Document QgMbGyyM7pdJOREggrnaw8GyE

calculation of the output of the sieve cylinders based on work by Dr. !. I. Berney -- part VI Before making use of the equation of filtration for the calculation of the output of the sieve cylinder, it was necessary to carry out a series of experiments under factory conditions, as the equation of filtration was derived at on the basis of data obtained from ex perimental work carried out on the special filter and there are substantial differences between filtra tion through this filter and through a sieve cylinder. The main differences are that the filtrating surface of the special filter is immobile while that of the sieve cylinder is rotating and hydrostatic pressure, with a sieve cylinder, is not constant. - These experiments, referred in AC/M No. 7-S July/ August 1968, were conducted on a sheet forming machine equipped with one sieve cylinder diameter 850 mm, with felt speeds of 37,8, 33, 28,9, 23,6 and 17,7 metres/minute and with suspensions of different concentration (0.03 to 0,l2`gm/cms). Con centration of each suspension was kept constant by preparing the suspension of a required concentration in a mixer and then feeding the vat of the machine without dilution. In the course of the experiments, the thickness of the layer, its specific weight and the volume of fil trated material through the sieve cylinder were ' measured and the physical mechanical properties of the manufactured sheets were controlled. A graph was plotted from the data obtained from these .experiments and those carried out on the special filter (fig. 27). In table 8 are referred the thickness and weight of the elementary layer, the volume of filtrated material and the necessary calculations for the plotting of the graph. The plotted data, graph (fig. 27), obtained from the experiments carried out under factory conditions, t ' / " January . ftbsuary correlate to form a straight line (relation between t/V and V2), and consequently correspond to the equation of filtration (3-7). The comparison of the graphs of filtration, obtained from the experiments carried out on the special filter and those carried out on the actual forming machine, leads to the conclusion that the value of the coefficient of resistance k* does not depend on the type of equipment used for the filtration. Suspen sions of the same composition were also investi gated on the special filter. It resulted that the value of B, when filtration took place on the sheet for ming machine, was higher than the value of !i when filtration took place on the special filter; in all cases the difference was of the order of approximately 2.4. When calculating the output of the sieve cylinder of an asbestos-cement forming machine, B and I will be symbolized as B,,, and Vom- respectively and can be determined as follows: Bm = B + 2,4 (3-19) and V * = B + 2,4 - vi/*.+ 21 A<j> " ] 0 + A* (3-20) Ku2 can be determined by equation (3-17). The above indicated difference of the value cf B under different filtration conditions, can be ex plained by the difference of pressure during the in stable period of the process (sec AC/M No. 11-12. Nov.-Dec. 1968). The pressure on the sieve cylinder will be at a maximum when 1/3 of the wire will be in the suspension (1-3 fig. I see AC/M No. 5. May 1968) or in other words after 1-1.5 second* from the beginning of the process of filtration. CTD001152 .7 > ft On the special filter, however, maximum pressure to determine these is explained in the fo"owir.2 is observed after 0,2 seconds from the beginning of paragraphs. i the process. Therefore, in the period of time (0.9 to 1,2 secs.) when on the filtrating wire a compact layer is not yet formed, filtration on the special filter takes place with a higher pressure than on the in equation (3-18); a is the