SIX-STRAND CONTINUOUS CASTING AT SAND SPRINGS North America's first six-strand, low-Ievel, continuous, billet-casting machine has been placed in service

A

rmco Steel Corp. officially put into commercial operation North America's largest and probably the world's first six-strand, low-level, continuous billet-casting unit at its Sand Springs, Okla., works. Average heats of 75-80 tons are cast from one electric arc furnace operating on a tap-to-tap cycle of 31/4 hr. The casting machine replaces a bottom-pour teeming practice for ingots 12% in. sq by 80 in. long that kept yields at low levels. Thus, Armco is now realizing significant improvements in both production rate and in yield, which is now over 95%. Furthermore, it has a casting machine geared to future demands when it may be necessary to add another melting furnace. The new DMB casting unit is a compact installation, with the ladle only about 8 ft above ground level, while the pit for the machine is about 9 ft below floor level. This is a "bow" type unit, so called because the strands curve on a uniform-radius, making a full 90° arc from mold to roll out. Actually, at no time is the strand ever full vertical, since the strand begins to curve in the mold itself. The radius of arc is 174 in. Billets are square, measuring 2%, 3, or 41f4 in. according to the mold selected.

HOW IT WORKS The la dIe, equal in capacity to the 75-ton furnace that produces the metal, transports the metal to the casting area at a temperature between 2925 0 and 2965°F, in roughly 8-min, furnace to tundish. The tundish is preheated to 1900°F hefore the ladle is tapped. From the tundish, the steel is fed into six separate molds, which cast six separate strands simultaneously. Each strand has its own separate stopper at the tundish, so that if trouble should develop in one strand flow can be stopped, and the other five 866-JOURNAL OF METALS, AUGUST 1965

strands continue in operation to finish the cast. Each mold consists of a water-cooled system around a 28in. long curved copper sleeve. These sleeves can be removed for cleaning, repair or replacement to change the size of the billet. During the cast, each mold oscillates continually to reduce the possibility of the strand sticking to the mold. Length of the stroke and its frequency are adjusted to the individual cast. Rapeseed oil is fed continually from slots at the top of the mold, also to help keep the steel free from the mold wall. After leaving the mold, treated water is sprayed on the strands under controlled quantity, pressure, and temperature; flow rate is 2500-gpm. Since this is the area where "breakout" would be most probable, rolls both support the strand and guide it through its design radius. The strand is actually pulled through. At the bottom of the arc, the strands are straightened by rollers, and are automatically cut to 22-ft lengths by six sets of 150-ton flying shears. These shears travel horizontally at the same speed as the strands during the cut, then return to position. The cut billets move along the rollout table until they are ejected into collector cradles. After cooling, an overhead crane removes them to the merchant mill.

AUTOMATIC CONTROL During the cast, each strand is monitored and controlled from its own console, either manually or automatically. The operator can alter the casting speed slightly to meet variations in operating conditions. On the basis of present operating experience, automatie operation seems to offer the best approach, with the operator putting the machine on automatie as soon as he can.

The heart of the automatic system is mold level control, effected by controlling flow from the tundish to the mold. The monitoring unit is a lead-shielded Cobalt-60 element emitting gamma rays through the mold, to be picked up on the other side of the mold by a detector element. This detector induces an electrical output signal proportional to the radiation intensity it receives, which is itself a function of the metal-level in the mold. The tundish stQPper rod opens and closes in response to this signal. Constant cooling water temperature and constant voltage are required for accuracy, and if wide variances are experienced in these conditions, the operator must use manual override for mold-Ievel manual control. Flow from the tundish to the mold is controlled by the action of six clay-graphite stoppers and rods. The rate of flow is controlled by raising or lowering the stopper rods over the nozzles, and thus increasing or decreasing the "head" of metal in the tundish. The gamma ray control maintains elose-control flow between the cone-shaped stoppers and nozzles. N ozzles now have to be replaced after each heat. This is done at a set-up station where refractory dryout and initial tundish preheat takes place. When the tundish is transferred to the casting machine station, actuating rods are attached to the stopper rods, and the latter are carefully aligned with the nozzles. Continuous-continuous casting is not possible at this time, since tundish linings are frequently changed and the stoppers have to be changed after each cast. (DMB engineers have, however, gone two heats in a row and actually approached three. Improved refractories could stretch this out.)

