There are many methods of pipe bending, generally divided into manual pipe bending and mechanical pipe bending.
There are many kinds of mechanical bending methods, such as the pressing bending method, rolling bending method, back bending method and extrusion bending method.
No matter what kind of pipe bending method, the main contradiction in the whole pipe bending process is how to overcome the problem of local deformation.
The most widely used in engineering is the manual pipe bending and back-bending method. The back-bending method is to bend the pipe on a rotary pipe bender, which can be divided into two types: die-bending and die-free bending.
Manual pipe bending does not require special equipment and complex process equipment, and it can bend pipes with various radii, angles and spatial orientations. However, this pipe bending method is labor-intensive, low in productivity, and unstable in quality.
Hot bending is often used for hand-bent steel pipes, and cold bending should be used for stainless steel and non-ferrous metals.
Fill the pipe with filler before bending the pipe. The steel pipe filler is generally pure and dry fine sand. The stainless steel and non-ferrous metal fillers should use low melting point substances such as rosin and lead to prevent wrinkles and reduce ovality.
This type of pipe bender uses die bending. The main molds are disc-shaped sheaves and claw heads.
When bending the pipe with the disc-shaped groove wheel, the bending die is on the outside of the pipe, half of the pipe bend lies in the groove, and the other half of the pipe in the bending area is pressed by a small roller with groove (also called a pressing roller).
The end of the tube is fixed on the disc-shaped bending die by the chuck. If the pressing roller does not move, the disc-shaped bending die automatically rotates to complete the bending of the tube, which is called the pull-bending type;
If the pipe is pushed, the disc-shaped bending die is driven to rotate to complete the bending, which is called push bending;
If the disc-shaped bending die does not move, the pressing roller presses the tube and rotates around the disc-shaped bending die to complete the bending, which is called press bending.
When bending the tube with the horn core head, the bending die is on the inside of the tube. The horn core head is like a horn, the axis length is 1/4 of the circumference, the bending radius is the same as that of the elbow, and the maximum bending angle is 180°.
The thin end of the horn core head is slightly thinner than the inner diameter of the tube blank, the tube blank is inserted from the thin end, and the thick end is the outlet, which is slightly thicker than the inner diameter of the tube blank. When bending the tube, the tube blank is first heated and then inserted into the mold. Under the action of thrust, the tube undergoes two processes of bending and expansion, and it is bent and formed when it slides out of the end of the core head.
The pipe bender used in this pipe bending method does not need a bending die that specifically determines a certain bending radius.
It can be divided into two types: pull-bend and push-bend. The pipe bending machine has a rotating arm, and the length of the arm can be retracted. When bending the pipe, the pipe is fixed on the rotating arm. The distance from the central axis of the pipe to the rotation center of the rotating arm is the bending radius.
When working, the pipe is covered with a copper induction coil, and the induction coil is passed through the intermediate frequency (for thicker pipes) or high frequency (for thin pipes) to locally heat the pipe to 900~950 ° C, and then bend the pipe.
If the rotating arm actively rotates, the back-bending of the pipe is called pull-bending; if the end of the pipe is thrust, the pipe pushes the rotating arm to rotate, so as to realize the return-bending of the pipe, which is called push-bending.
Then spray water from a circle of small holes inside the induction coil to the bent pipe section to cool it quickly. The purpose of the water spray is to limit the heating section and deformation zone to a very small extent, thereby preventing the tube from wrinkling and squashing.