Document wDVe20QX8bbZjjqv7g6XGoeZd

688 CHAPTER 50 1959 Guide Table 2 ... Regain of Hygroscopic Materials Moisture Content expressed kt Percent of Dry Weight of the Substance at Various Refafire Hutnidifitt--Temperature, 75 F Cfoafflcotion Mutaiol Description Relative Humidity--Percent 10 20 30 40 50 60 70 80 90 Natural Textile Fibers Cotton Cotton Sea island--rov- 2.5 3.7 4.6 5.5 6.6 7.9 9.5 11.6 14.1 ing American--cloth 2.6 3.7 4.4 5.2 5.9 6.8 8.1 10.0 14.3 Cotton Wool Silk Linen Linen Jute Hemp Absorbent Australian me- rino--skein Raw chevennes --skein Table cloth Dry spun--yam Average of sev- eral grades Manila and sisal--rope 4.8 4.7 3:2 1.9 3.6 3.1 2.7 9.0 12.5 15.7 18.5 20.8 22.8 24.3 25.8 7.0 8.9 10.8 12.8 14.9 17.2 19.9 23.4 5.6 6.9 8.0 8.9 10.2 11.9 14.3 18.3 2.9 3-6 4.3 5.1 6.1 7.0 8.4 10.2 5.4 6.5 7.3 8.1 8.9 9.8 11.2 13.8 5.2 6.9 8.5 10.2 12.2 14.4 17.1 20.2 4.7 6.0 7.2 8.5 9.9 11.6 13.6 15.7 Authority Hartshorne bchioesing Fuwa Hart- shorne Schloes- ing Atkinson Sommer Storch Fuwa Rayons Viscose Nitrocellulose Cuprammoninm Cellulose Acetate Average skein 4.0 5.7 6.8 7.9 9.2 10.8 12.4 14.2 16.0 Robertson 0.8 1.1 1.4 1.9 2.4 3.0 3.6 4.3 5.3 Robertson Paper M. F. News- Wood pulp--24% 2.1 3.2 4.0 4.7 5.3 6.1 7.2 8.7 10.6 NBS print ash H.M.F. Writ- Wood pulp--3% 3.0 4.2 5.2 6.2 7.2 8.3 9.9 11.9 14.2. NBS ing ash White Bond Rag--1% ash 2.4 3.7 4.7 5.5 6.5 7.5 8.8 10.8 13.2 NBS Com. Ledger 75% rag--1% ash 3.2 4.2 5.0 5.6 6.2 6.9 8-1 10.3 13.9 NBS Kraft Wrap- Coniferous 3.2 4.6 5.7 6.6 7.6 8.9 10.5 12.6 14.9 NBS ping Misc. Organic Materials Leather Catgut Glue Rubber Wood Soap Tobacco Sole oak-- tanned Racquet strings Hide Solid tires Timber (average) White Cigarette 5.0 8.5 11.2 13.6 16.0 18.3 20.6 24.0 29.2 Phelps 4.6 3.4 0.11 3.0 1.9 5.4 7.2 4.8 0.21 4.4 3.8 8.6 8.6 5.8 0.32 5.9 5.7 11.0 10.2 6.6 0.44 7.6 7.6 13.3 12.0 7.6 0.54 9.3 10.0 16.0 14.3 9.0 0.66 11.3 12.9 19.5 17.3 10.7 0.76 14.0 16.1 25.0 19.8 11.8 0.88 17.5 21.7 12.5 0.99 22.0 19.8 33.5 23.8 50.0 Fuwa Fuwa Fuwa Forest P. Lab. Fuwa Ford Foodstuffs White Bread Crackers Macaroni Flour Starch Gelatin 0.5 1.7 3.1 4.5 6.2 8.5 11.1 14.5 19.0 Atkinson 2.1 2.8 3.3 3.9 5.0 6.5 8.3 10.9 14.9 Atkinson 5.1 7.4 8.8 10.2 11.7 13.7 16.2 19.0 22.1 Atkinson 2.6 4.1 5.3 6.5 8.0 9.9 12.4 15.4 19.1 Bailey 2.2 3.8 5.2 6.4 7.4 8.3 9.2 10.6 12.7 Atkinson 0.7 1.6 2.8 3.8 4.9 6.1 7.6 9.3 11.4 Atkinson Misc. Inorganic Materials Asbestos Fiber Silica Gel Domestic Coke Activated Charcoal Sulfuric Arid Finely divided Steam activated H0> 0.16 5.7 0.20 7.1 33.0 0.24 9.8 0.40 14.3 41.0 0.26 12.7 0.61 22.8 47.5 0.32 15.2 0.81 26.2 52.5 0.41 17.2 1.03 28.3 57.0 0.51 18.8 1.24 29.2 61.5 0.62 20.2 1.46 30.0 67.0 0.73 21.5 1.67 31.1 73.5 0.84 22.6 1.89 32.7 82.5 Fuwa Fuwa tSelvig Fuwa Mason Process and Product Air Conditioning 689 relative humidities. The effect of temperature as compared to the relative humidity is comparatively unimportant, al though sudden changes in temperature cause a slight change in regain even when the relative humidity remains sta tionary. Changes in temperature do, however, affect the rate of absorption or drying, although this property gener ally varies with the nature of the material, its thickness and density. When hygroscopic materials absorb moisture from the surrounding air, they deliver to the air sensible heat equiv alent to the latent heat released by the moisture to the material. This amount of heat should be included in the load estimate. Conditioning and Drying In general, the materials may be exposed to desirable humidities for treatment coincidentally with the manufac ture or processing of the materials, or they may be treated separately in special enclosures. This latter treatment may be classified as conditioning or drying. The usual purpose of conditioning or drying is to establish a desired condition of moisture content and to regulate the physical properties of the material. When the final moisture content is lower than the initial one, the term drying is applied (See Chap ter 53). If the final moisture content is to be higher, the process is termed conditioning. In the case of some textile products and tobacco, for example, drying and condition ing may be combined in one process for the dual purpose of removing undesirable moisture, and accurately regulating the final moisture content. Frequently, conditioning or drying is made a continuous process in which the material is conveyed through an elongated compartment by suitable means, and subjected to various controlled atmospheric conditions. Control