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# How to loft multi section equal elbow

Multi section equal elbow, also known as “Xiami elbow”, is the most common setting out in actual production and is often used in pipeline construction and thermal insulation construction projects.
The number of elbow joints ranges from 3 to dozens or even hundreds; Some are made of plates, while others are made of finished tubes;
The bending angle ranges from 0 ° (excluding 0 °) to 180 ° (including 180 °). 90 ° is the most common one. 180 ° can be split into two 90 ° elbows for butt joint.
Because of the high frequency of use, today we will explain in detail how to carry out the lofting of multi section equal elbows.
1. Several important parameters for setting out calculation are described:

• (1). A is the angle of the elbow, R is the radius of the center line corner of the elbow (bending radius). It is required that 180>＝ A>0, R>=D. If the pipe is narrow, D0.6 * D is allowed, but the pipe resistance will increase. (The bending radius is not clear, please read the article “What is the bending radius of an elbow” in the riveter knowledge plate);
• (2). The elbow shall be cut into m sections, and the value of m shall be input according to the actual number of sections. During calculation, the two ends shall be calculated as half sections, and the middle section shall be calculated as one section, that is, the turning angle of each section is A/(m-1). M must be an integer. It is required that 3<=m<=48. The larger the value of m, the smoother and more beautiful the elbow will be, but the workload and cost will also increase. Generally, 15<=A/(m-1)<=25 will be taken;
• (3). The circumference is divided into n equal parts, and the circumference of the pipe must be divided into n equal parts to calculate the real length of each line segment. The value of n is determined by the operator according to the diameter and accuracy requirements, but it must be an integral multiple of 4. The larger the value of n, the higher the accuracy of the expanded map, but the workload of drawing the expanded map increases accordingly. Generally, n=16~36 can be used for accurate blanking by manual line drawing, and the numerical control cutting machine or engraving machine can be used for blanking or drawing the template in 1:1, and the n value can be larger;
• (4). The wall thickness of the round pipe, t, is 0 in the case of finished pipe manufacturing calculation, and the plate thickness should be entered in the case of plate cutting and coiling. The calculation of the material bank is based on the medium cost.

The following is an example of a five section, right angle elbow. The calculation parameters are shown in the figure below: Calculation parameters Parameter name Parameter value Outer diameter of round pipe (D) 620 Bending radius (R) 650 Number of elbow joints (m) 5 Bending angle (A) 90.0° Wall thickness of round pipe (t) 8 Circumference bisection (n) 16

The figure drawn according to the calculation data is as follows:

Overall expanded drawing: expanded length=1922.65, width=1034.34.
The starting point of the horizontal line at the top of the data on the figure is 0, the data increases downward, and the right bisector increases. 1). Fabricated with finished pipe (assuming the length unit is mm)

• (1) The finished pipe with a length of 1034.34mm should be cut;
• (2) . Divide the circular tube 16 equally and mark the dividing point;
• (3) Draw a horizontal line from L0 to L16: 129.29, 152.59, 172.33, 185.53, 190.16, 185.53;
• (4) . Connect the ends of two adjacent horizontal lines to form a circular line on the pipe (cut along this line when cutting);
• (5) . Continue to draw a horizontal line at the end of the horizontal line as the starting point, with the length of K16 to K0: 258.59, 212, 172.51, 146.12;
• (6) . Connect the ends of two adjacent horizontal lines to form a circular line on the pipe (cut along this line when cutting);
• (7) Repeat (5) and (6) according to the number of middle sections, and note that the data order is alternate;
• (8) Finally, it is cut along the loop line;
• (9) After the fabrication of each section of circular pipe, welding treatment shall be carried out. When the wall of circular pipe is thick, groove treatment shall be carried out.

2). Made of sheet (assuming the length is in mm)
1. End joint fabrication

• (1) Draw a rectangle with length=1922.65mm and width=190.16 on the plate;
• (2) . Divide 1922.65 into 16 equal portions, each 120.17mm long;
• (3) Make a long side vertical line and indicate the serial number. The length is L0 to L16: 129.29, 152.59, 172.33, 185.53, 190.16, 185.53;
• (4) Connect each end point smoothly, then form a cutting line, and cut along this line to obtain the end section plate;
• (5) Rolling to form end section circular tube.

2. Middle section production
The middle section is actually a back-to-back splicing of two end sections, so it can also be completed by making 2+middle sections * 2 end section plates, especially for skin insulation works

• (1) Draw a rectangle with length=1922.65mm and width=380.32 (190.16 * 2) on the plate, and draw the centerline;
• (2) Divide 1922.65 into 16 equal portions, each 120.17mm long;
• (3) Make a middle vertical line through each bisection point, indicate the serial number, and draw a plain line with the length from K0 to K16: 258.59, 212, 172.51, 146.12…. The length of the middle segment plain line of the corresponding serial number=the length of the end segment plain line of the corresponding serial number * 2;
• (4) Connect each end point smoothly, and then form a cutting line along which the middle section plate can be obtained. To make full use of the material, cut it into the shape of carp tail;
• (5) Coiling to form medium pitch circular tube.

After the fabrication of each section of circular pipe, welding treatment shall be carried out. When the plate is thick, groove treatment shall be carried out.