Full resolution (JPEG) - On this page / på denna sida - Second part - IX. Mining Industry and Metal Production - 2. The Iron and Steel Industry. By the late Prof. J. G. Wiborgh - Ingot iron (Steel)
<< prev. page << föreg. sida << >> nästa sida >> next page >>
Below is the raw OCR text
from the above scanned image.
Do you see an error? Proofread the page now!
Här nedan syns maskintolkade texten från faksimilbilden ovan.
Ser du något fel? Korrekturläs sidan nu!
This page has never been proofread. / Denna sida har aldrig korrekturlästs.
wrought iron.
743
over the edge of the anvil; the more bendings the steel will stand without
breaking, the less red short it is. For percentages of carbon below 0*5o,
however, it is customary at a red heat to punch a hole near the edge of the iron
bar, and if cracks appear, the iron is red short.
After it has been ascertained in aforesaid manner that the steel has the
desired degree of hardness, it is tapped from the converter into moulds. Only
in case the test of red shortness has proved unsatisfactory, ferro-manganese is
added in the converter before the tapping. As has already been said, such an
addition is generally not necessary for steel, but must nearly always be made for
soft iron.
As long as there were small and insufficient stoves at the Bessemer blast
furnaces, it was often difficult to make a sufficiently hot iron, wherefore the s$eel
also turned cold in the tapping. This circumstance caused Mr. Caspersson
(1880) to design a ladle, which, after finished blowing, is secured to the mouth
of the converter, and as the converter afterwards is turned down, part of the
steel runs into the ladle, and is afterwards in the usual way poured into
the moulds.
The largest portion of the steel is by means of this device left in the hot
converter during the tapping, and is not subjected to the cooling which therefore
takes place when the steel is tapped all at once into a large and comparatively
cool ladle. Fig. on paxe 744 shows a converter with a Caspersson converter-ladle
attached. The converter-ladle is, however, attented with certain disadvantages,
among others that the moulds must be placed close to the converter and be
moveable. At the present time this kind of ladle is less commonly used, and
generally only in cases when soft steel or iron is to be made.
During the tapping still other samples of the steel are taken, from which
carbon determinations are made by Eggertz’ colorimetric test, frequently also for
other substances, such as phosphorus, silicon, manganese, and sulphur.
As a rule, the carbon tests agree very accurately with the degrees of
hardness determined during the process by means of forging tests, which are
also denoted in percentages of carbon. This ought indeed to be the case, the
Swedish Bessemer steel being high in carbon and comparatively free from silicon
and manganese. Only exceptionally, as when the steel has been too hot and has
become too hard by taking up silicon and manganese, these tests do not agree.
In order to protect the moulds against the hot steel, some sawdust or oil
is placed in the bottom, and in order to prevent a further generation of gas
after the mould is filled, it is covered with a cast iron lid, sand, or the like.
As several hours generally elapse between the blows, both the converter and
ladles cool off and must therefore be specially heated before the blowing, which
is sometimes accomplished by coke or charcoal, but usually with blast furnace
gas which is burned in burners especially designed for this purpose.
The Swedish converters are small. The diameter of the bottom is I to 1*3
meter, the diameter of the cylindrical part is l’s—1*7, and the height 2—2-5
meters, all inside measurements. In order to retain the heat in the furnace as
much as possible, the mouth is made narrow, 200 or, at the most, 300
millimeters.
At one of the Swedish Bessemer works, namely Avesta, a very small converter
is used. In 1878, a small Bessemer furnace of ordinary construction was erected
there, intended for charges only weighing 200 kilograms. This furnace has since
been exchanged for one somewhat larger, according to Robert’s design, and the
size of the charge is a little over one ton. This latter Bessemer furnace has
only one tuyere, and in tapping the steel, Caspersson’s converter-ladle is used.
The real advantage of these small converters is that the process does not
require such large and powerful blowing-machines, but, on the other hand, the
<< prev. page << föreg. sida << >> nästa sida >> next page >>
