Silicone foam is made from a low-viscosity liquid silicone rubber. These relatively low viscosity liquids can be pumped to the vulcanizing equipment. The liquid is cast onto a smooth liner (giving silicone foam its smooth surface appearance) and processed through curing ovens. Silicone foam can be supplied as an open cell, closed cell or combination of both, open and closed cell material. Silicone foam is typically lighter in density, compresses with less force and has a lower compression set than silicone sponge.
RTV Silicone Foams
RTV Silicone Foam is a very soft, two-component silicone foam which cures at room temperature by an addition cure reaction. When the A and B liquid components are thoroughly mixed in 1:1 or 10:1 ratio, the product will expand and cure to a foamed elastomer. They are expands 2-6 times its original volume. Cured silicone foam is high heat resistance (will resist up to 250°C), water resistant, UV resistant and resists oxidation and ozone degradation. Silicone foams generally have low compression set, which means they recover their original shape after being compressed.
How to Use
After dispensing required amounts of Parts A and B into mixing container, mix thoroughly for 30 seconds. RTV silicone foam cures quickly, Do not delay between mixing and pouring, Elevated temperatures will result in a reduced pot life and cure time.
Note: A small amount of Hydrogen gas is released as part of the A:B reaction. Use only with adequate ventilation and do not breathe fumes. Also do not smoke or have other ignition sources in proximity to this product during mixing and pouring.
HTV Silicone Foams
While HTV silicone foams nominally a room-temperature vulcanization (RTV) technology, they use an addition cure mechanism which is typical for high-temperature vulcanization (HTV) products. Mixing the components produces a reaction that releases hydrogen gas as a foaming agent. The foam expands in its liquid stage and cures to a foamed solid elastomer within 10 minutes at room temperature. This cycle can be accelerated by elevating the temperature.
Curing of Silicone Foams
The two-part silicone foam is dispensed — typically with a robotic applicator — directly on the part surface. Silicone foam can be mixed either in a static or dynamic mixer. A dynamic mixer is recommended, however, because the type and degree of mixing and shear can affect the density, cure and cell structure of the finished foam. To ensure optimal foam structure a good mixing of the components is required. When the A and B components are mixed, the following reactions occur:
Silicone Foams create the foaming gas during the crosslinking reaction (hydrogen as a by-product).
Foam expansion: typical expansion ratio: 1:2.5 to 1:4 (HTV), 1:3 to 1:6 (RTV).
Curing (formation of the elastomeric network).
All reactions are temperature-dependent but at different rate constants.
Open-Cell vs Closed-Cell
The main difference between these two types of silicone foam is pretty obvious. One option has cells that are closed and one has cells that are open.
Open cell silicone foam is full of cells that aren’t completely encapsulated. In other words, the cells are deliberatly left open. This makes the foam a softer, more flexable material.
Closed cell silicone foam is made up of cells that are, as the name suggests, completely closed. The cells are pressed together, so air and mositure are unable to get inside the foam. Because of this, closed cell tends to be less springy with soft cell foam offering more spring to it.
The major difference between the two silicone foam options is that open cell silicone foam has tiny cells which are not completely closed. The open cells are filled with air and this affects the way the silicone foam feels and performs. Closed cell silicone foam has cells which are sealed off so air doesn't get inside the structure at all.
Advantages
Silicone foams are ideal for gaskets, insulation, seals and vibration dampening, especially in applications where the sealing surface is not smooth and the temperatures vary widely, due to silicone’s excellent versatility. Here we explore a range of silicone foam’s unique advantages:
Silicone foam is available in both open-cell or closed-cell foam structure.
Open cell foam structure allows high absorption of water, moisture and dust – making it ideal in a typical sponge used for washing cars.
Closed cell foam structure doesn’t accommodate for the absorption of water, moisture or dust – making it ideal in sealing applications where water and dust need to be kept out. This type is inherently hydrophobic (repels water).
Low flammability – Compliance with the most stringent flame ratings, enabling uses in anti-fire measures and glazing seals (UL94 rated).
Low density – reducing overall weight and improving dimensional stability.
Excellent compression set resistance – rebound to original thickness quickly.
Resistant to temperature extremes (-50°C to +250°C).
Heat curing (HTV) and room temperature curing (RTV) materials allow for flexibility in design.
Self-foaming – does not require an added blowing agent Provides a low modulus sealing option.
Withstands weathering, ozone, corona, radiation, moisture, chemicals, weak acids and bases, oils and fuels
Applications
Since silicone rubber foam is very lightweight, very soft and has good cushioning effect. Silicone rubber foam is widely used in automotive, railway, daily necessities, aircraft, chemical, medical machinery, health supplies, sports goods and other industries.
Which is widely used as a filling material making sofa, seating in railway carriages, aircraft flame retardant underlayment, military equipment gasketing, mannequin, mattresses, shoulder pad, breast forms, silicone foam sheet, silicone foamed sealing strip, silicone foam mat, silicone foam tube and so on, as filler, cushions, insulation, sound insulation, shock-proof materials.