Thermally efficient, cover for metal containment vessel, related system and methods
A thermally efficient cover for the molten metal held in a furnace, tundish, ladle, crucible or other containment vessel. Through substantially horizontal movement, this cover allows for periodic removal, particularly by retraction, for accessing contents of that furnace from a top aperture in the containment vessel. This invention further relates to a covered furnace system and methods of use.
The invention relates to a molten metal containment system, either portable or stationary, for the containment of ferrous and non-ferrous metals. More particularly, this invention relates to a means for increasing the thermal efficiency of metal containment vessels with an automated cover to reduce heat losses of molten metal held in that vessel assembly. This cover allows for the automated periodic removal, particularly by retraction, for accessing the contents of that furnace assembly. Ideally, relative movement of this cover over an aperture in the vessel assembly is programmable based on preset time increments. This invention further relates to a covered vessel system and methods of using the same.
BACKGROUND OF THE INVENTIONMolten metal containment vessels including furnaces, tundishes, ladles and/or crucibles, and other means for holding certain ferrous and non-ferrous metals are well known. The most thermally efficient of these vessels use high quality insulating refractories in the furnace walls to reduce heat losses through those walls. Lids and covers for such vessels have been designed to minimize heat loss through their intrinsic design and the use of effective insulation. Many such vessels, however, require repeated access to the molten metal bath. Access is most frequently needed to withdraw molten metal from the vessel to, for example, feed a castings system.
In such systems, a ladle is often used to withdraw metal from the vessel and transfers this metal to a down sprue, shot sleeve, or some other entry point to the casting process. Such access to molten metal is most often provided through a free surface of molten metal, although other means for metal withdraw, such as a pump, have also been used. Pumps can be expensive, complicated to operate, and may not provide metal withdraw with a geometry that best suits the casting process. The most frequently encountered means for withdrawing molten metal from such vessels is simply dipping a ladle through a free surface of molten metal and filling the ladle.
A free (or exposed) surface of molten metal results in a high rate of heat loss from radiation, conduction and convection heat transfer mechanisms. This is illustrated in the table below, wherein heat loss rates from a 5,000 lb capacity holding furnace for molten aluminum are provided.
Combined heat loss rates for the walls, bottom, and top of the furnace are 13 kW. By comparison, the dip out well of the furnace is a free surface of aluminum that results in a heat loss of 8.4 kW. Regardless of the effectiveness of the insulation used or design of the furnace sidewalls, ends and bottom, the free surface of molten metal results in an 8.4 kW drop or roughly 40% of the total heat loss.
It is known to provide such metal containment assemblies with some sort of cover to minimize heat losses from the free molten metal surface. For instance, Simko U.S. Pat. No. 5,234,660 shows a ladle cover assembly made from insulating ceramic fiber mats or “batting”. Miller et al. U.S. Pat. No. 4,524,702 shows a supposedly readily repairable, lightweight ceramic fiber cover, over a metal mesh under frame, for heated vessels such as a soaking pit.
It is also known to employ mechanically retractable components in the casting of metal parts. One representative example is the pouring of molten metal through a retractable shield for pour control as taught by Tabatabaci et al. U.S. Pat. No. 6,591,895.
SUMMARY OF THE INVENTIONIn a first aspect, this invention is directed to a furnace assembly for molten metal, ferrous or non-ferrous. The assembly includes a metal containment area or reservoir with at least one aperture, and means for heating that reservoir to keep its metal contents molten. The assembly further includes a cover for the aperture of the reservoir, that cover being configured for periodic removal (or retraction) from over that reservoir aperture for allowing access to the molten metal therein for a limited time. Preferably, that aperture cover can be mechanized for periodic removal from over the reservoir aperture. More preferably, movement of that cover can be programmed for prescribed timed intervals and/or for command retractions on an “as needed” basis. When this cover has been fully, or possibly even partially, retracted, access to the reservoir allows for additives to the melt and/or withdrawals (or “tapping”) of the molten metal contents to it.
