Blowing pressure

The multi-layer article is made using moulds between which a cavity clearance is freely set. A skin material lined with foam is placed between the upper and lower moulds and molten PP containing a chemical blowing agent is supplied through a resin melt conduit in the lower mould when the cavity clearance is between (C plus 15) mm and (C plus 50) mm, where C is the thickness of the skin material lined with the foam. The upper mould is lowered at a specific rate and the molten resin is pressed at a specific pressure to fill the cavity ends with the molten resin to complete the moulding of the resin body. The body is pressed for a certain time to form a skin layer, the upper mould is lifted up to decrease the compression pressure of the skin material lined with the foam to a pressure lower than the blowing pressure of the PP resin to form and solidify the foamed body, the upper mould is lowered to apply pressure to the moulded article and finally the article is cooled in the mould. 

Stretch-blow processing is used to develop biaxial molecular orientation. If blow pressure alone were used, the stresses in the preform wall would be predominantly circumferential, producing orientation only in the hoop direction of the bottle. However, the additional stresses generated longitudinally by the stretch rod result in biaxial orientation. 

Sootblowers. The installation of half-track sootblowers at the scrubber inlet in 1969 eliminated the problem of massive inlet deposits. The sootblowers have been operating at normal blowing pressures and have not required any abnormal maintenance. 

The blowing pressure is usually below 100 psi except for acetal, which can go as high as 150 psi. These pressures allow one to go to aluminum tooling. The clamping force is set at 1.25 times the blowing pressure times the projected area. Other mold materials used are zinc alloy, steel, and beryllium copper. 

For any sand used, the higher the air pressure, or ramming pressure, used to form the sand shape the greater will be the bulk density of the resultant sand body. Fig. 3 shows the relationship between tensile strength and blown sand bulk density for two different sand systems. The lowest strength on each curve was obtained using 0.35 MPa, 50 psi, blow pressure. 

We ve looked at how to excite our sotmd synthesis models, but there is more to the interactive control of a model than just putting energy into it. Parameters such as damping or position of excitation must also be controlled in many models. Blowing pressure or velocity for wind models is another parameter that must be controlled. Table 14.1 contains a brief list of the many physical parameters we might want to control, depending on the system and interaction. 

Flexibility (cold or hot air blowing, pressure or vacuum drying, drying in inert atmosphere)... 

The air supply was cut off just after the temperature of the highest layer of the bed reached its maximum point and began to decrease. The blowing time was about 20 minutes and the blowing pressure was measured with a manometer every minute. A change in temperature inside the bed was measured by six sets of thermocoiq>les (R) placed in the center of the reaction vessel. 

Figure 3 - Changes in Blowing Pressure with Time Obtained Using the Tube Test...

WALL THICKNESS IN. (MM) BLOW PRESSURE (PSD NORMAL CYCLE TIME (S) CYCLE TIME WITH VACUUM ASSISTANCE (S) CYCLE TIME VACUUM ONLY (S)... 

Pock mark n. An imperfection on the surface of a blow-molded article, an irregular indentation caused by inadequate contact of the blown parison with the mold surface. Contributory factors are insufficient blowing pressure, air entrapment, and condensation of moisture on the mold surface. 

Projected area n. In molding, the area of a cavity, or all the cavities, or cavities and rurmers, perpendicular to the direction of mold closing force and parallel to the parting plane. In injection molding and blow molding, this area must be safely less than the quotient of the force apphed to hold the mold closed divided by the maximum melt pressure or blowing pressure within the mold. In transfer molding, it must also be about 15% less than the cross-sectional area of the pot. 

Blow pressure, screw speed, cooling time, and melt temperature have significant effects on blow molding process. 

Check exhaust-possibly add exhaust time Check core rod openings Increase blow pressure Check core rod openings Reduce injection pressure Increase temperature in parison mold at fold location... 

Material not homogeneous Temperature of parison too cold Increase blow pressure Increase cycle time Parison not packed Vents... 

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