Extruded silver bars are produced through an extrusion process, which involves forcing silver through a special die to create bars with a uniform cross-sectional shape. Extrusion methods result in bars that are consistent in size, weight, and finish, which appeals to investors and some collectors. Here’s a breakdown of how extruded silver bars are made and how they differ from cast silver bars.
Producing Extruded Silver Bars
Manufacturing extruded silver bars first involves producing a silver billet, which is then heated and made into a bar by an extrusion press before it cools and is cut.
- Melting the Silver: Silver is exposed to heat in a furnace until it reaches a molten state. The furnace reaches temperatures above the melting point of silver, above 1,700° Fahrenheit.
- Forming the Billet: The molten silver is poured into a mold to create a billet—a solid block of silver that will be shaped during extrusion. This step ensures that the silver is in a standard shape and size to be reheated and extruded into a silver bar. The billet is cooled and becomes solid, forming a dense block of silver.
- Heating the Billet: Next, the billet is heated to make it malleable enough for extrusion, though it isn’t heated to the melting point again. This step softens the billet and is crucial to prevent cracking and breaking. The temperature must be controlled to ensure pliability that retains structural integrity.
- Extrusion Process: The softened billet is placed into an extrusion press, which shapes metal by pushing it through a die. This die differs from a standard coin die, which has obverse and reverse sides. The extrusion die is a thick, circular steel disc with an opening that determines the shape of metal extruded from it. A powerful ram forces the billet through the extrusion die, resulting in a long, continuous bar with a uniform profile.
- Cooling: After it comes from the press, the extruded silver bar is cooled so its shape and final structure are solidified and set. Fast, rapid cooling can result in a silver bar with greater hardness, while a slower cooling process results in a more ductile silver bar.
- Cutting and Finishing: Once cooled, the bar is cut into smaller bars of desired lengths. Additional finishing steps, like polishing or stamping with the manufacturer’s logo, weight, and purity marks, may also be applied. These finishing touches, which often include hallmarks, make the bars easier to trade since they have been marked with their fineness, weight, and maker’s mark.
Advantages of Extruded Silver Bars
Extruded silver bars offer several benefits:
- Uniformity: The extrusion process ensures that each bar has a consistent size, weight, and appearance, making them ideal for investors seeking standardized bullion.
- Efficiency: The extrusion process is relatively quick and cost-effective, enabling the production of large quantities of bars in a shorter timeframe.
- Greater Strength: Extrusion often increases the silver’s strength due to the work hardening that occurs as it passes through the die. This hardening gives the bars more durability.
How are Extruded Silver Bars and Cast Silver Bars Different?
You will find cast and extruded silver bars in the bullion market, but they differ in their production processes.
Production Process Differences
Extruded Silver Bars:
- Preparation: Starts with a billet of solid silver, which is heated to a malleable temperature.
- Extrusion: The billet is forced through a die under high pressure, which shapes the silver into a long, solid bar with a precise cross-section.
- Finishing: The long bar is cut into smaller sections and polished or stamped.
Cast Silver Bars
- Melting: Silver is melted to a liquid state in a furnace.
- Pouring: The molten silver is poured into a mold that defines the shape and size of the bar.
- Finishing: Once it has solidified, the cast silver bar is removed from the mold and may undergo additional steps like polishing.
Other Differences Between Cast and Extruded Silver Bars
- Extruded bars are valued for their uniform cross-sections and precise dimensions, which can make them more valuable for applications requiring exact measurements.
- Extruded bars typically have a smoother, more refined surface than cast bars, which often display a rougher texture due to the mold’s characteristics.
- Extruded bars tend to have greater mechanical strength, as the extrusion process aligns the material’s grain structure, which can enhance durability.
Value of Extruded Silver Bars
The method used to produce silver bars can impact their value. Extruded silver bars may have a slight premium over cast bars due to their uniformity and refined appearance, especially for buyers looking for visually appealing bullion.
