Beginners Guide: The basics of Urethane Resins
An Introduction to Urethanes
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 Ratio||Color||Viscosity (CPS)||Pot Life (min.)||Demold Time||Density (lbs/cu. in.)||Tensile Str (psi)||Elong. at Break (%)||Link to store page|
|40 Shore A||100:75||Amber||825||20-25||2.5-3 hrs||.038||800||525||Urethane 40 Shore A|
|60 Shore A||100:55||Amber||1350||12-15||2.5-3 hrs||.038||1400||500||Urethane 60 Shore A|
|60 Shore D||100:44||Amber||2600||26||2.5-3 hrs||.037||6014||646||Urethane 60 Shore D|
|75 Shore D||100:100||White||275||30-40||3-4 hrs||.038-.040||5000||20||Urethane 75 Shore D|
|Fast Set (84 D)||100:100||Gray||2600||10||30-40 min||.062||4500||2||Fast Set tooling resin|
Things to Keep in Mind
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.