This video provides an updated, in-depth guide to crafting custom crucibles for melting metals, utilizing a mixture of silicon carbide grit and sodium silicate (water glass). It details the precise steps for preparing the mixture, pressing it into various molds—including innovative 3D-printed designs with specialized pressing tools—and the initial microwave curing process to set the crucible and facilitate the removal of an inner glass former. The tutorial then comprehensively explains two methods for hardening the crucibles: one involving wrapping them in ceramic fiber sheet and microwaving to glowing red temperatures, and a preferred alternative using ceramic fiber kil paper. Throughout, the creator discusses the benefits of hardening (increased strength and crack resistance) in relation to crucible size and intended application, while also emphasizing critical safety precautions and practical drawbacks associated with handling hazardous ceramic fiber dust.
DIY Silicon Carbide Crucibles: A Step-by-Step Guide to Making and Hardening
0:00 Introduction & Materials: The video offers an updated guide on making crucibles. Begin with silicon carbide (any grit, or a mix) and add 8-10% sodium silicate (water glass) as a binder.
0:37 Mixing & Molding: Mix the materials thoroughly. Gradually fill a glass mold, pressing the silicon carbide down firmly. Shape the interior of the crucible by removing material from the center.
1:21 Microwave Curing (Glass Removal): Microwave the crucible on a ceramic fiber sheet until the glass mold cracks. An ice cube can assist cracking, but avoid over-cracking. Carefully remove the broken glass and use sanding tools for final shaping.
2:04 Initial Heat Treatment: Before first use, heat the crucible in a metal melting chamber. This is important even if you don't plan to fully harden it.
2:21 Hardening - When and Why: Hardening significantly strengthens the crucible and reduces cracking. Its necessity depends on factors like shape, thickness, height, and how it will be used. Taller crucibles particularly benefit. Natural hardening can occur with high melting point metals or fluxes over time.
3:19 3D Printed Molds: Custom 3D printable molds are introduced; older free versions are available, and new, improved designs (offering different sizes and thicknesses) are accessible via Patreon/Printables.
4:01 Mold Assembly & Pressing Tool: The new molds are assembled with PLA parts, a soft filament lid (or PLA if careful with removal), an M5 screw, and binder clips. A specialized handle attachment for the pressing tool makes compaction much more efficient.
5:30 Filling 3D Molds: Fill the 3D molds in layers, pressing down firmly with the handle tool. The creator plans future updates to these molds with new sizes and patterns.
6:56 Freezing for Demolding: Freeze the filled mold for at least 2 hours (or overnight) to aid in clean demolding.
7:07 Demolding Process: Unlock and carefully pull out the inner mold, then the lid. A flexible lid (soft filament) simplifies removal; a rigid PLA lid might deform if left in during baking.
7:42 Hardening Method 1 (Ceramic Fiber Sheet): Wrap the crucible in a ceramic fiber sheet, secure with rubber bands, and microwave until it glows red. This intense heat causes hardening.
8:12 Post-Hardening Cleanup & Safety: After cooling, unwrap the crucible and use a wire brush to remove ceramic fiber. Key Takeaway: Always wear a respirator and gloves when handling ceramic fiber due to its hazardous dust which can cause skin irritation and respiratory issues.
8:35 Creator's Rationale for Avoiding Hardening: The creator sometimes avoids this hardening method due to the unpleasantness and health risks associated with loose ceramic fiber dust. Notes that ceramic fiber-lined melting chambers are less hazardous once covered and hardened by use.
9:53 Hardening Method 2 (Ceramic Fiber Kil Paper - Preferred): This is the preferred method. Cut ceramic fiber kil paper to size, wrap it around the crucible, and glue it in place (gloves still recommended). Heat the crucible until the kil paper virtually disappears or fuses with the silicon carbide.
11:11 Kil Paper Hardening Results: Insufficient heating will leave the kil paper merely burnt but still intact. Proper heating ensures the paper fuses with the crucible. This method is generally better for smaller crucibles as it's easier to achieve the necessary high temperatures and avoids loose ceramic fiber.