New breakthrough in mechanical seal design method
2016-12-09
New breakthrough in
mechanical seal design method
From the perspective of the design method of mechanical seals, the design rules in the ASME boiler and pressure vessel code and the design parameters of mechanical seal gaskets recommended by Rossheina and Markl have been widely used in the design of bolted flange connections for a long time. These coefficients, called m and y, have been used for half a century, and they can usually meet industrial requirements, but their fatal disadvantage is that they have not been verified by experiments, and they cannot be extended to new products and products because of the lack of standard test methods. In addition, the coefficient of the ASME code does not consider the leakage rate, which is obviously unscientific; therefore, it is necessary to find a design method that considers both the leakage rate and the tightness of the connection as a design criterion. In order to solve these problems, PVRC and other technical associations started a series of research projects in the 1970s, and have completed the room temperature gasket test (ROTT), and proposed a new design test method based on the test results. The American Society of Mechanical Engineers (ASME) thematic T. Working Group (SWG) is making further additions. In addition, a research group of the American Society for Testing and Materials (ASTM) is also evaluating the gasket sealing test method proposed by PVRC and starting a new round of tests to draft a standard to enable manufacturers to provide users with new or improved gaskets. coefficient. Once these works are completed, there will be two important changes: ① The non-prescriptive appendix of the new seal design will appear in ASME-Vf-1, which is effective at the same time as the current appendix and will eventually replace it, including the new gasket The sheet constant (Q, 'and 〇, the load design formula will also be changed accordingly; ② promulgation and implementation of the new ASTM gasket test standards, and can be used to determine the gasket constant. These changes will allow designers to use the actual gasket The gasket constant verified by the manufacturer or supplier in accordance with the new standard.
It is worth pointing out that the new gasket constant and method are different from the traditional ASME code method. The latter does not consider the sealing performance of the gasket connection, but is mainly used to determine the design of the bolt planting load or to prove that the flange size according to the stress criterion can meet the design requirements. Therefore, the success of the seal design depends only on the accuracy and suitability of m and y, and these values u200bu200bare questionable. 'The design parameters in the new design method come from the leakage rate data obtained by the standard test method, so it considers The sealing requirements of bolted connection design are required to first calculate the minimum pre-tightening required for the gasket to achieve and maintain the leakage rate corresponding to a certain sealing degree and the sealing parameters during operation, and then calculate the gasket through a series of formulas related to the gasket constant It is obvious that this method is scientific and reasonable to determine the minimum shim stress necessary to achieve and maintain such a leakage level, so as to determine the load and size of the axolotl bolt. 193.html,
Research and development of mechanical seals (2) new method of mechanical seal preload control
