When you are preparing to purchase quality urethane components for your unique applications, educating yourself on the distinct differences between the two most common processes used for manufacturing urethane parts is vital. Open cast molding and injection molding are the two most popular methods for transforming liquid urethanes into component parts.


Open cast molding, the type utilized for all SjoBrand products, involves liquid urethane being poured into an open mold and then placed in a heated compression press to spread the material evenly throughout the mold. Injection molding requires liquid urethane to be injected into a closed mold with holes or “bleed gates” allowing air to be pushed out of the mold during injection so the urethane can spread evenly.

In general, open cast production is vastly superior in quality and lifespan of the product. A few of the instances of superiority are… Range of durometer…open cast lends itself to an extreme variety of durometers (hardness), ranging from very soft to very hard. This range ability is a significant advantage for your customer needs.

Low cost tooling…in general, tooling for open cast production is significantly less expensive than the tooling for injection molded products.

Excellent Adhesion…When your component requires the ability to snugly adhere to another part, open cast molding is a far superior option when compared to injection molding. While injection molding is fast and inexpensive, it yields less uniform parts with increased likeliness of uneven or rough sides. The slow cure process of open cast molding allows the liquid urethane to spread evenly within the mold, ensuring smooth surfaces when the component is removed.

Fatigue strength…If it is a priority for your component part to be resistant to breaks, open cast molding is vastly superior to injection molding. Since the heat curing process builds strong links in the hardening urethane material, the finished material features superior molecular bonds to that of injection molding. An open cast molded component offers superior tensile strength, making it ideal for products that will be subjected to high levels of vibration or impact. Since injection molding doesn’t involve the same slow heat curing process, the resulting material doesn’t have the same closely linked structure in the hardened urethane material, making it more susceptible to breakage.


For all sales inquiries, please contact:
Jeff Sjoberg - jeff@sjobrand.com