MUFFLE FURNACE CLEANINGASSEMBLY

Cross Reference To Related Applications This application claims the benefit of Provisional Patent Application No. 60/739,998, which was filed November 28, 2005.

Field of the Invention

This invention generally τelates to a furnace cleaning assembly and more specifically to a cleaning assembly capable of removing debris from inside a graphite muffle furnace.

Background of the Invention.

Many industries use furnaces for heating and firing materials as part of manufacturing processes. Often these processes must be carried out at high temperatures, for example temperatures above 1300 ⁰ C.

A muffle furnace is generally a horizontal furnace configuration where the product enters the front and exits the rear of the muffle and is used for high-tcmpcrature applications such as sintering, chemical vapor deposition, making carbon fibers, etc. The iπnermosi walls of the furnace are heated by conduction and radiation from one or more heaters, which surround the wails. A graphite slot furnace typically is a long, narrow furnace having an internal muffle furnace wherein the muffle walls are made of graphite in order to withstand high temperatures, often in the range of 1300 ⁰ C to 3000 ⁰ C. The material to be heated is placed inside of the graphite muffle. During operation of the furnace the muffle will often accumulate debris from heating the product. For example, if carbon fibers are heated in the furnace, hydrocarbons are often driven off the fibers as a gas and combine with other by-products to form a residue, which collects on the bottom of the furnace as debris. The debris needs to be removed or it will inhibit the operation of the furnace, however, because of the high temperature of operation, the muffle furnace can be difficult to clean.

Current preferred methods of removing debris from a graphite muffle furnace involve dragging a graphite scraper through the furnace. The scraper is attached to a graphite rope or braid, which is used to pull the scraper. The graphite scraper is pulled from one end to the other of the muffle thereby pulling the debris to the end of the muffle. This process is often repeated

multiple limes in order to thoroughly clean the muffle furnace. Once the debris is at the end of the muffle, it can be easily removed from the furnace.

A serious limitation to lhis cleaning process is that, although the graphite rope can be used at high temperatures, it is often not sufficiently strong and often breaks. When the graphite rope breaks, the scraper is difficult to remove from the high temperature furnace and results in a loss of productivity and the necessity for costly repairs. Thus, an improved cleaning system is needed for high temperature furnaces, and in particular for graphite muffle furnaces.

Summary of the Invention A muffle furnace cleaning assembly includes a scraper and a chain attached to it. The chain is fabricated, at least in part, from silicon carbide. Desirably, the chain is fabricated from alpha silicon carbide.

The scraper is adapted to clean the bottom of the muffle furnace. That is, the scraper is fabricated so that, when it is pulled by the chain through the muffle furnace, the scraper is capable of contacting at least portion of any debris that may be present at the bottom o f the furnace and moves the debris toward one end of furnace.

In a preferred embodiment, the chain and scraper are moved by a drive system, for example _^ the drive system may include a motorized wheel containing sprockets, which interlock with the chain. Desirably, the chain operates in a continuous loop and includes a chain return track. Preferably, one end of the chain is attached to the front of the scraper and the other end of the chain is attached to the back of the scraper so that changing the direction of the drive system can reverse the direction of movement of the chain and the scraper. Thus, the chain can pull the scraper through the furnace in either direction. In a preferred embodiment, the drive system includes sprockets that are fabricated from plastic, provided that the plastic is formulated to withstand high temperatures

Brief Description of the Figures

FIG. 1 shows a schematic representation of one embodiment of a graphite slot furnace. FIG. 2 .shows a schematic representation of a cross-section of the graphite slot furnace of FIG. 1.

FIG. 3 schematically depicts one embodiment including chain links that are fastened together by means of a bolt and a nut.

FIG. 4A schematically depicts a view of one embodiment of the invention including a top view of a scraper in a muffle furnace. FIG. 4A schematically depicts a view of one embodiment of the invention including a cross-section view of a scraper in a muffle furnace.

FEG. 4C is an enlarged view of FIG. 4A.

FIG. 4D is an enlarged view of FIG. 4B.

Detailed Description of the Invention

As described above, the invention addresses the need to reliably clean a high temperature furnace, such as a muffle furnace, especially a graphite muffle furnace that is part of a graphite slot furnace, without the unreliable characteristics of using a graphite rope.

The invention includes a scraper that is preferably, at least in part, fabricated from graphite, so as to withstand high operating temperatures. Suitable scrapers are adapted to clean the bottom of a muffle furnace. That is, the scraper is fabricated so that, when it is pulled υr pushed through the muffle furnace, the scraper is capable of contacting at least portion, of any debris that, may be present at the bottom of the furnace and moves the debris toward one end of furnace. An example of a suitable scraper is a graphite block that contacts debris at the bottom of the muffle furnace when pulled through the furnace. In one embodiment, the scraper includes a graphite block and a scraper blade attached to the block.

The scraper is attached to a chain. For example, the scraper may be attached to the chain by means of a clamp. Preferably, the chain passes through the scraper and is held to the scraper by a pin. The chain is at least in part fabricated from silicon carbide. Silicon carbide (SiC) is a ceramic compound composed of silicon and carbon and has two common forms, the alpha form and the beta form. Preferably, the chain is fabricated from alpha silicon carbide. Desirably, the chain is sufficiently long so that, when attached to the scraper located in the furnace, at least a portion of the chain extends exterior to the furnace.

In one embodiment, an alpha silicon carbide chain is attached to a graphite scraper, wliich enables the scraper to be pulled through the furnace. An alpha silicon carbide chain is much

stronger and more durable than, a graphite rope and is stable under high-temperature operating conditions.

