Ram pressure

Time, pressure, and temperature controls indicate whether the performance requirements of a molded product are being met. The time factors include the rate of injection, duration of ram pressure, time of cooling, time of piastication, and screw RPM. Pressure requirement factors relate to injection high and low pressure cycles, back pressure on the extruder screw, and pressure loss before the plastic enters the cavity which can be caused by a variety of restrictions in the mold. The temperature control factors are in the mold (cavity and core), barrel, and nozzle, as well as the melt temperature from back pressure, screw speed, frictional heat, and so on in the plasticator. 

Fig. 8-73 A 2-D molding area diagram (MAD) that plots injection pressure (ram pressure) vs. mold temperature.

Fig. 8-74 After a 3-D molding volume diagram (MVD) is constructed, it can be analyzed to find the optimum combination of melt temperature, mold temperature, and injection or ram pressure.

The total pressure in tons exerted by the ram on the platens of a hydraulic press. It is calculated by multiplying the area of the ram by the hydraulic pressure and converting to tons sometimes called press capacity or ram pressure. 

The rubber mix is extruded by a screw through a non-retum valve into a separate chamber from which it is injected into a mould by a simple ram set at an angle to the screw. The tight fitting separate piston gives accurate delivery of the rubber mix allowing more efficient application of ram pressures up to 160 MPa. This pressure can inject even unusually high viscosity natural rubber mixes of Mooney viscosity (ML1+3, 120 °C) up to 100. 

The compressed air introduced from the atmosphere through the air-intake is termed ram air , and the associated pressure is termed ram pressure . Ram pressure is built-up when the airflow velocity is decelerated in flow fields. The air-intake is designed as an aerodynamic tool to obtain maximum ram pressure.lh Air-intakes are designed to decelerate supersonic flow to subsonic flow by the formation of shock waves in front of them. The combustor in which the fuel gas is burned with the ram air is termed a ramburner . 

Though the specific impulse of a solid rocket is determined by the energetics of its propellant, the specific impulse of a ducted rocket is determined by the mixture ratio of the fuel flow rate from the gas generator and the airflow rate induced from the atmosphere. The ram pressure in the rambumer is raised by the shock wave formed at the air-intake. The combustion in the rambumer further increases the... 

Pressure tests are performed in an external pressure chamber by applying equal pressure to both solvent and water phase (powder bed) to simulate solvent pressure in an actual casting. Ram pressure is simulated by applying a differential positive pressure across the septum which acts on the powder bed. Thus, bed volume change, bed sorption, and total volume change can be followed during cure as a function of time, temperature, solvent pressure, and ram pressure. 

This same apparatus permits estimates to be made of the so-called jacketed compressibility (the reciprocal of the effective bulk modulus) during early cure. This is accomplished by applying momentary pressure to the bed alone (ram pressure) and observing the corresponding bed volume change in the water meniscus. 

SOLVENT PRESSURE (PSIG) 0 NOMINAL RAM PRESSURE (PSIG) 0 BED SORPTION O B BED VOLUME CHANGE A TOTAL VOLUME CHANGE A A + B ... 

Figure 20. Effect of ram pressure on maximum bed volume change during cure at 80° F.

Figure 21 shows that the relatively large bed volume change observed for 30-p.s.i.g. ram pressure are accounted for by solvent expressed from the bed, and the total volume change is actually much less than the bed volume change. 

Figure 21. Dual dilatometry effect of ram pressure on isothermal propellant cure...

Vibration and limited ram pressure consolidate granular material in molds of various sizes and designs. Briquetting, compacting, molding Table presses, concrete block and brick machinery... 

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