Blade gap

Fig. 3. Paper formers (a) top-wire former (b) Roll and Blade gap former. (Valmet Corporation)...

Note this asstunes that the belt is set into motion after the doctor blade gap is filled with fluid. Other solutions will exist with other initial conditions. 

Formulation cellulose acetate, 22.2 g acetone, 66.7g (doctor-blade gap 0.25 mm). 

As the observed power deficit had been explained to a very large extent, several measures were identified to enable its reduction. One measure would be to optimize the flow conditions for the inflow and outflow areas of the compressor and turbine sections in order to minimize the pressure drop losses and to achieve an optimum inflow into the blading. Moreover, a reduction of the blade gap losses would be required. That could be achieved by a reduction in rotor vibration and better selection of materials. The materials for both the rotor and the stationary blade carrier should be selected to optimize thermal expansions to achieve minimum gaps at operating conditions. One approach would be the replacement of the non-cooled austenitic stationary blade carrier in favor of a ferritic one, with cooling provided at necessary locations. Preferably no cooling at 750 C should be provided at all, taking into account possible improvements in avaible blade and rotor materials. A third approach that seems to be possible would be a further optimization of the stationary blade profiles and rotor blade profiles. 

Reduction of the blade gap losses by designing essentially vibration-free rotors. The materials for the rotor and the stationary blade carrier should be related to each other in such a way that minimum gaps will be achieved at operating conditions ( e. g., replacement of the non-cooled, austenitic stationary blade carrier by a ferritic one). Cooling must be provided as needed when the ferritic material requires lower operation temperamres. 

In a typical tape casting process, the slip or slurry is poured into a puddle or reservoir behind the doctor blade, and the carrier to be cast upon is set in motion. The doctor blade gap between the blade and the carrier defines the wet thickness of the tape being cast. Other variables that come into play include reservoir depth, speed of carrier movement, viscosity of the slip, and shape of the doctor blade (to name just a few). The wet film of slip passes into a drying chamber of some sort, and the solvents are evaporated from the surface, leaving a dry tape on the carrier surface. 

In some manufacturing settings and in most laboratory operations, the doctor blade gap is not fixed and can be adjusted using micrometers. This type of doctor blade assembly is shown in Figure 4.7. The... 

Because of its importance in determining tape thickness, great care must be taken to create and maintain a consistent and uniform blade gap. The doctor blade itself is usually surface ground and polished to... 

The uniformity of the blade gap from cast to cast can also be a source of variation in tape thickness (wet and dry). Many manufacturers use an adjustable mounting system for the doctor blade, which is set to height before each cast. Many of these blades are set by hand and are subject to human error. This human factor can significantly affect repeatability. To avoid this, some manufacturers simply minimize the... 

The previous section in this chapter discussed a variety of different control techniques for governing the slip height. Reservoir height does not usually have as large an effect on tape thickness as does the blade gap. In theory, this means that the doctor blade gap can be seen as a rough control for wet-tape thickness, while reservoir height can be used to fine-tune the wet thickness. Not many casters use this technique. 

At this point the slip is ready to cast. Casting is done on a silicone-coated Mylar carrier in a continuous tape casting machine. The doctor blade gap setting, speed of casting, etc. are determined by the tape thickness desired as an end product. 

The slip is then ready for casting. The doctor blade gap setting and speed of casting will determine the final tape thickness. This cast is also made on a silicone-coated Mylar carrier. 

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