Process Improvement in Preparation of Ball Valves

The industrial application of ceramic injection moulding has been limited to small components because of the associated binder burnout problems. Injection moulding may improve the manufacture of alumina ball valves for the process industries by reducing costly and potentially damaging machining operations. However, these components are too large to be produced using conventional thermoplastic binders. Aqueous injection moulding allows most of the binder system to be driven off as water vapour, cutting process time, reducing burnout difficulties, and causing less environmental pollution. The manufacture of ball valve blanks from alpha -alumina was carried out using a die cavity of 25.4 mm outside dia. Improved processing parameters were efficiently identified using orthogonal arrays as described by Taguchi. The following factors were evaluated for their influence on defects: binder content in solution, die temperature, injection velocity, injection time, barrel temperature, injection pressure, hold pressure, and residence time in the mould. Binder content in solution was found to be the most influential factor. The defects observed included cracking, poor make up, and distortion. Ball valve blanks of significantly improved quality were successfully manufactured under the preferred conditions.