Something has been said under another heading of the nature and
requisite quality of the materials entering into the structure of the
boiler. Too much emphasis cannot be laid upon the necessity for the use
of the very best iron and steel that can be manufactured, and the most
skillful and thorough workmanship that can be performed in constructing
the boiler.
It is becoming the practice, both for land and marine boilers, for
boiler plate makers to furnish “test pieces” from each sheet or plate
that goes into the construction of a boiler, and a sheet showing the
tensile strength of each sheet or plate that enters into its make up.
But irrespective of this practice each plate entering into boiler
construction will be found to have one of the following marks, which
designate its quality and method of manufacture. The name “Charcoal
Iron” is used because in its manufacture wood charcoal is employed
instead of mineral fuel.
“Charcoal No. 1 Iron” (C. No. 1) is made entirely of charcoal iron. It
has a tenacity of 40,000 pounds per square inch in the direction of the
fibre. It is hard, but not very ductile, and should never be used for
flanging.
“Charcoal Hammered No. 1 Shell Iron” (C. H. No. 1 S.), although not
necessarily hammered, has been worked up before it is rolled into
plates. It has a tenacity of 50,000 to 55,000 pounds per square inch in
the direction of the fibre. It is rather hard iron, and should not be
flanged. It is used for the outside shell of boilers.
“Flange Iron” (C. H. No. 1 F.), is a ductile material which can be
flanged in every direction. It has a tenacity of 50,000 to 55,000
pounds per square inch along the fibre.
“Fire Box Iron” (C. H. No. 1 F. B.), is a harder quality, designed
especially to withstand the destructive effect of the impinging flame,
and is used for boxes and flue-sheets.
The letters in the brackets exhibit the plate stamp.
Cast iron and copper were used in an early day for steam boilers and
the former is still extensively used for certain forms of low pressure
steam heaters made for various purposes, such as green houses, etc.