Chapters on Papermaking ... by Clayton Beadle

Author:Clayton Beadle
Language: eng
Format: epub
Publisher: C. Lockwood and Son
Published: 1908-03-25T05:00:00+00:00

It- 4\ J^ !

£i.^'^

Fig. 12.

slightly less; whereas, of course, the rate of travel where the stuff is reduced to a fine film between the roll and the bed-plate is approximately equal to the circumferential speed of the roll-bars, wmch can easily be calculated for any roll when the revolutions per minute and size of roll is known.

At or near where the mid-feather ends on the back-fall side— ijB. at the point where the vertical depth, and consequently the sectional area, of the stuff is greatest, the rate of flow is the lowest; the reason being that the total volume per minute passing any given spot at any given period of time during the beating is a regular quantity. It follows, then, that the rate of flow in feet per minute is inversely proportional to the sectional area. And it follows, therefore, that when once the rate of flow in feet per minute at any given point in its travel round the beater is known, the rate of speed at all other points can be readily calculated. Figures exemplifying this statement are given later in this chapter.

For the purposes of the experiment about to be related, an

engine of bleached sulphite wood was taken and filled in to a fair consistency. The total weight of the pulp in the beater was 590 lbs. As this pulp on sampling was found to contain thirteen per cent, of moisture, the actual amount of air-dry pulp would be—

590 X (100-13) X 100 ^ „. .. •100 X 90 oi .

The furnish in the boater was as follows :—

Bleached sulphite wood (air dry weight) 570 lbs.

Sulphate of alumina 36 „

9 galls, of size, representing in dry rosin 8 „

OLarcn ... ... ... ... ... ^o ,,

China clay 60 „

Eepresenting— or, sav

Combustible materials 603 „ 600 lbs.

Non-combustible * 96 „ 100 „

699

99

After the experiment was completed, a sample of stuff weighing 1000 grains was carefully taken, and the residue dried down, and was found to weigh 78 grains. Fifty grains of this was ignited and found to weigh 6 grains, showing 12 per cent, of ash on the dry weight. This gives us the following percentages:—

Eesidue on evaporation, reckoned on original weight of stuff, is therefore—

Per cent.

Combustible (fibre and starch) ... 6*9

Incombustible (minerals and alum) 0*9

Total 7-8

Of combustible furnish, about 4 per cent, is starch ; therefore

6*9 X 4 we must deduct —iTjTr^ = ^'^ P^^ cent, from the 6'9 per cent.,

leaving 6*6 per cent, as the proportion of fibre on the total weight

ofbeaten stuff.

As we have 570 lbs. of air-dry wood pulp in the furnish, the

total weight of the stuff in the beater, including w^ater, etc.,

equals—

570 X 100 ^,„„ ,, , ^ — = 8637 lbs. '

The time that the stuff was in the beater was a<jtually 5^ hours, but only 5 hours of this was actually taken up in the process of beating.

The time of travel was noted (1) ^ hour after filling ;

(2) 3 hours after filling ; (8) 5 hours after filling.

Table XV.

Table

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