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4.2.2 Type of RTV Silicone RubberRapid Prototyping & Manufacturing TechnologiesRTV silicone rubber can be divided into two types; condensation and additiontypes, the following table shows the differences among them.FeaturesCondensation Type• Lower costs• Broader product range• Less sensitive to exact mixratio• Accelerator catalystsavailable to speed up cure• Mixing of grades possible toachieve desired hardnessAddition Type• Low shrinkage, below 0.1%• Marginally higher tensilestrength• Slightly tougher rubber• Need for careful and accuratemixing• Good abrasion resistance• Can be accelerated using heatShrinkageWhenTemperatureIncreaseWhenHumidityIncreaseWhenQuantity ofCuring AgentIncreaseSlightly higher than the additiontypeCuring Time decreases(5 o C----7hrs;25 o C-----5hrs;50 o C-----4hrs(max temp))Curing Time decreasesCuring Time decreases but thereare limits• Tolerant to the addition ofsilicone fluid as a softenerLowCuring Time decreases(50 o C-----2hrs;100 o C-----30min;150 o C-----10min;)Curing Time decreasesCuring speed will not be alteredbut will adversely affect thephysical properties.*Quantity of curing agent must becarried out as accurately aspossible.CuringImpedimentsRemarksNoBy product will come out.Dimensions of mould will beslightly affected. (about 0.5%)YesWarm the rubber mold to thecuring temperature before pouringresin into a thermally cured therubber mold to raise dimensionalaccuracy.Page 27IC Professional Training