(1) Surface dry time


It refers to the time when one component RTV silicone rubber loses its viscosity when it touches the surface with fingers during curing in atmospheric environment. Generally, it refers to the time distance when the silicone rubber plane sealant is extruded out for airing and the surface is not touched by hands under the standard conditions.






(2) Curing depth


It refers to the thickness of the rubber layer of silicone rubber plane sealant solidified from the outside to the inside within a certain period of time after sizing, such as: 2-3mm / 24h, 0.6mm/h, etc.






(3) Extrudability (defined in accordance with ASTM c1183)


According to the requirements of ASTM c1183 specification, under the specification conditions, using Semco pipe and specific nozzle (diameter of 3.2mm), under the specific pressure conditions, the extrusion weight per unit time is called extrudability.






(4) Immediate seal pressure


It refers to that the silicone rubber plane sealant is applied on the flange plate plane with a certain diameter, and then immediately closed to control the reasonable thickness of the rubber layer, and then the air pressure is applied according to a certain rate, and the maximum accepted pressure is the instant sealing pressure.






(5) Curing characteristics in oil


It refers to that the silicone rubber plane sealant is punched in the fixed mold, and then the mold is put into the oil, recording the thickness of silicone rubber plane sealant solidified from the outside to the inside within a certain period of time to characterize the oil curing characteristics of silicone rubber plane sealant.






(6) Holding rate of shear strength for drying time


It refers to that the shear test piece which has been applied with glue shall be placed for a certain time under the specific high temperature and high humidity conditions, then the bonding shall be stopped, and the curing shall be stopped after being placed for 168h under the specification conditions, and the shear strength shall be tested, and the shear strength shall be compared with the 168h test of direct bonding and curing under the specification conditions, so as to calculate the strength persistence rate.






(7) Thermal stability without curing


It refers to putting the uncured silicone rubber plane sealant in the high temperature environment for a certain period of time, and then it can still be cured under the standard conditions. It is clarified that the silicone rubber plane sealant is stable under the temperature conditions. If the thermal stability temperature of sealant is ≥ 100 ℃, it means that the uncured sealant can continue to cure after heating at 100 ℃.






According to the different content of phenyl (phenyl: silicon atom) in silicone rubber, it can be divided into low phenyl, medium phenyl and high phenyl silicone rubber. When the rubber crystallizes or approaches the glass transition point or the two conditions overlap, the rubber will show a stiff state. The introduction of large volume groups can destroy the regularity of the polymer chain, which can reduce the crystallization temperature of the polymer. At the same time, because the introduction of large volume groups changes the force between the polymer molecules, it can also change the glass transition temperature. Low phenyl silicone rubber (C6H5 / Si = 6 ~ 11%) has excellent low temperature resistance due to the above reasons, and has nothing to do with the type of phenyl monomer used. The brittleness temperature of vulcanizate is - 120 ℃, which is the best rubber at low temperature. Low phenyl silicone rubber has the advantages of vinyl silicone rubber, and the cost is not very high, so it has the trend of replacing vinyl silicone rubber. When the content of phenyl is increased, the rigidity of molecular chain will be increased, which will lead to the decrease of cold resistance and elasticity, but the ablation resistance and radiation resistance will be improved. When the content of phenyl reaches C6H5 / Si = 20-34%, the medium phenyl silicone rubber has the characteristics of ablation resistance, while the high phenyl silicone rubber (C6H5 / Si = 35-50%) has the excellent radiation resistance.