Highlight what the possible consequences the following would have on the casting:

Highlight what the possible consequences the following would have on the casting:

1. a. pouring the agar duplicate gel 15C above the recommended temperature

   • After heated to sol state (98oC), the agar agar is allowed to cool to around 50oC before pouring. The material is best poured at as low as temperature as possible, whilst maintaining the sol state, in order to minimize contractions which occur during gelation. Pouring the agar duplicate gel 15oC above the recommended temperature would possibly cause the agar to contract more, which could alter the negative shape of the model, therefore making the duplicate model, and casting inaccurate. Pouring agar temperature too high could also have an effect on the setting time of the agar.
   • Cause melting of the survey/blockout wax on model

2. b. heating the muffle to only 800C

   • For cobalt chrome castings, ammonium phosphate investment material is used. The strength of a phosphate-based investment material increases during heating. At temperatures between 800-900°C a chemical reaction between silica and the binder, forms complex silico-phosphates. This is what causes the improved strength of the material. If the muffle was only heated to 800°C, the complex silico-phosphates may not form, resulting in a not as strong material and so it may not be able to withstand the impact of the molten alloy during casting.
   • lead to insufficient burnout, can result in technical problems such as incomplete casts + insufficient mould expansion