Step by step Reaction Injection Molding Process

Step by step Reaction Injection Molding Process

In this guide, you will learn how reaction injection molding works – from choosing the right material, processing to the last step.

So, before starting your next RIM process, read this guide.

What is Reaction Injection Molding?

Another name for Reaction Injection Molding is RIM. It refers to a process you can use to form polymer components. For example, you can use polymerization within the mould following the activated reaction.

Reaction Injection Molding
Reaction Injection Molding

Step 1: Material Selection

The first step in the RIM process is material selection. The proper material selection determines the end properties you want in the final product. The widely used materials include:

  • Polyamide – resistance to wear, high strength, good thermal stability and chemical resistance
  • Epoxies – high strength, low shrinkage, low toxicity, electric insulation
  • Polyester – retain its shape, moisture resistance, don’t tear, non-biodegradable
  • Polyurethane – good bonding properties, resistance to water/ oil/ fluid, good resilience, wide colour ranges
  • Fibre Composites – high impact resistance, high dampness, high strength-to-weight ratio, resistance to corrosion

The end properties also rely on the percentage of chemical additives you use. Different ratio mixes lead you to the varying

  • Elasticity
  • Stretching at low-stress capability
  • Structure Flexibility
  • Durability

Carefully select the material, as each material imparts different end characteristics.


Step 2: Tank Feeding

The second step is to put the two different materials of your choice and the additives within the tanks. The tanks refer to the reactant tanks.

RIM Process
RIM Process

Step 3: Heating

Each reactant tank has an embedded system to control the temperature of the material. This will allow you to keep the material in its optimum state. Different materials have different temperature requirements.

Some material has altered their chemical composition at the higher temperature. Therefore, this step is essential to keep the material in its desired state.

Step 4: Metering

Controlling the amount of material before mixing is of paramount importance. You can control the amount of material with the help of a metering unit. It allows you to feed the exact amount of material as per the ratio/ percentage/ proportion needed.

Over or mixing affects the product formation as well as the end properties of the product. This is why metering is essential.

Step 5: Mixing

After metering, there comes the mixing of the material. Two materials then get mixed in appropriate proportions homogenously. The blender performs this operation. A pressure range that you can apply to the blender is 1500 to 3000 psi. After this, the material is ready for dispensing.

Step 6: Dispensing

The term dispensing means injecting the material into the mould. This is possible because of the nozzle. In this step, the mixing head performs this operation. When the mould fills up completely, the mixing head stops putting in more material. An embedded sensor helps you achieve this task.

After dispensing, the reaction takes place within the mould. The response is of an exothermic type. After the reaction completes, the curing and solidification of polymers end up.

Step 7: Cooling

Later in the process, the end product cools off. Then, finally, it releases the trapped heat and cools down to room temperature.

Step 8: Discharging

The polymer is ready to discharge or for shipping. You can assess the final quality of the component to facilitate this process.

Reaction Injection Molded Part
Reaction Injection Molded Part


As you can see, RIM is slightly different from the normal injection molding processes.

However, it is a function and practical process that suit modern plastic injection molding industry.

For any questions or inquiries on reaction injection molding processes, contact us now.

More resources:

Reaction Injection Molding – Source: Science Direct

RIM – Source: Wikipedia

Reaction Injection Molding – Source: Thomanet

Injection Molding Vs. Rim – Source: Knowledge Center

Request An Instant Quote

We have a strong and efficient team which can offer you and instant and professional quote.

Our product manager will give you a quick demand portrait according to your design, drawing, standard, testing methods and other requirements. And we have a strong supporting team to fulfill your demand with our deep technology and know-how base. We can offer you a solution or a few options. And you will decide which one you prefer.

Upload File
Update cookies preferences
Scroll to Top