A spruing assembly for receiving investment material in the production of an investment mold for castings by the "lost wax" process which includes a hollow chamber to receive the investment material. Included within the chamber is one or more sprue for supporting the wax pattern(s) to be cast and one or more corresponding predetermined shaped reservoir(s) being slidably moveable up or down the sprue to create the heat center of the investment mold. Where a long span casting is to be produced all the reservoirs are connected to form a continuous reservoir or Feeder Bar which conforms to the curve of a long span dental arch. A base member is provided within the chamber for supporting the sprue.

BACKGROUND OF THE INVENTION 
The present invention relates to investment casting, and more specifically, 
to a spruing assembly for receiving investment material in the production 
of investment mold castings. 
In dental technology, castings are used to restore dental structures and 
diseased teeth to their original or modified anatomy. The cast 
restorations can take two forms, namely a crown or inlay or a coping. In 
the form of a crown or inlay, the cast restoration itself actually has all 
the required anatomy whereas, in the form of a coping, the casting merely 
serves as a metal substrate to which is bonded porcelain sculpted into the 
desired dental anatomy. These dental castings may restore a single tooth, 
or they may restore multiple teeth as in a bridge or splint. 
For many years the Lost Wax Process employed sprues in the production of 
dental, jewlery and other industrial castings. The sprues, which may be 
plastic, metal or wax, are mounted on a crucible former which is 
positioned at the base of a cylinder or casting ring. The sprue extends up 
into the ring and supports a wax pattern of the design to be cast. In 
dentistry, the part to be cast is created in wax on a duplicate of the 
tooth being restored, the duplicate being called a die. After the wax 
pattern on the die is completed a sprue is attached to it and using the 
sprue as a handle, the wax pattern is removed from the die and the free 
end of the sprue is inserted into the crucible former of a base and a ring 
is placed around the base. The ring is filled with investment which is a 
cement-like refractory material. After reaching final set, the investment 
is heated in an oven to melt and eliminate the sprues and wax pattern to 
drive out gases and moisture, this being termed the burnout step, Molten 
alloy is then cast through the sprue channel into the resulting mold 
cavity in the investment. 
In dental technology, the sprues are often equipped with enlargements along 
their proximal end, known as reservoirs. These reservoirs provide a ready 
supply of molten alloy during the casting process until all the parts of 
the wax empty chamber have been filled, thus reducing the porosity and the 
occurrence of voids i.e. empty areas, in the casting. The use of 
reservoirs has been discussed previously in U.S. Pat. No. 3,340,923 issued 
to J. W. Benfield on Sep. 12, 1967, and in U.S. Pat. No. 4,081,019 issued 
to F. M. Kulig on Mar. 28, 1978. In both of these patents the reservoir is 
an integral, fixed part of the sprue. 
One of the problems that arise with this arrangement is that the reservoir 
cannot be moved on the sprue; there is no way to modify the effect of the 
reservoir as needed by castings of various sizes and alloys. 
This invention has a novel reservoir that can be placed at any location on 
the sprue, as determined by the user to be the most effective in its 
function according to the alignment of the sprue, the size of the casting 
and the alloy being used. The sprues which may be plastic, wax or metal, 
hollow or solid, are provided in any gauge and length. A sprue is selected 
of a gauge suitable for each particular casting and cut to a length 
appropriate for each specific use. 
Another problem that arises with reservoirs that are a fixed part of the 
sprue is that the reservoir may not be positioned at the heat center of 
the mold and therefore would not ensure the availability of sufficient 
molten alloy. It is important that the alloy remain molten until all parts 
of the wax empty chamber are supplied with sufficient alloy to yield a 
perfect casting. The reservoir's diameter is larger than the sprue's and 
thus has more bulk to hold heat which is necessary to keep the alloy 
molten during the casting process until all the investment cavities have 
been filled without voids. "Heat Soaking" insures that the heat center of 
the mold is kept as hot as possible to help maintain the alloy in its 
molten state. Thus, during burnout, the investment mold is heat soaked or 
held for 30 minutes or more at the maximum temperature of the investment 
being used (1400-1700 degrees F). The heat center is created by the bulk 
of reservoirs and is insulated by the surrounding mass of investment. The 
heat center is the area of the investment mold that retains the heat 
longer than other areas and alloy in it remains molten longer and is able 
to supply molten alloy to all parts of the wax-empty mold being cast. 
Thus, the location of the reservoir(s) is critical to this process. Hence, 
by adjusting sprue length and having movable reservoirs, one has the 
flexibility in positioning the reservoir(s) and the wax pattern properly 
in relation to the heat center of each mold and the reservoir(s) can then 
be locked into the desired position on the sprue with molten wax. 
