Vacuum ports

An amine-terminated poly ether (ATPE) is prepared as follows. Charge poly(tetramethylene oxide) diol (PolyTHF 1000, BASF, 75.96 g, 0.0759 m) to a 500-mL three-neck round-bottom flask fitted with a thermocouple, a mechanical stirrer, and a vacuum port. Add tert-butylacetoacetate (24.04 g, 0.1582 m) and apply vacuum. Heat at 175° C for 4 h, Fourier transform infrared (FTIR) analysis should indicate complete loss of the polyol OH absorption at 3300 cm. The room temperature viscosity of the product should be about 520 mPa-s. React this acetoacetylated product (85.5 g, 0.0649 m) with cyclohexylamine (14.5 g, 0.1465 m) at 110° C under vacuum for several hours. Cool the resultant cyclohexylaminocrotonate poly ether product to room temperature (1790 mPa-s at room temperature). 

Of course all surfaces that are at such low temperatures must be kept out of contact with the ambient environment. This is achieved by a detachable and rotable vacuum shroud that surrounds the two expander stages and the sample, all of which must be kept under high vacuum while they are cold to avoid collisional heat transfer. By default, evacuation of the assembly occurs through vacuum ports mounted on the main body of the expander, but in some cases it is advantageous to have extra ports on the vacuum shroud itself. Furthermore, the first expansion stage of closed-cycle cryostats, where a temperature of 35 10 K is attained, is usually fitted with... 

Fig. 9.50 Schematic view of a three-chamber co-rotating disk devolatilizer. The molten inlet feed is deposited on the disk surface of the first chamber by a spreading block (SB). The film is exposed to vacuum via the vacuum port. The melt is collected at the channel block (CB) and forced to flow over the top of the disk to the feed port of the second chamber. Similarly, the melt is fed into the third chamber from where the devolatilized melt exists.

Rinsing Tanks Aluminizing Cells Fig. 21. Diagram of the Sigal aluminum plating unit with vacuum port. 

Figure 6.1 Schematic diagram of the shock tube with test section, droplet injection mechanism, and recording devices 1 — droplet generator 2 — high-speed pressure transducers 3 — low-speed pressure transducer 4 — vacuum port 5 — thermocouples 6 — diaphragm chamber bleed 7 — low-speed pressure transducer S — thermocouple and 9 — helium input and low-speed pressure transducer.

Many standard methods are used to devolatilize materials. Flash devolatilizer or falling strand devolatilizer are synonyms of equipment in which the falling melt is kept below the saturation pressure of volatiles. Styrene-acrylonitrile copolymers devolatilized in flash devolatilizer had a final eoncentration of ethylbenzene of 0.04-0.06. Devolatilization of LLDPE in a single-serew extruder leaves 100 ppm of hydrocarbon solvent. 500 ppm chlorobenzene remains in similarly extruded polycarbonate. It is estimated that if the polymer contains initially 1-2% solvent, 50-70% of that solvent will be removed through the vacuum port of an extruder. These data seem to corroborate the information included in the above... 

Trials are therefore an essential precursor to selection of the cleaning method. Dry blasting with fine glass beads produces a polished surface with minimal environmental impact. However, care needs to be taken with injection gates, vacuum ports and sprues, since they can become easily blocked or not be cleaned at all ... 

All the volatiles are removed through the vacuum port. If the melt viscosity of the blend is too high, then a melt gear pump may be used to reduce head pressure and... 

Figure 5.2 Top Sketch of a jet separator device used to couple a packed column GC to a mass spectrometer. The dimensions are typically d = 100 p.m and d2 and d3 both 250-300 p.m. The two tubes leading to the MS and from the GC, and drawn down to small apertures, must be accurately aligned. Such devices are normally fabricated of an inert material such as borosilicate glass. Bottom Schematic diagram of an experimental jet separator designed with an adjustable inter-jet gap, in (A) cross-section and (B) axial view, (a) delivery capillary connected to transfer line from GC (b) gap adjustment threaded disk (c) nozzles (d) window (e) receiving capillary connected to the ion source (f) gap zero-setting threaded disk (g) expansion chamber (h) vacuum port (i) brass body of device (j) cartridge heater (not visible in cross-section). Reproduced from Pongpun, J. Mass Spectrom. 35, 1105 (2000), with permission of John Wiley Sons, Ltd.

A very useful reactor assembly for pilot-scale polymerization of lactide and glycolide polymers and copolymers is an 8-CV mixer from Design Integrated Technologies (DIT) of Warrington, Virginia. The 8-CV is a dual cone mixer (8 qt. capacity) equipped with double helical mixer blades, a gas inlet line, and a large vacuum port. 

Close the injection port and open the vacuum port to apply the vacuum inside the bagged preform assembly. Carefully check for and fix any air leakage. 

Fill the resin into the resin reservoir. Keep the vacuum port on. Open the resin injection port to allow the resin to be drawn into the vacuum bagged fiber preform assembly. 

Close the injection port and keep the vacuum port open until the resin cures into the solid phase. The vacuum will keep the preform assembly tightly pressed against the mold and will also maintain the uniform compressive pressure on the preform to create a composite part with a uniform thickness (i.e., a uniform compression ratio or a uniform fiber volume fraction). 

The infusion behavior is identical to standard VARTM processes where the vents are placed at the last location of fill. The membrane layer enables any point of the fabric surface to be connected to the vacuum port thus reducing the need for an optimized placement of the venting system. Nevertheless, the post-infusion behavior can be significantly different compared to standard VARTM processing. No resin bleeding occurs as the vent is placed on the impermeable membrane surface. Hence, the pressure behavior and consequently the overall thickness gradient and fiber volume... 

---