concentration of the suspension tem cm:>. which is known; sieve cylinder; the volume of filtrated material (F,) Tj - is the viscosity of the liquid (gm sec cmr. a: increases while B decreases (see equation 3-9). the same temperature of the suspension. Ta Equipment for filtration with an agitator but without ble 7 (AC/M No. 11-12, November Decembcr a vacuum pump, was constructed. It was observed 1968) can be used for the determination of that the filter sinks in the suspension at a much this value; slower rate than in the equipment which has a vacuum pump; the slow rate of sinking of this filter increases the pressure of filtration. The values of B, registered t - is the time of filtration, equal to -- (soe fa. 1. "c AC/M No. 5, May 1968) where uc represents the during the filtration by this equipment differ consider speed of the felt. L depends on how deep',;, tine ably less from the corresponding values obtained sieve cylinder is immersed in the suspension sec during filtration on the sieve cylinder of the forming table 9). When the sieve cylinder is irr.me-scd machine; this fact proves the correctness of the for 0,6 of its diameter, L equals 0.56> 71D: given explanation in connection to the causes which and when immersed for 0,7 of its diameter. t < account for the differences in value of constant B. Having thus proved the possibility of applying equa L equals 0,633 x IJDC </7D. represents the circumference of the sieve cylinder,'. tion (3-18) also for the filtration through the sieve t cylinder of the forming machine, the next step would Constants k6 and V can be determined from data be to determine V and to calculate the output of obtained experimentally during the filtration on tre the forming machine. special filter and using equations (3-14) and ic-I'-a In equation (3-18); substituting however, K0-\ v-ith t ri a' * Vp IV) 2,4 KJ = IV + A<f> the values contained can be determined and how P is the value of hydrostatic pressure (gm cm:t. Maximum pressure P,,, during the work of the ste'-e cylinder (see fig. I, AC/M No. 5, May 196ji is eraal to the difference between the level of the suspensttr. in the vat and the level of the liquid inside the ste-e cylinder. However, P,, cannot be introduced in the equation of filtration; the equation is er.'.y aha for filtration at constant pressure (during the w of the sieve cylinder, pressure increase; from 0 to P,, and again decreases from P,, to 0). It i> therefore necessary to find the average value of h;.dro-taito pressure during the process of filtration arc the average value will be symbolised by /f. To ohta.n this, it is necessary to assume that pres>u:e i; a 0-1 function of time and determine the average value of ? this function. / V' The method of calculation will not be gi-e- ' the resuits are indicated in table 9. Fig. 27. Grjph of ihc filtration of suspension I) On ihe specie I filler: *- 212 Icm'pmp*'; ft 0.7 siwem. 2. On ihc sieve cylinder of Ihc forming mjvhirc: - 21*5 ion jjm)1'1: D - 3,1 sce'em. For Ihc composition of the suspension see table 8. From table 9 it can be seen that when the sieve cylinder is in the suspension for 0,6 of its diameter. Pc is equal to 0,33 Dt and for 0,7, !\ is ecaai to 0,40 Dc. CTDOOII53 M CV> No o f experiment Fell speed metres/min. V cm'/cm1 ' Thickness o f layer 8* (cm) Specific weight o f sheet ya gm/cm* a) Registered values. wU1tn* Co 9 P0 . Table 8 Data or the experiments performed on a sheet forming machine. =0 fEJ 1icuUco: E* . ~A U9 .S I *E 1 `E Ou * t fJ ~ t o c % -a *_ oa = t &= 32 34 35 36 37 38 ,39-B 22 I8-B 4 ; 37,8 i 37,8 i 37,8 37,8 37,8 j 37.8 33,0 28,9 23,6 : 17,7 2,60 2,60 2,60 2,60 2,60 2,60 2,95 3,40 4,20 5,50 0,03 0,06 0,08 0,10 0,12 0,15 0,08 0,08 0,08 0,08 1,04 0,0143 1.70 0,0243 0,0312 0,73 0,72 0,0187 1.73 0,0330 0,0432 0,75 -- 3,60 