Moving Side Walls

Moving Side Waiis A moving side wall is a section of the cavity which fonns the side (or a portion of the side) of the product. The Section either moves straight sideways, similar to a side core, or it slides up (together with the withdrawing core and the product) and outward at the same time. This compound motion (up and out) frees the side wall from any projections that are formed by that section of the cavity and from any cores that have openings. 

Much effort has been expended to try and produce flat-top foams. In one process polyethylene sheets placed along the side-walls of the trough rise with the foam. In another technique the reactants are metered from the mixing head into a fixed trough in which partial expansion takes place. The foaming material is then drawn over a weir by a moving band of paper and then drawn down a slope so that the top surface maintains a constant level as the material expands. 

If the hood has side walls the opening to the outside must be large enough to permit work inside the hood and it must also be designed to facilitate flow into the opening and diminish the possibilities for the moving air to transport contaminants to the surroundings. 

The direction of the electric current varies from one location to another. A uniform magnetic field normal to the channel bottom is applied. By coupling of the electric and the magnetic forces, a Lorentz body force is yielded which is perpendicular to the electric and magnetic fields and directed towards the side walls. The direction of this force also alternates. As a result, the fluid is moved up- and downwards. The net effect is eddy-type convection. 

Force balances on a differential element for these four cases appear in Fig. 4.12. The moving plate exerts a force of C fw K F / A) in all cases, where C is the portion of the wetted perimeter of the moving plate and fw is the kinematic coefficient of friction. The stationary channel walls in Cases (a) and (b) exert a force C2fwK(F/A), where fw is the static coefficient of friction and C2 is the portion of the wetted perimeter of the lower plate and side walls that is stationary. This force points in the direction of increasing force. Thus it points to the left in Case (a) and to the right in Case (b). 

At steady flow conditions the moving plate exerts a force on the solids in the (6 + (f>) direction. This force is separated into two components one in the down-channel direction, which was used in the force balance, and the other in the cross-channel direction, which was neglected. The latter will have the following effects it will increase the normal stress on the side wall, A, in Fig. 4.15, and it will alter the stress distribution within the solids. Assume for the sake of simplicity that the St. Venant principle holds, that is, the externally applied force by the plate is completely balanced by the additional force on the side wall A, and within the solids (which will be considered to be located far from the places where these tractions act), there will be no effect. In other words, we neglect the changes in the stress distribution within the solids. The cross-channel force component, F, is... 

Ejection Rail. After compression the lower punch impacts the ejection rail (or on some machines an ejection roller). Upon impact the tablet is broken free from the die side wall and begins to move up the die as the machine rotates. The ejection rail should be made of a tough, abrasion resistant material such as aluminum bronze alloy. 

In the spiral wire mesh type, the edges of the wire scrape against the sides of the column. This causes a thin film of liquid to form on the side wall and, in addition, increases the surface area considerably as the wires move across it. The wire is spun so as to throw the vapors back down into the column. If spun the opposite way, it can suck the system dry in a few minutes. The spinning spiral band operates in the same manner. These are expensive columns, but they have a low holdup and a high throughput. 

The effect of temperature is to increase the mobilities about 2%/°C. Because the column of liquid cools most at the side wall, the ions closer to the center move faster, thus providing a parabolic front and a corresponding zone broadening. If the capillary diameter is small, this center effect is minimal, and a flat zone front occurs, which permits much higher resolution. 

Vertical" Shutoffs If the product requires openings only in the side wall, there is a simpler and less expensive method available to create such openings withciBtt 4 e4irea moving side prions. The only cond on is that the walls must have ample side draft, in the order of 5% or more, as shown in Fig. 4.27 on p. 56. 

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