Tube sheets are widely used in industries such as petrochemical boilers and refrigeration steam turbines

Thread Content

1. Tube sheet processing technology: Tube sheets are widely used in industries such as petrochemicals, boilers, refrigeration, and steam turbines. Tube sheet processing is an important step in the manufacture of heat exchangers, and it plays a crucial role in the production of these devices. 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 heat exchangers. As chemical processing equipment and power plants become larger, the diameter of their heat exchangers also increases; tube sheets with a diameter of 4m to 5m are common, and some even reach a diameter of around 7m. Large tube sheets are characterized by a large number of tubes, with these tubes being closely spaced together; they also have small diameters and deep depths. High requirements are placed on their precision and surface finish, which in turn imposes significant demands on the processing of such tube sheets. 2. The traditional tube sheet processing methods may vary slightly among different manufacturers, but generally speaking, they involve marking lines first (the lines drawn form a grid, hence they are called grid lines), making sample punching marks, drilling small holes with a small drill bit, followed by actual drilling. If high precision is required for the surface finish of the holes, reaming is also necessary, and finally chamfering is performed. Let’s analyze this set of processes. Starting with marking: it’s straightforward for standard tube sheets (honeycomb structure), but it becomes quite troublesome when the design is complex. Speaking of drilling, the operator uses a swing arm drill to make holes: he adjusts the position of the swing arm, then lowers the drill bit, lifts it back up to adjust the swing arm’s position again. Several actions are required to drill one hole, which results in high labor intensity for the operator and low efficiency. In summary, traditional tube sheet processing methods are low in precision, time-consuming, and labor-intensive, making tube sheet processing a bottleneck in the entire production process; whenever tube sheet processing is mentioned, people frown. 3. Advanced tube sheet processing methods: In fact, a major issue restricting tube sheet processing is equipment-related problems. In traditional tube sheet processing, a swing arm drill is its main equipment. Due to its manual operation characteristics, the method of operation is relatively fixed, leaving little room for potential improvement. Although methods such as drill dies can be used to improve efficiency, they do not solve the fundamental problem. Only by finding a solution on the device itself can the problem be resolved fundamentally. Abroad, multi-axis CNC drilling machines are widely used for hole machining; swing arm drills are no longer employed. CNC surface drilling machines can replace manual marking and drilling, thereby **improving machining accuracy and efficiency**. In recent years, our country has also begun to achieve local production of such drilling machines, but the products manufactured by most manufacturers have relatively small beds (2m–3m) and few spindles (one or two). Large tube sheets cannot be processed. It cannot completely replace imported products. Therefore, for large tube sheets that require high machining precision (over 7m), they can only be processed abroad. Imported CNC machine tools are expensive, have a long installation period, are difficult to maintain, and may not be suitable for China’s national conditions. There is an urgent need for domestic machine tool manufacturers to produce ultra-large CNC drilling machines to meet the needs of tube sheet processing manufacturers. 4. Application of domestically produced super-large CNC drilling machines in tube sheet processing. Shanghai Nickel-based Heavy Industry Co., Ltd. is a manufacturer dedicated to the research and development as well as production of CNC machine tools. Since the successful development of the first super-large CNC drilling machine, the PD4040A/4, in 2003, its technology has continued to improve, and dozens of such machines have been produced and distributed across the country. Some users purchased two super-large CNC drilling machines from Fanuc at once. This CNC drilling machine features a power head with a gantry-type movement structure, as well as multiple spindles (2 to 12 spindles). Users can choose the size of the worktable and the number of spindles at the time of ordering. The maximum size of the workpieces that can be processed is 7m×7m (machines capable of processing even larger tube sheets are available upon request). Its main products are the PD4040 model, capable of processing pieces with a maximum size of 4m×4m, and the PD7045 model, which can handle pieces up to 7m×4.5m in size. These machines typically feature 4 spindles and four CNC-controlled drilling heads that can move independently; the minimum distance between the drilling heads is around 500mm. The maximum diameter of solid holes that can be drilled at one time is Φ50mm (optional), while the thickness of the workpieces that can be processed is around 200mm (optional). The machines feature double-sided drive without any play, and they have a total of 10 CNC axes (optional). They also come equipped with CAD/CAM functions that allow conversion of CAD files into machining programs, as well as the possibility of manual programming. These machines can be used for tasks such as CNC drilling, reaming, honing, and chamfering. This eliminates the need for manual line marking and drilling, resulting in a qualitative leap in tube sheet processing technology. **It improves processing accuracy and production efficiency. Thanks to its high efficiency, tasks that used to take a month to complete can now be finished in just a few days. The bottleneck in tube sheet processing throughout the entire production process has been completely eliminated. 5. Specific usage methods of super-large CNC drilling machines: The super-large drilling machines produced by Fanuc adopt a control system based on PC (computer) + CNC (CNC unit) + PLC (programmable controller). Enter the CAD drawing of the tube sheet in a PC, convert it to a DXF file, then run the host computer software developed by Fan CNC. By opening this DXF file and entering the coordinate values of the workpiece’s reference points, the part program along with related information can be generated automatically. The part program is generated by the machine, avoiding the errors that can occur when creating part programs manually. Then, the part program is sent to the CNC through the communication software WINDNC between the PC and the CNC, and the program is retrieved from the CNC to carry out the machining. Monitor the operating status of the machine through communication between the PC and the PLC. (6) The following is an example of a drilling program for a part: %, MX, N0001 Z2700.000 N0002 X1360.000 Y2640.000 U720.000 V2000.000 N0003 (B0,C0,D1,E0) N0004 M55 N0005 Z2000.000 N0006 X1360.000 Y2640.000 U720.000 V2000.000 N0007 (B0,C0,D1,E0) N0008 M55 N0009 X1400.000 Y3040.000 U720.000 V2400.000 N0010 (B0,C1,D1,E0) N0011 M55 N0012 Z1500.000 N0013 X1360.000 Y3040.000 U720.000 V2000.000 N0014 (B0,C0,D1,E0) N0015 M55 N0016 M30 (7) The following is an example of information related to a part program: 1. Programming method: CAD 2. File processed: D:PD4040BDXF3270f30.dxf 3. Number of duplicate holes removed: 0 4. Total number of holes drilled: 5500 5. Verification of total hole count: 5500 6. Number of holes drilled in slots 1#, 2#, 3#, 4#: 1239, 1428, 1559, 1274 7. Number of times the drilling head was idle: 1020 8. Utilization rate of the drilling head: 84.36% 9. Number of drilling units: 1630 10. Drilling diameter: 30.000 11. Diameter of the tube sheet: 3270.000 12. Number of rows of holes: 9313 13. Last sequence number in the program: N4984 14. Coordinates of the reference point (U): 2000.000 15. Coordinates of the reference point (Z): 2000.000 16. Movement direction of the Z-axis: Forward 17. Type of tube sheet: Standard 18. Time when the program was executed: 2005-2-3 12:49:44 By reviewing the information related to a part program, it is possible to analyze it and reduce the chances of errors. Choosing the right ultra-large CNC drilling machine for tube sheet processing is essential for improving processing accuracy and production efficiency. The early adoption of super-large CNC drilling machines is of positive significance for improving product quality, increasing the technological content of products, enhancing a company’s competitiveness, and cultivating talent in CNC applications.