| ... | ... | @@ -44,39 +44,70 @@ You pour a certain mass of part B: |
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You add the same mass of part A:
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And you strongly mix it with the fork taking care of scratching the edges of the cup:
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Once casted, this mold can be reused a lot of times (~100) until it gets a bit sticky. Also, remember that it can be easier to duplicate this casting step instead of duplicating the backing mold or making a bigger one.
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The silicone is ready you do not need to degas it. Then you slowly pour it in the backing mold, making sure that every edge of the mold is reach. You do not need to take care about bubble they will go away. You can also pour it in access without cleaning, it is easier to clean once cured:
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After about 5 hours (over night if you want to be sure):
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You can, now, safely pull the silicone mold away from the backing mold. It is very resistant so do not hesitate to pull it strongly:
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To be sure that the mold is correctly cured, once demolded you can cure it few more hours at 60 C (this is not absolutely necessary but better if you want to keep your mold longer). Here is an example of mold you can get:
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Once casted, this mold can be reused a lot of times (~100) until it gets a bit sticky. Also, remember that it can be easier to duplicate this casting step instead of duplicating the backing mold or making a bigger one.
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Picking the right urethane
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Before casting urethane, you need first to choose the best for what you want to do. The photoelastic signal is a function of the strain, the larger the more you will have fringes. But if fringes are too dense they will overlap and you will not be able to measure anything. This will happen if you load your sample too much or if it is too soft. On another hand if the sample is too stiff or if you do not load it enough the photoelastic signal will be too weak to see something or to measure accurately. Note that this also depends on the thickness of you sample. That is why, depending on your sample's shape and on how you load it you need to pick the right urethane stiffness.
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The castable urethane we use here is the [Clear Flex](https://www.smooth-on.com/product-line/clear-flex/): 'a water white clear urethane liquid rubber compounds designed for applications that require absolute clarity'. It is available in three different shore stiffness: 30, 50, 95. The one we use here is the [Clear Flex 50](https://www.smooth-on.com/products/clear-flex-50/). It is the most commonly used for centimetric samples that will undergo few Newton loadings. Also, not that playing (non linearly) on the quatity of cross-linker (part A) you add in the urethane, you can tune the material stiffness. But be careful because you also play on the curing time!
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If you want to slightly color the sample for imaging purpose you should use [So Strong](https://www.smooth-on.com/products/so-strong/) dye. In the following we color our sample in green because it is usually the optimum color for polarisers.
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Casting method
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--------------
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Once you have chosen the good stiffness, the next step consists in making urethane rubber and pouring it in the silicone mold. This once is the tricky part...
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Everything you need for this step is:
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*
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*
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*
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*
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*
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*
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*
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* Pouring polymer and crosslinker
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* Adding color
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* degassing the urethane
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* pouring in molds
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sticky use talk
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| ... | ... | @@ -150,19 +181,8 @@ Once casted, this mold can be reused a lot of times (~100) until it gets a bit s |
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Picking the right urethane
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--------------------------
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[Clear Flex](https://www.smooth-on.com/product-line/clear-flex/)
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[this one](https://www.smooth-on.com/products/clear-flex-50/) is the most commonly used
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if you want to slightly color the sample for imaging purpose you should us [So Strong](https://www.smooth-on.com/products/so-strong/) dye
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Casting method
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--------------
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* Pouring polymer and crosslinker
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* Adding color
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* degassing the urethane
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* pouring in molds
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