pattern-making composition
gas been cooled, the master mold is opened and the
pattern is taken. A plurality of patterns are usually ',
25 assembled to form a pattern tree, which is then embedded `~
into a refractory molding composition. The molding ~`
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composition will be regarded as "refractory" if it
withstands without deformation the action of a molten
metal from which the piece of jewellery is made. When the
pattern tree has been embedded in the refractory molding -~-~
S composition, the pattern-making composition of which the
pattern tree is made is expelled being heated. lf the
pattern-making composition is a wax or a low-melting
metal, it will be melted out (lost-wax casting processl.
If the pattern-making composition is a plastic, it will
be burnt out. The molten metal is then poured into the
casting mold thus made. To ensure that the metal from
which the pieces of jewellery are to be made will
penetrate into the last corners and branches of the
casting mold, the latter is rotated during the pouring
lS (centrifugal castingS or the pouring is assisted by the
~pplication of a vacuum (vacuum casting). When the tree
consisting of the pieces of jewellery has solidified and
cooled, it is removed and the pieces of jewellery are
separated from each other.
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In the making of pieces of jewellery comprising
one or more set jewels it is also already known to embed
such jewels in the casting. For that purpose a master pattern
of the piece of jewellery in which the jewels are set is
made and that master pattern is used to make the master
mold, which is a negative replica of the piece of jewellery
and has openings for the jewels. The jewels for the piece
of jewellery are inserted into said openings of the master
mold, into which the pattern-making composition is then
poured or injected. The resulting pattern of the piece of
Jewellery is processed further as described hereinbefore.
But it is difficult to place the jewels into the master mold
in the correct positions and so to fix them that after the
pouring or injecting of the pattern-making composition the
~ewels will exactly have the positions which they are in-
tended to occupy in the subsequently made piece of jewellery.
The position of the jewels is often changed as they are em-
bedded in the poured or injected composition and the extent
to which the jewels are embedded in the injected composition
may vary from pattern to pattern. This may also be caused by -~
a variation of the Jewels from each other.
From French Patent Specification 1,599,866 it is
already known to embed jewels in a wax pattern, to assemble
such wax patterns in a wax pattern tree and to process them
further to make cast pieces of jewellery by a lost-wax
casting process. But in that case the pieces of jewellery
are not inserted on the wax pattern into a setting but are ~`
inserted into a wax pattern which has been made without a ~ -
setting. As a result, the cast piece of Jewellery also fails
to have a separate setting for the jewels.
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From FR-A-2,366,812 it is known to make a master
pattern in which a jewel is set in a setting which has al-
ready its final shape, whereafter the jewel is carefully
taken out so that the setting is not changed, and the empty -
master pattern is ased to make a rubber mold, in which a
plastic pattern is then cast with a setting into which the
Jewel is inserted. Such patterns are then assembled to form
a pattern tree, which is embedded in gypsum, whereafter the
plastic is expelled and noble metal is cast into the re- -
sulting casting mold. That practice has the disadvantage
that the pattern must be made from a material which is so
elastic that jewels can be inserted into the finished set- ~
ting. Difficulties will arise with the usually employed P-
pattern waxes because they are lnelastic. For this reason
it is recommended in FR-A-2,366,812 to use a plastic, which
is expelled by a two-stage thermal process, namely, by melt-
ing followed by a shocklike heating to the temperature which
is required for the casting of the metal and at which the
plastic is decomposed. A further disadvantage resides in
that the jewel will not firmly be retained unless it has
exactly the same size and shape as the jewel that had been
inserted into the master pattern and this will not be the ~ `
case, as a rule, so that expensive subsequent work on the
cast piece of ~ewellery will be required.
It is an ob~ect of the invention so to improve
the process described first hereinbefore that exactly fit-
ting ~ewels in the piece of jewellery will be obtained in
the simplest possible manner without a need for subsequent
setting work on the piece of jewellery.
That object is accomplished by a process having
the features stated in claim 1 or 2. Desirable further fea-
tures of the invention are subject matters of the dependent
claims.
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In the process in accordance with the invention,
just as in the known process, a master pattern of the piece
of jewellery to be made is malde first. That master pattern
has one or more settings in dependence on the number of
the intended jewels, but the jewels are not inserted into
the master pattern. For instance, in a pin setting the pins
intended to set the jewels are not bent inwardly but are
maintained in their original orientation. The master pattern,
into which a jewel has not yet been inserted, is then used
to make a negative mold as a master mold and a pattern of
the piece of jewellery is cast in that master mold. In that
case the pattern-making composition preferably consists of
a wax.
