Bending methods

There are many ways to bend pipes, generally divided into manual pipe bending and mechanical pipe bending.

There are many mechanical bending methods, such as the 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 manual pipe bending and back bending pipe bending process. The back bending method is to bend the pipe on a rotary pipe bender, which can be divided into two types: molded pipe bend and dieless pipe bend.Manual pipe bending

Manual pipe bending does not require special equipment and complicated process equipment, it can bend pipes with various radii, angles and spatial directions. However, this pipe bending method has high labor intensity, low productivity and unstable quality.

Hand-bent steel pipes mostly adopt hot bending, and cold bending is suitable for stainless steel and non-ferrous metals.

Fill the pipe with a filler before bending the pipe. The filler for steel pipes is generally pure and dry fine sand. The filler for stainless steel and non-ferrous metals should use rosin, lead and other low melting point substances to prevent wrinkles and reduce ovality.

Die bend pipe

This type of pipe-bending machine uses die bending. The main molds are disc-shaped sheaves and croissant core heads.

When bending the pipe with a disc groove wheel, the bending die is on the outside of the pipe, half of the bent pipe 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 pressure roller).

The end of the pipe is fixed on the disc-shaped bending die by the chuck. If the pressure roller does not move, the disc-shaped bending die actively rotates to complete the pipe bending, which is called stretch bending;

If the pipe is pushed to make the disc-shaped bending die rotate passively to complete the pipe bending, it is called push bending;

If the disc-shaped bending die does not move, the pinch roller compresses the pipe and rotates around the disc-shaped bending die to complete the bending, which is called press bending.

When bending the pipe with a croissant core, the bending die is inside the pipe. The croissant core is shaped like a horn, the axis length is 1/4 of the circumference, the bending radius is the same as that of the bend pipe, and the maximum bending angle is 180°.

The thin end of the croissant core is slightly thinner than the inner diameter of the tube blank, and 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.

No die bend

The pipe bending machine used in this pipe bending method does not need to specifically determine the bending die of 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 stretched. When bending the pipe, the pipe is fixed on the rotating arm. The distance from the central axis of the pipe to the rotating center of the rotating arm is the bending radius.

When working, the tube is covered with a copper induction coil, and the induction coil is passed through the intermediate frequency (for thicker tubes) or high frequency (for thin tubes) to locally heat the tube to 900~950°C, and then bend the tube.

If the rotating arm actively rotates to bend the pipe, it is called stretch bending; if the end of the pipe is pushed, the pipe pushes the rotating arm to rotate, so as to realize the 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 make it cool quickly. The purpose of the water spray is to keep the heated section and deformation zone to a very small size, thereby preventing wrinkling and flattening of the tube.

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