Beginners Guide: The basics of Urethane Resins

An Introduction to Urethanes

Urethane Resins

Whether you are creating molds, parts, prototypes, or tools, urethane resins are more than up for the task. But what are urethane resins? How do you use them, and what can they do for your project? Let’s take a look in this week’s informational blog.

What are Casting Urethanes?

Casting Urethanes are a group of versatile materials that can be used alone, in combination with each other, or even with composite materials. They are used to create molds that range from soft and flexible, to rigid and durable with great impact and abrasive resistance. They are designed to be poured into open or closed molds in order to create short-run parts, molds or tools. The polymers in urethanes are suitable for custom elastic machine parts, pliable molds or hard plastic prototypes, or coatings and lenses.

Types of Urethanes

Fibre Glast carries a number of types of urethanes, with different characteristics and hardness levels that can be used for a number of different uses. The hardness of the cured polymer they created is measured in what is called a Shore Durometer Scale, with higher numbers representing stiffer substances. A letter classification will also let you know where the particular urethane is, (from softest to hardest) O, OO, A, B, C, D. So for example, Fibre Glast’s 40 Shore A will be much softer and pliable compared to the 75 Shore D. Below, we have a table with the various measurements for each urethane carried by Fibre Glast.

 Mix RatioColorViscosity (CPS)Pot Life (min.)Demold TimeDensity (lbs/cu. in.)Tensile Str (psi)Elong. at Break (%)Link to store page
40 Shore A100:75Amber82520-252.5-3 hrs.038800525Urethane 40 Shore A
60 Shore A100:55Amber135012-152.5-3 hrs.0381400500Urethane 60 Shore A
60 Shore D100:44Amber2600262.5-3 hrs.0376014646Urethane 60 Shore D
75 Shore D100:100White 27530-403-4 hrs.038-.040500020Urethane 75 Shore D
Fast Set (84 D)100:100Gray26001030-40 min.06245002Fast Set tooling resin

Things to Keep in Mind

Using Urethanes

Working with urethanes can be slightly different, when compared to other resins. Moisture is extremely harmful to urethanes, and can lead to unpleasant, tacky finish. For this reason, it is recommended that fabricators avoid any sort of potential moisture contamination while working with urethanes. This includes using a plastic paint stirrer as opposed to the more common wooden ones (wood is notorious for absorbing moisture!)

For mold releases, it is recommended that you use a non-water based release agent. An Easy Clean Mold Release or Non-Silicone High Temp Paste Wax work great, for these types of applications. Do not use silicone molds when working with urethanes, as it may inhibit curing.
Finally, in order to extend the shelf life of your urethane products, make sure that non excess moisture is allowed into the can before sealing. Using a product such as a Poly Purge Dry Gas Blanket will help to keep humid air from sitting in your cat, harming your product. Consider rotating your cans every so often during storage to reduce settling.

Interested in learning more about urethanes? Check out our white papers, Casting and Molding Using Urethanes and Composites, Introduction to Urethane Casting Resins, and Step-by-step guide to fast set urethane resins.

Any other questions? Let us know in the comments section below. Be sure to check out our Facebook,and follow us on twitter @Fibreglast for more information the composites industry.

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1 zunoorain { 03.30.17 at 7:57 am }

i have purchased closed cell polyurethane liquids.

when i mix and pour two liquids in mold/Die, it starts expanding/foaming and takes the shape of mold, but the product gets sponge like holes mostly small but some holes are big
what is its solution?

2 { 07.24.17 at 1:39 pm }

Typically this is a result of an inconsistent mix of the liquid foam. Try mixing a smaller batch and step-casting in your mold.

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