Hose may be secured with a bursting strength of more than 1,000 pounds to
the square inch. Many operators prefer to distinguish between the oxygen
and acetylene lines by their color and to allow this, red is used for the
oxygen and black for acetylene.
_Other Materials._--Sheet asbestos and asbestos fibre in flakes are
used to cover parts of the work while preparing them for welding and during
the operation itself. The flakes and small pieces that become detached from
the large sheets are thrown into a bin where the completed small work is
placed to allow slow and even cooling while protected by the asbestos.
Asbestos fibre and also ordinary fireclay are often used to make a backing
or mould into a form that may be placed behind aluminum and some other
metals that flow at a low heat and which are accordingly difficult to
handle under ordinary methods. This forms a solid mould into which the
metal is practically cast as melted by the torch so that the desired shape
is secured without danger of the walls of metal breaking through and
flowing away.
Carbon blocks and rods are made in various shapes and sizes so that they
may be used to fill threaded holes and other places that it is desired to
protect during welding. These may be secured in rods of various diameters
up to one inch and in blocks of several different dimensions.
CHAPTER III
ACETYLENE GENERATORS
Acetylene generators used for producing the gas from the action of water on
calcium carbide are divided into three principal classes according to the
pressure under which they operate.
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