Precautions for pipe bender with anti-wrinkle die when processing pipes
When processing pipes with mandrel tube bender, the material inner side of center-line is compressed. When the pipe is bent to a certain angle, the material will be pushed back and exceed the tangent point due to the large compression force of the material. The pipe will form wrinkles if the machine doesn’t have mandrel to support this area. To use anti-wrinkle die increase support in this area to make the pipe wall uniformly thickened after compression; this can avoid the production of wrinkle. But the anti-wrinkle die can’t eliminate wrinkles if the wrinkles have formed due to improper adjustment. Even if it is flattened by the mandrel and the bending die later, the wrinkles cannot be eliminated. When the bending completed, a large wrinkle will be formed on the tube.
The anti-wrinkle die should be applied a layer of oil during bending. But it is also cause wrinkles if the oil are too much or too thick in this area.
Ball mandrel is often used at the same time as anti-wrinkle die. The work of anti-wrinkle die is to prevent pipes from wrinkling during bending; the work of ball mandrel is to keep the tube after leaving the mandrel support point, this can prevent tube from collapsing. If there are some pipes with thin wall, large diameter and small bending radius need to be processed, workers should pay attention to the following tips to avoid wrinkle:
1.To reduce a drag between mandrel and inner wall of pipe. The inner chamber shall be blown by wet sand before bend the pipe.
2.The Pipe bending machine tool and spindle shall be rigid enough.
3.The mandrel rod shall be rigid enough try to eliminate shaking and stretching caused by the rod.
4.The radial clearance between the inner diameter of the mandrel and the pipe should be not greater than 10% of the wall thickness.
5.The clamping die, compression mold, mandrel and anti-wrinkle mold should be properly adjusted; especially the pressure of compression mold should be carefully selected and adjusted.
There is a thorny problem that clamping of clamping die during bending the pipe with large diameter. This requires that the straight line between the two bends of the pipe be longer and the clamping die be wider. To do that can Increase clamping force to ensure completion of bending. If the clamping die is too narrow and don’t have enough clamping force during bending, the pipe will slip and didn’t go on, the bend processing can’t continue.
- To select an appropriate amount of lubricating oil.
- The material supply status is also very important. For stainless steel pipes, the hardness is HB=180 ～ 220, and HB=180 is the most suitable.
The shape of anti-wrinkle die is important. The groove through which the pipe slides should slightly larger than the outer diameter of the pipe; it can be 10% of the wall thickness. And carefully polish to prevent pipe from scratching.
The front section of anti-wrinkle die should be produced very thin and extend to the contact point of the bending die. The anti-wrinkle die is supported by the bending die, and fixed to form a closed cavity. When installing the anti-wrinkle die, in order to reduce resistance during bending, there should be a small taper. The pressure of the die should be adjusted properly. When installing and adjusting the anti-wrinkle die, the best way is to use the function of “mandrel adjustment” under the condition of clamping die is tightened.