How to Make Metal Granules with Perfect Uniformity and Sphericity
Technical Guide to Precious Metal Granulation: How to Make Metal Granules with Perfect Uniformity and Sphericity
In the precious metal processing industry, granulation serves as the vital bridge between melting and finished product manufacturing. High-quality metal grains require more than just precise chemical composition; they must achieve superior physical consistency—meaning grains that are perfectly uniform in size and spherical in shape.
Leveraging the advanced technology of CDOCAST professional granulation machine, this guide analyzes four critical dimensions—temperature control, orifice design, circulation systems, and automated thermal management—to help you produce the “perfect grain”.
*Click here to watch the video
1. Melting Temperature Control: Optimizing Liquid Fluidity
The fluidity of the molten metal is the primary factor determining the final quality of the grain.
• The “+100°C” Thermodynamic Principle: Industry practice proves that the melting temperature should be set approximately 100°C above the metal’s melting point.
• Pure Gold: Melting point 1064°C; recommended setting: 1160°C–1170°C.
• Pure Silver: Melting point 962°C; recommended setting: ~1060°C.
• Surface Tension Activation: As molten metal flows through the graphite crucible, it loses heat rapidly upon contact with air. Adding 100 degrees of “superheat” ensures the droplets retain enough kinetic energy to contract into spheres via surface tension the moment before they hit the water.
• Eliminating the “Tail” Phenomenon: Insufficient temperature increases viscosity, leading to irregular flakes or grains with long “tails”. Maintaining proper superheat is essential for achieving high “roundness”.
2. Water Tank Temperature: Specialized Management for Different Metals
Water temperature is the most critical variable affecting the hardening speed and shape of the grains.
• Gold Granulation (55°C): Gold has high density and rapid thermal conductivity. A water temperature of 55°C is strictly recommended to slow down the cooling rate. This grants the gold droplets sufficient “self-shaping” time, resulting in lustrous, pearl-like premium grains.
• Silver Granulation (40°C): Silver forms regular spheres more easily at lower temperatures. We recommend 40°C to balance solidification speed with surface tension, preventing surface depressions or dimples.
• Risk Mitigation: While temperatures between 50°C–55°C optimize roundness, internal cooling lags can cause grains to “stick” or bond if they collide at the bottom of the tank. This highlights the necessity of the CDOCAST circulation and constant temperature system.
3. Mold Orifice Diameter: Defining Aesthetic Standards
Grain size is directly controlled by the diameter of the holes in the bottom of the granulation crucible.
• For Gold: A 0.8mm bottom hole is recommended. This produces a finished grain size of approximately 1.5–2.5mm, which is ideal for precise weighing, packaging, and a high-end visual aesthetic.
• For Silver: A 1.0mm bottom hole is recommended. Since silver is often produced in larger volumes, this larger diameter ensures smooth flow and produces full-bodied grains with excellent metallic texture.
4. CDOCAST Water Circulation: Eliminating “Local Overheating”
In continuous production, static water creates a “hot zone” where metal droplets enter the tank.
The CDOCAST professional circulation water tank uses high-flow pumps to create water turbulence. This rapidly disperses heat from the entry point, preventing unsolidified grains from sticking together and ensuring a uniform temperature throughout the entire tank. This consistency ensures that every batch of grains meets the same physical specifications.
5. Automated Constant Temperature Control (Optional Feature)
To eliminate human error, CDOCAST machines support a customized Water Tank Constant Temperature Device, which is essential for industrial-scale production.
• Automatic Heating: In winter or during initial startup, if water is too cold (below 20°C), metal droplets may “explode” into irregular flakes. The system automatically heats the water to the target 40°C or 55°C.
• Automatic Cooling: During prolonged production, the system prevents the water from overheating by automatically adding cooling water or activating a heat exchange system. This “Dynamic Thermal Balance” locks the water temperature within the optimal range for granulation.
Summary of Operating Standards
To achieve maximum yield and market competitiveness with your CDOCAST granulation machine, follow these standards:
✔ Preparation: Stabilize the circulation water temperature (Gold: 55°C / Silver: 40°C).
✔ Melting: Heat the solution to “Melting Point + 100°C”.
✔ Matching: Select the correct graphite mold (0.8mm or 1.0mm) based on the metal.
✔ Smart Control: Enable the automated temperature system to maintain water fluctuations within ±1°C.
For more information on granulation solutions for specific alloys, visit www.cdocast.com to consult our technical experts.