Introduction
The production process of sanitaryware is intricate and complex. From raw material preparation to high-temperature firing, any minor oversight in any step may lead to product defects or even total scrap. These defects have complex causes and diverse manifestations: some are visible immediately after forming, others remain hidden until the firing stage, while others are directly caused by improper firing process control.
Introduction
The production process of sanitaryware is intricate and complex. From raw material preparation to high-temperature firing, any minor oversight in any step may lead to product defects or even total scrap. These defects have complex causes and diverse manifestations: some are visible immediately after forming, others remain hidden until the firing stage, while others are directly caused by improper firing process control.
| Common Defects | Root Cause | Preventive Measures | ||
Cracking | Insufficient plasticity of raw materials, excessively fine slurry particle size, uneven moisture content in plaster molds, inconsistent thickness of green bodies, interruption during slip casting. | Maintain slip temperature between 25-35°C; ensure adequate weathering and aging periods for raw materials; adjust body formulation to maintain optimal plastic clay content; inspect plaster molds for uniform moisture distribution before use; avoid interruptions during slip casting. | ||
| Bubbling | High carbonate/sulfate content in body or glaze materials; incomplete removal of deliquescent substances; improper firing temperature or atmosphere control. | Optimize body and glaze formulations to reduce impurities; control firing ramp rates and maintain reducing atmospheres to ensure complete oxidation and decomposition.
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| Pinholes | High organic matter or iron oxide content in body material; rapid heating causing volatile loss; poor glaze fluidity or excessively thin glaze application. | Select raw materials to reduce organic content; adjust firing curve to avoid rapid heating during high-temperature stages; optimize glaze formulation to enhance fluidity. | ||
| Orange Glaze | Excessive temperature rise during glaze melting, uneven glaze thickness, or poor high-temperature flow. | Control firing temperature and heating rate to ensure uniform glaze melting; optimize glaze grinding and application processes. | ||
| Glaze Cracking | Mismatched expansion coefficients between body and glaze, excessive firing temperature, or improper cooling schedule. | Adjust body and glaze formulations to match expansion coefficients; optimize firing curve and control cooling rate. | ||
| Deformation | Unsuitable body structure design, improper loading method, or inadequate control of firing temperature or holding time. | Optimize product design to avoid excessive thickness variations; standardize kiln loading procedures to ensure flatness of saggers and spacers; strictly control firing temperature and holding time. |
Yellowing
Causes: Excessively rapid heating, insufficient reducing atmosphere, excessive TiO₂ content in raw materials.
Prevention: Adjust firing curve to extend reduction phase duration; control TiO₂ content in raw materials, add masking agents if necessary.
Smoke Stains
Causes: Incomplete oxidation of body, excessive calcium content in glaze, inadequate kiln ventilation.
Prevention: Optimize the firing atmosphere to ensure complete oxidation of the body; adjust the glaze formula to reduce calcium content; enhance kiln ventilation.
Underfiring and Overfiring
Causes: Underfired products exhibit yellowing, high water absorption, poor glaze luster with roughness, low strength, and a dull sound when tapped. Overfired products show deformation, glaze bubbling, or glaze running.Primary causes include excessively high or low firing temperatures, improper control of high-temperature holding times, unreasonable loading density, or significant temperature variations during firing, leading to localized overfiring or underfiring. Prevention: Conduct firing experiments (trial firings) to determine the optimal firing temperature range (the safe zone between the start of sintering and the onset of overfiring) and holding time for different products and body-glaze formulations. This forms the foundation for all control measures. |  |
Lack of Luster
Cause: Also known as loss of brilliance. This defect arises from the formation of microcrystals in the glaze layer and inadequate glaze fusion, resulting in a dull surface. Implement rapid cooling during the initial cooling phase to prevent glaze crystallization and enhance surface gloss.
Prevention: Optimize glaze formulation and preparation. Precisely control firing schedules. Use temperature cones or thermal analyzers to determine the optimal glaze firing curve, including heating rate, maximum firing temperature, holding time, and cooling rate. Within the critical temperature range for glaze glass transition, appropriately control cooling speed to avoid rapid cooling causing glaze crystallization.
Summary: Preventing ceramic forming defects requires a multi-faceted approach encompassing raw material selection, process parameter control, and equipment maintenance. Strict adherence to process specifications and timely adjustment of production parameters can effectively reduce defect occurrence.