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Quick thermal conditioning of molds  #10 (92), 2010

Helmut Eckardt

One of the latest Wittmann Group's developments is a quick heating and cooling system applying innovative BFmold™ technology. The technique offers plastics processing industry new opportunities in production of injection-molded articles with high surface quality.

The method of heating up the mold up to the softening or glass temperature (or even higher), is not a new achievement. BATTENFELD had executed the first successful
tests back in the seventies. Heating up the mold, and its subsequent cooling down, had been achieved by means of water as the tempering medium. Presently, this procedure is known as variothermal tempering. The concern with variothermal tempering is the need for the very high use of energy, and extended cycle times. Therefore, variothermal tempering could not be used economically or profitably.

KIMW, the established Kunststoffinstitut Ludenscheid (=  Plastics Institute Ludenscheid) in Germany, has developed a new cooling system that is very close to the inner contours of the cavity – the so-called BFMOLD™ technology, enabling
an especially high water flow rate.

The fundamentals of the BFMOLD™ technology can be described as follows:
•  The region of the mold that is lying behind the cavity is milled out – only a few milli- meters away from the cavity’s surface.
•  The excavation is filled with small steel balls.
•  The forces that are acting on the cavity from  the injection cavity pressure, are now transmitted to the mold’s base frame. This prevents deformation  (e.g. deflection) of the cavity.
•   In comparison to conventional cooling, the squeezed steel balls allow for a volumetric flow rate that is four times higher than previous technology.
•   Only the mold sections next to the cavities are heated up. Heating up only the cavity’s surface, and cooling it down, can be achieved quickly and energy efficiently.

Specifically, when using BFMOLD™ technology (respectively variothermal tempering) WITTMANN  has developed a powerful heating/cooling unit: The TEMPRO plus C160 VARIO that is equipped with a hot water circuit and a
cold water circuit. The WITTMANN  TEMPRO plus C160 VARIO temperature controller has the following physical characteristics:
•  Max. temperature: 160°C.
•  Max. heating capacity: 12 kW.
•  Max. cooling capacity: 70 kW at dT = 150°C.
•  Max. volumetric flow rate: 60 l/min.
•  Standard configuration of the valve switch unit at the temperature controller.
The application that has been presented at the Com
petence Days 2010 was realized on a BATTENFELD HM 110/525 injection molding machine with UNILOG B6S control. The mold was operated with variothermal tempering. The part that was to be molded had its perils:
 •  The material had to be black ABS.
•  The part showed many cut-outs.
•  High gloss polished surfaces were needed.

For the purpose of comparison, the first trial parts were molded in the conventional way; at a mold temperature of 80°C and in a 30 second cycle time. In this first trial, the joint lines at the cut-outs of the finished parts were clearly visible. The second trial, using variothermal mold tempering, the mold was heated up during the period between its opening and closing to a temperature of 120°C at the start of injection. Following the injection of the material, the temperature controller switched to the cooling procedure, also using a 30 second cycle time. The results of the second trial yielded a finished part of impressive high gloss quality. The part reflected the perfect high gloss polished surface of the cavity, with no unaesthetic joint lines and no sink marks.
For an even quicker mold switchover from heating to cooling – and vice versa – it is possible to mount the valve switch unit closer to the mold on the clamping plate of the injection molding machine.
This technology is capable of being integrated into molds for a wide range of application including large-dimensioned and relatively flat parts (for example LCD panels). In many cases it would be sufficient to arrange for BFMOLD™ in specific areas only, where joint lines and other imperfections are not acceptable and where high gloss is desired. Thus by using a TEMPRO plus C160 VARIO and variothermal tempering, the surface quality of molded parts can be improved selectively and essentially. In addition, BFMOLD™ is uitable for the tense cooling
of parts. The BFMOLD™ technology is distributed exclusively by WITTMANN BATTENFELD and WITTMANN. In combination with temperature controllers of the TEMPRO plus C160 VARIO series it helps to reduce energy consumption, time and money.

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