Overview of Custom Rubber and Polyurethane Molding Processes

Overview of Custom Rubber and Polyurethane Molding Processes

Written by Alison Lurie, In Technology, Published On
December 15, 2022

Individuals often turn to a company specializing in molded elastomeric products when they cannot find what they need. They know with the help of polyurethane molding they can obtain plastic parts for their consumer goods or industrial parts. Thanks to the tight tolerances and complex geometries available with this production method, this is one option anyone should consider when in need of parts of this type.

Polyurethane is an extremely versatile material that yields different properties based on its formulation. The mechanical properties range from hard and tight to soft and pliable. As a result, specific compounds can be used to produce engineering-grade parts that deliver high performance. They are frequently found in the furnishings, construction, transportation, industrial, and manufacturing sectors. However, Custom Rubber and Polyurethane Molding may be needed to create the desired part. Why is polyurethane in high demand?

Overview of Custom Rubber and Polyurethane Molding Processes

Polyurethane Properties

Polyurethane can be created to meet the needs of the project. Manufacturers use the Shore Hardness Scale to determine the hardness of the material, with the Shore D scale being used to measure polyurethanes that are rigid and hard. They turn to the Shore A scale when they wish to measure a soft, semi-rigid polyurethane for hardness.

Furthermore, the manufacturer can provide the desired level of abrasion resistance when using polyurethane to create a part. They do so by altering the composition of the polyurethane resin. However, this is only one of several characteristics the manufacturer can alter. When creating custom polyurethane molded parts, the manufacturer can control the tear strength, the impact strength, and more.

Molding Techniques

Thanks to the flexibility of polyurethane, it can be molded, shaped, or formed to meet the needs of the consumer. The manufacturer uses one of several techniques when creating these products. Injection molding is commonly used to create moldings and can be used for thermoplastic and thermoset polyurethanes. Once it is molded, the product is machined using the negative image of the desired product.

Reaction injection molding is similar in many ways to injection molding. The key difference lies in the raw materials used. Manufacturers often choose this option when possible, as their costs are reduced.

Compressional molding is ideal for large products. The mold is created in two pieces. The manufacturer then adds polyurethane in a predetermined weight. When the two halves are compressed, this polyurethane takes the shape of the mold.

Rotational molding is ideal for creating hollow pieces with no seams. Powdered polyurethane is loaded into a mold, which is then heated while rotating. This spreads the material throughout the inner surface of the mold. Once this process is complete, the product is allowed to cool before being removed from the mold.

Blow molding is also used to create hollow products. However, polyurethane is heated and placed in a tube. With the help of compressed air, the polyurethane is then inflated until it takes the shape of the mold. Once cooled, the mold is removed.


Casting is similar to injection molding, but the mold is made of silicone rather than hard metal. This process is ideal for low to medium-volume products, as the mold wears quickly. However, this method is less expensive than using a mold made from metal.

Open Cast Molding

The easiest molding technique is open-cast molding. Manufacturers use this process for high-hardness polyurethane products. This rapid process allows for finished products in a few weeks. However, the resin and curative liquid must be at the correct temperature to ensure the heated liquid solidifies. Any material can be used with this molding method, and the process is cost-effective.

Raw Material Options

Manufacturers find they can choose from a range of polyurethane components. Polyols and diisocyanates serve as the main components, and the manufacturer decides which curatives and additives to use in the formulation. Options include polyether, polyester, polycarbonates, aliphatic diisocyanates, aromatic diisocyanates, and various molecules.

Blowing agent options include chemical agents, physical ones, surfactants, catalysts, and more. Other products may also be used in the creation of polyurethane products.

For example, a manufacturer may use a degassing aid when creating products. As they mix the components of the polymer system, they must be aware that the mixing can lead to gases becoming trapped. These gases result in a product of lower quality. To avoid this issue, the manufacturer makes use of degassing aids to eliminate the trapped gases.

Polyurethanes may combust, which is of concern. This is especially true of polyurethane foams. As a result, manufacturers would be limited in how they can use these products. To avoid this concern, the manufacturer uses polyurethanes that are flame resistant when creating building insulation or parts for use in automobiles.

To alter the color of a product, manufacturers use colorants. This ensures the process of coloring the polyurethane in no way affects the product’s thermal and mechanical properties.

Finally, coefficient of friction, or COF, additives alter the coefficient of friction of the product. At times, a high COF is needed when there will be sliding between surfaces. In contrast, a low COF is required when more friction is needed between materials. Harder polyurethane products need a lower COF. By altering the additive formulation, the manufacturer can change the COF.

Rubber Molding

Rubber molding, unlike polyurethane molding, has fewer options. Manufacturers use compression or injection molding in many cases. They may also choose to use a combination of the two methods through a process known as transfer molding. This process starts by converting raw material into a pre-form. The manufacturer takes this pre-form and places it in a pot before forcing the materials into the mold.

Polyurethane molding is more complex than rubber molding, as manufacturers have more options when it comes to the molding process. However, both methods are beneficial to manufacturers, depending on the product being created. Speak with a reputable provider to learn which material and method are needed, as they can provide the benefits and drawbacks of each option. They are an excellent resource when it comes to ensuring the right material and method are used.

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