In a second aspect, this invention addresses an improved, more efficient, system and method for casting metal alloys that has less radiation heat losses than current practices. The system and method achieve such improvements with a removable/retractable cover over the furnace, tundish, ladle or crucible in which molten metal is held for subsequent processing.
The structure, operation, and methodology of the invention, together with other objects and advantages thereof, may be better understood by reading the detailed description in conjunction with the accompanying drawings in which:
The molten metal maintained in a typical holding furnace needs to be periodically accessed by ladles (and other devices) for purposes of metal withdrawal or “tapping”. When there is no cover over such furnaces, approximately 2.2 kW of power will be lost or dissipate, primarily by radiated heat, from the open surface of an aluminum melt.
A retractable cover primarily designed for reducing radiation losses by reflection will improve furnace energy efficiencies. Such a cover need only retract when access to the molten metal in the furnace/container is needed. More importantly, the retractable cover, system and methods of this invention do NOT move air in and out of the head space above a furnace melt by any sort of fanning action or effect. A large permanent door that has to be repeatedly lifted and then lowered back into place over a furnace aperture, especially as often as 1-2 times per minute, would lower furnace efficiencies by such “fanning” back and forth.
One preferred cover design would use relatively thin refractory cloth, one having a low emissivity/reflectivity rating. That cloth should be lightweight, yet somewhat flexible, perhaps even “foldable”. One representative material is a ceramic fiber, or fiber cloth, like the type made and sold by 3M as Nextel® 312. Other materials include various silica-based cloths such as well known “S Glass”, and calcium aluminate mats such as the line of Fiberfrax® products sold by Carborundum Company.
Preferably, the aforementioned material is wound or otherwise situated on one or more torsion spring-loaded rolls for opening by retracting, on cue or when prompted, thereby allowing limited duration metal access. In one embodiment, material retraction on these rolls is robotically controlled using an air cylinder, solenoid or other activation means. Alternately, the material may be wound by rolls loaded by a rack and pinion-type system.
A more preferred molten metal furnace cover according to this invention should possess low mechanical inertia so as to not require excessive energy for retraction. The material should also be relatively “lightweight”. As used herein, lightweight is meant to cover materials with a bulk density range between about 20-70 lb/ft3. Also considered lightweight herein are covers with a material density between about 50-250 lb/ft3. This includes many refractory products. Preferred lightweight materials should also have preferential porosity, void fraction and/or material density combinations.
Ideally, relative movement of the cover to the furnace top (and its aperture there through) should be substantially planar, and more preferably horizontal to the plane of said furnace top. Retraction of a cloth cover over the furnace aperture can be accomplished by several, preferred mechanical means. These include: moving the cover mostly laterally from at least one roll situated directly over that furnace aperture. Ideally, that cover roll can be spring-loaded for movement using an air actuator, a hydraulic actuator and/or one or more electrical solenoids. On a preferred basis, the spring-loaded cover roll (or rolls) further includes at least one traction motor.
For optimum efficiencies, relative movement of the cover can be programmed with movement of an automated metal withdraw device. The frequency of molten metal withdraw is determined by the cycle time of the casting process being supported by the furnace. Representative cycle times include mechanically opening and closing the cover: more than 10 times per minute for removing metals from that furnace for uses elsewhere in the metal part production process. For still other applications, the cover may be programmed to open and close roughly 5 to 10 times per minute, or 2 to 4 times per minute for (reason?). In other applications, the cover timing may be set to automatically open and close less than 2 times per minute, or possibly as infrequently as more than once per hour. Finally, for any programmable timer, there can be included a manual override for rapid cover retraction in the event of an unplanned emergency, or to otherwise allow melt access during an unscheduled cycle time.
