80 The N.Z. Journal of Science and Technology. [Mar. 
acid and basic types, according to the nature of the lining of the vessel, and 
again into side and bottom blown according to the method of blowing. The 
basic type requires high-phosphorus, low-silicon pig (say, 3 per cent. P and 
0-5 per cent. Si) for the charge, and with the addition of lime and the use of 
magnesite or dolomite for the lining the carbon and phosphorus are both 
burnt out during the blow. This pig is difficult to obtain, and the working- 
costs with this furnace are higher than with tte acid type. The bottom- 
blown vessels require a pressure of 30 lb. of air for the blow, and this means 
the provision of large and expensive blowing-engines, while side-blown 
vessels, owing to the smaller pressure from the iron above the tuyeres, need 
a blowing-pressure of only 5 lb. per square inch, and this can be arranged 
for with the much cheaper positive-pressure blowers. The advantage of 
the bottom-blown vessel is that the output is slightly greater in continuous 
working and the loss of metal in blowing slightly less; but these advantages 
have little bearing for the purposes we are considering. This leaves us 
with the side-blown acid-lined converter, of which the best-known type is 
the Tropenas. Two 1-ton vessels could attend to an output of 500-1,000 
tons per year, which would be a reasonable figure to assume as the basis 
for a beginning in a New Zealand foundry, and the plant would comprise 
a cupola to melt the charge, a positive-pressure blower and a motor to drive 
it, and a small furnace to heat the “ physic ” additions to the charge— 
i.e., ferro-manganese, ferro-silicon, ferro-aluminium, ferro-titanium, &c. The 
lining of the converter is comprised of silica bricks and ganister, and will 
need constant attention and frequent remaking — hence the need for two 
vessels. The cost of this plant at pre-war prices would be about £6,000. 
The charge will consist of (1) pig iron of a very close analysis containing 
4 per cent, or over of carbon, 2 per cent, or more of silicon, and not more 
than 0-04 per cent, of phosphorus or sulphur ; (2) mild-steel scrap* contain¬ 
ing not above 0*04 per cent, of phosphorus or sulphur (if such is freely 
available and cheaper than the haematite pig above mentioned, it can be 
used in quantities up to 40 per cent, of the pig) ; (3) steel-casting scrap, 
which will always be available to the extent of at least 30 per cent, of the 
charge from risers, runners, &c., from the foundry. The difficulty with 
this process lies chiefly in the sulphur. The foundry coke available in New 
Zealand contains at least 1 per cent, of sulphur, and it is practically 
impossible to obtain either the haematite pig or the mild - steel (boiler¬ 
plate, &c.) scrap with under 0-05 per cent, of sulphur. The result is that 
with the remelted foundry scrap to be worked off and the loss of metal in 
blowing (20 per cent.) there is no possibility of obtaining castings with under 
0*08 per cent, of sulphur, and little probability of beating 0-1 per cent. It is 
possible to desulphurize in the cupola by using an excess of lime flux in a 
jacketed cupola, or in the ladle by adding calcium chloride or fluoride (the 
“ Saniter ” process), but both these processes require metallurgical skill and 
care such as a small-foundry man cannot reasonably be expected to give. A 
modification of these acid-lined, side-blown converters, known as the “ Stock ” 
oil-fired converter, is decidedly better for New Zealand conditions. Here, 
in addition to the ordinary converter, means of heating the converter charge 
while in the converter by an oil-flame is added; thus the pig iron used can 
be lower in carbon and silicon, and therefore somewhat cheaper. If desired, 
the whole charge can be placed cold into the converter, and if Pennsylvania 
oil (which is low in sulphur) is used to heat and melt the charge, castings 
of very excellent quality low in sulphur can be poured. This procedure 
will, of course, be expensive, but might be used with advantage for special 
castings. In special cases, too, it may be cheaper to melt small charges 
in this way at times when the cupola is cold. The working-cost of the 
* Throughout this paper “ mild-steel scrap ” includes wrought iron. 
