Test Your Rheology IQ

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Test Your Rheology IQ

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Bimodal high density polyethylene, HDPE

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We will try to imagine how bimodal molecular weight distribution rise. We will focus on two main properties: processing and mechanical . We start from normal (unimodal) molecular weight distribution (please, start to analyze the graph). Macromolecules with short chains , are easiest to process, polymer has lower viscosity , long chains are responsible for mechanical properties the grow. Considering, what left (middle), can be replaced. The idea was simple, eliminating average properties, we receive polymer with key properties. Return to the most important, processing and final product properties , considering molecular weight distribution . Short fractions or single monomers are gaseous substance, waxes, their impact is questionable (easy degradation, responsible for bad odor) and appear for unimodal distribution , changing the distribution we eliminate them. Long fractions generally affect mechanical properties , e.g. stiffness , it is possible to reduce wall thickness (sho...
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6. Balance of fill analysis - Validation procedure for injection molds

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The sixth step in validating a injection mold with the overall process shown in injection mold validation flow chart is balance of fill analysis . The steps before: 1. Mold certification 2. Dry cycle mold 3. Process stability test 4. Gage repeatability & reproducibility (R&R) test 5. Mold viscosity test Purpose: The purpose of the balance of fill analysis is to evaluate the thermal and flow balance of the plastic distribution system in the mold. The plastic distribution system encompasses the hot or cold runner system, as well as the core and cavity. Only a naturally or symmetrically balanced manifold should be specified. The cavity-to-cavity weight difference is an indicator of the quality of the hot runner system. It is critical to have the flows balanced to each cavity or the part-to-part variation may be large and process capability may not be achievable. Recall, the purpose of the mold validation procedure is to reduce variation throughout the injection mold. A typical m...
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Injection mold validation procedure

To validate an injection mold, there are numerous items one must take into consideration before the mold is completed and work is ready to begin. First, it is advisable to hold a mold design review meeting with all involved parties prior to tool manufacture. Invite the mold builder, hot runner supplier, steel supplier, press supplier, resin supplier, and a strategic molder for the design review. Involving everyone early on in the process and keeping them informed throughout the building of the mold avoids needless complications. Once all the suppliers have been identified it is vital that they are all given training on the injection mold validation procedure , IMVP. The training should be done well in advance of the first mold qualification, if you have a pilot tool stage this is an ideal time. It could be done whilst the production tools are being manufactured. It is strongly advised the tool builder is made aware of the requirements of mold certification (steel measurements) before...
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