Innovative Solutions with Molded Polyurethane: Exploring Its Dynamic Uses

May 9, 2024, 11:29 AM by The Stoner Molding Solutions Team
Choosing the right method of molding can be confusing and difficult, particularly when dealing with a material like polyurethane. Polyurethane molding provides countless industries with an incredibly useful and resilient material. However, knowing which choice to make when forming your flexible foams and hard plastics requires a lot of research.
 Bright yellow polyurethane parts and pieces on display

Read on through this blog, and you'll see the most common methods of molding urethane rubber and polyurethane foam into usable forms. These products can be incredibly desirable throughout multiple industries, and our products can help you get the most out of your molded urethane products. Once you've decided on how to produce your molded polyurethane, consider our inventory of products to enhance and improve your production line.


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What Is Polyurethane?

The polyurethane elastomer material is one of the most commonly used and demanded materials in industrial components and commercial goods. Elastic polymer materials are synthetic materials that can stretch and deform before bouncing back to their original shape. This flexibility can be enhanced or altered through various formula changes, creating products with very specific uses.

Cast polyurethane is one of the most popular uses of this material, common in vehicles and furnishings. Products as different as hard plastic skateboard wheels and soft molded polyurethane foam vehicle furniture can come from similar origins. Because of this flexibility, this material can be run through a different plastic forming process for every use case.

Five Ways to Mold Polyurethane

Polyurethane and additive resins are versatile and are used in industry and commercial products. The mechanical properties of polyurethane foams and elastomers make them attractive materials for a wide array of urethane molding methods.

The five primary methods of polyurethane molding are open casting, spin casting, reaction injection molding, multi-component over-molding, and continuous feed production. These each provide unique benefits and drawbacks to their processes. Read on for a more in-depth explanation of each option.

Open Casting

The polyurethane casting process involves hand or machine mixing polyol and isocyanate with a variety of additives.  This ratio of ingredients is crucial to the final properties of the finished product.  The batch is then poured into a mold for curing. Molds used in open casting can be made of silicone, polyurethane, metal, or composites.  After curing, the resulting product is removed and trimmed or post-cured.

Open casting is used in small—to large-volume production environments. Molds are heated to the appropriate casting temperature for the polyurethane. Ease of release is critical in an open-casting process to facilitate the quick turnover needed for each mold.

Spin Casting

Spin Casting is a closed molding technique used to produce precise size and durometer parts. It incorporates horizontal, vertical, or multi-axis rotation to create a uniform part. Spin casting is used when the flow of the polyurethane formula is naturally slow. During the process, the mold is spun along its central axis at a set speed while casting material is poured into it. The centrifugal force then pulls the material into the cavities of the mold.

Spin casting can be used to create a perfect finish on the part and layer multiple types of polyurethane into a single part.  Mold design, rotation speed, and injection times can be critical, and equipment can be costly.

Reaction Injection Molding (RIM)

RIM processes differ from open molding processes in two critical ways.  First, the polyurethane components are machine-metered and mixed as they are injected into the heated mold cavity.  Second, the components are isolated from atmospheric air throughout the process.  The liquid polyurethane can be pulled through with the assistance of a vacuum pump or fed from the bottom, allowing air to escape through vent ports on the top of the mold. 

This process can decrease cure times and improve part properties. Structural reinforcement, such as fiberglass, can be added to make some truly unique parts. However, due to the complex nature of the injection process, tooling costs can be very high, and mold changeover is more time-consuming.

Brightly colored polyurethane molded products on display

Multi-Component (Over-molding)

Over-molding is a type of molding that combines multiple materials into one part or product. It's also known as two-shot molding because it's a two-step process. The first step is molding a substrate in one material, and then the second step is over-molding with another material. This process can be done using a single-shot (insert molding) or two-shot (multiple-shot molding) technique.  This can be used to fuse a polyurethane part with a non-polyurethane part without a secondary adhesive.  It is often employed to manufacture intricate medical devices and large industrial cables.

Continuous Feed Production

Continuous feed production allows for the formation of a specific-dimension part without interruption of liquid polyurethane injection. The polyurethane components are heated and mixed in line, then poured onto a conveyer, which may be a belt or a set of multi-cavity molds. A second conveyor covers the top of the mold during the curing process. On the back end of the conveyor, pieces are cut or trimmed using robotics.

Continuous feed molding can be very high volume but does not allow for the molding of a wide variety of parts in a single production line.


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Benefits of Polyurethane

A rack of polyurethane tubes with a variety of textures and geometries.

When you choose polyurethane for your molded goods, you can tailor your product to specific performance characteristics based on the formula. This material is Incredibly customizable, and based on the formulation and molding method, you can impart your product with:

  • Flexibility
  • Durability
  • High Capacity
  • Impact and Abrasion Resistance
  • Liquid Resistance
  • Mold, Mildew, and Fungus Resistance
  • Economical Manufacturing Process
  • Short Production Time
  • Heat and Electrical Insulation

Polyurethane molding has notable benefits and is particularly attractive in marine and industrial plastic products. When you work with polyurethane, you choose one of the most flexible materials. Whether you produce for niche hobbyists, mass-market consumer goods, or industrial products, this material will exceed your expectations!

Make the Most of Your Molded Polyurethane Process

With polyurethane, your molding facility has one of the most popular and useful plastics. But knowing how to best form your products from this miracle material takes a lot of knowledge and expertise. This is where the professionals at Stoner Molding Solutions can help. Our team has aided dozens of molding facilities, helping nail down the process's most technical aspects.

We are also here to provide products that will smooth out and improve the most difficult aspects of your workflow. Molded urethane rubber can be particularly difficult to remove cleanly, and injection molds require regular lubrication and cleaning, to name a few. Stoner Molding products will help speed up and simplify your polyurethane moldings for greater production and ease. Call us today and we will help you choose the most effective products for your process for speed, efficiency, and improving your bottom line!


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