Why Enamel Slurry Must Be Sieved

In the enamel production process, sieving the slurry is an indispensable, critical step — not an optional one. Its central value lies in ensuring the surface quality and functional performance of enamel products from the source, and it is relevant across stages such as RTU milling and wet milling.

During the wet-milling stage, the primary purpose of sieving is to accurately remove coarse particle impurities from the slurry. These coarse particles may originate from residual raw materials or insufficient milling; if the slurry containing them is applied directly, the finished pieces can show pitting, bumps, or other surface defects. Such defects not only spoil surface smoothness but may also weaken the bond between the enamel layer and the substrate, reducing the enamel’s wear resistance and corrosion resistance.

Even if the RTU enamel powder has already been dry-sieved to remove obvious coarse particles, a second sieving is still required after wet milling and wet mixing. This is because when the powder contacts water it can form agglomerates or lumps due to uneven water uptake or inadequate stirring — lumps that dry sieving cannot break up. Sieving disperses and removes these agglomerates, producing a more uniform particle distribution in the slurry, which helps ensure an even enamel thickness during application and prevents firing defects such as warping or enamel cracking caused by local thickness variations.

In addition, the sieving process effectively eliminates a large portion of the air bubbles in the slurry. If trapped bubbles enter the firing stage, they can produce pinholes or blisters on the enamel surface, seriously impairing the product’s sealing and appearance. The physical compression and filtration during sieving help expel air entrained in the slurry and increase slurry density.

In summary, sieving enamel slurry serves as a second purity check on raw materials and an important method for optimizing slurry performance. It is a refined production step that enamel manufacturers cannot omit in practical production.

jack@nolifrit.com