Improved Method and Apparatus for Moulding and Vulcanizing Palate-plates for Artificial Teeth.
Year: 1889

page_text: Date of Application, 23rd Nov., 1889-Accepted, 11th Jan., 1890
COMPLETE SPECIFICATION.
Improved Method and Apparatus for Moulding and Vulcanizing
Palate-plates for Artificial Teeth.
to be
I, LUDWIG PRITZIUS, of Ludwigshafen on the Rhine, Bavaria, Germany, do
hereby declare the nature of this invention and in what manner the same
performed to be particularly described and ascertained in and by the following
statement -
My invention relates to an improved method and apparatus for moulding and
vulcanizing palate plates for artificial teeth by means of which it is possible to produce
a counter die and matrix made of gypsum of any set of teeth modelled in wax, to dry
the said mould of gypsum, then to put plastic caoutchouc into the dried mould and
finally to press the caoutchouc while still in a plastic condition and to harden the same
in applying direct heat and mechanical pressure.
The improved method and apparatus afford an essentially simplified and reliable
mode of working palate plates made of caoutchouc, the quality of which is not only
equal but even superior to that of plates produced by the vulcanizing apparatus
hitherto in use, that is to say the plates produced. by my new apparatus are more
dense and harder.
The hardening of caoutchouc for the purpose of manufacturing a set of artificial
teeth, which process is commonly termed "vulcanizing" in the art of dentistry, has
been effected hitherto by means of apparatus of varying shape and construction, but
having all the common feature, that the vulcanizing process can be carried out only in
a wet way.
a
The vulcanizing of caoutchouc requires high degree of heat, and hitherto either
water or steam has been introduced for this purpose into a steam tight vessel (the so
called "vulcanizing apparatus") for heating under pressure the caoutchouc to be
vulcanized to a certain degree.
Such apparatus when used have already frequently exploded owing to the pressure
of steam.
The main object of my invention is to avoid the danger of such explosions, which
danger is well known to exist in all vulcanizing apparatus heretofore employed, owing
to the use of steam.
The vulcanizing process is carried out by means of my new apparatus in a dry way,
that is to say, in gypsum free from water, in applying mechanical pressure together
with direct heating.
My improved method is based upon the fact, that the vulcanizing process of the
palate plates, that is the conversion of the caoutchouc from the soft plastic state into
a hard and horn like one, does not require any moisture and that this can consequently
advantageously be dispensed with.
On the contrary the use of steam, apart from the danger of explosion has even the
disadvantage that the vulcanized product becomes readily porous, while, when steam
is dispensed with, the vulcanized product becomes dense.
The steam does not act merely as water converted into a gaseous condition, but
owing to its considerable expansive power it exerts a great pressure upon the cuvette
which is weakly held together, and upon the contents of the latter, whereby a pressure
uniformly acting from all sides during the vulcanizing process attained.
This pressure is replaced in the new apparatus by mechanical means, namely, by
screw pressure.
The transmission of the heat produced by the flame to the enclosed object, which
was effected hitherto by the water and steam, is obtained in the new process directly
by metallic pieces closely surrounding the caoutchouc to be vulcanized.

page_text: Not only is the water excluded which hitherio was partially evaporated and
surrounded the cuvette containing the mould of gypsum and the caoutchouc placed
therein, but even the moisture contained in the gypsum is entirely expelled from the
apparatus before the vulcanizing process itself is commenced.
This latter circumstance is an extremely important feature of the present invention
and it gives the new process quite a special value.
My improved apparatus is arranged in such a manner, that it may be used for
moulding in gypsum the set of teeth modelled in wax and for drying the mould of
gypsum before the caoutchouc is introduced therein, for submitting to pressure the
introduced caoutchouc and finally for vulcanizing the latter under the pressure so
applied.
The new apparatus is shewn in the Figures 1 to 9 of the accompanying drawings.
Figure 1 is an elevation of the apparatus, Fig. 2 a plan view, Fig. 3 a longitudinal
section, Fig. 4 a horizontal section on linc ac, Fig. 5 a top view of the apparatus
with the pressing case removed; the other figures shew details and tools for operating
the apparatus.
The heating base a carries two rings b and c arranged one above the other; the
inner surfaces of which are conically shaped, are pressed by means of a cover d and a
pressing and closing casing e upon the bottom a. The latter has a projecting portion
C.
which is embraced by the ring which supports a second ring
The inner conical surface of the ring c forms the continuation of that of the
ring b.
The rings are furnished on their circumference with semicircular recesses for
receiving a guide rod g of semi circular cross section. This rod g is fastened to the
cover d and it prevents the rings bande from turning, when the cover d has been
placed upon them and the guide rod is engaged with the semi-circular recesses.
The cover d closes the hollow space formed by the inner walls of the rings b and c
and the bottom a. The cover is provided at its centre with a hole y for introducing a
thermometer tube into the middle space; a groove s is formed by turning on the
upper surface of the cover d, and communicates with the hollow space through the four
passages kk k³ 1.
All these parts are united together so as to form a single piece and for this purpose
the casing e, the inner lower part of which is threaded, is firmly screwed on the
bottom a the circumference of which is also furnished with threads. In the upper part
of the casing e are arranged two passages having for their purpose to allow of
the escape from the inner space the steam formed in drying the mould of gypsum,
and the gases produced in vulcanizing the caoutchouc; by these means any pressure
is avoided in the apparatus and in consequence also all danger is obviated.
In the centre of the upper part of the casing e is a head piece t having a
horizontal perforation for receiving a lever, whereby the apparatus is readily
screwed up tightly.
The hole o serves at the same time to discharge the steam produced in the
inner space when the mould made of gypsum is dried. The head piece is furnished
with a vertical aperture p, the inner walls of which are threaded for receiving a
press screw (see Fig. 6).
This opening serves also to receive a tube (see Fig. 7) in which may be
arranged a thermometer passed through the hole y into the interior of the apparatus
for observing the temperatures during the drying of the gypsum and the vulcanizing
of the caoutchouc introduced.
Air escapes 12 13 14 are arranged in the casing e for allowing the air to escape
when the apparatus is mounted or exposed to pressure.
The apparatus is used in the following manner:
An impression as exact as possible of the teeth, the gums, or of the edge of
the jaw and of the palate is made in the known way and into this impression is
pourcu gypsum so that a mould of the whole mouth will be obtained.
After the gypsum has become solid and the wax has been removed therefrom,

