US 3661369 A
Heating apparatus including a radiation source and reflector means for focussing reflected rays at an image focus. The source of radiant energy and reflector means are mounted upon an adjustable support which is linearly movable in a vertical direction to position a heating apparatus above a working surface.
Description (OCR text may contain errors)
Cl H. l
[ May 9, 1972 Elam 3,661,369
unuou umauib 1' ill Costello l 54] HEATING APPARATUS HAVING SIMPLIFIED FOCUSSING MEANS  Inventor: Bernard J. Costello, Ringoes, NJ.  Assignee: Argus Engineering Company, Inc.,
8 Hopewell, NJ,
l  Filed: May 1, 1970 l 21 Appl. No.: 33,725
 U.S. Cl ..263/2 R, 263/6 R, 263/40 R  Int. Cl ..F27b 9/14, F27b 3/06  Field ofSearch ..263/6 R, 2 R, 40 R  References Cited UN lTED STATES PATENTS 1,810,643 6/1931 Colby ..263/2 R 2,026,370 12/1935 Winkler ..263/40 R 2,457,654 12/1948 Furkert ..263/6 R 2,519,616 8/1950 Watkins..... 263/40 R 3,151,851 10/1964 Negley ..263/40 1 Primary Examiner-John J. Camby Auornev-Ostrolenk, Faber, Gerb & Soffen 57 1 ABSTRACT source of radiant energy and reflector means are mounted upon an adjustable support which is linearly movable in a vertical direction to position a heating apparatus above a working surface.
The working surface is comprised of means movable in two mutually perpendicular directions within a plane perpendicular to the direction of movement of said heating apparatus. Said means is further adapted to receive and support the object to be heated. lndicator means located outside of the heating area, is coupled to the heating apparatus and includes pointer means adaptable to be positioned immediately above the region of the object to be heated. The support assembly is Further means may be provided for locking the supporting surface in position to prevent its jarring when moved into the working position.,Also, novel reflector means may be provided for projecting the object being heated upon a screen for viewing purposes to accurately control the level of heating required whereby the radiation employed for heating is utilized as the illuminating source for the projection apparatus.
17 Claims, 13 Drawing Figures PATENTEDMAY 91912 2,661,369
SHEET 3 BF 3 EEEE- BACKGROUND There exists a wide variety of applications wherein it is extremely important to provide precision heating of materials. For example, there are various operations employed in the construction of dental prosthetics which require such precision heating. Such operations include high temperature brazing, soldering, coating of dental implants with ceramic, and melting of metals for casting of teeth. The reference to precision implies control of both the size of the area heated and the temperature to which the workpiece is exposed.
Historically, several methods have been employed by dental technicians and other like operators to perform these tasks. The most common technique is one in which a hand-held torch that is completely controlled by the operator is employed for such precision heating. Other methods include induction heating, resistance heating, and furnace and electrical arc heating. No one method has been found effective in performing all of the operations previously mentioned. Therefore, the practice in the dental industry is to rely upon central laboratories to perform most of the services required. Such laboratories, which usually serve a large number of clients, are in a position to warrant this range of equipment since the demand for use of each system is spread over a large number of customers.
This practice is uneconomical for the dental practitioner, not so much in a direct cost sense, but more as a result of the inconvenience of having to deal with a vendor (i.e., a dental laboratory) engaged in such a craft oriented function. The dentist loses control over the quality of the implant. Also the time involved in preparing and sending materials and specifications between the parties is excessively long if the interest of the patient is to be best served.
Also, it is quite often necessary to repair, or change implants on very short notice. If the part in question must be returned to the laboratory for such services, the patient is further inconvenienced by still another return visit to the dentist. The operation could be performed in the office, in
many cases, if a general purpose, broadly applicable heating device were available.
THE PROBLEM lt is therefore desirable to provide a system for performing various heating operations necessary in the construction of dental prosthetics. Such a system or systems ideally must meet the following criteria;
1. The system must be capable of performing precision heating operations as will be more fully described in this application.
2. The system must minimize dependence upon operator skill for successful operation.
. The system must be capable of quick conversion from one type of operation to another.
4. The system must be convenient to operate and require a minimum of understanding. I
5. The system must perform the operations to be described in detail hereinbelow in rapid sequence. That is, the operation may be performed in a series of short steps, and, in an uninterrupted manner.
. The system must preferably be within a cost range that will not require intense and repeated use to amortize or justify the need for such a piece of equipment in the average dental office.
OPERATIONS PERFORMED Several operations employing precision heating are widely used in the construction of prosthetics. The most common are:
high temperature soldering of metal tooth crowns; glazing of ceramic coatings on crowns; and melting of metals for irivestment casting of crowns.
HIGH TEMPERATURE BRAZING OR SOLDERING J tually occupy when implanted in the patients mouth. This is done by making a wax impression of the teeth to be capped, after they have been prepared for capping. The impression is used to make a ceramic base, that is, a replica of the teetii; from a castable material.
This replica, which is identical to a portion of the patients mouth, holds the crowns in the exact relative spacing. Quite often, dovetails are made in adjoining crowns to aid in location. In its simplest embodiment, a small gap is left between the crowns in order to accept a filler alloy that is compatible with the metals in which the crowns to be joined are made. A sliver of the filler alloy is placed between the crowns and melted. The filler alloy flows between the crowns by capillary action to form a sound and firm connection.
The materials normally employed in such operations are usually noble metals and/or their alloys. Occasionally, a fluxing agent such as phosphorousmay be added to the alloy to aid in wetting the alloy to the metals of the crowns being joined.
Several important factors must be controlled in the soldering operations to make it both feasible and acceptable. The
first of these is the preservation of the shape of the crowns and replica must be remade from the start. Therefore, the
procedure is not only expensive but is time consuming.
Damage to the crowns while soldering may be the result of any one of a variety of mishaps, the most obvious of which is overheating.
The cast tooth is an alloy of noble metals and small amounts of base metals. If the crown is even moderately overheated, the base metals will burn and change the surface condition of the casting. In some alloys this will be found to occur even though melting does not occur.
Obviously, the next degree of damage, the change in the surface, is gross deformation due to melting. Once melting occurs the casting is, for all practical purposes, destroyed and must be remade.
A more subtle problem which occurs in joining crowns is that of maintaining the correct spatial relationship between the crowns so that they will fit the tooth stubs remaining in the patients mouth. Displacements of as small an amount as 0.005 inch can cause severe pain to the patient after the implant is in place.
