What does RTV mean?
RTV stands for Room Temperature Vulcanization (cure). Despite the low-temperature connotations conveyed by this name, RTV silicones consist of both Room Temperture Cure and Heat Cure grades. |
| |
What is the cure mechanism of a condensation cure product?
Condensation cure silicone products cure when exposed to atmospheric moisture. Moisture in the air is generally required to cure (or vulcanize) condensation cure products. The cure process begins from the outer surface, and therefore time is required for complete cure. The cure time is affected by the reaction mechanism and viscosity of the material. Generally, at 25C and 50%RH, condensation cure RTV silicones cure through in 24 to 48 hours. Full physical properties may take up to 7 days to develop. |
| |
What is the depth (bead thickness) limitation for a condensation cure grade?
For 1-part, condensation cure products, the depth (bead thickness) limitation is approximately 1/4". For 2-part, condensation cure products, the depth (bead thickness) limitation is approximately 1". |
| |
Can I accelerate the cure time of a 1-part product?
Condensation cure silicone cure rates depend on humidity, silicone thickness, and to a smaller degree heat . Increasing the relative humidity around the silicone or reducing the thickness of the material will reduce the time to cure the material. Increased heat (not over 50C) will somewhat reduce cure time but as mentioned will do so to a much smaller degree than humidity or thickness. |
| |
What is the cure mechanism of an addition cure product?
Addition cure silicone RTV products may be 1 or 2-part and cure when exposed to heat . Although some heat cure products can cure at room temperature, higher heat greatly accelerates the cure. 1-part heat cure products typically have an inhibitor in the formulation that stops the product from curing until an activation temperature, greater than room temperature, is achieved and the inhibitor is driven off and the cure reaction is allowed to proceed. |
| |
What does "tack free time" mean?
Tack free refers to the amount of time it takes for a condensation cure silicone product to form a cured outer layer (the cured outer layer is not tacky like uncured material). |
| |
What is "mix ratio"?
Mix ratio is a term used to state the amount of each material to be in a multi-component material. The mix ratios for 2-part products are described on the individual product data sheets and are given as a ratio by weight of each material. |
| |
What does "pot life" or "work life" mean?
The amount of time after a 2-part grade is mixed with its curing agent that it will remain useful or pliable. |
|
|
How do I remove silicone?
Before it is cured: use a putty knife to remove any of the uncured paste. Wipe the area clean with isopropyl alcohol to remove any leftover residue. After it is cured: First mechanically remove as much of the silicone as you can with either a knife or a razor. A solvent (mineral spirits, toluene, xylene, acetone) can them be used to remove any oily residue or any remaining silicone, It may be necessary to soak the silicone in a solvent overnight to break it down. |
| |
Can I thin a silicone?
Silicone can be thinned using a solvent in which the silicone is
miscible, generally an aromatic solvent such as toluene or xylene. As always, be sure to follow the producer's instructions when using solvent products and always use in a well-ventilated area. The shrinkage of the silicone and the cure time will increase with the addition of solvent. Alternative suggestions would include nonreactive fluids or an RTV with a lower viscosity. |
| |
What can I do to improve the adhesion of the silicone adhesive to my parts?
The first step to good adhesion is to have clean surfaces for the
silicone to bond to. For difficult to bond substrates, Yantai E.S.T silicone Tech off ers a number of primers that can be used to improve and maximize adhesion. |
| |
How do I ensure that air is removed from 2-part grades?
If you are hand mixing, air may become added to the material
during the mixing process. Vacuum de-airing is most effective in removing air prior to use. Automated mixing equipment that utilizes a static mixer can eliminate the need to de-air prior to dispensing. On complex high-density electronics, air can sometimes be trapped under components during the potting process. Where this is a concern, potting under vacuum or vacuum de-airing after potting can remove the trapped air. An alternate approach may be to use a grade with a low viscosity and longer potlife and to cure at lower temperatures (if heat-cure grade), allowing entrapped air to escape prior to the cure of the material. |
| |
What is cure inhibition, and how do I prevent it?
Cure inhibition is a phenomenon that may be observed in additioncure grades. These materials use a platinum catalyst to drive the curing reaction. Surfaces containing water, sulphur, nitrogen compounds, organic metal compounds, or phosphate compounds, may inhibit cure.
Cure inhibition is characterized by a gummy or sticky appearance of the silicone at the interface between the silicone and offending substrate. Inhibition can be prevented by application of a barrier coat, cleaning of the offending material prior to application of the silicone material, replacing the offending material with a suitable alternative, or selection of a condensation cure grade. |
| |
| |
| |
|