It should be noted that common features in the different views of this invention are shown with the same reference numeral(s). For alternate embodiments of the same component, there is consistent numbering though in the next hundred series. When referring to any numerical ranges herein, it should be noted that all numbers within the range, including every fraction or decimal between its stated minimum and maximum, are considered to be designated and disclosed by this description. As such, disclosing a preferred cloth thickness, or cloth width ranging from 20 to 30 inches, expressly covers widths sizes of 20.5, 21, 22 and 23.5 inches . . . and so on, up to about 27.5, 28, 29 and 29.99 inches. The same applies for every other numerical and/or quantitative range herein including those for kW's saved, temperatures observed and even varied cycle times between cover opening and closing (or retraction and deployment).
Referring now to
For better heat efficiencies by minimizing radiant heat loss, the aperture 14 is at least temporarily covered by a cloth-like material 16. As shown, a preset length of said material 16 is stored (or wound) about a take-up roller 18. Atop the roller stand, there is situated an actuator 20 for extending and retracting a rod 22 which causes the take-up roller to move back and forth over the top planar face 12 of container 10. Such movement effects a gradual unwinding of material 16 from the lone roller 18 of this embodiment. More importantly, movement of the material 16 repeatedly off the roller 18 to deploy over the aperture 14 and then back onto the roller 18 for a temporary, partial retraction of the cover does not disturb or unnecessarily fan the molten metal contents of container 10. With a nominal, substantially horizontal retraction and deployment of material 16, this invention achieves a substantial heat savings. In the accompanying views,
In
In
While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiments but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims, which scope is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures as is permitted under the law.
Claims
1. A cover for a molten metal container, said container having an access point through which molten metal may be periodically extracted, said cover comprising:
- a. a mechanical support for positioning at or near the access point on the container;
- b. at least one cover segment that is capable of: (i) folding onto itself and (ii) reducing heat loss from the molten metal in the container through its access point;
- c. means for repeatedly moving the cover segment with the mechanical support for temporary positioning over the access point of the container, said moving means enabling said cover segment to be held adjacent said access point when not temporarily positioned over said access point; and
- d. means for programming the cover to extend and retract over the container access point on a timed cycle selected from the group consisting of: more than 10×/minute; 5 to 10×/minute; 2 to 4×/minute; less than 2×/minute; and 1× or more per hour.
2. The molten metal container cover of claim 1, which further comprises:
- means for cycling movement of the cover segment back and forth, over the access point, for a predetermined length of time to reduce molten metal heat loss through the access point.
3. The molten metal container cover of claim 1 wherein said cover segment extends and retracts from the mechanical support to coordinate with metal extraction from the container.
4. The molten metal container cover of claim 3, wherein extension and retraction of said cover segment is performed mechanically.
5. The molten metal container cover of claim 1, wherein the cover comprises a radiation shield.
6. The molten metal container cover of claim 1, wherein the cover consists essentially of a ceramic fiber cloth.
7. The molten metal container cover of claim 1, wherein the cover segment moves substantially parallel to the access point in the container.
8. The molten metal container cover of claim 7, wherein the access point is a top aperture in the container and the cover segment moves back and forth over the top aperture in a substantially horizontal direction.
9. The molten metal container cover of claim 8, wherein extension and retraction of said cover segment includes reciprocating movement from at least one roll.
10. The molten metal container cover of claim 9, wherein the cover segment is adapted for extending and retracting between a pair of rolls immediately adjacent the top aperture.
11. The molten metal container cover of claim 9, wherein the roll is spring-loaded.
12. The molten metal container cover of claim 11, wherein the spring-loaded roll includes at least one of: an air actuator, an electrical solenoid and a hydraulic actuator.
13. The molten metal container cover of claim 11, wherein the spring-loaded roll includes a traction motor.
14. The molten metal container cover of claim 8, wherein the roll is loaded by a rack and pinion system.
2134785 | November 1938 | Goldberg et al. |
4726568 | February 23, 1988 | Nicholson |
Type: Grant
Filed: Feb 10, 2009
Date of Patent: Oct 29, 2013
Patent Publication Number: 20100201049
Inventor: C. Edward Eckert (New Kensington, PA)
Primary Examiner: Scott Kastler
Application Number: 12/322,962
International Classification: B22D 41/14 (20060101);