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RTV325 High Temperature Resistant Silicone Rubber

PRODUCT DESCRIPTION RTV325 is a room-temperature vulcanizing silicone rubber that was especially designed for casting solid polyurethane and polyurethane foam parts. It is also acceptable for casting candle wax and epoxy. RTV325 has the following advantages over other RTV silicones:


1.        Improved heat resistance. RTV325 can withstand temperatures up to 600°F, making it ideal for casting low melting point metals such as pewter and lead.

2.        Fast Cure

3.        Minimum Shrinkage: The shrinkage rate is lowest when the Slow Catalyst is used. Even if the Fast Catalyst is used, the shrinkage is minimal. This is a particularly valuable property in the production of multi-piece molds that require exact registration to minimize the parting lines.

4.        High Durometer. The stiffness of the cured rubber makes molds self-supporting, reducing the need for of external supports and rounds.


MIXING INSTRUCTIONS  Proportion Part A and Part B in a ratio of 10 Parts A to 1 Part B by weight. Stir thoroughly either by hand or by mechanical mixer until a uniform color is achieved. Mix until all streaks of white disappear. If facilities permit, deaerate in a vacuum chamber at a minimum of 28 inches of mercury until material rises to approximately double the volume and collapses. Carefully pour rubber over the pattern and allow to cure for the required time. Water mist can sometimes help slow-curing rubber “catch-up” to normal cure time.


RELEASE AGENTS  Silicone can adhere to many different materials, and precautions should be taken to prevent it from bonding with your original pattern and when casting parts in the mold. Before pouring the silicone into the mold box, be sure to lightly spray the pattern and mold box surface with Eager Plastics’ Ease Release 800 to prevent any bonding. If a parting mold (i.e., two-piece mold) is to be made, also use Ease Release 800 spray between layers of silicone. Porous surfaces need to be sealed with spray shellac or another suitable sealing agent prior to spraying with Pattern Release. After the mold has been separated from the pattern, apply a release agent to the inside of the mold prior to casting any parts for better mold life. Use Ease Release 200 if casting urethane and epoxy, unless parts are to be painted. Casting of wax does not require the use of a release agent. For other materials, please contact us for recommendations.


Typical Properties of  RTV1000 Separate Compounds & Mixtures


Base Rubber         Slow (BLUE) Cat.                 Fast Cat.                               

Color                                      Off -White                   Dark Blue                      Pale blue                   

Viscosity, cps                          130,000                          1,000                                 100                     

Specific Gravity                           1.35                             0.99                                  0.99                    

Working Time                              N.A.                         1.5 hrs                               6 min.                    

Cure time                                      N.A.                       16-24 hrs                            2-3 hrs.                

Shelf-life                                   6 months                    6 months                         6 months                   



Typical Properties of Cured RTV325 Silicone Rubber (7 Day cure at 77°F and 50% relative humidity)

Hardness, Shore A Scale                                              50-55                             50-55                              

Tensile Strength, psi                                                       550                                 530

Elongation, %                                                                   170                                 160

Tear, die B lbs/in                                                               28                                   28

Shrinkage, %                                                                      0.1                                 1.0





RTV DILUENT THINNING AGENT  is a low-viscosity silicone fluid. It lowers the viscosity of the mix and thins the RTV325, making it more pourable. Normally 10% by weight is used, but it can also be used to much higher levels. At the 10% addition level, the sacrifice of physical properties is non-existent. In fact, the opposite is often reported; some properties, namely release, seem to be improved. Consequently, RTV Diluent is sometimes used as a release agent to improve release and extend mold life.


CURING AGENT ACCELERATOR  is a clear amber fluid with a mild odor. This accelerator has a powerful effect on the curing speed. Small amounts have a dramatic effect.


RTV PRIMER  will cause RTV325 to bond to most porous surfaces such as wood. Primer can be brushed, sprayed or dipped. Pour RTV within one hour of applying primer.


THICKENING AGENT  There is no known thickening agent for RTV silicones. Some success has been achieved by adding Cab-O-Sil to the mixture. If a thicker system is needed, try RTV184, which has a thixotropic activator, or one of our brushable urethanes such as Brush-On 40 or Brush-On 50.


Warning:  Uncured product may cause respiratory or skin irritation with possible sensitization. Use only with adequate ventilation. If skin contact occurs, wash thoroughly with soap and water. In case of eye contact, flood with water and call a physician. Use of gloves and face shield is recommended.  This product should not be used near food or where prolonged skin contact may occur.


Disclaimer:  This information is based on sources that we believe to be accurate. It is offered in good faith, but without guarantee, since conditions of use are beyond control. All risk of use are assumed by the user.


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