The last significant hazard is that which may occur to the ceramic replica used to hold the crowns while soldering. Whereas the replica is not normally reused, it is desirable to keep the replica intact in the event of an accident in later steps of the implant construction process. Thus, saving the replica for reuse clearly avoids the necessity for making a new one, if required.
u CERAMIC COATING OF CROWNS Once a crown or group of crowns is constructed, the appearance of the crown in the patients mouth is important if it is visible. For this reason, a coating (overlay) is often applied to the crown. This coating performs a cosmetic function as well as being a surface preparation to make the tooth look and feel more natural. Great pains are taken to color and stain the coating so as to appear as natural as its real neighbors in the final grouping within the mouth.
Two general types of coatings are used for this purpose plastic and ceramic. Both coatings are applied as slurries to the prepared crown and then fused in place by heating. The fused micro-surface of the coating is smooth and enamel-like. The macro texture and color is dependent upon the skill of the technician in applying the slurries to the crowns. The ideal result is a tooth surface that cannot be distinguished from the real thing.
Ceramic coatings will be described in greater detail hereinbelow. As compared to plastics, such ceramic coatings are much more difficult to apply properly but are also found to be more durable and attractive.
Two techniques for the application of ceramic coatings are presently employed vacuum firing and air firing. It is generally agreed that vacuum firing produces the most dense and tenacious coating. The air firing technique is more convenient, and less elaborate equipment is required.
INVESTMENT CASTING The last significant area of application which is of interest consists of the technique for melting small quantities of alloy for investment casting of crowns and like structures.
Investment casting is an ancient art requiring several very critical steps. Since a complete description of the investment casting process is considered to be beyond the scope of the present invention, only those aspects which have immediate bearing will be discussed hereinbelow.
In performing the technique, a prepared mold which is usually a shell of a ceramic-like material, is produced. The inside surface of the mold is the negative" of the part to be cast. The molten metal is poured into the shell and allowed to cool. The shell is then broken away to recover the casting.
Investment casting is a one-time process since the mold is expended and useless after performing its function. Therefore, high reliability and high yield are imperative if the best economy and service are to be achieved.
Several factors determine the quality of the casting, temperature level is very important in that it determines the fluidity and integrity of the alloy. It is typically desired to hold the melt temperature within a range of: 2 percent of optimum temperature.
Another factor to be considered is the method used to force the metal into the mold. Three common methods which are presently in use are gravity, vacuum and centrifugal force. In certain cases, one or more of these methods are often combined to achieve a desired effect.
SOLUTION TO THE PROBLEM I have invented a facility for performing all of the above desired operations, which facility has the versatility and simplicity to fulfill all of the aforementioned criteria. The facility utilizes focused radiant energy as a heating source. The enormous versatility and advantages of focused radiation will become obvious upon consideration of the detailed description of the invention which is set forth hereinbelow.
The facility I have invented is adaptable to high temperature soldering, overlay firing, and investment casting of prosthetics, as well as other similarly related applications which require precise heating of a well defined area or region and precise control of the temperature level and duration of exposure to heating. All of the operations described hereinabove may be performed in air, a controlled atmosphere, or in a vacuum.
The invention is comprised of a high intensity source of radiant energy positioned at the primary focal point of a reflector. All energy from the radiant source that strikes the reflector is directed to a point in space hereinafter referred to as the secondary focus. Any absorbing object placed at the secondary focus will become hot by radiant heating. The reflector and radiant energy source are mounted upon an adjustable supporting structure which is adapted to permit the source and reflector to be moved either upwardly or downwardly substantially along an imaginary vertical line. This structure is positioned above a supporting surface assembly for positioning and supporting an object to be heated. The object supporting assembly is movable along guiding means between first and second stops and is further capable of being moved in mutually perpendicular directions in an horizontal plane. An indicator member having a suitable pointer at is free end is mechanically connected to the structure which includes the radiant energy source and reflector.
In operation, the object supporting means is moved away from the reflector and radiant energy source until it reaches the first stop member. The object to be heated is then placed upon the supporting surface assembly and the reflector means is adjusted until the pointer free end is positioned immediately above the area to be heated. Further adjustment may be made by moving the supporting surface means in a horizontal plane until the area to be heated is immediately beneath the pointer member.
After the aforementioned adjustment procedure, the supporting surface means is moved toward the reflector and radiant energy source and against the second stop member whereby the physical relationship between the pointer, the second stop means and the radiant energy source and reflector is such that the object to be heated is precisely positioned within the image focal point of the reflector. Energizing the radiant energy means over a prescribed time period provides the necessary heating which is constrained to only that area of interest.
In applications where it is desired to provide a "line" of radiant energy, a line heater in the form of an elongated reflector may be employed. In such applications, the pointer may take the form of an elongated pointer bar representing the imaginary line focal zone or, alternatively, may take the form of a pair of spaced pointers whose tips represent the ends of the imaginary line focal zone.
Vacuum means may be combined with the supporting surface assembly for firmly locking the supporting surface means into position immediately after adjustment thereof. The vacuum means may also be employed in conjunction with an enclosing chamber member for those applications wherein it is desired to perform the heating operation in a vacuum or controlled atmosphere.
A viewing apparatus may also be provided for facilitating observation of the immediate area being heated wherein said viewing apparatus utilizes the radiant energy for heating as the illumination source for projecting the area of interest upon a viewing screen. i
A crucible, having two crucible halves each pivoted upon a pair of knife-edge supports, is provided with a fusible element for automatically separating the halves of the crucible when the charge of material within the crucible reaches the desired temperature level. Radiant heating positioned above the crucible and directed downwardly toward the crucible assures good uniform heating of the charge contained in the crucible before the fusible material is melted to permit the molten charge to be dispensed into a mold or other suitable container.
It is, therefor, one object of the present invention to provide a novel radiant energy heating means including means for rapidly and accurately locating the object to be heated precisely within the secondary focus of the heating apparatus.
Another object ofthe present invention is to provide a novel method and apparatus for precisely heating an object wherein the region to be heated may be simply and accurately controlled by providing means for rapidly and accurately positioning that portion of the object to be heated within the image focus of the radiant energy source.
\Still another object of the present invention is to provide a novel radiantly heated crucible assembly having a fusible element for automatically dispensing a charge of material when the material is elevated to the desired temperature level.
