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• In an open furnace, the electrode can obtain heat from three sources: radiation from the furnace mouth, conduction from the burden, and its own resistance. In a fully sealed furnace type (such as the 75 MVA furnace of Finnish design), however, only resistance heat exists, and radiant and conductive heat are essentially zero. If the actual operating current is lower than the design value, the current density falls and the resistance heat decays rapidly in accordance with the I²R relationship, so the electrode paste "cannot be baked through". (Key point)
• Case: A 75 MVA sealed ferrochrome furnace (public industry literature) had a design electrode current of 125 kA and a current density of 4.9 A/cm², but actually operated at 80 kA and 3.0–3.4 A/cm² for long periods. As a result, the baking speed of the electrode paste was markedly slower than the design value; after baking, the electrode had high porosity and poor strength, and tip loss, petal loss and hard break occurred continuously, with neither paste unit consumption nor power consumption reaching the design values. After modification — adjusting the formulation (faster baking, lower ash), increasing the heater power, raising the paste column above the melt level, increasing the diameter of the cylindrical paste while reducing its height, and lowering the circulating water flow to raise the water temperature — the unit consumption finally dropped from about 15.7 kg/t to 9–11.5 kg/t, and the power consumption fell by about 180 kWh/t.
• Popular science note — how current density is calculated: design current / (radius × radius × 3.14). For example, with an electrode diameter of 1600 mm and a design current of 125 kA, the calculated current density is 6.2 A/cm².

• Large ferrochrome furnaces mostly use cylindrical paste (which makes it convenient to measure the paste column height above the melt). However, the diameter of cylindrical paste is smaller than that of the electrode shell, so during melting it must flow laterally to fill the shell. When the paste is too soft, the pitch and fine powder migrate to the periphery during this flow while the coarse aggregate stays in the center, forming segregation. After baking, the center of the electrode lacks binder and is loose and fragile, so it is consumed preferentially during smelting: a cavity appears in the center of the tip, the periphery is divided by the ribs into separate small blocks, and finally the electrode breaks off at the root, forming "petal loss".
• Measured data corroborate this: from the inner zone (zone A) to the outer zone (zone F) of a baked electrode, the ash content decreases from 3.65% to 2.07% and the true density increases from 1.816 to 1.984 g/cm³ — more aggregate on the inside and more fines on the outside, so segregation definitely exists.
• Countermeasures:

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SiMn smelting is a reduction-smelting process intermediate between the slag-forming and slag-free methods, in which the reductant (coke) in the furnace participates extensively in the reactions. The electrode not only conducts electric current; the carbon at its tip also takes part directly in the reduction of metal oxides, forming "chemical consumption". Industry statistics show that the electrode consumption rate of SiMn furnaces is about 1.2 times that of ordinary ferromanganese furnaces.