tailieunhanh - Foseco Ferrous Foundryman's Handbook Part 2

Tham khảo tài liệu 'foseco ferrous foundryman's handbook part 2', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Tables and general data 15 Calculation of average grain size The adoption of the ISO metric sieves means that the old AFS grain fineness number can no longer be calculated. Instead the average grain size expressed as micrometres pm is now used. This is determined as follows 1 Weigh a 100 g sample of dry sand. 2 Place the sample into the top sieve of a nest of ISO sieves on a vibrator. Vibrate for 15 minutes. 3 Remove the sieves and beginning with the top sieve weigh the quantity of sand remaining on each sieve. 4 Calculate the percentage of the sample weight retained on each sieve and arrange in a column as shown in the example. 5 Multiply the percentage retained by the appropriate multiplier and add the products. 6 Divide by the total of the percentages retained to give the average grain size. Example ISO aperture pm Percentage retained Multiplier Product 710 trace 1180 0 500 600 180 355 425 808 250 300 5160 212 212 5364 180 212 3540 150 150 2880 125 150 1590 90 106 689 63 75 105 63 38 19 Total 20 335 Average grain size 20 335 204 pm 16 Foseco Ferrous Foundryman s Handbook Calculation of AFS grain fineness number Using either the old BS sieves or AFS sieves follow steps 1-4 above. 5 Arrange the results as shown in the example below. 6 Multiply each percentage weight by the preceding sieve mesh number. 7 Divide by the total of the percentages to give the AFS grain fineness number. Example BS sieve number sand retained on sieve Multiplied by previous sieve no. Product 10 nil 16 nil 22 16 30 22 44 30 60 44 100 60 150 100 200 150 pan 200 Total AFS grain fineness number 100 or 68 AFS Foundry sands usually fall into the range 150-400 pm with 220-250 pm being the most commonly used. Direct conversion between average grain size and AFS grain fineness number is not possible but an approximate relation is shown .