The present invention relates to novel radiant energy heating apparatus which includes projection means for projecting an image of the area of interest being heated in which the radiant energy source serves the dual functions of providing the necessary radiant heating and providing sufficient illumination for the projection system.
These as well as other objects of the present invention will become apparent when reading the accompanying description and drawings in which:
FIG. 1 is a basic schematic view of a radiant heating system.
FIG. 2-is a perspective view showing the heating apparatus designed in accordance with the principles of the present invention.
FIG. 2a shows an elevational view of sembly ofFIG. 2.
FIGS. 2b and 2c are perspective views showing alternative embodiments for the mechanical pointer of FIGS. 2 and 2a which may be employed in conjunction with line focal images.
F IG. 3 shows and elevational view of a portion of the apparatus of FIG. 2 modified for heating objects in a vacuum.
FIG. 3a is a top view showing the gasket assembly which may be employed in the embodiment of FIG. 2 for locking the work plate relative to the subplate.
FIG. 4 is an elevational view of a FIG. 2 which is adapted to include paratus.
FIG. 5 is an elevational view showing a portion of the apparatus of FIG. 2 and adapted to perform the operations associated with investment casting.
FIGS. 6a and 6b are top and elevational views respectively of an assembly which may be employed to permit the work late to move in mutually perpendicular directions relative to the sub-plate, which components are employed in the apparatus of FIG. 2.
FIG. 7 shows a portion of the investment casting apparatus of FIG. 5 in greater detail.
FIG. 7a shows an alternative crucible embodiment which may be employed in place of the crucible embodiments of FIGS. 5 and 7.
A general description of focused radiant heating systems is portion of the apparatus of projection and viewing apset forth in US. Pat. No. 3,469,061 and copending applica tions Ser. Nos. 710,546, filed Mar. 5, 1968 now US. Pat. No. 3,522,407 and 872,232, filed Oct. 29, 1969 now U.S. Pat. No. 3,609,283.
Very briefly, the present invention, FIG. 1 shows such a focused radiation system as being comprised of a high intensity source of radiant energy 10 which is placed at the primary focal point of a reflector 12 whose concave surface 11 is highly reflective to radiant energy emitted by the source 10. All energy from source 10 which strikes the reflector, i.e., rays 14a and 14b, for example, is directed to a point 13 in space which will hereinafter be referred to as the secondary focus. Rays 15a and 15b, respectively, represent the rays 14a and 14b after they have been reflected and directed toward the secondary focus. Any absorbing object placed at the secondary focus will become heated by the radiant energy striking the object. A supporting surface 16 may be provided for positioning and supporting the object to be heated at the proper location relative to the focused radiant energy apparatus.
The facility of the present invention is shown in greater detail in FIG. 2 and the initial description set forth hereinbelow shall be specifically related to the locating and focusing means developed to provide simple and accurate placement of the radiant heating system.
In working with focused radiation on irregular shapes, the major problem is that of positioning the object so that the portion of the object to be heated is located within the focal zone a portion of the asand for purposes of sufficiently understanding downwardly in the Z axis. Radiant source irregular and non-repetitive shapes at the secondary focus of with relatively good accuracy. The problem arises due to the fact that the radiation, or light, is invisible until it strikes the work piece. Also, the light is extremely intense thereby making it uncomfortable to observe without very dark glasses.
to define the zone. The types of structures being heated in dental work are not typically large enough, flat enough or suf ficiently uniform to provide an effective focusing surface, thus rendering this technique unreliable and impractical.
The latter technique, that of mechanical pointers, is inconvenient arid cumbersome to use. In focused radiant energy systems, the most effective reflector is one that has the shortest focal length and largest possible diameter. Of course there are practical limits to each of these parameters, but each tends to restrict observation and manipulation in the focal zone. The introduction of a mechanical pointer into the heating region further restricts the zone and makes the operation much more tedious and difficult.
The apparatus [have invented utilizes a mechanical pointer which is positioned well outside of the heating system, thereby allowing complete freedom of manipulation and observation in the placement of the work piece.
The apparatus is shown in FIG. 2 and includes the radiation source 10 and reflector 12 which may, for example, be an ellipsoid of revolution. These components are fixedly mounted to a rack member 17 which is slidably mounted relative to a stationary post 18 having its lower end secured to a surface 19. Post 18 is adapted to provide for slidable movement between stationary post 18 and rack member 17. A gear member 21 is pivotally mounted to stationary post 18 by any suitable means and has an extending shaft 22 provided with a manually operable control knob 23 for rotating gear 21 which meshes with the rack member 17 to move rack member 17 and hence radiation source 10 and reflector 12 either upwardly or 10 and reflector 12, however, are fixed in the X and Y directions so as to be prohibited from movement in the X-Y planes.
A pointer assembly 24 has a first end thereof secured to the reflector assembly 12 and is provided with a pointer 25 at its free end for defining an imaginary focal point 13' which lies in a horizontal plane parallel to the X, Y plane that also contains the true secondary focus 13. The imaginary focal point 13' is displaced from the true secondary focus by a distance D measured in a horizontal plane and which distance lies along a line parallel to the X axis. The pointer may be hinged, i.e., pivotted, to the reflector means by means of a suitable bracket 26 secured to the reflector l2 and adapted to receive a pin 27 for pivotally mounting the pointer to the bracket. Pointer arm 25 is provided with a suitable opening (not shown) to receive pin 27. An adjustable threaded screw 28 may be provided to engage a second vertically aligned tapped opening 29 in arm 24 to permit adjustment of the pointer 25 to lie in the same horizontal plane as the actual secondary focus 13. The pointer may alternatively be either hinged or arranged to be completely removable from reflector 12 for convenience.
A subplate 30 is mounted to be movable in the X direction by a pair of guide rails 31 rigidly secured to surface 19 and free to move along the X axis through the distance D which corresponds to the displacement between the true secondary focus 13 and the imaginary secondary focus 13. This movement is limited by stops 32 and 33 which are positioned in the path of movement of subplate 7 and which may be made adjustable, if desired, to provide for readjustment and realignment of the apparatus for purposes to be more fully described.
e The plate 34 which constitutes the work plate upon which a work piece is supported, is movably mounted upon subplate 30 so as to be enabled to move in the XY plane. Subplate 30, however, is free to move only linearly in either a forward or rearward direction along the line parallel to the X axis due to the constraints placed upon the subplate movement by the supporting rails 31. The extent of said movement is limited to the distance D.
