Venting groove

FIGURE 1.55 Venting groove for high injection speed, reduction of air resistance by a short length of the gap a... 

With compression moulding, to ensure dimensional consistency, it is necessary to allow the excess material to move away from the edge of the cavity so that the lands between the cavities can contact with minimum thickness of rubber (flash) between them. Spew grooves and channels are provided of sufficient dimensions to accommodate this excess, and also to allow the escape of air from the mould cavity. In some cases, where the shape is complex, it may be necessary to provide extra venting to allow air to escape from a blind area, where it is likely to be trapped. 

Gating and venting must be done with an eye to the effects of reinforcement orientation and bubble track formation downstream of flow obstructions. The size and number of vents required depends upon the volume of the part and the rate of fill used in addition to the shape of the part itself. Preferred vent geometry is a groove. 003-.005 inches deep and 3/8 inches wide. This does not permit excessive flash and polymerizes closed rather quickly. 

Figure 6.7 Density distribution in GeoDeck tongue and groove board of high overall density (d = 1.24 glow ). Note the lowest densities were of the ribs. The board was manufactured using a vented extruder.

Fi. 4 is a simple acidimeter, with a stopper fitted to it, having a groove to correspond with tho lip, and a vent-hole drilled through it to admit the air. 

The grooves of this rifle are cut with a twist, which turns the bullet once in three feet six inches. There are aia grooves, and the spaces between them are left entirely square to the interior surface, presenting a kind of dove-tail appearance. The grooves are not quite so wide as the spaces between them. The breech is furnished with a vent or breathing hippie, about the diameter of a common pin, and hushed with platiiium. The lock has back-a< n,... 

The sample is loaded at atmospheric pressure into an external or internal loop, or groove in the valve core and introduced into the mobile phase stream by a short rotation of the valve. The volume of sample injected is normally varied by changing the volume of the sample loop or by partially filling a sample loop with a fraction of its nominal volume. External sample loops have volumes from about 5 p.1 up to about 5 ml, although typical injection volumes for conventional diameter columns are 10-50 xl. Injections from 1 p,l to about 40 nl require micro-injection valves equipped with replaceable internal loops [7,32-34]. Injection volumes less than about 40 nl are performed by positioning a split vent between the injector and the column. Typical injection volumes that preserve column efficiency for packed columns of different internal diameters are summarized in Table 5.1. For packed capillary columns with internal diameters < 0.2 mm direct injection will usually require the use of a split vent to minimize volume overload unless on-column focusing is possible. Injection volumes about 5 times larger than those indicated in Table 5.1 are sometimes used to increase sample detectability but with some decrease in the column separation power. 

Air vent n. A passageway, typically a fine groove or scratch, between a mold cavity and the outside edge of the mold face, that... 

The adjustable depth of the grooves allows a grooved feed to be easily used on vented extruders. The groove depth can be adjusted to make sure that vent flow does not occur. 

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