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 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.Continue Reading