Introduction and boring stuff
Let’s get the boring things over with first in this introduction.
Up front this section is included for those of you that want a broader knowledge and understanding of silicones and is not at all essential to the practical art of mould making.
Here goes
Often there is confusion between silicone and silica
It may come as a surprise, but silicon and silicone are two very different things. In short, silicon is a naturally occurring chemical element, whereas silicone is a synthetic substance. Silicon is the 14th element on the periodic table. It’s a metalloid, meaning it has properties of both metals and non-metals, and is the second most abundant element in the Earth’s crust, after oxygen.
Silicones however are any of a large class of siloxanes that are unusually stable over a wide range of temperatures used in lubricants and adhesives and coatings and synthetic rubber and electrical insulation
There are many types of silicones with various properties
Silicones exhibit many useful characteristics, including
- Low thermal conductivity
- Low chemical reactivity
- Low toxicity
- Thermal stability (constancy of properties over a wide temperature range of −100 to 250 °C).
- The ability to repel water and form watertight seals.
- Does not stick to many substrates, but adheres very well to others, e.g. glass.
- Does not support microbiological growth.
- Resistance to oxygen, ozone, and ultraviolet (UV) light. This property has led to widespread use of silicones in the construction industry (e.g. coatings, fire protection, glazing seals) and the automotive industry (external gaskets, external trim).
- Electrical insulation properties. Because silicone can be formulated to be electrically insulating or conductive, it is suitable for a wide range of electrical applications.
- High gas permeability: at room temperature (25 °C), the permeability of silicone rubber for such gases as oxygen is approximately 400 times that of butyl rubber, making silicone useful for medical applications in which increased aeration is desired. Conversely, silicone rubbers cannot be used where gas-tight seals are necessary.
Top of Form
Uses & Benefits
Silicones impart a number of benefits to the products in which they are used, including enhanced flexibility and moisture, heat, cold and ultraviolet radiation resistance. Silicones can be manufactured in many forms, including solids, liquids, semi-viscous pastes, greases, oils and rubber.
Personal Care Products
Silicones used in personal care products reduce the white residue and tacky feel of antiperspirants in deodorants. They are also “long-lasting” and help to retain the color and luster associated with cosmetics, shampoos and conditioners, as well as impart better shine, and allow skin care products to be made with stronger SPF. Wetting and spreading qualities provide for smooth and even application of cosmetics, lotions, sunscreens and cleansers.
Energy
Silicone improves the efficiency, durability and performance of solar panels and photovoltaic devices, making them more cost-effective. Because they can withstand the sun for years, silicones are ideal materials for solar panel and photovoltaic applications.
Electronics
Keypads, keyboards and copier rollers are made with sturdy, durable silicones – as are many components of computers, mobile electronics and home entertainment equipment. Silicones also play an essential role in enabling LED lighting technology. Silicones high thermal stability and excellent dielectric properties allow for use in a variety of electrical transmission applications.
Aviation
Because silicones can withstand stress and temperature extremes, silicone adhesives and sealants are used to seal and protect doors, windows, wings, fuel tanks, hydraulic switches, overhead bins, wing edges, landing gear electrical devices, vent ducts, engine gaskets, electrical wires and black boxes.
Architecture and Construction
Silicones are key to construction and renovation of commercial and residential buildings – from enabling glass walled skyscrapers to enabling energy efficient architecture. At home, silicone sealants and caulks are used to reduce energy usage and prevent damage from moisture and bacteria build-up.
Kitchenware
The flexible, non-stick surface of silicone bakeware and cookware is easy to clean and does not impart flavor or odor to food. Cake pans, muffin moulds, and baking mats can go from the freezer to the oven, microwave or dishwasher without affecting food taste or quality.
Paints and Coatings
Newer silicone-enhanced paints keep the exterior coatings of houses, bridges and railway cars flexible so they withstand freeze and thaw cycles without cracking. Silicone coatings on highway, oil rig and road surfaces are less likely to corrode due to exposure to oils, gasoline, salt spray and acid rain.STort
Sporting Goods and Apparel
Silicones seal out water from goggles and diving masks. Silicones enable new techniques to design sportswear that is lightweight, durable, water repellent and high performing, while allowing the fabric to maintain “breathability.”
Silicone Rubbers
All of this is very interesting but complicated.
In this handbook we are interested in silicone (not silicon) rubbers.
There are 3 types of silicone rubber, so we need to be specific on the type required
- Solid Silicone Rubber or High Temperature Vulcanized, HTV
HTV quality or high temperature vulcanized silicone rubber is used in the compression moulding press. Special silicone rubber materials are chosen based on their intended use,
HCR solid silicone rubber grades are peroxide curing. They can be processed by conventional methods, such as extrusion, calendaring, compression and transfer moulding, or injection moulding. They cure in heat and is ideal for manufacturing a variety of silicone rubber articles to be fire, oil or heat resistant.
Liquid Silicone Rubber, LSR
Liquid silicone rubber is a high purity platinum cured silicone with low compression set, great stability and ability to resist extreme temperatures of heat and cold ideally suitable for production of parts, where high quality is a must. Due to the thermosetting nature of the material, liquid silicone injection moulding requires special treatment, such as intensive distributive mixing, while maintaining the material at a low temperature before it is pushed into the heated cavity and vulcanized. Liquid silicone rubbers (LSR) are two-part dispensable silicone materials that are readily mixed and rapidly heat-cured.
Whether you need industrial or food-contact formulations, liquid silicone rubbers offer:
- Excellent processing performance
- Fast cure rates
- Reduced cycle times
- Lower production costs and appropriate fabrication methods for liquid silicone rubbers include liquid injection moulding and coating.
This is all very interesting but boring as hell. We are interested in making moulds, so let’s get on to it.
