Calculating CTE Match between Enamel and Copper

Calculating CTE Match between Enamel and Copper

釉料与铜胎膨胀系数的匹配计算

type:tutorial · level:advanced · material:copper · scale:decorative-object · scale:jewellery · equipment:furnace · stage:finishing

标签：膨胀系数, 配方计算, 应力判定, 弯曲试片, 釉料设计

铜的线膨胀系数约 17.3×10⁻⁶/K，瓷釉宜控制在 12–15×10⁻⁶/K，冷却后釉层受压应力不易开裂。配方估算用加和法：各氧化物质量分数乘其膨胀因子（SiO₂ 约 0.27、Na₂O 约 4.3、CaO 约 1.4、B₂O₃ 约 0.66）求和。降 CTE 加石英与硼酸，升 CTE 加钠钾氧化物；每调整 1% SiO₂，CTE 约变化 0.027×10⁻⁶/K。验证用弧度试片法：条形铜片单面搪釉烧成后置于平面，釉面朝上拱起说明压应力过大，下凹说明张应力过大，平直方为匹配。

Copper expands at ~17.3×10⁻⁶/K; enamel should sit at 12–15×10⁻⁶/K so the glaze cools under compression and resists cracking. Estimate by additive calculation: sum each oxide's weight fraction times its expansion factor (SiO₂ ~0.27, Na₂O ~4.3, CaO ~1.4, B₂O₃ ~0.66). Add silica and boric acid to lower CTE, alkali oxides to raise it—each 1% SiO₂ shifts CTE by about 0.027×10⁻⁶/K. Verify with the strip test: a one-side-enamelled bar laid flat that arches glaze-up carries excess compression, cups with excess tension, and matches only when straight.