75 tons from the lurnace

IS

led through six

GOOD QUALITY CONTROL Quality control of the steel (essentially regular grades of carbon steel are cast) is especially rigorous within pre-determined limits. As a companion to the new casting unit, a new chemicallaboratory was constructed about 50-yds from the melt shop. Sampies arrive directIy by pneumatic tube for evaluation. Reporting procedures are immediate, by close-circuit TV and an intercom system. As soon as analysis is completed, results are written on a chemical analysis card. This card is placed under the camera, and the image is projected on a receiver screen in the melt shop. Results can be discussed over the intercom. Birdsboro Corp. engineered and buHt the machine from general designs supplied by Demag-Mannesmann-Bohler, of West Germany. Armeo is operating the unit under a licensing agreement with "SSG" and "OSIG", continuous casting associations of West Germany and Austria, and Mannesmann A. G. provided technical assistance. The general contractor was Huber, Hunt & Nichols, Inc. This new unit is part of Armco's "Project 600". This is a 6 year plant modernization and improvement program with projected spending in excess of $~OO million. Another continuous-casting plant, deslgned along the same principles, is being built in Armco's Butler plant. This is a single strand unit designed to cast a variety of steels into slabs. L.F.G

strands, converting oll 01 it to billets in 1 hr.

EUROPIUM FOR COLOR TV FROM THE NEWEST AND LARGEST RARE-EARTH SEPARATION PLANT

Rare-earth concentrates are first roasted ... ... Rore-eorth concentrotes are first roasted

and and then then passed passed through through a solvent a solvent extracextraction process. tion process.

In final the final step,step, europium europium oxideoxide is stripped is stripped In the from from the organic the organic solvent. solvent.

824-JOURNAL OF METALS, AUGUST 1965

The most important rare earth deposit in North America is that owned by Molybdenum Corp. of America at Mountain Pass, Calif.some60 miles west of Las Vegas, Nev. With reserves of more than 3 billion lb of rare earth oxides in an ore averaging some 10% rare earth oxides, this deposit has been a major source of rare earth supplies for the western world. Neverthe1ess, markets have been limited, and processes for separating the individual oxides have been expensive. Since 1955, the mine has been operated at one-fourth to one-third of capacity_ At Mountain Pass, rare earth oxides occur in the form of a mineral known as bastnasite--a mixture of rare earths in a fluocarbonate form. The ore is passed through grinding and hot-flotation circuits to product a concentrate averaging 60% rare earth oxides wh ich can be further processed to the 68-72% level-alm ost pure mineral. Most of this concentrate has been and a large quantity still is being shipped to York, Pa., for further treatment according to a process described in an article by P. R. Kruesi on p. 847 of this issue. From 1964 to 1965, rare earth markets have completely changed as the bombshell of the color TV market dropped into the picture. This television application is the most recent important development in rare earth use. In this case, europium, one of the rare earth metals, is used as an ingredient in phosphor coatings applied to color television tubes to attain brighter, truer co10rs, and to improve the quality of the television picture. Europium was in the ore from the Mountain Pass mine--but even in pure bastnasite, its oxide EUz08 amounted to only 0.11 % of the total oxides_ The problem was rare earth oxides. that of developing an economic extraction process as rapidly as possib1e in order to reap the advantages of this market. Taking advantage of previous research work by AEC-sponsored 1aboratories, particu1arly that at Ames, Iowa, Molybdenum Corp. called upon the services of the Co10rado School of Mines Research Foundation in September 1964 to deve10p a suitable solvent extraction technique. Before the end of that year, pilot plant work had been pushed sufficiently far to evo1ve evolve a flow sheet. The matter was then put in the hands of Bechtel Corp., who by the first week of July 1965 had a

europium oxide plant in operation at Mountain Pass, Calif. The plant was designed, constructed, and p1aced on stream in about 7 months. This $1.5 million plant is already producing the unheard quantity of 20 lb per day of europium oxideprobably the 1argest largest operation of its kind in existence. The europium-oxide extraction process of Molybdenum Corp., takes as its raw material the bastnasite flotation concentrate of average analysis shown in Tab1es Tables land 11 of the artic1e article on p. 847. A relatively pure fluocarbonate material containing 1ess less than 3% non-bastnasite minerals, it is first roasted to remove carbon dioxide. A major constituent is cerium oxide (50%), which is separated by a leaching operation. The 1each leach liquor is passed into a continuous two-stage solvent extraction (liquid ion exchange) process upon which patent applications are pending. An organic phosphate is the solvent. In the first step, the europium and other elements adjacent to europium in the rare earth series are separated from the bulk of the other light rare earths, resulting in a byproduct containing lanthan um, neodymium, and praseodymium oxides. In the second step, europium is separated from samarium, gadolinium, and yttrium oxides. The process recovers very dilute europium liquors (0.002 1b lb per gal) at very high yield at a purity of 99.9%. Byproducts are presently being stockpiled awaiting the development of suitable markets. It appears that Molycorp's solvent extraction can be adapted to the separation of the individual oxides in the byproducts. Commenting on the new process, William R. Kuntz, president of Molybdenum Corp., commented: "We believe that this method of separating the rare earths is more economical than any other process known today. The new process, together with increasing demand by consumers, and our huge rare earth reserves, will lead to lower prices, greater industrial research, and new applications for these valuable raw materials." Europium oxide has present commercial application in two diverse fields. It is used as a nuclear poison, fie1ds. or control material, in atomic reactors and, of course, it is an ingredient in the new red phosphor for color television tubes. FWS