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Volume 48, 1915
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Art. LIV — The Manufacture of Iron and Steel in New Zealand.

[Read before the Technological Section of the Wellington Philosophical Society, 13th October, 1915]

The manufacture of iron and steel is the most important industry a nation can possess, and it is hardly too much to assert, that empire and power follow directly on and are measured by the production of iron and steel. Most English metallurgists recognize this so clearly that there must be a great (though as yet unexpressed) jubilation over the fact that Germany provoked this war a quarter of a century too early for her recent superiority in iron and steel production to assert itself unmistakably. Now that the engineering trades have clearly proved themselves the basis of all military and naval strength, we can hope that the tremendous and phenomenal strides of the German metallurgical industry within the last few years will be appraised by all our allied statesmen as the most desperate and inexorable menace to the peace and freedom of the world, and that definite, decisive steps will be taken to prevent the German Empire procuring that predominance over the European nations which would be the inevitable outcome of, say, twenty years more of her present superiority in the iron trade. Luckily, these steps are simple and obvious enough. The orefields on which Germany depends are in Lorraine and Luxemburg, and her fuel lies in Westphalia. The removal of these provinces from the domination of Prussia to the government of their racially congenial neighbours, France, Belgium, and Holland, would end at once the German Empire as an arbiter in the iron trade and a menace to peace and freedom in Europe. By careful effort and the sinking of some metallurgical fallacies Great Britain would again become the arbiter of European metallurgy, and her place as premier nation of the world would be assured once more. Every part of the Empire should strive for this one end—the supremacy of Great Britain in the iron and steel trade, and her consequent supremacy among the nations of the world in military and naval might and power. The effort should be to develop the cheapest Empire source of manufactured iron to the greatest possible extent, and to spoon-feed by tariff operations an uneconomic supply in any province at the expense of the cheapest source elsewhere in the Empire should be realized as a suicidal policy that will only tend to keep the Empire in the same desperate position it has been in for the last ten years. Iron and steel supremacy, which inevitably spells military and naval supremacy, can be attained only by concentrating all our iron-manufacture in the most economical position, where vast operations in the one province will induce economics impossible in smaller efforts, and where metallurgical skill and facility will become a racial trait of the inhabitants. A national outlook will warn us against the destructive fallacy of making each or any province of the Empire independent of the others in this industry, since it has been the selfish and disconnected policies of her colonies in regard to iron-importation that have endangered England's supremacy in the past, and no little part of Germany's might and power in August, 1914, can be traced directly to the want of foresight among English and colonial statesmen with regard to the fostering of the relatively declining national production of iron and steel.

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The question of iron and steel manufacture in New Zealand must be considered in the light of these remarks.

So far as our present scanty knowledge goes, the potential iron-ore fields of the Dominion are—(1) the Parapara district, (2) the Taranaki ironsands, (3) Mount Royal, (4) Mount Peel, (5) the Cheviot district. Our knowledge, however, of all iron sources save Parapara is where it was left by Sir James Hector in 1873, and our crying need is for an organized survey of all the likely deposits. Until that is accomplished we can only consider the possibilities of Parapara and Taranaki.

Parapara.

Bulletin No 3 (n.s.) of the Geological Survey Department establishes the fact that Parapara, Onakaka, and Tukurua Blocks comprise an extensive surface outcrop of at least 20,000.000 tons of ore, occurring in an easily mined and smelted form and in an accessible position; but the bulletin gravely errs on the optimistic side when reference is made to the metallurgical problem involved. The surface analysis given in the bulletin has since been supplemented by tunnel analyses published in the 1914 Laboratory Report, and beyond material error we may assert that the ore has the following composition:—

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Per Cent.
Iron 48 to 50
Alumina 3 to 6
Phosphorus 0.15
Silica 10 to 15
Water 10
Sulphur 0.08

Such ore would need calcining or roasting to expel the water and sulphur, and a product would result—

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Per Cent.
Iron 50 to 55
Silica 11 to 16
Alumina 3 ½ to 7
Phosphorus 0.17
Sulphur 0.03

This product contains too much silica to be economically dealt with in an electric smelting-furnace, and, while it could possibly be purified by magnetic concentration after fine crushing, the treatment adds expense, and the product could not compete for cheapness or purity with Taranaki ironsand. Small hot-blast furnaces using charcoal fuel are in use in America, Sweden, and Styria, but there they work with exceptionally pure ore, needing very little flux, and produce a very valuable steel-making pig in a costly manner. Such a furnace would burn all the timber off 1 acre of forest for every 20 tons of pig made, and is only practicable in heavily wooded districts within reach of navigable waters. With the impure ore of Parapara, and in a country of dear labour and difficult transport, a charcoal furnace is not economically possible.

The roasted ore would give a white steel pig running—Phosphorus, 0–35 per cent.; sulphur, 0–08 per cent.; silica, 1 per cent.; and worth £2 15s a ton: or, making grey foundry pig, would give—Phosphorus, 0–35 per cent, sulphur, 0–05 per cent; and worth £3 per ton.*

[Footnote] * The prices given are based on those current in July, 1914, f.o b. Glasgow.

