The bend pipe can be divided into stewing bend pipe, stamping bend pipe and welding bend pipe according to different manufacturing method. Simmer bend is divided into cold and hot simmer two. This chapter focuses on the structure, characteristics, operation and other knowledge of the commonly used tube cleaning equipment, as well as the cutting calculation of the simmer bend pipe.General knowledge of elbowA bend is a pipe that changes the direction of a pipe. At the cross, turn, head etc., can see the elbow.The heating system has the advantages of good flexibility, high pressure resistance and low resistance. Therefore, it is often used in construction.The main forms of the elbow include: elbows of various angles, U tubes, back and forth bending (or called "B" bend) and curved elbows, as shown in Figure 1 - 1.An elbow is a pipe with an arbitrary bend angle, used in the bend of a pipe. The bending radius of the elbow is indicated by R. When R is bigger, the bending part of the pipe is larger, the elbow is smoother; the bending part of the pipe is smaller and the bending is more urgent when the R is smaller.A bend is a pipe with two curved angles (usually 135 degrees). Back and forth Wanguanzi curved end of the distance between the center line and is called bending height, represented by the letter H. The interior heating vertical branch pipe is connected with the dry pipe and the radiator. When the pipe is connected with the contact which is not on the same plane, it is generally necessary to use the back and forth bending.The U tube is a regular semicircular tube. The distance between the ends of the pipe line is equal to two times D, and the bending radius is R. The U tube can be used instead of two 90 degree elbows and is often used to connect the two round fin radiators placed up and down.An arc bend is a pipe with three curved angles. The middle angle is generally 90 degrees, and the side angle is 135 degrees. An arc bend is used to bypass other pipes, and curved elbows are often used in sanitary equipment piping provided with cold and hot water.The size of the bend is determined by the diameter, the bending angle and the bending radius of the three. The bending angle shall be determined according to the drawing and the actual situation of the construction site, then the sample plate shall be produced, the sample shall be simmered according to the model, and the bending angle of the heating system shall be checked according to the requirements of the heating system. Model can be cooked round bar system, the diameter of the rounds according to the size of the stew diameter, 10-14mm can. The bending radius of the bent pipe shall be determined according to the size of the pipe diameter, the design requirements and the relevant regulations. Neither too big nor too small to choose too small. Because the bending radius is too large, not only for the material, and occupied part of the tube bending is large, it will bring difficulties to the pipeline assembly; the bending radius is chosen too hours, due to excessive elongation and elbow thinning of the back wall, reduce its strength, and in the side wall of elbow is compressed form wrinkle state. Therefore, the general provisions: the bending radius of hot bending elbows should be no less than 3.5 times the pipe diameter; cold bending pipe bending radius should not be less than 4 times the pipe diameter; bending radius of welding elbow should be no less than 1.5 times the pipe diameter; stamping elbow bending radius should be not less than the pipe diameter.When bending the pipe, the metal on the inside of the elbow is compressed and the wall of the pipe is thickened; the metal on the back of the elbow is stretched and the tube wall is thinned. The smaller the bend radius, the more serious the wall thinning at the back of the elbow and the greater the effect on the back strength. In order to make the bending of the pipe does not change the original work performance, it is generally stipulated that the tube thinning rate shall not exceed 15% after bending of the pipe. The tube wall thinning rate can be calculated by pressing type:In A, the thinning rate of pipe wall at the outside of the pipe after bending (%);DW - pipe outer diameter (mm);R -- bend radius of pipe (mm).When the bend is bent, the thickness of the bent pipe section changes from the original circle to the ellipse because of the change of the thickness of the inside and outside side walls of the pipe bend section. Bend section shape change, will make the flow section area of reducing tube, thereby increasing the fluid resistance ability, but also reducing the pipe under internal pressure of the pipe so general elliptic rate do the following provisions: diameter less than or equal to 150mm, the elliptical ratio shall not be greater than 10%; the diameter is less than or equal to 200mm. The ellipticity of not more than 8%.The ellipticity of the pipe can be calculated by pressing type:Formula T -- ellipticity (%);D1 - the maximum diameter (mm) at the maximum elliptical deformation;D2 - the maximum diameter (mm) at the maximum elliptical deformation.When the cold bend pipe or hot bend pipe is made of water, gas pipe and straight welded pipe, the welds of the pipe shall be located at 45 degrees from the center line of the side, as shown in figure 1-2. In order to avoid bending, the pipe weld cracking.Bend generally do not allow wrinkles, such as some rough places, the height is not greater than the following provisions: diameter less than or equal to 125mm, no more than 4mm; the diameter is less than or equal to 200mm, no more than 5mm.