Professional analysis of stamping technology in the mechanical processes of tube sheet manufacturing plants

Thread Content

A tube sheet is a component in which holes slightly larger than the outer diameter of the tubes are drilled in a circular steel plate; the tubes are inserted through these holes and then welded in place. In the calculations for fixed tube sheets, the axial stress of the shell, the axial stress of the heat exchange tubes, and the pulling force q between the heat exchange tubes and the tube sheet are determined under various operating conditions with temperature differences. If any of these values fails to meet the strength (or stability) requirements, it is necessary to install expansion joints. In the strength verification calculations for fixed tube sheets, once the thickness of the tube sheet is determined, if no expansion joints are used, the strength of the tube sheet may be insufficient; however, by installing expansion joints, the required thickness for the tube sheet can be achieved. At this time, expansion joints can also be installed to thin the tube sheet, but the decision should be based on a comprehensive evaluation of factors such as material consumption, manufacturing difficulty, safety, and economic efficiency. U-shaped expansion joints are commonly used in fixed-tube-sheet heat exchangers, offering advantages such as a compact and simple structure, good compensation performance, and low cost. The precision of tube sheet processing, particularly the tolerance of tube hole spacing and tube diameter, as well as verticality and surface finish, greatly affects the assembly and performance of the chemical equipment listed above. As chemical processing equipment and power plants become larger, the diameter of their tube sheets also increases; tube sheets with a diameter of 4m–5m are quite common. Large tube sheets are characterized by a large number of tubes, which are arranged closely together; the tube holes are small and deep, and high requirements are placed on precision and surface finish. The girth plates used for pressure vessels of categories 3 and 4 require a high level of precision; the traditional methods for hole machining involve marking with a bench vise and drilling using a swing drill. As chemical processing vessels become larger, the diameter of the tube sheets also increases, and their thickness grows as well. CNC technology has been adopted in the processing of tube sheets, with CNC drilling machines being used to drill holes, supplemented by swing arm drills for further hole processing. Using machining centers for high-efficiency and high-precision hole drilling is also gradually being adopted by some large enterprises. There is a growing demand for large and thick tube sheets in the fields of nuclear power, desalination, and central air conditioning heat exchangers. In actual production, process tests that mimic the stamping process are commonly used, such as drawing performance tests and bulging performance tests, to evaluate the stamping properties of materials, thereby ensuring product quality and a high pass rate. Stamping is a forming process in which a press and dies are used to apply external force to sheets, strips, tubes, profiles, etc., causing plastic deformation or separation so as to obtain workpieces (stamped parts) of the desired shape and size. Stamping and forging both belong to plastic processing (also known as pressure processing), and together they are referred to as forging and stamping. The blanks for stamping are mainly hot-rolled and cold-rolled steel plates and strips. Compared to castings and forgings, stamped parts feature thinness, uniformity, light weight, and strength. Stamping can produce components with ribs, fins, undulations, or flanges that are difficult to manufacture by other methods, in order to enhance their rigidity. Thanks to the use of precision molds, the accuracy of the workpieces can reach the micron level; they also feature high repeatability and consistent specifications, allowing for the stamping of features such as holes and protrusions. Cold-stamped parts generally do not require further machining, or only require minimal machining. The precision and surface condition of hot-stamped parts are lower than those of cold-stamped parts, but they are still better than cast and forged parts, with less material removal required. Stamping is an efficient production method. By using compound dies, especially multi-station progressive dies, multiple stamping operations can be carried out on a single press, enabling fully automated production from uncoiling and leveling of the material to cutting, shaping, and finishing. It features high production efficiency, good working conditions, and low production costs; generally, hundreds of units can be produced per minute. Classified by process, they can be divided into two main categories: separation processes and forming processes. The separation process, also known as blanking, aims to separate the stamped part from the sheet metal along a specific contour line, while ensuring that the quality requirements of the separated surface are met. The purpose of the forming process is to cause plastic deformation in the sheet metal without breaking it, so as to produce workpieces of the desired shape and size. In actual production, multiple processes are often applied together to a single workpiece. Blanking, bending, shearing, drawing, bulging, spinning, and straightening are several major stamping processes. The surface and internal properties of sheet metal used for stamping have a significant impact on the quality of the stamped products. It is required that the thickness of the stamping material be precise and uniform; its surface should be smooth, free from spots, scars, scratches, or surface cracks; it should have a uniform yield strength without any obvious directional variation; a high uniform elongation rate; a low yield-to-tensile strength ratio; and low work hardening. Except for hydraulic presses used for forming thick plates, stamping equipment generally uses mechanical presses. Centered around modern high-speed multi-station mechanical presses, by equipping them with machinery for uncoiling, leveling, finished product collection, and conveying, as well as a die library and quick changeover devices, and controlling everything through computer programs, a highly productive automatic stamping three-dimensional production line can be established.