Instructions for using rubber molds
Vulcanizes at 300 - 325 degrees F
Lightly powder each half of the rubber molds with fine powder or talc blowing off any excess.
Add models and locking nuts to one half of the rubber.
Note: Sometimes air can get entrapped during vulcanization, so it is recommended that four "V" shaped 1/4" notches be cut at 3,6,9, and 12 o'clock into the outside of the un-vulcanized rubber. See below diagram.
Place completed mold in preheated mold frame.
Hand crank pressure first and let stand approximately 2 minutes.
Jack mold to approximately 1k lbs. pressure.
Jack mold to the final pressure within the first 10-15 minutes generally 1.5k-3k lbs.
(every mold is different; some pieces are deep and require more pressure and others are flat and require less pressure so final pressure will often vary)
Allow rubber to vulcanize under pressure for 1 hour for every inch of rubber.
Rubber molds are a popular choice in the pewter casting industry due to their flexibility, durability, and ability to produce intricate designs. The following guidelines provide a comprehensive overview of the best practices for using rubber molds effectively in the casting process.
1. **After vulcanization of the Mold**: For optimum quality castings make sure mold is clean and free of any debris or contaminants.
2. **Mold Release Agents**: Casting talc is recommended before each pour. It acts as both a releasing agent and helps flow the metal flow into the cavities.
3. **Heating the Mold**: For optimal results, preheating the rubber mold can enhance the flow of the pewter and reduce the risk of defects. A temperature range of 120°F to 150°F (approximately 49°C to 65°C) is generally recommended. This preheating process helps in achieving a smoother finish and better detail retention in the final product.
4. **Pouring the Pewter**: When pouring the pewter into the mold, it is crucial to do so at the correct temperature. The ideal pouring temperature for lead-free pewter alloys typically ranges between 450°F to 500°F (approximately 232°C to 260°C). Pour the pewter slowly and steadily to minimize air bubbles and ensure that the mold fills completely.
5. **Cooling and Demolding**: After pouring, allow the pewter to cool and solidify within the mold. The cooling time can vary depending on the thickness of the cast piece and the specific alloy used. Generally, a cooling period of 1 to 5 minutes is sufficient. Once cooled, gently flex the rubber mold to release the cast piece, taking care to avoid any sudden movements that could damage the mold.
6. **Post-Casting Care**: After demolding, inspect the cast piece for any imperfections or defects. If necessary, minor adjustments can be made using sanding or polishing techniques. Additionally, proper cleaning and storage of the rubber molds after use will prolong their lifespan and maintain their performance for future casting projects.
By following these instructions, users can maximize the effectiveness of rubber molds in pewter casting, ensuring high-quality results and enhancing the overall casting experience. With over 70 years of combined technical experience in alloying, utilizing these best practices will contribute to achieving exceptional performance and reliability in your casting endeavors.