When comparing injection mould vs cast processes, there are many things to consider. While injection moulding can be cost effective when producing larger quantities, injection-moulded polymers do not offer the superior physical properties of open-cast thermoset polyurethane. That’s because the hot cast process provides a long slow cure and post cure that enhances the cross-linking of the polyurethane molecule, something that cannot be accomplished in the relatively short processing time associated with injection moulding.

So, although producing open-cast thermoset polyurethane components may be more labour intensive, the result is a greater range of physical properties which translates into better overall performance in the long run, as well as significant cost savings.

Open Cast Moulding

When you’re preparing to purchase high quality urethane components for your unique application, it makes sense to educate yourself on the distinct differences between the two most common processes used for manufacturing polyurethane parts. Open cast moulding and injection moulding are the two most popular methods for transforming urethanes into an extensive variety of parts and components. Open cast moulding involves liquid polyurethane being poured into an open mould and then placed in a heated compression press to spread the material evenly throughout the mould. Injection moulding requires liquid polyurethane to be injected into a closed mould with holes or “bleed gates” which allows air to be pushed out of the mould during injection so the polyurethane can spread evenly.

While these two methods seem relatively similar at first glance, there are many differences between them. In the battle of open cast moulding vs. injection, open cast moulding is often the winner, and there are several reasons why.

Range of Durometers

Durometer is the measurement of hardness in a material, a term which can also dictate the material’s resistance to indentation. Open cast moulding allows for the most extensive durometric range for the final product, with the ability to produce components from 00 to 80D, meaning very soft to very hard. The ability to manufacture products with such a wide range of hardnesses means that open cast moulding allows for increased versatility of part design.

Low cost tooling

While injection moulding can be fairly inexpensive when manufacturing larger quantities of a product, there is a clear discrepancy in terms of quality. When working with small to medium sized production runs, open cast moulding offers the combination of a low cost paired with superior quality. Additionally, because open cast moulding yields a higher quality end product, more money can be saved over time as the product will outlast those made by injection moulding.

Excellent Adhesion

When your component requires the ability to snugly adhere to another part, open cast moulding is a far superior option when compared to injection moulding. While injection moulding is fast and cheap, it yields less uniform parts with increased likeliness of uneven or rough sides. The slow cure process of open cast moulding allows the liquid urethane to spread evenly within the mould, ensuring smooth surfaces when the component is removed. While a rough surface from injection moulding can be smoothed, additional time will be needed for tooling, resulting in an increased cost.

Fatigue Strength

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


Edhar engineers specialist polyurethane products and solutions for the industrial and mining industries. Our focus lies with manufacturing various urethane wear products suited for highly abrasive conditions.
Read More

Contact Information

Phone    083 293 1541
Email sales@edhar.co.za
Find Us

Unit 1
Buffalo Thorn Complex
Business Partners
Cnr Kock & van Belkum Str
South Africa