Hi everyone!
In this tutorial I show you how to cast a 2 part silicone mould
using @easycompositestv AS40 Addition Cure Silicone Rubber.

AS40 is a high quality 'addition cure' (platinum cure) silicone rubber for more demanding mould making applications.

Addition cure rtv silicone should be used in applications where very accurate dimensional reproduction of an original part is required such as in rapid prototyping, where higher temperature tolerance is required or where the maximum number of repetitive releases will be possible.

Our addition cure silicone has been chosen for its excellent dimension reproduction; it is incredibly low shrink and therefore can be used to make a mould for prototype parts that interconnect (like a nut and bolt) to engineering tolerances. It has excellent styrene and polyurethane resistance and a high tear strength.

Translucent Colour

AS40 is unpigmented and highly translucence, making it particularly suitable for use both in making moulds where being able to see the casting inside is helpful, and for making silicone components where its clear appearance mean it can be easily pigmented to any colour, including pure black or white, or vivid red and blue, which is not possible to achieve when using opaque silicones or those which use a pigmented catalyst as a visual indicator.

In common with all clear silicones, because both the silicone and the catalyst are clear, this does mean there is no visual indication as the catalyst is mixed into the silicone and so extra care should be taken to ensure they are thoroughly combined. In applications where the silicone does not need to be clear, a small amount of one of our liquid silicone pigments can be added to the AS40 catalyst before it is added to the silicone, thus providing a visual indication of when the catalyst is fully combined.

Vacuum Level for Successful Degassing

To achieve its excellent properties for tear-strength, stability and longevity, AS40 does have a higher viscosity compared to less high-specification silicones. This high viscosity does tend to mean more air entrapment during mixing and also means that only very high levels of vacuum will achieve the ‘self-collapsing’ point necessary to fully degas the silicone. Situations where AS40 does not seem to fully degas under vacuum can be resolved by fixing small leaks in vacuum fittings, or by servicing worn-out vacuum pumps.

Suggested Uses

Use our AS40 Addition Cure Rubber to produce accurate moulds of complicated parts, precisely reproducing the dimensions of the original part. Completed silicone moulds can be used for repetitive casting applications, ceramics, vacuum casting and general mould making.

Advantages

Very accurate reproduction of dimensions (very low shrinkage)
Translucent
High tear strength
Styrene and PU resistant
How to Buy

Easy Composites' AS40 Addition Cure Silicone Rubber is available in four different pack sizes: 0.5kg, 1kg, 5kg and 27.5kg. All packs include the correct ratio of silicone rubber and catalyst (hardener). Please choose the pack size you want from the drop-down list.

Further Information

Mixing Ratio

100 p.b.w. Addition Cure Silicone Rubber

10 p.b.w. Addition Cure Silicone Rubber Catalyst

Brief Description of Typical Use


A part to be copied is positioned within a 'setup box' which will contain the silicone rubber whilst it cures.

The silicone rubber is thoroughly mixed with its catalyst at the correct ratio and then placed in a de-gassing chamber to remove any air trapped within the mixed silicone. If a de-gassing chamber is not available it might be possible to satisfactorily de-gas the silicone using the 'stretch pour' method (see accompanying datasheet for more info).

Once the silicone has been de-gassed it is carefully poured into a single place at the bottom of the setup box (to avoid accidental aeration) and once the setup box is full of rubber the whole box is placed in the vacuum chamber to de-gas again. The silicone will cure at room temperature in 24hrs or can be cured at an elevated temperature to hasten then cure (see accompanying datasheet).

Compatibility Information - Dos and Don'ts

Although by no means an exhaustive list, the mould materials, pigments and additives listed below have all been tested and are known to work well with AS40 Addition Cure Silicone.

Compatible Moulds

Almost all Plastic moulds*
Metal moulds
Addition Cure Silicone moulds with a release agent
Compatible Pigments

RTV Silicone Colour Pigment (for vivid opaque colours)
Translucent Tinting Pigment (for less vivid opaque colours)
Compatible Fillers

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