The fin-type electric heating tube processed by winding square hangs have regular ripples on the outer surface of the tube, and a certain pretension is given between them (due to the effect of tension and bending, the fins and the surface of the tube are in contact Indentation is formed), which increases the contact area between the sheet and the tube, reduces the thermal resistance, and greatly improves the power teaching per unit area of the tube. Generally it can be increased by 4-10 times. This processing method is continuous, with high productivity, and fins: tightly connected with the tube to the junction table, saving energy and materials。
What we turned around was the inner-shaped warp piece. The fins and the outer surface of the tube were tightly bound, and they were not loose. The diameter of the finned electric heating tube is usually 8 to 12 mm, and the height of the fin is 6 to 10 mm. Generally, the relative bending radius of the strip after standing vertically on the tube is ro: P / h <2 5 (pn: center of gravity Radius of layer curvature; h: original height of the strip). In order to reduce the springback of the radius of curvature of the fins after unloading, axial tension is added before the material is bent.
First, the pipe is clamped on the machine tool, and the tape is fixed on the pipe by the winding device. The spring is applied by the spring of the winding device and the pressure block to pick up the tape. . While the pipe rotates one turn, the winding device opens a pitch. After the forming of the winding device and the relative movement with the pipe, the tape is vertically, spirally and uniformly wound on the tube to form fins. This is to take the tape Stretching first and then bending, vertical cold winding in the process of plastic deformation of the round tube, the strip material is subjected to the combined action of axial tension and bending force distance, and its stress and stress become complex.
Axial tensile force is applied to the tape first, and all the fibers in the section are subjected to plastic stretching. The uniform elongation of the well produces stress under the action of tension. Then apply a sag M to the tape, the stress in the cross section changes, the outer layer fiber that has been stretched during bending continues to undergo plastic deformation, the stress on it increases, and the inner layer fiber unloads, so At the end of bending, there must be a fiber layer in the cross section, and the stress and strain of the fiber layer remain unchanged. In this way, the layers of fibers above the fiber layers are in a stretched state during the bending process, and the fibers below are compressed. During the bending process, as the curvature increases, the inner layer of fiber
Unloading, when the tensile stress will be reduced to zero and the curvature is further increased, compressive stress will appear in the cross section, when the internal fiber undergoes bending deformation up to。