In operation, the work plate 34 containing a work piece 35, is placed upon the subplate 30. Subplate 30 is pushed against stop member 32. Preferably, the heat source and reflector assembly is moved vertically upward in a direction parallel to the Z axis so as to provide sufiicient clearance for placement of the work piece and work plate 35 and 34, respectively, beneath the pointer assembly 24. Manually operable handle 23 is then manipulated so as to bring the pointer to the same level (or height) as the portion of the work piece 35 which is to be irradiated. Work plate 34 is then adjustably maneuvered in the X Y plane so as to place the area of the work piece to be heated beneath the tip 25 of the pointer assembly 24. In this position, the portion of the work piece to be irradiated is located at the imaginary focal point 13'. Obviously, the pointer and reflector assembly may be moved downwardly either before or after manipulation of work plate 34. The adjusting mechanism for assemblies 10, 12 and 24 is preferably operated so as to bring the tip 25 of the pointer to a position about one-sixteenth inch above the area to be heated upon the work piece.
Since points 13 and 13 lie in the same plane, and this plane is controlled by the Z direction mechanism (i.e., the mechanism for locating the assemblies l0, l2 and 24 in the vertical direction), the true focus is always at the same relative level as the imaginary focus, and is represented by the tip 25 of pointer assembly 24.
As was mentioned hereinabove, adjustment of the work plate within the X-Y plane, brings the area to be heated directly beneath the pointer 25. This is done without moving the subplate which has previously been moved to abut stop member 32. The downward adjustment of the pointer to contact the center of the zone to be heated exactly locates the imaginary focal point upon the surface of the work piece to be irradiated.
The pointer may then be either removed or pivoted upward and away from the work piece. The work piece is now accurately positioned in the imaginary focus and may further be conveniently handled or operated upon for further preparation, such as alloy placement, fluxing, or application of overlay material. The full significance of the apparatus and procedure will become apparent upon still further discussion of the operations and other ancillary features which are capable of being achieved by the apparatus.
The final step consists of moving subplate 30 away from stop member 32 and into engagement with stop member 33. This places the work plate 34 and work piece 35 within the heating zone, with the precise portion of the work piece to be irradiated being located within the true focal zone 13. The source may then be energized to perform the heating operation. The entire sequence, including all placements and adjustments, can be performed in a period well under 1 minute. The simplicity of the apparatus resides in the fact that the work piece and work plate, once positioned immediately beneath the tip of pointer assembly 24 is very accurately moved a distance D by movement of subplate between stops 32 and 33. Deviation in the direction lateral to this movement (i.e., in the direction substantially parallel to the Y axis) is totally eliminated and constrained by the guide rails 31. Accurate pre-alignment of pointer 24 relative to the true focal zone exactly locates the pointer tip 25 lying in the same horizontal plane as the true focal zone 13 and to be a distance of exactly D removed from the true focal zone. Accurate positioning of stops 32 and 33 assure movement of subplate 30 and hence work plate 34 and work piece 35 the distance D.
As an obvious alternative, the work plate 34 may be omitted entirely and the top surface of the subplate may be employed for supporting the work piece 35.
In applications in which the region to be radiated is a line" image, the radiant energy source 10, shown in FIGS. land 2, may be comprised of an elongated energy source positioned at the first focal point as shown in FIG. 1, which is to be used in conjunction with an elongated reflector assembly such as, for example, the line energy source and reflector assembly of FIGS. 2-4 shown in patent application Ser. No. 774,898, filed Nov. 12, 1968 and assigned to the assignee of the present invention. Similarly, the line heater may be of the type sold by the Argus Engineering Company, identified as Model 91 in a brochure entitled Conray Basic Models" printed and distributed by the Argus Engineering Company. Sincethe radiant energy is reflected to form a line image, the mechanical pointer is likewise modified so as to take the form as shown in FIGS. 2b and 2c, for example. FIG. 2 b shows a pair of mechanical pointers 24a and 24b each being secured to the line reflector l2 and having their pointer tips 250 and 2512, respectively, lying along an imaginary straight line 13" which represents the imaginary focal line with the tips 25a and 25b defining the end points of the line. As another alternative, the mechanical pointer may take the form of a pointer arm 24c having an elongated bar 24d secured at its free end with the bar being tapered to form a knife-like head 24e along the bottom of bar 24d to represent the imaginary focal line which is substantially parallel to the true image focal line formed by the reflected radiant energy from reflector 12'.
As another alternative, the adjustable assembly of FIGS. 61: and 6b may be employed. As shown in these two figures which are top and end views, respectively, of the subplate 30 and the work plate 34 including the-adjustable assembly, the under surface 34a of work plate 34 is provided with first and second pairs of rollers 81-82 and 85-86, which rollers are secured to the under surface 34a by pins such as, for example, the pins 83 and 87 shown in FIG. 6b. The pair of rollers 80 and 81 which are rotatably mounted upon pins 82 and 83, shown best in FIG. 6a, are arranged to be rollably received within a channel member 70. The roller members 84 and 85 are arranged to be rollably received within a channel member 71. As shown best in FIG. 6a, channels 70 and 71 are arranged in spaced parallel fashion. The underside of channel 70 has secured thereto a pair of pins 74 and 75 which pivotally mount a pair of rollers 72 and 73, respectively. Channel member 71 has secured thereto a pair of pins 78 and 79 which pivotally mount roller members 76 and 77, respectively. The roller members 72 and 76 pivotally mounted to channels 70 and 71, respectively, are reliably received within an elongated cavity 30b provided in the top surface of subplate 30. Rollers 73 and 77, which are pivotally mounted to channels 70 and 71, respectively, are rollably received within a second elongated groove 30a provided in the upper surface of subplate 30. The elongated grooves 30a and 3022 are arranged in substantially spaced parallel fashion.
In operation,. the work plate 34 may be rolled in the direction shown by arrows 88, causing the roller pairs 8081 and 84-85 to roll along the channels 70 and 71, respectively. Work plate 34 may be moved in the direction shown by double-headed arrow 89 whereby the rollers 72-76 and 73-77 will move within the depressions 30b and 30a, respectively,
thereby enabling work plate 34 to move in mutually perpendicular directions relative to subplate 30. The rollers may be adapted to fit snugly within their cooperating members to prevent accidental movement of the work plate after the work piece is aligned relative to the pointer.
