ASTM D1238 - Testing High Fluidity Samples with a Piston Holding Device
ASTM D1238 defines the method to measure the rate of extrusion of molten thermoplastics using a Melt Flow Tester. The sample is extruded through a die with specified dimensions under prescribed conditions of temperature and load. For materials with melt flow rate (MFR) greater than 10 g/10 min, the standard specifies the use of a support for test masses – and if needed for the piston, too – in order to prevent the piston from travelling during the pre-heat period. The goal is to ensure that enough sample is left for the measuring phase and that measurements can start at the correct distance from the die at the right time.
We were asked to test high fluidity samples of PP (polypropylene) and PA (nylon) having an MFR higher than 50 g/10 min. This required significant care and adjustments of the test method in order to achieve reproducible results with a basic melt flow tester. So, we performed the tests on a semi-automatic CEAST MF50 tester, equipped with a piston holding device. This feature consists of a retractable piston support that removes any load from the sample and prevents the piston from unwanted travelling during pre-heat period. The device is based on a pneumatic cylinder with a fork-shaped support that is automatically activated according to the test method settings. The operator is able to manually adjust the piston resting position before starting the test. Using the MF50, we tested the samples and easily obtained the desired starting position for measurements, together with a predictable starting time in the range specified within the standard.
InstronCEAST MF50多砝码熔体流动速率测试仪根据MFR和MVR方法执行熔体流动速率（熔融指数）的测试，该方法完全符合ASTM D1238规程A，B，C，D和ISO 1133 A和B的规定，用于单砝码和多砝码测试。 多砝码测试最多可以执行5个砝码按递增，递减或自由顺序测试，并具有完全可程控的预热和测量步骤。 所有砝码均预装在机器里并且由机器执行砝码操作，无需操作员干预，从而消除了所有安全隐患。 直接接触式高分辨率编码器可测量活塞位移。 机筒中的温度曲线极其稳定且准确。 其他高级功能包括大触摸屏，用于全面的测试编程，管理和诊断功能，以及基于Windows CE的嵌入式PC，能够存储测试方法和测试结果。 通过USB和以太网端口轻松导出数据。 独特的应力传感器功能可支持压料和驱料功能。 还提供自动熔体切割和料筒清洁配件。
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