Abstract In order to solve the problems of internal leakage and leakage in medium temperature medium pressure stop valve, the research and development of double sealed stop valve has obtained national patent. This paper describes the characteristics of double seal structure; selection and combination of packing material and sealing material selection of the metal sealing material. Key words double seal shut-off valve packing seal surfacing 1 Foreword Shut-off valve as a general-purpose valve, in steam system, fuel system, domestic water system, compressed air system, medium temperature and pressure system has been widely used, however, Due to the choice of packing, packing method is not reasonable and other reasons, there is widespread leakage phenomenon, at the same time as the sealing surface of the welding material selection is not reasonable, there is also the phenomenon of internal leakage. In order to solve the temperature in the medium pressure globe valve leakage, leakage problems, the author after several years of research and development of double sealed globe valve, double sealed globe valve sealing performance than the traditional structure of the globe valve has significantly improved. Double sealed structure has obtained national patent, patent number is ZL98 2 26953.6. 2 Study of double seal structure Globe valve sealing surface material matching commonly used in two ways: metal to metal seal (referred to as metal seal) and metal to non-metallic soft material seal (referred to as soft seal). Metal seal globe valve seal structure shown in Figure 1 (a) shows the sealing principle shown in Figure 1 (b) below. As can be seen from Figure 1 (b), there are many kinds of convex peaks and grooves in the microstructure of the sealing surface. In order to make the sealing valve not leak when the closing valve is closed, it is necessary to improve the processing precision and roughness of the sealing surface Grade, and apply a large closing force to the sealing surface. Due to the sealing surface to exert a great force, the sealing surface must have a lot of contact stress, for the use of "sticking" tendency of the metal as the valve flap, seat sealing surface material of the valve, opening and closing moments , Inevitably there is chafing phenomenon, which is one of the main reasons for such short life of the globe valve. In addition, the metal seal shut-off valve, even to improve the machining accuracy, to achieve zero leakage is not easy thing. Figure 1 soft seal globe valve seal structure shown in Figure 2, embedded in the soft material seal ring or pressure ring fixed on the valve. As the sealing valve is easy to achieve tight seal, to ensure that the amount of leakage is zero, and in the processing can reduce the sealing surface machining accuracy requirements, so strict requirements for sealing gas valve and other gas stop valve gas, the soft Sealed structure has been widely used. However, the soft seal sealing surface of the soft sealing pressure poor, due to the manual closing force of the closing force is difficult to limit, when the valve sealing surface contact with the valve sealing surface can guarantee the seal, the closing action can not stop, and therefore easy Permanent deformation of soft materials, especially when the valve is closed for a long time, due to the long-term pressure overload of the soft sealing surface so that it has permanent deformation, once opened and then closed easily failure. Figure 2 for the soft seal globe valve seal tight but poor sealing surface pressure capacity, metal seal globe valve sealing surface pressure capacity, but may be scratches, and to make metal seal globe valve to zero leakage, will inevitably increase the deadline Valve processing precision grade characteristics, the author proposed the concept of double-sealed within the globe valve, that is, the metal seal, the advantages of their own soft seal together to form a metal seal-based seal, the soft seal for the secondary seal of the new sealing structure . In the process of analyzing and studying the double inner seal structure, two schemes as shown in FIG. 3 and FIG. 4 are designed, and the schemes are studied. Figure 3 Figure 4 (1) Option One (Figure 3): Figure 3 (a) is closed, Figure 3 (b) is open, the flexible ring is elastic structure, lined with spring. When closed, the valve disc moves downwards, first touching the soft seal to deform it and then into contact with the metal seal face. The force exerted downwardly through the valve stem is mainly borne by the metal seal face. The metal sealing surface and the soft sealing surface together form a valve sealing surface. The metal sealing is the main sealing and the soft sealing is the secondary sealing. When the metal sealing surface has a small amount of leakage, the sealing can be completely guaranteed by the soft sealing surface. This dual seal structure, the valve flap first contact with the soft seal ring, because the moment of closure of the high-speed flow of media may damage the soft seal, so the program less than ideal. (2) Scheme 2 (Figure 4): Figure 4 (a) is closed, 4 (b) is open. The structural seal is composed of a valve disc, a soft material sealing ring and a metal sealing surface of the valve body, and the sealing ring is fixed on the valve body by a pressure ring. Double sealed structure of the metal seal for the axial main seal, soft seal radial secondary seal, when the metal sealing surface leak, the leakage of the medium can be sealed with a soft material seal ring, the soft seal ring