An Improvement of the Sealing Performance in Stamped Steel Bolted Flanged Joints by Using Liquid Sealant Under Internal Pressure

It is important to improve the sealing performance of bolted flanged joints subjected to internal pressure. Recently, bolted joints with flexible flanges of stamped steel have been used in an oil-pan structure of automobile from a lightweight viewpoint. However, it is difficult to improve the sealing performance of flexible bolted flanged joints due to the reduction of the interface pressure. In this paper, a liquid sealant is applied to a box-shaped flexible bolted flanged joints such as oil-pan structures subjected to internal pressure in order to improve the sealing performance. In the experiments, an internal pressure when a leakage occurred was measured in the case where box-shaped bolted flanged joints in which liquid sealant was applied to the interfaces between aluminum flexible flanges (the upper) with thickness of 1 and 3mm and the steel (aluminum) flange with 10mm thickness (the lower) and where the bolt positions are changed. The flexible flanges were fastened by M8 bolts and nuts with an initial clamping force after being joined by the liquid sealant. In addition the bolt positions are changed. Experiments to measure a pressure when a leakage occurs were also conducted on bolted joints with asbestos gaskets. In addition, the effects of the bolt distance and bolt initial clamping force (preload) on the sealing performance were examined. The bolt distance was varied as 40, 60 and 70mm. The experiments were also conducted on bolted joints in which similar thickness stamp steel flanges were joined. Moreover, the interface stress distribution of flexible bolted joints with liquid sealant is analyzed using finite-element method. A method for estimating a pressure when leakage of internal fluid occurs is demonstrated using the interface stress distribution and the strength of the sealant. The effects of the bolt distance and bolt positions and stiffness of flanges on the sealing performance are examined. Discussion on the sealing performance is made