In another embodiment, a muffle furnace is adapted to include an alignment track. Desirably, the alignment track is a recessed channel in the bottom of the furnace. Suitably, the scraper is adapted so thai part of the scraper fits into the channel. The alignment track keeps the scraper optimally positioned as it is pulled through the furnace.

FIG. 1 shows a schematic representation of one embodiment of the present invention. FIG. 1 depicts a slot furnace including a graphite scraper 10, which is connected to an alpha silicon carbide chain 12. In a preferred embodiment, the chain, and consequently the scraper attached to the chain, is moved by a drive system 13 at each end of the furnace. For example, the drive system may include a motorized wheel containing sprockets, which interlock with the chain. ^' Rotation of the wheel assembly moves the chain. Desirably, the chain operates in a continuous loop and includes a chain return trade 14. Preferably, one end of the chain is attached to the front of the scraper and the other end of the chain is attached to the back of the scraper, hi this way, changing the direction of the drive system can reverse the direction, of movement of the chain and the scraper. Thus, the chain can pull the scraper through the furnace in either direction.

In a preferred embodiment, the drive system includes sprockets that are fabricated from plastic, provided that the plastic is formulated to withstand high temperatures (high-temperature plastic), for example, high-temperature Teflon™. In certain cases, sprockets fabricated from materials such as steel are undesirable, since they may damage the silicon carbide chain and cause it to break.

In one desirable embodiment, the cleaning assembly includes a heat exchanger that is used to cool the silicon carbide chain, which prolongs the useful life of the chain. For example, a portion of the assembly may be equipped with a water jacket, 15 (FlG. 1), providing an enclosure through which the chain can pass. Water is passed through the water jacket cooling its walls. The chain passes through the water jacket area (beat exchanger) and heat is removed from the chain conduetϊvcly. In one desirable embodiment, a heat exchange unit is provided at each end of the furnace so that, as the chain exits or enters the furnace, the chain passes through a heat exchange and heat is removed from the chain.

FIG. 2 depicts a schematic view of a cross-section of the furnace of FIG. 1 showing the graphite scraper 20, the graphite muffle 22, and the furnace heating elements 2ϊ . The graphite scraper may be of any suitable shape, provided that at least one edge of the scrapei is capable of contacting debris located in the muffle furnace. For example, in FIG. 2, wherein the muffle furnace 22 is rectangular in shape, the lower portion of the scraper 20 is also rectangular in shape so as to efficiently contact the bottom of the muffle furnace, In one desirable embodiment, the scraper is fabricated so that the bottom of the scraper conforms to the shape of the bottom of the muffle furnace. In addition to a bottom portion, the scraper will have an upper portion that provides strength to the scraper and allows for attachment of the chain. Desirably the upper portion of the scraper is preferably fabricated with multiple cutouts _τ for example, it may have a honeycomb structure, to reduce weight and, thus, reduce stress on the chain, while still providing the scraper with structural stability.

In one suitable embodiment, the scraper is adapted so that a portion of the scraper contacts debris at the top of the muffle furnace and a second portion of the scraper contacts debris at the bottom of the muffle furnace. Thus, by pulling the scraper through the furnace, debris may be removed form both the top and bottom of the furnace. In another embodiment, the scraper is adapted so as to be able to contact debris at the top, sides, and bottom of the muffle furnace simultaneously.

Desirably the silicon carbide chain includes a plurality of links wherein the links are connected together to form the chain. In one suitable embodiment, the links are connected by pins and fasteners. For example, the links may be fabricated so that a pin may pass through at least two links and consequently hold the links together. The pin may be held in palace by a fastener, for example a cotter. Desirably the pin and fastener are fabricated, at least in part, of silicon carbide. JJQ another suitable embodiment, the pin includes a bolt having threads and the fastener is a nut adapted to thread onto the bolt and thus hold the bolt in place. In one desirable embodiment, the bolt is held in place by a threaded nut and the nut is also glued to the bolt. Suitable glue is capable of withstanding high-temperatures, for example, certain Ceramabond™ adhesives such as adhesive Ceramabond™ 503 available from AREMCO, are often suitable. FIG. 3 schematically depicts one embodiment wherein the links of a silicon carbide chain, 30,

are fastened together by means of bolt 31 , which is held in place by threaded nut 32. Desirably, nut 32 is also glued to bolt 31.

FIG. 4A - 4D show a schematic representation of a partial view of one suitable embodiment of the invention. FIG. 4A shows a top view of a scraper including blade 41 and graphite bock 40. A silicon carbide chain 42 passes through the scraper (only two links of the chain are shown). The chain is connected to the graphite block by pin 43. FϊG. 4A also shows a top view of the scraper located in a furnace, which includes an alignment track 44 (the sides and top of the furnace are not shown). The alignment track keeps the scraper positioned properly in the muffle furnace. FIG. 4B depicts a frontal cross-sectional view of the scraper, showing the alignment track 44 and the scraper blade 41. FIG. 4C shows an enlarged view of FIG. 4A including the chain 42, and the graphite block 40 and the pin.43 that connects the chain to the block. The front and back edges of ύie scraper blade, 41 A and 41B ₁ are also shown. FIG. 4D is an enlarged view of FIG. 4B and shows pins 45 that connect the scraper blade to the graphite block 40. A portion of the graphite block 40 is located in the alignment track 44. The scraper blade 41 is in close proximity to the bottom of the muffle furnace 46.

Embodiments of the invention may provide reduced cost, higher productivity, improved quality, and ease of manufacture. While the invention has been described by reference to various specific embodiments, it should be understood that numerous changes may be made within the spirit and scope of the inventive concepts described. Accordingly, it should be recognized that the invention is not limited to the described embodiments but has full scope defined by the language of the following claims.