Ultrahigh Velocity Water-Cooled Copper Taphole

The present invention is directed toward a taphole for use with a melting furnace and more particularly toward an ultrahigh velocity water-cooled copper taphole.

Because of the extremely high heat generated by the molten material flowing through the taphole of a melting furnace, it has been known for sometime that provisions must be made for cooling such tapholes. This has been conventionally accomplished by constructing the taphole from steel and water cooling the steel. However, this approach has been less than effective and results in an unpredictable, varying buildup or "skull," of solid material at the working surface of the cooled metal and a correspondingly uneven discharge of molten material.

As explained more fully in applicant's U.S. Pat. No. 4,032,705 (the entire subject matter thereof being included herein by reference), applicant has discovered that the rapid, consistent removal of large quantities of energy (in the range of 1 BTU per square inch per second) through a water-cooled metal barrier, without damage to that barrier, requires that the metal have excellent thermal conductivity and a reasonably high melting point, and be force-cooled at a constant temperature by the creation and efficient removal of steam at its back face.

Converting 1 pound of water into steam requires 967 BTU's of heat at 212.degree. F. (or 536 calories per gram at 100.degree. C.). If water can be made to present itself consistently to the area to be cooled and there to turn into steam, and then to leave the area immediately to make room for more water to arrive, a highly efficient and predictable cooling system results. The area to be cooled must, of course, be kept free of accretion to obviate the film effects which are adverse to efficient thermal transfer.

Experimentation has shown that the best way to remove the steam film as rapidly as it forms is by applying ultrahigh velocity cooling water to the back surface of the metal barrier. A cooling water velocity of at least 10 feet per second has proved to be required, and this velocity must be at the surface of the metal, not merely at the center of a substantial cooling passage of which the metal barrier is one of the walls. The preferred water cooling velocity is at least 20 feet per second. It should be readily apparent that such velocities require high flow rates through small passages, thereby generating pressure drops of the order of 20 to 60 psi, depending on the surfaces, shapes and length of the area to be cooled.

To enhance the effectiveness of this cooling, a readily workable metal of reasonable cost and melting point and high thermal conductivity is required. From a table of the physical properties of the elements, a selection of an easily workable, relatively inexpensive material with a melting point above 1,000.degree. C. and good thermal transfer capability results in the following list:

Chromium, molybdenum and nickel are not really easily workable and they are relatively expensive. Furthermore, these materials have thermal conductivities which are from 3 to 5 times poorer than that of copper.

Because of the relatively low melting point of copper and the corresponding higher melting point of iron, the automatic and quite incorrect choice in the past for a water-cooled taphole has been steel. This has been true even though it has a thermal transfer ability less than 1/5 that of copper. Furthermore, for a number of reasons, the water-cooled steel has a tendency to form films thereon of a highly insulating nature.

Compounding this technical felony is the fact that, to applicant's knowledge, no attempt has been made to ensure the efficient removal of heat energy from the back face of the taphole orifice by the encouragement of steam formation, against a clean surface, made effective by the immediate removal of that steam by new cooling water moving at "ultrahigh velocity." It should be pointed out that the use of stainless steel only makes matters worse since stainless steel grades have thermal transfer abilities 16 to 24 times poorer than copper.

The present invention overcomes the problems of the prior art and provides a taphole orifice which allows a film of solid material of predictable, constant thickness to freeze on its working face so that the discharge of molten material is smooth and consistent. The taphole according to the invention includes a cylindrically shaped copper shell having a central opening through which molten material from a furnace passes and includes a reduced inner diameter portion defining an orifice. A plurality of narrow holes are formed in the shell wall adjacent the orifice but isolated therefrom and are interconnected to form a plurality of highly restrictive flow passages. Coaxially arranged about the copper shell is a coolant guide having a surface which is closely spaced from the copper thereby defining another highly restrictive flow passage which is also in communication with the plurality of passages around the orifice. A liquid coolant is supplied to the passages where the velocity of the same is made to accelerate to an ultrahigh velocity of at least 10 feet per second across nonworking surfaces of the copper shell forming parts of said passages to thereby sweep away steam generated upon the surfaces.

For the purpose of illustrating the invention, there is shown in the accompanying drawing one form which is presently preferred; it being understood that the invention is not intended to be limited to the precise arrangements and instrumentalities shown.

The sole FIGURE is a cross-sectional view of an ultrahigh velocity water-cooled copper taphole constructed in accordance with the principles of the present invention.

Referring now to the drawing in detail, there is shown in the sole FIGURE a longitudinal cross-sectional view of an ultrahigh velocity water-cooled copper taphole constructed in accordance with the principles of the present invention and designated generally as 10. The forward end of the taphole 10 (the left side as shown in the FIGURE) is secured to a graphite nozzle 12 in a known manner. The nozzle 12 is not part of the present invention per se and is shown in phantom merely to show the environment of the present invention. The nozzle 12 is, in turn, fitted in the crucible wall of a melting furnace in a manner known to those skilled in the art.

