Q: I am looking for a suitable fastener for use in a high heat furnace that is running at 2000F but the actual hearth wear flames go up to 3000F. The furnace is not under vacuum and has a normal atmosphere. We are finding that the 304 bolts are failing rapidly and we tried Inconel bolts which are doing better but still failing in about 2-3 weeks. Do you have any recommendations?
A: At those temperatures in an oxygen rich environment you need to consider ceramic fasteners. As long as your loads are not too high and thermal shock is not an issue, I think this would be your best option. Since your hearth can get up to 3000F, I would recommend using Alumina ceramic bolts which provide thermal resistance to 3000F. In addition, Alumina is almost inert to corrosion including acids, solvents, salts and organics.