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Steelworker Volume 02 - Building manual for how to work with steel | Next
Figure 3-65.—90-degree bend made with ten separate wrinkles. |
conform to the bend or bends of the pipe to be made.
It is used to lay off the bend area on the pipe and as a
guide during the pipe or tube bending operation.
Figure 3-61 shows the use of a center line template.
These templates are made of wire, or rod, and are
shaped to establish the center line of the pipe to be
installed. The ends of the wire are secured to special
clamps, called flange spiders. A clearance disc, which
must be the same diameter as the pipe, is used if there
is any doubt about the clearance around the pipe.
HOT BENDS
Hot bends are accomplished on a bending slab
(fig. 3-62). This slab requires little maintenance
beyond a light coating of machine oil to keep rust in
check.
As a preliminary step in hot bending, pack the pipe
with dry sand to prevent the heel or outside of the bend
from flattening. If flattening occurs, it will reduce the
Figure 3-61.—Center line template.
Figure 3-62.—Bending on a slab.
cross-sectional area of the pipe and restrict the flow of
fluid through the system.
Drive a tapered, wooden plug into one end of the
pipe. Place the pipe in a vertical position with the
plugged end down, and fill it with dry sand. Leave just
enough space at the upper end to take a second plug.
To ensure that the sand is tightly packed, tap the pipe
continually with a wooden or rawhide mallet during
the filling operation. The second plug is identical with
the first, except that a small vent hole is drilled through
its length; this vent permits the escape of any gases
(mostly steam) that may form in the packed pipe when
heat is applied. No matter how dry the sand may
appear, there is always a possibility that some
moisture is present. This moisture will form steam that
will expand and build up pressure in the heated pipe
unless some means of escape is provided. If you do
not provide a vent, you will almost certainly blow out
one of the plugs before you get the pipe bent.
When you have packed the pipe with sand, the
next step is to heat the pipe and make the bend. Mark
the bend area of the pipe with chalk or soapstone, and
heat it to an even red heat along the distance indicated
from A to B in figure 3-63. Apply heat to the bend area
frost on the outside of the bend and then on the inside.
When an even heat has been obtained, bend the pipe
to conform to the wire template. The template is also
used to mark the bend area-on the pipe. -
Figure 3-63.—Heating and bending pipe to conform to wire
template.
3-27
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