Vacuum injection

The different modes of injection, i.e., gravity injection, pressure or vacuum injection, and electrokinetic injection, are addressed. Also, several practical experimental issues are described, such as correct treatment of electrolyte solutions and the importance of a rigorous capillary rinsing procedure. 

The observed precision is comparable to the values we previously reported for biosynthetic human insulin (16). It also is similar to independent results obtained using a totally automated system (2.9% RSD) and much better than that reported for manual injection (11.8% RSD), both using a hydrodynamic injection technique (21). Finally, the observed precision for the percent desamido, which is really an area ratio similar to what would be obtained by comparison to an internal standard, is excellent for the 10-nL or larger injections. Although the data are insufficient to make a definitive conclusion, it suggests that the observed error is comparable to that obtained from many chromatographic techniques. It also suggests that one of the predominant sources of error is imprecision in the injection volume. The error in injection volume was recently characterized (19). They also reported approximately 1-3% RSD in peak areas for vacuum injection of various compounds. 

Figure 3 A series of CZE electropherograms for bovine serum albumin (BSA), anti-BSA, and complexes of BSA-anti-BSA. Operating conditions uncoated capillary, 50 pm X 70 cm, 40 cm to detector, 15 kV applied voltage, UV detection at 214 nm, vacuum injection 30 kpa-s, buffer 60 mM phosphate, pH 7.8,1 M AccuPure Zl-methyl reagent (Waters), sample dissolved in phosphate buffer, pH 7.0. (a) Injection of anti-BSA purified on protein G column first, (b) Injection of BSA, monomer purified by SEC first, (c) Mixture of BSA monomer and anti-BSA, with anti-BSA in excess, (d) Mixture of BSA monomer and anti-BSA, with BSA in excess (peak assignments peak 1 = 1 1 complex peak 2 = 1 2 complex, other peaks as indicated) (59).

Hydrodynamic injection can be performed in three different ways. (1) In pressure injection, a precisely controlled external pressure is used to force a controlled amount of sample into the capillary. (2) In vacuum injection, a vacuum is applied to the buffer reservoir at the detector end of the capillary for a controlled period of time at a regulated reduced pressure. (3) For gravity flow injection, the sample vial with one end of the capillary is elevated to a certain height above the other end of the capillary for a given period of time. Gravity forces a sample plug into the capillary. 

Boey. F.. Reducing the void content of a FRC using a vacuum injection molding method. Polymer Testing, 9(6), 363-379 (1990). 

Boey. F., and Liu, C. Y Vacuum injection moulding for fibre reinforced composites. Experimental Techniques, Mar./Apr., 48-51 (1991). 

This process has been used since the 1940s to provide better control of the molding cycle to fabricate parts that are more precise. Those that used it were Bell Laboratories (USA) and D. V. Rosato. This technology is to combine IM of the compound with a complete or partial vacuum in the mold cavity, to facilitate the impregnation of the reinforcement. The vacuum injection process requires a perfect seal around the edge of the mold. Development included applying vacuum from the hopper, through the plasticator, and into the mold. It has very little interest. 

Table 9.70 Basic processing (bag, flexible plunger, vacuum injection, matched die, and compression) methods as a function of part design...

Design factor Bag molding Flexible plunger molding Vacuum injection molding Matched die molding Comp, molding... 

Boat hulls were among the earliest applications of modern reinforced plastics. The United States Navy introduced their first 8.5 m (28 foot) fibreglass personnel boat in 1947, and was contracted to pass 3000 vessels by 1966. The orders for the first two vessels specified construction by the pressure bag method and by the vacuum injection system in order to achieve higher quality than was obtained by the then current hand-lay-up technique [1]. One of the earliest large GRP structures for submerged... 

Any moisture contamination of the cell has a deleterious effect on its operation. Therefore, all cell assembly operations are usually carried out in a dry room or dry box. Alternatively, the cell then may be put in a heated vacuum oven for 16-24 h in order to extract residual water from the cell core before electrolyte filling. In the next process, the cell is filled with the electrolyte using a vacuum injection apparatus. Electrolyte is added to the cell by a precision pump and then vacuum filled to ensure that the electrolyte permeates and completely fills the porosity in the separator and electrode structures. Precision pumps meter the exact amount of electrolyte needed for good cell operation. The electrolyte salt usually is LiPF dissolved in a... 

Brouwer, W., Van Herpt, E., Labordus, M., 2003. Vacuum injection moulding for large structural applications. Compos. Part A 34, 551-558. 

There are other variations of the RTM, VARTM and CRTM process which belong to the class of LCM processes such as RTM light in which a caul plate is introduced on top of the bag, resin infusion under flexible tooling (RIFT), resin film infusion (RFI) and vacuum injection preform relaxation (VIPR). In addition many of the same processes are known by different acronyms. It is useful to note that as the science base of RTM improved and led to better understanding of the variables and parameters that influence the flow and dry spot creation in RTM, it led to approaches and creative ideas to improve the process and cut down the cost. This learning continues today to evolve new modifications to the LCM family of processes. For example in VIPR one can now introduce flow control effectively to modify the flow front and create a part that is better than the SCRIMP process and is of consistent quality. ... 

In the vacuum injection process (Vacuum Assisted Resin Injection [VARlj), which is the most simple resin injection process, molds with a fixed and a flexible mold half and molds with two fixed mold halves are used (Figure 1.227). The textile semifinished part is inserted into the cavity, the mold is closed, and a vacuum is applied. The vacuum ensures that the mold stays closed and the reinforced structure is compacted. After opening the inlet, the structure is impregnated by infusing the matrix into the fiber material. After curing, the finished component can be removed from the mold. 

FIGURE 1.232 Flat mold for the vacuum Injection process... 

FIGURE 1.233 Mold A/ith a defined outer contour for the vacuum injection process... 

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