RTV/Urethane Molds
Bastech, Inc.'s model shop has the capability to provide services from custom finishing, painting and assembly of SLA and SLS models to RTV silicone molding urethane reproductions and urethane foam epoxy molding.
- RTV Silicone Molding
- Urethane Reproductions
- Urethane Foam Epoxy Reproductions
- Custom Finishing & Painting
- Machined Patterns
RTV Silicone Molding
RTV (Room Temperature Vulcanization) silicone molding is a well-recognized rapid tooling method for producing small quantities of production-like prototypes of plastic injection molded parts. Short mold lead times are coupled with exceptional detail and surface finish. Complex parts with undercuts can be produced using this process. RTV molding is very cost effective at low quantities while maintaining good accuracy and excellent detail. Prototype parts can be color matched and textured with a variety of material characteristics. Durometers range from very soft foams or rubbers through very rigid nylon-like materials. Some functional testing can be performed.
Use RTV silicone Molds when your project requires short lead times, low volumes, production-like characteristics, and fine detail and surface finish.
Understanding Urethane Molding
Urethane molding is a process where a master pattern, typically created by stereolithography, is used to cast a silicone mold that can then be injected with various urethane materials.
Step-by-step Process
1. Create and prepare master pattern. Usually the best choice for master pattern is a SLA model. However, existing parts or machined parts can also be used with success. If an SLA model is used, it can be polished for a smooth finish or textured for a custom look. The finish of the pattern will transfer to the mold and cast urethane pieces.
2. Create the silicone mold. The mold parting line and vent and fill holes are determined based upon the part geometry. There are various methods for creating a parting line; two of the methods used by Bastech are clay for a two pour mold or tape for a single-pour mold. To create a two-part mold, the parting line is clayed and the part is enclosed in a box. silicone is poured around the model to create its negative. The part is then flipped, the clay is removed and the second half of the mold is poured. Once the silicone has cured, the master is removed and the mold is cleaned and prepared for injection.
3. Inject and pressurize mold. Urethane material is mixed and/or colorized and injected into the mold through fill holes using low-pressure pneumatic gun injection method. The mold is placed into a pressure pot to compress air bubbles that may have been trapped during injection.
4. Remove parts from mold. After the allotted cure time has passed, the molds are removed from the pressure pot, opened, and the part is then carefully removed.
5. Post-finish urethane reproductions. Gates and flashing are removed from urethane parts. Straightening is sometimes required. The parts may also be painted, polished, or functionally assembled. Threaded inserts, if not added during molding, can be added at this time.
| Material | Description Material Data Sheets (Click on link below) |
Advantages | Considerations | Applications |
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Urethanes and polyurethanes come in wide varieties of material characteristics |
A rubber mold is created from an SLA model. Urethane material is then filled into the void and a duplicate part is created. |
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| Semi-Rigid Urethane | TC-889 A/B Rigid Shore D Urethane Casting Material These semi-rigid, tough materials exhibit excellent cured physical properties including high abrasion resistance and high impact strength. Shore D resins cure relatively fast at room temperature producing tough, impact resistant castings. They are recommended when a resilient surface hardness is desired and applications requiring exceptional wear resistance. |
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| Flexible Polyurethane Elastomer | F-70 A/B 70 Shore A Polyurethane Elastomer Shore A hardness products are excellent multi-purpose materials for making a wide variety of products including molds used to cast concrete, plaster and various plastic materials. Shore A hardness products offer application versatility with both brushable and castable material systems. These products are safe and easy to handle. Shore A hardness products can be hand or machine cast for producing keypads, small molds, overmolded finishes, and for use as encapsulating and potting compounds. These products offer convenient work times and excellent physical properties. In most instances, parts can be turned around in 1-2 hours depending on part size and configuration.
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| Other Urethanes & Polyurethanes | Link to BJB Enterprises, Inc. | Review BJB's full line of casting grade resins | ||