Cast Iron Enamel Pre-treatment
Release time:
2026-05-22 10:11
Source:
Surface Cleaning of Cast Iron
Before enamel coating, castings should undergo surface grinding, annealing, and sandblasting to clean them.
During the casting process, castings inevitably have some casting defects such as mold seams and loose sand. These require manual cleaning and grinding to achieve a smooth and even surface.
Annealing Treatment:
Castings used for enamel coating should ideally be pearlitic gray cast iron. However, due to variations in casting temperature, sand moisture content, residence time in the mold cavity, and cooling rate among different foundries, cementite crystal structures may remain on the casting surface. These are detrimental to enamel coating and sintering, easily leading to pinholes and bubbles. To eliminate these defects, a firing treatment is performed before enamel application.
The firing temperature is generally controlled between 770-800 degrees Celsius. The firing time varies depending on the wall thickness of the casting. Generally, castings with a wall thickness of 3-6mm are fired for 20 minutes; those with a wall thickness of 6-10mm are fired for 30 minutes. If the temperature exceeds 830 degrees Celsius, the graphite in the casting will recrystallize, and some free carbon will precipitate. This can easily lead to pinholes and bubbles in the enamel during firing, causing defects on the porcelain surface. The firing process is crucial, especially for colored enamel.
Shot Blasting Treatment：
Currently, most companies use shot blasting equipment. Examples include: drum shot blasting machines, hook-type shot blasting machines, through-type shot blasting machines, and tracked shot blasting machines. Some also use air compressors to blast quartz sand. Sandblasting machines generally use a mixture of high-manganese steel shot (1-1.2mm in diameter) and cut steel wire shot, with the steel wire length typically 0.8-1.2mm. The sandblasting time is generally set at 3-5 minutes. After sandblasting, the casting surface must be cleaned and stored properly, and must be free of dirt and oxides.
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