Ceramic electrical insulator
Ozark Ceramics Europe

A Mineral Insulated (MI) Cable is a metallic cable with ceramic powder insulation packed tightly around the inner wires. Insulators for use in Mineral Insulated Cable production go by many names including crushable insulators, swageable insulators, preforms, beads, pellets, cores, or blocks. This is a uniquely engineered product which is designed to crush into a fine powder upon compression by modest forces.
MI Cable is made by stringing ceramic preforms with thermocouple element wires and loading the threaded assembly into a refractory metal sheath. This assembly can then be subjected to a series of drawing operations to reduce the diameter and elongate the part. The end result is a long coil of small diameter cable with a tight packing of ceramic powder to electrically insulate the wires and sheath.
Dimensionally, the requirements are obvious. Tight dimensional control is needed to permit design engineers to adequately predict the finished results. The holes must be properly positioned and accept the wire under all combinations of tolerance limits. The threaded assembly must fit into the sheath in very long lengths. The ends need to be square and smooth to prevent voids which may cause elongation problems.Because the assemblies usually consist of many insulators strung together, length tolerances are not critical, but uniform lengths are easier to use.