• density and specimen weight (sand rammer); • permeability (drum or gage-type permmeter); • green compression (strength machine); • green shear (strength machine); • methylene blue (MB) clay (MB clay tester); • American Foundry Society (AFS) or 25 micron clay (au- toclay or 25 micron clay washer);
• sieve analysis, AFS grain fineness and distribution (sieve set and sieve shaker);
• loss on ignition (LOI) (tester consisting of muffle furnace, crucibles, desiccator and crucible tongs);
• volatiles (volatiles crucible with lid and tongs). Landers Foundry brought in an independent sand con- sultant to study its laboratory procedures. After the consul- tant determined the lab was completing the tests carefully and accurately, the sand technicians proceeded to investigate its sand quality by performing the necessary tests.
Compactability and Moisture Tests on the original sand blend proved the moisture
requirement in the sand was high, measuring 4-5% at a compactability level of 35-40%, the normal temper level desired at molding. The compactability-moisture ratio was between 7 and 9. A high ratio indicates there is a large amount of moisture-absorbing material in the sand. While the silica base aggregate requires little moisture, the moisture requirements of the other additives in the blend are higher. Although present in a smaller percentage than sand, clay/ bentonite is the primary moisture absorber. Seacoal, dead clay and other additives also require moisture. The high amount of additives, as compared to silica,
was the cause of the high moisture requirement in Landers Foundry’s molding sand. High moisture causes gas defects, rough castings, metal penetration, poor flowability and com- paction, swells, expansion defects and other problems.
Density and Specimen Weight Specimen weight and density, which depends on sand com-
position, measured low in Landers Foundry’s molding sand upon first testing. Silica is the heaviest component, so the greater the silica content, the higher the density and specimen weight. The low density and specimen weight at Landers Foundry indicated a low silica level and a high amount
Landers Foundry’s com- pactability and moisture ratio increased over time to match the automatic molding machine’s ex- pected numbers.
• 湿压强度（强度测试仪） • 湿剪切强度（强度测试仪） • 吸蓝量（吸蓝量测试仪）
• AFS（美国铸造协会标准）或者25微米膨润土（自动 或者25微米洗砂机）
• 过筛测试，测试粒度及其分布（套筛及相应振动器）
• 灼减测试（灼烧仪器，包括保温炉、坩埚、干燥器 和坩埚钳）
• 挥发性测试（挥发坩埚及相应盖、坩埚钳） Landers 铸造厂请来一位型砂顾问来检查其实验室
流程，当顾问确定实验室已经能够仔细且准确地完成 测试后，公司的型砂技术人员开始用前面提到的一系 列测试来研究公司的型砂质量。
紧实率和含水量
对新砂的测试表明，型砂对含水量要求很高，造型 中常见的紧实率为35-40%，此时含水量为4-5%。紧 实率与含水量的比值大约在7至9之间，较高的比值表 明型砂中吸水材料较多。硅砂对于水分需求很少，而 其它添加物对水分要求则高得多。尽管膨润土和型砂 相比比重很小，但是却吸取了大部分水分，煤粉、死 粘土和其它添加物也吸取了一定水分。 相对硅砂来说， Landers 铸造厂的型砂中添加物过 多，导致对含水量的需求增大。而过高的含水量导致 了气孔、表面粗糙、机械粘砂、透气性差和紧实、胀 砂、不平整等其它问题。
密度和样重
密度和样重取决于型砂的组分，而Landers 铸造 厂的型砂在第一次测试中密度和样重偏低。硅砂是 最重的组分，所 以硅砂含量越高 则密度与样重越 大。Landers 铸造 厂的型砂密度和样 重偏低说明硅砂含 量低而其它更轻的 组分含量高。
密度与样重偏低 和硅砂含量低会导
随着时间流逝，紧实率 与含水量的比值不断增 加，最终达到Landers 铸造厂运行的设备上的 比值。
Summer 2011
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