The pattern thus made is then provided with jewels
in that the ~atter are inserted into the settings provided
for that purpose. Because the pattern is 2 positive replica
of the piece of jewellery, the jewels can be inserted into '~
the settings from the entirely exposed top surface of the `~
piece of jewellery, as is the case with an original piece
of ~ewellery but it is not necessary to insert them into
difflcultly accessible openings of a negative mold (master
mold) in a difficult operation as in the lost-wax casting
process. The lnsertion of the jewels into the settings of
the pattern made of the pattern-making composition (parti-
cularly of a wax pattern) may be effected, e.g., by means of
a slender vacuum applicator, which is used to suck and hold
the ~ewel and to insert the jewel into the setting, the je-
wel is then left in the setting when the suction air has
been shut off. Thereafter the jewel needs only to be fixed
in the setting. The jewels are preferably fixed in their
settings in that the settings are softened by the action of
heat and are plastically deformed. This is preferably ac-
complished in that a tool which conforms to the top end of
the setting is heated and engaged with the setting and is
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forced against the jewel so that the setting is deformed
in a single step, This is possibIe not only wlth pln or
tab settings, which locally embrace the jewels as with fin-
~ers, but also with frame settings, which embrace the je~
wel throughout its periphery. In case of a frame setting
the tool for plastically deforming the setting will -~
suitably consist of a tool which has at its tip a frame-
like contact surface and that surface will be engaged with
the rim of the frame setting and forced against the peri-
pheral edge of the jewel.
In case of a pin setting or a tab setting, on the
other hand, it is desi~rable to employ a tool which has pro-
jections which correspond to the positions of the pins or
tabs and when the tool has been heated are placed on the
pins or tabs so that they are softened and flow and em~
brace the adjacent edges of the jewel; this can be accompli-
shed by a short contact with the tool. It has been found
that it is not necessary to deform all pins or tabs to fix
the jewels because a pin which has been deformed under the
action of heat will more closely contact the edge of the
Jewel than a metal pin which is forced against the edge of
the ~ewel in the conventional manner. For this reason only
part of the pins or tabs ~re preferably deformed în pin or
tab settings whereas the other pins or tabs are left unde-
formed. In that case the still undeformed pins will provide ~ -
the customary appearance of a conventional pin setting al-
though some pins have been deformed. In a pin setting com-
prising four pins per jewel, only two mutually opposite pins
will preferably be deformed in a setting that comprises six
pins.
The jewels can be so easily inserted into and
fixed in the model that said operation can perfectly be
performed even by unskilled labors after a brief instruction.
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For this reason the process in accordance with the inven-
tion can be adopted to special advantage for the industrial
mass production of pieces of jewellery. Even in the trial
phase of the process in accordance with the invention it
has been found that the costs of setting jewels can be
drastically reduced: In comparison with the conventional
technique, in which the jewels are inserted into the cast
ring rail, the setting costs can be decreased to 1/10 and
in comparison with the conventional lost-wax casting pro-
cess the costs can still be reduced to 1/4.
The further processing of the pattern made in
accordance with the invention is performed in the manner
which is known per se for the centrifugal casting or vacuum
casting of pieces of jewellery. This will be explained in
the example described hereinafter.
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A master pattern of metal is made in a manner
known per se for a piece of jewellery consisting, e.g., of
a ring, which is to be provided with a plurality of ~ewelsO
The master pattern has pin settings for the jewels but the
Jewels are not inserted. The master pattern is placed be-
tween two blocks of a thermoplastic silicone elastomer, which
are subsequently heated and forced against each other. As
a result, the silicone elastomer is plastically deformed to
hug the master pattern so that a faithful impression of the
master pattern i~s formed in the two blocks. The two blocks
which have thus been deformed constitute the two parts of a
master mold, into which a wax is subsequently injected.
When the wax has been cooled, the master mold is opened and
the wax pattern of the piece of jewellery is taken. There-
after a vacuum applicator is used to insert the intended
~ewels into and fix them in the settings which are formed ~ ;
in the wax pattern and consist each, e.g., of four pins.
This is accomplished in that a forklike tool having prongs
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which are electrically heated and are spaced apart like
two mutually opposite pins is engaged with two mutually
opposite pins of a given setting and is slightly forced
against the latter so that the pins are softened and upset
and embrace the adjacent edge of the jewelO Thereafter, a
wax pattern :tree is made in a manner known per se from a
number of wax models thus made and is inserted into a flask,
into which a fine gypsum, such as alabaster, is poured.
When the gypsum has set, the flask is heated so that the
wax is molten out and the gypsum cast of the wax pattern
tree is left in the flask. The flask is heated to a tempe-
rature of about 750C and is inserted into a centrifugal ~
casting machine and a molten 14-carat gold alloy is poured ~ ;
into the flask and is permitted to solidify in the rotating
flask. When the flask has been cooled to about 40C the gyp-
sum is crushed to expose the cast tree. The pieces of je-
wellery are then severed from the tree and cleaned and optio-
nally polished.
The described process is particularly suitable
for pieces of ~ewellery comprising small jewels which can be
set with short pins having a length not in excess of 2.5
or 3 mm.