The work plate may be lifted off the subplate at any time in cases where it is desired to mount a fragile work piece upon the work plate at a remote location or to perform subsequent operations upon a work piece at a remote location.
In applications where the alignment of the work piece need not be extremely precise, the stop 32 may be omitted (or it need not be positioned exactly the distance D plus the length of the subplate from stop 33) and the work plate or subplate (if the work plate is omitted) may be provided with a guideline 34g. By aligning the region of the work piece to be irradiated directly above the guideline 343, the region to be heated will thus be positioned in the true focal image of the reflector with a reasonable degree of accuracy when the plate 34 is moved against the stop 33.
FURTHER REF INEMENT AND FEATURES Several of the operations mentioned for dental work are best performed in a vacuum environment. The adaption of a vacuum feature to the above described system has been found to be simple and convenient. Furthermore, the vacuum system has been found to provide an advantageous locking feature which may be employed between the subplate and work plate and which is very valuable even in instances when a vacuum environment is not being employed.
FIG. 3 shows a portion of the system of FIG. 2 wherein like elements are designated by like numerals. As shown in FIG. 3, work piece 35 is positioned upon work plate 34 and is covered with a bell jar-type 36 of enclosure. The bell jar is preferably formed of a radiation transmissive material such as quartz, Pyrex, or Vycor. The work plate 34 is provided with an annular-shaped recess 34a for receiving a sealing gasket 37 which is obviously resilient so as to permit the marginal edge of bell jar 36 to be urged into firm, airtight, sealing engagement with the gasket as a result of evacuation of the hollow interior region defined by work plate 34 and bell jar 36. The sealing gasket is preferably formed of a non-radiation absorbing elastomer such as clear silicone rubber or the equivalent.
A gasket 38 is also provided between work plate 34 and subplate 20, which gasket 38 is also shown in FIG. 3a wherein the configuration of the gasket is designated by the phantom lines of FIG. 3a which represent the exterior and interior peripheries thereof. Gasket 38 permits the freedom of movement of work plate 34 relative to subplate 30 in order to permit the work piece 35 to be placed in the appropriate heating zone by initially adjusting the plate to place the work piece 35 beneath the pointer in the same manner as was described hereinabove.
When the interior region mentioned hereinabove is evacuated, the sub-atmospheric pressure between plates and 34 causes the plates to be rigidly held in position relative to one another. It has been found that the atmospheric holding force is more than sufficient to join bell jar 36 to work plate 34 and to join plates 34 and 30 into a very rigid assembly which is not easily displaced.
Appreciation of the function of gasket 38 can best be understood from a consideration of FIG. 3a in which work plate 34 is shown as being displaced toward the right relative to subplate 30 by a distance a and is further shown as being displaced by a distance d in the positive direction of the Y axis.
In order to evacuate the hollow interior region between bell jar 36 and work plate 34, subplate 30 is provided with an elon gated opening 39 whose right-hand end is coupled through a suitable coupling assembly 40 to conduit 41 and whose lefthand end opens in the upper surface of subplate 30. Work plate 34 is provided with a vertically aligned bore 34b which communicates with the upper and lower surfaces of the work plate. Conduit 41 is provided with a valve 42 for selectively coupling or decoupling a vacuum pump with conduit 41.
In the case where the heating operation takes place in the vacuum, the vacuum pump source (not shown for purposes of simplicity) connected to conduit 41 causes the interior region between bell jar 36 and work plate 34 as well as the interior region defined by the lower surface of work plate 34, the upper surface of subplate 30 and gasket 38 to be evacuated when valve member 42 is opened. Once the desired vacuum condition is achieved (which may be determined by providing a gauge 43 in the vacuum line), valve 42 may then be closed and the vacuum source may be deenergized. Obviously, the ap paratus may further be employed in vacuum systems where the vacuum source is continuously operated in order to maintain a desired evacuation.
In applications wherein it is desired to merely lock work plate 34 relative to subplate 30 and wherein no vacuum environment is required during the heating operation, a suitable plug 44'may be inserted (for example, threadedly engaged) into bore 34b so as to seal this opening. The vacuum source may then be coupled to conduit 41 by opening valve 42 so as to evacuate the hollow interior region defined by the lower surface of work plate 34 and the upper surface of subplate 30 and gasket 38. Only a small negative pressure level is required to maintain these two plates in their relative positions. Obviously, the evacuation operation is performed after work plate 34 and hence work piece 35 are positioned relative to the pointer assembly 24.
It has been found to be desirable in some casesto introduce a back-filling gas, such as hydrogen, while the vacuum chamber is being evacuated. This may be performed in the present invention by providing a vent hole 45 in work plate 34 which, at its left-hand end, is coupled through conduit 46 and HEATING OBSERVATION FEATURE Visual monitoring of the heating operation is vital especially in the case of dental preparations since each part has rather unique heating properties and characteristics. It is impossible to effectively assign time-power parameters to mechanically control the heating cycle. It isoften necessary, therefore, for the technician (or other operator) to manually control the power level of the source as well as controlling the ON-OFF function.
Radiant heating, as described herein, is accompanied by a very significant amount of visible radiation. This visible light is so intense that it is impossible to visually monitor the operation being performed without the use of some aid or protective means. I have employed two observation aids on the described apparatus: filters and optics.
The filter may be simply a dark plastic, or glass, lens that absorbs most of the radiation. The filter may be hinged to the front of the system for convenience. For example, as shown in FIG. 2, a filter comprised of flat sheet 50 is coupled to one arm 51a of an elongated hinge 51 whose other arm 51b is secured to surface 19 by fastening means 52. By pivoting sheet 50 about its hinge 51, the filter may be moved from the flat position (shown in solid line) to the viewing position (shown by dotted lines 50). Obviously, any other suitable arrangement may be employed for both placement and configuration ofthe filter assembly.
