FAQ

General Inquiries

Silicon is an element. Pure silicon is used to make semiconductors. Silica is a naturally occurring mineral. It makes up 21% of the earth’s crust. Examples are sand and quartz.

Silicones are a class of synthetic polymers based on a backbone of alternating silicon and oxygen atoms with organic groups hanging on the backbone like ribs.

Silicon is an element. Pure silicon is used to make semiconductors. Silica is a naturally occurring mineral. It makes up 21% of the earth’s crust. Examples are sand and quartz. Silicones are a class of synthetic polymers based on a backbone of alternating silicon and oxygen atoms with organic groups hanging on the backbone like ribs.

RTV: is shorthand for Room Temperature Vulcanizing. It is a unique type of system that can be cured with a catalyst to form a tough silicone rubber. It cures without an exotherm (internal heat buildup) and very little shrinkage. This is why it can reproduce a surface feature as small as a finger print. There are two groups of silicone RTVs; addition or platinum cured (ppm !) and condensation or tin cured.

The platinum system has an advantage in that the cure can heat accelerated and has virtually no shrinkage during room temperature curing. It has the disadvantage that the same things that poison the catalytic converter on a car, heavy metals, sulfur compounds, and amines can poison the platinum catalyst. (These are frequently found in tooling shops.)

The tin system has the advantage of not being easily inhibited. During cure a small amount of an alcohol is evolved. This can cause a slight amount of shrinkage (less than 0.5%) If the cured RTV is to come in contact with a wet urethane it should be air dried overnight or heated to remove the alcohol to prevent bubbling on the urethane surface

Density is weight of a material in a given volume. One pound of water fills 27.5 cubic inches. Specific Gravity (SpG) is the weight of a material compared to an equal volume of water. Il take 2 pounds of a material with a specific gravity of 2.0 to fill 27.5 cubic inches. Since RTV and most plastics are sold by the pound and are used by volume, specific gravity is an important factor in comparing the actual cost of materials.

Pound Volume Cost is used to compare the actual cost of materials. Multiply the cost per pound by the specific gravity to find the pound volume cost. If your 5 gallon pail kit costs $450.00 and weighs 49.5 total pounds 450/49.5 = $9.09 per pound. If its specific gravity is 1.29 its pound volume cost $9.09 x 1.29=$11.73. If a competitive material costs only $ 8.99 per pound but has a specific gravity of 1.35 its pound volume cost $8.99 x 1.35 =$12.17. It is not a bargain.

Viscosity: is a measure of how easily a material will pour. It is reported in centipoise (cPs). The higher the value the thicker the material is. Water has a viscosity of 1.0 cPs, Pancake syrup is about 1000 cPs and honey is about 10,000 cPs. Molasses in January would be several hundred thousand. For best flow material should at least be at room temperature. Heating the material may help in pouring some molds. If needed, heat the base before adding the catalyst. Be careful, heating will shorten the pot life of the mixed material.

Pot Life: can also be called gel time, working time, or pour time. It gives the user an idea of how long he has before the material becomes too thick to use. Most materials should be poured well ahead of time to ensure good flow and to permit air bubbles to rise and break.

Demold Time: is the earliest time a cured product can safely be removed from a mold without distorting the part. Heating some materials will shorten their demold time.

Cure Time: is the length of time before a material is finished and ready for use. Some materials require up to a week to fully cure. Most silicone RTVs will develop over 90% of their fully cured properties within 24 hours. Additional heating can be used to accelerate the cure of many urethanes, epoxies and addition cure RTVs.

Shrinkage: is a reduction in size experienced with some materials during cure. Many urethanes and some epoxies contain solvents that evaporate causing significant shrinkage. Most silicones have little or no shrinkage during cure. They may exhibit some progressive shrinkage when used with resins that tend to attack silicone polymers.

Durometer: is an instrument used to measure hardness. The durometer gauge uses a needle-like probe that is pushed into a material to measure its hardness. The farther the needle penetrates the lower the “durometer” hardness. The Shore A scale is used for elastomers and the Shore D scale for rigid plastics.

Tear Strength: is the force needed to propagate a cut in an elastomer when it is stretched. It is reported in pounds per inch.

Tear Strength: is the force needed to propagate a cut in an elastomer when it is stretched. It is reported in pounds per inch.

Elongation: is measured at the same time as tensile strength. It is the amount the elastomer has stretched when the sample breaks. It is reported as a percentage (%).