The taphole 10 is comprised essentially of three major parts: an inner copper member 14, an intermediate coolant guide 16 and an outer jacket 18. Except for the forward portion of the copper member 14 which will be explained in more detail hereinafter, each of the elements 14, 16 and 18 is relatively thin-walled tubularly shaped and preferably cylindrically shaped, i.e. having a circular cross section. The inner copper member 14, coolant guide 16 and jacket 18 are also arranged to be coaxial with each other.

The inner surface 20 of the copper member 14 is the working surface of the taphole 10 and defines the opening through which molten material from a furnace passes (from left to right in the FIGURE). The thickness of the wall of the copper member 14 is increased at the forward end thereof as shown at 22 so as to produce a reduced inner diameter portion defining an orifice 24. The orifice 24 includes an inner working surface 26 which is continuous with the inner working surface 20 of the copper member 14.

In order to effectively cool the working surface of the orifice in the manner described hereinabove, a plurality of holes are drilled into the thickened wall portion 22 to form a plurality of passageways such as shown at 28. Each passageway is formed by drilling a first hole 30 from the outer surface of the copper member 14 toward the working surface 26 of the orifice 24. A second hole 32 starting at a position which is axially offset from the first hole 30 is also drilled inwardly toward the working surface 26 of the orifice 24 so as to intersect the inner end of the first hole 30.

Each passageway 28 is, therefore, substantially V-shaped and includes wall surfaces 34 which lie behind the working surface 26 of the orifice. The surface 34 is in relatively close proximity to the working surface 26 but is isolated therefrom. Each of the holes 30 and 32 forming the passageways 28 is only approximately 5/32 of an inch thereby defining a highly restrictive narrow flow passage for a liquid coolant. It should be readily apparent that while only two such passageways 28 are shown in the FIGURE, any desired number of such passageways may be utilized and are preferably equiangularly spaced around the axis of the orifice 24. In the preferred embodiment, twelve such passages are utilized.

As stated above, the coolant guide 16 is coaxially disposed around the copper member 14. The forward most end of the coolant guide 16 is welded or otherwise secured to the outer surface of the copper member 14 at a position 36 which is located between the openings 30 and 32. A narrow annular space 38 remains between the inner copper member 14 and the coolant guide 16 and extends substantially the entire length of the taphole 10. This space 38 forms a part of the highly restrictive narrow flow passage and is in communication with the passageways 28 through the holes 32.

An annular space 40 also remains between the coolant guide 16 and the outer jacket 18. This annular space 40 extends from a point near the forward end of the taphole 10 to a point adjacent the discharge end of the taphole but spaced therefrom. Adjacent the forward end of the taphole 10, the jacket 18 is secured to the copper member 14 such as shown at 42. An O-ring 44 provides a liquid seal between the two elements. The forward most end of the annular space 40 is in communication with the passageways 28 through the holes 30.

The annular space 46 between the coolant guide 16 and the jacket 18 at the rear of the taphole 10 is isolated from the major portion of the annular space 40 by an O-ring seal 48 located between the coolant guide 16 and jacket 18. The annular space 46 communicates with the annular space 38 through a plurality of openings 50 located in the rearward most end of the coolant guide 16. These openings 50 can be formed by either castellating the end of the coolant guide 16 or by drilling a plurality of holes therethrough. An inlet port 52 communicates with the annular space 40 and an outlet port 54 communicates with the annular space 46.

The taphole 10 functions in the following manner. Molten material such as molten slag, for example, flows from the furnace and nozzle 12 through the orifice 24 and thence along the working surface 20 of the copper member 14 until it is discharged from the discharge end of the taphole. As the molten material flows through the taphole, intense heat is transferred to the copper member 14. Water or other desired liquid coolant is forced into the inlet port 52, through the annular space 40 and thence into the passageways 28 through openings 30. The liquid coolant flows out of the passageways 28 through the openings 32 and through the annular space 38. At the rearward end of the taphole 10, the liquid coolant flows through the openings 50 into the annular space 56 and out the outlet port 54. Because of the highly restrictive narrow flow passages in the passageways 28 and in the annular space 38, in combination with the pressure of the incoming liquid coolant, the coolant is forced across the surfaces 34 and the outer surface of the copper member 14 at an ultrahigh velocity of at least 10 feet per second to sweep away steam generated upon these surfaces, thereby effectively cooling the copper member 14.

As a result of the effective cooling provided by the present invention, a skin or "skull" of solid slag material of predictable, constant thickness freezes on the working surfaces 26 and 20 of the orifice and taphole so that the discharge of further molten material is smooth and consistent. Furthermore, this skull is thermally insulating thereby protecting the copper from excessive temperatures. The skull also protects the copper working surface from physical wear.

It should be noted that while port 52 has been referred to as the inlet port and port 54 as the outlet port, these can be reversed. The liquid coolant can be made to flow in the opposite direction entering the port 54 and leaving the port 52 with the same cooling effect. Furthermore, it should be pointed out that coolant guide 16 and jacket 18 may also be made from copper or may be made from stainless steel or any other desired material.

The present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof and accordingly, reference should be made to the appended claims rather than to the foregoing specification as indicating the scope of the invention.