THE GROUP
Pipe Bending - when pipe bending is used
Every fitting is a possible source for a future leak. Vibration, pressure, corrosion, and chemical breakdown of the fitting materials are causes of fitting failure. In some circumstances pipefitters and plumbers wish to have as few fittings and welds as possible to avoid future sources of leakage. This can be important in heating pipes which are to be buried in concrete, boiler piping inside boiler casings, hydraulic piping, and others. The best solution to these situations is often to substitute pipe bends in place of fittings wherever possible. When a pipe is bent , the outside of the bend is stretched and the inside is compressed. The stretched outside has safety considerations. When the pipe wall is stretched it becomes thinner. The general practice, with standard weight pipe , is to minimize this thinning by limiting the radius of the bend to no less than five times the pipe size. A bending wheel is a steel or cast iron circle that is pressed into the pipe to make the bend . A groove is machined into its perimeter to a depth of one-half the pipe diameter. If the bending wheel is measured across its greatest width and this is divided by 2, the radius of the bend that this particular bending wheel will make is obtained. Pipe bending on too short a radius will flatten the pipe and reduce its carrying capacity.
There are two kinds of pipe bending methods. In the first, the bending wheel is pressed into the pipe , which is held in position by two " bending blocks ". The beginning contact point between the machine and the pipe is the center of the arc of the finished bend.
The other kind of bending machine grasps the pipe to the wheel at the beginning of the bend and then rotates the wheel, forcing the pipe to bend with the wheel as it rotates. This makes all calculations start at the beginning of the arc of the bend. This is the type process found in small hand benders used for hydraulic, gas, and air pressure lines, but it is also used in heavy pipe fabrication shops where pipe sizes 8" IPS and more are bent on a machine weighing many tons.
If we make a 90° bend in the center of a piece of pipe 24 inches long, how long will the pipe tangents be? We can't be exactly sure, except to say that they will not be 12 inches long. We can't be certain because the size of the pipe is not known and, therefore, the radius of the bending wheel is not known. But the reason that the length of the pipe tangents added together is greater than 24 inches is that the pipe takes a short-cut across the angle of the bend. This shortcut results in what pipefitters call gain.
The pipe bending machine
This machine has been designed to bend pipes already cut and is especially suitable for bending long elements or those requiring multiple curves at both ends of the pipe. The pipe ending machine can bend pipes whose ends have already been worked (e.g., profiling, tapering, etc.), within the limits of compatibility with bending head dimensions.