News Column

Researchers Submit Patent Application, "Furnace System with Active Cooling System and Method", for Approval

July 25, 2014



By a News Reporter-Staff News Editor at Health & Medicine Week -- From Washington, D.C., NewsRx journalists report that a patent application by the inventor MELLEN, Jonathan Y. (Concord, NH), filed on December 28, 2012, was made available online on July 10, 2014 (see also The Mellen Company Inc.).

The patent's assignee is The Mellen Company Inc.

News editors obtained the following quote from the background information supplied by the inventors: "Heat-treatment and temperature gradient furnaces are used in a number of production processes, such as for annealing of metals and ceramics, for annealing and oxidation processes for semiconductors, for 'growing' of crystals, and for other heat-treatment material process applications. Temperature gradient furnaces commonly have a series of zones to control temperatures around the area of a workpiece to promote crystal growth or to promote particular mechanical or electrical properties within a material. Each material application process requires steep gradients in temperature and the holding of consistent temperatures over long periods of time with minimal variation to produce uniform properties within the material.

"As an example, in an application to grow large-area single-crystals, the crystals commonly formed from a melt of crystalline material are placed in a refractory container or ampoule and heated within a furnace at a constant temperature until molten. The molten material is then cooled slowly at one end until crystallization starting from a single nucleation from the melt sets in. Currently, the cooling at the crystallization temperature must be done slowly and progressively along the length of the material, so that the crystal lattice can form entirely on the single nucleation so as to produce a single crystal. Optimum conditions for single crystal growth call for substantially steep and well-controlled temperature gradients that move relative to the material. Furnaces that produce fairly reliable temperature gradients are known, such as the furnace described in U.S. Pat. Nos. 4,518,351 and 4,423,516 issued to Robert H. Mellen, where the furnace uses a plurality of heating elements sandwiched between respective insulating layers to form temperature zones across the material workpiece. The temperature within each zone is set and maintained or ramped up to a prescribed temperature by powering the heating elements using feedback from thermal sensors within each zone to adjust power requirements and create temperature gradients through the zones of the furnace.

"Temperature adjustments for each specific zone provide for a more accurate gradient in temperature within the area of the work. However, variations or ripple at set temperatures within the temperature gradient is one of a number of factors that affect the quality of the monocrystals or properties and uniformity of other heat-treated materials. It has been extremely difficult to produce large area, single-crystals or other heat-treated materials that have low compositional variation and homogeneous mechanical or electrical properties. A factor in producing the temperature gradient is related to loading of the heating elements, where unless a heating element is continually loaded, its response to control can be slow and erratic causing inconsistent temperature fluctuations and temperatures exceeding the prescribed temperature gradients. Another factor affecting composition and material properties is the problem of heat flowing radially from the axis of the temperature gradient within the furnace chamber. Such heat flow produces undesired temperature variations within planes perpendicular to the axis of the gradient. This can cause deleterious effects in crystal growth particularly along the interface of the crystal and ampoule where temperature variations may cause a concave shape with respect to the crystal. The concave interface shape may promote new grains to form causing growth to be inward towards the bulk of the crystal reducing compositional homogeneity. Additionally, current crystal growth process techniques and other heat-treatment material processes require lengthy periods to adjust gradients over small areas within the work region, where cooling of the heating elements may require hours. Additional time is also required to reduce the temperature of the furnace to move the workpiece to perform additional process steps or to remove the crystals or materials from the furnace.

"Therefore, proper furnace design for a single temperature zone or multi-temperature zone furnace is a compromise between insulating capability and the ability to effectively change temperatures inside the furnace. A well-insulated furnace is capable of high temperature ramp rates in the positive direction, but in cooling, the same insulation that allows the furnace to heat up quickly, makes the furnace unable to cool quickly, specifically because of the increased insulation.

"In contrast, a furnace that is designed to cool quickly will have little or no insulation, which allows the furnace to drop temperature quickly. However, in this furnace design it is difficult to ramp the temperature up quickly without significant increases in power. This additional power degrades the life of the heating elements causing the furnace to have a shorter operational life. Less insulation also dissipates significant amounts of heat into areas around the furnace requiring fans and air conditioning systems around the furnace units to maintain acceptable ambient temperatures. Alternately, a water cooling system may be used to dissipate the additional heat increasing both system and facility costs where plumbing and refrigeration to cool and pump the water through the furnace system is required.

"Therefore, significant additional costs for cooling systems and facility infrastructures must be considered in using single temperature zone, multi-temperature zone or other furnace systems of the prior art. What is not known is a less costly and more effective cooling system for a well-insulated furnace that provides suitable temperature gradients, assists in maintaining minimal variations in temperature, and cools rapidly thereby increasing throughput in the production of heat-treated materials."

