Pressure cavity fill

Fig. 3. P-T-x diagram of the system hydroquinone - argon x — mole fraction of hydroquinone, = fraction of cavities filled by argon [yA =. 3(l — x)/x). The pressures of the triple points A and B of the a and ft modifications of hydroquinone have been exaggerated in order to make these points visible.

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. 

The apparatus for constant volume method (Figure 17.1) consists of a metal cell having two cavities separated by the test piece. The high pressure cavity is filled with the test gas at the required pressure and this pressure must be measured to an accuracy of 1%. 

In this section two prediction techniques are discussed, namely, the gas gravity method and the Kvsi method. While both techniques enable the user to determine the pressure and temperature of hydrate formation from a gas, only the KVSI method allows the hydrate composition calculation. Calculations via the statistical thermodynamics method combined with Gibbs energy minimization (Chapter 5) provide access to the hydrate composition and other hydrate properties, such as the fraction of each cavity filled by various molecule types and the phase amounts. 

For an ideal gas Equation 5.22a may be considered as elementary probability of cavity i occupation by molecule J. This is one of the most useful equations in the method of hydrate prediction, and it may also be recognized as the Langmuir isotherm. If the equation were written for one guest component J, it would contain the Langmuir constant Cjj as the only unknown for a given pressure and fraction of the cavities filled (or fraction of monolayer coverage). 

In Chapter 5 of this book we derived the equations that govern the pressure flow between two parallel discs for a Newtonian fluid. In a similar fashion, we can derive the equations that govern flow rate, gate pressure, and pressure distributions for disc-shaped cavities filling with a shear thinning fluid. For the equations presented in this section, we assumed a power law viscosity. For the velocity distribution we have... 

Once the process has been optimized, plastic conditions should be recorded such as fill time, peak pressure at fill, cavity pressure,184 melt temperature, mold temperature, melt flow rates, and gate seal time. Record all basic machines setpoints on the setup sheet such as the transfer time (fill time) and weight, overall cycle time, and total shot weight, part weight, % runner, etc. 

Wan and Isayev (1996) examined a hybrid approach of control-volume finite-element and finite-difference modelling of injection moulding of rubber compounds. The effect of vulcanization on viscosity and yield stress during cavity filling is reported. On comparing two versions of the modified Cross viscosity models - with and without the effect of cure - the use of a viscosity model that accounts for the cure was found to improve the accuracy of the cavity-pressure-prediction models. When the modified Cross model was further extended to include the yield stress and was implemented in the simulation program a significant improvement in the prediction of cavity pressure was obtained in the case of low injection speed. 

The apparatus necessary for the constant volume method is described in ISO 1399 [22] and BS 903, part A17 [23]. It consists of a metal cell having two cavities separated by the test rubber sheet. The high pressure cavity is filled with the test gas at the required pressure, and this pressure is measured and should be kept constant during the measure. The increase in pressure on the low pressure side is measured as a function of time. The curve obtained follows the shape shown in Hgure 7.14. Thus... 

When the mold contains more than one identical mold cavity, it is important that the cavities fill equally. The usual approach to accomplishing this is to balance the flow paths for the plastic, so that distances and geometry, and thus pressure and flow, are equalized. Where nonidentical objects are being produced, this job is even more complex, but that seldom applies in packaging applications. It is also important to design the runner geometry to avoid dead spots, where plastic can accumulate and be subjected to an excessive heat history. 

This type of procedure can be used in setting up, as an example, a complicated molded IM product. As shown in Figure 5.69 IMM control settings involve melt temperature, mold cavity filling speed, shot size, melt pressure packing, etc. With proper control, high quality parts are fabricated. 

A similar experiment is currently being designed at Sherbrooke University [12]. The goal is to build and test a true shock tube with two cavities filled with gases at different pressures, divided by a breakable membrane. The aspect ratio of the channel is 100 and a pressure ratio of 2 is planned for a Reynolds number of 100. These cmiditions could be achieved in a 5 mm diameter/500 mm long tube with pressures of 1 and 2 mbar, respectively. But the low pressures typically exclude the possibility for flow visualization or measurement. Therefore, a more favorable solution is planned that will create the same hydrodynamic flow. 

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