page_text: the teeth to be supplied and the palate plate serving to fix the same are modelled
by means of wax on the said gypsum-cast and the exact form such as is required
to be in caoutchouc for carrying the artificial teeth and for rendering them fit for
use, is given to the wax and to the teeth.
The gypsum cast G with the set of teeth modelled in wax are then put into
the lower ring b, as illustrated in Fig. 9 and gypsum is poured round the
outside of the same. The gypsum poured in is then prepared in the known way
in the lower moulding box consisting of ring band bottom a in such a manner,
that in pouring the gypsum into the upper moulding-box consisting of ring c and
cover, the material contained in the latter does not adhere when lifted from the
material of the lower moulding box. Ring is then placed upon ring band
gypsum is poured into the upper moulding box until it is entirely filled as
shewn in Fig. 9.
In the centre of the upper moulding box an aperture y y' is left extending close
to the contiguous surfaces of the lower mould and serving to receive a thermo-
meter so that during the drying and afterwards during the vulcanizing process
in the mould the temperature can be measured close to the object to be treated.
The separating surface of the upper and lower moulding box is marked in Fig. 9
by a thick line.
The cover d is then placed upon the ring c and the casing e is screwed down
to such an extent, that its lower edge is tightly pressed against the projecting
part of the bottom a, so that all the several parts of the apparatus are exactly
adapted one to the other, while the superfluous gypsum may run off through the
channels, whence it is removed afterwards.
After the gypsum has become solid in the mould, the casing e is screwed off
and the cover d and the ring e containing the upper die made of gypsum which.
is firmly connected with the cover d are also taken off
The lower mould is moderately heated a source of heat arranged under the
bottom a, until the wax becomes soft and may be removed by means of a suitable
tool.
After the wax has been removed the ring c with the cover d firmly connected
thereto by the counter cast, are placed upon the ring b and the casing is screwed
again on the bottom a.
At
To dry the mould of gypsum the inner space is heated to about 130° (
about 90° C. the water contained in the gypsum begins to issue through the
passages kkk into the grooves where it is converted by the continued
heating into vapour which escapes through the openings 12 and the holes a
and p of the casing into the open air.
When the thermometer indicates about about 140° C. steam will no longer be
produced, all the water having escaped from the gypsum.
This is ascertained by the fact that steam ceases entirely to escape and that the
thermometer indicates suddenly very high temperatures. By the introduction of
the thermometer into the middle space of the apparatus the exact temperature of
this place may be accurately ascertained, as the difference of temperature between.
the outer casing and the inner space is about 60 degrees.
By the above described operation a completely dry mould of gypsum of con-
siderable hardness is attained.
For making the palate plate the casing e is screwed off and the upper part of
the box consisting of ring c and cover d is removed and the caoutchouc being a
soft and elastic mass, is introduced in small pieces into the mould (which is still
hot) of the lower moulding box consisting of ring b and bottom a.
After the quantity of caoutchouc necessary for manufacturing the palate plate
has been placed into the mould, pressure is applied in the following way:
The upper box is again put upon caoutchouc contained in the mould and the
casing e is screwed downwards so that its upper part is tightly pressed against
the cover d. As in this position of the casing è a pressure has not yet been

