Venting slot

When a parison is blown, a large volume of air must be displaced from the mold cavity in a short time. Because blowing is carried out at relatively low pressure, it is essential to provide venting to allow this air to escape without resistance. Unless a gloss finish is required on the molding, it is common practice to sandblast the cavity to a fine matt finish. This helps air to escape as the expanding parison touches the cavity face but it is not sufficient in itself. Vent slots may be cut at appropriate points into the mold parting face to a depth of 0.05 to 0.15 mm. The appropriate point is where there is a possibility for air to collect as the hot plastic expands in the cavity. 

Venting can also be provided within the mold cavity by means of inserts equiped with vent slots, porous sintered plugs, or by holes with a diameter not greater than 0.2 mm. Such holes are machined only to a shallow depth and are relieved by a much larger bore machined from the back of the mold. 

For example, many components in front of the driver can be appraised the dashboard, the steering wheel, the instrument panel, the windscreen. The dashboard has its own sensory characteristics (shape, materials, acoustics), but it is also made up of several elements that can be considered separately with their own sensory properties the radio buttons, the ventilation, the headlights, the vent slots, the speakers, etc. 

Concerning the technique of sprue design, it should be noted that the venting and positioning of the tool are of the utmost importance. The basic principle should be to fill the tool from the lower side and turn it into such a position that the reactive mixture travels the shortest possible distance from the position of entry to the farthest point of the mould cavity. In this manner, turbulence and air traps are minimized. The vent slots must be cut at the highest point of the tool. Often the best tool position and vent location must be determined empirically and optimized prior to production. 

The number and diameter of venting bore holes and the width of the venting slots have to be dimensioned sufficiently large to allow a fast venting (exhaustion). On the other hand, the vents should not leave any markings at the molded product. 

Slotted nozzles and core vents are available in various diameters. The open cross section of the slotted nozzles is a little bit larger than the one of the core vents. Slotted nozzles are more sensitive during installation and operation. 

A unique feature of toe cap/finish used in CSD bottles is the interrupted threads. The interrupted threads create a vent slot, which provides an escape route for the gas in the bottle on slight turning of toe cap. The internal pressure generated on a standard 28 mm diameter cap, at room temperature, is about 15 kgj and can more than double at temperatures reached in storage or while in transport. 

The gas distribution system can be composed of a network of perforated pipe, slotted or vented concrete block, or metal grating. When there are no space hmitations, single-level filters are used. In regions where footprint space is hmited, hke Japan, multiple-deck filter beds have become commonplace. If inorganic compounds are being treated, corrosion-resistant materials of construc tion are used due to the acidic by-products of the bioreaction. 

While gas liquid separation should occur primarily in the gas boot, smaller gas bubbles will be liberated as the flowstream velocity slows farther downstream The gas released by this secondary separation should be routed into the vapor space of the tank This is accomplished bv providing vent holes at the top of the central nser and by placing a vent in each spreader. The vent for the upper spreader should end just below the top of the tank. The vent for the lower spreader should end above the top of the upper slots, just below the upper spreader. The cross-sectional area of each vent should he large enough to keep vapor velocities low This will prevent the vapor from lifting water as it moves up the vent. 

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