seal material can be completely radial structure To avoid the axial soft seal easily crushed defects, while the structure of simple processing, compared with the ordinary shut-off valve, the cost will not increase much. According to the comparison and analysis of the two schemes, the double inner seal structure of the second scheme is selected as the selected structure. According to the principle of double seal structure, a double sealed globe valve prototype with a nominal pressure of 2.5MPa and a nominal diameter of 50mm is designed and manufactured The prototype hydrostatic life test to verify the rationality of this structure. Static pressure life test carried out 10000 times, the prototype performance intact, no leakage. The test results show that the double inner seal structure is reasonable and can be used as a new inner seal structure on the globe valve. 3 filler sealing material selection and combination of the way At present, the globe valve products use a single flexible graphite ring packing. Flexible graphite ring packing is made of flexible graphite sheet cut into strips wound on the same diameter as the stem made of the stem, the production process is simple, the price is cheap. But a single flexible graphite ring packing in the application of some problems, mainly in the short service life, the operation of less than a thousand on the leak. The main reason for the above problems is that due to the graphite particles are transferred to the valve stem and deposited on the valve stem during contact with the valve stem, the surface of the valve stem becomes rough on the one hand and the valve stem reciprocates on the other hand Part of the movement in the process of graphite deposited on the surface of the stuffing box letter, resulting in the volume loss of the filler, the filler at the leak. This is evidenced by both laboratory tests and field results. In order to solve the problems existing in the use of flexible graphite ring packing, the author studied the combination of flexible graphite packing and flexible graphite ring packing. The test pressure was 2.5MPa. The packing box was filled with five layers of packing, Flexible graphite braided packing, the middle three layers of flexible graphite ring packing, the test results show that this packing combination is ideal, with the valve stem flexible graphite braided filler not only without graphite transfer, and the flexible graphite ring packing transferred to the valve stem Graphite on the wipe effect, to avoid the volume of the filler to reduce significantly improve the reliability of the packing, after 10,000 times the life of the filling pressure test without leakage. 4 metal sealing surface welding materials selection study In the steam system, domestic water systems, compressed air systems use a large number of cast-steel stop valves, the sealing surface is in the media for a long time, subject to erosion and erosion of the medium; the same time, to ensure that the deadline Valve seal, the sealing surface is bound to exert a certain seal pressure, due to the role of the seal than the pressure, cut-off valve disc, the valve seat between the friction and wear. Therefore, in order to ensure the closing of the valve seal to prevent leakage, the sealing surface of the material and formation of the inevitable to be taken into account. At present, there are 6 kinds of ways to form the sealing surface of the globe valve: (1) It is directly processed on the valve body and the valve disc of the globe valve. This mode is mainly used for the copper globe valve, stainless steel globe valve and oil medium Stop valve; (2) processed with a suitable material into a ring, the seal with a mechanical connection, or threaded connection method, or lamination method, or welding method were fixed on the valve body and valve flap; (3) closing the valve body, the valve flap respectively welded stainless steel and processed into a sealing surface; (4) the valve base metal heat treatment nitriding method to form a sealing surface, this method is mainly used for the base material for the special alloy cut- Valve; (5) The thermal spraying method is used to spray a layer of suitable material on the surface of the base metal to form the sealing surface by processing; (6) Applying a suitable material to the metal surface of the base body by the method of cold- The method is suitable for pressure, temperature is not high, there are corrosion-resistant valve. The current carbon steel globe valve sealing surface is mainly used in the valve body, the valve flap welding stainless steel and processing methods. Medium temperature medium pressure carbon steel globe valve sealing surface used surfacing materials are Cr13-type, Cr-Mn-based and cobalt-based carbide electrode. Cr13 electrode surfacing layer can be heat-treated to make the hardness greater than 35HR, thereby enhancing the sealing surface of the anti-pressure capacity, however, Cr13 surfacing layer alloy structure is simple and can not form a dense, high-strength multi-phase compound structure, Therefore, with Cr13 electrode surfacing welding surface, large miscibility, "sticking" tend to be large, anti-scratch poor. Although the valve body can be adjusted by heat treatment, valve seal surface hardness, so that the formation of hardness difference, but even if the seal pair has the best hardness difference, the seal of the anti-scratch ability is not very satisfactory. At the same time, Cr13 surfacing material crack resistance is not good, easy to crack in the surfacing, the use