Chemical machining milling

FIGURE 7.39 Schematic representation of three types of ESI emitter tips, which were microfabricated on PC or PMMA. I, machine-milled 3D tip II, machine-milled 2D tip III, hand-polished 3D tip [213]. Reprinted with permission from the American Chemical... 

Sizing devices are now trimly fitted to the compactor body and controlled by variable speed drives. Most compactors no longer require a second machine (mill) in tandem to size compacts as required by slugging technology. Roller compactors have clean-in-place (CIP) systems that offer environmental and safety features. These systems minimize human exposure to chemicals and improve cleaning efficiencies. Fig. 7. 

In addition, many grades of paper and paperboard are used in direct or indirect contact with foods. Thus, many mills only use paper chemicals that have been cleared for use by the U.S. Pood and Dmg Administration (PDA) (3), so that it is not necessary to segregate machine broke (off-grade paper and edge clippings that are reclaimed for their fiber value) and white water. Most of the chemicals discussed in this article are approved by the PDA for use in paper and paperboard that are intended for appHcations in food processing and packaging. However, there are various restrictions on both the specific functional uses and amounts of paper chemical additives which can be used, so the PDA status should be confirmed by the suppHer before use. 

Water Clarification. Process water that aeeds to be clarified comes from several differeat sources ia the recycling mill rejects from screeas and mechanical cleaners rejects from washers, thickeners, and flotation cells water that drains from the pulp as it is converted iato paper oa the paper machine (white water) and water from felt washers. These waters contain different dissolved chemicals and suspended soflds and are usually processed separately. 

Triglycerides are important constituents of resin. In softwood, the triglycerides account for 20—40% of total resin content, and in hardwood, 40—50%. The paper industry uses the term pitch for resins that create problems in paper machines. Traditionally, pitch is controlled or reduced by aging the wood, by use of chemicals to avoid deposits on the roUs, or by intensive washing of the pulp. AH these methods add to the cost of paper production. An alternative is to add a Upase to the pulp in a reaction lasting about one hour with the help of agitation. Results from Japanese paper mills show substantial... 

Typical applications in the chemical field (Beaver, op. cit.) include detarring of manufactured gas, removal of acid mist and impurities in contact sulfuric acid plants, recovery of phosphoric acid mists, removal of dusts in gases from roasters, sintering machines, calciners, cement and lime Idlns, blast furnaces, carbon-black furnaces, regenerators on fluid-catalyst units, chemical-recoveiy furnaces in soda and sulfate pulp mills, and gypsum kettles. Figure 17-74 shows a vertical-flow steel-plate-type precipitator similar to a type used for catalyst-dust collection in certain fluid-catalyst plants. 

Schnell, A. Sabourin, M.J. Skog, S. Garvie, M. Chemical characterization and biotreatability of effluents from an integrated alkaline-peroxide mechanical pulping/machine finish coated (APMP/ MFC) paper mill. Water Sci. Technol. 1997, 55 (2-5), 7-14. 

If long-fibre cellulose is to be used as a nitration material then noils from combing machines or waste from a spinning mill are usually used. Such wastes are usually contaminated with lubricating oils and before the chemical treatment they should be... 

W.J. Mead (Ed.), Balling devices, Briquet machines, Grinding, Mills colloid, Mills roller, Screening, in Encyclopedia of Chemical Process Equipment, Reinhold, New York, 1964. 

The processes occurring in a high-speed newsprint paper machine have been discussed above. There are several additional considerations of note in the overall process picture. Paper for the most part is a commodity item (i.e., production costs are more economical per unit when large tonnages of uniform specifications are produced). Most mills have a break-even point at an 85% capacity so it is vital to operate mills at design capacity. Economies of scale are also found for pulp and paper mills at levels of about 1000 tonnes of paper per day for full chemical mills and 200—400 tonnes of paper per day for semichemical or mechanical mills. Thus, the outputs of paper mills are... 

Found suitable for bare aluminum (nonclad), machined, or chemically milled parts which must be corrosion-protected... 

---