Plastics Technology

MAY 2012

Plastics Technology - Dedicated to improving Plastics Processing.

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14th in a series fitted at the initial installation, then retro- fitting will increase the cost but will still have a good payback. Insulation projects are cheap, easy to accomplish, and gener- ally have a payback of 12 to 18 months, depending on the difficulty of installation. A thermographic camera survey will rapidly identify pipes that will suffer from parasitic heat gain and result in excessive chiller operation. Figure 1 shows a typical installation where some of the piping is insulated (lower and right areas) but the uninsulated areas (middle left area) are clearly seen as being colder than the insulated areas. These areas will gain heat, increase the water temperature, and require the chiller to be set at a lower temperature to deliver the same tempera- ture to the point of application. A thermographic survey is quick and provides excellent Fig. 3: This injection machine had not been used in two years, but the cooling circuit was left on, wasting energy. Condensation is clearly visible at left, and the thermo- gram at right also indicates vulnerability to parasitic heat gain. visual evidence, but it is relatively simple to find areas of para- sitic heat gain by other means. If the piping feels cold to the touch or shows visible condensation, then parasitic heat gain will be taking place. Figure 2 shows a section of pipe with vis- ible condensation. The condensation on the pipe is an indicator of high parasitic heat gain and the plant is paying money to condense all of this water out of the air. rTip: Use the cooling- and chilled-water map to identify areas of uninsulated or poorly insulated chilled-water piping. These will be obvious in many cases because of the condensa- tion that drips onto the floor. rTip: Parasitic heat gains will be highest on metal piping and that should be your first priority. Plastic piping (ABS or PVC) is less susceptible to parasitic heat gain, but it will still occur. This should be the second priority. rTip: Do not forget to look at the flexible plastic hoses from the drops to the machines. These will also suffer from parasitic heat gain. Maintenance will often strap the flexible hoses together with cable ties for neatness. This brings the cold-flow hose into intimate contact with the warmer return hose and increases para- sitic heat gain. It looks tidy and neat but it is not energy efficient. rTip: Try not to run chilled-water piping in the roof void area. This will always be the hottest part of the plant (heat rises). INSULATE COOLING-WATER PIPES, TOO For most plastics processing plants in temperate areas, there is no real benefit in insulating (non-chilled) cooling-water piping. Cooling water is closer to ambient temperature than chilled water and insulation is not generally required, especially where plastic piping is used. The only exception is where cooling-water pipes run through high-temperature areas. Cooling-water insulation is not as profitable as chilled-water insulation and can have payback periods as long as four years. STOP WASTE! Pumping chilled water to idle machines is an outright waste that is seen at many plants. The machines are idle but the water continues to flow because the isolation valves are difficult or impossible to reach and the staff has not been told to isolate the machine. Local isolation valves that are easily accessible and clearly signposted should be used to prevent the supply of cooling water to machines and tooling that are not being used. The best solu- tion is to use automatic valves that are controlled by the control circuit of the machine. rTip: Include a run-on timer to remove any residual heat. rTip: Use the cooling-water map to identify areas that can be easily isolated. Figure 3 shows a cooling circuit on an inoperative injection molding machine. Condensation is clearly visible and yet this cooling circuit had not been used for two years! For all of that time, the machine had cooling water circulating through it, using energy to operate the pumps and remove parasitic heat gain. What a waste. MOLD-TEMPERATURE CONTROLLERS If portable mold temperature controllers are used to either cool or heat specific tools, then it is good practice to look at the tubing that carries the cold or hot fluid. This can often be insulated easily to reduce the energy use by the mold-temperature controller. NEXT: MINIMIZE COOLING WATER DEMAND BY RAISING PROCESS TEMPERATURES. ABOUT THE AUTHOR Dr Robin Kent is founder and managing director of Tangram Technology Ltd. in Hitchin, Herts., U.K. Tangram provides consulting and training in plastics engineering and design. Kent has 36 years' experience in injection molding and extrusion as technical director for several processing companies in Europe. Articles in this series are adapted from Energy Management in Plastics Processing (2008, 265 pages, pidbooks. com). Contact rkent@tangram.co.uk or visit tangram.co.uk. PLASTICS TECHNOLOGY MAY 2012 55

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