UN373 High Fluidity White Bronze


UN373 All-Purpose High Fluidity Bronze Alloy.

Composition: 15% ZINC, 18% NICKEL, 67% COPPER + Deoxidizers

As-Cast Hardness: 93.0 Hv.

UN373 Casting White HIGH FLUIDITY BRONZE is a nickel based white alloy designed to cast jewelry samples, models, belt buckles, art objects, etc. It finishes to a White color and easily solders with silver or low white gold formulas. UN373 has a much better resistance to tarnishing. This product may be used for rolling or hand-fabrication purposes . UN373 also contains a silicon de-oxidizer for clean casting.. Rhodium plating of finished pieces of jewelry is highly recommended.

CASTING TEMP 1110° C - 1130° C / 2030° F – 2066° F

NOTE: Melt temperature may vary with type of unit. UN373 White HIGH FLUIDITY BRONZE may be Rhodium plated as normal.

FLASK TEMPERATURE: Normal recommended temperature in the range of 580° C to 700° C / 1076° F – 1292° F depending on size of flask, karat & type of jewelry.

FLUXING Boric Acid is the recommended flux. Use as little flux as possible. Do not use carbon fluxes or any fluxes designed for refining; i.e., soda ash, saltpeter, etc. Avoid flux in bottom pour automatic casting units.

QUENCH TIME: 25 – 30 minutes depending on the size of flask & type of jewelry.

RE-MELTING SCRAP An 80 % Fresh to 20 % Scrap ratio is recommended for scrap usage.

INVESTMENT: Most standard investment removers will successfully remove the REMOVAL investment powder. Fluoric-based investment removers are the best for removing the silicon oxide invisible coating. Use of aggressive acids causes stress corrosion and surface damage and is therefore not recommended. Ortho-phosphoric acid may also be used for this alloy.


UN373 is a Nickel based Soft White Bronze that can be used for fabrication of plate and wire fabrication giving a Standard White color. Alloy UN373 Soft Bronze Alloy can also be used for Investment-Casting. For plates or sheets less than 0.5 mm (0.020”), & other applications where this alloy seems hard or exhibits edge cracking, & may require anneal of the sheets.

MELTING: The UN373 All-Purpose White Bronze Alloy should be melted “as is” in a clean crucible. Initial melting temperature should be 1010º C/ 1850º F. Drop temperature by about 5ºC before pouring. Boric acid flux should be used to skim out the dross and slag to keep the metal clean during the melting process. The metal should be mixed well with a stirring rod before pouring to assure a good mix.

POURING TEMP FOR INGOTS: 1005° C - 1010° C / 1841º F - 1850º F

POURING: Metal should be poured into a pre-heated, vertical graphite or lightly lubricated iron mold. A steady even pouring motion should be used slowing down at the end of the pour to prevent shrinkage in the top of the ingot. Use a round rod mold for wire and a 2 piece L shaped mold (preferably of a width of 3.0 inches and thickness not exceeding 0.125” inches) for plate and sheet.

AIR-COOLING: The metal ingot should be removed from the mold and slowed cooled in air for softening. Do not quench in water as quenching will harden the metal.

FABRICATION: The metal ingot should be cleaned of all adhering oxide or fluxes before rolling. The ingot should be rolled or drawn to a 50% reduction in size before annealing. After annealing continue the reduction at 50% before annealing again. Clean the ingot after each anneal. Keep rolls, dies and metal clean to prevent defects in the finished stock.

ANNEALING (Softening): Annealing temperature 600º C / 1112º F for 20 minutes and AIR-COOLED. A boric acid fire coat should be applied before annealing in open atmosphere ovens to protect the metal from heavy oxidation.

REMELTING: Use 20% scrap to 80 % fresh mix when re-melting to prevent oxide build up in the metal.

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  • Model: UN373