As a supplement to the background information on this patent application, NewsRx correspondents also obtained the inventor's summary information for this patent application: "In accordance with the invention, an active cooling furnace may have a single temperature zone or be provided with a plurality of individually controlled heating elements, each arranged symmetrically around the axis of the furnace chamber and layered sequentially with separating thermally insulating layers. In the multiple zone or electrodynamic gradient (EDG) furnace as an embodiment of the present invention, each heating element is positioned concentrically within a respective thermally conductive annulus that is loosely thermally coupled to the heating elements which are concentrically placed inside an insulating or heat dissipating medium. The heat dissipating medium is disconnected to the element with an airflow inlet path and outlet path concentrically symmetric through the insulating medium. Active cooling devices directed towards the airflow inlet are positioned along the furnace chamber where in a first embodiment each zone of the furnace includes an active cooling device. In operation, a temperature gradient is set using a prescribed process by manual entry or by using a software program from a computer system. Temperature sensors adjacent the heating elements provide data to the computer system to adjust the programmed temperatures over time to the desired gradients by controlling energy input to the individual heating elements.

"In a first embodiment, the active cooling circuitry monitors the adjustment of input power to the heating elements from a furnace controller. Changes in input power may correspond to three states of heating, holding and cooling with the heat-treatment materials process. In a heating state where there is maximum power output to the heating elements of the furnace, the active cooling circuitry may slow or stop the cooling device to reduce heat dissipation within the furnace chamber. In a holding state, the active cooling circuitry may introduce a thermal load through the flowing of air around the furnace chamber to dissipate heat and maintain the amount of input power from the furnace controller in an accurately controllable range necessary to maintain the furnace chamber at a holding (target) temperature. In this state, in a first embodiment, the active cooling circuitry may adjust the rotation of the fans of the cooling device from moderate to ultra-low speeds to control airflow providing minimal airflow to reduce temperature variation resulting from continual adjustments in increasing and decreasing power to the heating elements thereby maintaining a smaller variation and more constant temperature. The airflow at ultra-low speeds is directed symmetrically around the furnace chamber, thereby drawing heat evenly away from the chamber and reducing hot or cold spots within the chamber. In a crystal growth application, by reducing temperature variations within the chamber, more constant temperatures at the interface of the crystal may be maintained thereby promoting a convex interface shape and preventing new grain formation improving the compositional homogeneity and electrical properties of the crystal.

"At low or minimal power output from the furnace controller, the active cooling circuitry may drive the active cooling device at maximum speed to rapidly cool the furnace chamber, reducing cooling times from hours to minutes. The symmetrical airflow around the chamber at maximum speeds, draws heat both radially and axially away from the furnace chamber, dramatically increasing cooling times. Cooling times are reduced based on the size and dimensions of the furnace, where smaller furnaces may cool in under an hour where without active cooling from nine to ten hours would be needed. The improved cooling times provide for further process steps to be performed more quickly increasing heat-treated materials production.

"An object of the present invention is an active cooling system that establishes steep temperature gradients in a furnace system.

"Another object of the invention is an active cooling system that reduces temperature variations in a furnace system.

"Another object of the invention is an active cooling system that performs rapid cooling in a furnace system.

"A further object of the invention is an active cooling system for a furnace system that improves mechanical and electrical properties in heat-treated materials.

"A still further object of the invention is an active cooling system for a furnace system that promotes low compositional variation in the growth of crystals.

"The present invention is related to a method of actively cooling a furnace comprising the steps of acquiring a furnace controller output from a furnace controller, the furnace controller output corresponding to an amount of power provided to a heating element included in a furnace; and generating an active cooling control output based, at least in part, on the acquired furnace controller output, the active cooling control output configured to drive an active cooling element coupled to the furnace, the active cooling element configured to adjust a flow rate of a cooling medium in the furnace. The method of actively cooling a furnace is related to the furnace controller output by a predetermined transfer characteristic wherein the furnace controller output is less than a low threshold and the active cooling control output is at or near a maximum, corresponding to a maximum flow rate of the cooling medium configured to cool a zone of the furnace. The method of actively cooling a furnace is further related to a furnace controller output that is greater than a high threshold and the active cooling control output that is at or near a minimum, corresponding to a minimum flow rate of the cooling medium configured to facilitate temperature uniformity with a zone of the furnace.

"The method of actively cooling a furnace is also related to the furnace controller output that is below a range of optimal power levels for the furnace and the active cooling control output that is at a value configured to allow the cooling medium to dissipate sufficient heat in a zone of the furnace to cause the furnace controller to increase furnace controller output to within the range of optimal power levels. The method of actively cooling a furnace includes the further steps of determining whether a process is completed based on a duration that the acquired furnace controller output is less than a low threshold where the low threshold maybe 5% and the maximum is 100%, or the high threshold is 50% and the minimum is 5% and the range of output power levels is 50% to 70%. The method of actively cooling a furnace further comprising the step of directing the cooling medium through a channel in the insulation of the furnace and around a heating element.

