Document a1N5rqdpRbD0j7yGamBjYRdGb

686 __________________ Chapter 39:1945 Guide penalties for excesses. Deficiencies result in loss of.revenue to seller and loss'of desirable quality to buyer. Manufacturing economy therefore requires that the moisture content be.maintained at a percentage'favorable to rapid and satisfactory manipu lation and to a minimum loss of material through breakage. A uniform condition is desirable in order that high speed machinery may be adjusted permanently for the desired production with a minimum loss from delays, ...wastage of raw material and defective product. In the processing of hygroscopic materials, it is usually necessary to secure a final moisture content suitable for the goods as shipped. Where the goods are sold by weight, it is proper that they contain a normal or standard moisture content. Moisture Content and Regain The terms moisture content and regain refer to the amount of moisture in hygroscopic materials. Moisture content is the. more general term and refers either to free moisture (as in a sponge) or to hygroscopic moisture (which varies with atmospheric conditions). It is usually expressed as a percentage of the total weight of material. . Regain is more specific and . refers only to hygroscopic moisture. It is expressed as a percentage of the bone-dry weight of material. For example, if a sample, of cloth weighing 100.0 grains is dried to a bone-dry weight of 93.0 grains, the loss in weight, or 7.0 grains, represents the weight of moisture originally contained. This expressed as a percentage of the total weight (100.0 grains) gives the moisture content or 7 per cent. The regain, which is expressed as a percentage of the bone-dry weight, is 7 0 or 7.5 per cent. The use of the term regain does not imply that the material as a whole has been completely dried out and has re-absorbed moisture. During the processing of certain textiles, for instance, complete drying during manu facturing is avoided as it might appreciably reduce the ability of the material to re-absorb moisture. A basis for calculating the regain of textiles is obtained by drying under standard conditions; a sample from the lot and the dry weight thus obtained is used as a basis in the calcu lations to determine the regain. The moisture content of a hygroscopic material at any time depends upon the nature of the material and upon the temperature and especially the relative humidity of the air to which it has been exposed. Not only do different materials acquire various percentages of moisture after prolonged exposure to a given atmosphere, but the rate of absorption or drying varies with the nature of the material, its thickness and density. Table 2 shows the regain or hygroscopic moisture content of several organic and inorganic materials when in equilibrium at a dry-bulb tem perature of 75 F and various relative humidities. The effect of relative humidity on regain of hygroscopic substances is clearly indicated. The effect of temperature is comparatively unimportant. In the case of cotton, for instance, an increase in temperature of 10 F has the same effect on regain as a decrease in relative humidity of one per cent. Changes in temperature do, however, affect the rate of absorption or drying. Sudden changes in temperature cause temporary fluctuations in regain, even when the relative humidity remains stationary. The regain or moisture content affects the physical properties of textiles to a marked degree, changing the strength, pliability and elasticity. The fact that the regain of textiles will come into equilibrium with the Industrial Air Conditioning 687,., Table 2. Regain of Hygroscopic Materials Moisture Content Expressed in Per Cent of Dry Weight of the Substance at Various Relative Humidities--Temperature, 75 P ClabsiITCATIOK Matsrial . Dbscsiftion Rxlatxvb Humidity--Pbh Cxnt 10. 20 30 40 50 60 70 80' 90 AUTflOBtTY Cotton Sea island--roving 28 3.7 4.6 5.5 6.6 7.9 98 118 14.1 Hartshorns Cotton American--cloth 2.6 3.7 4.4 5.2 5.9 6.8 8.1 10.0 148 Sehloesing Cotton Absorbent 4.8 9.0 128 15.7 18.5 208 22.8 248 258 Fuwa Natural Textile Fibers Wool Silk linen Australian merino---skein 4.7 7.0 8.9 10.8 12.8 14.9 17.2 19.9 23.4 Hartshorns Raw chevennes--skein 3.2 5.5 6.9 8.0 8.9 102 11.9 148. 188 Milnwiing Table cloth 1.9 2.9 3.6 48 5.1 6.1 7.0 8.4 108 Altrinwnn Timm Dry span--yam 3.6 5.4 6.5 7.3 8.1 8.9 9.8 118 138 SflTnmw Jute Average of several grades 3.1 5.2 6.9 8.5. 102 128 14.4 17.1 208 8torch Hemp Manila and sisal rope Z7 4.7 6.0 7.2 8.5 9.9 11.6 13.6 15.7 Fuwa - Rayons Paper Visecee Nitrocellu lose Cupramonium Average skein Cellulose Acetate Fibre M. F. Newsprint Wood pulp--24% ash H. M. F. Writing Wood pulp--3% ash White Bond Rag--1% ash Com. Ledger 75% rag--1% ash. Kraft Wrapping Coniferous 4.0 5.7 68 7J9 9.2 10.8 12.4 148 16.0 Robertson 0.8 1.1 1.4 1.9 2.4 3.0 3.6 48 58 Robertson 2.1 38 4.0 4.7 5.3 6.1 72 8.7 10.6 u.aaofa 3.0 .4-2 5.2 6.2 78 88 9.9 11.9 148 u. a b. of a. Z4 3.7. 4.7 5.5 6.5 78 88 108 138 u. as. of a 3.2 48 5.0 5.6 68 6.9 8.1 108 13.9 u.aaofa 38 4.6 5.7 6.6 7.6 SJ9 105 12.6 14.9 U.RB.ofa Leather Sole oak--tanned 5.0 88 118 13.6 16.0 188 206 24.0 298 Phelps Catgut Racquet strings 4.6 7.2 8.6 102 1Z0 14.3 178 198 21.7 Fuwa Misc. Glue Organic Rubber Materials Wood Hide Solid tire Timber (average) 3.4 48 5.8 6.6 7.6 9.0 107 118 128 Fuwa an 021 032 044 0.54 066 076 088 099 Fuwa 3.0 4.4 5.9 7.6 98 1U 14.0 178 228 Forest F. Lab. Soap White L9 3.8 5.7 7.6 10.0 12.9 16.1 198 238 Fuwa Tobacco Cigarette 5.4 8.6 11.0 13.3 16.0 198 25.0 338 500 Ford White Bread 05 U 3.1 4-5 68 8-5 1L1 148 198 Atkinson Crackers 2.1 2.8 38 3.9 .5.0 6-5 88 10.9 14.9 Atkinson Food* Staffs Macaroni Flour 5.1 7.4 88 102 11.7 13.7 168 198 22.1 Atkinson 2.6 4.1 58 6.5 8.0 9.9 12.4 15.4 19.1 Bailey Starch 28 3.8 5.2 6.4 7.4 88 98 106 12.7 Atkinson Gelatin' Asbestos Fiber Finely divided 07 1.6 28 3.8 4.9 6.1 7.6 98 11.4 Atkinson ai6 0.24 026 032 041 051 062 073 084 Fuwa Misc. Shea Gel Inorganic DomesticCoka 5.7 9.8 12.7 15.2 17.2 18.8 202 218 22.6 Fuwa 0.20 0.40 0.61 081 1.03 1.24 1.46 1.67 189 Sehrig Activated Charcoal Steam activated 7.1 14.3 22.8 26.2 28.3 29.2 300 3U 32.7 Fuwa Sulphuric Ariil BtSO* 33.0 41.0 47.5 528 57.0 618 67.0 738 828 Mason conditions of the surrounding air and vary with its temperature and relative humidity is the fundamental basis for the control of physical qualities during manufacture. During the preparation processes in a cotton mill, the cotton fibers should be in a condition to be easily carded. These preliminary processes are carried out best in a relative humidity