Pipe rolling or tube bending is the general name for the forming metal process which is used to form a rolled pipe or tube permanently. There is a difference between freedom-bending and form-bound process. There is also a difference between cold forming and heat supported process.
Form bound rolling process which is like press bending is used in forming a work piece in order to make it into a shape of a die. A rolling machine is used to form a straight tube stock to a rolled pipe or different forms of rolled pipes and to shape the piece into a form that is needed.
The procedure is also used in forming shapes that are complex out of various kinds of elastic metal. The process of freedom bending which is like three-roll-push bending usually shapes the work piece, therefore the bending curve does not depend on the tool geometry.
A rolled pipe generally uses round stock. In other cases, rectangular and square pipes and tubes are bent for various specifications of jobs. There are factors involved in the process of tube bending. These factors used in shaping the material are the thickness of its wall, lubricants that are needed by the tube or pipe bender and tooling.
There are many angles and methods used to bend or roll a pipe and tube. The common and simple rolls consist of creating U-bends which are 180 degrees bend and elbows which range from 2 to 90 degrees. More intricate geometries are two-dimensional and three-dimensional bends. The difference between the two is that the 2D pipe has overtures on the same plane and 3D has overtures on various planes.
A bend that has a bend in the elevation or plan view is called a two plane bend. To calculate a 2 plane bend one has to know the bend’s rotation and angle which is known as dihedral angle.
When the work piece is bending, it changes the thickness of its wall. The wall on the outer radius of the pipe or tube becomes thinner while the inner wall becomes thicker. To avoid such from happening, the tube has to be sustained externally or internally to reserve the cross section. The inner part of the wall can wrinkle depending on the bending process, bend angle and the wall thickness.
The process begins with inserting a tube into a pipe roller and fastening it into the place between two dies which are the forming die and the clamping block. The tube is also held loosely by other two dies, the pressure die and the wiper die.
Pipe rolling uses mechanical force to push tubing against a die. This forces the pipe to imitate the shape of the die. Another type of processing is pushing stock through rollers to bend it in a curve that is simple.
A heat coil is put around a tiny section of the pipe at the bending point. Then it is heated to between 430 and 1200 degrees Celsius. When the pipe is hot, pressure is inserted on the pipe to make it bend. The heat on the pipe is then finished with air or with water spray. Large pipes like petroleum pipe lines, freeway signs and power plants are the ones that use heat induction bending.