A prominent feature of the production process for sanitary ceramics is slip casting – specifically, the raw and auxiliary materials for the blank, prepared in accordance with the formula, are first placed in a ball mill, ground with water to make slip, and then the slip is poured into molds made of gypsum or other materials to form green bodies. Among several forming methods in ceramic production, the slip casting process features the lowest manual efficiency and the highest drying energy consumption. For years, attempts have been made to adopt other more optimal methods, yet no breakthrough has been achieved to date.
The production process flow of sanitary ceramics can be divided into the main production process flow, the glaze slip preparation process flow, and the gypsum mold preparation process flow. For the low-pressure quick-drain casting and high-pressure casting processes, the aforementioned gypsum mold preparation process flow is replaced by the low-pressure quick-drain mold preparation process flow and the high-pressure casting mold preparation process flow respectively.
1) Main Production Process Flow of Sanitary Ceramics
Raw material storage → Raw material weighing → Slip grinding (ball mill) → Slip conditioning and storage → Slip tank filling → Slip supply → Slip casting → Green body demolding and finishing → Green body drying → Semi-finished product inspection → Glazing → Firing → Finished product inspection → Qualified product packaging and warehousing.
2) Key Process Parameters
Slip grinding time in ball mill: 9–15 hoursSlip specific gravity: 1.78Slip moisture content: 28%Slip storage time: Approximately 7 daysSlip casting time: Around 90 minutes (varies by product type)Setting time: Around 30 minutes (varies by product type)Wet green body thickness: ≥ 8 mmGreen body moisture content: 21%–23%Green body drying time: 1–5 days (varies by product type)Green body moisture content after drying: ＜ 1%Green body drying shrinkage: 2%–3%Green body weight (dry weight): 10–50 kg (varies by product type)Gypsum mold service life: 80–100 uses, maximum up to 120 usesRatio of total glaze slip (dry weight) to total green body (dry weight): Approximately 8%Firing temperature: 1190℃–1240℃ (temperature measured by pyrometric cones)Firing time: 11–20 hours (tunnel kiln, gaseous fuel)Loss on ignition (LOI): 6%–8%Firing shrinkage: Approximately 9%Green body thickness after firing: No part of the product shall be less than 6 mm, excluding supporting blanks added to prevent product deformation. (Except for individual parts of special products such as thin-edge basins)Water absorption:
Vitreous sanitary ceramics: Water absorption ≤ 0.5%
Stoneware sanitary ceramics: 0.5% ＜ Water absorption ≤ 15.0%Kiln for secondary firing: Shuttle kiln, tunnel kilnSecondary firing temperature: 1170℃–1210℃Secondary firing time: Approximately 24 hours
