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Tag: Silicones

  • Playing With the Cure Time of Molds and Casts

    Playing With the Cure Time of Molds and Casts

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    Every mold making and casting material comes with its own specific range of cure time. This is nothing but the time that the material will take to get completely cured. It can range from just a few minutes to hours or even a few days. The mold or cast has to be left to air dry on its own and there is nothing much that the artist can do in the meanwhile.

    Similarly, the pot time or working time is the time on hand to work with the product after it is mixed until it starts to set. After this, the material will not work properly.

    For instance, alginate is renowned for its quick setting and curing time, whereas materials like latex rubber require days on end to cure before they are ready for use. Most silicones have a cure time between 18 to 24 hours.

    What to do?

    Artists use various measures to speed up or prolong the cure time. In fact, delayed-setting and quick curing options are available for alginates, plasters, silicone and other materials. Sometimes, fibers, fillers, talc or magnesium oxide (for plaster) are added to achieve the same effect.

    For certain materials like silicone, fast catalysts are also available. These can be added to the silicone rubber to significantly reduce the cure time, sometimes to even just an hour! Care is needed as adding too much catalyst may make the material start curing even before it can be applied.

    Alternatively, techniques like hot air dryer, dehumidifier or baking in an oven are used to hasten the cure time. In fact, plaster casts are often baked to reduce the curing time to 12 to 24 hours. However, too much of the hot air can also cause the mold or cast to crack or spall. Also, silicone does not react very well to heating from dryers or lamps; it may just break out in unsightly bubbles all over the mold or cast.

    Temperature variation

    It should be noted that the pot time and cure time is generally measured at normal room temperature. It will definitely vary depending on the atmospheric and climatic conditions prevailing at the time of working/curing. For instance, cooler temperatures tend to increase the pot time and cure time while warmer weather is sure to reduce both working time and cure time.

    This phenomenon can be easily used to vary the pot/cure time to suit your convenience when trying how to make molds. All you have to do is gently warm the material (both base and catalyst for two-part materials) before using them. This will speed up the chemical reaction and the mold or cast will take lesser time to cure. But keep in mind that the working time is also reduced and the material will start setting much more quickly. Do not overheat the materials either.

    Similarly, cure time can be easily increased by refrigerating the material (both base and catalyst again) prior to use of how to make molds. This will give more time for working with the material per se.

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    Source by Ed McCormick

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  • Tin-Cure and Platinum-Cure Silicones

    Tin-Cure and Platinum-Cure Silicones

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    Silicone rubber is a material of choice for many mold makers and casting artists. The excellent flexibility, superior strength, enhanced resistance and long life work in its favor apart from the versatile usage for almost any application.

    Silicone rubber comes as a two-part formula that can be poured, sprayed or brushed on the model/mold. In fact, it is safe and can be used for both mold making and casting as long as it suits your application. Another benefit is that silicone does not stick to anything, so a release agent is mostly not required.

    Silicone rubber is often used for general mold making applications as the molds manage to capture fine details and can be made very quickly as well. Most materials – all types of resins, foams, wax and some low-melt metals – can easily be cast in silicone molds. It is also suitable for making soaps and candles, sculpture reproduction, cold casting. Special rubber variants can be used for making food molds, realistic masks, doll reborning, special effects and even life casting.

    Types of silicone

    Silicone rubber polymers come in two variations – platinum-cured and tin-cured. Both these types are very different from each other and are not even compatible with one another. Let’s find out how:

    • Tin cured silicone rubber uses tin salts (usually 5%) as a catalyst to initiate the cure from liquid state to solid. This is also known as condensation cure. Platinum cured rubber has a platinum catalyst (usually 10%) for curing and is also known as addition cure.
    • Tin cured silicones require moisture for proper curing and excess humidity can accelerate the cure time whereas humidity does not have any effect on the curing of platinum variants at all.
    • Tin cured variants are less expensive and also prove to be easier to use while platinum based ones turn out to be quite expensive.
    • Tin cured silicone molds and casts may tend to shrink a bit at times while the platinum cured counterparts enjoy virtually nil shrinkage.
    • Tin based silicone is tear resistant and even considered biodegradable. Its counterpart is considered very pliable and tough.
    • Platinum cure silicones offer exceptional heat resistance and work better in high temperatures than tin cure ones. The former can even be heat accelerated for faster curing.
    • Platinum cured silicones require very accurate and careful mixing, but this is not the case with tin cure ones.
    • Tin cured silicones are primarily suited for general silicone mold making, prototype applications and prosthetic works. Platinum cured silicones provide good dimensional stability and work well for precision molding, special effects applications, encapsulations and paints. The latter comes in food safe, skin safe and transparent versions also.

    So, go ahead and make your silicone mold by all means, but do choose the type of silicone rubber with care.

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    Source by Ed McCormick

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