Venting

As is the case in molds for thermoforming, the design of injection molds must provide for venting to remove trapped air, which otherwise will mar the finish of the molded object, and may, in extreme cases, prevent accurate mold filling. The simplest way to accomplish this is to build vent holes into the mold parting line, where the core and the cavity come together. For large molded objects, this may be insufficient, and additional vents may be needed. 

If a dust explosion occurs in a closed vessel at 1 atm, the pressure will rise rapidly (up to and sometimes beyond 600bar/s) to a maximum of around 10 bar. 

Vents are susceptible to corrosion and proper choice of the material, e g., alloys or high chromium steel containing a chromium fraction greater than 10%, are preferred. However, if alloys containing copper are in contact with melt PP for an extended time they can cause degradation of the material. The location of vents is quite important for thin-walled mouldings where high injection speeds are necessary. 

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Figure 6.30 shows the grand composite curve plotted from the problem table cascade in Fig. 6.186. The starting point for the flue gas is an actual temperature of 1800 C, which corresponds to a shifl ed temperature of (1800 — 25) = mS C on the grand composite curve. The flue gas profile is not restricted above the pinch and can be cooled to pinch temperature corresponding to a shifted temperature of 145 C before venting to the atmosphere. The actual stack temperature is thus 145 + 25= 170°C. This is just above the acid dew point of 160 C. Now calculate the fuel consumption ...

Vapor Treatment. The vapors from the tank space can be sent to a treatment system (condenser, absorption, etc.) before venting. The system shown in Fig. 9.1 uses a vacuum-pressure relief valve which allows air in from the atmosphere when the liquid level falls (Fig. 9.1a) but forces the vapor through a treatment system when the tank is filled (Fig. 9.16). If inert gas blanketing is required, because of the flammable nature of the material, then a similar system can be adopted which draws inert gas rather than air when the liquid level falls. 

This eliminates the vapor space but sealing the edge can be a problem. Double seals can help and sometimes a fixed roof is also added above the floating roof to help capture any leaks from the seal. However in this case, the space between the fixed and floating roof now breathes and an inert gas purge of this space would typically be used. The inert gas would be vented to atmosphere after treatment. 

Figure 9.4 A thick-walled pressure vessel might be economical when compared with a thin-walled vessel and its relief and venting system.

If air is used, then a single pass with respect to each feedstock is used and no recycle to the reactor (Fig. 10.4a).-Thus the process operates at near stoichiometric feed rates to achieve high conversions. Typically, between 0.7 and 1.0 kg of vent gases are emitted per kilogram of dichloroethane produced. ... 

A greater amount of steam would be generated if the noncondensible vent was treated using catalytic incineration rather than absorption. The... 

Product quality specification Contractual agreements Capacity and availability Concurrent operations Monitoring and control Testing metering Standardisation Flaring and venting Waste disposal Utilities systems... 

M. Klobukowski, S. Huzinaga, Y. Sakai, Computational Chemutr.y Review., of Cur,vent Trend. Volume 3 49, J. Leszczynski, Ed., World Scientific, Singapore (1999). 

The apparatus to use is seen in figure 13 which consists of a burette, thermometer, Erlenmeyer flask and a two-holed rubber stopper that has a small V-shaped wedge cut out of one side of the rubber stopper to allow the inside contents to vent. 31.5g of orangy-red fuming nitric acid (see chemicals section) is poured into the Erlenmeyer flask and the rubber stopper with its burette and thermometer is placed on to the... 

In a plastic container the chemist dissolves her golden yellow freebase oil into some DCM, ether or ethanol. The chemist then starts a steady dripping of the sulfuric acid into the HCl/salt and white, puffy HCI gas will start to exit the glass rod or pipette which is at the end of the hose. That tip is then plunged into the sol-vent/freebase solution to bubble the gas through the solvent. 

To a vigorously stirred suspension of 4 mol of lithium amide (see II, Exp. II) in 2.5 1 of liquid ammonia were added in 25 min 2 mol of propargyl alcohol (commercially available, purified before use by distillation at 100-120 mm). The suspension became very thin. Subsequently, the dropping funnel was combined with a gas inlet tube reaching about 1 cm beneath the surface of the ammonia. The vent on the splashing tube was removed. Methyl iodide (2 mol) was added to the vigorous-... 

Epichlorohydrin (1 mol) was added dropwise over a period of 1.5 h to a solution of 2.2 mol of sodium acetylide in 1.5 1 of liquid ammonia. During, as well as for a period of 1.5 h after, the addition the temperature of the mixture was kept at about -45°C. The cooling bath was removed after this period and the mixture was agitated vigorously for another 3 h. The thermometer and vent were removed, and 75 g of powdered ammonium chloride v/ere added in 2-g portions with vigorous stirring. The atimonia was allowed to evaporate. 

Apparatus 3-1 round-bottomed three-necked flask with a combination of dropping funnel and gas inlet tube, reaching 1 cm beneath the surface of the NH3, stirrer and a combination of thermometer and vent (see Chapter I, Fig. 1). 

Apparatus 1-1 round-bottomed, three-necked flask with a dropping funnel, a mechanical stirrer and a thermometer, combined with a vent, for the addition of bromine and the dehydrobromination to 1-bromocyclooctene 1-1 flask (see Fig. 1) for the preparation of cyclooctyne. 

Apparatus 2-1 three-necked, round-bottomed flask with a thermometer, a mechanical stirrer and a vent. 

Apparatus. 3-1 Three-necked round-bottomed flask, provided with dropping funnel, stirrer and thermometer + vent for the bromination and acetalization 10-1 wide--necked flask for the dehydrohalogenation, manual swirling. 

Apparatus 1-1 three-necked flask with a dropping funnel, a mechanical stirrer and a thermometer, combined with a vent. 

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