ASTM F2523-13(R2020) pdf free download

ASTM F2523-13(R2020) pdf free download.Standard Practice for Blowout Resistance of Room-Temperature Vulcanized Elastomers
4. Summary of Practice
4.1 Condensation cures RTVs as a one-component system cure when exposed to moisture in the ambient air or as two-component systems when those components are mixed together. RTVs are often used to seal joints where three flanges meet (T joints) such as an automotive engine’s front cover, engine block, and oil pan. Because of machining and assembly tolerance variations, these T joints may have a slight misalign- ment or gap. We also find gaps in the half-round area of the oil pan to block and in the valley between the intake manifold and block on certain V-engines as a result of manufacturing tolerances. The RTV is used to seal in fluids. In some assembly line applications, soon after the RTV is applied and the flanges fastened together, the system is subjected to an air decay test at a designated pressure. This test is used to determine an RTV’s capability to withstand loss of integrity at this designated pressure. 4.2 When using this practice, one must first determine the maximum gap based on stack tolerances of the system. A two-piece round fixture uses the top portion to mirror the system gap (default gap is 1 mm), while the bottom half provides the mating flange and the connection for the pressure input. The gap is machined into the top half of the fixture in a “pie slice” 60° angle. A continuous bead of RTV is applied to the entire bottom portion of the fixture, the top half is carefully attached, and the fixture is pressurized to the prescribed limits and held for a specified time period. If the RTV is not capable ofsealing at the pressure applied, a sudden loss ofpressure will occur.
11. Potential Failure Modes of Test Procedure
11.1 Inconsistent results in the procedure may be due to several reasons and shall be reviewed. Some of these may be:11.1.1 Inconsistent RTV bead applied. RTV should be applied in an amount sufficient to fill the gap when the fixture is assembled and bolts torqued. Insufficient RTV will result in voids within the fixture gap. These voids will result in premature failure when running Method A, and possible lower pressure values when running Method B. Excessive RTV applied in the fixture gap will result in an internal and external dam of RTV that will resist movement of air by the applied pressure. This can result in artificially high time to blow out (Method A) and resistance to blow out pressure (Method B). 11.1.2 Misplacement of bead. RTV bead biased toward the inside or outside can result in non-fill of the fixture gap, resulting in lower time to blow out (Method A) and resis- tistance to blow out pressure (Method B). Addition of RTV to compensate for this offset of the bead placement can result in an excessive amount ofRTV, and is further discussed in 11.1.1. 11.1.3 Air entrapment in RTV bead. Entrapment of air or other contaminants that create voids in the RTV can create results similar to insufficient RTV application, and is further discussed in 11.1.1. 11.1.4 Improper gap. The induced gap should be machined precisely to the agreed dimension within the tolerance limit stated in 6.1.3 (1 mm is the default gap). Failure to properly set gap will result in correlation issues between laboratories. Use of fixtures with improperly low gaps can result in artificially high results. Use of fixtures with improperly high gaps can result in artificially low results. 11.1.5 Improper torque sequence or setting. Improper se- quence can result in inconsistent gap fill or shifting of RTV bead, or both, thus providing inconsistent and imprecise results. Low bolt torque can result in shimming of fixture creating a slightly larger than desired gap, and artificially low data.