Advanced TCU Controls Both Temperature & Flow Rate
Unlike most TCUs, which control only water temperature, Nextherm controls both temperature and flow rate by means of a positive-displacement gear pump with a variable-frequency drive (VFD).
A new mold-temperature-control unit (TCU) designed by a molder for molders, is said to overcome many of the limitations of existing TCUs. Called Nextherm, the system comes from Aquatech, a Piovan Co., and is sold here by Universal Dynamics (Una-Dyn), a sister company. Both are located at the new headquarters of Piovan North America in Fredericksburg, Va.
Nextherm is the invention of Kenneth Johnson, who has more than 49 years of experience in the field, most of that as a mold-design engineer and program engineer in the Plastics Molding Systems Engineering Dept. of The Gillette Co. (now part of Procter & Gamble). When he retired from Gillette, Johnson set out to build a better TCU that would ameliorate mold-cooling problems he had faced throughout his career. The answer was a system called iCool (Intelligent Process Cooling System). That system has now been licensed exclusively and on a global basis to Piovan, which has renamed it Nextherm.
Unlike most TCUs, which control only water temperature, Nextherm controls both temperature and flow rate by means of a positive-displacement gear pump with a variable-frequency drive (VFD). The system also uses proprietary software that computes the heat-transfer balance during the molding cycle in order to balance cooling against heat input from the melt, so as to provide a stable mold temperature throughout the cycle.
Nextherm does not require sensors inside the mold. Instead, it uses pressure sensors in coolant flowing to and from the mold and magnetic flow sensors to measure flow coming from the mold. The positive-displacement gear pump provides a reliable measure of flow into the mold. The 15.5-in. touchscreen display shows supply and return water temperatures and pressures, differential temperature and pressure (ΔT and ΔP), and flow rate.
The user can set a maximum pressure differential (up to 150 psi) to protect seals and water lines, and the system will perform a quick test to automatically “learn” the maximum flow rate possible for that mold within that pressure limit. This “LearnMold” mode also automatically ramps the flow rate down from the maximum to generate a pressure/flow curve for the tool, which is checked—and revised, if necessary—on every subsequent startup of the tool to determine whether flow conditions inside the mold have changed.
Using a 5-hp variable-speed pump, Nextherm can match the output of commonly used centrifugal pumps from 0.5 to 10 hp (using no more than 3.2 hp). The gear pump is said to be much more energy efficient than centrifugal pumps; less waste heat from the pump reduces the load on the central chiller or cooling tower, increasing its effective capacity. Tests at one molder have shown cycle-time reductions of 35-50% with this system.
Tighter control of actual mold-temperature control (as opposed to water temperature) claimed for this system offers other potential benefits, such as ability to use a lower melt temperature and/or a higher water temperature. Una-Dyn/Aquatech currently offers a 30-gpm Nextherm unit, though future plans include models with 60, 90 and 120 gpm.
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