Jewelry Casting Plaster
Overview
Jewelry Casting Plaster is a refined calcium sulfate hemihydrate formulation specifically engineered for investment casting in jewelry production. Unlike standard gypsum products, it contains additives to control setting time, reduce bubble formation, and withstand molten metal temperatures. Developed for the lost-wax process, this material creates precise molds that capture intricate details from wax patterns. When fired, it forms a porous structure allowing wax burnout and metal flow while maintaining dimensional accuracy for jewelry pieces typically weighing 1-100 grams.
Physical and Chemical Properties
The plaster achieves its working properties through controlled calcination of gypsum (CaSO₄·2H₂O) to form hemihydrate. Particle size distribution (usually 10-50 microns) directly affects surface finish quality. Specialized formulations may include silica flour (20-30%) to enhance thermal shock resistance. Key performance metrics include wet compressive strength (≥500 psi), dry compressive strength (≥2000 psi), and linear thermal expansion (≤1.2% at 700°C). The material exhibits pseudoplastic rheology when mixed with water (typically 30-35% by weight), allowing smooth pouring while preventing segregation.
Main Applications
Primary use involves creating expendable molds for casting gold, silver, platinum, and bronze jewelry components. The plaster's fine detail reproduction makes it ideal for filigree work, stone settings, and textured surfaces. Dental technicians also use similar formulations for crown and bridge casting. Industrial applications include small precision castings for aerospace components and art sculptures. Some manufacturers produce color-indicator versions that change hue when reaching proper burnout temperatures (typically 600-800°C), ensuring complete wax removal before metal pouring.
Safety and Storage
Although non-toxic, dry powder requires handling with NIOSH-approved dust masks (N95 or better) to prevent respiratory irritation. Work areas should have adequate ventilation during mixing. Spills should be vacuumed rather than swept to minimize airborne particles. Storage life ranges 6-12 months in original packaging when kept below 30°C and 50% relative humidity. Moisture absorption causes premature setting and strength reduction. Opened bags should be resealed with desiccant packs and used within 3 months for optimal performance.
B2B Procurement Guide
Industrial buyers should specify technical requirements including: particle size (usually ≤75 μm), water-to-powder ratio, setting expansion (0.1-0.3%), and working time. High-volume users (100+ kg/month) can request custom blends with adjusted setting times or enhanced refractoriness. Quality verification tests should evaluate: surface finish (ability to replicate 20 μm details), burnout characteristics, and metal penetration resistance. Leading manufacturers provide technical datasheets with complete physical property profiles and benchmark comparisons against industry standards like ISO 6873 for dental gypsum products.
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