0,69 0,0265 1,74 0,0460 0,0552 0,83 0,265 3.77 0,67 0,0289 1.76 0,0509 0,0670 0,76 -- 0,60 0,0350 1,69 0,0590 0,0720 0,82 -- 0,57 0,0340 1,72 0,0585 0,0855 0,68 -- 0,75 0,0300 1,73 0,0520 0,0600 0,865 0,254 3,94 0,83 0,0350 1,72 0,0602 0,0580 o,sso 0,244 4,10 0,975 0,0380 1,77 0,0672 0,0780 0,860 0,232 4.32 1,12 0,0460 1,60 0,0736 0,0S96 0,823 0,204 4,91 0,520 0,476 -- _ 0,56 0,69 0,95 1,26 0,0094 0,0110 0,0118 0,0130 0,0140 -- 0,0110 o.o ;c6 0,0105 0,0082 b) The comparison of the values of the volume offiltrated materia! and weight of the layer registered in the course of the factor experiments and calculated on the basis of the equations of filtration (see fig. 28). Time Felt speed Concentration of filtration metres/min. a gm/cm* /, secs. 37,8 37,8 37,8 37,8 37,8 33,0 28,9 23,6 17,7 0,03 0,06 0,08 0,10 0,12 . 0,08 0,0S 0,0S o,os 2,60 2,60 2,60 2,60 2,60 2,95 3,40 4,20 5,50 Calculated values Registered values y, cm'/cm' . C, gm/cm' K, cm'/cm' C, gm/cm* 0,98 0,71 0,67 0,65 0,62 0,73 0,82 0,95 1,08 0,0248 0,0352 0,0445 0.0538 0,0618 0,0485 0,0550 0,0630 0,0716 1,04 0,72 0,69 0,67 0,60 0,75 0,83 0,975 1,120 0,0243 0,0330 0,0460 0,0509 0,0590 0,0520 0,0602 0,0672 0,0736 Difference between calculated and registered values in percent. V 1 5,5 1 1,4 2,9 3.0 ; 3.3 : C 2,0 6.7 3,2 6,0 4,7 2.6 6,7 1.2 8,2 2,6 6,2 3,5 3.0 Diameter of sieve cjlinder - 850 m/m. Hvdrosijtic Pressure: Maximum *18 cm: average 33 cm. Temperature of suspension 23 'C. Composition of asbestos-cement nuvs: Asbestos J-6-25 and P-5-65, 50*^ of each type. Cement, t>pe 4^' Fineness of grinjiny: residue on sieve MW, 7.5 *,, vi/cni Ratio of components: Asbestos 13.5 \ - Cement 86.5 |10| CTD001154 7HC AC. ` If these known values are substituted in equation (3-18), then an equation of the third degree is ob tained with only one unknown. To ease calculation by means of equation (3-18), an alignment chart was composed (see fig. 2S). Points tjA<f> and V,,J- are joined by a straight line; where the straight line meets curve V, we get the volume of filtrated material. It would also be possible to obtain the solution of equation (3-18) by way of analysis. If equation (3-18) is written in the following way: ? + 3Piy + 2ql = 0 where v is the changing value, in this case the volume of filtrated material V: t V--------r = 0; A<f> B 3Pl = A<f> -tP ) axik<f> then by application of the known formula: $ -- <h - V7i2 + P\ The substitution of the value of Pi and qY will give: + few - V(wW#T' + Although this will give the volume of the filtrated material V, its introduction in equation (2-2) will not make possible the determination of the output Table 9 Average hydrostatic pressure and length of the wet part of the perimeter of the sieve cylinder in relation to (he diameter of the cylinder mould. Diameter of sieve cylinder Dt, mm. 720 850 1000 1200 Average hydrostatic pressure Pt cms. coefficient of immersion 0.6 0.7 ! 0,75 1 23,7 28,8 20,0 34,0 35,70 33,0 40,0 42,00 36,0 4S.0 50,30 1 -. . _ J O o Wet part of perimeter-, L cms. coeffici' nt of immersion 0,6 0.7 0,75 128 143 151 169 178 I9S 214 238 l 151 17S 210 252 j14| of the sieve cylinder because the coefficient lection k,. is still unknown. The coefficient of collection as established the work done on the special filter, is not app where a sieve cylinder is involved because ir.t of ky depends largely on angle y (see AC M N July-Aug. 1968) and this angle changes subs;: during the rotation of the sieve cylinder, quently, the average value of ky had to be mined directly on the factory machine. Table 8 contains the registered values of :h ficient of collection obtained during this w, results that with felt speeds ranging between 38 m/min and concentration between 0.C6 arc C i.c. conditions very near to actual manufa conditions, the coefficient of collection