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Several meanings of silicone rubber process performance indicators

(1) Surface drying time
It refers to the time when the single-component room temperature vulcanized silicone rubber is exposed to the atmospheric environment, and the surface is touched with a finger, and the viscosity is lost. Normally refers to the time distance when the silicone rubber flat sealant is squeezed out to dry under normal conditions, and the surface does not stick to the hand.

(2) Cure depth
It refers to the thickness of the silicone rubber flat sealant cured from the outside to the inside within a certain time after the application of the silicone rubber flat sealant in a fixed mold under the specified conditions, such as: 2 ~ 3mm / 24h , 0.6mm / h and so on.

(3) Extrudability (defined in accordance with the specifications of ASTMC1183)
According to the ASTM C1183 specification request, under the specified conditions, using a Semco pipe and a specific nozzle (3.2mm diameter), under a specific pressure condition, the extrusion weight per unit time is called extruderability.

(4) Instant sealing pressure
It means that the silicone rubber flat sealant is glued on the flange surface with a certain diameter and then closed immediately to control the adhesive layer to have a reasonable thickness and then apply air pressure at a certain rate. The maximum pressure it receives is the instant sealing pressure.

(5) Solidification characteristics in oil
It refers to the silicone rubber flat sealant is placed in a fixed mold, and then the mold is placed in the oil. The thickness of the silicone rubber flat sealant cured from the outside to the inside in a certain period of time is used to characterize the oil of the silicone rubber flat sealant Medium curing characteristics.

(6) Shear strength adherence rate during drying time
It means that the sheared test piece that has been sized is placed for a certain period of time under a specific high temperature and high humidity condition, and then it is closed and bonded, and it is left to stand for 168 hours under standard conditions to stop curing, and its shear strength is tested. Under the conditions of direct bonding and curing for 168h, the shear strength of the test was stopped and the strength adherence rate was calculated.

(7) Thermal stability when uncured
It refers to putting the uncured silicone rubber flat sealant in a high-temperature environment for a certain period of time, and then it can still be cured under standard conditions, which clarifies that the silicone rubber flat sealant is stable under this temperature condition. If the sealant thermal stability temperature is ≥100 ° C, it means that the uncured sealant can continue to be cured after being heated at 100 ° C.

According to the phenyl content (phenyl: silicon atom) in silicone rubber, it can be divided into low phenyl, middle phenyl and high phenyl silicone rubber. When the rubber is crystallized or close to the glass transition point or the two conditions overlap, the rubber will appear stiff. The introduction of an appropriate amount of large-volume groups can damage the regularity of the polymer chain, which can reduce the crystallization temperature of the polymer. At the same time, the introduction of large-volume groups changes the force between the polymer molecules, so the glass can be changed temperature. Low phenyl silicone rubber (C6H5 / Si = 6 ~ 11%) has excellent low temperature resistance due to the above reasons, and it is independent of the type of phenyl monomer used. The vulcanizate has a brittle temperature of -120 ° C, making it the best low-temperature rubber today. Low phenyl silicone rubber has the advantages of vinyl silicone rubber, and the cost is not high, so there is a tendency to replace vinyl silicone rubber. When the phenyl content is greatly increased, the rigidity of the molecular chain will be increased, resulting in a decrease in cold resistance and elasticity, but the ablation resistance and radiation resistance will be improved. The phenyl content reaches C6H5 / Si = 20 ~ 34 % Is medium phenyl silicone rubber with ablative resistance, high phenyl silicone rubber (C6H5 / Si = 35 ~ 50%) has excellent radiation resistance.