High precision double side surface grinding or fine grinding is a super finishing process performed by removing material from two surfaces of a component resulting in extremely precise geometric accuracy and surface finish. Typically, it is the last grinding step of a mechanical production chain utilized to improve and/or correct the geometry of parts coming from sintering, sawing, molding or similar operations. Depending on the application, the stock removal also can be taken from just one surface.
GMM1200 Double Side Surface Grinding Machine Disc Grinder,High Precision Surface Grinding Machine,Precision Surface Grinder,Oil Nozzle Surface Grinding Machine Xinxiang SKF machinery Co., Ltd. , https://www.grindingmachine.nl
[Keywords:] valve; sealed packing; calibration method 0 Introduction In industrial production, valve leakage as an important indicator to test, measure the quality of the produced valve is always the focus of attention, but also the difficulties that many researchers try to overcome. In general, valve leakage is roughly divided into two categories, external leakage and internal leakage. The valve quality is evaluated from two different aspects. The inner leakage is the leakage of the medium in the internal position of the valve, which refers to the leakage between the valve seat and the opening and closing part; the leakage is the leakage of the medium to the environment, mainly the stem and the stuffing box, the flange, the stuffing box and the valve. Leakage that occurs between the body, fixed shaft and valve body, bypass connection, and valve body. Under normal circumstances, external leakage will directly lead to environmental pollution, loss of media and even major safety accidents, and valve packing is the main source of leakage of the valve leakage, so we must pay enough attention to the performance of valve packing.
1 Standards and Status Quo of Valves and Packing Tests in China 1.1 Standards of Domestic Valves and Packing Tests At present, the standards issued by China for valve testing mainly include GB/T13927-2008 “Industrial Valve Pressure Test†and GB/T12224-2015 “Steel Valve General Requirements, GB/T26480-2011 "Valve Inspection and Test", GB/T26481-2011 "Valve Evacuation Test", etc. These standards have set clear and strict regulations for the performance of various types of valves. Detailed and unambiguous inspections of valves and test items, procedures, pressures, durations, test media, leakage reception, etc. For packing, the standards issued by China include GB/T23262-2009 Test Method for Non-Metallic Sealed Fillers, JB/T6620-2008 Test Method for Flexible Graphite Woven Fillers, and JB/T7760-2008 Valve Packing and Seal Test Standards. JB/T7760-2008 "Valve Packing Seal Test Specification", JB/T 6617-1993 "Valve Flexible Graphite Packing Ring Technical Conditions". These standards provide clear specifications for the composition, density, mechanical properties, temperature loss, etc. of the filler.
The publication of these standards provides guidance for valve manufacturers and users on the testing and acceptance of valves. It provides a strong guide for the selection and acceptance of fillers by valve manufacturers in China, and greatly contributes to the improvement of valve sealing performance in China. The contribution of China’s industrial security has provided a relatively complete guarantee and will push the development of China’s modern industry to a new height.
1.2 Status Quo of Valves and Packing Tests Although China has developed relatively complete valve testing standards, there are more or less problems in the implementation of these standards. For example, GB/T 26481-2011 "Valve fugitive test" only stipulates the product test for valve fugitiveness, and does not specify the type test for valve fugitiveness, resulting in the valve manufacturer manufacturing the valve. It is not possible to select grades of packing with different performance grades according to different operating conditions of the valve to achieve economical efficiency; GB/T 24925-2010 "Technical conditions of cryogenic valves" corresponds to the requirement for leakage of soft seal valves that are not visible Leakage, this requirement is far higher than the current international standards, the current domestic manufacture of the valve basically do not meet such requirements. For the filling test standards, the published standards fail to provide clear requirements for filler manufacturing and acceptance requirements for different working conditions, and fail to specify the requirements for fugitive emissions of packing, packing and acceptance requirements. This makes the domestic valve manufacturers in the selection of high-performance filler, can only refer to foreign standards, and these foreign standards are also a unified high standard requirements, failed to consider the different conditions of application of different filler grade requirements.
The standards of valve sealing and packing tests currently being formulated in China have been greatly improved compared with before, but these standards still cannot meet the current needs of China's valve industry development, making China's rapid industrial development, manufacturing in China, and the creation of China's The process is affected.
2 Valve packing test 2.1 Introduction to packing test device The specific device for packing test consists of the packing seal test bench and the characteristic test part of the packing itself. The packed seal test bench is used to simulate a valve that uses packing as a stem seal and has the function of detecting leakage at the valve packing. During the test, the valve stem is in a horizontal position. Considering the different orientation of the valve stem when the valve is actually used, it is considered that the position of the valve stem can be changed at any time during the test and does not interfere with the result of the valve test. In addition, the test device shall be equipped with a drive device to simulate the lifting or rotating motion of the valve stem. The drive device shall ensure that no lateral and lateral stresses are applied to the valve stem. The device should be equipped with a thermocouple and a temperature monitor to ensure that the temperature stability of the stuffing box and the fluid piping during the entire thermal cycle is provided and continuously monitored to avoid interference with the valve packing performance test results. The device used for leakage measurement shall be a certified ionizing flame steam analyzer, and the data obtained from the test shall be collected and recorded.
