Power-feed

Flame spraying is no longer the most widely used melt-spraying process. In the power-feed method, powders of relatively uniform size (<44 fim (325 mesh)) are fed at a controlled rate into the flame. The torch, which can be held by hand, is aimed a few cm from the surface. The particles remain in the flame envelope until impingement. Particle velocity is typically 46 m/s, and the particles become at least partially molten. Upon impingement, the particles cool rapidly and soHdify to form a relatively porous, but coherent, polycrystalline layer. In the rod-feed system, the flame impinges on the tip of a rod made of the material to be sprayed. As the rod becomes molten, droplets of material leave the rod with the flame. The rod is fed into the flame at a rate commensurate with melt removal. The torch is held at a distance of ca 8 cm from the object to be coated particle velocities are ca 185 m/s. 

Intercontib ntai, ibter jslan(i or i iihilar sea arib river trossirrgs br d c. power, supply and telecommunications submarine cables may use earth return in order to reduce the loop resistance of the power feeding path and to save... 

The most recent system is a 220 kilowatt fuel cell/gas turbine power plant operating at the University of California s National Fuel Cell Research Center located in Irvine, California. The first-of-a-kind hybrid power plant consists of a 200 kilowatt fuel cell generator pressurized at about 3.5 atmospheres in combination with a 20 kilowatt two-shaft gas turbine. The system was first run at the Pittsburgh facility and started operating at Irvine in June, 2000. Total run time until July, 2000 was 264 hours. Electric energy delivered was 42 megawatt-hours. Electric efficiency was 51% (LHV). An electric power feed-through mounted on the pressure vessel devel-... 

Q5. The power feed to the actual coils is not clear, I see a Jumper and diode between the two coils but really no other hook-ups for the coils except where the swingers are contacting the coil ends - is this where they obtain their power ... 

Q5. The power feeds into one coil and then to the other where the disc cap wire also feeds in, then it goes into the second coil. The ground seems to be neutral at this point. Not sure about the purpose of the ground, other than for the charging of the coils at start-up. 

As was mentioned previously, pressurized conditions have been reported for microwave-assisted organic synthesis [50], The reactions were carried out at a domestic microwave oven and commercially available screw-up pressure vessels made of Teflon, PET and PEEK, which are both microwave transparent (Fig. 5.1). It has to be pointed out that reactions under such conditions have to be strictly controlled with an efficient power feed-... 

Equation 5 expresses the variation in the concentration of monomer A in the feed stream entering the reactor as a function of time. Since this variation is a power function of time, the process has been named "power feed."... 

Another useful power feed equation permits the calculation of the fraction of a given component, A, in the final polymer,... 

Normalized plots of several power feed profiles are shown in Figure 2. For the special case where x = 1,(Wi=W2,R]=2R2), the feed profile is linear with time. Curvature is introduced by suitable changes of the initial monomer weights in the two tanks when x > 1, the curve is concave to the abscissa when x < 1, the curve is convex. With proper mixing in the near tank, these feed profiles can be verified experimentally. 

The addition of a third monomer tank to the basic power-feed arrangement expands the possible feed profiles available for investigation. As illustrated in Figure 3, one such arrangement involves a stirred middle tank which receives a monomer mix from the far tank and pumps a varying mixture to the near tank. The arrangement is essentially a power feed on top of a power feed and can be analyzed in the same manner as carried out with the two tank systems, except that C2, the concentration of monomer A in the second (middle) tank is not constant but is given by... 

Whereas the two-tank arrangement permits monomer feed profiles which vary smoothly in one direction, the three-tank scheme leads to inflections and concentration reversals as illustrated in Figure 4. Such reversals are useful in preparing hard-soft-hard, hydrophilic-hydrophobic-hydrophilic polymer variations and the like. In addition, three tank power feed has been useful as a means of calculating monomer inventory in copolymerization experiments (4). 

The modulus in this case is the secant modulus at 1% strain. Both polymers had the same composition 39/59/2 - methyl methacrylate/ butyl acrylate/acrylic acid. The power feed example was prepared such that butyl acrylate varied 0.83 — 0.30 and methyl methacrylate varied 0.15 — 0.68 as the polymerization proceeded, with x = 0.83. While both examples show the usual trend of high modulus at low temperature to low modulus at higher temperature, the power feed polymer exhibits a much broader transition region than the uniform example. 

The power feed example utilized a feed profile with increasing butyl acrylate, 0 — 0.65, decreasing methyl methacrylate concentration, 1.0— 0.35, and x = 1.3. 

Figure 5. Stiffness-temperature comparison of two emulsion polymers having the same overall composition. In the power feed example, the methyl methacrylate concentration varied (0.15 - 0.68) and the butyl acrylate concentration varied (0.83 0.30), with x = 0.83.

Figure 6. Stress relaxation comparison of two emulsion polymers having the same overall composition. The power feed example utilized a feed profile with increasing butyl acrylate (0-> 0.65), decreasing methyl methacrylate (1.0 -> 0.35), and x = 1.3. The time axis has been shifted to a reference temperature of 26°C.