Still another problem that arises with fixed reservoirs occurs when the 
configuration of sprues vary depending upon the length of the restoration 
being involved in the restoration. Thus, the longer the restoration the 
greater the number of sprues that will be required and if the restoration 
has multiple units that vary in thickness it will require sprues of 
various gauges. Additionally, some alloys function better with short 
sprues while other alloys are best served by longer sprues. Thus, all 
these variations necessitate flexibility in positioning the reservoirs so 
they can function ideally within the heat center of the mold i.e. by being 
the last part of the casting to cool and solidify they are thus able to 
supply molten alloy to the wax empty chamber allowing it to completely 
fill without voids or defects. 
Another problem that arises with fixed reservoirs occurs when the 
configuration of sprues vary depending upon the curvature of the dental 
arch involved in the restoration. In such applications, the casting 
requires multiple sprues at various positions and angles. When reservoirs 
are locked into fixed locations on sprues, segments can be cast consisting 
only of a few units because as they progress along the arch the fixed 
reservoirs no longer fall within the mold's heat center. Accurately 
assemblying the short segments into a final full span is difficult and may 
not be possible. 
The present invention eliminates the rigidity of spruing where reservoirs 
are locked into a fixed position on the sprue inasmuch as the reservoirs 
are freely located on the sprue and therefore maintained in the mold's 
heat center. Therefore, a long span restoration following the curve of the 
dental arch is no longer an obstacle to one-piece casting because the 
sprues with their adjustable reservoirs can follow the curvature of the 
arch. At the conclusion of spruing, the individual reservoirs can be 
connected with wax, which, in turn, creates a continuous reservoir of 
molten alloy during casting. Thus, long span castings of multiple 
restorations as a single unit can be routinely produced. 
Another advantage of the present invention provides the ideal spruing 
system for casting multiple units as a one-piece casting that eliminates 
the requirement for soldering. Soldering to connect multiple units is not 
only time consuming but errors of fit in units is often caused by the 
actual technique of soldering. To be able to eliminate soldering is a 
significant advance in the accuracy of the fit of multiple unit 
restorations and construction of implant superstructures. For most 
accurate results to obtain a one-piece casting, hollow plastic sprues may 
be used with a ringless casting which eliminate the requirement for 
soldering. 
Further, whether the arrangement of multiple sprues is in a "tee-pee" 
alignment, in a vertical alignment or in a horseshoe alignment, they are 
all easily adaptable with the present invention-to produce accurate 
one-piece castings. 
Present technology utilizes either a solid plastic or wax rod to create a 
Feeder(Runner) Bar for spruing multiple units. A hollow plastic device has 
been disclosed in U.S. Pat. No. 4,558,841 issued to M. Engleman et al on 
Dec. 17, 1985 for spruing multiple units. Plastic is superior to wax in 
that it provides resistance to distortion and fracture of the sprued 
ensemble. Hollow plastic is superior to solid plastic in that there is no 
concern that the hollow plastic will expand during burnout and crack the 
investment mold. Unfortunately, none of these devices are completely 
satisfactory in that they either do not permit spruing a long restoration 
that follows the dental arch or provide rigidity of the ensemble when it 
is removed from the dies and placed in the crucible former. 
Using the present invention, a custom made Feeder(Runner) Bar is created 
that has the strength of plastic and the advantages of hollow plastic by 
connecting all the reservoirs with wax. With spruing completed the entire 
unit can be removed without fear of distortion of the sprues or Feeder Bar 
and then placed in the crucible former of the base. If there is no 
distortion or cracking of the sprues or the wax patterns as they are 
removed from the dies, it is assured that the one-piece casting will be 
made that will be reseated on the dies and subsequently on the patient's 
teeth perfectly. 
Accordingly, it is an object of the invention to provide an enhanced 
spruing assembly for producing high quality castings of either a minimal 
number of units or of long multiple unit spans. 
Another object of the invention is to provide an improved spruing assembly 
which provides reservoir means slidably moveable up or down a sprue means 
to within the heat center of the investment mold. 
Still another object of the invention is to provide a spruing assembly in 
which a reservoir, which is provided for a sprue, has a predetermined 
shape and surface which will distribute stress equally over its entire 
surface in the investment mold to avoid voids or defects when supplying 
molten alloy to the spruing assembly. 
A further object of the invention is to provide a novel spruing assembly 
for casting multiple units as a one-piece casting. 
Still a further object of the invention is to create a hollow plastic 
Feeder (runner) Bar for long spans that will accurately follow the curve 
of a dental arch. 
