Advantages
The low viscosity, low temperatures and low pressures inherent to the RIM process provide distinct benefits as compared to other plastic processing methods.
- Very large parts with lower cost tooling = lower investment
- The flowability of the liquid polyurethane components enables them to fill molds for very large parts with minimal pressures. Products as large as 96” by 36” inches and weights up to 23 pounds can be made with inexpensive tooling options.
- Flexibility of part design due to material green strength and high material memory
- Unlike injection molding, the RIM process allows much more design flexibility because of its ability to be “peeled” from the tool and return to its molded shape
- Quick turnaround for tooling and products
- Our proprietary tooling, as well as full aluminum tools can be built in half and sometimes less than half the time of conventional injection molding tooling. For your small part prototype needs (less than 3 pounds), parts can be generated in as little as a week utilizing urethane materials which are consistent with your injection molded product characteristics.
- Wide variety of physical properties. Higher strength to weight ratio than comparable plastic products.
- Utilizing various fillers and additives, a typical exterior body panel can be run with of 10,000 psi to 280,000 psi flex mod while providing superior impact strength when compared to the standard injection molded materials used for these type products. Smaller prototype parts can go as high as 1,000,000 psi flex mod.
- Class A Surfaces when required
- The surface finish on parts molded with RIM materials allow for Class A painted surfaces. For example, automotive products such as fenders, spoilers, rocker panels and fascia (bumper covers) can match the high-gloss painted sheet metal parts they are mounted next to in final vehicle assembly.
- Minimize or eliminate secondary parts and operations
- Inserts of many types can be placed into a mold prior to injection of the urethane material. As an example, molding of metal brackets into the part eliminates post molding assembly. Tubular frame containing electrical lines are used to manufacture a “roll bar” with integral chmsl light for convertibles.
- No sink marks, variable wall thickness allowed
- Due to the chemical reaction than occurs with urethane materials, sink marks are non existent. The RIM process, unlike other molding processes, offers you the flexibility to design parts with significant wall thickness variation. Wall thickness ranges from 2mm to 30mm in the same part.
In addition to high strength, polyurethane Reaction Injection Molding (RIM) parts exhibit heat resistance, thermal insulation, dimensional stability, and a high level of dynamic properties. They also offer resistance to inorganic and organic acids as well as many other potentially damaging materials and chemicals including a large number of solvents. Resistance to weathering and aging is another plus, though extended exposure to the sun’s ultraviolet rays typically results in a color shift at the surface of unpainted product. Low processing temperatures (95F to 150F) and low injection pressures (30 to 100 psi) make the Reaction Injection Molding (RIM) process more economical than other molding methods for large parts.
In general, it uses considerably less energy to make the same injection molded thermoplastic product and requires less equipment and floor space. It’s also more automated than other thermoset molding alternatives. No energy consuming remelting of a solid thermoplastic is necessary, and the cycle times of the Reaction Injection Molding (RIM) process can be competitive with thermoplastic injection molding of similar sized parts.
With this process, designers can exploit the encapsulation abilities of polyurethanes Reaction Injection Molding (RIM) systems to mold in-metal parts such as bushings, hinges, and frames. Many designers have used this capability to reduce or eliminate secondary manufacturing steps.
For more information on design and RIM capabilities please contact us at Troy Tooling or visit a Bayer Corporations website dealing with Reaction Injection Molding (RIM) Technology at www.rimmolding.com
How does Reaction Injection Molding (RIM) Work?
Two liquid reactants – polyisocyanate component and resin mixture – are held in separate temperature controlled feed tanks equipped with agitators. From these tanks, the polyol and isocyanate are fed through supply lines to metering units that precisely meter the reactants, as high pressure, to the mixhead. When injection begins and valves in the mixhead open, the liquid reactants enter a chamber in the mixhead at pressures between 1,500 and 3,000 psi where they are intensively mixed by high-velocity impingement. From the mix chamber, the liquid flows into the mold at approximately atmospheric pressure and undergoes an exothermic chemical reaction, forming the polyurethane polymer in the mold. Shot and cycle times vary, depending on the part size and the polyurethane system used. An average mold for an elastomeric part may be filled in one second or less and be ready for demolding in 30- 60 seconds. Special extended geltime polyurethane RIM systems allow the processor to fill very large molds using equipment originally designed for molds with smaller volumes.
Drawing and information compliments of Bayer Corporation