The second system which may be employed consists of a projection system and ground glass screen provided to produce an observable image. This method has several significant advantages in that it is a fixed system requiring no operator attention and can be designed to magnify the image, thereby producing a larger and more detailed picture of the operation in progress. The uniqueness 'of the projection system lies in the fact that the radiation employed for heating also provides the intense light necessary for magnification and projection. FIG. 4 shows the projection system in which a por tion of the system of FIG. 2 is reproduced and further wherein like elements as between FIGS. 4 and 2 are designated by like numerals. As shown therein, radiation source 10 emits rays such as 14a and 1417 which impinge upon the reflective surface and are both reflected and focused as rays 15a and 15b, for example. Reflector 12 is provided with an opening 53 to provide for visual access of the projection system. A lens system 54 picks up light reflected from the work surface and causes it to be focused upon a ground glass 56 after having impinged upon and been reflected by an inverting mirror 55. The projection system components 54 through 56 may be secured by any suitable bracketing or support means to the reflector assembly so as to be fixed and moved with the reflector in the Z rdirection under control of manually operable handle 23 shown in FIG. 2. As such, the projection system is always capable of transmitting an image originating at the true focus of the heating system 13 without any need for further adjustment.
DETAILED DISCUSSION OF OPERATIONS PERFORMED Focused radiant heating offers unique advantages in the types of operations (especially in the dental preparation field) which the facility is capable of performing. Each will be discussed hereinbelow as regards their novel features and to further explain the significance of the facility described hereinabove.
HIGH-TEMPERATURE SOLDERING As was stated previously, the joining of crowns to make a group implant is performed by high-temperature soldering. A filler alloy compatible with the cast metal is melted, and, with the proper fluxing agent, is allowed to wet the adjoining surfaces of the casting. This operation may be performed in air, in a reducing atmosphere, a neutral atmosphere, or in a vacuum.
One of the most vexing problems in soldering by conventional means is the distortion which is found to occur if the joint structure is not uniformly heated. By this I mean that the periphery of the joint area must experience simultaneous heating so that the thermal distortion is normal to the surface being joined. In this manner, the crowns will return to their correct relative position upon cooling.
Focused radiant heating as described herein, has been found to produce the least possible joint distortion when compared to conventional heating methods. The reason for this advantage is the fact that the joint is simultaneously heated from multiple directions as a result of both direct and reflected rays originating from the irradiating means. The cone of incident energy impinging upon the work piece is typically of an ineluded angle which is greater than 120. By placing the work piece inside the apex of the cone, all exposed surfaces of the joints are caused to be uniformly heated.
Flame techniques, in which a single torch is employed, are capable of heating onlyone side of the joint at once. Fanning, or moving, the torch will improve this condition, but the control is still dependent upon the operator's skill. Similarly, multiple torches may be used, but the operation becomes cumbersome and difficult to set up.
A further advantage which accrues through the use of focused radiant heating lies in the fact that the work piece is completely free from heater-borne contamination or disturbance. Thus, the joint is cleaner and more accurately controlled than that produced by any other method.
Most importantly, the method described herein is the only convenient method which may be employed for soldering in a vacuum. Furnace soldering is a general heating method that indiscriminantly heats the entire structure. Resistance, induction and conduction methods all require elaborate set-ups with hardware provided in close proximity to the joint and are, therefore, highly impractical arrangements as compared with the apparatus of the present invention.
OVERLAY FIRING Overlays are applied to crowns for appearance and comfort to the wearer. They must be capable of withstanding all hazards that natural enamel is exposed to and must look and feel like the real tooth.
Ceramic overlays are the strongest and most durable types. They are also the most expensive and the most difficult to apply properly. The normal sequence in making an overlay starts with the technician brushing a slurry onto the prepared area of the crown. This slurry is typically comprised of ceramic particles suspended in an appropriate binder-vehicle fluid. The application is performed in stages in order to build up to the proper thickness of coating and further in order to achieve the correct coloring and texture. Between each application, the crown is fired to fuse the ceramic. All presently available methods employed for fusing have been found to take 15 minutes, or longer. This, obviously, extends the operation (from start to finish) to a rather prolonged time period, especially when a number of overlay applications are required- It is necessary to fuse between application operations because conventional heating is performed by conduction. The surface of the overlay cannot be allowed to fuse together and form a skin before the underlaying slurry is fused. Skinning will cause entrapment of gases and delamination of the overlay. The limit of the skin formation, of course, is the maximum thickness of material that may be applied at one time. I
Conductive heating is the primary mode of energy transfer even though the ceramic is often fired in a vacuum using infrared radiation. The conventional firing furnace utilizes long wavelength infrared radiation, the bulk of which is readily absorbed by ceramic or glassy materials. The absorption takes place in the first few thousandths of an inch of the material. Any deeper heating penetration must be conducted through the remaining thickness and into the crown metal.
The reason for employing a skin formation technique is that conductive heating requires a thermal gradient for energy transfer. Since the energy must pass through the overlay material, the thermal gradient has a negative slope (i.e., reduces in thermal level from the surface of the overlay material to the inner depth thereof), the surface of the overlay material is, therefore, always at a higher temperature level than the underlying material until equilibrium is reached.
, Focused radiant heating which employs a high-intensity source of radiating energy, the bulk of which is comprised of wavelengths shorter than 2.80 microns, is capable of penetrating the commonly used ceramic slurries. This permits a high percentage of the energy to be absorbed at the metal-ceramic interface, thus causing the underlayments to be heated by conduction from the inside outwardly. Actually, the combination of heating by radiation transmission losses and inside-out conductive transfer causes the overlay to melt simultaneously throughout its entire thickness.
An immediate consequence of this capability of being able to heat deeply within an overlay is that the full required thickness of overlay can be applied in a single operation. An experienced technician can even apply staining and coloring ingredients before the first firing. The entire operation can thus be reduced to a single firing requiring an elapsed time of no more than 1 to 2 minutes duration.
INVESTMENT CASTING In the investment casting of crowns, less than 1 ounce of metal is typically melted at one time. Employing this technique, it is within the capability of small, focused radiant heating devices having energy sources of 1,000 to 2,000 watt capacity. In addition, it is most desirable to perform the moldfilling operation in a vacuum. These criteria plus the inherently clean and simple operation of focused heating apparatus makes investment casting an ideal operation to be performed through the use of the apparatus described herein.
Referring to FIG. 5, in which like elements are designated with like numerals'in regard to FIGS. 2 and 3, the prepared mold 66 is placed upon work plate 34. A crucible holder 67 supports a crucible 68 which is positioned immediately above mold 66 so that the crucible lies over the filling hole 69 of mold 66. The crucible 68 is formed of two sections 68a and 68b which are pivoted about a pivot pin 70 further secured to crucible holder 68 so as to permit the crucible sections 68a and 68b to rotate in opposing directions and thereby open at the bottom. When the charge provided in crucible 68 is heated to the correct temperature level, the crucible is opened remotely by mechanical means (not shown) mechanically linking the crucible halves to an externally mounted control handle. Obviously, this mechanical configuration may take any one of a number of preferred forms, depending only upon the needs of the user, and a detailed description has been omitted herein for purposes of simplicity.