The dynamic mechanical responses of the two power feed latexes are quite different from either of those discussed above. 

In Figure 9, the polymer was prepared via a linear power feed profile in which the near tank contained only ethyl acrylate and the far tank contained only styrene. In Figure 10, the polymer was prepared with the tanks reversed the monomer feed began with styrene and ended with ethyl acrylate. In both cases, the transition regions are much broader than those observed with the uniform feed or staged feed examples. 

The broadened transition response is a general characteristic of power feed polymers as evidenced by the results of stiffness-temperature, stress relaxation and dynamic mechanical measurements. 

Figure 9. Dynamic mechanical properties of a model latex made with c power feed process ethyl acrylate varied 1 —> 0 and styrene varied 0...

The effect of non-uniform polymer composition is shown in Figure 11 for the case of a 50/50-methyl methacrylate/ethyl acrylate copolymer made by a linear power feed process in which the near tank initially contained only ethyl acrylate and the far tank only methyl methacrylate. Compared with its uniform counterpart, the non-uniform polymer had a T D approximately 25° lower and a respectable... 

The toughness parameter q is defined by Equation 13. The effect of nonuniform polymerization is shown for a 50/50 copolymer in which the power feed profile involved a decreasing ethyl acrylate concentration (0 1), with x = 1 (linear). (( ) power feed, q = 0.19)... 

The "onion skin" growth mechanism is supported by filming experiments in which film formation is greatly effected by the nature of the monomer composition added last in the polymerization. In power feed examples, as well as in staged feeds, hard and hydrophobic compositions hinder film formation while softer and more hydrophilic compositions aid film formation. Curiously, in this respect, it was found that the filming characteristics of all-acrylic latexes responded to non-uniform polymerization techniques much more dramatically than did their styrene-acrylic counterparts. 

Figure 12. Monomer feed profile using a linear power feed. Overall polymer composition 47.5/47.5/5—styrene/ethyl acrylate/methacrylic acid.

Figure 13. The effect of nonuniform polymerization on the expansion behavior of carboxylic emulsion polymers. The power feed example was prepared using the monomer feed profile illustrated in Figure 12 ((%) uniform feed power feed).

In order to design experiments to test the influence of process variables on polymer infrastructure, a simple but general process design is needed. For these studies a new sequential feed polymerization process called "power-feed" was chosen (7 -8, 9). The advantage of this technique is that almost any conventional monomer feed profile can be simulated and described by an equation containing only three independent variables. In addition, a number of novel monomer composition profiles can also be constructed with this approach. The composition of the monomer feed to the reactor can be described by ... 

The latexes were prepared using a conventional semi-batch emulsion polymerization system modified for power-feed by the addition of a second monomer tank. Polymerization temperatures ranged from 30-85°C using either redox or thermal initiators. Samples were taken periodically during the polymerization and analyzed to determine residual monomer in order to assure a "starved-feed" condition. As used in this study this is a condition in which monomer feed rate and polymerization rate are identical and residual monomer levels are less than 5%. 

Figures 2, 3 and 4 illustrate the differences between conventional mixed feed, staged and power-feed copolymers whose average composition is 50/50 ethyl acrylate/styrene. In the case of the staged polymerization, all the ethyl acrylate was fed first followed by the styrene. The power-feed copolymer was prepared with ethyl acrylate linearly increasing as a function of time, i.e., x = 1.0, = 0.

The differences in the three polymerization processes are immediately apparent in the spectra. For the conventional copolymer, Figure 2, there is a predominance of BAB triads (EA = A). The power-feed copolymer appears to have relatively higher concentrations of mixed (AAB = BAA) and homo (AAA) triads. In the case of the stage polymerization, Figure 3, the carbonyl resonance is essentially identical to that for poly(ethyl acrylate), that is, AAA triads. 

Figure 4. The 13C NMR spectrum of a 50/50—styrene/ethyl acrylate copolymer prepared using a linear power feed profile with ethyl acrylate increasing 0—> 1.0, and styrene decreasing 1.0 —> 0 with time...

Figure 5. Linear power feed profile for a 50/50—styrene/ethyl acrylate copolymer in which ethyl acrylate decreases 1.0 -> 0 and styrene increases 0 -> 1.0 with...

A series of computer programs was written to test models for predicting sequence distribution for the power-feed copolymers. The programs consist of ... 

The feed generator calculations are based on the two-tank and three-tank power-feed equations. The three tank equation, described in the previous paper 7), has the form ... 

C nuclear magnetic resonance spectroscopy can be employed to study changes in copolymer sequence distribution brought about by differences in monomer feed profiles. Sequence distributions characteristic of conventional, staged, and power-feed copolymers are easily distinguishable in a model system of the type described here. 

Figure 9. Correlation of calculated and measured triad fractions for a model 50/50—styrene/ethyl acrylate copolymer prepared with a linear power feed profile in which ethyl acrylate increases 0—> 1.0 and styrene decreases 1.0 — 0 with time (n = 0.16 r2 = 0.82 (A) EA-EA-EA EA-EA-STY = STY-EA-EA ...

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