Doctor blades adjustable

In roll and knife apphcation, the adhesive forms a thick fillet behind the adjustable knife (doctor blade). Adjustable springs press the knife or doctor blade against the web to obtain the desired adhesive thickness (Figure 8.3). There are several possible shapes for the knife in order to adjust to the viscosity and rheology and to the amount of adhesive required. The adhesive may be fed by gravity, either along the knife or directly on the web or it may be pumped into a trough, which is also adjustable. The roll allows the web to advance as the adhesive is applied [9]. 

The coatings were applied to one side of a steel substrate by means of a spray gun for the lower viscosity coatings, or by doctor blading with an adjustable Gardner knife for the higher viscosity materials. A casting technique was also used in which a known volume of the coating material was poured into a known area defined by heavy tape and was allowed to spread while on a level surface. 

Screen Preparations, 100 micron thick x-ray intensifying screens were prepared using standard doctor blade coating techniques. The final phosphor volume was 50% when the coatings were dried. In most instances, the phosphor suspensions were prepared using polyvinyl butyral binders with viscosities adjusted to 2000 centipoise for the doctor blade operation and care was taken to avoid convection cell formation (9). A cross section of the screen construction is shown in Figure I. The completed screens consist of polyester (Mylar) base about 10 mil. thick, a 50 micron thick (TI02 (rutile) reflector layer, a 100 micron thick phosphor layer, a 10 micron thick clear cellulose acetate butyrate top protective layer. 

In solvent casting, a thin film is prepared on a solid substrate by casting a solution of polymer onto the substrate, followed by evaporation of the solvent. Thicker films with some control over film thickness can be prepared. Enhanced control over thickness is achieved in the so-called doctor-blading approach, where the thickness of a viscous polymer solution is adjusted down to the 10 nm range by removing excess solution using a knife (the knife—substrate spacing is controlled). 

As illustrated in Fig. 4.34, the key component of the tape casting facility is the assembly of the doctor blade. It consists of an adjustable doctor blade mounted in a frame with a reservoir to hold the slurry before it is cast under the blade to form the... 

The dimensions of resin baths are restricted to minimize the volume of catalyzed resin and can be heated to control the resin viscosity to promote fiber wetting, although this will reduce the working life of the bath. To facilitate lacing up, the roller assembly in the resin bath is manufactured in two parts—a lower fixed set of rollers submerged in the resin bath and a moveable upper set, under which the fiber is positioned. The assembly is then pressed down to push the fiber into the bath to contact with the lower set of rollers. This system facilitates an easy lace-up procedure and ensures good compaction to expel all air and promote fiber wetting. Alternatively, the fiber can be passed over a drum upon which the correct amount of resin has been metered and adjusted by a doctor blade. 

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... 

Fig. 4.7 Standard doctor blade assembly with adjustable blade.

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 slip is then ready to cast on a silicone-coated Mylar carrier in a continuous tape casting machine. The doctor blade gap, casting speed, etc. are adjusted to yield the desired tape thickness. This formulation has been used to produce the highest green bulk density achieved for an alumina tape 2.81 g/cc. 

Usually, adjustable springs press the knife or doctor blade against the web. There are several possible shapes for the knife (Fig. 41) in order to adjust to the viscosity and rheology and to Ae amount of adhesive required. The adhesive may... 

Formulated thermoplastic rubber solutions can be applied to various substrates with conventional equipment such as doctor blades, roll coaters, etc. Solution viscosity can be adjusted both through solids concentration and solvent composition as discussed earlier. 

Blades being foils with zero foil angle, whereas counter blades are blades which are not fix mounted but are pressed with adjustable forces perpendicularly to the wire. Their main target is to doctor off the water and to improve formation quality. 

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