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To make pig of this low value economically cheap production is essential; hence large furnaces, hot blast, labour-saving appliances, and an output of at least 1,000 tons a week are required. The cheapest flux for the silica in the ore is limestone, of which (assuming slags running 40 per cent silica, 16 per cent alumina, and 39 per cent lime for the white iron, and 35 per cent silica, 14 per cent, alumina, and 46 per cent lime for the grey) 12 cwt would be required per ton of white iron and 15 cwt per ton of grey iron. Such limestone must be over 95 per cent, calcium carbonate, and should not contain over 1 per cent, of magnesia. The presence of such pure limestone in accessible position and sufficient in quantity for an output of 40,000 tons per year is problematical, but geologists generally are reassuring on this point; frequently, however, speaking with an imperfect appreciation of the metallurgical requirements, as in Bulletin No 3.

The only suitable fuel available at present in large quantities is the hard dense Westport coke, which would probably run from 0.7 per cent, to 1.2 per cent, sulphur. One ton would be required for making white iron, and 25 cwt for grey, per ton of iron. Also per ton of iron 4–6 tons of highly preheated air would be required. The capital cost can now be assessed. Two furnaces (one stand-by) would be required, 80 ft. high, 20 ft in diameter, and 20,000 cubic feet capacity. This would give 1,000 tons of pig iron per week from 2,200 tons of ore, 1,000–1,250 tons of coke, 400–600 tons of limestone, and 5,000 tons of air, and would cost £50,000 in England and about £90,000 in New Zealand. Estimating the cost of mining the ore at 4s 6d, of calcining it at 1s 3d., of limestone at 7s 6d, and of coke at £1 15s (all per ton), we would have—

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Table I —Parapara Pig
White Pig for Steel Cost per Ton Pig Grey Pig for Foundry Cost per Ton Pig
s. d. s. d.
5,000 lb roasted ore 13 9 5,000 lb. roasted ore 13 9
1,350 lb. limestone 4 6 1,680 lb. limestone 5 6
2,200 lb coke 35 0 2,800 lb coke 43 9
Labour 7 0 Labour 8 0
Repairs 1 6 Repairs 1 9
Interest and depreciation 2 0 Interest and depreciation 2 0
5 tons air Nil 5 tons air Nil
At furnace 63 9 At furnace 74 9
Worth in Glasgow, July, 1914 55 0 Worth in Glasgow, July, 1914 60 0

The exportation of pig is clearly out of the question, and sole dependence must be placed on the New Zealand market, which would at present absorb about 4,000 tons per annum of grey foundry pig of Parapara quality, leaving 46,000 tons of white pig for steel-making. This pig is too impure to produce higher-quality steels for the foreign market, and there is little demand for such in New Zealand, hence the only outlook is for cheap steel for the bar and rod trade. This can only be made from Parapara pig by the basic open-hearth process, where we are at once confronted with the sulphur difficulty, both in the pig and in the coal for use in the gas-producers. The coal now mined in the Liverpool seam of the State mine runs under 1 per cent sulphur, but is probably too caking in its nature for easy and cheap treatment in a gas-producer, however, it could certainly be used for this purpose, but would cost over £1 a ton.

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The pig from Parapara ore offers a very difficult metallurgical problem when used for steel-making, and one which has prevented the use of such ores to any extent in other countries, as the solution involves a subsidiary process which increases the cost of steel-production. As given, the white pig contains 0–08 per cent, sulphur and 1 per cent, silica, both too high for the basic open-hearth process. Either could easily be reduced in the blast furnace, but only at the cost of increasing the other, so that the attempted solutions fall under two main headings: (1) Making a high Si, low S, pig, and desiliconizing by (a) blowing in a converter or (b) washing in a bath of molten basic slag; (2) making a low Si, high S, pig, and desulphurizing by (a) using manganese-ores as a flux, (b) pouring the molten pig on to nitrate of soda (Heaton process), or (c) using CaCl2 and CaF2 as a flux (Samter process). All these operations require skill and add to the cost. None of them have survived in practice, and all are of doubtful utility.

However, assuming this difficulty was overcome by one of the processes, an ingot steel would be obtainable costing £5 a ton in the ladle (against £3 5s. in England), and suitable only for bar and rod trade, which includes wire and gauge plates for galvanizing. New Zealand could absorb 50,000 tons a year of this material, but the selling-price of that manufactured in New Zealand would be at least £4 a ton above the imported. Parapara steel would be quite unsuitable for rails, boiler-plate, and good structural material, and the conclusion is inevitable that—(1) Parapara ore presents a very difficult problem to the steel-maker; (2) its content of phosphorus and sulphur is such that it is economically unsuited for the production of high-class steel, such as boiler-plate; (3) the cost of fuel and transport in New Zealand is at present prohibitive to the foundation of a large iron and steel industry; (4) the value of the ore is too low to encourage the idea of exporting it.

