35

C—3a

Table 7. —Comparison of the "International" Grinder used in the Mill Tests and the Experimental-size Grinder used at the Forest Products Laboratory.

Table 8.—Grinding of Tawa at Great Western Paper Co. Mill, Ladysmith, Wisconsin: Log of Grinder-runs.

Ratio Laboran „, International Laboratory | tory Grinder to a s ' Grinder. Grinder. i International Grinder. I '• | 1. Cylinder, diameter .. .. .. (in.) 16 7-25 1 to 2-2 2. Cylinder, area .. .. .. .. (sq. in.) 201 41-25 J 1 to 4-9 3. Pocket, width. .. .. .. .. (in.) 15 8 1 to 1-9 4. Length of wood ground .. .. .. (in.) 24 9 1 to 2-7 5. Area of wood in contact with stone in one pocket (3x4) .. . . .. (sq. in.) 360 72 1 to 5 6. Ratio of cylinder area to area of wood in contact with stone in one pocket .. 1 to 1-79 1 to 1-74 1 to 1 7. Number of pockets .. .. .. 3 2 1 to 1-5 8. Face of stone .. .. .. .. (in.) 24 12 1 to 2 9. Diameter of stone . . . . .. (in.) 57 25 1 to 2-3 10. Total area of wood in contact with stone (7x5 -r- 144) . . . . . . .. (sq. ft.) 7-5 0-5* I 1 to 15 11. Speed of stone .. .. .. .. (r.p.m.) 180f 460 ■ 1 to 0'39 12. Peripheral speed .. .. .. .. (ft./m.) 2,685 3,015 | 1 to 0-89 13. Effective grinding area per minute (12 X 10)J (sq. ft.) 20,170 1,508 j 1 to 13-4 * Only one pocket was used at a time on the laboratory grinder when grinding tawa. t Speed used when grinding tawa. J If 1 square foot be taken as the unit of area, the area of stone passing a unit area of wood per minute will be (the peripheral speed X 1) sq. ft. The " effective " grinding-area per minute will be therefore : Peripheral speed X total area of wood in contact with the stone.

Wood. Production. Dale. Shift. Hour. Pul1 ' Lap8 ' Pulp (dry) ' ouiiace. t Grinding llacks Wood — filled. J ground. Wet Moisture Dry Ppr r . Per Weight. Content. Weight. rer uora - 24 Hours. Grinder-run No. i. 1928. Hours. Cords. lb. Per Cent. lb. lb. Tons. Feb. 7 1 9.30 a.m. A, B, C 2.00 p.m. C 3.00 .. 5-5 5 .. 2,400 73'5 636 2 6.30 B, C 10.30 C 11.00 .. 8 3 .. 4,660 73-5 1,235 Feb. 8 .. 3 2.30 a.m. B, C 6.30 C 7.00 ' .. 8 3 .. 4,705 73-5 1,247 1 10.30 .. 3'5 .. .. 2,985 72-6 818 25 11 2-75 14,750 .. 3,938 1,432 | 1-89 Grinmk-RWN NO. 2. Feb. 9 .. 1 1.15 p.m. B, C 2 3 2 4.00 B, C 7.00 C 10.00 B, C 11.00 .. 8 4 .. 4,410 72-0 1,235 Feb. 10 .. 3 1.00 a.m. C 4.00 B, C 7.00 C 8 3 . ... 5,055 72-0 1,415 1 10.00 B, D 2.00 p.m. D 3.00.. 8 3 ....... 5,305 74-0 1,380 2 5.00 D 7.30 .. 4-5 .. .. 4,540 74-0 1,180 30-5 13 3-25 19,310 .. 5',210 1.600 | 2-05 * Types of burrs used were as follows : A, smooth roll used for removing old surface ; B, four-point (four teeth per inch) straight-cut burr ; C, 14-point diamond-cut burr : ,D, 12-point diamond-cut burr. All burrs wero new. They were used in the order indicated. t Average pressure in cylinder, 30 lb. For other conditions see Table 7. X One rack equals } cord. These were the number of racks tilled on each shift, and not the number of racks ground.