of Cr13-type welding material to be preheated before welding, hardness after welding to adjust the difference between the heat treatment, which increases the manufacturing process of the globe valve cost. Cobalt-based alloy surfacing electrode is an ideal surfacing material, corrosion resistance, crushing resistance, erosion resistance, cavitation, anti-scratch ability are good, commonly used to surfacing the use of harsh conditions, anti-wear , High resistance to corrosion of the globe valve sealing surface. With cobalt-based hardfacing electrode surfacing welding sealing surface of the globe valve static pressure life are generally more than 6000 times. However, cobalt-based hardfacing materials surfacing welding process is complex, the price is more expensive (is the price of Cr13-type electrode 18 times), from the cost of manufacturing considerations for medium temperature check valve selection of cobalt-based alloy welding electrodes is not the preferred choice . Since the mid-80s, for the Cr13 electrode surfacing into the sealing surface anti-abrasion ability is not weak, the relevant domestic units have been successfully developed a 85 chromium-manganese nitrogen surfacing electrode, 137 chromium-manganese surfacing electrode . 85 electrode surfacing alloy Cr-Mn-N alloy, with excellent resistance to water, steam, oil and other weak corrosive media corrosion, using this electrode surfacing globe valve, valve, sealing surface has a very good Of the anti-scratch performance, anti-galling performance better than the best hardness difference Cr13 type surfacing alloy. 85 electrode surfacing welding process is simple, good crack resistance, surfacing without the need to implement preheating, insulation and slow cooling and other process measures, while the valve body, flap welding with the same electrode, and without the use of complex heat treatment Process adjustment valve, valve seal surface hardness difference, which is extremely convenient for tissue production, reducing production costs. I used the 85 electrode overlay welding valve, the valve flap, manufactured a nominal pressure of 2.5MPa, nominal diameter of 50mm double sealed globe valve, and the double sealed globe valve 10000 static pressure life test after the test on the globe valve Disintegration observation, valve body, valve seal surface no obvious scratches. The No. 137 electrode is an improvement of the No. 85 electrode, and its surfacing alloy is a Cr-Mn-B alloy. Compared with the electrode surfacing alloy No. 85, the No. 137 electrode surfacing alloy has excellent crack resistance, machinability and resistance Corrosion on the slightly worse, and the price is more expensive (about 85 times the electrode price 1.5 times), but the anti-scratch performance and cavitation performance has improved significantly for high temperature (medium) pressure check valve Surfacing. In summary, for medium temperature carbon steel globe valve, from the overall performance, surfacing process, processing costs and other aspects of consideration, the sealing surface surfacing material selection 85 electrode is more appropriate. 5 prototype test results According to the axial direction of the metal seal, the radial seal for the soft packing double sealing principle, in accordance with GB / T12235-1989 "steel stop valve and lifting check valve" standard design, manufactured PN2.5, DN50 double sealed globe valve prototype, and the double sealed globe valve prototype tested the shell, liquid seal test, gas seal test, static pressure life test, the test results shown in Table 1. Table 1 Item Standard value Test value Shell test Test pressure (MPa) 3.8 3.8 Duration (s) ≥15 15 Result No visible leakage and structural damage No visible leakage and structural damage Upper seal test Test pressure (MPa) 2.8 2.8 (S) ≥15 15 Result No visible leakage No visible leakage Liquid seal test Test pressure (MPa) 2.8 2.8 Duration (s) ≥15 15 Leakage rate (drop / min) 0 0 Gas seal test Test pressure MPa) 0.5 ~ 0.7 0.6 Duration (s) ≥15 0 Leakage rate (bubble / min) 0 0 Static pressure life test 10010 It can be seen from the prototype performance test results that the double sealed globe valve has reliable sealing performance, long static pressure life, Far better than the normal structure of the globe valve. About the author: Liu Huiyuan, male, 36 years old, university, senior engineer. Address: 230031 Hefei City, Anhui Province General Machinery Institute of Mechanical Valve Room. Liu Huiyuan (General Machinery Research Institute of Machinery) Liu Yang (General Machinery Research Institute of Machinery) Zheng Qinglun (General Machinery Research Institute of Machinery) Huang Shaogu (General Machinery Research Institute of Machinery) Li Jun (Nanchang Institute of Nonferrous Metallurgy) Anhui Chemical Engineering Design Institute) Item Standard value Test value Shell test Test pressure (MPa) 3.8 3.8 Duration (s) ≥15 15 Result No visible leakage and structural damage No visible leakage and structural damage Upper seal test Test pressure (MPa) ) 2.8 2.8 Duration (s) ≥15 15 Result No visible leakage No visible leakage Liquid seal test Test pressure (MPa) 2.8 2.8 Duration (s) ≥15 15 Leakage rate (drop / min) 0 0 Gas seal test Test pressure (MPa) 0.5 ~ 0.7 0.6 Duration (s) ≥15 0 Leakage rate (bubble / min) 0 0 Static pressure life test 10010
Vegetable Display Refrigerator
Vegetable Display Refrigerator,Vegetable Display Chiller,Vegetable Display Cooler,Vegetable Chiller Showcase
ZHENGZHOU KAIXUE COLD CHAIN CO., LTD. , https://www.supersnowfreezer.com