. into the opening in the mold member 66. Obviously, the press The crucible is thus opened remotely and the charge is thus caused to fall by gravity into the opening 69 of mold 66. The remote opening function maybe performed, for example, by magnetic actuation, or by mechanical means extending through the work plate 34. Alternatively, the crucible may be designed so as to tip about its pivot pin to provide a pouring action or may further be designed to have a removable plug at its bottom end, whereby the end result is the same regardless of the specific technique employed.
Crucible 68 is preferably formed of a ceramic, quartz, carbon, or vitreous carbon material. The lattermost material is preferred due to its durability and high-temperature strength. In addition, its black color allows it to be readily heated by focused radiation represented by rays 15a and 15b, for example. It is thus clear from this description that investment casting operations can utilize the apparatus of the present invention with the same high degree of success as was described with regard to some of the operations set forth hereinabove.
FIG. 7 shows a portion of the apparatusof FIG. wherein an assembly is provided for pivoting the crucible halves 68a and 68b. As shown in FIG. 7, a hollow conduit 91 is mounted along the exterior of crucible support member 67 such as, for example, by brackets 67a, 67b and 67c. The lower end of conduit 91 is coupled to an opening 92 in work plate 34 by a coupler assembly 93. The opposite end of opening 92 is coupled through a conduit 94 and valve 95 to a pressure source 96 which may be an air or hydraulic means. The upper end of conduit 91 is coupled to a T-shaped member 97 having a pair of pistons 98 and 99 mounted therein and protruding in opposing directions. The crucible halves 68a and 68b are provided with projections 100 and 101 which lie immediately adjacent the free ends of piston members 98 and 99, respectively.
In operation, when the material contained within the crucible is elevated to the desired temperature, valve means 95 is opened to force either air or a liquid under pressure through conduit 94, opening 92 and conduit 91 so as to cause the pistons 98 and 99 to both move outwardly against the projection 100 and 101, respectively, to cause the crucible halves 68a and 68b, which are pivoted at 70, to rotate in opposing directions and thereby cause the molten charge contained with the crucible to drop downwardly, as shown by arrow 102,
sure or hydraulic arrangement may be replaced by a mechanical arrangement adapted to perform substantially thesame function. I FIG. 7a shows another preferred embodiment of the crucible arrangements of FIGS. 5 and 7 in which the two crucible halves 68a and 68b are each provided with a semicircular shaped ledge 68c and 68d, respectively. Each of these ledges is supported by a pair of knife-edge pivots 110 and 111 (only one knife-edge pivot of each of the pairs being shown in FIG. 7a it being understood that the other knife-edge pivot of each pair is positioned on the opposite sides of the crucible halves). The knife-edge pivots may be supported by a supporting structure similar to the supporting structure 67, shown in FIG. 5. The pivots are arranged to support the crucible flanges 68c and 68d so as to cause the crucible halves to pivot in the directions shown by arrows 112 and 113, respectively, so long as no means is provided for holding the crucible halves together. The crucible halves are provided with hollow interiors for supporting a charge of material to be heated to the .molten stage. Each crucible half is provided with an opening 114 and 115 near their lower edges, which openings are in alignment with one another. A fusible element 116, such as, for example, a thin wire, is inserted through the aligned openings 114 and 115. The free ends 116a and 1161) are bent inwardly as shown so as to hold the crucible halves together until the fusible element melts, at which time the crucible halves are free to pivot about the knife-edged pivots 110 and ill in the directions shown by arrows ll} and H3, rcspeu in operation. the heating source comprised of a radiant energy source and reflector l2 (see FIG. 5) focuses radiant elevated in temperature as a result of the impinging radiant energy. The heating of the crucible and charge of material from the top causes the temperature gradient to extend from the top downward with the top of the crucible being at the highest temperature, thereby causing the fusible element to be the last component to be raised to the desired elevated temperature. The advantage of employing infrared energy is derived from the fact that infrared radiant energy is a known constant source of energy and provides substantially homogenous and uniform heating of the material. The fusible element may be selected by determining the temperature gradient existing between the molten charge and the region in which the fusible element is positioned (openings 116a and 116b). By knowing this temperature gradient, a fusible element can be selected which will melt at its center location only after the molten charge has been elevated to the desired temperature. Since the center portion of the fusible element will melt and cause separation of the crucible halves 68a and 68b prior to the melting of the remaining portions of the fusible element, the fusible element will be restrained from dropping into the mold or other container into which the molten charge is dispensed. The advantage of the use of a radiant energy source can be further appreciated from a consideration of the disadvantages of other heating sources. For example, a heating torch will fail to provide uniform homogeneous heating of the molten charge and will therefore fail to cause melting of the fusible element at the appropriate temperature level. The use of an induction heating apparatus is unsatisfactory for the reason that induction heating equipment tends to heat only metal components, thereby causing the fusible element to heat too rapidly before heating of the molten charge to the appropriate temperature level.
It can, therefore, be seen from the foregoing description that the present invention provides a novel apparatus and method for heating materials through the use of a radiation source wherein the heating zone of the material to be so treated may be rapidly and accurately positioned within the major zone of influence of the heating apparatus, wherein the heating zone may be easily and carefully observed to control the parameters of time and temperature and wherein the heating operation itself is performed in a more uniform manner as compared with conventional techniques. The descriptions set forth hereinabove make it quite obvious that the apparatus and method set forth herein are highly advantageous for use in the dental field.
Although this invention has been described with respect to its preferred embodiments, it should be understood that many variations and modifications will now be obvious to those skilled in the art, and it is preferred, therefore, that the scope of the invention be limited not by the specific disclosure herein, but only by the appended claims.
