Document okZeMvngeonjL9OdQOBpV5y7

' }9$L,, *, Mill Bus Studies .' ' m** y* **& . *>%' M, A. Dibble, 13* & ~ ir* L. 11. Smithy 1'!?* ftp. R. B. Bawls, Flint ft?. & Udder, Plant $r. G , Conte, Berlin ,lfe. P. B, Evans,' Lab. ft*. H 1. Hopkins, iim. ft- Mr.* Hu* XBu. Selby* Mb. " . . A Mr. W. P. Colio .& u iiiaiu. uaiiorliBiii-TM^' . . .- : Jtaly. 26, 1946 ' ' xmwm sams no, ' F" COpy `INDEXED" isW' EU& MILL Previous stediee of tell pill finding have stew ; that efficient grinding requires a cascading action. (Jk Hannal of Ball Millini 1,:D, 884 .end lass M& Mill Grinding Study > Flint 1956) ;ga the presence of liquid of low viscos ity (one eentlpbise) cascading is present up to about- 9C$ of . critical speed where the critical speed is the theoretical - speed at which the outer row of tells will be carried around the mill tee to the centrifugal action of the mill. Rscorn- mended plant practice is to grind at about 60 to 75$ of cri tical speed. ' .' ' Studies earned out at the .Philadelphia Laboratory.' with the glass end mill tedieate that with high viscosity . 'bases cascading does not occur at speeds as high as 65$ of critical speed. ' The following equations relate l&w .approxi mate masisusi speed for cascading (or most'efficient grinding), to the viscosity of the has being ground. . 5 s Mill 6* Mill Cycles per hour 1050 - 0*5 *L ' Cycles per how? * 1650 - 0.45 *L. n.** viscosity of tea- in' centipisos at temperature of grind. .She show equations apply to bases of density of about on and to mill speeds of 35p of critical or higher. they mr& deri ved from data obtained with a 1.5* mill. -. . ' . She res hit of the study indicate that with mill bases of high viscosity (XgOO coatipoisos or more), the cascading action is diminished and inefficient grinding results* Boteeing th tell sis from 5/8" to 3/16 reduces the cascading and to retain a similar pattern., it is .necessary to re duce the base viscosity by about 80$. therefore, whoa tell sis is reduced the expected increase in efficiency will be observed only if the ml.ll base viscosity is very low. * N 30708 To obtain a' osso&dtog action with pebbles, it is neeetcsy to reduce fete liquid viscosity to it lower lew! than to fete vm* of stool telle* tvm with a low density liquid,, tbs viececity should not exceed ^00 op., sad with the high density mill bases bo w being ground, this is probably high,' Shore my bo little difference la way aces between stirring in a vat ' md grto&tog to a mill as far .as grinding action is concerned. The es c of the concept of critical speed as a ori* terton of oasoadlng'action in a mill nay have Imparted a false sons of security and led to the development of bases which can not- possibly be ground by a oas ceding action. Plant studiesshould be made to determine the limiting speeds and viscosities for grinding by cssceding actios* la ball still grindtog by a cascading action there to a pert lea called tbe *dead space" to which the tells .move at a rednoed speed. From the appearance of the glass end mill to . operatte using aixtwe .of small and large steal tells the liq uid moves through this space continuously and so loss to effic iency occurs through isolation of a portion' of the base to this sect-torn of the mill, She presence of a dead spa*" is probably of less; importance than mill speed and base viscosity to. determtotog .grinding efficiency. Products prepared by tell mill grind ing te often inferior to quality to similar products prepared to a & F. mixer or by the Flint Process... Shis poor quality to steettote related to inferior dispersion end this to turn may be tensed by the use of inefficient tell mill grinding conditions. Complete dispersion will fe mors readily obtained If the base be ing ground is relatively low to density and low to viscosity funder 1000 ceatipose), 'irtengemiAto mm tetog m&& to #sw np'a program for a plant study of the Important factors diseased above. . mmmmiA imommi S0H-*fel j, Q>* 3, 0a 1IQR1XI0 ^ DUP030002818