Usage of insulated refractory castable furnace for making joint-less bangles

Abstract

Joint-less bangle making is one of the oldest art forms in the country and usages of traditional furnaces for manufacturing the bangles had their flaws. The efficiency of the furnaces, heat loss through the walls, and artisans’ health issues due to the flue gases released were some of the reported issues. Rural Technology Action Group (RuTAG) at IIT Delhi identified a feasible solution after many iterations, ending up with a four layered furnace structure. There are two insulation layers of varying thickness sandwiching a layer of refractory castable and a steel casing providing the housing on top of the layers mentioned. Temperatures around 1300 °C is required to melt the glass inside the furnace to produce the bangles and such temperatures are quite high for ordinary concrete to sustain due to its thermal properties. High performance concrete (Refractory castable) was chosen for this particular purpose and the subsequent refractory castable model will be analysed using STAAD.Pro CONNECT Edition. Steady state temperatures for different layers can also be found out using simple equations and be used for applying the temperature loads in the software. Thermal Properties like refractoriness, permanent linear change and thermal conductivity are important parameters for selecting the suitable castable. Testing of the refractory castable and insulation blankets is of prime importance and their performance in such high temperatures has to assessed before using them for constructing the furnace. Specimens of insulating blankets sandwiching the castable can be heated to the required temperatures using an electric furnace and cooled after several hours of heating simulating a cyclic temperature loading. The insulation blankets are connected with the castable via refractory connectors. The change in the dimensions and shape of the specimens was found to be within the limits and subsequently the insulation and castable can be used for such purposes.