SUMMARY OF THE INVENTION 
High quality castings of individual a multiple parts is achieved in 
accordance with the present invention by using a spruing assembly which 
includes a base and a centralized sprue base former supporting one or more 
sprue means upon which is slidably mounted a reservoir means and located 
within the heat center of the investment mold. When the spruing assembly 
is to be used for casting multiple units as a one-piece casting, a 
plurality of sprue means is provided together with corresponding 
reservoirs which are connected together to effectively form a Feeder Bar 
to create a continuous reservoir for molten alloy during the casting 
process. A plastic tapered ring is provided which engages the base and 
surrounds the spruing assembly to form a hollow chamber to receive the 
investment material. 
The foregoing and other objects, features and advantages of the invention 
will be apparent from the following particular description of a preferred 
embodiment of the invention, as illustrated in the accompanying drawings.

DETAILED DESCRIPTION 
Referring to the drawings, and particularly to FIG. 1, the sprue 1 may 
consist of a hollow plastic tube and the reservoir 2 may consist of a 
hollow plastic ball that fits on the sprue and can be moved up or down 
theron so it may be secured in the most ideal position on the sprue in 
order to maximize its function as a reservoir of molten alloy and heat 
source. Referring now to FIG. 2, there is shown a cross section of the 
sprue 1 with its hollow opening and of the reservoir 2 with its hollow 
opening to allow it to be positioned on the sprue 1 as shown in FIG. 3. 
The sprue 1 may be of any gauge but for purposes of describing this 
invention it may be of 6 gauge, 8 gauge or 10 gauge. Likewise, the length 
of the sprue 1 may vary but is determined by the distance of the wax 
pattern to be molded from the support for the sprue 1. Sprues will be 
provided greater than this distance so that they may be cut to the 
preferred length as determined by the requirements of each casting. The 
sprue 1 may be solid wax or plastic but hollow plastic is preferred 
because of plastic's superior strength and hollow to lessen the 
possibility of damaging the investment mold during burnout. 
The reservoir 2 that fits on the sprue 1 is preferably round in shape with 
a smooth curved surface to distribute stress equally over its entire 
surface so as not to create undo pressure during burnout. The reservoir 2 
is hollow with openings on opposite sides in order to allow the sprue 1 to 
pass through. Because solid plastic expands during burnout before it melts 
and vaporizes, the expansion can damage the investment walls surrounding 
it, wheras, if the plastic is hollow, as is the case in the present 
invention, it does not expand but instead, will collapse on the hollow 
space so there is no concern about damage to the investment mold. The 
diameter of the reservoir 2 will vary according to the gauge of the sprue 
1 and is usually about double the sprue diameter. The position of the 
reservoir 2 from the wax pattern to be molded is preferably in the range 
of 2 mm(0.0788 inches) to 7 mm(0.2758 inches). 
The present invention can be used for casting single units but its greatest 
benefit is for casting multiple units or large castings 20 which require 
multiple sprues and for the elimination of the need for soldering these 
units into one piece as soldering can introduce errors in the accuracy of 
the fit of the casting. In addition to the disadvantages of solid 
reservoirs discussed above, reservoirs as described in U.S. Pat. No. 
3,985,178 issused to A. J. Cooper on Oct. 12, 1976 cannot be used for more 
than four units because the flat ends of the reservoirs do not permit 
desirable positioning of the reservoirs. Either they must be cut away to 
permit good connections or the corners will overlap forcing the tops 
apart. If only the corners are connected proper positioning of the wax 
patterns is not possible. Square reservoirs introduce a serious additional 
problem in that the angles of the corners upset the smooth flow of molten 
alloy as it flows through to the mold cavity. All of the casting spaces 
must be smooth and curved in order to eliminate turbulence in the flow as 
turbulence is responsible for voids and defects in the completed casting. 
The round reservoirs of the present invention eliminate these placement 
difficulties and permit the maximum number of wax patterns to be utilized 
simply by adjusting the position of the reservoir on each sprue. 
Referring now to FIG. 4 there is shown a plurality of sprues 1 of 
appropriate length and gauge being attached to a wax pattern 3 overlapping 
multiple dies 4. Hollow round reservoirs 2 with openings at each end which 
correspond to the sprue diameters are placed on the sprues within the 2 
mm-7 mm distance from the wax patterns 3. Solid round or rectangular 
reservoirs can be used rather than hollow round reservoirs but they have 
serious disadvantages. Solid reservoirs are more likely to damage 
investment mold during burnout in the same manner as already described for 
solid sprues. Rectangular reservoirs are much more likely to create 
problems than round reservoirs. The corners of rectangular reservoirs 
localize stress at a point to create greater impact on the investment than 
a round surface which will distribute stress over its entire surface. 
Corners in the investment mold lead to turbulence, mold cracking or 
finning which produce distorted finished castings. 