The embodiments of the invention in which an exclusive privilege or property is claimed are defined as follows:
1. Apparatus for rapidly and accurately heating specified regions of a work piece comprising: e
a heating assembly including a source of radiant energy, and
a reflector member having a reflective surface for focusing reflected radiation from said source at a predetermined true image focal zone;
a mechanical pointer assembly mounted upon said heating assembly;
a supporting surface;
a supporting assembly, coupled to said heating assembly positioned upon said supporting surface;
said supporting assembly including means for adjusting the relative distance between said heating assembly and said supporting surface;
it first movable plate and means positioned upon said supporting surface for constraining movement of said movable plate along an imaginary straight line which is substantially parallel to said supporting surface:
i it said mechanical point or assembly including an arm having a pointer tip at its free end; said pointer tip and said true image focal zone lying in an imaginary line parallel to said imaginary path of constrained movement of said first plate;
first and second mechanical stop means positioned in the path of movement of said first movable plate to limit the movement of said first movable plate between first and second positions, respectively;
a second movable work plate and means positioned between said first and second movable plates to enable said second movable plate to experience movement in the common plane between the plates which is substantially parallel to said supporting surface;
the amount of allowable travel between. said first and second stop members being substantially equal to the distance between the pointer tip of said mechanical pointer and said image focal zone measured in said horizontal plane.
the upper surface of said second movable plate being adapted to support a work piece whereby adjustment of said second movable plate and said mechanical pointer to position the specified region of the work piece to be heated immediately beneath the extreme tip of the mechanical pointer precisely locates the region of the work piece to be heated within an imaginary focal zone when the first movable plate is moved against said first stop member which preparatory adjustment exactly locates the region of the work piece to be heated in the true image focal zone when said first movable plate is subsequently moved against said second stop member.
2. Apparatus for rapidly and accurately heating specified regions ofa work piece comprising:
a heating assembly including a source of radiant energy, and
a reflector member having a reflective surface for focusing reflected radiation from said source at a predetermined true image focal zone;
a mechanical pointer assembly mounted upon said heating assembly;
a supporting surface;
a supporting assembly coupled to said heating assembly positioned upon said supporting surface;
said supporting assembly including means for adjusting the relative distance between said heating assembly and said supporting surface; I
said mechanical pointer assembly including an arm having a pointer tip at its free end;
a movable plate and means positioned upon said supporting surface for constraining movement of said movable plate along a first imaginary straight line which is substantially parallel to said supporting surface;
first and second alignment means positioned in the path of movement of said movable plate to limit the movement of said movable plate between first and second positions, respectively;
the pointer tip of said mechanical pointer free end being positioned to lie in a second imaginary straight line containing said true image focal zone to define an imaginary image focal cone, said fist and second imaginary straight lines being parallel;
the amount of allowable travel between said first and second stop members being substantially equal to the distance between the pointer tip of said mechanical pointer and said image focal zone measured along said second imaginary straight line;
the upper surface of said movable plate being adapted to support a work piece whereby positioning of the work piece on said movable plate and adjustment of said mechanical pointer to position the specified region of the work piece to be heated immediately beneath the extreme tip of the mechanical pointer precisely locates the region of the work piece to be heated within an imaginary focal zone when the movable plate is moved against said first stop member, which preparatory adjustment exactly locates the region of the work piece to be heatedin the true image focal zone when said movable plate is subsequently moved against said second stop member.
3. The apparatus of claim 1 further including gasket means positioned between the adjacent upper and lower surfaces of said first and second movable plates, respectively;
a vacuum source;
a conduit connected to said vacuum source;
said first movable plate having a hollow opening, said opening having a first end communicating with the upper surface of said first movable plate and within the confines of said gasket, and having a second end communicating with said conduit for evacuating the interior region defined by said gasket and said first and second movable plates to rigidly hold the first and second movable plates in their relative positions.
4. The apparatus of claim 2 wherein said constraining means comprises at least one rail mounted upon said supporting surface;
a guide channel formed in the underside of said first movable plate for slidably receiving said rail.
5. The apparatus of claim 2 wherein said constraining means comprises first and second rails mounted upon said supporting surface;
first and second guide channels formed in the under-side of said first movable plate for slidably respectively receiving said first and second rails.
6. The apparatus of claim 2 wherein said constraining means is comprised of an elongated groove provided in said supporting surface;
' said first movable plate having an elongated projection along its bottom surface being slidably mounted within said groove.
7. The apparatus of claim 2 wherein said constraining means is comprised of first and second elongated grooves provided in said supporting surface;
said first movable plate having first and second elongated projections along its bottom surface being slidably mounted within said first and second grooves, respectively.
8. The apparatus of claim 2 wherein said mechanical pointer assembly is comprised of a mounting bracket secured to said heating assembly;
an elongated arm having a first end releasably coupled to said mounting bracket; the pointer tip being mounted upon the free end of said arm.
9. The apparatus of claim 2 wherein said mechanical pointer assembly is comprised of a mounting bracket secured to said heating assembly;
an elongated arm having a first end pivotally coupled to said mounting bracket; the pointer tip being mounted upon the free end of said am.
10. The apparatus of claim 9 wherein said arm further comprises means coupled to said mounting bracket for adjusting the location of said pointer tip relative to said heating assembly.
11. The apparatus of claim 2 further comprising a vacuum source and a conduit having a first end coupled to said vacuum source; 7
said first movable plate being provided with a hollow opening having a first end communicating with the upper surface of said first movable plate and a second opening communicating with the second end of said conduit;
said first movable plate having a continuous closed loop groove provided in its upper surface; a resilient gasket positioned in said groove;
a bell jar positioned upon the upper surface of said first movable plate and having its periphery resting upon said gasket to enable the interior region defined by said bell jar and the upper surface of said first movable plate to be evacuated by said vacuum source.
12. The apparatus of claim 11 wherein said bell jar is formed of a radiant energy transmissive material.
Q13. The apparatus of claim 11 further comprising:
a reservoir containing a gas under pressure; and a second conduit having a fist end connected to said reservoir;
said first movable plate being provided with a second open ing having a first end communicating with the upper surface of said first movable plate and a second end communicating with the second end of said second conduit;
adjustable valve means being provided in said second coriduit between said reservoir and said first movable plate to adjust the amount of gas introduced into the evacuated region. 14. The apparatus of claim 2 further having projection apparatus comprising:
a focusing leans positioned a spaced distance from said work piece;
an image forming display surface;
an inverting mirror for deflecting reflected light rays passing through said focusing lens and originating from said work piece upon said display surface whereby said focusing lens focuses the reflected light originating from said work piece upon said display surface. 15. The apparatus of claim 14 wherein said projection apparatus is mounted to said heating assembly so as to have the distance apart to substantially define the end points or" said elongated line image.