in a value, can be admitted to be equal to 0.53. sieve cylinder of diameter 500 mm, ks is equal If in equations (2-3 and 2-4). k; is substituted average value (ky -- 0,S3). then the foilowir mulae will be obtained allowing to caiaula thickness of the asbestos-cement layer (oai) a weight of asbestos-cement delivered by the si linder (Gr). Sx</> and yx.'b will symbolize respethe thickness and specific weight of the ia; ,, , 0,83oK hxS =------ --- cm YP Ce = 0,%3aV uc Bc gm/sec. In industry, the output of a sheet forming rr for example, is expressed by the number of of any standard size produced per hour. Ir to introduce this unit of measure into the i. mula, it is necessary to establish the weigh: bestos-cement obtained during one hour of pro and divide this by the weight of one standard accounting for losses resulting from ofT-cuis correspond in average to 10%. The useful production will therefore be: Gc = 0,90 x 3600 x 0,S3 aV uc Bc cm The weight of a standard sheet with a \o: say 680 cm3 will be equal to yx6 y. 680 gm The weight of aibestos-ccment obtained c.r. hour of work divided by the weight of a sheet, will give the output of the sieve eyhr.c 0,90 >: 3600 >: 0,83 aV it, 3, nc = X 6S0 3,95 aV uc 3C number sheet, hr. CTD001155 Kom* (cm^cm*)1 Fig, 28. * Alignment char! for the solution of the equation of filtration of asbcsio^-ccment suspensions by means of formula; / K (C- + I.'). its: CTD001156 ., Table 10 Calculation of the productivity of sieve cylinders under different technological conditions (ya^4 = 1,5 gm/cm'; K,, --0,6; B, --170 cm). No. o f example No. of cylinder y ,,` (em'/cm1) Temperature "C cm/sec V per alignment chart cm'/cm' Data of suspension Data on sieve cylinder and machine Calculation of productivity Ce E * 1 23 I 0tM> 4e3 1 EM E V * Q es" 4 E0 Eu 8 + s> Eu a,* -4|\? 1 < 'is 1 5 hr C v* re"o. *>es 1 mo j: A ca * v f*'" tj O f. L* ^- *=. J .6 7 8 9 10 11 12 13 14 13 16 17 IS 19 1 1 268 0,4 30 7,95 0,10 100 178 53,4 33 2,04 1,64 1,58 0,78 0,043 1870 _ 2 268 0,4 30 7,95 0,08 100 178 53,4 33 3.34 1,46 2,29 2,04 0,84 0,037 1610 -- 3 268 0.4 30 . 7,95 0,06 100 178 53.4 33 3.34 0,95 3,52 2,93 0,92 0,030 1300 -- Total of 3 sieve cylinders -- -- 0,110 4780 0,254 j 2 1 268 0,4 30 7,95 0,12 100 178 53,4 33 -I 3,34 2jSB 1,25 1,30 0,72 0,048 2050 2 268 0,4 30 7.95 0,10 100 178 53,4 33 3,34 2,04 1,64 1,58 0,78 0,043 1870 - 3 268 0,4 30 7,95 0,08 100 178 53,4 33 3,34 1,46 2,29 2,04 : 0,84 0,037 1600 Total of 3 sieve cylinders -- -- .0,128 5520 v-,234 _3 1 268 0,4 30 7,95 0,10 100 178 60 33 2,96 2,04 1,45 1,58 ' 0,72 0.040 1930 2 268 0,4 30 7,95 0,08 100 178 60 33 2,96 1,46 2,03 2,04 0,7S 0,035 1690 -- 3 26S 0,4 30 7,95 0,06 100 178 60 33 2.96 0,95 3,12 2,93 , 0,86 0,028 1360 -- Total of 3 sieve cylinders -- -- 0,103 49S0 0,264 4 1 268 0,4 15 11,20 0,10 100 178 53,4 33 3.34 2,91 1,15 1,25 : 0,67 0,037 1600 ____ 2 268 0,4 15 11,20 0,08 100 178 53,4 33. 3,34 2,08 1,61 1,55 0,76- 0.033 1430 -- 3 268 0,4 15 11,20 0,06 100 178 53,4 33 3.34 1,68 1,99 1.33 ; 0,89 0,026 1090 -- Total of 3 sieve cylinders -- -- 0,096 4120 0.224 5 1-2 226 0,20 30 7,95 0,10 50 3-4 226 0,20 30 7,95 0,08 50 5-6 226 .0,20 30 7,95 0,06 . 50 89 53,4 89 53,4 17 .1,67 3,34 0,5 17 1,67 2,38 0,7 0,92 , 0,48 j 1,20 ! 0,52 0,025 .x 2 0,022 1075 x2 934 ____ -- -- t i ! x2 x2 89 53,4 I' 1.67 1,55 1,08 1,75 0,54 0,017 726 -- ' t 1 x2 x2 Total of 6 sieve cylinders of 0 50 ems -- -- -- 0,128 5470 0,280 6 1 170 0,5 30 7,95 0,10 100 I7S 53,4 33 3,34 1,29 2.60 2.36 0.87 0,048 2100 -- 2 170 0,5 30 7,95 0,08 100 178 53,4 33 3,34 0,93 3,60 2,9S 0,94 0,042 1820 -- 3 170 0,5 30 7,95 0,06 100 178 53,4 33 3,34 0,60 5,57 4,40 1,05 0,014 14S0 -- Total of 3 sieve cylinders -- -- 0,124 5400 0.2S6 _7 1 300 0,4 15 11,20 0,09 100 17S 41,7 33 4,27 2,74 1,56 1,2S 0.S2 0,041 -- 2 . 