Pipe bending can be categorized into three types: drawn bends, pressure bends and welded bends.
The drawn curves can be divided into cold drawn and hot drawn. This chapter mainly introduces the structural features, capabilities and operation of commonly used pipe bending equipment along with the calculation of pipe bending material.
I. General knowledge about pipe bending
A bent pipe is a pipe fitting that changes the direction of the piping. Bent pipes can be seen where pipes cross, bend, or wrap around beams.
Drawn bent tubes have excellent expansion capacity, high pressure resistance and low strength, making them commonly used in construction.
The main shapes of bent tubes include various angles of elbows, U-shaped tubes, forward and backward bends (also known as Z-bends), and curved tubes, as shown in Figure 1-1.
An elbow is a pipe fitting with an arbitrary bend angle, used at bends in a pipe. The radius of curvature of the elbow is represented by R. When R is larger, the bent part of the pipe is larger, making the curvature smoother. When R is smaller, the bent part of the tube is smaller, resulting in a steeper curvature.
A forward and backward bend is a pipe connection with two bend angles (usually 135°). The distance between the center lines of the bent ends of a pipe bent back and forth is called the height of the forward and back bend, represented by the letter h. It is generally used when connecting internal heating risers with mains and radiators and when connecting pipes with joints that are not in the same plane.
A U-shaped pipe is a semicircular pipe fitting. The distance d between the center lines of the two ends of the tube is equal to twice the radius of curvature R. U-shaped tubes can replace two 90° elbows and are often used to connect two arranged round-wing radiators vertically.
Generally, wrinkles are not allowed to develop during pipe bending. If there are individual irregular areas, their height must not exceed the following limits: when the diameter is less than or equal to 125mm, it must not exceed 4mm; when the diameter is less than or equal to 200mm, it must not exceed 5mm.
II. Calculation and Cutting of Flexible Tube
Before carrying out pipe bending work, the length of the bent section of the pipe must first be calculated and the starting point of bending should be marked so that the correct semi-finished part can be obtained after bending.
1 . Calculation of the tube bent at 90°
Pipes bent at 90° are most widely used in pipeline engineering, and their bending radius varies due to different manufacturing methods. For cold bent pipes, R=(4~6)D is generally used; for hot-bent tubes, R = 4D is considered; For stamped elbows or welded elbows, R=(1~1.5)D is generally used. After determining the bending radius, the cutting length of the bent part can be calculated and the heating length during hot bending can be determined, as shown in Figure 1-3.
As can be seen from the figure, after the tube is bent, the outer arc and inner arc of the bent section are not the actual lengths of the original straight tube, but only the center line length of the bent tube remains unchanged before and after bending. bends, and its unfolded length is equal to the original length of the straight section of the tube. Now, let's assume that the starting and ending points of the folded section are a and b.
When the bending angle is 90°, the length of the bent section of the tube is exactly 1/4 of the circumference of the circle drawn with radius r, and its arc length is represented by the radius of curvature, which is
Arc length ab=2πR/4=1.57R
From equation (1-3), it can be known that the unfolded length of the tube bent at 90° is 1.57 times the radius of curvature.
- 1-Reducer
- 2 engines
- 3 tubes
- 4 Support Roll
- 5 heating coil
- 6-Heating Zone
- 7-Chuck
- 8-swingarm
