Elastomers are the hard-working hero of many a product design. In this series of posts, we’re exploring the flexible properties and use cases for a range of elastomers and examining their use in new product development.
Porticos has extensive knowledge and experience with the integration of elastomers into physical devices. We’re here to help; please get in touch!
Read Previous Post: Elastomers in Product Development: Material Properties
Over the last several articles, we have discussed what elastomers are, how they are made, and what properties describe their behavior and value. But the design engineer must eventually specify an elastomer and then justify that selection. Where to start?
Engineers rely on judgment and shared knowledge. Knowing that a thing has worked gives one confidence that it will work again. Porticos engineers have, over the decades, gravitated towards some engineering elastomers that have proven themselves in specific applications. Here are some recurring favorites:
Durability
Almost nothing beats polyurethane for sheer toughness. It is so tear- and abrasion-resistant that it is used for the soles of hiking boots. At Porticos, we have used it for many rigorous applications, including o-ring seals for a highly abrasive cryogenic fluid.
High Temperatures
Silicone is one of the more delicate elastomers, but above a certain temperature, it is simply the only choice. Silicone is both biocompatible and autoclavable, so it is a darling of the medical device industry. Need extra temperature/chemical resistance? We’ve had great success with fluorosilicone.
Low Temperatures
EPDM (ethylene propylene diene monomer) rubber is a favorite at temperatures down to -45°C, though butyl rubber can be more cost-effective. But when designing for really cold temperatures, silicone can be formulated to stay “rubbery” down to -100°C.
Overmolding
This one is trickier. An overmold must be chemically and thermally compatible with a rigid substrate (usually another polymer) so it’s necessary to define the pair together.
Thermoplastic Polyurethane (TPU) on a nylon substrate is a great combination for many applications. It is costs-effective, tough, and resistant to many chemicals. You’ll find this combination on, among other things, many power tools.
For less demanding (or more cost-sensitive) applications, Styrene Block Copolymers (SBCs) bond well to ABS. Though it’s not quite as durable, it’s more economical, and just fine for impact or grip zones on handheld devices.
Face-Sealing
Closed-sell silicone foams have a great combination of chemical- and temperature-resistance, and are available in a range of stiffnesses, making them a good choice for water and dust seals. BISCO is a good example of this material.
Tendons
A “tendon” is a flexible element that is loaded in tension. EPDM rubber is great for this application. Those rubber straps that truckers use to secure tarps? They are usually molded from EPDM. Good weather and ultraviolet resistance, too.
In Conclusion
A bit of advice: empiricism beats speculation every time. If you have the time and facilities then you should always test competing elastomers in the exact application for which you are designing.
We hope that this series of articles has helped you to become more comfortable in selecting the right elastomers for that evaluation. Porticos stands ready to help with any aspect of New Product Development, including elastomer guidance and testing. Feel free to contact the team with questions!