It may be pointed out here that the analysis given in Bulletin No. 3 of the Geological Survey of what is stated to be excellent pig iron made from Parapara ore in Melbourne in 1873 proves that the metal in question was a commercially useless steely product, probably made in a blacksmith's fire.

Taranaki Sands.

This ore occurs as a very finely divided sand over a large stretch of sea-coast extending from Waitotara to the Awakino River, and forms workable deposits at Patea, New Plymouth, Waitara, and Mokau at least. While no useful estimate can yet be made of quantity, it is certain that millions of tons of iron could be obtained. Earlier analysis made this ore appear of remarkable purity, but lately this has been disproved, and it is virtually certain that the sand contains about 0–5 per cent, phosphorus, estimated on the iron. Whether this percentage can be lessened by magnetic concentration is a moot point, but Mr. Donovan's valuable paper (see p. 503 in this volume), goes far to disprove the probability. Accepting his figures, the average of the Patea and New Plymouth sands, after magnetic concentration, runs about 56 per cent. Fe, 10 per cent TiO2, 0–25 per cent. Va, which would give a pig running 0–5 per cent phosphorus, suitable for heavy foundry-work and for steel by the basic process. Certainly this is a purer and (neglecting its form) more valuable ore than that of Parapara, but it cannot be compared with Swedish or Styrian, and, indeed, would not be accepted as a structural steel ore by the majority of English engineers.

The titanium present might give some trouble in the blast furnace, and neither it nor the vanadium add anything to the value of the ore, as

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neither would appear in the pig. However, the form of this ore is against any hope of successful utilization in the blast furnace, even if the purity made it worth while. Possibly the first suggestion to briquette such ores was made by Mr. Pharazyn before the Wellington Philosophical Society in 1869, and to this day those ignorant of metallurgical history vainly hope for success along this line. The problem of utilizing finely divided ore on the blast furnace arises wherever iron is smelted (flue-dust and fine stuff); but so far no method of briquetting or sintering has ever been successful, beyond making possible the use of the product to the extent of about 10 per cent of the total charge. The very nature of the briquetting process is against the product holding solid under the high temperature and great pressure of the modern furnace, and in the same way sintering (or fritting a mass of ore and coal together to form what some fancifully term ferro-carbon) cannot be efficacious beyond the temperature at which fritting takes place. Metallurgical experience throughout the world has made the fallacy of such ideas an axiom. At the most, a fritted product can be made which will stand quick passage through a low shaft furnace, and give a molten semi-steel containing under 2 per cent, carbon, which is quite useless commercially. The prospect of large works using Taranaki sand seems hopeless unless the ore is valuable enough to justify electrical treatment, or unless some cheaper electrical furnace is introduced. At present electrical furnaces use only expensive charcoal or coke as the source of the carbon chemically necessary for reduction, and the necessary heat is provided by electricity separately generated, while all the products of combustion are wasted. But if powdered coal in excess (thousands of tons of coaldust are destroyed every year in New Zealand as valueless) were fed in with ironsand to the top of a small shaft furnace, and the waste gases burnt under boilers to produce the small quantity of electricity needed to quickly carbonize and melt the already white-hot mass of mingled reduced iron and particles of coke, it is probable a much cheaper process would result. Assuming that the ore, fuel, and air are highly preheated by the waste gases, and remembering how efficient powdered coal is as a heating agent, it should be possible to smelt ironsand at the expense in fuel of 30 cwt of coaldust, which presupposes an efficiency of about 20 per cent. Even in Taranaki this should not cost over £1 a ton, and if the low figure of 30 per cent is taken as the concentration factor of the sand we would have—Grey Pig for Foundry

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Table II— Taranaki Pig
Magnetic concentrate, 30 per cent of original sand; iron, 56 per cent; TiO2, 10 per cent; phosphorus, 0.3 per cent; sulphur, trace. Electric furnace, 60 tons per week. Cost, £25,000)
Grey Pig for Foundry Cost pet Ton Pig
s d
Ore, 6 tons (mining, 2s 6d, drying, 6d.; concentrating, 1s 6d) 27 0
30 cwt. powdered coal 30 0
5 cwt. limestone 2 0
Labour 12 0
Repairs 8 0
Interest and depreciation 8 0
At furnace 87 0
Worth in Glasgow, July, 1914 66 0
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The resulting pig would at this price have a New Zealand market of about 4,000 tons per annum for foundry use, but the small cost of the plant—say, £25,000—would enable even this small output to be manufactured as an economic proposition. Another 1,000 tons could be refined while still molten to cast steel for steel castings, a good demand existing for these at remunerative prices. This, however, is the greatest extent to which the utilization of New Zealand iron-ores is likely to rise for many years, and all talk of plate and rail mills, shipbuilding, &c., and of New Zealand as a factor in the steel and iron business of the world, is quite ridiculous at present.