Carat : 18 - 22
Colour : Indian Yellow
Melting Temp of Alloy : 890 0C
Application: The alloy SP 181 is the most widely used alloy for diamond jewellery. It imparts right set of properties which helps artisans to achieve firm diamond setting. It also gives a colour which is popular for 18 carat diamond studded Indian jewellery.
Recommended Practice: 18K 22K
Application : Casting /H-made Casting / H-made
Alloying Temp. : 10400C - 10600C 10600C - 10800C
Casting Temp. : 10200C - 10500C 10500C - 10700C
Flask Temp. [Normal Cast] : 6300C - 6500C 6400C - 6600C
Flask Temp. [Stone Cast] : 6100C - 6300C 6200C - 6400C
Quenching Time : 10 - 15 minutes. 15 - 25 minutes
The actual casting temperatures and flask temperatures shall be decided by the parameters like the section thickness of the items (thick, medium or thin), the overall size/bulk of the cast tree, the design intricacies etc.
As a thumb rule, for thinner sections higher temperatures are selected and for thicker sections lower temperatures are preferred. At the same time, designs demanding higher form filling capabilities, higher than normal temperatures are an obvious choice.
The 18 carat casings have a tendency to get hardened and subsequently give problems of cracking especially when flasks are cooled very slowly. For this reason, it is recommended that the flasks are cooled as fast as permitted by the quality of diamonds and also by the design parameters.
Pre-Alloying is strongly recommended simply to ensure better homogeneity in castings as well as in hand made products. Also, for still better results, pre-alloying in an inert atmosphere is always preferred.
Cast Tree Cleaning & Drying procedure: After primary removal of the investment during quenching, submerge tree in a hot (80-100oC) 50% phosphoric acid solution for 15-20 minutes. Rinse well with cool water to remove remaining investment powder and base metal oxides. Dry with compressed air.