CHANGES IN PRACTICE
No startling changes of practice in the metallurgy of tungsten are known to have taken place, but there has been a steady betterment of the art, improvement in the quality of ferrotungsten, a shifting in localities of reduction, and a considerable change in the manner of use. The wasteful, lazy demand for ores of high concentration and of great purity common before the war has given way before more enlightened and intelligent practice, until firms both in this country and in England make a specialty of using low-grade or impure ores, though seemingly much more advance has been made here than abroad. One firm, the Chemical Products Co. (Washington, D. C.) was organized specifically to buy ores carrying less than the 60 per cent. tungsten trioxide (WO3) demanded by other American firms, and ores containing sulphur, copper, arsenic, bismuth, tin, antimony, phosphorus, or other impurities to which most users objected. Two firms, the Black Metal Reduction Co., and the Tungsten Products Co., both of Boulder, Colorado, were organized to handle materials such as tailings carrying as little as 1 per cent. tungsten trioxide, and they said that they were able to pay for gold and silver in the ore.
Several firms make tungsten trioxide or tungstic acid (H2WO4) for ferrotungsten makers. Firms have also made artificial scheelite (CaWO4) for the same trade, using off-color ores in the process. Powdered ferrotungsten made by chemically precipitating an iron tungsten salt from solution and reducing it to a metallic powder carrying 4 to 11 per cent. iron has been produced by several firms and seems to have started a demand for powdered ferrotungsten, so that firms are now finely grinding the massive ferrotungsten. Claims for better furnace practice which greatly cuts down the consumption of current and makes a saving of 90 to 96 per cent. instead of the usual 80 per cent. are also made. Several firms are making ferrotungsten powder and tungsten powder in iron tubes or other iron containers instead of in the graphite crucibles used before the war.
In the milling of tungsten ores, the tendency in this country is to get away from the uneconomic method of making concentrates very high in tungsten trioxide (carrying more than 60 per cent. WO3). Few operators really know what the heads run, and the determination of losses is mere guesswork. Some of the most careful operators in the Boulder field before closing down at the beginning of 1919 were making a high-grade product carrying nearer 50 per cent. than 60 per cent. tungsten trioxide, and a lower grade product carrying about 20 per cent. tungsten trioxide, not attempting to raise its tenor. This practice cuts down the losses largely. When the great shortage of tungsten ore came in 1916, users were compelled to take lower grade concentrates, and some improved their metallurgy accordingly. This change has made the sale of 50 per cent. concentrates easier. Even in England, 60 to 65 per cent. ores were accepted where formerly a content of 67.5 per cent. or 70 per cent. WO3 was demanded.
Formerly scheelite sold 50 cents per unit below other tungsten minerals, even though freer from bothersome impurities, but with the graduation from rule-of-thumb methods to more thoughtful, careful and scientific practice, it came to command a premium. Huebnerite seems to be still sold with and as “wolfram” in England, but in this country it must be sold according to its composition, for to most metallurgists the manganese is undesirable, though at least one firm now makes ferrotungsten from huebnerite without prejudice or difficulty. This growth in knowledge and technique has caused the price of the tungsten minerals to rank about as follows in the order named: Scheelite, ferberite, wolframite and huebnerite. This applies to tungsten used in the manufacture of tungsten and ferrotungsten for steel making. Scheelite is not wanted in this country for making filaments.
Before the war the United States imported considerable quantities of German ferrotungsten, but metallurgists claim that the ferrotungsten now made in this country is superior to any from Germany. For the present, of course, the German export trade is dead. England, formerly a small producer, is now making large quantities of ferrotungsten and tungsten powder at a number of plants. One of the producers, the High Speed Steel Alloys, Ltd., Widnes, near Liverpool, “is under government assistance and is owned by 31 of the leading consumers of Sheffield.”[75] The article quoted stated that the output was at the rate of 500 tons of tungsten per annum. The Thermo-Electric Ore Reduction Corporation,[76] Luton, was at the same time producing 140 tons of tungsten per month. The ferro produced carried 80 per cent. and the powder 98 per cent. of metallic tungsten. Only one company in the United States was producing as much as 60 tons of tungsten per month during the same war period. The Thermo Electric Ore Reduction Corporation owned mines from which it expected to produce each year 4,000 long tons of concentrates carrying 65 per cent. tungstic oxide. There are at least seven other manufacturers of tungsten or ferrotungsten in England.
[75] Mining Journal, London. “High Speed Steel Alloys, Ltd., Visit of Inspection to the Works,” vol. 115, Nov. 25, 1916, p. 779.
Julius L. F. Vogel has since written an article (Min. Jour., London, vol. 20, p. 16, Jan., 1919) in which he says that government aid, though proffered, was not accepted. This statement confirms the government policy.
[76] Mining Journal. “Thermo-Electric Ore Reduction Corporation, Ltd., Visit to the Luton Works,” vol. 115, p. 797, Dec. 2, 1916.
France had a number of ferrotungsten plants before the war, and these are thought to be still in operation.
At the beginning of the war about half of the tungsten used in the United States was introduced into steel in the form of ferrotungsten and about half in the form of tungsten powder. This practice has changed, so that now more than three-fourths of the tungsten used is introduced as ferrotungsten, largely, it seems, because of the ferro being now manufactured in purer form and partly because tungsten powder could not be obtained for a while. At one time tungsten ores were put in the charge and the tungsten alloyed directly with the steel; in fact, tungsten steels were first made in this way, although the process was patented in this country as new. The practice seems to have been dropped because of the introduction into the steel of impurities that may be eliminated when tungsten or ferrotungsten is made first.
In the making of tungsten steels a considerable change has taken place through the increased use of the electric furnace. One considerable producer, the Latrobe Electric Steel Co., makes all of its high-speed tool steel in this way. The Vanadium Alloys Steel Co., one of the larger producers, makes a large part of its steel in the electric furnace, and the Crucible Steel Co. and some other steel companies are understood to make a part or all of their steels thus.
The removal of tin, copper and other impurities from ferrotungsten by grinding and chemical treatment has made possible the use of impure ores in the production of high-grade ferrotungsten in the electric furnace.