Cooling compression molding

Fig. 10.55 DSC thermograms of PPHP + Millad-3988 at different concentrations (a) 0.07 wt%, (b) 0.14 wt%, and (c) 0.21 wt%, carried out using sections cut from 0.7 mm thick, fast cooled, compression-molded sheets (Pendyala et al. 2004)...

The density of slowly cooled compression molded films was determined using a density gradient column. Water and 2-propanol were mixed according to ASTM-1505-85. The error in the density estimation was no greater than 0.0003 g/cc. 

Samples of /the polymers for physical evaluation were prepared by film casting from toluene solution at 90°C. and allowing the crystallization to occur by cooling the melt. It was observed that phase separation occurred in the melt in the case of the H2-BIB but not for the H2-BBB. These materials could also be compression molded at 1<40°C., but optimum results appeared to be obtained with the film-cast samples. 

Sample Temperature Rise Owing to Irradiation. A temperature rise of 2.9°C. during irradiation was found at the center of 0.033-inch thick water-cooled polystyrene samples for a beam current of 10 fxa. This temperature was measured several times, using thermocouples compression-molded into the center of the samples. The thermocouple leads entered the sample from the direction shown in Figure 1. Several different thermocouple junction sizes were used, with the same measured results. 

During high temperature compression molding, the polymeric powder is poured into a positive pressure mold that is heated and then cooled under pressure. The cooled mold is then opened to yield a fully sintered UHMWPE article. 

Before testing, the samples were compression molded, usually at 10°F above the milling temperature, using a cycle with a five-minute preheat and three minutes at a pressure of 40,000 pounds ram force. Specimens were then transferred to a cooling press and cooled under pressure. 

PS-25 PPO the mixture was heated to 300°C, maintained at this temperature for 6 minutes, compression molded into a film, and cooled slowly to room temperature in the press. 

This section will illustrate the tools taught in the above sections in the form of examples applied to steady state problems. Example 8.3 applies the finite difference method to a simple one-dimensional fin cooling problem and illustrates the nature of the system of equations that is normally achieved. Example 8.4 present a 2D compression molding problem where an iterative solution method is introduced. 

Fig. 36 Fracture surfaces of thick, compressed A18749 resin sintered at 350 °C for (a) 5 min and (b) 30 min and (c) the sample in (b) reheated for an additional 30 min at 350 °C followed by slow cooling in a compression-molding press with no pressure applied...

Characterization. Film samples about 0.25-mm thick were prepared by compression molding the polyurethanes under dry nitrogen at 180°C and 3 MPa pressure. After molding for 20 min, the samples were allowed to cool slowly in the press under dry nitrogen flow. Figure 2 shows the thermal history of the 180°C-molded films. No discoloration was observed when the samples were removed from the mold. The two soft-segment polyurethanes were compression molded at 120°C. The films were allowed to stand at least one week at room temperature in a dessicator before being evaluated with the Rheovibron DDV-IIB Dynamic Visco-... 

The polymers used and some of their physical properties are listed in Table I. Polymers were mixed and blended on a two-roll mill at 450 K. Samples were compression molded at 450 K for 7 min and cooled in the press with tap water for 5 min. ASTM D412 6.35-mm (Va in.) dumbbells were cut parallel to the mill grain from sheets having 1.9-mm (75 mils) thickness. Instron tensile tests were carried out at least 48 hr after molding. Pull rate was 50.8 cm/min (20 in./min). 

Usually called injection-compression molding (ICM). Details are in Chapter 4. The essential difference when compared to IM lies in the manner in which the thermal contraction in the mold cavity that occurs during cooling (shrinkage) is compensated. With conventional injection... 

This process resembles the open molding process except it is closed like a two-part compression mold (Chapter 14). A measured amount of plastisol is poured or pumped into the closed mold cavity, similar to close molding except that a slight pressure of about 5 psi (34.5 kPa) is applied. The mold is heated to fuse the plastisol then cooled. Later the mold is opened and the product stripped out. This process can provide for accurate thickness control, filling very complex shaped parts, and so on. 

Fig. 13 Influence of the cooling rate on the impact performance of /S-modified PP (MFR 0.3 dg min-1). The specimens were compression molded and tested at 1.5 ms-1. The arrows indicate the temperature at which the ductile-brittle transition occurred...

Fig. 14 Spherulitic structure of compression molded samples (core) obtained with different cooling rates a rapid, b conventional and c slow...

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