of Rate of Chemical Reactions A typical example of control of the rate of chemical re actions occurs in the manufacture of rayon. The pulp sheets are conditioned, cut to size, and passed through a mercerizing process. It is essential that, during this process, close control of both temperature and relative humidity should be maintained. The temperature controls the rate of reaction directly, while the relative humidity maintains a constant rate of evaporation from the surface of the solution, and maintains a solution of known strength during the mercerizing period. Another well-known example in this class is the drying of varnish which is an oxidizing process dependent upon temperature. High relative humidities have a retarding effect on the rate of oxidization at the surface, and allow the internal gases to escape freely as the chemical oxidizers cure the varnish from within This produces a surface free from bubbles and a homogeneous film throughout. Desirable temperatures for drying varnish vary with the type. A relative humidity of 65 percent is beneficial. Control of Rate of Biochemical Reactions In the field of biochemical control, industrial air condi tioning has been applied to many different and well-known products. All problems involving fermentation are nlucy-H under this heading. As biochemistry is a subdivision of chemistry, subject to the same laws, the rate of reaction may be controlled by temperature. An example of this is the dough room of the modem bakery. Yeast develops best at a temperature of 80 F. A relative humidity of 70 percent is maintained to hold the surface of the dough open to allow the carbon dioxide gasses formed by the fermentation to pass through and produce a loaf of bread, when baked, of even, fine texture without large voids. Control of Rate of Crystallization The rate of cooling of a saturated solution determines the size of the crystals formed. Both dry- and wet-bulb temperatures are of importance, as the one controls the rate' of cooling, while the other, through evaporation, changes the density of the solution. In the coating pans for pills, gum, and nuts, a heavy sugar solution is added to the tumbling mass. As the water evaporates, each separate piece is covered with crystals of sugar. A smooth, opaque coating is only accomplished by blowing into the kettle the proper amount of air at the right dry- and wet-bulb temperatures. If the cooling and drying are too slow, the coating will be rough and semitranslucent, and the appearance unsightly; if too fast, the coating will drip through to the interior. Only by balancing temperature, relative humidity, and volume of dr to the sugar solution, can the proper rate be obtained and a perfect coating assured. Control of Temperature for Close Machining Tolerances Where tolerances must be held within 2 or 3 ten-thou sandths of an' inch, as in the manufacture of precision instruments, tools, and high quality lenses, temperature variations may cause expansion and contraction of material to an extent that will seriously affect the quality of the work. This type of work usually requires close temperature control to assure accuracy and uniformity of the product. Usually the temperature level with respect to the product is not as important as controlling the temperature within close limits. For this reason, conditions are usually selected within the comfort range. Control of Dew Point for Protection of Polished Surfaces In the manufacture of certain metal articles, the presence of fingerprints, tarnish, or etching cannot be tolerated in the finished article. If these articles are manufactured under conditions of effective temperatures that will cause the hands to perspire, an unsatisfactory product will result. The salt and acid contained in body perspiration, when deposited on the highly polished article, can show corrosion and rust within a few hours if examined under a microscope. It is- therefore important to maintain temperatures and relative humidities (dew point) low enough to prevent sweating of the hands. In addition, the manufacture of polished surfaces usually requires a better-than-average job of air filtering to avoid abrasion of the surfaces. Control of Humidity for Reduction of Static Elec tricity The presence of static electricity is often detrimental to the satisfactory and economical processing of many light materials, such as textile fibers and paper. It is also ex tremely dangerous where explosive atmospheres or materials are present. Fortunately, this hazard is minimized by in-