Spraying and firing of Cast-Iron Enamel (2)

Release time:

2026-11-05 09:58

Source:

China Enamel Industry Association

Firing Kilns/Furnaces

Box-type kilns: Suitable for large castings. They require lower initial investment but involve high labor intensity and offer low efficiency due to their intermittent production nature.

Tunnel kilns: Typically utilize mesh belts or roller conveyors; for large components, overhead conveyor systems (hanging chain-type kiln cars) are often used.

Regardless of the firing equipment, workpieces must be dried after the coating (enamel) application. During the drying phase, the workpiece temperature must not exceed 160°C; this temperature is sufficient to remove structural water from the enamel layer. Once dried, the workpieces can proceed directly into the firing furnace. The initial zone of the firing furnace should not exceed 600°C, allowing for the removal of crystalline water from the enamel layer. If the workpieces enter the high-temperature firing zone (above 730°C) too abruptly, the enamel layer is prone to cracking—the rapid evaporation of crystalline water can rupture the coating, exposing the substrate (a defect known as "exposed base"). Such pieces cannot be repaired and must be discarded as scrap. In the main firing zone, the firing duration is typically maintained between 10 and 15 minutes, depending on the specific characteristics of the enamel frit. Upon exiting the furnace, the workpieces can be cooled using forced-air cooling (fans).

The cover coat is generally applied and fired in two separate stages. This approach yields a higher success rate and a superior aesthetic finish. Applying the entire coating in a single pass results in an excessively thick layer, which is prone to cracking during firing and produces a poor surface color.

Enamel coating thickness: The ground coat (base layer) is typically 0.8–1.2 mm thick, while the cover coat (applied in two stages) should ideally be 1.6–2.4 mm thick. If the enamel layer is too thin, the impact resistance may be high, but the aesthetic quality suffers. Conversely, if the layer is too thick, the appearance may be excellent, but both impact resistance and thermal shock resistance are compromised. Therefore, it is essential to determine and maintain an optimal coating thickness. The manufacturing process for cast-iron enameling is a complex operation with high, multifaceted technical requirements. One cannot prioritize a single performance metric at the expense of others; the final quality of the enameled cast-iron product is determined by a combination of factors, including specific operational procedures, customer requirements, the type of enamel used, the skill level of the operators, the quality of the cast-iron substrate, the design of the furnace or kiln, and the carefully established firing profiles.

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