Which RIM Molds and Product Designs Are Used In Reaction Injection Molding?

by Marco Hogge

Injection Reaction Many different types of plastic items are molded using the low-pressure, low-temperature process known as molding. It is common practice to use reaction injection molding (RIM) to create sturdy, lightweight parts that may be painted. Design Octaves uses stiff materials that have a flammability certification.

Design Octaves uses a two-component system of polyol and isocyanate liquids that are combined at high pressure and then metered into the closed tool at low pressure to create the RIM molding material. After expanding to fill the tool, the substance is discharged after about 5 minutes.

Multiple pieces can be produced on a single typical injection molding machine thanks to the removable mold, which is built using a different method. The thing that has already hardened is taken out and put in a location where it will continue to harden. After going through this article, you will come to know what is RIM and which molds and product designs are used in this process.

RIM Molds and Product Designs

1. Mold Design

Pouring System

The “injection system” or “pouring system” is made up of runners, venting holes, and gates. The wall thickness and cavity flow of the molded pieces determine the shape and height of the gate in RIM mold design. A straight bar gate is often selected for big-capacity molds, whereas a fan gate is preferred for lower-capacity molds.

The primary runner should be placed directly on the mold; however, it is important to pay attention to its placement to ensure that the material enters the cavity from the lowest point of the product’s cross-section. In order for the air to be forced out of the cavity during injection, the venting hole needs to be placed near the end of the material flow.

Mold Temperature and Control System

Here, we’ll just use the RIM metal mold as an illustration to explain. Typically, a sleeve is placed inside the mold, and water is passed through it to heat or cool the mold. The metal mold should have a 50mm thickness, and the casing spacing should vary depending on the processing resin.

Mold temperature accuracy for polyurethane RIM is typically 4°C, preferably 1°C, with a typical range of 40 to 80°C. And the casing spacing should be 80100mm.

Parting Surface

There is a standard requirement for the parting surface’s position, which is that it be slightly below the contour of the processed part. This is done to prevent residual air from the cavity from being forced out of the mold as the material expands and fills the cavity.

2. Product Design

Product Thickness

Similarly to conventionally injected goods, it is important to avoid designing RIM products with excessively thick or thin walls. Consider polyurethane foam RIM products as an example; the standard wall thickness should be limited to 6.35–12.7mm. When the wall thickness exceeds 12.7mm or falls below 3.17mm, appropriate corrective action should be taken.


The goal of utilizing reinforcement is to increase the product’s hardness. Avoid using heavy and short reinforcement in favor of thin and lengthy reinforcement. To avoid affecting the gas emissions during the material flow, the reinforcement should be built up concurrently with the material flow.

Release Shape

The recommended RIM product release slope is 2°; slopes that are either too large or too short will hinder the release of the product.

Rounded Corner

RIM products must have internal corners with a radius of at least 3.175mm and external corners with a radius of at least 1.578mm.


The bump should be placed along the edge of the inner rib portion and have a demolding slope of 2°. If the bump’s design height is greater than 6.57mm, a brace plate must be added to it. When forming in the introduction hole placed precisely. The introduction whole and boss size both significantly affect the release strength and should be considered.


Reaction injection molding has a unique benefit over standard injection molding in terms of the molding material employed. More time and costlier molding materials are needed for response injection reaction molding. The liquid formulation is typically supplied into a reservoir, heated, mixed, and then put into a mold in a prepared chamber where it cools and solidifies.

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