Blow pressure curve

Figure 33.33 Blow pressure curve (heat set bottles). (Courtesy Sid el)...

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. 

The preform blowing into a bottle can be best followed up by analyzing a pressure curve, which is a recording of the transient pressure in the blowing article as a function of time. A typical blowing curve... 

A blow-moulded container, cylindrical in shape but with one spherical end, is prepared from the polysulphone whose creep curves at 20°C are illustrated in Figure 9.9. The cylindrical part of the container has an outside diameter of 200 mm and is required to withstand a constant internal pressure of 7 MPa at 20°C. It is estimated that the required service lifetime of the part will be one year and the maximum allowable strain is 2%. What will be the minimum wall thickness for satisfactory operation ... 

We start by describing an important phenomenon If in equilibrium a liquid surface is curved, there is a pressure difference across it. To illustrate this let us consider a circular part of the surface. The surface tension tends to minimize the area. This results in a planar geometry of the surface. In order to curve the surface, the pressure on one side must be larger than on the other side. The situation is much like that of a rubber membrane. If we, for instance, take a tube and close one end with a rubber membrane, the membrane will be planar (provided the membrane is under some tension) (Fig. 2.4). It will remain planar as long as the tube is open at the other end and the pressure inside the tube is equal to the outside pressure. If we now blow carefully into the tube, the membrane bulges out and becomes curved due to the increased pressure inside the tube. If we suck on the tube, the membrane bulges inside the tube because now the outside pressure is higher than the pressure inside the tube. 

The discharge limit of the blow tank used was about 26 tonne/h with the 53 mm bore pipeline and approximately 50tonne/h with the 81 mm bore pipeline. Within this capability of the conveying facility, however, tests were carried out with conveying line pressure drop values of well over two bar and the materials were all capable of being conveyed at solids loading ratios of well over one hundred. A minimum of fifty individual tests were undertaken with every material/pipeline bore combination, in order to draw the various families of curves required. 

This importance of H has been further utilized in predicting transition by Wazzan et al. (1981), by noting that similar correlation exist for the parameters such as pressure gradient, suction/ blowing, heating/ cooling etc., if it is plotted in terms of transition shape factor. In Fig. 2.13, this correlation is shown by the upper curve that is premised on linear instability studies with N = 9. The lower curve gives Rccrit as computed from Fig. 

If the above is a bit vague. I m sorry. The remainder of this issue could be fill with info on the precursor wave, sound pulse curve,harmonics, blow by, pressure differentials, etc. I don t claim to undei stand all of that any more than you do. I do know that I ve never heard anyone down grade Werbell s basic design which is accepted as better than any of its predecessors. I know of no recent designs that cai equal or better the Sionic s performance. 

A variety of standard and specialized applicators exist for pressure-sensitive labeling. Standard portable head applicators provide top, side, and bottom labeling. These applicators use one of several basic methods available for application of automatic pressure-sensitive labels. In a tamp-blow method of application, the label is dispensed from the backing web and held in position by vacuum on a tamp pad. The tamp pad is indexed 0.8-1.5 cm away from the product, and then the label is applied to the product by a gentle blast of air. Tamp-blow applications are used for a large array of packages that have irregular, curved, or recessed surfaces. 

We all know that the pressure inside a bubble is higher than atmospheric. When we blow a soap bubble at the end of a tube and then allow contact with the atmosphere, the air will immediately escape from the bubble it shrinks and rapidly disappears. This is a manifestation of a more general rule if the interface between two fluid phases is curved, there always is a pressure difference between the two sides of the interface, the pressure at the concave side being higher than that at the convex side. The difference is called the Laplace pressure / L. 

The idea is the same as discussed for the bowed dislocation, but we have added a dimension. If we reduce the area of the surface, we lower the energy. Hence, if a surface is curved, we can imagine that there is a force that wants to reduce the area of the surface the force acts on an area of the surface and force divided by area is pressure. Picture how you can take a small ring, hll it with a soap him, and blow a bubble. The pressure is provided by the air if you stop blowing, the surface becomes hat again. 

The profiles of the temperature and pressure loss per unit bed height (AP/L) at 5, 7, and 9 minutes after the blowing started are shown in Figures 7 (a) - (c). The heat wave, the peak of die temperature profile curve corresponding to the most actively reacting zone, moved gradually fiom the bottom to the top as the reaction proceeded. 

Blow air is applied first at a low pressure, and is followed by high pressure toward the end of the forming process. As can be seen from the blow curve... 

Figure 7 shows the rate of blow-by versus discharge pressure. As mentioned before, the curve is essentially constant for different pump speeds. At 10,000 psi and 225 rpm, blow-by amounts to 17 per cent of the theoretical capacity of the pump. 

Figure 8 presents volumetric losses other than blow-by for 5,5 and 7.5 per cent clearance space. The curves indicate clearly that these losses become quite large at discharge pressures close to 10,000 psi. 

It is desired to blow mould a cylindrical plastic container of diameter 100 mm and wall thickness 2.5 rtmi. If the extruder die has an average diameter of 40 mm and a gap of 2 nun, calculate the output rate needed from the extruder. Comment on the suitability of an inflation pressure in the region of 0.4 MN/m. The density of the molten plastic may be taken as 790 kg/m. Use the flow curves in Fig. 5.3. 

Figure 3.21 gives experimental curves representing a variation in the film thickness vs. the blow-off time. The curves have been obtained at Ap = 0.25 mm of water (t = 0.4 dyne/cm and I = 2 cm). The curves that have been obtained at other pressure differentials differ from the given curves in their slope as an increase or a decrease in the pressure differential is equivalent to a decrease or an increase in the blow-off time. 

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