Conversion from low to medium frequency can be advisable for commercial reasons and reasons of energy policy. Some of the advantages of medium-frequency systems are listed below:
starter blocks and laborious starting procedures are not required
no laborious scrap drying or dry storage required
increased electrical efficiency through charge operation
melting with higher output and shorter melting times
improvement of thermal efficiency due to the smaller furnace size
lowest possible energy consumption with optimum flexibility
saving of maintenance and repair cost
increased operating safety
reduction of the fireproofing costs for the same throughput
increase in overall economy
old energy consumption with 13-t furnace with mains frequency, 750 kWh/t (2,800 kW)
new energy consumption with the same furnace, 640 kWh/t (4,800 kW – 250 Hz)
Zinc vapour is an accompanying phenomenon of melting which is unavoidable when melting plate materials containing zinc. The zinc vapour emitted from the melt must be extracted and filtered out by suitable extraction devices. The negative effects on the durability of acidic crucibles can be reduced to a reasonable level by suitable measures. Using the following procedure, the working life of a crucible should not be significantly lower than when working with zinc-free plate: The sintering charge and the complete 2nd and 3rd charges are melted with zinc-free scrap. From the 4th charge, scrap contaminated with zinc can be used. After interruptions in operations, the 1st charge is again melted with zinc-free scrap.
Wood’s metal melts at 70 to 72 °C.[1] This alloy of bismuth has the following composition: 25% Pb, 12.5% Cd, 12.5% Sn, and the rest Bi.[1][2]
References
Woodsches Metall (Wood’s metal). Gießerei-Lexikon, bismuth alloy with 25% Pb, 12.5% Cd, 12.5% Sn, remainder Bi, melting point 70 to 72 °C. Accessed 27 August 2026.
Welding is the term for the joining of 2 metallic materials with a welding material that
melts at approximately the same temperature. Welding rods are used for flame
welding, and electrodes for arc welding. In the process of inert gas welding, a
special wire is fed in continuously from a roll. These processes include MIG
(metal/inert gas) and TIG (tungsten/inert gas) welding.
Water / Water exchangers are used for higher outputs and an available operating water system. In regions with high air temperatures these are used in conjunction with evaporation coolers to maintain the minimum cooling water supply temperature of 34 °C for frequency converters and 45 °C for induction furnaces.
Exchangers function like an electrical transformer. If for example 34.5 m3/h flow
through the furnace circuit, which must be cooled down from 65 °C to 38 °C,
103.5 m3/h must flow on the cooling tower side or operating water side, which
in turn will be heated up from 21 °C to 30 °C.
The product of volume x temperature difference must be the same on both sides.
103.5 m3/h x 9 K=34.5 m3/h x 27 K ➜ 931.5 mm3 K/h=931.5 m3 K/h
Water distribution via collector pipes on the supply and return side requires the observation of
“Tichelmann’s principle”, if the collector pipes are connected relatively close to
each other with short cooling water paths. In older induction furnaces, the supply
and return lines on both sides were installed directly next to the coil connections.
In this case, the flow direction had to be the same in both pipes, i.e. on the right side
the water flows in total from the top and in order to the coil sections. On the left
side, the water flows in order from the top down and in total away at the bottom.
Tichelmann’s principle refers to the optimum distribution of collective flows
between individual flows and the return of individual flows to collective flows.
Expressed more simply, the flow direction must be the same in both systems.
With water, this can be solved for volumes of over 10 l/min. as shown in the figure, part A. With volume regulation by means of narrow pipes (DN 5 – 8 mm)
and lengths of 3 -6 m, this principle can be dispensed with, see the figure, part B.
A: Tichelmann principle at low water resistances. B: Volume regulation via narrow water hoses with high water resistances.
Voltage is the term for the electrical voltage. This is the measure of the potential between 2 electrical phases at 3-phase or 2 poles under direct current. The voltage is measured in Volts. 1 Volt is the voltage that causes an electrical current of 1 Ampere to flow through an electrical resistance of 1 Ohm.[1]
References
Bureau International des Poids et Mesures: The International System of Units (SI). 9th edition 2019, Table 4, p. 23: electric potential difference, unit volt, V = W/A. Retrieved 27 Aug 2026.
A Volt is the unit of measure of electrical voltage. The definition is that 1 Volt is the voltage that causes an electrical current of 1 Ampere to flow through a resistance of
1 Ohm. Ohm’s law: U=R x I.
Vermicular graphite, also called compacted graphite, is a worm-shaped form of graphite whose morphology lies between flake graphite (lamellar graphite) and nodular graphite (spheroidal graphite). In the production of ductile iron (nodular graphite iron), vermicular graphite is usually an undesired result of insufficient magnesium treatment or delayed casting.
Vermicular Graphite as a Casting Defect in Ductile Iron
It forms when the magnesium treatment of the melt is insufficient, or when the treated iron is left standing for too long before casting, a phenomenon known as fading; instead of the intended fully spheroidal graphite structure, worm-shaped particles appear, which is regarded as a casting defect in that context. In foundry practice, vermicular graphite typically shows up unexpectedly during nodular graphite iron production. Because the mechanical properties of ductile iron depend on a fully nodular graphite structure, any deviation toward worm-shaped graphite lowers ductility and strength. Foundries control this risk by dosing magnesium precisely and by pouring the treated melt promptly, since the magnesium effect fades over time and the graphite morphology drifts from nodular toward vermicular and, eventually, flake-like shapes.
Compacted Graphite Iron (CGI) as a Deliberate Material
Beyond its role as a defect, the same worm-shaped graphite morphology is also produced intentionally in modern foundries as compacted graphite iron (CGI). By closely controlling the magnesium content within a narrow process window, foundries can generate a stable vermicular graphite structure on purpose. CGI combines higher strength and stiffness than grey cast iron with better thermal conductivity and castability than ductile iron, which makes it a popular choice for cylinder blocks, exhaust manifolds, and brake components. This dual role, unwanted defect in one process and engineered target structure in another, depends entirely on whether the vermicular structure was intended and controlled, similar to how Meehanite cast iron relies on controlled inoculation to achieve its own defined graphite structure.
Comparison of Graphite Forms
Graphite Form
Typical Shape
Tensile Strength
Thermal Conductivity
Flake graphite (lamellar)
Interconnected flakes
Low
High
Vermicular graphite (compacted)
Worm-shaped, elongated particles
Medium
Medium
Nodular graphite (spheroidal)
Rounded nodules
High
Low
Frequently Asked Questions
What causes vermicular graphite to form?
Vermicular graphite forms when the magnesium treatment of a ductile iron melt is insufficient, or when the treated iron stands too long before pouring, causing the magnesium effect to fade. Both conditions push the graphite morphology away from full nodularity toward a worm-shaped, compacted structure.
Is vermicular graphite the same as compacted graphite iron?
The graphite morphology is the same, but the context differs. When worm-shaped graphite appears unintentionally during ductile iron production, it is treated as a defect. When the same morphology is produced deliberately and controlled within a defined process window, the resulting material is called compacted graphite iron (CGI), an engineered alloy in its own right.
Why is vermicular graphite considered a defect in ductile iron?
Ductile iron relies on a fully spheroidal graphite structure for its characteristic ductility and strength. Worm-shaped vermicular graphite interrupts this structure, reducing elongation and mechanical performance, which is why foundries treat its unplanned occurrence as a casting defect linked to inadequate magnesium treatment or fading.
Standard
Compacted graphite iron, the deliberately produced counterpart of vermicular graphite, is classified in ISO 16112, which defines grades based on tensile strength, hardness, and microstructure requirements.
