Plastics Technology

DEC 2014

Plastics Technology - Dedicated to improving Plastics Processing.

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SITUATION 2: LIMITS ON LINE SPEED Let's take a second hypothetical example and assume that an extrusion processor is running polypropylene at an average melt temperature of 210 C (392 F), has a mate- rial residence time in the barrel of about 4 min, and is operating at a rate of 100 lb/ hr. This engineer wants 100% activation of the CFA from temperature alone, and doesn't want to rely on shear effects to activate it. Based on the information from the kinetic model, this engineer is in good shape. It is predicted that 99% of the CFA will activate at those temperatures in just a little over 3 min. But then the production manager comes to the engineer and wants to double the line speed to 200 lb/ hr, which would cut the overall residence time of the material in the barrel to 1.5 min. Using Fig. 5, we'd be able to predict that the CFA activation would go down. It will achieve a little less than 20% activation on temperature alone, and then you'll be in the same situation that was discussed in the first example—fighting shear effects. The alternative is to use the model to guide process changes to maintain 100% activation from melt temperatures. In this example, the engineer would want to increase the temperatures to an average of about 230 C (446 F). The model allows the engineer to visualize and estimate limits on the process. There is an upper and lower limit to the line speed at a particular processing temperature, because you need the CFA to activate within a particular zone to be effective. If it activates too early and the melt isn't pressurized enough, the gas will escape; and if it isn't given enough time it won't activate completely and you'll be wasting the CFA. Joel Lischefski is the laboratory manager of Teel Analytical Laboratories, Baraboo, Wis. He has more than 15 years of experience working in R&D;, testing, and manufacturing laboratories and is the Technical Chair of the Polymer Analysis Div. for the Society of Plastics Engineers. Contact: (608) 355-3080; jlischefski@ teel.com; teel.com. Dan Clark is a chemist at Teel Analytical Laboratories with more than six years of experience in multiple laboratory settings. Dan has worked closely with a variety of diferent analytical instruments, including TGA and DSC. Contact: dclark@teel.com. SITUATION 3: LIMITS ON PROCESSING TEMPERATURES The kinetic model allows for the identifca- tion of temperature limits as well. Given a particular line speed and material residence time, an engineer will need to make sure that the CFA is activating in the correct screw/ barrel zone where there is sufcient pressure to keep the gases produced from escaping. Let's say a process was designed so that the material was conveyed and melted at an average of 220 C (428 F) over the course of 1.5 min. Then, after this zone the material is pressurized for the CFA to react and produce the gas. The kinetic model produced would tell you that you are likely losing 50% of the gas being generated because you're activating it too early, before it's pressurized. That's money being wasted because the reaction kinetics aren't understood. In this example the model would tell us we should lower the temperature below 190 C (374 F) in order to prevent more than 1% of the CFA from being activated too early. The application of these testing processes and techniques allows for the characteriza- tion of CFAs and the estimation of processing limits that will be applied to a particular process design. Knowing how the reaction progresses ahead of time will allow for intel- ligent design of a production process to avoid needless waste of the CFA while ensuring a consistent activation, which helps improve process quality. The techniques can also save valuable time and money in trial-and-error development work by providing information to engineers up front before equipment and processes are chosen. Seeing quality is easy More filtration Higher quality Low operation costs More material flow Less power consumption Lower operating pressures Fimic models reach a maximum filtration area of 588 in 2 . With this ample area, the flow of material is easier, the operating pressures are lower and the power consumption is reduced. It is possible to choose the model on the base of hourly throughput and on the level of f iltration required. AUTOMATIC SELF-CLEANING SCREEN CHANGER The best simply works better. Reclaim, simplified. 203.255.9444 • www.adgs.net 62 DECEMBER 2014 Plastics Technology PTonline.com T ips & Technique s

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