2.2 Procedure for the fugitive test The test medium in the fugitive test is generally methane gas with a purity of not less than 97%. The test temperature is room temperature to 260°C and the test pressure is 0-4137 kpa. The test required 1510 mechanical cycles and 5 thermal cycles. The test duration is 5 days x max 8 hours/day, mechanical cycles up to 2 hours/day, temperature cycles once per day, 150 mechanical cycles at ambient temperature and 150 mechanical cycles at high temperatures. The tester shall record the leakage at the beginning of the test and every 50 cycles and perform an effective analysis and calculation. Allow the valve packing to be adjusted once. If the leak rate of the valve exceeds the regulation after the adjustment, the test should be terminated to avoid unnecessary safety accidents and waste. At the same time, the valve is inspected and remanufactured if necessary. The probability of a safety accident occurring during the production process of a valve with a relatively large fugitive leakage will be greatly increased, which will adversely affect the profitability of the company's production and even threaten the safety of people's lives. For the above procedure requirements, China can make appropriate adjustments according to the characteristics of different operating conditions to make the test more reasonable and economical.
2.3 Corrosion Tests Corrosion tests are performed to correlate the corrosive effects caused by the filler to assess the effect of the filler inhibitor and the metallurgical composition of the stem on the corrosion rate and weight loss. The test should measure and record the composition of the filler, the type and content of the inhibitor, the application and configuration of the inhibitor in the filler. The 28-day environmental corrosion test was performed by placing the compression test fixture with the filler in an environmental corrosion test container, and the 35-day high-temperature corrosion test was performed by placing the compression test fixture with the filler in a high-temperature heating chamber to obtain valid data. To effectively evaluate the effect of filler inhibitors and valve stem components on corrosion rate and weight loss. During the test, it should be ensured that the temperature and pressure are continuously stable and effectively monitored, so as to avoid the distortion of the test result caused by the change of the parameters.
2.4 Procedures for test of filler material The filler material test is a test for the loss of filler weight, density, filtrability analysis, and lubricant content. Test sample packings should be randomly selected to effectively test the manufacturer's products. In order to avoid the influence of temperature changes during the test results, it is of great significance to ensure that the temperature conditions are consistent and stable throughout the test. The filler weight loss test is performed on lamellar graphite (flexible graphite) and woven graphite separately according to the contact environment and the effect. The lubricant content test includes the measurement of the content of PTFE and wet lubricant. The requirements for the difference in compositional elements of the filler can be set with different working conditions, and special element or component inspection requirements are set.
3 Conclusion Valve packing in China's industrial production process is extremely important, involving all aspects of industrial production, and has an important significance for the progress and development of China's industry. If the valve packing leaks during use, it will cause great waste, cause serious pollution to the environment, and even lead to serious safety accidents. Therefore, China's test calibration method for valve packings needs to combine energy-saving, environmental protection, and internationally relevant requirements, and at the same time, develop reasonable and perfect standards according to the actual national conditions and requirements of different working conditions, so that all enterprises can be in the production process. Get more effective guidance, so as to bring more effective impetus to the development of our country's industry.
ã€references】
[1] Hong Xiaofei, Hou Jianxiong, Hu Haihua. Optimization analysis of maintenance methods for high-parameter valves (fillers) [J]. Equipment Management and Renovation, 2016.
[2] Ma Weiping, Wu Jie, Zhan Yiwei, Yan Ci, Fan Qing. Calibration method of valve packing performance test [J]. North Gas & Oil, 2013.10.
[3] API Std 622-2011 Type Testing of Process Valve Packing for Fugitive Emissions [S].
Exploring the calibration method for valve packing performance test
ã€Abstract】With the development of China's industrial technology, energy conservation and environmental protection awareness, the Environmental Protection Agency and the Ministry of Environmental Protection have required refineries and petrochemical plants to initiate LDAR equipment leakage inspection procedures, which has greatly promoted the valve manufacturers to gradually adopt high-performance fillers. This, in turn, prompts filler manufacturers to continuously improve the manufacturing level of fillers, which will present a growing trend in filler seal technology. However, the standards for testing and acceptance of the fillers specially designed for different performance grades in China are imperfect, resulting in the lack of guidance for valve manufacturers to select suitable fillers with different performance levels. This article through the analysis of the existing standards and status quo of China's valve and filler test, introduces the filler test device, fugitive test procedures, corrosion test, filler material test procedures and recommendations, China's valve sealing packing performance test calibration method The improvement provides some practical advice.