RIM Service

Reaction Injection Molding(RIM) Introduction 

Reaction Injection Molding(RIM) Introduction 

Reaction injection molding sounds like plastic molding but the word reaction signals a big difference between the two. In reality, reaction injection molding utilizes chemical reactions to create more lightweight, strong, tough, complex, and more customizable parts in a more cost-effective way than standard injection molding. 

It is a new manufacturing technology that is used to produce high-quality and high-style thermoset plastic parts. It was first launched in 1969 by Bayer but with the passage of time became the premier plastic molding process. In the same year, it was introduced in the USA for auto requirements by Congress. Spoilers, trunk lids, fenders, and doors have been manufactured by using reaction injection molding technology. 

Reaction Injection Molding (RIM) is quite a new term that takes low pressure and low temperature to mold various types of plastic parts. This process is specifically used for automotive, industrial, and medical industries. 

Oftentimes, RIM is utilized to mold lightweight and strong parts that can be easily painted. The reaction injection molding material consists of isocyanate and polyol liquids that will be mixed at high pressure and then metered to the close tool at low pressure. 

The material then eventually expands, hardens, and thickens to fill the tool and then finally ejects in about five minutes. Advantages inherited in this process fall into three categories like low temperature, low pressure, use of reactive liquid intermediate. RIM is also known for reactive injection molding. Let understand the RIM process in detail for better understanding. 

RIM processes

 RIM takes low-viscosity liquid polymers. Unlike injection molding RIM always uses cost-efficient and lightweight thermoset polymers. Basically, it has some steps which are known as polymer liquids, mixing, tooling & curing. Below we will explain all the steps in detail. 

Polymer liquids 

In reaction injection molding two or more two liquids are usually (polyol and isocyanate) are measured separately in a mixing head where they are mixed at high pressure by the courtesy of a piston that breaks the loop and allows the liquids to mix. 


The liquids are mixed at high pressure (1200 psi) and use an impinging mixer before the transformation of the mold for the curing process. In the mixing head with the pressure between 1,500 to 3,000 psi. The pressure is relatively low as compared to other molding processes. 

The liquid polymers demand low pressure and low temperature to accomplish the final part than traditional ingredients ex gratia metals, reaction injection molding offers a money-saving benefit by using lightweight Machined aluminum mold. This makes reaction injection molding a suitable technology for large parts. 

Curing & cooling 

Then the mixed polymers cure inside the mold by using a mixture of low pressure (approximately 100 psi) and heating around 180 degrees Fahrenheit (almost 82 degrees Celsius). The temperature used in reaction injection molding is quite low between 75 and 120F and mold between 130 and 170F (266 to 338F). 

Low temperature means low energy consumption with other competitor processes. Low pressure produces very complex parts even mounting bosses, slots, ribs, and cut areas are possible too. Parts carpeted by reaction injection molding are as thin as 0.100 in and as thick as 1.5 in.

The cure time of the mold varies from one minute to several minutes depending on the complexity, thickness, and size of the parts. Here we tried to explain all the essential steps of the RIM process.

RIM Service

Types Of RIM (reaction injection molding)

Depending on the polymers, reaction injection molding can produce a number of physical parts and some generic examples of these parts are elastomeric, solid, flexible foam, and rigid foam. This gives RIM the upper hand over other traditional injection moldings, vacuum molding, and cast molding. 

Parts of reaction injection molding can enhance further through the addition of fiberglass in the liquid polymer that is known as reinforced reaction injection molding. Moreover, to increase the strength of the parts fiber mesh can be utilized and this process is known as structural reaction injection molding. 

Advantages of reaction injection molding 

Low Clamping Pressure: One of the biggest advantages of reaction injection molding is its low-temperature requirement that means large parts can be achieved by investing low cost. 

Differing wall thickness

Mold-in inserts

Better economies for special parts with lower volume as compared to traditional injection molding

Allows for these parts consolidation as compared to sheet metal

Tooling is generally less expensive than traditional injection molding

Labor requirements become lower, especially as compared to what is needed by resin transfer molding. 

Lower energy taking than injection molding

Less floor space requirements than that of  injection molding .

Applications Of RIM Today 

In recent times, RIM has had its roots in almost every field of life including agriculture equipment, sporting goods, business equipment, electronic enclosures, furniture industry, and various appliances. The reaction injection molding reached 5 × 107 lb in 1975. Automotive bumpers are produced on the force of 100 to 150 tons as compared to its counterpart injection molding that needs 3500 tons or more. 

Why RIM Is Different From Other Molding Process 

Reaction Injection Molding is quite different from other molding processes because in the starting phase materials become liquids according to the room temperature. The materials are of polyisocyanate, polyol, and promoter for chemical reactions which take place during mild processes. 

The reactive materials are prepared individually then inserted into a mixing head in the form of fine-stream liquid where they are mixed thoroughly. In this stage, mixed liquids are inserted into the heated mold for the part to cure. 


Our Thoughts 

In this article, we make you understand about reaction injection molding, its different steps, its advantages, and its applications. Further, why reaction injection molding has the upper hand over other traditional injection molding processes. 

At Bohoa, our goal is to make every part of a specific field stronger, bigger, and lighter. From fiber technology to reaction injection molding, we offer composite solutions for heavy trucks, transportation, spas, construction, and agriculture. 

We are feeling proud to have an industry leader in polyurethane and we struggle to maintain this status. Regardless of your business operations, we always offer the best polyurethane composite solutions. If you are in need of smart solutions, don\’t hesitate, just contact us today to get the best quote!

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