Doctor roller

Figure 36-2. Processing by roller coating or coating, (a) coating by roller, (b) roller coating with imprinting roller, (c) coating by doctor roller, (d) coating by spray coating (can also be called injection casting).

Eye protection between doctor rollers and chill ] 3 Worn razor blades in bin... 

Doctor bar Device for regulating the amount of material on the rollers of a spreader. 

In the coating of continuous metal coils, reverse roller coating is often used. In this technique the web is moving counter to the application roller direction, so that the paint is partly wiped off by the moving coil. Shear leads to better flowout. Another type of reverse roller coating is used for the application of stiff paste fillers to chipboard. Application is by forward roller, but this is immediately followed by a reverse roller, which presses the filler into the board and doctors it smooth. 

Application of controlled amounts of foam to the substrate is by knife-on-roller, knife-on-blanket, floating knife, horizontal pad or furnishing roller with doctor blade, or by squeegee across a printing screen. 

The spreader most commonly found in the rubber industry has a working width across the application roller/blade of 1.5 metres. Wider spreaders (up to 4 metres) exist for very wide cloth coating but they require special control of the bending of the doctor blade and have compensatory mechanisms to overcome this problem. 

Alternatively, the doctor blade can impinge onto a small conveyor belt system which supports the travelling fabric. This mechanism is less commonly used than the rigid roller as it leads to reduced control of the thickness of the spread. For precision work, using very consistent cloth, an accurately machined chromium plated steel roll can replace the rubber covered roller. 

Roller Coaters and Sheet Coaters. These arc often used in coil coating where very large, flat surface areas need to be painted quickly. In these methods, the objects to be painted are passed between a doctor blade and applicator rolls. These methods arc suitable only for coatings that arc to be baked. 

The primer can be applied by brush, roller and doctor blade, or spraying. To lower the viscosity for spraying, the recommended solvent must be used. The most important point when applying the primer by spray is to ensure that the spray is still solvent-wet when it reaches the part. Dry material can cause poor bond strength. 

Wheel or rotary cylinder—the wheel or cylinder picks up adhesive from an open pot, tray or bath. This is thinned by a doctor blade or transfer roller system. The thinned layer is then transferred to the substrate. Viscocity properties are critical. 

While on the subject of pleomorphism and the hke, there is a video out titled The Rise and Fall of a Scientific Genius, about the career and findings of the much-cited Royal Rife, written and directed by Shawn Montgomery. A review was furnished in the January 2004 issue of the Townsend Letter for Doctors Patients, and another in the November 2005 issue. Mentioned is the fact that in the early part of the twentieth century, Rife s work was respected by eminent medical researchers and physicists and was financially supported by Henry Timken, Jr., of the Timken Roller Bearing Company. (A device invented by Rife had saved the company millions of dollars.) A laboratory was provided by Timken in San Diego, and Rife received the cooperation of a Dr. Milbank Johnson, head of the local medical society, who was affiliated with the University of Southern California. Two prominent bacteriologists also worked with Rife Dr. E. C. Rosenow of the Mayo Clinic and Dr. Arthur Kendall of Northwestern University. 

Direct hot melt can be performed in a variety of ways. In one method, the reinforcing fiber web is dipped into a melt resin bath. A doctor blade, scraper bar, or metering roller controls the resin content. Alternately, the melt resin is first applied to a release paper, the thickness of the resin being determined by a doctor blade. The melt resin on the release paper is then brought into contact with a collimated fiber bundle and pressed into it in a heated impregnation zone. 

Solution adhesives are applied at 10-25% total solids content by spray, doctor knife, reverse roll coater, roller, or by spatula or trowel. The adhesive is dried at room temperature or in air ovens, care being taken to eliminate the fire and health hazards associated with some solvents. 

---