Selection of initial gasket width

Abstract

Correctly selected gasket width for forced-type detachable sealed joint is one of the conditions of leaktightness of the joint under the operating conditions at minimal material content of the joint itself. In this article, the calculation of the initial gasket width has been made more precise taking account of the real nature of radial deformation of the gasket upon axial loading. The calculating expression obtained has been used to determine the initial appropriate width of the gasket. Experiments have been carried out to study the conditions of radial deformation of the gasket. The experimental and calculated results are virtually congruent. The data reported in this article help disclose the real nature of gasket deformation in flanged joint, which allows one to remove errors from the calculating expressions used, determine the allowance for reducing the material content without impairing the leak-tightness of the flanged joint and the strength of its constituent elements, and select a more optimal flanged joint design. A requisite condition for normal performance of a detachable sealed joint is use of a gasket with an optimal width. A gasket in a forced-type joint is loaded for its assembly with a greater force than in the operating state. If the pressure of the sealing medium is raised, the gasket, upon unloading, must retain its resilient state. This condition can be assured only if the joint is assembled with a fixed compressive force, which creates a specific load q gk on the gasket. The load must not be higher than the limiting value, at which the gasket material retains its resilience under the operating conditions. Some sources [1] reported the values of the axial load q gk on the gasket, at which its material retains resilience. For instance, q gk of 3.5 and 5.0 MPa is recommended for soft and hard rubber, respectively, 25 MPa for fluoroplastic-4 (polytetrafluoroethylene, also known as Teflon), 100 MPa for AD-type aluminum, and 160 MPa for copper. Retention of the resilience of the gasket material and leak-tightness of the joint also depend on the gasket width. If the gasket width is more than the optimal, greater force will be required for preloading the fastening threaded elements, which will increase the material content of the joint and, consequently, its cost. If the gasket width is less, the leak-tightness may be lost under the operating conditions because of loss of resilience of the gasket material in the joint assembling process. Various recommendations are offered in the technical literature (without sufficient justification) for selecting the width of sealing gaskets. Only in [2] is given a fairly substantiated expression for determining the requisite width of the gasket: