What are the processing methods of the tube sheet
The tube sheet is refers to in the circular steel plate to drill the hole which is slightly bigger than the outer diameter of the pipe, passes through the tube to weld the fixed one kind of fitting. Tube plate for tubular heat exchanger, boiler, pressure vessel, steam turbine, large central air-conditioning industry. The material of the tube plate will be selected according to the bad environment. The detection of the tube sheet includes the hole position, the aperture tolerance, the inner hole finish, the burr, etc..
For three or four kinds of pressure container tube sheet need high accuracy, the traditional machining method is fitter, rocker drill holes. In recent years, with large-scale chemical container, the diameter of the tube plate is also increasing, the thickness is gradually increasing, tube plate processing also introduced numerical control technology, is now widely used nc drilling machine drilling holes with radial drill hole processing. Use a processing center for high efficiency and high precision machining is gradually accepted by some large enterprises. At present large thick tube plate in nuclear power, desalination, and central air conditioning demand presents the tendency of increasing in the field of heat exchanger.
What is the processing method of tube sheet?
1, the traditional tube processing methods: Although the manufacturers of the processing technology is slightly different, but in general, nothing more than the first crossed (due to draw the line into a grid, called grid lines), proofing Chong points, with a small drill drill holes, and then the official drilling, if the hole wall finish requirements are high, but also reaming, the final chamfer. Analysis of this process, first said crossed, if the standard tube board (honeycomb) Fortunately, if the complex graphics, crossed very troublesome. Say the drilling, the operator drilled with a rocker drill, adjust the rocker positioning, and then drop the drill, and then lift the drill bit to re-adjust the rocker positioning, drilling a hole to do a few actions, and operational workers of labor intensity, low efficiency. In short, the traditional tube plate processing methods, low precision, time-consuming, laborious, making the tube plate processing into a bottleneck in the entire production process, a talk about tube processing, people frowned.
2, advanced tube sheet processing methods: In fact, control tube sheet processing a major problem is the equipment problem. In the traditional tube plate processing, the rocker drill is its main equipment. Because of its manual operating characteristics, the operation method is relatively fixed, it is difficult to have the potential to tap. Although it can be used to improve the efficiency of drilling tools, but can not solve the fundamental problem. Only from the equipment to find a way to fundamentally solve the problem. Foreign pipe machining has been widely used multi-axis CNC drilling machine, no longer use the rocker drill, CNC plane drilling machine can replace the artificial crossed, drilling, can greatly improve the processing accuracy and efficiency. China in recent years began to achieve the localization of such drilling, but most manufacturers of products, the bed is smaller (2m ~ 3m), the spindle (1 or 2) not much. Can not process large tubesheet. Can not completely replace imported products. Therefore, for the processing of high precision tube board (more than 7m), can only go abroad to process. The import of CNC machine tools, expensive, long installation cycle, not easy maintenance, not necessarily suitable for China’s national conditions. People urgently need domestic machine tool manufacturers to produce ultra-large CNC drilling machine to meet the needs of tube sheet processing manufacturers.
Surfacing composite pipe sheet processing requirements:
1, before welding should be surfacing process assessment.
2, the base material to be surfacing and composite materials after processing (drilling) before the surface, according to JB4730 surface inspection, the test results shall not have cracks, into the exhaust hole, and should meet the level Ⅱ defect display.
3, shall not use the heat transfer tube and tube plate welding and bridge between the gap welding method of tube plate surfacing.
Evaporator tube sheet processing requirements:
1, the tube plate surface should be smooth, smooth, does not allow mezzanine, cracks and other defects, surface roughness Ra value of not more than 1.6μm.
2, the expansion of the tube plate hole surface is not allowed to penetrate the longitudinal and spiral to the scoring.
3, tube plate aperture tolerance should be consistent with GB151-1989 in Table 3-11 requirements. The surface roughness Ra of the tube hole is not more than 12.5 μm.
4, hole bridge width deviation should be consistent with GB151-1989 in Table 4-2 () requirements.
CNC technology processing tube board advantages:
1, a wide range of adaptability, flexibility, can be processed in different batches of tubesheet;
2, in accordance with the pre-programmed procedures for processing tube plate, processing tube board consistency is good, repeat the high precision;
3, the machine itself stiffness number, high precision and good maintainability, is conducive to long-term stability of processing quality;
4, automation, high efficiency, suitable for processing thick and heavy tube plate.
Tube tube processing expansion tube processing: the tube inserted into the tube tube empty tube hole, and then the mechanical device into the tube plate, from the inside of the tube pressure to expand and fasten a cold processing methods.
Composite tube sheet processing requirements:
1, in order to ensure the smooth progress of the pipe, pipe plate and the need to ensure that the tube between the concentricity of the hole, so the overall layout and tube plate drilling.
2, the tube plate processing order is as follows: first of the carbon steel tube plate for the initial processing, first processing the sealing part of the lining surface, split the diaphragm seal part of the rectangular groove and the surface of the complex, and then according to map welding ring, Rectangular cross-section stainless steel strip and multi-layer stainless steel plate, and finally the overall finishing and drilling.
Machining of spliced tube sheet:
1, splicing tube plate docking joints should be 100% ray or ultrasonic testing, according to JB4730 ray detection is not less than Ⅱ level, or ultrasonic testing in the Ⅰ level qualified.
2, in addition to stainless steel, the stitching board should be used to eliminate stress heat treatment.
Tube plate processing to check and control the hole diameter and allow the deviation of the approach:
1, tube plate hole diameter and allowable deviation should be implemented according to GB15l.
2, after drilling should be not less than 60 ° tube plate in the central area of the tube hole, in this area to allow 4% of the hole on the hole than the GBl5l Table 16 to Table 2l in the value of 0.15mm.
Tube plate processing in the surface roughness requirements:
1, when the heat transfer tube and tube plate welding connection, the pipe surface roughness Ra value of not more than 25μm.
2, when the heat transfer tube and pipe plate expansion connection, the pipe surface roughness Ra value of not more than 12.5μm.
Corrosion problem in tube plate welding: An effective way to solve the corrosion of pipe and pipe welds is to isolate the surface of the tube sheet from the water, that is, to coat a protective layer on the metal surface. Application examples: the new production of heat exchangers, directly in the plant on the tube surface sandblasting treatment, to a standard, the ambient temperature selection of 15 ~ 35 ℃, relative humidity of not more than 85%, with bristles will be equipped with a good TS406 directly coated on the tube surface, to be the first dry and then brush the second road to smooth and smooth surface without qualified holes.
Tube plate welding processing deformation of the form: arch deformation; wave deformation.
Tube plate welding processing deformation reasons:
1, assembly and welding in the wrong order;
2, the welding direction is not correct;
3, welding parameters unreasonable, causing local overheating;
4, did not use appropriate auxiliary measures.
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