"The present invention further relates to a furnace system with active cooling comprising active cooling control circuitry configured to acquire a furnace controller output from a furnace controller, the furnace controller output corresponding to an amount of power provided to a heating element included in a furnace, and an active cooling element coupled to the furnace, the cooling element configured to flow a cooling medium in a channel associated with a zone of the furnace and wherein the active cooling control circuitry is configured to generate an active cooling control output based, at least in part, on the acquired furnace controller output with the active cooling control output configured to drive the active cooling element to adjust a flow rate of the cooling medium.

"The furnace system with active cooling includes active cooling control circuitry that comprises a processor configured to execute an active cooling application, and a memory coupled to the processor, the memory configured to store the active cooling application and a predetermined transfer characteristic configured to relate the active cooling control output to the acquired furnace controller output. In the furnace system with active cooling, the active cooling control output is configured to drive the active cooling element to achieve a maximum flow rate of the cooling medium when the acquired furnace controller output is less than or equal to a predetermined low threshold with the maximum flow rate of the cooling medium configured to cool an associated zone of the furnace. The furnace system with active cooling wherein the active cooling control output is configured to drive the active cooling element to achieve a minimum flow rate of the cooling medium when the acquired furnace controller output is greater than or equal to a predetermined high threshold with the minimum flow rate of the cooling medium configured to facilitate accurate temperature sensing in an associated zone of the furnace.

"In the furnace system with active cooling, the active cooling control circuitry comprises a timer configured to provide a measure of a duration of time that the furnace controller output is equal to or less than a low threshold, a magnitude of the duration configured to differentiate between a cooling state within a process and a cooling state at a completion of the process. The furnace system with active cooling wherein the active cooling control output is configured to drive the active cooling element to change a flow rate of the cooling medium wherein the change of flow rate is inversely proportional to a change in the acquired furnace controller output when the acquired furnace controller output is less than or equal to a predetermined high threshold and greater than or equal to a predetermined low threshold, the change in flow rate of the cooling medium configured to facilitate maintaining a target temperature in a zone of the furnace. Other objects and advantages of the present invention will become obvious to the reader and it is intended that these objects and advantages are within the scope of the present invention. To the accomplishment of the above and related objects, this invention may be embodied in the form illustrated in the accompanying drawings, attention being called to the fact, however, that the drawings are illustrative only, and that changes may be made in the specific construction illustrated and described within the scope of this application.

BRIEF DESCRIPTION OF THE DRAWINGS

"Various other objects, features and attendant advantages of the present invention will become fully appreciated as the same becomes better understood when considered in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the several views, and wherein:

"FIG. 1 is a perspective view of a furnace system with active cooling in a first embodiment of the present invention.

"FIG. 2 is a top view of a furnace system with active cooling in a first embodiment of the present invention.

"FIG. 3 is an exemplary system block diagram including a furnace system and an active cooling system, consistent with the present disclosure.

"FIG. 4 is an exemplary system block diagram for the active cooling control circuitry depicted in FIG. 3 consistent with the present disclosure.

"FIGS. 5A and 5B are plots of exemplary relationships between furnace controller output and active cooling control output, consistent with the present disclosure.

"FIG. 6 is an exemplary system block diagram including a furnace system and an active cooling system including temperature sensing, consistent with the present disclosure.

"FIG. 7 is an exemplary system block diagram for the active cooling control circuitry depicted in FIG. 6, consistent with the present disclosure.

"FIG. 8 is a flowchart of exemplary operations for an active cooling system consistent with the present disclosure.

"FIG. 9 is an elevation view of a first embodiment of an active cooling device in a first embodiment of the present invention.

"FIG. 10 is a perspective view of a first embodiment of an active cooling device in a first embodiment of the present invention.

"FIG. 11 is an exploded view of a first embodiment of an active cooling device in a first embodiment of the present invention.

"FIG. 12 is a side view of a first embodiment of a funnel bracket of the active cooling device of FIG. 11 in a first embodiment of the present invention.

"FIG. 13 is a perspective view of a first embodiment of a core assembly of the furnace system with active cooling in a first embodiment of the present invention.

"FIG. 14 is a top view of a first embodiment of a core assembly of the furnace system with active cooling in a first embodiment of the present invention.

"FIG. 15 is a top view of a first embodiment of a heater core assembly of the furnace system with active cooling in a first embodiment of the present invention.

"FIG. 16 is a perspective view of a first embodiment of a heater core assembly of the furnace system with active cooling in a first embodiment of the present invention.

"FIG. 17 is a perspective view of cut out of a first embodiment of a core assembly of the furnace system with active cooling in a first embodiment of the present invention."

For additional information on this patent application, see: MELLEN, Jonathan Y. Furnace System with Active Cooling System and Method. Filed December 28, 2012 and posted July 10, 2014. Patent URL: http://appft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&u=%2Fnetahtml%2FPTO%2Fsearch-adv.html&r=3137&p=63&f=G&l=50&d=PG01&S1=20140703.PD.&OS=PD/20140703&RS=PD/20140703

Keywords for this news article include: Crystal Growth, The Mellen Company Inc.

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Source: Health & Medicine Week


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