Frequently Asked Questions

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What items do I need to have to cast a polyurethane part?

At the bare minimum you will need the following:

  • A kit of Simple Resin polyurethane.
  • A kit of Elasto-Mold mold making soft rubber urethane.
  • Mixing containers and mixing sticks.
  • Hand and eye protection.
  • A mold box.
  • A part to replicate.

Some or all of these items can be found in one of our Simple Resin Casting Kits.

How do I mix the two components properly?

The recommended way to mix the two components is as follows:

 

  • Pour an equal amount of both Part A and Part B into a mixing container.
  • With a mixing stick start to stir in a circular motion.
  • Be sure to periodically scrape the sides and bottom of the container so that you include all of the polyurethane in the mixture.
  • Most urethanes will need between 15-30 seconds of mixing to get a good mix.
  • If you are mixing a water clear material, you’ll want to add 15-20 seconds to your mixing time.
How long do I have to mix and pour the material?

When considering how long you have to work with a product before it cures you need to look at that individual product’s work time.  If the product has a 3 minute work time (like Brilliant White, True Translucent etc.) you will want to have the product mixed and poured within ~2 minutes of when the two parts were combined.  That will give the product time to find its way into all the details of the mold before it cures out.

There are other factors that can affect work time:

 

  • The starting temperature of the two parts – All the work times of Simple Resin products are taken at a starting temperature of 77F.  As a general rule, every ten degrees Fahrenheit that you increase the starting temperature will cut your work time in half.  For example, if you are casting parts in a garage that is 87F then a product with an original work time of 3 minutes will cure out closer to 1:30 minutes.  If you are mixing materials in the basement in the winter and it is 67F then you can expect the work time to be extended.
  • The mass/ thickness of the part you’re casting – Polyurethane cures out by generating heat.  The thicker the part, the more heat is generated causing the product to cure out faster.  As an example, if you are mixing up a half pound of material the work time will be longer than if you are mixing up 10 lbs of material.  Along those same lines, if you are pouring a part that has a thick section it will cure out faster than if you mixed the material and poured it on the table in a thin film.  Every part will slightly vary so these are just for general knowledge, but hopefully, this answers some of the questions around work time and the variables involved.
How can I speed up the time I have to wait before I demold my part:

If you heat up the mold to ~100F before you pour the mixed polyurethane into it, your urethane will cure out a lot faster.  If you combine that with placing the mold (with the mixed urethane in it) back into the ~100F it will drastically speed up how quickly you can demold the part.  As was mentioned in the FAQ section “How long do I have to mix and pour the material” polyurethane creates heat during the reaction between the two parts.  If more heat is added after it is mixed it will only serve to speed the reaction up.  The thickness of the part still needs to be considered.

The other factor to consider is that the work time is directly related to the demold time.  The faster the work time, the faster the demold time (as a general rule).  If you need to demold the part faster, then make sure you get a product with the fastest gel time that still allows you to mix and pour the product effectively.

Can you explain viscosities

Below is a list of common liquids and their viscosities:

 

Water

Olive Oil

Maple Syrup

SAE 30 Motor Oil

Latex House Paint

Shampoo

Karo Syrup

1 cps

100 cps

150 cps

500 cps

1500 cps

3000 cps

5000 cps