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Cold bending and hot bending in pipe bending

Before bending the pipe

Pipe bending is a kind of processing technology in the bending of profiles. Good pipe bending is an art. It requires us to think in many ways before performing the bending.

When bending a pipe, you need to consider many different factors to get the job done as well as possible.

You need to make sure that you have enough experience to do the job well, you have all the right equipment, and you are using the right method to bend.

There are many types of bending, but the simplest classification method is to divide them into hot bending and cold bending.

There are pros and cons to both hot and cold bending, depending on the type of material you need to be bent and the angle of the bend required.

Cold bending

Cold bending refers to all types of bending that do not use any additional heat to bend the pipe.

Cold bending is done by machines without inducting any heat into the material to be bent. These machines will generally wrap a pipe or sheet of material around a shape with a force that causes the pipe to bend.

This process is quick and the materials don’t need to cool down afterwards; however, cold bending can have disadvantages if materials are fragile.

Cold bending machine vs hot bending machine

Normally, the work pieces are bent under cold conditions (cold pipe bending).

The work piece has to be heated only when working with very thick sheet metal or very small bending radii, in order to keep the required bending forces down and to avoid brittleness of the material due to low temperature.

Cold bending machinery is usually lower in cost than hot bending machinery, as it is less complex. This can make it an attractive option for smaller companies.

WHO NEEDS COLD BENDING?

Cold bent steel has many applications.

  • Curved steel formed by cold bending is frequently used in the construction of buildings and bridges and is especially impressive when left exposed to view;
  • Shipbuilders, railroads and automobile manufacturers also use cold bent steel products;
  • The petrochemical industry uses curved and coiled piping for processing and transporting their products;
  • Cold bent steel also has many other industrial and food-processing uses as well.

Features of pipe bending for cold bending

Cold bending of bending pipes
Cold bending of bending pipes

The cold bending process is usually performed by wrapping a tube or other material around a mold or shape, causing the tube to bend. The process is quite fast, or even faster, because there is no need for cooling or processing in any particular way after performing the bending.

Since the machines used for cold bending are usually not very expensive, and because they are not particularly complex or advanced, cold bending is a good choice for small companies without a large budget.

This is also a good method for companies that do not specialize in bending but only need to perform it every once in a while.

Disadvantages of cold bending

The downside of all types of cold bending is that it is impossible to bend completely.

Cold aluminum profile bending machine

Pipe cold bending machine

Hot bending

Hot bending generally refers to different types of induction bending. Hot bending are highly effective at bending pipes because they are fast, precise, and make few errors.

Features of pipe bending for Hot bending

Induction bending is a very effective method of pipe bending because it is fast, accurate and almost error-free.

The induction bending process is performed by heating a certain point of the pipe, which can then be bent effortlessly. It does not require any filling material, and the result of bending tends to keep deformation to a minimum.

Many induction bending machines also choose this type of bending because of its sufficient energy. The heating process is the most time-consuming element of the process, after the heating process is completed, bending does not require much time at all.

Disadvantages of hot bending

The downside of hot bending may be that the material must be cooled later, increasing the time spent on each pipe, and the machines tend to be more expensive than cold bending equipment. To

Advantages of cold bending of pipe bending

Metal properties

Cold bending of bending tubes
Cold bending of bending tubes

Due to the work hardening of the metal during cold bending, the metal tube after cold bending is much harder than the metal tube after hot bending, but cold bending will not destroy the original properties of the metal. After cold bending, there is no need to clean and remove the oxide scale, and there will be no thermal deformation.

Energy consumption

Compared with hot bending, cold bending requires more bending power, and the springback and residual stress are significantly increased. And cold bending cannot bend sharp bends with a small radius of curvature.

Advantages of hot bending of pipe bending

Hot bending has the incomparable adaptability of cold bending.

  • For example, the straight line distance between two adjacent elbows on a pipe can be kept small, and even continuous bending can be carried out without leaving straight pipe sections;
  • Can process materials with poor cold ductility into elbows;
  • It can process elbows that require a lot of mechanical energy during cold bending, and can bend brittle materials that are easy to break during cold bending. Hot bending can be bent into a small radius elbow on the pipe.
  • For carbon steel pipes and most alloy steel pipes, the bending radius of hot bending is much smaller than that of cold bending, and the bending radius can be as small as 0.7 to 1.5 times the outer diameter of the pipe.

Disadvantages of hot bending

The equipment is complex, the processing cost is high, the production efficiency is low, and the surface finish is poor.

For copper pipes, the cold bending process is used, which eliminates the possibility of “hydrogen disease” due to the elimination of high temperature heating.

square tube bending machine for sale
square pipe bending machine

China’s marine elbow technical conditions

  • The pipe bending should be cold bending as far as possible, and hot bending is only allowed under the following conditions:
  • The bending radius of the pipe is smaller than the bending radius specified by the cold bending, or smaller than the bending radius of the existing mold.
  • The pipe shape is complicated or there is no straight pipe section between the elbows, so it cannot be tightened on the pipe bender.
  • If the tube wall is too thin, it is prone to large collapse and wrinkles after cold bending.
  • For pipes with larger diameters or infrequently used, there is no such mold at present.
  • When the pipe wall is too thick to be cold-formed.

THEORY OF THE COLD PIPE BENDING PROCESS

VVideo of cold-formed Φ168mm steel pipe (Malaysia)

Video of cold-formed Φ510mm steel pipe (UAE)