300 0.4 15 11,20 0,07 too 178 41,7 33 4,27 1,87 .2,2S 1,68 0,92 0,036 -- - Total of 2 sieve cylinders -- -- 0,077 2590 ..04 j Note. \Shen calculating the productivity of the sieve cylinder with rf 500 m/m (example No. 5) the value A\ cqu.iK 0,7U and therefore inteaJ ot the \alues 3,95 in column I# and U.83 in column 17, are applied correspondingly the values 3,70 and 0.78. I20; CTD001157 THE AC V Production of standard sheets per hour in relation to 1 ms of useful surface of the sieve cylinder (im mersed in'the suspension), is the specific productiv ity, symbolized as U,. Referring to fig. 1 (see AC/M No. 5, May 1968), the useful surface of the sieve cylinder is: <3`24) where: L is the section of the sieve cylinder immers ed in the suspension in cms. Bc is the length of the filtrating surface of the sieve cylinder in cms. -If-felt speed is expressed in accordance with equation (2-5) and dividing the value obtained from equation (3-23) by the value Fc, the following expression can be written: nc 3,95aV-uc-Bc x 10 Fc ~ y4LBc = 3A5JLVD` *121 = _3,95_x 10*a (V_ \ LtDc yoqj \ 1 / number sheet/hour/m3 (3-25) It results that the specific productivity of the sieve cylinder is proportional to the concentration of the suspension a and to the average rate of filtration Vjt. The thickness of the layer ky.<t> can be introduced in equation (3-23), using equation (3-22) and this will give: 1TC = 4,76 r19t./number sheet/hour (3-26) The results of the experiments carried out under factory conditions are referred in table 8. The weight of the asbestos-cement layer, obtained per unit of filtrating surface of the sieve cylinder was calculated using the equation of filtration and was compared to the values obtained experimentally (see also table 8). Such comparison indicated (see table) that the- tech nological calculation of the sieving part of the form ing machine, based on the equation of filtration with different concentrations and felt speeds, corresponds to the experimental data obtained. Details of the calculations of the output of the sieve cylinder, will be fully explained in the following chapter, with practical examples. In a subNcquent chapter, the dependence of the physical mechanical properties of asbestos-cement, on the wolfing con ditions of the machine, will be examined. 1221 Details of the calculation of the output of the sie\. cylinder using the equation offiltration and example.' The thickness of the asbestos-cement layer and th output of the sieve cylinder -- under different tech nological conditions -- can bc calculated by mean of the equation of filtration. The influence of th dimensions of the sieve cylinder on its output ca: also be determined as well as a number of othe calculations: Example No. 1: An asbestos-cement sheet formin machine operates with 3 sieve cylinders of 1000 mr diameter, immersed in the suspension, during wor) for 0,6 Dc\ and felt speed 32 m/min corresponding t 53,4 cm--sec. It would be required to determine the thickness c the layer and the output of the sieve cylinder unde the following technological conditions: specific weigh of sheet 1,5 gm/cm3 -- temperature of suspensio 30 C -- concentration of suspension in the firvat 0,10 gm/cm3, in the second vat 0,08 gm err and 0,06 gm/cm3 in the third. The characteristic of filtration are the following: ki> -- 268 (cm gm); and K0: = 0,4 cm3/cm4 with Pf> = 40 gmem'. For the determination of V according to the aligr mentjehart, it is necessary to calculate the values c 1/A6 and Vm,*\ the calculation is the following: The time of filtration is: t = -- where L is ih "c length of the part of the perimeter of the sieve cylinde immersed in the suspension and ur.lhe speed of th. felt. If the sieve cylinder is immersed for 0.6 of r diameter, then the coefficient of immersion k, (S; table 9) is