Coil-layer process

The Ply Wall Process. This design is a combination of the coil-layer and multilayer designs the spiral construction of the shell section is combined with three-sheet longitudinally welded seams. 

Conversion treatments based on phosphates of trivalent chromium, which yield a deep emerald green layer. The baths comprise chromium anhydride, phosphoric acid and hydrofluoric acid. This type of conversion is widely used for products that are lacquered by the coil-coating process and used in the building industry. The weight of the layer ranges from 400 to 800 mg-m , and its thickness is roughly 400 nm for a deposition of 1 g-m . These layers combine good corrosion resistance with excellent adherence for lacquer. 

This type of coil was prepared from copper cladded printed circuit board material by applying photolithographic techniques. The p.c. board material is available with difierent copper thicknesses and with either a stiff or a flexible carrier. The flexible material offers the opportunity to adapt the planar coil to a curved three dimensional test object. In our turbine blade application this is a major advantage. The thickness of the copper layer was chosen to be 17 pm The period of the coil was 100 pm The coils were patterned by wet etching, A major advantage of this approach is the parallel processing with narrow tolerances, resulting in many identical Eddy current probes. An example of such a probe is shown in fig. 10. 

The process is indicated on the chart in Figure 24.9, taking point B as the tube temperature. Since this would be the ultimate dew point temperature of the air for an infinitely sized coil, the point B is termed the apparatus dew point (ADP). In practice, the cooling element will be made of tubes, probably with extended outer surface in the form of fins (see Figure 7.3). Heat transfer from the air to the coolant will vary with the fin height from the tube wall, the materials, and any changes in the coolant temperature which may not be constant. The average coolant temperature will be at some lower point D, and the temperature difference B — D will be a function of the conductivity of the coil. As air at condition A enters the coil, a thin layer will come into contact with the fin surface and will be cooled to B. It will then mix with the remainder of the air between the fins, so that the line AB is a mix line. 

The layers are heated to 280°C or higher for a few seconds up to several minutes. The coated metal coils are then processed, i.e., deformed, profiled, or stamped. The resulting coated products are broad in scope they are employed in a variety of areas from packaging and the vehicle industry to household items and building materials. 

Metal in gap (MIG) or ferrite heads are produced with a combination of machining, bonding, and thin-film processes. Thin-film inductive heads are manufactured using thin-fihn processes similar those of semiconductor 1C technology (discussed in Chapter 19). The thin-film head production process is rather unusual, as it involves both very thin and very thick films. We choose to present here a detailed summary of the fabrication process of thin-film inductive heads with a single-layer spiral coil. This may serve, once again to, illustrate the centrally important role of electrochemical deposition in connection with modem information technology. 

Flory and Krigbaum developed these ideas into a theory of solution nonideality that is useful in the present context. As the two coil domains overlap as shown in Figure 13.13, the concentration of chain segments in the lens-shaped volume of overlap doubles compared to its value in the separate layers 0 - 20. Solutions tend to dilute spontaneously and not become more concentrated therefore we expect AG in the lens to be positive for this process. The total free energy change associated with the overlap depends on both AGov and the volume of the lens that is,... 

However, as Ringard-Lefebvre et al. [58] have noted, such comparisons are only valid if the assumption that polymer molecules which in bulk solution form tightly bound three-dimensional coils could, during the spreading process from organic solvents onto aqueous subphase, extend to cover the available area with every polymer segment on surface layer. 

Characterization. All measurements were carried out with dried specimens (particles or sheets). It is established that the thickness of the water-loaded polymer layer is higher than in the dried state, because dried polymer coils collapse [21], The amount of polymer, however, is not changed after the drying process. Thus an average equilibrium state is always measured. 

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