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(as cooling water in a TCU, for instance), you may want to investigate whether the overall water-system pressure is at normal levels. instance—long before the problem became too serious to ignore. That's why it is best to keep a detailed log of the heat-transfer conditions associated with each mold you run. After you have GRADUAL APPEARANCE OF COOLING PROBLEMS gotten the process operating properly, record the heat-transfer While a sudden change in heating or cooling performance due to system parameters that result in a stable process and quality parts: a malfunction may be relatively simple to diagnose, the gradual •Composition of heat-transfer áuids in the system (water, development of quality problems can be more insidious. In fact, 30% propylene glycol, type of oil, etc.) you may have been compensating for a growing heat-transfer •Process-áuid áow rates, temperatures, and pressures in and out issue for some time—by changing other process settings, for of all heat exchangers, tools, and processes. •Equipment in the system, including pump motor horsepower, actual electrical amps drawn, TCU heater sizes, and cooling-valve size. •Ambient temperature when all of the previous data was recorded. •Resin type and throughput rate. These data should be logged every time a particular job is started up and anytime heat-transfer and process parameters are changed. Not only will this help you when you set up a job that has not been run for some time, it will also give you an historical record that could identify a gradual loss of system effciency long before it becomes critical to part quality. Some of the problems such a log might signal include: •Fouling of internal water lines in the mold. Suspended or dissolved solids can build up on channel surfaces, reducing áuid áow and limiting heat transfer between the steel and cooling water. •Fouling of lines in cooling equipment. EAC Pelletizer 5032 Recycle Dryer EDGE Pelletizing System The same types of issues can apply to the heat exchangers and piping in chillers and TCUs. Filters can be used to remove many suspended solids, but dissolved solids like lime need to be addressed by a water-quality specialist familiar with the water in your region. In a closed-loop system, periodic checking of water chemistry and conductivity can also warn when dissolved-solids content is reaching problematic levels. •Cooling-tower water contamination. A tower can become contaminated by all sorts of airborne debris (tree seeds, leaves, etc.), as well as algae. A full-áow strainer on the tower outlet can eliminate a lot of the problems, and a properly sized pump tank will allow solids to settle out of the water before it is pumped into the heattransfer system. Here, too, it is important to watch dissolved solids. Towers cool by evaporation and solids can build up, so 26 February 2013 Plastics technology