also equal to 0,6 and L equal to 17S cm 178 = 3,34 secs. 53,4 Constant A<}> is determined using equation (3-1: Y fi1 0 A4> Pressure P, will be the same for all 3 sieve cylindc and as the coefficient of immersion is equal 0,6 then pressure P, will be equal to 33 cms (s: table 9). As the average hydrostatic pressuie results to be .' cms. in the coiuse of thiwork, and that of the "O' carried out in the laboratory was -10 cm>. the resu! inc difference is less than 1.5 times am! hence the would be no need for the recalculation ot kA and I CTD001158 1HE AC the values'found during the laboratory work can therefore be used. For the viscosity of the suspension at 30 C, see table 7 (AC/M No. 11-12, Nov./Dec. 1968): rt at 30 C = 7,95 g sec/cm:. Therefore the following can be written: For the first sieve cylinder: A<f> -- k<j> 3V a 7,95 x 0,10" = 268 33 7,95 x 0,0316 = 268 -- 2,04 sec/cm3 33 and t 3,34. = 1,64 cm3 A4> 2,04 For the second sieve cylinder: 7,95 x 0,08" 7,95 x 0,0226 A$ = 268 33 "268 33 = 1,46 sec/cm3 and t 3,34 = 2,29 cm3. A<f> ~ 1,46 For the third cylinder: 7,95 x 0,06" A<f> = 268 33 7,95 x 0,0147 268 33 = 0,95 sec/cm3 and 3,34 3,52 cm3. A<f> 0,95 The initial volume of the filtrated material will be determined using equation (3-20): and therefore: 2,4 KJ = Y02 + A<f> For the first cylinder: 2,4 2 A VeJ = IV + = 0.4 + y^- = 0.4 + 1.18 = 1,5S. For the second sieve cylinder: V s 0,4 + = 0,4 -r 1,64 2,04 1,46 For the third cylinder: 2,4 Vo.,' = 0,4 + * - = 0,4 + 2,53 = 2,93 The volume of filtrated material for the first, second and third sieve cylinders can be established using i i 24 the alignment chart fig. 28. These values are ll following: First: 0,7S cm3/cm2; second 0,84 ern'em3; tiz.ii 0,92 cm3/cm\ The introduction of the values of filtrated mater! and concentration, in equation (3-22) will give thickness of the layer delivered by the first, seco: and third sieve cylinders: For the first : 0,83 X 0,10 x 0,78 Saxfi = - = 0,043 ems 1,5 For the second: 0,83 x 0,08 x 0,84 8a^ = = 0,037 cms. For the third: 0,83 X 0,C6 x 0,92 1,5 = 0,030 cms. and consequently the thickness of the layer deliver by the three sieve cylinders wiii.be: 0,043 + 0,037 + 0,030 = 0,110 cms Equation (3-23) will consequently yield the ouip of each sieve cylinder in sheet/hour and for 3 s:-. cylinders the summed up output will be: n= (>Vi + a2Vt + o3V3)u,Bf = -yy- (0,10 x 0,78 + 0,08 X 0,84 + 0,C6 x 0.92s 53,4 x 170 = 4780 sheets/hour. It is to be remembered however, that actual procc tion of the machine will be equal to the calculi output only in the absence of fault and if conce tration, temperature and filtration properties of : suspension will not be changing. As the variat: of concentration is almost inevitable, it is con quently necessary to base all calculations on t average value of the concentration. Table 10 was prepared and can be used for su sequent examples in order to abbreviate caicuiatio: Example 2. By bow much will output be increas when all conditions remain unchanged and only e concentration of the suspension is increased as f. lows: in the first vat: from 0,10 to 0,12 cm c in the secondvat: from 0,08 to 0,10 cm errf in the third vat: from 0,06 to 0,08 gin cm1 Inthis case, k<!>, r; and P,. are the same as in example CTD001159 Tht Av r 9 The calculated values of A<f>, t/A4> and Voml are given in table 10 ind. 13, 14, 15. The values of V -- determined according to the align ment chart fig. 28 -- are given in table 10 index 16 and the thickness of the layer in the same table, index 17. The calculation shows that the above increases in concentration will give a layer of 0,128 cms and consequently the output will be increased from 4780 to 5520 sheets/hour corresponding to an in crease of 15,2%. Example 3. By how much will the output of the machine be