page_text: exerted on the palate plate to be manufactured, the middle press screw shewn in
Fig. 6 is applied and tightly screwed, so that the contents of ring (the upper box)
are pressed by the cover d against the ring (the lower box).
C
The space existing between the upper part of the casing e and the cover d is made
to disappear by screwing the casing e completely downwards. But before doing this
the press screw must be withdrawn either completely or so far that it does not enter
into contact at all with the cover, as otherwise it would be impossible to screw the
casing downwards owing to the difference of pitch of the press-screw and of the casing.
The pressure is complete, when the upper part of the casing is tightly pressed
against the cover d, and the lower edge of the casing against the projecting portion of
the bottom a as illustrated in Fig. 3.
To effect the pressure in an easy and convenient manner a quadrangular casting
such as illustrated in Fig. 8 may be used. This casting is fastened to the working
table and adapted exactly into the lower hollow space (also of quadrangular shape of
the bottom a; a sufficient hold is furnished by these means on pressing, for preventing
the apparatus from turning.
The caoutchouc after having been pressed in the above described manner into the
mould is then vulcanized.
This is effected by heating the caoutchouc contained in the closed and hardened
mould of gypsum up to 155 or 160° C. by means of any suitable source of heat
arranged under the bottom a, the apparatus being tightly closed. The length of time
required for heating is dependent on the intensity of the source of heat, it is ordinarily
about half an hour. The flame is then immediately extinguished and the apparatus is
left to itself. Within the following quarter of an hour the heat will still increase
to 180° or 185° C. and then decrease within an hour to 140° or 130° C. The
vulcanizing process is extremely rapidly carried out by the above described mode of
working.
Excellent products are obtained by heating the tightly screwed mould gradually
and slowly (within about one hour) up to 160° C. and maintaining this temperature
during 2 hours, and by reducing the latter then to 140° whereupon the flame is
extinguished.
After the heating is terminated, the palate-plate is hardened and finished so as to
render it fit for use.
Owing to the inner conical shape of the rings b and c the moulds of gypsum may
be easily taken out of the apparatus so that the latter is ready for further use.
The above described apparatus permits of working in a perfectly reliable and safe
manner, any danger of explosion being entirely excluded.
In comparison with hitherto known methods and apparatus the new process and
apparatus offer in addition to the absence of any danger of explosion the following
advantages:
All the several apparatus and parts which were heretofore requisite for the
production of a caoutchouc palate plate are, according to the present invention
combined into one. In the same are contained, besides the substitute for the steam
pressure:
1. The Cuvette which was previously separately treated, and which receives the
gypsum mould and the mouth piece; this Cuvette is replaced by the double ring bc,
which rests on the base a of the apparatus and is covered by the casing d.
2. The preliminary heater of the caoutchouc; by the heating of the apparatus
to 180° C. for driving off the water in the plaster of paris, the caoutchouc becomes
heated on its introduction sufficiently to have the necessary degree of softness for
moulding.
3. The separate fixed press which was employed for pressing the parts of the cuvette
together after the softened caoutchouc was introduced, also the cuvette-strap which
was necessary for holding the parts of the cuvette together after they had been
removed from the press.
These two parts are replaced by the casing, which constitutes a great simplification

page_text: and improvement in the manufacture of pallet plates of caoutchouc, the casing
serves:
a, for pressing the contents, which is partly effected by the central screw, and
after removal hereof, by the action of the screw thread at the bottom of the casing.
The casing effects this purpose very advantageously because the whole of the upper
surface thereof is available for exerting a uniform pressure upon the contents, while
with the apparatus generally used the pressure on the cuvette is effected by one or
With
generally two screws applied either at the side or centrally through the strap.
these arrangements the pressure on the cuvette is often one sided, owing more particu-
larly to an unequal distribution of the caoutchouc, and the palate plates were conse-
quently often defective or useless. By applying the strain uniformly round the
circumference, the pressure becomes correspondingly uniform.
b, for maintaining this uniform pressure during the vulcanizing, the pressure being
at present maintained by steam.
c, for the reception and discharge of the moisture contained in the gypsum as also
of the gases given off during the vulcanizing process, thus avoiding all risk of
explosion.
d, as conductor of heat to the interior, by enclosing all the parts and bringing
these into intimate contact with itself, whereby a very effectual heating is afforded.
e, as boiler during the heating and the resulting driving off of the moisture from
the gypsum, because without this, the steam which is first generated at the bottom of
the mould would tend to drive the same forcibly out of the rings. By enclosing the
same as described and maintaining pressure on the parts any such destructive action
of the steam is prevented, the steam being allowed to escape gradually by the
passages.

page_text: 2. The use for carrying out the manufacture referred to in the preceding claim, of
apparatus consisting of a bottom heating plate &, two rings b, c, of which the first
serves as the lower and the second as the upper mould box, and which are pressed
down upon the plate by a cover d and an enclosing pressing case e in such manner that
the steam given off during drying and the gases given off during vulcanizing
are allowed to escape through channels formed in the casing, substantially as
described.
Dated this 23rd day of November 1889.
ABEL & IMRAY,
Agents for the Applicant.