What are the differences between cast and sintered Alnico parts, and what are the processes?
Cast parts are formed by pouring molten metals, or alloys, into sand or ceramic molds. The molds have sprues and runways to direct the molten metal to one or more female cavities with the desired magnet shape. The cavities are vented for the gasses that form, and there is shrinkage on cooling, so post-casting clean up and / or grinding operations are usually needed. Sintering is a molecular joining of pure metal powders, or alloys, with heat, but without liquefying them. Wax is blended into the sinter powder before pressing so the pressed parts keep their shape. The binder burns off in the furnace before the sintering process begins. Automatic presses allow sintered magnets to be formed quickly and continuously, so this is usually a lower cost process, but die pressing places practical limits on size to about 150 grams, and length is limited to roughly 2.5 times the diameter. Sintered parts shrink somewhat when fired, but are very consistent in size so they can often be used as is, or