increased when felt speed is increased from 32 to 36 m/min. while all other operating conditions are as in example 1. When felt speed changes, only 2 values change: t and t/A<j>', these values are contained in table 10. The calculation indicates that the felt speed increase will result in a decrease of the thickness of the layer from 0,110 cms to 0,103 cms but the total produc tivity will increase from 4780 sheets/hour to 4980, corresponding to 4 %. Example 4. By how much will productivity increase if the temperature of the suspension is increased from 15 to 30 C. All other conditions per example 1. The calculations referred in table 10 show that the increase in temperature from 15 to 30 C leads to an increase of the output by 16% i.e, from 4120 sheets/hour at 15 to 4780 at 30 C. Example 5. If in each of the 3 vats of the machine, instead of one sieve with a diam. of 1000 mm, two sieves of diam.. 500 mm each are installed in total 6--500 mm. 0 sieve cylinders instead of 3--1000 mm. What would the results of this change be when all other conditions of operation of the machine remain unchanged? Evidently, the reduction in diameter of the sieve cylinders will cause the change of L - Pt - / - A<!> - The calculation of L - Pt and t does not present any difficulty as these values decrease proportionally to the reduction in diameter of the sie\e cylinders. The pressure however with a sieve cylinder of 500 mm. 0 -- equal to 17 cms -- differs by more than 1.5 times from the presstue when the data was established in the laboratory (40 cms) and consequently the values of A^ = 26S and I u'-' = 0,4 which ueie obtained in the laboratory using the special filter, have to I26! be recalculated using equations (3-14) and (3-17): 268 268 175 = 400'1 '2,09 226 (cm/gm)11 1,76 = P F0* = 0,4 x H = 0,4 x _17 40 0,4 X 0,42 x 1,18 = 0,20 (cm3/cm:)-. Under typical conditions of manufacture, index s is equal to 0,20. The results of the corresponding calculations indicate that the change of the 3 -- 1000 mm 0 sieve cylinders with 6 -- 500 mm 0. results in an increase of the output from 4780 to 5470 sheets/hour, equivalent to 14% and this in spite of the fact that the working surface of the filtrating wire is not increased as a result of the change. Two otherwise identical sheet forming machines, but one equipped with 2 vats and 4-500 mm. 0 sieve cylinders and the other with 2 vats and 2-1000 mm. 0 sieve cylinders, regularly show differences of .12-15% in output, always in favour of the 4 cylinder machine. This confirms the correctness of the cal culations by means of the equation of filtration. Example 6. Conducted investigation has proved that the filtration properties of an A/C suspension de pend to a great extent on the composition of the cement used (this will be treated in a subsequent chapter). The filtration properties of the suspension containing a given type of cement was characterised by the following values, in the course of the conducted investigation: k<fi = I70 (cm/gm)1'5; V0S = 0,5 (cm'/cm5)'1. ' Using cement of this type which would give to the suspension filtrating properties with values us above, instead of the cement which was used in the pre viously described series of experiments (Ad< = 26S and >V = 0,4), by how much would the output be in creased when all other conditions are per example I? According to the data in table 10. the productivitv with the introduction of this new variable will in crease from 4780 to 5400 shects/hour corresponding to nil increase of 13%. In practice, conditions can be met under which, the asbestos-cement suspension, due to the properties of the cement used, lias k<j> -= 700 and at limes ever. k6---- 1000 (cnv'gm)' b In such cases, productivity will drop by 30-40% compared to the output per example I. CTD001160 THf AC *- PT?