Demolding unit

Demold Density Dew point The process of removing a specimen or cast from a mold. The mass per unit volume of a material. The temperature at which the water vapor present in the gas (e.g. air or nitrogen) saturates the gas and begins to condense. 

The infrared method for the estimation of the NCO groups decrease in the PU postcure processes has been used by many authors [333, 334]. In the case of our PUs, we have determined the decrease in NCO group absorbance of the IR spectrum at 2 290 cm on 20fi thin PU films cast from the reaction melt between two teflon sheets. The kinetic measurements started immediately after demolding. The films were maintained under the same maturation conditions as in the case of thicker sheets. These values have been converted into a NCO group equivalent concentrations per unit volume of polymer taking into account the measured absorbance and the polymer thickness. In every case, corrections for variation of thickness of PU films with time were made. The NCO group molar extinction coefficient was established on standard solutions of DBDI in benzene [17]. 

To cope with the production of quite large parts, this unit incorporates multiaxis robots to demold and transport the molded part. The whole twin unit, which features a combined injection rate of 18 Ib./sec., is managed by a Unilog 90(X)B control system that made its debut at the 1989 Dusseldorf Plastics Fair. The mold alone weighs 127 t (140 tons) for the 1.5 m (2 yd. ) container, measures 305 x 153 x 216 cm (120 x 110 x 85 in.), and has an opening force of 545 t (600 tons). The top and bottom tie bars are 9h ft. apart and the side-to-side platen space is 18 ft. at a maximum mold thickness of 8i ft. 

Elastomer molded parts are too easy to bend which means that the common ejector units for elastomers are only applicable to a limited degree. Adjusted devices are then often needed to demold and strip off the molded parts. A more often used example for such a device to demold undercuts is the elastic expansion of the molded parts... 

For demolding undercuts and internal threads, collapsible cores (Figure 2.38) are used. Two technical solutions are available as a standard mold unit ... 

An injection molding machine (Fig. 7.1) can be divided into six components plastification/injection section, clamping unit, mold including the runner system, control system, and tempering devices for the mold. The most important part of the process is the mold, which is made of at least two parts to allow ejection (demolding) of the molded part. The injection molding process can be divided into six steps. Table 7.1 presents the main function of each step. 

The post-cooling process reduces the cooling time by cooling the part after demolding in a downstream-unit. The advantages of this process are the low residence time of the blown part in the mold (6). Because of high investment costs, the post-cooling processes are only used for special performance. 

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