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Technical Information: Reaction Injection Molding (RIM)
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What is it?
Simply stated, in this process two liquid components - - component "A", a formulated polymeric isocyanate, and component "B", a formulated polyol blend, are mixed in a high pressure head and then pumped into a mold cavity. A reaction then occurs in the mold, resulting in a high density polyurethane structural foam part.
How, Why & When to Use It:
- To produce covers, bases, keyboards, bezels and housings for computers, business machines and medical applications.
- For prototype through medium volume applications (1 - 2,000 pieces).
- There is considerable design freedom to produce complex shapes.
- Molds can be resin, spray metal, cast aluminum or machined aluminum.
- Tooling is low cost and allows for ease of modification.
- A variety of castings, sheet metal and threaded inserts can be molded in place.
- Alternative foams are available which offer a range of insulating properties.
- UL traceability.
Design & Technical Information
Size
Up to 48 in.
Weight
Up to 18 lbs.
Finish
If required:
- No bake prime and paint
- RF shielding
- Silk screening
Wall thickness
Can vary but should not be less than 1/4 in., although local thicknesses of 1/8 in. can be produced.
General tolerance
Note: tighter tolerances can be negotiated.
0 in. - 3 in. +/- 0.010 in.
3 in. - 6 in. +/- 0.015 in.
6 in. - 12 in. +/- 0.020 in.
12 in. - 18 in. +/- 0.030 in.
18 in. - 48 in. +/- 0.040 in.
Holes
All holes molded to size.
Draft
Recommended 1 - 2 degrees, but no draft is possible when specified.
Radii and fillets - should be as liberal as possible (1/8 in. to 1/4 in.).
Density
Can be varied, depending on foam used, to offer a variety of insulation properties.
A variety of materials are available that offer a range of insulating and mechanical properties with 94V-0.
Detailed specification sheets are available on request (email requests to sales@armstrongmold.com)
Comparison Chart RIM vs. Injection Mold Properties
| Material | Units | R I M | Polystyrene | ABS | Modified PPO |
| Specific gravity | 0.85 | 0.85 | 0.89 | 0.85 | |
| Thickness | (in.) | 0.25 | 0.25 | 0.25 | 0.25 |
| Flexural modulus | (psi) | 220,000 | 275,000 | 240,000 | 261,000 |
| Flexural strength | (psi | 9,500 | 5,700 | 6,000 | 6,800 |
| Tensile strength | (psi) | 5,800 | 2,300 | 3,000 | 3,400 |
| Elongation | (%) | 10 | 20 | - - | 16 |
| Gardner impact + + | (in-lb) | 74 | 28 | 52 | 55 |
| Falling ball | (ft-lb) | - - | - - | - - | 18 |
| Dart impact | (ft-lb) | - - | - - | 10 | - - |
| Heat distortion temperature | |||||
| @ 66 psi | (F) | 212 | 183 | 177 | 205 |
| @ 264 psi | (F) | 180 | 168 | 162 | 180 |
The above properties are intended as a guide only and may vary depending on thickness and shape. |
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