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What Is Reaction Injection Molding?

At first glance, the only difference between traditional injection molding and reaction injection molding (RIM) seems to be one word. However, in truth there is a world of difference between the two processes. RIM utilizes chemical reactions to produce stronger, tougher, more lightweight, more complex and more customizable parts in a significantly more cost-efficient manner than standard injection molding.

At Romeo RIM, we have been providing high quality reaction injection molded parts to our customers for over 30 years. Our award-winning molding machinery has produced everything from spas to farm machinery to our revolutionary low weight, high energy absorbing HELP bumpers. We’re here to help you understand just what is so special about RIM and why it just might be right for your parts.

The Reaction Injection Molding Process

Reaction injection molding utilizes low-viscosity liquid polymers. Unlike traditional injection molding, RIM always uses lightweight, cost-efficient thermoset polymers. Here at Romeo RIM, we utilize high-quality polyurethanes such as those developed by our partner, Covestro LLC.

The process begins with two liquids: isocyanate and polyol, which are stored in large tanks. High-pressure pumps circulate the liquids between the tanks and a multi-stream mix-head in a speedy, continuous loop. A piston then retracts inside the mix-head, breaking the loop and allowing the two liquids to combine.

The liquids are mixed at high velocity (1200 psi) using an impinging mixer before being transferred into the mold for the curing process. As liquid polymers require less pressure and lower temperatures to complete the part than traditional ingredients such as metals, RIM provides a further money-saving benefit via the use of lightweight machined aluminum molds.

The mixed polymer cures inside the mold using a combination of low pressure (approximately 100 psi) and heating of the mold to around 325 degrees Fahrenheit (163 degrees Celsius). Cure times within the mold vary from one to several minutes depending on the size, complexity and thickness of the part.

Types of Reaction Injection Molding

RIM can be used to produce a number of finishes depending on the polymers chosen. Some common examples of finishes are solid, elastomeric, rigid foam, and flexible foam. This gives RIM a greater versatility in the type of parts it produced when compared not only to traditional injection molding but also to processes such as vacuum forming and cast molding.

Products created by RIM can be further enhanced via the addition of glass fibers to the liquid polymer, which is known as reinforced reaction injection molding (RRIM). Alternately, parts can be strengthened with a fiber mesh in a process called structural reaction injection molding (SRIM). These two variant processes can create parts that are even stronger and tougher, while still retaining the low weight and superior aesthetics of all RIM-created pieces.

Advantages of Reaction Injection Molding

Polymer products created via reaction injection molding are typically known for being lightweight and flexible, especially when compared to more traditional materials such as steel, aluminum, or sheet molding compound (SMC). This lowered weight boasts a number of benefits.

A vehicle with bumpers or fenders made from polyurethane will be more fuel-efficient than one using heavier materials, saving the driver or company thousands of dollars in gas money. Machinery made from these lighter components will be easier to lift, use and handle. Launching your personal watercraft or installing your new spa tub will be a breeze with RIM-created polyurethane hulls, sides and other parts.

However, lighter weight isn’t the only advantage of choosing RIM. Thermoset polymer products are stable and flexible as well as strong, tough and durable, capable of resisting impact and wear without deforming. Wood rots, steel rusts, but polyurethane remains bright and shiny and retains its original shape after years of exposure to the elements!

At Romeo RIM, all of our automobile and machinery parts are impact resisted and crash tested. In particular, our HELP bumpers boast superior energy absorption when compared to other similar products.

In addition, reaction injection molded parts are non-corrosive and chemically resistant. This makes RIM the perfect choice for everything from heavy machinery to personal spas!

Aesthetic Advantages

Unlike other processes, RIM allows for in-mold painting, producing eye-catching Class A finishes in either high or low gloss – right out of the mold. In addition to saving time and money usually needed for expensive, time-consuming post mold finishes, Romeo RIM’s in-mold paintjobs are perfectly adhesive, and can last years without chipping or flaking away.

In-mold painting is not the only aesthetic benefit that comes with choosing RIM. RIM allows for the creation of molds with varied wall thickness – something that is completely impossible with traditional injection molding due to part shrinkage. RIM can be used to create far more intricate, detailed, complex and customizable parts than any other process available.

If that wasn’t enough, RIM also provides the opportunity for adding B-side geometry, including louvers, ribs, bosses and opening. RIM molds allow for the encapsulation of a variety of inserts, further setting it apart from traditional injection molding, cast molding and vacuum forming.

RIM-produced products also make excellent thermal and acoustic insulators, further increasing their versatility and usefulness in a wide variety of industries.
Whatever your industry, whatever your project, reaction injection molding can create the parts you need. Contact us today to become part of Romeo RIM’s 30+ year history of creating high quality, perfectly crafted products for hundreds of satisfied customers.