After all the sprues 1 have been attached to the wax-up, the reservoir 
positions are adjusted on the sprues 1 so that they are all in the same 
horizontal level. The reservoirs 2 are then firmly secured in place with 
wax and connected to each other with wax thus forming a continuous 
reservoir from one end of the wax-up to the opposite end as shown in FIG. 
4. This continuous reservoir, known as a Feeder Bar, is a continuous bar 
with all portions becoming mutually supporting in function. This Feeder 
Bar is more effective than those heretofore in that it has been custom 
made for each individual case to adapt in shape to the curve of the dental 
arch and to the irregularities in size and position of the individual 
waxed units. 
The dental arch which supports teeth is a rough curve as it moves from the 
posterior molar area of one side of the jaw forward around the anterior 
area and then back posteriorty to the opposite molar area. The canine 
areas on the left and right sides exhibit the greatest angulation and 
deviation from a gentle curve. A restorative span of wax patterns 
following this curve will demonstrate unequal spaces between the wax 
patterns and their sprues as well as different sprue lengths. If the span 
includes the canine areas, the variations will be increased. By utilizing 
sprues of different lenths and positioning the reservoirs optimally on 
each sprue, one can compensate for the differences created by the curve of 
the dental arch. The present invention makes this possible and unlike 
previous efforts, the length of the span is not limited to only three or 
four units. 
Referring now to FIG. 5, the spruing assembly, indicated generally by 
reference numeral 5, constructed according to the invention, includes a 
base member 6 having a centralized sprue base former 7 filled with a wax 
plug 8 and a casting ring 9 supported by the base member 6 to form a 
hollow chamber to receive investment material 11. The base member 6 may be 
made of plastic material and be predetermined in shape. The base former 7 
is ellipsoidal in shape and has an opening at the top to receive the wax 
plug 8. Special designed grooves 10A and 10B are provided in the base 
member 6 to receive and securely maintain the ring 9. The base member is 
reusable since it is removed after the investment material has set. The 
casting ring 9 may be made of plastic material and is tapered toward the 
bottom of the ring 9 to facilitate removal of the investment mold by 
popping it out after the final set of the investment which thereby permits 
the ring 9 to be reusable. While the plastic ring 9 is shown in FIG. 5 as 
having a graduated round shape, it should be apparent that it is within 
the skill of the art to use other shapes, as for example, oval shapes 
with, of course, the shape of the grooves of the base member 6, being-of 
similar shape to receive and secure the ring 9 in the base member 6 of the 
assembly 5. 
Referring now to FIGS. 4 to 6, when proceeding with the casting of a dental 
item and the like, in accordance with the invention, the combination of 
the sprues 1 and Feeder Bar of associated reservoirs 2 connected to the 
wax patterns 3 is removed from the dies. The tee-pee arrangement of sprues 
1 is then inserted into the wax plug 8 of the sprue base former 7 as shown 
in FIG. 5. FIG. 6 shows a vertical view of the assembly 5 which 
demonstrates the different lengths of the sprues as they follow the curve 
of the dental arch. It is to be noted that all the reservoirs 2 are 
positioned in a continuous arc regardless of the length of the sprues 1. 
Following this, the proper size ring 9 is inserted into the grooves 10A 
and 10B of the base member 6 to form the hollow chamber for receiving the 
investment material. 
High heat resistant investment material is next poured into the ring to 
completely surround the wax patterns 3, sprues 1 and reservoirs 2 and 
allowed to set for a predetermned period of time. After the investment 
material has set, the investment mold is removed and then placed into a 
burn-out oven and heated to a high temperature. As the temperature rises, 
the wax in the investment mold begins to melt and is conducted out through 
the sprues. As the temperature continues to rise, the wax pattern, sprues 
and Feeder Bar begin to melt creating hollow internal spaces. As the 
heating continues the melting and liquifying, the melted wax and plastic 
flows out through the spaces created by the melted sprue members. After 
all the wax and plastic have been melted out of the mold, leaving a cavity 
in the mold, the investment mold is placed in a casting machine which is 
used to force molten alloy into the investment mold by the centrifugal 
action of the casting machine. After the casting is completed, the 
investment mold is broken away from the cooled metal and individual items 
can be cut off the cast assembly, cleaned and fitted onto the dies of the 
model. 
Thus, with this arrangement of the present invention, multiple units may be 
obtained with one casting operation. 
While the invention has been particularly shown and described with 
reference to a preferred embodiment hereof, it will be understood by those 
skilled in the art that several changes in form and detail may be made 
without departing from the spirit and scope of the invention. Accordingly, 
it is intended by the appended claims to cover all such modifications and 
changes as fall within the true spirit and scope of the invention.