Hot And Cold Pipe Bending Techniques: Advantages And Disadvantages
Pipe bending techniques are varied and offer different advantages and disadvantages within particular settings. This article offers an introduction to pipe bending techniques and the choices that inform which option to use.
For the physical act of bending pipes, many different processes have been discovered and perfect over the course of humankind’s long metalworking history, some of which use mechanical force and some of which require heat treatment. The most frequently used among them are ram, roll and heat induction. Others include the rotary-draw, sand-packing and hot-slab forming techniques.
The first of all pipe bending techniques ever used was probably ram pipe bending, as it could be executed without the assistance of excessive heat. One simply pushes a die against the pipe using mechanical force, causing the pipe to conform to the contour of the die. You can obtain more deformation the thinner the metal you’re bending is.
The maximum angle for this pipe bending technique is usually 90 degrees. It is still used in the making of furniture tubing, conduit pipes and handrails.
Roll pipe bending involves using a series of spool-like rollers to apply pressure to the pipe, which passes through them. The location of the rollers can be changed to obtain the radius you need. You can use this process for forming helical pipe coils. Another use is for making the long sweeping sections used in steel construction and some roofing components.
Rotary draw pipe bending machines fit a steel die flush inside the pipe and rotate a steel die to cause the pipe to conform to the radius of the die. This steel plug supports the pipe from the interior and reduces the potential for any cross section flattening. A clamp device secures the pipe, while the bending machine rotates to the die. This process can produce high quality; tight radius bends and has a lot of applications.
In the case of heat induction, a coil is placed around the pipe. The coil heats a section of the pipe to a temperature between 800 and 2200 F. The temperature depends on the material. The pipe passes through the coil at a gradual rate while a bending force is mechanically applied to the pipe. The products thus obtained are generally of high quality, but cost significantly more to produce.
The sand-packing and hot-slab forming pipe bending techniques involve placing the pipe in a furnace and heating it to above 1600 F. It is an old process but one that hasn’t really been improved on for its flexibility when it comes to unique applications, and so is still in common use.
The mechanical properties of the materials are altered during the process of bending. Cold forming causes yield and tensile strengths to rise by 10%, while elongation may decrease by as much as15%. Bending of the pipe will also tend to result in distortions of the cross section. The distortions are greater the tighter the radius of the pipe.
You really do not need expensive tools to bend pipes. The cheapest method is ram style bending, which is perfectly suitable for making electrical conduits and other light gauge products.
If you are interested in a good finish and constant diameters, the best method is rotary draw bending. For larger circumferences, ring roll bending is the best solution. To obtain the smallest amount of deformation, you can use mandrel bending. It is used in the manufacturing of turbocharger exhaust pipes, dairy tubing, stainless and aluminum tubing and in any other applications where non-deformed diameter is extremely important.
If you haven’t found mention of a form of pipe bending appropriate to your needs, try a little googling – the online metalsmithing community is large and enthusiastic, so you’ll be sure to find a site or forum on which your question has already been answered. Choosing the right solution from the stable of pipe bending techniques will be key to achieving the high performance results you’re looking for.